International Nuclear Information System (INIS)
Khadkikar, S.B.; Vinodkumar, P.C.
1987-04-01
Confinement model for gluons using a 'colour super current' is formulated. An attempt has been made to derive a suitable dielectric function corresponding to the current confinement model. A simple inhomogeneous dielectric confinement model for gluons is studied for comparison. The model Hamiltonians are second quantized and the glueball states are constructed. The spurious motion of the centre of confinement is accounted for. The results of the current confinement scheme are found to be in good agreement with the experimental candidates for glueballs. (author). 16 refs, 3 tabs
Modelling the gluon propagator
Energy Technology Data Exchange (ETDEWEB)
Leinweber, D.B.; Parrinello, C.; Skullerud, J.I.; Williams, A.G
1999-03-01
Scaling of the Landau gauge gluon propagator calculated at {beta} = 6.0 and at {beta} = 6.2 is demonstrated. A variety of functional forms for the gluon propagator calculated on a large (32{sup 3} x 64) lattice at {beta} = 6.0 are investigated.
Dynamical gluon mass in the instanton vacuum model
Musakhanov, M.; Egamberdiev, O.
2018-04-01
We consider the modifications of gluon properties in the instanton liquid model (ILM) for the QCD vacuum. Rescattering of gluons on instantons generates the dynamical momentum-dependent gluon mass Mg (q). First, we consider the case of a scalar gluon, no zero-mode problem occurs and its dynamical mass Ms (q) can be found. Using the typical phenomenological values of the average instanton size ρ = 1 / 3 fm and average inter-instanton distance R = 1 fm we get Ms (0) = 256 MeV. We then extend this approach to the real vector gluon with zero-modes carefully considered. We obtain the following expression Mg2 (q) = 2 Ms2 (q). This modification of the gluon in the instanton media will shed light on nonperturbative aspect on heavy quarkonium physics.
Semirelativistic potential model for three-gluon glueballs
International Nuclear Information System (INIS)
Mathieu, Vincent; Semay, Claude; Silvestre-Brac, Bernard
2008-01-01
The three-gluon glueball states are studied with the generalization of a semirelativistic potential model giving good results for two-gluon glueballs. The Hamiltonian depends only on 3 parameters fixed on two-gluon glueball spectra: the strong coupling constant, the string tension, and a gluon size which removes singularities in the potential. The Casimir scaling determines the structure of the confinement. Our results are in good agreement with other approaches and lattice calculation for the odderon trajectory but differ strongly from lattice in the J +- sector. We propose a possible explanation for this problem.
The Mixed Quark-Gluon Condensate from the Global Color Symmetry Model
Institute of Scientific and Technical Information of China (English)
ZONG Hong-Shi; PING Jia-Lun; LU Xiao-Fu; WANG Fan; ZHAO En-Guang
2002-01-01
The mixed quark-gluon condensate from the global color symmetry model is derived. It is shown that themixed quark-gluon condensate depends explicitly on the gluon propagator. This interesting feature may be regarded asan additional constraint on the model of gluon propagator. The values of the mixed quark-gluon condensate from someansatz for the gluon propagator are compared with those determined from QCD sum rules.
International Nuclear Information System (INIS)
Weiler, T.
1981-01-01
An overview is presented of the attributes of gluons, deducible from experimental data. Particular attention is given to the photon-gluon fusion model of charm leptoproduction. The agreement with QCD and theoretical prejudice is qualitatively good
Gluon condensation and modelling of quark confinement in QCD-motivated Nambu-Jona-Lasinio model
International Nuclear Information System (INIS)
Bel'kov, A.A.; Ebert, D.; Emel'yanenko, A.V.
1992-01-01
The possibility of modelling of a quark propagator without poles realizing quark confinement is considered on the basis of a nonperturbative gluon propagator including gluon condensation and a dynamical gluon mass. The property of spontaneous chiral symmetry breaking is retained providing us with a reasonable pattern of low-lying meson properties. 2 figs.; 1 tab
The quark-gluon model for particle production processes
International Nuclear Information System (INIS)
Volkovitskij, P.E.
1983-01-01
The quark-gluon model for hadronization of strings produced in soft and hard processes is suggested. The model is based on the distribution functions of valence quarks in hadrons which have correct Regge behaviour. The simplest case is discussed in which only the longitudinal degrees of freedom are taken into account
Gluon and quark jets in a recursive model motivated by quantum chromodynamics
International Nuclear Information System (INIS)
Sukhatme, U.P.
1979-01-01
We compute observable quantities like the multiplicity and momentum distributions of hadrons in gluon and quark jets in the framework of a recursive cascade model, which is strongly motivated by the fundamental interactions of QCD. Fragmentation occurs via 3 types of breakups: quark → meson + quark, gluon → meson + gluon, gluon → quark + antiquark. In our model gluon jets are softer than quark jets. The ratio of gluon jet to quark jet multiplicity is found to be 2 asymptotically, but much less at lower energies. Some phenomenological consequences for γ decay are discussed. (orig.)
Viscosities in the Gluon-Plasma within a Quasiparticle Model
Bluhm, M; Redlich, K
2009-01-01
A phenomenological quasiparticle model, featuring dynamically generated self-energies of excitation modes, successfully describes lattice QCD results relevant for the QCD equation of state and related quantities both at zero and non-zero net baryon density. Here, this model is extended to study bulk and shear viscosities of the gluon-plasma within an effective kinetic theory approach. In this way, the compatibility of the employed quasiparticle ansatz with the apparent low viscosities of the strongly coupled deconfined gluonic medium is shown.
Attractive Casimir effect in an infrared modified gluon bag model
International Nuclear Information System (INIS)
Oxman, L.E.; Amaral, R.L.P.G.; Svaiter, N.F.
2005-01-01
In this work, we are motivated by previous attempts to derive the vacuum contribution to the bag energy in terms of familiar Casimir energy calculations for spherical geometries. A simple infrared modified model is introduced which allows studying the effects of the analytic structure as well as the geometry in a clear manner. In this context, we show that if a class of infrared vanishing effective gluon propagators is considered, then the renormalized vacuum energy for a spherical bag is attractive, as required by the bag model to adjust hadron spectroscopy
Monte Carlo evidence for the gluon-chain model of QCD string formation
International Nuclear Information System (INIS)
Greensite, J.; San Francisco State Univ., CA
1988-08-01
The Monte Carlo method is used to calculate the overlaps string vertical stroken gluons>, where Ψ string [A] is the Yang-Mills wavefunctional due to a static quark-antiquark pair, and vertical stroken gluons > are orthogonal trial states containing n=0, 1, or 2 gluon operators multiplying the true ground state. The calculation is carried out for SU(2) lattice gauge theory in Coulomb gauge, in D=4 dimensions. It is found that the string state is dominated, at small qanti q separations, by the vacuum ('no-gluon') state, at larger separations by the 1-gluon state, and, at the largest separations attempted, the 2-gluon state begins to dominate. This behavior is in qualitative agreement with the gluon-chain model, which is a large-N colors motivated theory of QCD string formation. (orig.)
Semirelativistic potential model for low-lying three-gluon glueballs
International Nuclear Information System (INIS)
Mathieu, Vincent; Semay, Claude; Silvestre-Brac, Bernard
2006-01-01
The three-gluon glueball states are studied with the generalization of a semirelativistic potential model giving good results for two-gluon glueballs. The Hamiltonian depends only on 3 parameters fixed on two-gluon glueball spectra: the strong coupling constant, the string tension, and a gluon size which removes singularities in the potential. The Casimir scaling determines the structure of the confinement. Low-lying J PC states are computed and compared with recent lattice calculations. A good agreement is found for 1 -- and 3 -- states, but our model predicts a 2 -- state much higher in energy than the lattice result. The 0 -+ mass is also computed
A QCD derivation of the additive quark model from two and three gluon exchanges
International Nuclear Information System (INIS)
Lipkin, H.J.
1982-06-01
The contributions to the Pomeron from two and three gluon exchanges are shown to give the correct combinatorial factors for the additive quark model relation between meson and baryon Pomeron couplings, even though two-quark and three-quark operators are involved. Similar results hold for the contributions to hadron masses from three-gluon vertices as well as one-gluon exchange. The color algebra reduces the multiquark couplings to a linear function of quark number. (author)
Gluon field strength correlation functions within a constrained instanton model
International Nuclear Information System (INIS)
Dorokhov, A.E.; Esaibegyan, S.V.; Maximov, A.E.; Mikhailov, S.V.
2000-01-01
We suggest a constrained instanton (CI) solution in the physical QCD vacuum which is described by large-scale vacuum field fluctuations. This solution decays exponentially at large distances. It is stable only if the interaction of the instanton with the background vacuum field is small and additional constraints are introduced. The CI solution is explicitly constructed in the ansatz form, and the two-point vacuum correlator of the gluon field strengths is calculated in the framework of the effective instanton vacuum model. At small distances the results are qualitatively similar to the single instanton case; in particular, the D 1 invariant structure is small, which is in agreement with the lattice calculations. (orig.)
Shadowing of gluons in perturbative QCD: A comparison of different models
International Nuclear Information System (INIS)
Jalilian-Marian, Jamal; Wang, Xin-Nian
2001-01-01
We investigate the different perturbative QCD-based models for nuclear shadowing of gluons. We show that, in the kinematic region appropriate to the BNL relativistic heavy ion collider experiment, all models give similar estimates for the magnitude of gluon shadowing. At scales relevant to CERN large hadron collider (LHC), there is a sizable difference between the predictions of the different models. However, the uncertainties in gluon shadowing coming from a different parametrization of the gluon distribution in nucleons, are larger than those due to different perturbative QCD models of gluon shadowing. We also investigate the effect of initial nonperturbative shadowing on the magnitude of perturbative shadowing and show that the magnitudes of perturbative and nonperturbative shadowing are comparable at RHIC but perturbative shadowing dominates over nonperturbative shadowing at smaller values of x reached at LHC
Renormalizability of a quark-gluon model with soft BRST breaking in the infrared region
Baulieu, L; Gomez, A J; Lemes, V E R; Sobreiro, R F; Sorella, S P
2010-01-01
We prove the renormalizability of a quark-gluon model with a soft breaking of the BRST symmetry, which accounts for the modification of the large distance behavior of the quark and gluon correlation functions. The proof is valid to all orders of perturbation theory, by making use of softly broken Ward identities.
The quark and gluon condensates in the Nambu-Jona-Lasinio model
International Nuclear Information System (INIS)
Ebert, D.; Volkov, M.K.
1991-10-01
Systematic study of the role of the nonperturbative gluon condensate arising in a QCD motivated NJL model is presented. The effects of the gluon condensate on meson coupling constants, the pion decay constant, quark condensate and mass formulae are investigated. An interesting result is the decrease of the scale Λ of chiral symmetry breaking. (author). 21 refs
Quark and gluon propagators in the spherical bag model
Energy Technology Data Exchange (ETDEWEB)
Kulish, Yu V [AN Ukrainskoj SSR, Fiziko-Tekhnicheskij Inst., Kharkov
1983-12-01
The quark and gluon propagators in a spherical cavity have been obtained by summation of the quark field modes (J-1/2, J is the total moment) and gluon field modes (J=1). The requirements for the spatial components of the gluon propagator Gsub(ik)(x, x') and the quark propagator S(x, x') to be Green functions of the wave equations result in the coincidence of directions for anti x and anti x' vectors. Relations have been derived which allow verification of the self-consistency of approximations used to calculate dynamic values.
Quark and gluon propagators in the spherical bag model
International Nuclear Information System (INIS)
Kulish, Yu.V.
1983-01-01
The quark and gluon propagators in a spherical cavity have been obtained by summation of the quark field modes (J-1/2, J is the total moment) and gluon field modes (J=1). The requirements for the spatial components of the gluon propagator Gsub(ik)(x, x') and the quark propagator S(x, x') to be Green functions of the wave equations result in the coincidence of directions for anti x and anti x' vectors. Relations have been derived which allow verification of the self-consistency of approximations used to calculate dynamic values
Quark Loop Effects on Dressed Gluon Propagator in Framework of Global Color Symmetry Model
Institute of Scientific and Technical Information of China (English)
ZONG Hong-Shi; SUN Wei-Min
2006-01-01
Based on the global color symmetry model (GCM), a method for obtaining the quark loop effects on the dressed gluon propagator in GCM is developed. In the chiral limit, it is found that the dressed gluon propagator containing the quark loop effects in the Nambu-Goldstone and Wigner phases are quite different. In solving the quark self-energy functions in the two different phases and subsequent study of bag constant one should use the above dressed gluon propagator as input. The above approach for obtaining the current quark mass effects on the dressed gluon propagator is quite general and can also be used to calculate the chemical potential dependence of the dressed gluon propagator.
Diffractive open charm production at DESY HERA. Experiment versus two-gluon exchange model
Energy Technology Data Exchange (ETDEWEB)
Baranov, S.P. [P.N. Lebedev Inst. of Physics, Moscow (Russian Federation)
2010-03-15
Diffractive production of D{sup *} mesons at HERA conditions is considered in the framework of collinear two-gluon exchange model. Theoretical results are compared with recent experimental data. (orig.)
Self-consistent one-gluon exchange in soliton bag models
International Nuclear Information System (INIS)
Dodd, L.R.; Adelaide Univ.; Williams, A.G.
1988-01-01
The treatment of soliton bag models as two-point boundary value problems is extended to include self-consistent one-gluon exchange interactions. The colour-magnetic contribution to the nucleon-delta mass splitting is calculated self-consistently in the mean-field, one-gluon-exchange approximation for the Friedberg-Lee and Nielsen-Patkos models. Small glueball mass parameters (m GB ∝ 500 MeV) are favoured. Comparisons with previous calculations are made. (orig.)
QCD-motivated Nambu-Jona-Lasinio model with quark and gluon condensates
International Nuclear Information System (INIS)
Ebert, D.; Volkov, M.K.
1991-01-01
A systematic study of the role of the nonperturbative gluon condensate arising in a QCD-motivated Nambu-Jona-Lasinio model is presented. The effects of the gluon condensate on induced meson couplings, the pion decay constant, quark condensate and mass formulae are investigated. An interesting result is the change of the scale Λ of chiral symmetry breaking and of the universal four-quark coupling constant κ. 20 refs
QCD-motivated Nambu-Jona-Lasinio model with quark and gluon condensates
International Nuclear Information System (INIS)
Ebert, D.; Volkov, M.K.
1991-01-01
We present a systematic study of the role of the nonperturbative gluon condensate arising in a QCD-motivated NJL model. The effects of the gluon condensate on induced meson couplings, the pion decay constant, quark condensate and mass formulae are investigated. An interesting result is the change of the scale Λ of chiral symmetry breaking and of the universal four-quark coupling κ. (orig.)
Deep inelastic lepton-hadron processes in gauge models with massive vector gluons
International Nuclear Information System (INIS)
Morozov, P.T.; Stamenov, D.B.
1978-01-01
Considered is a class of strong interaction models in which the interactions between coloured quarks are mediated by massive neutral vector gluons. All the vector gluons acquire masses by the Higgs mechanism. These models are not asymptotically free. The effective gauge coupling constant anti α vanishes asymptotically, and the effective quartic coupling constant anti h tends to a finite asymptotic value. The behaviour of the moments of the deep inelastic lepton-hadron structure functions is analyzed. It is shown that the Bjorken scaling is violated by powers of logarithms
Exactly solvable model of phase transition between hadron and quark-gluon-matter
International Nuclear Information System (INIS)
Gorenstein, M.I.; Petrov, V.K.; Shelest, V.P.; Zinovjev, G.M.
1982-01-01
An exactly solvable model of phase transition between hadron and quark-gluon matter is proposed. The hadron phase of this model is considered as a gas of bags filled by point massless constituents. The mass and volume spectrum of the bag is found. The thermodynamical characteristics of a bag gas in the neighbourhood of a phase transition point are ascertained in analytical form
International Nuclear Information System (INIS)
Sugano, K.
1987-01-01
The properties of gluon jets are reviewed, and the measured characteristics are compared to the theoretical expectations. Although neither data nor models for the gluon jets are in the mature stage, in general the agreement between experiment and theory is remarkable. There are some intriguing differences. Since the properties of gluon jets are deeply rooted in the basic structure of non-Abelian gauge theory, the study of gluon jets casts further light on our understanding of QCD. Finally, the future prospects are discussed
International Nuclear Information System (INIS)
Sugano, K.
1988-01-01
The properties of gluon jets are reviewed from an experimental point of view. The measured characteristics are compared to theoretical expectations. Although neither data nor models for the gluon jets are in the mature stage, there are remarkable agreements and also intriguing disagreements between experiment and theory. Since much interesting data have begun to emerge from various experiments and the properties of gluon jets are deeply rooted in the basic structure of non-Abelian gauge theory, the study of gluon jets casts further light on understanding of QCD. The future prospects are discussed
Propagation of cosmic rays through the atmosphere in the quark-gluon strings model
Erlykin, A. D.; Krutikova, N. P.; Shabelski, Y. M.
1985-01-01
The quark-gluon strings model succeeds in the description of multiple hadron production in the central rapidity region of nucleon-nucleon interctions. This model was developed for hadron-nucleus interactions and used for calculation of the cosmic ray propagation through the atmosphere. It is shown that at energies 10 to the 11th power to the 12th power eV, this model gives a satisfactory description of experimental data. But with the increase of the energy up to approximately 10 to the 14th power eV, results of calculations and of experiments begin to differ and this difference rises with the energy. It may indicate that the scaling violation in the fragmentation region of inclusive spectra for hadron-nucleus interactions is stronger than in the quark-gluon strings model.
Modified bag models for the quark–gluon plasma equation of state
International Nuclear Information System (INIS)
Begun, V.V.; Gorenstein, M.I.; Mogilevsky, O.A.
2011-01-01
The modified versions of the bag model equation of state (EoS) are considered. They are constructed to satisfy the main qualitative features observed for the quark–gluon plasma EoS in the lattice QCD calculations. A quantitative comparison with the lattice results at high temperatures T are done in the SU(3) gluodynamics and in the full QCD with dynamical quarks. Our analysis advocates a negative value of the bag constant B. (author)
Quasi-particle model for lattice QCD: quark-gluon plasma in heavy ion collisions
International Nuclear Information System (INIS)
Chandra, Vinod; Ravishankar, V.
2009-01-01
We propose a quasi-particle model to describe the lattice QCD equation of state for pure SU(3) gauge theory in its deconfined state, for T≥1.5T c . The method involves mapping the interaction part of the equation of state to an effective fugacity of otherwise non-interacting quasi-gluons. We find that this mapping is exact. Using the quasi-gluon distribution function, we determine the energy density and the modified dispersion relation for the single particle energy, in which the trace anomaly is manifest. As an application, we first determine the Debye mass, and then the important transport parameters, viz., the shear viscosity, η, and the shear viscosity to entropy density ratio, η/S. We find that both η and η/S are sensitive to the interactions, and that the interactions significantly lower both η and η/S. (orig.)
A massive quasi-particle model of the SU(3) gluon plasma
International Nuclear Information System (INIS)
Peshier, A.; Technische Univ. Dresden; Kaempfer, B.; Technische Univ. Dresden; Pavlenko, O.P.; AN Ukrainskoj SSR, Kiev; Soff, G.
1995-09-01
Recent SU(3) gauge field lattice data for the equation of state are interpreted by a quasi-particle model with effective thermal gluon masses. The model is motivated by lowest-order perturbative QCD and describes very well the data. The proposed quasi-particle approach can be applied to study color excitations in the non-perturbative regime. As an example we estimate the temperature dependence of the Debye screening mass and find that it declines sharply when approaching the confinement temperature from above, while the thermal mass continuously rises. (orig.)
Partial widths of boson resonances in the quark-gluon model of strong interactions
International Nuclear Information System (INIS)
Kaidalov, A.B.; Volkovitsky, P.E.
1981-01-01
The quark-gluon model of strong interactions based on the topological expansion and the string model ib used for the calculation of the partial widths of boson resonances in the channels with two pseudoscalar mesons. The partial widths of mesons with arbitrary spins lying on the vector and tensor Regge trajectories are expressed in terms of the only rho-meson width. The violation of SU(3) symmetry increases with the growth of the spin of the resonance. The theoretical predictions are in a good agreement with experimental data [ru
Revisiting the quasi-particle model of the quark-gluon plasma
International Nuclear Information System (INIS)
Bannur, V.M.
2007-01-01
The quasi-particle model of the quark-gluon plasma (QGP) is revisited here with a new method, different from earlier studies, one without the need of a temperature dependent bag constant and other effects such as confinement, effective degrees of freedom etc. Our model has only one system dependent parameter and shows a surprisingly good fit to the lattice results for the gluon plasma, and for 2-flavor, 3-flavor and (2+1)-flavor QGP. The basic idea is first to evaluate the energy density ε from the grand partition function of quasi-particle QGP, and then derive all other thermodynamic functions from ε. Quasi-particles are assumed to have a temperature dependent mass equal to the plasma frequency. Energy density, pressure and speed of sound at zero chemical potential are evaluated and compared with the available lattice data. We further extend the model to a finite chemical potential, without any new parameters, to obtain the quark density, quark susceptibility etc., and the model fits very well with the lattice results on 2-flavor QGP. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Kanki, T [Osaka Univ., Toyonaka (Japan). Coll. of General Education
1976-12-01
We present a quark-gluon-parton model in which quark-partons and gluons make clusters corresponding to two or three constituent quarks (or anti-quarks) in the meson or in the baryon, respectively. We explicitly construct the constituent quark state (cluster), by employing the Kuti-Weisskopf theory and by requiring the scaling. The quark additivity of the hadronic total cross sections and the quark counting rules on the threshold powers of various distributions are satisfied. For small x (Feynman fraction), it is shown that the constituent quarks and quark-partons have quite different probability distributions. We apply our model to hadron-hadron inclusive reactions, and clarify that the fragmentation and the diffractive processes relate to the constituent quark distributions, while the processes in or near the central region are controlled by the quark-partons. Our model gives the reasonable interpretation for the experimental data and much improves the usual ''constituent interchange model'' result near and in the central region (x asymptotically equals x sub(T) asymptotically equals 0).
Multiple production of hadrons at high energies in the model of quark-gluon strings
International Nuclear Information System (INIS)
Kaidalov, A.B.; Ter-Martirosyan, K.A.
1983-01-01
Multiple production of hadrons at high energies is considered in the framework of the approach based on a picture of formation and subsequent fission of the quark-gluon strings, corresponding to the Pomeron with αsub(P)(0) > 1. The topological (1/nsub(f))-expansion and the colour-tube model is used. Inclusive cross-sections are expressed in therms of the structure functions and fragmentation functions of quarks and their limiting values are in an agreement with the results of the reggeon theory. It is pointed out that an account of rapidity fluctuations of the ends of the quark-gluon strings, connected to valence or sea quarks, allows one to explain a number of characteristic features of the multiple production of hadrons. In particular the model, which takes into account multipomeron configurations, reproduces the experimentally observed rise of inclusive spectra in a central region and well describes both rapidity and multiplicity distributions of charged particles up to energies of the SPS-collider. It is shown that in this approach the KNO-scaling is only approximately satisfied and the pattern of its violation at energies √ s approximately 10 3 GeV is predicted. Inclusive spectra are investigated in the whole region 0 or approximately 0.1) Feynman scaling is violated only logarithmically and deviations from it are very rsmall at s 3 +10 4 GeV
Chala, Mikael; Perez, Gilad; Santiago, Jose
2015-01-01
We study the phenomenology of vector resonances in the context of natural composite Higgs models. A mild hierarchy between the fermionic partners and the vector resonances can be expected in these models based on the following arguments. Both direct and indirect (electroweak and flavor precision) constraints on fermionic partners are milder than the ones on spin one resonances. Also the naturalness pressure coming from the top partners is stronger than that induced by the gauge partners. This observation implies that the search strategy for vector resonances at the LHC needs to be modified. In particular, we point out the importance of heavy gluon decays (or other vector resonances) to top partner pairs that were overlooked in previous experimental searches at the LHC. These searches focused on simplified benchmark models in which the only new particle beyond the Standard Model was the heavy gluon. It turns out that, when kinematically allowed, such heavy-heavy decays make the heavy gluon elusive, and the bou...
International Nuclear Information System (INIS)
Fowler, G.N.; Navarra, F.S.; Plumer, M.; Lawrence Berkeley Laboratory, Nuclear Science Division, Berkeley, California 94720); Vourdas, A.; Weiner, R.M.
1989-01-01
The interacting gluon model developed to describe the inelasticity distribution in hadron-nucleon collisions has been generalized and applied to hadron-nucleus and nucleus-nucleus interactions. Leading particle spectra and energy distributions in hadron-nucleus and nucleus-nucleus collisions are calculated
Effective-gluon model description of inclusive meson production in π+- p and pp collisions
International Nuclear Information System (INIS)
Look, G.W.; Fischbach, E.
1977-01-01
The recently introduced effective-gluon (EG) model is applied to inclusive meson production at large transverse momentum (p/sub t)/from π +- p and pp interactions. In the EG model the dependence of the inclusive differential cross section on p/ sub t/ and center-of-momentum energy √s is characterized by a single universal constant B = 18 GeV 2 ; this constant is obtained by fitting to the inclusive data for pp → cX with c = π +- π 0 , K +- p, and p-bar. Since the EG model requires that the inclusive differential cross sections for π +- p → X/should be characterized by the same constant B, the dependence of these cross sections on p/sub t/and √s should follow from the previous analysis of pp → cX without the introduction of any additional parameters. The only new information required is the form of the momentum distribution function for partons in the incident pion. Several models for this function are considered and it it shown that all of the alternatives lead to approximately the same predictions. Comparison of theory and experiment indicates that the EG model description of the recent Fermilab data of Donaldson et al. is good to approximately 15--20 % per data point over a range of more than 10 5 in the magnitude of the inclusive cross section
Higgs boson decays and production via gluon fusion at LHC in littlest Higgs models with T parity
International Nuclear Information System (INIS)
Wang Lei; Yang Jinmin
2009-01-01
We study the Higgs boson decays and production via gluon fusion at the LHC as a probe of two typical littlest Higgs models which introduce a top quark partner with different (even and odd) T parity to cancel the Higgs mass quadratic divergence contributed by the top quark. For each model, we consider two different choices for the down-type quark Yukawa couplings. We first examine the branching ratios of the Higgs boson decays and then study the production via gluon fusion followed by the decay into two photons or two weak gauge bosons. We find that the predictions can be quite different for different models or different choices of down-type quark Yukawa couplings, and all these predictions can sizably deviate from the standard model predictions. So the Higgs boson processes at the LHC can be a sensitive probe for these littlest Higgs models.
International Nuclear Information System (INIS)
Bu Yanyan; Yang Jinmin
2011-01-01
Motivated by recent studies of deep inelastic scattering off the N=4 super-Yang-Mills (SYM) plasma, holographically dual to an AdS 5 xS 5 black hole, we use the spacelike flavor current to probe the internal structure of one holographic quark-gluon plasma, which is described by the Sakai-Sugimoto model at high temperature phase (i.e., the chiral-symmetric phase). The plasma structure function is extracted from the retarded flavor current-current correlator. Our main aim in this paper is to explore the effect of nonconformality on these physical quantities. As usual, our study is under the supergravity approximation and the limit of large color number. Although the Sakai-Sugimoto model is nonconformal, which makes the calculations more involved than the well-studied N=4 SYM case, the result seems to indicate that the nonconformality has little essential effect on the physical picture of the internal structure of holographic plasma, which is consistent with the intuition from the asymptotic freedom of QCD at high energy. While the physical picture underlying our investigation is same as the deep inelastic scattering off the N=4 SYM plasma with(out) flavor, the plasma structure functions are quantitatively different, especially their scaling dependence on the temperature, which can be recognized as model dependent. As a comparison, we also do the same analysis for the noncritical version of the Sakai-Sugimoto model which is conformal in the sense that it has a constant dilaton vacuum. The result for this noncritical model is quite similar to the conformal N=4 SYM plasma. We therefore attribute the above difference to the effect of nonconformality of the Sakai-Sugimoto model.
Interference contributions to gluon initiated heavy Higgs production in the Two-Higgs-Doublet Model
International Nuclear Information System (INIS)
Greiner, Nicolas
2016-03-01
We discuss the production of a heavy neutral Higgs boson of a CP-conserving Two-Higgs-Doublet Model in gluon fusion and its decay into a four-fermion final state, gg(→VV)→e + e - π + π - /e + e - ν l anti ν l . We investigate the interference contributions to invariant mass distributions of the four-fermion final state and other relevant kinematical observables. The relative importance of the different contributions is quantified for the process in the on-shell approximation, gg→ZZ. We show that interferences of the heavy Higgs with the light Higgs boson and background contributions are essential for a correct description of the differential cross section. Even though they contribute below O(10%) to those heavy Higgs signal cross sections, to which the experiments at the Large Hadron Collider were sensitive in its first run, we find that they are sizeable in certain regions of the parameter space that are relevant for future heavy Higgs boson searches. In fact, the interference contributions can significantly enhance the experimental sensitivity to the heavy Higgs boson.
KN s-wave phase shifts in a quark model with gluon and boson exchange at the quark level
International Nuclear Information System (INIS)
Silvestre-Brac, B.; Leandri, J.
1997-01-01
The kaon-nucleon s-wave phase shifts have been calculated in a quark potential model using the resonating group method (RGM). The interquark potential includes gluon, pion and sigma exchanges. The kaon and nucleon wave functions are expanded as a sum of Gaussian functions and the Hill-Wheeler (HW) equation is solved numerically. The I=0 phase shifts present too much attraction and in the I=1 channel too much repulsion is obtained. (orig.)
A model for color screening in a QCD plasma: the roles of thermal gluons and of confinement
International Nuclear Information System (INIS)
Calucci, G.; Cattaruzza, E.
2006-01-01
The study of the screening in the q anti q plasma, in a model which takes into account only static interactions, is continued with the introduction of two new dynamical elements: the presence of thermal gluons and a phenomenological description of the confinement. In the first case the qq correlation and the q anti q correlation are similar to each other and also similar to the correlation in the absence of gluons: the decay with the distance deviates slightly from a standard exponential decay. In the second case the two-body confining potential gives rise to correlation functions oscillating with the distance, so that only the total correlation, i.e. the space integral, has a more transparent interpretation; moreover, the qq correlations and the q anti q correlations show very definite differences. (orig.)
Abbiendi, G.; Akesson, P.F.; Alexander, G.; Allison, John; Amaral, P.; Anagnostou, G.; Anderson, K.J.; Arcelli, S.; Asai, S.; Axen, D.; Azuelos, G.; Bailey, I.; Barberio, E.; Barlow, R.J.; Batley, R.J.; Bechtle, P.; Behnke, T.; Bell, Kenneth Watson; Bell, P.J.; Bella, G.; Bellerive, A.; Benelli, G.; Bethke, S.; Biebel, O.; Boeriu, O.; Bock, P.; Boutemeur, M.; Braibant, S.; Brigliadori, L.; Brown, Robert M.; Buesser, K.; Burckhart, H.J.; Campana, S.; Carnegie, R.K.; Caron, B.; Carter, A.A.; Carter, J.R.; Chang, C.Y.; Charlton, David G.; Csilling, A.; Cuffiani, M.; Dado, S.; De Roeck, A.; De Wolf, E.A.; Desch, K.; Dienes, B.; Donkers, M.; Dubbert, J.; Duchovni, E.; Duckeck, G.; Duerdoth, I.P.; Etzion, E.; Fabbri, F.; Feld, L.; Ferrari, P.; Fiedler, F.; Fleck, I.; Ford, M.; Frey, A.; Furtjes, A.; Gagnon, P.; Gary, John William; Gaycken, G.; Geich-Gimbel, C.; Giacomelli, G.; Giacomelli, P.; Giunta, Marina; Goldberg, J.; Gross, E.; Grunhaus, J.; Gruwe, M.; Gunther, P.O.; Gupta, A.; Hajdu, C.; Hamann, M.; Hanson, G.G.; Harder, K.; Harel, A.; Harin-Dirac, M.; Hauschild, M.; Hawkes, C.M.; Hawkings, R.; Hemingway, R.J.; Hensel, C.; Herten, G.; Heuer, R.D.; Hill, J.C.; Hoffman, Kara Dion; Horvath, D.; Igo-Kemenes, P.; Ishii, K.; Jeremie, H.; Jovanovic, P.; Junk, T.R.; Kanaya, N.; Kanzaki, J.; Karapetian, G.; Karlen, D.; Kawagoe, K.; Kawamoto, T.; Keeler, R.K.; Kellogg, R.G.; Kennedy, B.W.; Kim, D.H.; Klein, K.; Klier, A.; Kluth, S.; Kobayashi, T.; Kobel, M.; Komamiya, S.; Kormos, Laura L.; Kramer, T.; Krieger, P.; von Krogh, J.; Kruger, K.; Kuhl, T.; Kupper, M.; Lafferty, G.D.; Landsman, H.; Lanske, D.; Layter, J.G.; Leins, A.; Lellouch, D.; Lettso, J.; Levinson, L.; Lillich, J.; Lloyd, S.L.; Loebinger, F.K.; Lu, J.; Ludwig, J.; Macpherson, A.; Mader, W.; Marcellini, S.; Martin, A.J.; Masetti, G.; Mashimo, T.; Mattig, Peter; McDonald, W.J.; McKenna, J.; McMahon, T.J.; McPherson, R.A.; Meijers, F.; Menges, W.; Merritt, F.S.; Mes, H.; Michelini, A.; Mihara, S.; Mikenberg, G.; Miller, D.J.; Moed, S.; Mohr, W.; Mori, T.; Mutter, A.; Nagai, K.; Nakamura, I.; Nanjo, H.; Neal, H.A.; Nisius, R.; O'Neale, S.W.; Oh, A.; Okpara, A.; Oreglia, M.J.; Orito, S.; Pahl, C.; Pasztor, G.; Pater, J.R.; Patrick, G.N.; Pilcher, J.E.; Pinfold, J.; Plane, David E.; Poli, B.; Polok, J.; Pooth, O.; Przybycien, M.; Quadt, A.; Rabbertz, K.; Rembser, C.; Renkel, P.; Roney, J.M.; Rosati, S.; Rozen, Y.; Runge, K.; Sachs, K.; Saeki, T.; Sarkisyan, E.K.G.; Schaile, A.D.; Schaile, O.; Scharff-Hansen, P.; Schieck, J.; Schoerner-Sadenius, Thomas; Schroder, Matthias; Schumacher, M.; Schwick, C.; Scott, W.G.; Seuster, R.; Shears, T.G.; Shen, B.C.; Sherwood, P.; Siroli, G.; Skuja, A.; Smith, A.M.; Sobie, R.; Soldner-Rembold, S.; Spano, F.; Stahl, A.; Stephens, K.; Strom, David M.; Strohmer, R.; Tarem, S.; Tasevsky, M.; Taylor, R.J.; Teuscher, R.; Thomson, M.A.; Torrence, E.; Toya, D.; Tran, P.; Trigger, I.; Trocsanyi, Z.; Tsur, E.; Turner-Watson, M.F.; Ueda, I.; Ujvari, B.; Vollmer, C.F.; Vannerem, P.; Vertesi, R.; Verzocchi, M.; Voss, H.; Vossebeld, J.; Waller, D.; Ward, C.P.; Ward, D.R.; Watkins, P.M.; Watson, A.T.; Watson, N.K.; Wells, P.S.; Wengler, T.; Wermes, N.; Wetterling, D.; Wilson, G.W.; Wilson, J.A.; Wolf, G.; Wyatt, T.R.; Yamashita, S.; Zer-Zion, D.; Zivkovic, Lidija
2004-01-01
Gluon jets with a mean energy of 22 GeV and purity of 95% are selected from hadronic Z0 decay events produced in e+e- annihilations. A subsample of these jets is identified which exhibits a large gap in the rapidity distribution of particles within the jet. After imposing the requirement of a rapidity gap, the gluon jet purity is 86%. These jets are observed to demonstrate a high degree of sensitivity to the presence of color reconnection, i.e. higher order QCD processes affecting the underlying color structure. We use our data to test three QCD models which include a simulation of color reconnection: one in the Ariadne Monte Carlo, one in the Herwig Monte Carlo, and the other by Rathsman in the Pythia Monte Carlo. We find the Rathsman and Ariadne color reconnection models can describe our gluon jet measurements only if very large values are used for the cutoff parameters which serve to terminate the parton showers, and that the description of inclusive Z0 data is significantly degraded in this case. We concl...
Energy Technology Data Exchange (ETDEWEB)
Chala, Mikael [Granada Univ. (Spain). CAFPE; Granada Univ. (Spain). Dept. de Fisica Teorica y del Cosmos; Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Juknevich, Jose [International School for Advanced Studies, Trieste (Italy); Istituto Nazionale di Fisica Nucleare, Trieste (Italy); Perez, Gilad [Weizmann Institute of Science, Rehovot (Israel). Dept. of Particle Physics and Astrophysics; Santiago, Jose [Granada Univ. (Spain). CAFPE; Granada Univ. (Spain). Dept. de Fisica Teorica y del Cosmos; European Organization for Nuclear Research (CERN), Geneva (Switzerland)
2014-11-15
We study the phenomenology of vector resonances in the context of natural composite Higgs models. A mild hierarchy between the fermionic partners and the vector resonances can be expected in these models based on the following arguments. Both direct and indirect (electroweak and flavor precision) constraints on fermionic partners are milder than the ones on spin one resonances. Also the naturalness pressure coming from the top partners is stronger than that induced by the gauge partners. This observation implies that the search strategy for vector resonances at the LHC needs to be modified. In particular, we point out the importance of heavy gluon decays (or other vector resonances) to top partner pairs that were overlooked in previous experimental searches at the LHC. These searches focused on simplified benchmark models in which the only new particle beyond the Standard Model was the heavy gluon. It turns out that, when kinematically allowed, such heavy-heavy decays make the heavy gluon elusive, and the bounds on its mass can be up to 2 TeV milder than in the simpler models considered so far for the LHC14. We discuss the origin of this difference and prospects for dedicated searches.
International Nuclear Information System (INIS)
Chala, Mikael; Juknevich, Jose; Perez, Gilad
2014-11-01
We study the phenomenology of vector resonances in the context of natural composite Higgs models. A mild hierarchy between the fermionic partners and the vector resonances can be expected in these models based on the following arguments. Both direct and indirect (electroweak and flavor precision) constraints on fermionic partners are milder than the ones on spin one resonances. Also the naturalness pressure coming from the top partners is stronger than that induced by the gauge partners. This observation implies that the search strategy for vector resonances at the LHC needs to be modified. In particular, we point out the importance of heavy gluon decays (or other vector resonances) to top partner pairs that were overlooked in previous experimental searches at the LHC. These searches focused on simplified benchmark models in which the only new particle beyond the Standard Model was the heavy gluon. It turns out that, when kinematically allowed, such heavy-heavy decays make the heavy gluon elusive, and the bounds on its mass can be up to 2 TeV milder than in the simpler models considered so far for the LHC14. We discuss the origin of this difference and prospects for dedicated searches.
Quark jets, gluon jets and the three-gluon vertex
International Nuclear Information System (INIS)
Fodor, Z.
1989-11-01
Using hadronic jets in electron-positron annihilation, we suggest a simple and model-independent method to see the differences between quark and gluon jets. We define and analyse special energy dependent moments of jets and choose those which are the most characteristic to the jet type. The method handles the energy of a jet in an adequate way. We discuss new methods using jet flavor tagging, ordinary flavor tagging of a definite quark jet or discrimination between quark and gluon jets, to test the triple-gluon vertex in electron-positron annihilation. An enriched sample of gluon jets, jets with the smallest energy in four-jet events, as well as a continuous tagging variable are also studied. 21 refs., 6 figs. (Author)
1990-01-01
This volume contains 14 review articles on the theory and phenomenology of the creation and diagnosis of quark-gluon plasma. They are written by active investigators of in the various research topics, which range from the QCD foundation through transport theory and thermalization models to the examination of possible signatures. The monograph should be useful not only to the experienced researchers in the subject but also to newcomers.
Gluon exchange in elastic hadron scattering
International Nuclear Information System (INIS)
Jenkovszky, L.L.; Paccanoni, F.; Chikovani, Z.E.
1991-01-01
It is generally accepted that the Pomeron, which determines the long-range component of the strong interaction, corresponds to exchange of gluons with the corresponding quantum numbers (the minimum number of such gluons is two). The C-odd partner of the Pomeron, the odderon, corresponds to exchange of an odd number of gluons (three or more). By means of a model of the nonperturbative gluon propagator, restrictions are obtained on the parameters of two-gluon (Pomeron) and three-gluon (odderon) exchange in hadron scattering. In the framework of this model an interpretation is proposed for the various asymptotic regimes in the behavior of the total cross section and of the differential cross section of elastic scattering at high energies
Electrical conductivity and shear viscosity of quark gluon plasma in a quasiparticle model
International Nuclear Information System (INIS)
Srivastava, P.K.; Mohanty, B.
2014-01-01
Relativistic heavy-ion collisions (HIC) have reported the formation of a strongly coupled quark gluon plasma (sQGP). To study the properties of this sQGP is the main focus nowadays. Among these the shear viscosity (η) and electrical conductivity (σ el ) could reflect the transport properties of the medium. By studying the shear viscosity or more specifically shear viscosity to entropy density ratio (η/s), one can understand the nature of interactions among the constituents of the produced medium, it gives a measure of the fluidity. Electrical conductivity represents the linear response of the system to an applied external electric field. The basic question one could ask is that whether the matter created at heavy ion collision experiment is an electrical conductor or an insulator. Recent lattice QCD as well as phenomenological studies have shown that these transport quantities show some kind of minimum in its variation with respect to temperature near the temperature corresponding to the transition from hadronic phase to quark-gluon phase
International Nuclear Information System (INIS)
Koller, K.; Krasemann, H.
1979-08-01
We investigate the Dalitz plot population and thrust angular distribution for the Orthoquarkonium decay Q anti Q → 3 scalar gluons. The Dalitz plot for scalar gluons is populated in corners where events are 2 jet like and this disagrees with existing Upsilon data. The scalar gluon thrust angular distribution is also in striking disagreement with the UPSILON data and so scalar gluons are completely ruled out. (orig.)
International Nuclear Information System (INIS)
Koller, K.; Walsh, T.
1978-03-01
We discuss what can be learned of the 3 S 1 quarkonium decay QantiQ → 3 gluoans QantiQ → γ + 2 gluons. The former is a way to find gluon jets and test QCD. The latter also allows us to measure gluoan + gluon → hadrons and look for pure gluonic resonances (glueballs). (orig.) [de
Quark-gluon vertex from the Landau gauge Curci-Ferrari model
Peláez, Marcela; Tissier, Matthieu; Wschebor, Nicolás
2015-08-01
We investigate the quark-gluon three-point correlation function within a one-loop computation performed in the Curci-Ferrari massive extension of the Faddeev-Popov gauge-fixed action. The mass term is used as a minimal way for taking into account the influence of the Gribov ambiguity. Our results, with renormalization-group improvement, are compared with lattice data. We show that the comparison is, in general, very satisfactory for the functions which are compatible with chiral symmetry, except for one. We argue that this may be due to large systematic errors when extracting this function from lattice simulations. The quantities which break chiral symmetry are more sensitive to the details of the renormalization scheme. We, however, manage to reproduce some of them with good precision. The chosen parameters allow us to simultaneously fit the quark mass function coming from the quark propagator with reasonable agreement.
International Nuclear Information System (INIS)
Novello, M.; Lorenci, V.A. de; Elbaz, E.
1997-02-01
In this paper we present a new model for a gauge field theory such that self-interacting spin-one particles can be confined in a compact domain. The necessary conditions to produce the confining potential appear already in the properties of the eikonal structure generated by the particular choice of the dynamics. (author)
Constituent gluon interpretation of glueballs and gluelumps
International Nuclear Information System (INIS)
Boulanger, N.; Buisseret, F.; Mathieu, V.; Semay, C.
2008-01-01
Arguments are given that support the interpretation of the lattice QCD glueball and gluelump spectra in terms of bound states of massless constituent gluons with helicity 1. In this scheme, we show that the mass hierarchy of the currently known gluelumps and glueballs is mainly due to the number of constituent gluons and can be understood within a simple flux tube model. It is also argued that the lattice QCD 0 +- glueball should be seen as a four-gluon bound state. We finally predict the mass of the 0 - state, not yet computed in lattice QCD. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Sichtermann, Ernst
2016-12-15
The fundamental structure of nucleons and nuclear matter is described by the properties and dynamics of quarks and gluons in quantum chromodynamics. Electron-nucleon collisions are a powerful method to study this structure. As one increases the energy of the collisions, the interaction process probes regions of progressively higher gluon density. This density must eventually saturate. An high-energy polarized Electron-Ion Collider (EIC) has been proposed to observe and study the saturated gluon density regime. Selected measurements will be discussed, following a brief introduction.
A pion and gluon exchange model of the non-annihilation part of the nucleon-antinucleon interaction
International Nuclear Information System (INIS)
Fernandez, F.
1988-01-01
The effect of quark antisymmetrization on the one-pion and one-gluon exchange between nucleons and antinucleons is explicitly calculated within the framework of the Born-Oppenheimer approximation. We found an effective short range part of the N-anti N interaction which is repulsive in all the spin-isospin channels. (Author)
Modeling Soft Gluons and Fiducial Cross Sections: New Physics or Old QCD?
CERN. Geneva
2014-01-01
In this talk I will describe some of the consequences of the consistently discrepant WW cross section measured at ATLAS and CMS. I will describe models where stops can be as light as 200 GeV satisfying naturalness constraints. I will also discuss the current states of the art modeling of QCD effects in the measurement of the cross section using p_T resummation. I will show that there is a sizable effect caused by a jet veto in extrapolating to the total cross section, but ultimately not enough to explain the current discrepancy.
International Nuclear Information System (INIS)
Kaidalov, A.B.; Volkovitsky, P.E.
1981-01-01
In the framework of the quark-gluon picture for strong interactions based on the topological expansion and the string model, the relations between t differences of hadronic cross- section are obtained. The system of equations for the contribution of secondary reggeons (rho, ω, f, A 2 and phi and f' poles) to the elastic scattering amplitudes for arbitrary hadrons is derived. It is shown that this system has a factorized solution and the secondary reggeon residues for all hadrons are expressed in terms of the universal function g(t). The model predictions are in a good agreement with experimental data [ru
International Nuclear Information System (INIS)
Granier de Cassagnac, R.
2010-01-01
The quark-gluon plasma (QGP) is a state of matter in which the universe was expected to be a few micro-seconds after the big-bang. Violent collisions of heavy ions are supposed to re-create this state in particle accelerators. Numerous signatures of this fugacious state have already been observed at the RHIC (relativistic heavy ion collider). The first evidence of the violence of collisions is the number of generated particles: about 6000 per collision, mostly hadrons. This figure seems high but in fact is less than theoretically expected and is the first sign of the formation of a QGP that saturates the density of gluons. Another sign, observed at the RHIC is the damping of the particle jets that are produced in the collision. This damping is consistent with the crossing of a medium whose density is so high that it can not be made of hadrons but of partons. In the RHIC experiments the collective behaviour of quarks and gluons shows that they are strongly interacting with one another. This fact supports the idea that the QGP is more a perfect liquid rather than an ideal gas in which quarks and gluons move freely. (A.C.)
Gluon radiation in diffractive electroproduction
International Nuclear Information System (INIS)
Buchmueller, W.; McDermott, M.F.; Hebecker, A.
1996-07-01
Order α s -correlations to the diffractive structure functions F L D and F 2 D at large Q 2 and small x are evaluated in the semiclassical approach, where the initial proton is treated as a classical colour field. The diffractive final state contains a fast gluon in addition to a quark-antiquark pair. Two of these partons may have large transverse momentum. Our calculations lead to an intuitive picture of deep-inelastic diffractive processes which is very similar to Bjorken's aligned-jet model. Both diffractive structure functions contain leading twist contributions from high-p perpendicular to jets. (orig.)
International Nuclear Information System (INIS)
Ayala, A.L.
1996-01-01
In this talk we present our detailed study (theory and numbers) on the shadowing corrections to the gluon structure functions for nuclei. Starting from rather controversial information on the nucleon structure function which is originated by the recent HERA data, we develop the Glauber approach for the gluon density in a nucleus based on Mueller formula and estimate the value of the shadowing corrections in this case. Then we calculate the first corrections to the Glauber approach and show that these corrections are big. Based on this practical observation we suggest the new evolution equation which takes into account the shadowing corrections and solve it. We hope to convince you that the new evolution equation gives a good theoretical tool to treat the shadowing corrections for the gluons density in a nucleus and, therefore, it is able to provide the theoretically reliable initial conditions for the time evolution of the nucleus-nucleus cascade. The initial conditions should be fixed both theoretically and phenomenologically before to attack such complicated problems as the mixture of hard and soft processes in nucleus-nucleus interactions at high energy or the theoretically reliable approach to hadron or/and parton cascades for high energy nucleus-nucleus interaction. 35 refs., 24 figs., 1 tab
Nayak, Tapan; Sarkar, Sourav
2014-01-01
At extremely high temperatures and densities, protons and neutrons may dissolve into a "soup" of quarks and gluons, called the Quark-Gluon Plasma (QGP). For a few microseconds, shortly after the Big Bang, the Universe was filled with the QGP matter. The search and study of Quark-Gluon Plasma (QGP) is one of the most fundamental research topics of our times. The QGP matter has been probed by colliding heavy ions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, New York and the Large Hadron Collider at CERN, Geneva. By colliding heavy-ions at a speed close to that of light, scientists aim to obtain - albeit over a tiny volume of the size of a nucleus and for an infinitesimally short instant - a QGP state. This QGP state can be observed by dedicated experiments, as it reverts to hadronic matter through expansion and cooling. This volume presents some of the current theoretical and experimental understandings in the field of QGP.
Proton-proton elastic scattering with massive gluons
International Nuclear Information System (INIS)
Sauter, Werner K.; Ducati, M.B. Gay
2001-01-01
In this contribution different approaches to generate a gluon mass are discussed. More specially a recent result for the gluon propagator with a dynamical mass, proposal by Gorbar and Natale, is used in connection with the Landshoff-Nachtmann model for the Pomeron to describe the elastic differential cross section for pp scattering, with good agreement. (author)
Gluon bremsstrahlung and elastic scattering of hadrons
International Nuclear Information System (INIS)
Povh, B.
2001-01-01
The differential and the total cross sections in high energy hadron-proton interactions give a beautiful insight in the low Q 2 structure of the nucleon. The cross section is composed of two parts: a large energy independent part corresponding to the interaction of the valence quark with the target without gluon radiation and an energy dependent part caused by gluon bremsstrahlung. The gluons are located at small transverse distances of about 0.3 fm from the valence quarks. The model with two scales, the size of the hadron (R 2 ∼ 1 fm 2 ) and the size of the gluonic cloud (r 0 2 ∼ 0.1 fm 2 ), correctly predicts the total and the differential cross sections and the behaviour of diffractive dissociation in hadronic and deep inelastic events. (orig.)
Directory of Open Access Journals (Sweden)
Zabrodin E.
2017-01-01
Full Text Available Proton-proton collisions at energies from √s = 200 GeV up to √s = 14 TeV are studied within the microscopic quark-gluon string model. The model is based on Gribov’s Reggeon Field Theory accomplished by string phenomenology. Comparison with experimental data shows that QGSM describes well particle yields, rapidity - and transverse momentum spectra, rise of mean 〈 pT 〉 and forward-backward multiplicity correlations. The latter arise in QGSM because of the addition of various processes with different mean multiplicities. The model also indicates fulfillment of extended longitudinal scaling and violation of Koba-Nielsen-Olesen scaling at LHC. The origin of both features is traced to short-range particle correlations in the strings. Predictions are made for √s = 14 TeV.
Effects of gluon radiation in hadronic collisions
International Nuclear Information System (INIS)
Gustafson, Goesta.
1989-10-01
In this talk I discuss effects of gluon emission in soft collisions, the so-called 'soft radiation' in the Fritjof model. It is seen e.g. that the pT in the fragmentation regions, the seagull effect, increases with energy in fair agreement with experiments. I also discuss the content of strange and heavier quarks in high-pT gluon jets. Within the dipole scheme for QCD cascades on finds a larger production of heavier quarks than in previous approaches. Qualitative agreement with data is obtained for the K/π ratio and D meson production
Quark-gluon plasma, and strangeness
International Nuclear Information System (INIS)
Rafelski, Johann; Letessier, Jean
2002-01-01
In order to recognize the new form of matter created at RHIC and SPS as the deconfined quark-gluon plasma state (QGP), we need to understand the expected properties of this phase near to the conditions of its formation and disintegration. Thus, we first develop a model of QGP considering the constrains arising from QCD properties and lattice results, and explore its properties. In the second part, we describe the kinetic theory of strangeness production in the QGP phase. We show that gluon fusion dominate and evaluate the degree of equilibration expected at RHIC
International Nuclear Information System (INIS)
Kaidalov, A.B.; Klochkov, M.A.; Sarychev, L.I.; Smirnova, L.N.
1989-01-01
The inclusive differential cross sections of Λ- and bar Λ-hyperon production in bar pp and pp interactions at momenta 12, 32, and 100 GeV/c are calculated in the quark-gluon string model and compared with experiment. The model satisfactorily reproduces the experimental data
Gluon gas viscosity in nonperturbative region
International Nuclear Information System (INIS)
Il'in, S.V.; Mogilevskij, O.A.; Smolyanskij, S.A.; Zinov'ev, G.M.
1992-01-01
Using the Green-Kubo-type formulae and the cutoff model motivated by Monte Carlo lattice gluodynamics simulations we find the temperature behaviour of shear viscosity of gluon gas in the region of deconfinement phase transition. 22 refs.; 1 fig. (author)
Inflating metastable quark-gluon plasma universe
International Nuclear Information System (INIS)
Jenkovszky, L.L.; Kaempfer, B.; Sysoev, V.M.
1990-01-01
We show within the Friedmann model with the equation of state p(T)=aT 4 -AT that our universe has expanded exponentially when it was in a metastable quark-gluon plasma state. The scale factor during that epoch increased by many orders of magnitude. 13 refs.; 5 figs
Bosonization with inclusion of the gluon condensate
International Nuclear Information System (INIS)
Ebert, D.; Volkov, M.K.
1994-01-01
The effects of the gluon condensate on the quark condensate and on masses and coupling constants of composite mesons are discussed within a QCD-motivated Nambu-Jona-Lasinio model for zero temperature as well as for the case of finite temperature and baryon number density. (orig.)
Quark-gluon plasma (Selected Topics)
International Nuclear Information System (INIS)
Zakharov, V. I.
2012-01-01
Introductory lectures to the theory of (strongly interacting) quark-gluon plasma given at the Winter School of Physics of ITEP (Moscow, February 2010). We emphasize theoretical issues highlighted by the discovery of the low viscosity of the plasma. The topics include relativistic hydrodynamics, manifestations of chiral anomaly in hydrodynamics, superfluidity, relativistic superfluid hydrodynamics, effective stringy scalars, holographic models of Yang-Mills theories.
Exploring Quarks, Gluons and the Higgs Boson
Johansson, K. Erik
2013-01-01
With real particle collision data available on the web, the amazing dynamics of the fundamental particles of the standard model can be explored in classrooms. Complementing the events from the ATLAS experiment with animations of the fundamental processes on the quark and gluon level makes it possible to better understand the invisible world of…
Energy Technology Data Exchange (ETDEWEB)
Weinzierl, Stefan, E-mail: weinzierl@uni-mainz.de
2017-03-13
This report is centred around tree-level scattering amplitudes in pure Yang–Mills theories, the most prominent example is given by the tree-level gluon amplitudes of QCD. I will discuss several ways of computing these amplitudes, illustrating in this way recent developments in perturbative quantum field theory. Topics covered in this review include colour decomposition, spinor and twistor methods, off- and on-shell recursion, MHV amplitudes and MHV expansion, the Grassmannian and the amplituhedron, the scattering equations and the CHY representation. At the end of this report there will be an outlook on the relation between pure Yang–Mills amplitudes and scattering amplitudes in perturbative quantum gravity.
Quark and Gluon Relaxation in Quark-Gluon Plasmas
Heiselberg, H.; Pethick, C. J.
1993-01-01
The quasiparticle decay rates for quarks and gluons in quark-gluon plasmas are calculated by solving the kinetic equation. Introducing an infrared cutoff to allow for nonperturbative effects, we evaluate the quasiparticle lifetime at momenta greater than the inverse Debye screening length to leading order in the coupling constant.
Production and recombination of gluons
International Nuclear Information System (INIS)
Temiraliev, A.T.
2006-01-01
Full text: Nonlinear Markov process of parton production has been considered. The Kolmogorov equation is applied for the evolution equation based on the approximation of independent gluons production in every decay act. We introduced a 'crossing' parameter and used the combination relations to obtain nonlinear recombination equation for the evolution of gluon structure function. (author)
International Nuclear Information System (INIS)
Cipriano, P.; Dooling, S.; Grebenyuk, A.; Gunnellini, P.; Katsas, P.; Hautmann, F.; Oxford Univ.; Jung, H.; Antwerpen Univ.
2013-08-01
In the forthcoming high-luminosity phase at the LHC many of the most interesting QCD measurements so far become prohibitively difficult due to the high pile-up. We suggest a program of QCD measurements based on the observed Higgs boson which can be started now and can be carried through also in the large pile-up environment at high luminosity. It focuses on gluonic processes at high mass scales, and their distinctive QCD features compared to classic probes such as Drell-Yan. It explores the strong-interaction sector of the Standard Model both at high transverse momenta and at low transverse momenta, by investigating issues on gluon fusion processes which have never been addressed experimentally before. We discuss a few specific examples and present results of Monte Carlo simulations.
Energy Technology Data Exchange (ETDEWEB)
Cipriano, P.; Dooling, S.; Grebenyuk, A.; Gunnellini, P.; Katsas, P. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Hautmann, F. [Sussex Univ., Brighton (United Kingdom). Dept. of Physics and Astronomy; Oxford Univ. (United Kingdom). Dept. of Physics; Jung, H. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Antwerpen Univ. (Belgium). Elementaire Deeltjes Fysica
2013-08-15
In the forthcoming high-luminosity phase at the LHC many of the most interesting QCD measurements so far become prohibitively difficult due to the high pile-up. We suggest a program of QCD measurements based on the observed Higgs boson which can be started now and can be carried through also in the large pile-up environment at high luminosity. It focuses on gluonic processes at high mass scales, and their distinctive QCD features compared to classic probes such as Drell-Yan. It explores the strong-interaction sector of the Standard Model both at high transverse momenta and at low transverse momenta, by investigating issues on gluon fusion processes which have never been addressed experimentally before. We discuss a few specific examples and present results of Monte Carlo simulations.
Heavy Flavour Production as Probe of Gluon Sivers Function
International Nuclear Information System (INIS)
Godbole, Rohini M.; Kaushik, Abhiram; Misra, Anuradha; Rawoot, Vaibhav; Sonawane, Bipin
2017-01-01
Heavy flavour production like J/ψ and D-meson production in scattering of electrons/unpolarized protons off polarized proton target offer promising probes to investigate gluon Sivers function. In this talk, I will summarize our recent work on transverse single spin asymmetry in J/ψ-production and D-meson production in pp↑ scattering using a generalized parton model approach. We compare predictions obtained using different models of gluon Sivers function within this approach and then, taking into account the transverse momentum dependent evolution of the unpolarized parton distribution functions and gluon Sivers function, we study the effect of evolution on asymmetry. (author)
Hadronization of the quark-gluon plasma
International Nuclear Information System (INIS)
Mueller, B.; Sano, M.; Sato, H.; Schaefer, A.
1986-11-01
We construct a model for hadronization of the quark-gluon plasma, based on the relativistic coalescence model. We relate the coalescence amplitude to the one-particle Wigner function for quarks in the plasma. The relation between the Wigner function and the nucleon structure function is pointed out. We derive explicit expressions for the production of mesons and baryons in the framework of the relativistic harmonic oscillator model of hadronic structure. (author)
International Nuclear Information System (INIS)
Fredriksson, S.
1984-01-01
The Stockholm diquark is a very small (0.1-0.2 fm), bound pair of two unequal quarks in spin 0 and colour 3*. If it exists, it is expected to simulate many of the trends presently attributed to perturbative gluon processes. The Stockholm group (S. Ekelin, M. Jaendel, T.I. Larson and myself) is therefore looking for reactions where the non-perturbative QCD phenomenon of diquark formation would give signatures completely different from those of perturbative gluonic contributions. I report here on some new suggestions for diquark effects in deep inelastic scattering, with emphasis on neutron-proton differences, proton production in the current fragmentation region and nuclear target (''EMC'') effects
Time evolution of the quark-gluon plasma
International Nuclear Information System (INIS)
Cooper, F.; New Hampshire Univ., Durham, NH
1993-01-01
We review progress in our understanding the production and time evolution of the quark gluon plasma starting with boost invariant initial conditions in a filed theory model based on the Schwinger mechanism of particle production via tunneling
Improving the simulation of quark and gluon jets with Herwig 7
Energy Technology Data Exchange (ETDEWEB)
Reichelt, Daniel [Technische Universitaet Dresden, Institut fuer Kern- und Teilchenphysik, Dresden (Germany); Richardson, Peter [CERN, Theory Department, Geneva (Switzerland); Durham University, Department of Physics, IPPP, Durham (United Kingdom); Siodmok, Andrzej [Polish Academy of Sciences, Institute of Nuclear Physics, Krakow (Poland)
2017-12-15
The properties of quark and gluon jets, and the differences between them, are increasingly important at the LHC. However, Monte Carlo event generators are normally tuned to data from e{sup +}e{sup -} collisions which are primarily sensitive to quark-initiated jets. In order to improve the description of gluon jets we make improvements to the perturbative and the non-perturbative modelling of gluon jets and include data with gluon-initiated jets in the tuning for the first time. The resultant tunes significantly improve the description of gluon jets and are now the default in Herwig 7.1. (orig.)
Gluon saturation and baryon stopping in the SPS, RHIC, and LHC energy regions
International Nuclear Information System (INIS)
Li Shuang; Feng Shengqin
2012-01-01
A new geometrical scaling method with a gluon saturation rapidity limit is proposed to study the gluon saturation feature of the central rapidity region of relativistic nuclear collisions. The net-baryon number is essentially transported by valence quarks that probe the saturation regime in the target by multiple scattering. We take advantage of the gluon saturation model with geometric scaling of the rapidity limit to investigate net baryon distributions, nuclear stopping power and gluon saturation features in the SPS and RHIC energy regions. Predictions for net baryon rapidity distributions, mean rapidity loss and gluon saturation feature in central Pb + Pb collisions at the LHC are made in this paper. (authors)
Improving the Simulation of Quark and Gluon Jets with Herwig 7 arXiv
Reichelt, Daniel; Siodmok, Andrzej
2017-12-16
The properties of quark and gluon jets, and the differences between them, are increasingly important at the LHC. However, Monte Carlo event generators are normally tuned to data from $e^+e^-$ collisions which are primarily sensitive to quark-initiated jets. In order to improve the description of gluon jets we make improvements to the perturbative and the non-perturbative modelling of gluon jets and include data with gluon-initiated jets in the tuning for the first time. The resultant tunes significantly improve the description of gluon jets and are now the default in Herwig 7.1.
From Color Fields to Quark Gluon Plasma
Energy Technology Data Exchange (ETDEWEB)
Fries, Rainer J. [School of Physics and Astronomy, University of Minnesota, Minneapolis MN 55455 (United States); Kapusta, Joseph I. [School of Physics and Astronomy, University of Minnesota, Minneapolis MN 55455 (United States); Li, Yang [School of Physics and Astronomy, University of Minnesota, Minneapolis MN 55455 (United States)
2006-08-07
We discuss a model for the energy distribution and the early space-time evolution of a heavy ion collision. We estimate the gluon field generated in the wake of hard processes and through primordial fluctuations of the color charges in the nuclei. Without specifying the dynamical mechanism of thermalization we calculate the energy momentum tensor of the following plasma phase. The results of this model can be used as initial conditions for a further hydrodynamic evolution.
Quark-gluon mixing in pseudoscalar and tensor mesons
International Nuclear Information System (INIS)
Eremyan, Sh.S.; Nazaryan, A.E.
1986-01-01
A mixing model of quark-antiquark ang gluonium states in η, η', i(1440) pseudoscalar and f, f', Θ(1690) tensor mesons is considered. Description of and predictions for 68 two-particle decays with these particles taking part in them are obtained. It is shown that i(1440) by 85% consists of gluonium and Θ(1690) is a pure gluonic state. The quark-gluon and gluon-gluon couplings in the pseudoscalar sector are obtained to be stronger as compared to the corresponding ones in the tensor case
Quantum chromodynamics as effective theory of quarks and composite gluons
International Nuclear Information System (INIS)
Fuss, T.
2004-01-01
The dynamics of quarks is described by a nonperturbatively regularized NJL model which is canonically quantized and fulfil a probability interpretation. The quantum field theory of this model is formulated in a functional space. The wave functions of the quarks and gluons are calculated as eigenstates of Hard-Core equations and the gluons are considered as relativistic bound states of colored quark-antiquark pairs. The effective dynamics of the quarks and gluons is derived from weak mapping in functional space. This leads to the functional formulation of the phenomenological SU(3) local gauge invariant quark-gluon equations in temporal gauge. This means that the local gauge symmetry is a dynamical effect resulting from the quark model
Bootstrapping quarks and gluons
Energy Technology Data Exchange (ETDEWEB)
Chew, G.F.
1979-04-01
Dual topological unitarization (DTU) - the approach to S-matrix causality and unitarity through combinatorial topology - is reviewed. Amplitudes associated with triangulated spheres are shown to constitute the core of particle physics. Each sphere is covered by triangulated disc faces corresponding to hadrons. The leading current candidate for the hadron-face triangulation pattern employs 3-triangle basic subdiscs whose orientations correspond to baryon number and topological color. Additional peripheral triangles lie along the hadron-face perimeter. Certain combinations of peripheral triangles with a basic-disc triangle can be identified as quarks, the flavor of a quark corresponding to the orientation of its edges that lie on the hadron-face perimeter. Both baryon number and flavor are additively conserved. Quark helicity, which can be associated with triangle-interior orientation, is not uniformly conserved and interacts with particle momentum, whereas flavor does not. Three different colors attach to the 3 quarks associated with a single basic subdisc, but there is no additive physical conservation law associated with color. There is interplay between color and quark helicity. In hadron faces with more than one basic subdisc, there may occur pairs of adjacent flavorless but colored triangles with net helicity +-1 that are identifiable as gluons. Broken symmetry is an automatic feature of the bootstrap. T, C and P symmetries, as well as up-down flavor symmetry, persist on all orientable surfaces.
Bootstrapping quarks and gluons
International Nuclear Information System (INIS)
Chew, G.F.
1979-04-01
Dual topological unitarization (DTU) - the approach to S-matrix causality and unitarity through combinatorial topology - is reviewed. Amplitudes associated with triangulated spheres are shown to constitute the core of particle physics. Each sphere is covered by triangulated disc faces corresponding to hadrons. The leading current candidate for the hadron-face triangulation pattern employs 3-triangle basic subdiscs whose orientations correspond to baryon number and topological color. Additional peripheral triangles lie along the hadron-face perimeter. Certain combinations of peripheral triangles with a basic-disc triangle can be identified as quarks, the flavor of a quark corresponding to the orientation of its edges that lie on the hadron-face perimeter. Both baryon number and flavor are additively conserved. Quark helicity, which can be associated with triangle-interior orientation, is not uniformly conserved and interacts with particle momentum, whereas flavor does not. Three different colors attach to the 3 quarks associated with a single basic subdisc, but there is no additive physical conservation law associated with color. There is interplay between color and quark helicity. In hadron faces with more than one basic subdisc, there may occur pairs of adjacent flavorless but colored triangles with net helicity +-1 that are identifiable as gluons. Broken symmetry is an automatic feature of the bootstrap. T, C and P symmetries, as well as up-down flavor symmetry, persist on all orientable surfaces
Quark-gluon mixing in scalar mesons
International Nuclear Information System (INIS)
Eremyan, Sh.S.; Nazaryan, A.E.
1986-01-01
Scalar mesons are considered within the quark-gluon mixing model. It is shown that there exists decouplet of scalar particles consisting of S* (975), ε (1400), S*' (1700), δ (980) and κ (1350) resonances. It has turned out that the long ago known S* (975)-resonance is a nearly pure glouball. A good description of all available experimental data on scalar meson decays is obtained
International Nuclear Information System (INIS)
Kaidalov, A.B.; Kondratyuk, L.A.; Tchekin, D.V.
2000-01-01
The electromagnetic form factors for pions and nucleons are considered within the model of quark-gluon strings, where the momentum-transfer dependence of hadronic form factors is determined by the intercepts of the corresponding Regge trajectories and by the Sudakov form factor. Analytic expressions found for form factors in the timelike region admit an analytic continuation to the spacelike region. The resulting form factors for pions and nucleons comply well with experimental data both for positive and for negative values of the squared momentum transfer q 2 . It is shown that the distinctions between the absolute values of the pion and nucleon form factors F π (q 2 ), G m (q 2 ), and F 2 (q 2 ) at positive values of q 2 and those at negative values of this variable are associated with the analytic properties of the double-logarithmic term in the exponent of the Sudakov form factor. The spin structure of the amplitudes for quark transitions into hadrons that is proposed in the present study makes it possible to describe fairly well available experimental data on the Pauli form factor F 2 and on the ratio G e /G m
Quarks and gluons in hadrons and nuclei
International Nuclear Information System (INIS)
Close, F.E.
1989-12-01
These lectures discuss the particle-nuclear interface -- a general introduction to the ideas and application of colored quarks in nuclear physics, color, the Pauli principle, and spin flavor correlations -- this lecture shows how the magnetic moments of hadrons relate to the underlying color degree of freedom, and the proton's spin -- a quark model perspective. This lecture reviews recent excitement which has led some to claim that in deep inelastic polarized lepton scattering very little of the spin of a polarized proton is due to its quarks. This lecture discusses the distribution functions of quarks and gluons in nucleons and nuclei, and how knowledge of these is necessary before some quark-gluon plasma searches can be analyzed. 56 refs., 2 figs
The gluon condensation at high energy hadron collisions
Energy Technology Data Exchange (ETDEWEB)
Zhu, Wei, E-mail: weizhu@mail.ecnu.edu.cn [Department of Physics, East China Normal University, Shanghai 200241 (China); Lan, Jiangshan [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)
2017-03-15
We report that the saturation/CGC model of gluon distribution is unstable under action of the chaotic solution in a nonlinear QCD evolution equation, and it evolves to the distribution with a sharp peak at the critical momentum. We find that this gluon condensation is caused by a new kind of shadowing–antishadowing effects, and it leads to a series of unexpected effects in high energy hadron collisions including astrophysical events. For example, the extremely intense fluctuations in the transverse-momentum and rapidity distributions of the gluon jets present the gluon-jet bursts; a sudden increase of the proton–proton cross sections may fill the GZK suppression; the blocking QCD evolution will restrict the maximum available energy of the hadron–hadron colliders.
The hadron to quark/gluon transition
International Nuclear Information System (INIS)
Brown, G.E.; Bethe, H.A.; Pizzochero, P.M.
1991-01-01
In this paper we are concerned with the hadron to quark/gluon transition. We describe the equilibrium states of hadronic matter by a Hagedorn spectrum; introducing scaling masses, as dictated by the restoration of chiral invariance with increasing temperature, we show that in the chiral SU(2) f limit there is a maximum hadron temperature (T H ) max ≅ 128 MeV. Since the quark/gluon perturbative phase involves restoration of conformal invariance, we take the bag constant to be the conformal anomaly, i.e. the gluon condensate. The stability condition P QG > 0 for the pressure requires that there is a minimum temperature; we find (T QG ) min ≅ 172 MeV for SU(2) f . According to the simple Hagedorn model, there appears to be a region of temperature between (T H ) max and (T QG ) min in which no admissible equilibrium states exist. Since the two phases cannot exist at a common temperature, in this model there is no QCD phase transition. (orig.)
One gluon, two gluon: multigluon production via high energy evolution
International Nuclear Information System (INIS)
Kovner, Alex; Lublinsky, Michael
2006-01-01
We develop an approach for calculating the inclusive multigluon production within the JIMWLK high energy evolution. We give a formal expression of multigluon cross section in terms of a generating functional for arbitrary number of gluons n. In the dipole limit the expression simplifies dramatically. We recover the previously known results for single and double gluon inclusive cross section and generalize those for arbitrary multigluon amplitude in terms of Feynman diagramms of Pomeron - like objects coupled to external rapidity dependent field s(η). We confirm the conclusion that the AGK cutting rules in general are violated in multigluon production. However we present an argument to the effect that for doubly inclusive cross section the AGK diagramms give the leading contribution at high energy, while genuine violation only occurs for triple and higher inclusive gluon production. We discuss some general properties of our expressions and suggest a line of argument to simplify the approach further
Gluon Polarisation Measurements at COMPASS
Silva, Luís
2012-01-01
One of the missing keys in the present understanding of the spin structure of the nucleon is the contribution from the gluons: the so-called gluon polarisation. This quantity can be determined in DIS through the photon-gluon fusion process, in which two analysis methods may be used: (i) identifying open charm events or (ii) selecting events with high $p_{T}$ hadrons. The data used in the present work were collected in the COMPASS experiment, where a 160 GeV/c naturally polarised muon beam, impinging on a polarised nucleon fixed target is used. Preliminary results for the gluon polarisation from high $p_{T}$ and open charm analyses are presented. The gluon polarisation result for high $p_{T}$ hadrons is divided, for the first time, into three statistically independent measurements at LO. The result from open charm analysis is obtained at LO and NLO. In both analyses a new weighted method based on a neural network approach is used.
Quark and gluon condensate in vacuum
International Nuclear Information System (INIS)
Vajnshtejn, A.I.; Zakharov, V.I.; Shifman, M.A.
1979-01-01
The mechanism of quark confinement has been reviewed. The fact that coloured particles in a free state cannot be observed is connected with specific properties of vacuum in quantum chromodynamics. The basic hypothesis consists in the existence of vacuum fields, quark and gluon condensates, which affect the coloured objects. The vacuum transparent relative to noncharged ''white'' states serves as a source of the force acting upon the coloured particles. It has been a sucess to examine strictly the action of the vacuum fields on quarks when the distance between them is relatively small and the force of the vacuum fields on quarks is relatively small too. It is shown that the interaction with the vacuum fields manifests itself earlier than the forces connected with the gluon exchange do. It is assumed that the vacuum condensate of quarks and gluons and its relation to properties of resonances and to the bag model exist in reality. The dispersion sum rules are used for calculating masses and lepton widths of resonances
Effective gluon operators and neutron dipole moment
International Nuclear Information System (INIS)
Bigi, I.; Ural'tsev, N.G.
1991-01-01
The role of the purely gluon CP odd six-dimension effective arising in various CP-breaking models is discussed. This operators of most interest in the nonminimal Higgs sector models, the right W models and supersymmetric theories, where it may induce the neutron dipole moment at the level of the experimental restriction. The method for evaluating the magnitude d n is proposed and the reasons are given in favor that the original Weiberg's estimate based on the naive Dimensional Analysis is overdone significantly. The Peccei -Quinn mechanism, impact on the magnitude of d n , which generally may be very essential, is discussed
CERN. Geneva
2017-01-01
Emissions of soft gluons from energetic particles play an important role in collider processes. While the basic physics of soft emissions is simple, it gives rise to a variety of interesting and intricate phenomena (non-global logs, Glauber phases, super-leading logs, factorization breaking). After an introduction, I will review progress in resummation methods such as Soft-Collinear Effective Theory driven by a better understanding of soft emissions. I will also show some new results for computations of soft-gluon effects in gap-between-jets and isolation-cone cross sections.
Gluon field distribution in baryons
International Nuclear Information System (INIS)
Bissey, F.; Cao, F-G.; Kitson, A.; Lasscock, B.G.; Leinweber, D.B.; Signal, A.I.; Williams, A.G.; Zanotti, J.M.
2005-01-01
Methods for revealing the distribution of gluon fields within the three-quark static-baryon potential are presented. In particular, we outline methods for studying the sensitivity of the source on the emerging vacuum response for the three-quark system. At the same time, we explore the possibility of revealing gluon-field distributions in three-quark systems in QCD without the use of gauge-dependent smoothing techniques. Renderings of flux tubes from a preliminary high-statistics study on a 12 3 x 24 lattice are presented
The unconfined quarks and gluons
International Nuclear Information System (INIS)
Abdus Salam
1977-01-01
The consequences of the lepton-hadron gauge unification hypothesis with unconfined quarks and gluons being the hall-mark are discussed. Quark and gluon decays into leptons are shown to provide a new source of multileptonic production in NN, νN and μN collisions. A theorem is stated and proved which highlights the differences between the dynamics of gauge versus non-gauge 1 - particles. Empirical manifestations of gauge coloured mesons are discussed. The question of exact confinement or not is concluded to be in the end an empirical one and must be settled in the laboratory
Fragmentation of quarks and gluons
International Nuclear Information System (INIS)
Soeding, P.
1983-10-01
The author presents a review about quark and gluon jets. He describes the particle contents of the different types of jets. Finally he considers the hadronization mechanism with special regards to three-jet events in e + e - annihilation and hadronization in nuclear matter. (HSI)
1995-01-01
This is a sequel to the review volume Quark-Gluon Plasma. There are 13 articles contributed by leading investigators in the field, covering a wide range of topics about the theoretical approach to the subject. These contributions are timely reviews of nearly all the actively pursued problems, written in a pedagogical style suitable for beginners as well as experienced researchers.
Vogt, Ramona
1998-01-01
Aspects of quark-gluon plasma signatures that can be measured by CMS are discussed. First the initial conditions of the system from minijet production are introduced, including shadowing effects. Color screening of the Upsilon family is then presented, followed by energy loss effects on charm and bottom hadrons, high Pt jets and global observables.
Quark and gluon tagging in dijet mass resonance search
Kellermann, Edgar
2013-01-01
Several models beyond the Standard Model predict new phenomena in particle physics, which would appear as resonant signals in dijet mass distributions. An example for such a resonance is the excited quark q, which is a consequence of Compositeness Models postulating that quarks and leptons are build by more fundamental particles. The main signature of an excited quark would be a dijet event, originated from the radiation of a gluon from the original excited quark when going back to its non-excited state, leading to a quark and a gluon in the final state (with a branching ratio of 83%) . Other examples are the heavy vector bosonsW0 decaying to two quarks and colour octet scalar S8 decaying to two gluons.
Quarks, gluons, colour: facts or fiction?
International Nuclear Information System (INIS)
Buchholz, D.
1996-01-01
A general method is presented that allows one to determine from the local gauge invariant observables of a quantum field theory the underlying particle and symmetry structures appearing at the lower (ultraviolet) end of the spatio-temporal scale. Particles that are confined to small scales, i.e. do not appear in the physical spectrum, can be uncovered in this way without taking recourse to gauge fields or indefinite metric spaces. In this way notions such as quark, gluon, colour symmetry and confinement acquire a new and intrinsic meaning which is stable under gauge or duality transformations. The method is illustrated by the example of the Schwinger model. (orig.)
The PLUTO experiment at DORIS (DESY) and the discovery of the gluon (A recollection)
Energy Technology Data Exchange (ETDEWEB)
Stella, Bruno R. [Rome-3 Univ. (Italy). Dipt. di Fisica; Istituto Nazionale di Fisica Nucleare, Rome (Italy); Meyer, Hans-Juergen
2010-08-15
With the aim of determining the contribution of the PLUTO experiment at the DORIS e{sup +}e{sup -} storage ring to the discovery of the gluon, as members of this former collaboration we have reconsidered all the scientific material produced by PLUTO in 1978 and the first half of 1979. It is clear that the experiment demonstrated the main decay of the Y(9.46 GeV) resonance to be mediated by 3 gluons, by providing evidence for the agreement of this hypothesis with average values and differential distributions of all possible experimental variables and by excluding all other possible alternative models. Moreover PLUTO measured in June 1979 the matrix element of the 3-gluon decay to be quantitatively as expected by QCD (even after hadronization) and, having checked the possibility to correctly trace the gluons' directions, demonstrated the spin 1 nature of the gluon by excluding spin 0 and spin 1/2. The hadronization of the gluon like a quark jet, hypothesized in the 3-gluon jet Monte Carlo simulation, was compatible with the topological data at this energy and was shown to be an approximation at 10% level for the multiplicity ({approx} < p {sub vertical} {sub stroke} {sub vertical} {sub stroke} {sub >}{sup -1}); the right expected gluon fragmentation was needed for the inclusive distributions; this was the first experimental study of (identified) gluon jets. In the following measurements at the PETRA storage ring, these results were confirmed by PLUTO and by three contemporaneous experiments by evidencing at higher energies the gluon radiation (''bremsstrahlung''), the softer one, by jet broadening, and the hard one, by the emission of (now clearly visible) gluon jets by quarks. The gluon's spin 1 particle nature was also confirmed. The PLUTO results on Y decays had been confirmed both by contemporaneous experiments at DORIS (partially) and later (also partially) were confirmed by more sophisticated detectors. (orig.)
The PLUTO experiment at DORIS (DESY) and the discovery of the gluon (A recollection)
International Nuclear Information System (INIS)
Stella, Bruno R.; Meyer, Hans-Juergen
2010-08-01
With the aim of determining the contribution of the PLUTO experiment at the DORIS e + e - storage ring to the discovery of the gluon, as members of this former collaboration we have reconsidered all the scientific material produced by PLUTO in 1978 and the first half of 1979. It is clear that the experiment demonstrated the main decay of the Y(9.46 GeV) resonance to be mediated by 3 gluons, by providing evidence for the agreement of this hypothesis with average values and differential distributions of all possible experimental variables and by excluding all other possible alternative models. Moreover PLUTO measured in June 1979 the matrix element of the 3-gluon decay to be quantitatively as expected by QCD (even after hadronization) and, having checked the possibility to correctly trace the gluons' directions, demonstrated the spin 1 nature of the gluon by excluding spin 0 and spin 1/2. The hadronization of the gluon like a quark jet, hypothesized in the 3-gluon jet Monte Carlo simulation, was compatible with the topological data at this energy and was shown to be an approximation at 10% level for the multiplicity (∼ vertical stroke vertical stroke > -1 ); the right expected gluon fragmentation was needed for the inclusive distributions; this was the first experimental study of (identified) gluon jets. In the following measurements at the PETRA storage ring, these results were confirmed by PLUTO and by three contemporaneous experiments by evidencing at higher energies the gluon radiation (''bremsstrahlung''), the softer one, by jet broadening, and the hard one, by the emission of (now clearly visible) gluon jets by quarks. The gluon's spin 1 particle nature was also confirmed. The PLUTO results on Y decays had been confirmed both by contemporaneous experiments at DORIS (partially) and later (also partially) were confirmed by more sophisticated detectors. (orig.)
Gluon mass generation without seagull divergences
International Nuclear Information System (INIS)
Aguilar, Arlene C.; Papavassiliou, Joannis
2010-01-01
Dynamical gluon mass generation has been traditionally plagued with seagull divergences, and all regularization procedures proposed over the years yield finite but scheme-dependent gluon masses. In this work we show how such divergences can be eliminated completely by virtue of a characteristic identity, valid in dimensional regularization. The ability to trigger the aforementioned identity hinges crucially on the particular Ansatz employed for the three-gluon vertex entering into the Schwinger-Dyson equation governing the gluon propagator. The use of the appropriate three-gluon vertex brings about an additional advantage: one obtains two separate (but coupled) integral equations, one for the effective charge and one for the gluon mass. This system of integral equations has a unique solution, which unambiguously determines these two quantities. Most notably, the effective charge freezes in the infrared, and the gluon mass displays power-law running in the ultraviolet, in agreement with earlier considerations.
'' Ideal Gas '' gluon plasma with medium dependent dispersion relation
International Nuclear Information System (INIS)
Gorenstein, M.I.
1995-01-01
An '' ideal gas '' model with temperature dependent particle mass is constructed for the gluon plasma equation of state. This simple model gives us an example of a system with temperature dependent effective Hamiltonian. To satisfy thermodynamical relations in these systems, standard statistical mechanics formulas have to be supplemented by special requirements which are considered in details. A self-consistent '' ideal gas '' formulation is used to describe Monte Carlo lattice data for the thermodynamical functions of SU(2) and SU(3) gluon plasma. 14 refs., 8 figs
Quark and gluon fragmentation in high energy e+e- annihilation
International Nuclear Information System (INIS)
Saxon, D.H.
1986-07-01
The paper on quark and gluon fragmentation in high energy e + e - annihilation is based on lectures given at the International School of High Energy Physics, Yugoslavia, 1986. Fragmentation Models, charged particle multiplicity, Bose-Einstein correlations, single particle inclusive distributions, hadrons in jets, leading particle effects, baryon production, comparison of quark and gluon jets, and the string effect, are all discussed. (UK)
Low-momentum ghost dressing function and the gluon mass
International Nuclear Information System (INIS)
Boucaud, Ph.; Leroy, J. P.; Le Yaouanc, A.; Micheli, J.; Pene, O.; Gomez, M. E.; Rodriguez-Quintero, J.
2010-01-01
We study the low-momentum ghost propagator Dyson-Schwinger equation in the Landau gauge, assuming for the truncation a constant ghost-gluon vertex, as it is extensively done, and a simple model for a massive gluon propagator. Then, regular Dyson-Schwinger equation solutions (the zero-momentum ghost dressing function not diverging) appear to emerge, and we show the ghost propagator to be described by an asymptotic expression reliable up to the order O(q 2 ). That expression, depending on the gluon mass and the zero-momentum Taylor-scheme effective charge, is proven to fit pretty well some low-momentum ghost propagator data [I. L. Bogolubsky, E. M. Ilgenfritz, M. Muller-Preussker, and A. Sternbeck, Phys. Lett. B 676, 69 (2009); Proc. Sci., LAT2007 (2007) 290] from big-volume lattice simulations where the so-called ''simulated annealing algorithm'' is applied to fix the Landau gauge.
Soft Probes of the Quark-Gluon Plasma in ATLAS
Wozniak, K W; The ATLAS collaboration
2014-01-01
Measurements of low-$p_{_{\\rm T}}$ ($<$ 5 GeV) particles in Pb+Pb collisions at the LHC provide valuable insight in the production and evolution of the quark-gluon plasma. In particular, measurements of the elliptic and higher order collective flow imprinted on the azimuthal angle distributions of low-$p_{T}$ particles directly probe the strongly-coupled dynamics of the quark gluon plasma and test hydrodynamic model descriptions of its evolution. The large acceptance of detectors like ATLAS makes it possible to measure flow event-by-event and to determine the correlations between different event planes and different flow harmonics.
The hard gluon component of the QCD Pomeron
International Nuclear Information System (INIS)
White, A.R.
1996-01-01
The authors argue that deep-inelastic diffractive scaling provides fundamental insight into the QCD Pomeron. The logarithmic scaling violations seen experimentally are in conflict with the scale-invariance of the BFKL Pomeron and with phenomenological two-gluon models. Instead the Pomeron appears as a single gluon at short-distances, indicating the appearance of a Super-Critical phase of Reggeon Field Theory. That the color compensation takes place at a longer distance is consistent with the Pomeron carrying odd color charge parity
High energy evolution of soft gluon cascades
International Nuclear Information System (INIS)
Shuvaev, A.; Wallon, S.
2006-01-01
In this paper we derive an evolution equation for the gluon density in soft gluon cascades emitted from any colored source, in the leading logarithmic approximation of perturbative QCD. We show that this equation has the same form as the BFKL equation in the forward case. An explicit expression for the total cascade wavefunction involving an arbitrary number of soft gluons is obtained. Renormalization of the colored source wavefunction turns out to be responsible for the reggeization of the source. (orig.)
High energy evolution of soft gluon cascades
Energy Technology Data Exchange (ETDEWEB)
Shuvaev, A. [St. Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg district (Russian Federation); Wallon, S. [Universite Paris XI, Laboratoire de Physique Theorique, Orsay Cedex (France)
2006-04-15
In this paper we derive an evolution equation for the gluon density in soft gluon cascades emitted from any colored source, in the leading logarithmic approximation of perturbative QCD. We show that this equation has the same form as the BFKL equation in the forward case. An explicit expression for the total cascade wavefunction involving an arbitrary number of soft gluons is obtained. Renormalization of the colored source wavefunction turns out to be responsible for the reggeization of the source. (orig.)
Screening in an expanding quark-gluon plasma
International Nuclear Information System (INIS)
Broniowski, W.
1988-12-01
Effects of expansion on the Debye length in quark-gluon plasma are calculated in an abelian, boost invariant model. It is found that for early times the screening is significantly more efficient than what follows from naive static considerations. 11 refs., 1 fig., 1 tab. (author)
Quark ACM with topologically generated gluon mass
Choudhury, Ishita Dutta; Lahiri, Amitabha
2016-03-01
We investigate the effect of a small, gauge-invariant mass of the gluon on the anomalous chromomagnetic moment (ACM) of quarks by perturbative calculations at one-loop level. The mass of the gluon is taken to have been generated via a topological mass generation mechanism, in which the gluon acquires a mass through its interaction with an antisymmetric tensor field Bμν. For a small gluon mass ( ACM at momentum transfer q2 = -M Z2. We compare those with the ACM calculated for the gluon mass arising from a Proca mass term. We find that the ACM of up, down, strange and charm quarks vary significantly with the gluon mass, while the ACM of top and bottom quarks show negligible gluon mass dependence. The mechanism of gluon mass generation is most important for the strange quarks ACM, but not so much for the other quarks. We also show the results at q2 = -m t2. We find that the dependence on gluon mass at q2 = -m t2 is much less than at q2 = -M Z2 for all quarks.
Very boosted Higgs in gluon fusion
Grojean, Christophe; Schlaffer, Matthias; Weiler, Andreas
2014-01-01
The Higgs production and decay rates offer a new way to probe new physics beyond the Standard Model. While dynamics aiming at alleviating the hierarchy problem generically predict deviations in the Higgs rates, the current experimental analyses cannot resolve the long- and short-distance contributions to the gluon fusion process and thus cannot access directly the coupling between the Higgs and the top quark. We investigate the production of a boosted Higgs in association with a high-transverse momentum jet as an alternative to the $t\\bar{t}h$ channel to pin down this crucial coupling. Presented first in the context of an effective field theory, our analysis is then applied to models of partial compositeness at the TeV scale and of natural supersymmetry.
Very boosted Higgs in gluon fusion
Energy Technology Data Exchange (ETDEWEB)
Grojean, C. [Univ. Autonoma de Barcelona, Bellaterra (Spain). ICREA at IFAE; Salvioni, E. [California Univ., Davis, CA (United States). Dept. of Physics; European Organization for Nuclear Research (CERN), Geneva (Switzerland); Padova Univ. (Italy). Dipt. di Fisica e Astronomica; INFN, Sezione di Padova (Italy); Schlaffer, M. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Weiler, A. [European Organization for Nuclear Research (CERN), Geneva (Switzerland); Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
2013-12-15
The Higgs production and decay rates offer a new way to probe new physics beyond the Standard Model. While dynamics aiming at alleviating the hierarchy problem generically predict deviations in the Higgs rates, the current experimental analyses cannot resolve the long- and short-distance contributions to the gluon fusion process and thus cannot access directly the coupling between the Higgs and the top quark. We investigate the production of a boosted Higgs in association with a high-transverse momentum jet as an alternative to the t anti th channel to pin down this crucial coupling. Presented rst in the context of an effective field theory, our analysis is then applied to models of partial compositeness at the TeV scale and of natural supersymmetry.
Gluon chains and multiquark hadrons
International Nuclear Information System (INIS)
Jadach, S.; Jezabek, M.
1979-01-01
A monopole approximation to the confining potential is proposed. In this approximation spatially separated groups of quarks carry a definite total colour charge. The potentials which lead to the formation of gluon chains are discussed. The generalization of a (3,3bar) chain notion, studied by Tiktopoulos, to the case of arbitrary colour charges is given. It is argued that these generalized chains may be unstable with respect to splitting into a system of weakly interacting chains of the (3,3bar) type. A unified picture of the high energy hadronic collisions, based on the gluon chain notion and the monopole approximation is proposed. In the meson-meson sector this picture is equivalent to the topological approach. For the other processes it is similar to the approach of Rossi and Veneziano. However, it is argued that the introduction of the junction line into the quark frame is superfluous. The results are expressed in the language of the coloured dual diagrams which provide a generalization of those of Harari and Rosner. (author)
Theoretical estimation of Photons flow rate Production in quark gluon interaction at high energies
Al-Agealy, Hadi J. M.; Hamza Hussein, Hyder; Mustafa Hussein, Saba
2018-05-01
photons emitted from higher energetic collisions in quark-gluon system have been theoretical studied depending on color quantum theory. A simple model for photons emission at quark-gluon system have been investigated. In this model, we use a quantum consideration which enhances to describing the quark system. The photons current rate are estimation for two system at different fugacity coefficient. We discussion the behavior of photons rate and quark gluon system properties in different photons energies with Boltzmann model. The photons rate depending on anisotropic coefficient : strong constant, photons energy, color number, fugacity parameter, thermal energy and critical energy of system are also discussed.
Ward identities for amplitudes with reggeized gluons
International Nuclear Information System (INIS)
Bartles, J.; Vacca, G.P.
2012-05-01
Starting from the effective action of high energy QCD we derive Ward identities for Green's functions of reggeized gluons. They follow from the gauge invariance of the effective action, and allow to derive new representations of amplitudes containing physical particles as well as reggeized gluons. We explicitly demonstrate their validity for the BFKL kernel, and we present a new derivation of the kernel.
Soft gluon resummation for gluon-induced Higgs Strahlung
Energy Technology Data Exchange (ETDEWEB)
Harlander, Robert; Zirke, Tom [Fachbereich C, Bergische Universitaet Wuppertal (Germany); Kulesza, Anna; Theeuwes, Vincent [Institute for Theoretical Physics, WWU Muenster (Germany)
2015-07-01
We study the effect of soft gluon emission on the total cross section predictions for the gg → HZ associated Higgs production process at the LHC. To this end, we perform resummation of threshold corrections at the NLL accuracy in the absolute threshold production limit and in the threshold limit for production of a ZH system with a given invariant mass. Analytical results and numerical predictions for various possible LHC collision energies are presented. The perturbative stability of the results is verified by including universal NNLL effects. We find that resummation significantly reduces the scale uncertainty of the gg → HZ contribution, which is the dominant source of perturbative uncertainty to ZH production. We use our results to evaluate updated numbers for the total inclusive cross section of associated pp → ZH production at the LHC. The reduced scale uncertainty of the gg → HZ component translates into a decrease of the overall scale error by about a factor of two.
Duality and multi-gluon scattering
International Nuclear Information System (INIS)
Mangano, M.; Parke, S.; Xu Zhan
1988-01-01
For the six-gluon scattering process we give explicit and simple expressions for the amplitude and its square. To achieve this we use an analogy with string theories to identify a unique procedure for writing the multi-gluon scattering amplitudes in terms of a sum of gauge invariant dual sub-amplitudes multiplied by an appropriate color (Chan-Paton) factor. The sub-amplitudes defined in this way are invariant under cyclic permutations, satisfy powerful identities which relate different non-cyclic permutations and factorize in the soft gluon limit, the two-gluon collinear limit and on multi-gluon poles. Also, to leading order in the number of colors these sub-amplitudes sum incoherently in the square of the full matrix element. The results contained here are important for Monte Carlo studies of multi-jet processes at hadron colliders as well as for understanding the general structure of QCD. (orig.)
HUNTING THE QUARK GLUON PLASMA.
Energy Technology Data Exchange (ETDEWEB)
LUDLAM, T.; ARONSON, S.
2005-04-11
The U.S. Department of Energy's Relativistic Heavy Ion Collider (RHIC) construction project was completed at BNL in 1999, with the first data-taking runs in the summer of 2000. Since then the early measurements at RHIC have yielded a wealth of data, from four independent detectors, each with its international collaboration of scientists: BRAHMS, PHENIX, PHOBOS, and STAR [1]. For the first time, collisions of heavy nuclei have been carried out at colliding-beam energies that have previously been accessible only for high-energy physics experiments with collisions of ''elementary'' particles such as protons and electrons. It is at these high energies that the predictions of quantum chromodynamics (QCD), the fundamental theory that describes the role of quarks and gluons in nuclear matter, come into play, and new phenomena are sought that may illuminate our view of the basic structure of matter on the sub-atomic scale, with important implications for the origins of matter on the cosmic scale. The RHIC experiments have recorded data from collisions of gold nuclei at the highest energies ever achieved in man-made particle accelerators. These collisions, of which hundreds of millions have now been examined, result in final states of unprecedented complexity, with thousands of produced particles radiating from the nuclear collision. All four of the RHIC experiments have moved quickly to analyze these data, and have begun to understand the phenomena that unfold from the moment of collision as these particles are produced. In order to provide benchmarks of simpler interactions against which to compare the gold-gold collisions, the experiments have gathered comparable samples of data from collisions of a very light nucleus (deuterium) with gold nuclei, as well as proton-proton collisions, all with identical beam energies and experimental apparatus. The early measurements have revealed compelling evidence for the existence of a new form of nuclear
HUNTING THE QUARK GLUON PLASMA
International Nuclear Information System (INIS)
LUDLAM, T.; ARONSON, S.
2005-01-01
The U.S. Department of Energy's Relativistic Heavy Ion Collider (RHIC) construction project was completed at BNL in 1999, with the first data-taking runs in the summer of 2000. Since then the early measurements at RHIC have yielded a wealth of data, from four independent detectors, each with its international collaboration of scientists: BRAHMS, PHENIX, PHOBOS, and STAR [1]. For the first time, collisions of heavy nuclei have been carried out at colliding-beam energies that have previously been accessible only for high-energy physics experiments with collisions of ''elementary'' particles such as protons and electrons. It is at these high energies that the predictions of quantum chromodynamics (QCD), the fundamental theory that describes the role of quarks and gluons in nuclear matter, come into play, and new phenomena are sought that may illuminate our view of the basic structure of matter on the sub-atomic scale, with important implications for the origins of matter on the cosmic scale. The RHIC experiments have recorded data from collisions of gold nuclei at the highest energies ever achieved in man-made particle accelerators. These collisions, of which hundreds of millions have now been examined, result in final states of unprecedented complexity, with thousands of produced particles radiating from the nuclear collision. All four of the RHIC experiments have moved quickly to analyze these data, and have begun to understand the phenomena that unfold from the moment of collision as these particles are produced. In order to provide benchmarks of simpler interactions against which to compare the gold-gold collisions, the experiments have gathered comparable samples of data from collisions of a very light nucleus (deuterium) with gold nuclei, as well as proton-proton collisions, all with identical beam energies and experimental apparatus. The early measurements have revealed compelling evidence for the existence of a new form of nuclear matter at extremely high
Bounds on the gluon mass from nucleon decay
Energy Technology Data Exchange (ETDEWEB)
Avila, M.A. [Universidad Autonoma del Estado de Morelos, Morelos (Mexico)
2001-04-01
Permanent confinement of quarks is assumed to hold in QCD. However, if the gluon has a small mass it is possible to produce-quarks in hadron decays, high-energy reactions or in the early-universe. This situation is modelled by a quark-diquark potential composed of a linear (or harmonic) plus a Yukawa term. We compare our prediction for the proton decay with the experimental lower bound on its life-time, and obtain an upper bound on the gluon mass. [Spanish] Se supone se cumple el confinamiento permanente de quarks en cromodinamica cuantica. Si el gluon tiene masa pequena es posible producir quarks libres en decaimiento hadronicos, reacciones de altas energias o en el universo temprano. Esta situacion es modelada por un potencial quark-diquark, compuesto de un termino lineal (o armonico) mas un termino Yukawa. Comparamos nuestra prediccion para el decaimiento del proton con la cota inferior experimental de su vida media y obtenemos una cota superior sobre la masa del gluon.
Physics of the quark - gluon plasma
International Nuclear Information System (INIS)
2001-09-01
This document gathers 31 contributions to the workshop on the physics of quark-gluon plasma that took place in Palaiseau in september 2001: 1) gamma production in heavy collisions, 2) BRAHMS, 3) experimental conference summary, 4) modelling relativistic nuclear collisions, 5) microscopic reaction dynamics at SPS and RHIC, 6) direct gamma and hard scattering at SPS, 7) soft physics at RHIC, 8) results from the STAR experiment, 9) quarkonia: experimental possibilities, 10) elliptic flow measurements with PHENIX, 11) charmonium production in p-A collisions, 12) anisotropic flow at the SPS and RHIC, 13) deciphering the space-time evolution of heavy ion collisions with correlation measurements, 14) 2-particle correlation at RHIC, 15) particle spectra at AGS, SPS and RHIC, 16) strangeness production in STAR, 17) strangeness production in Pb-Pb collisions at SPS, 18) heavy ion physics at CERN after 2000 and before LHC, 19) NEXUS guideline and theoretical consistency, 20) introduction to high p T physics at RHIC, 21) a novel quasiparticle description of the quark-gluon plasma, 22) dissociation of excited quarkonia states, 23) high-mass dimuon and B → J/Ψ production in ultrarelativistic heavy ion collisions, 24) strange hyperon production in p + p and p + Pb interactions from NA49, 25) heavy quarkonium hadron cross-section, 26) a new method of flow analysis, 27) low mass dilepton production and chiral symmetry restoration, 28) classical initial conditions for nucleus-nucleus collisions, 29) numerical calculation of quenching weights, 30) strangeness enhancement energy dependence, and 31) heavy quarkonium dissociation
Physics of the quark - gluon plasma
Energy Technology Data Exchange (ETDEWEB)
NONE
2001-09-01
This document gathers 31 contributions to the workshop on the physics of quark-gluon plasma that took place in Palaiseau in september 2001: 1) gamma production in heavy collisions, 2) BRAHMS, 3) experimental conference summary, 4) modelling relativistic nuclear collisions, 5) microscopic reaction dynamics at SPS and RHIC, 6) direct gamma and hard scattering at SPS, 7) soft physics at RHIC, 8) results from the STAR experiment, 9) quarkonia: experimental possibilities, 10) elliptic flow measurements with PHENIX, 11) charmonium production in p-A collisions, 12) anisotropic flow at the SPS and RHIC, 13) deciphering the space-time evolution of heavy ion collisions with correlation measurements, 14) 2-particle correlation at RHIC, 15) particle spectra at AGS, SPS and RHIC, 16) strangeness production in STAR, 17) strangeness production in Pb-Pb collisions at SPS, 18) heavy ion physics at CERN after 2000 and before LHC, 19) NEXUS guideline and theoretical consistency, 20) introduction to high p{sub T} physics at RHIC, 21) a novel quasiparticle description of the quark-gluon plasma, 22) dissociation of excited quarkonia states, 23) high-mass dimuon and B {yields} J/{psi} production in ultrarelativistic heavy ion collisions, 24) strange hyperon production in p + p and p + Pb interactions from NA49, 25) heavy quarkonium hadron cross-section, 26) a new method of flow analysis, 27) low mass dilepton production and chiral symmetry restoration, 28) classical initial conditions for nucleus-nucleus collisions, 29) numerical calculation of quenching weights, 30) strangeness enhancement energy dependence, and 31) heavy quarkonium dissociation.
Kaon versus pion interferometry signatures of quark-gluon plasma formation
International Nuclear Information System (INIS)
Gyulassy, M.; Padula, S.S.
1990-01-01
The advantages of kaon versus pion interferometry as a probe of quark-gluon plasma formation in high energy nuclear collisions are studied by comparing predictions of Lund resonance gas and plasma hydrodynamic models
Muoproduction of J/ψ and the gluon distribution of the nucleon
International Nuclear Information System (INIS)
Ashman, J.; Combley, F.; Salmon, D.; Wheeler, S.; Bee, C.P.; Brown, S.C.; Court, G.; Francis, D.; Gabathuler, E.; Gamet, R.; Hayman, P.; Holt, J.R.; Jones, T.; Matthews, M.; Wimpenny, S.J.; Coignet, G.; Toth, J.; Urban, L.; Drees, J.; Edwards, A.W.; Hamacher, K.; Korzen, B.; Kruener, U.; Moenig, K.; Pavel, N.; Peschel, H.; Nassalski, J.; Sandacz, A.; Windmolders, R.; Ernst, T.; Landgraf, U.; Schroeder, T.; Stier, H.E.; Stock, J.; Wallucks, W.
1992-01-01
Measurements are presented of the inclusive distributions of the J/ψ meson produced by muons of energy 200 GeV from an ammonia target. The gluon distribution of the nucleon has been derived from the data in the range 0.04< x<0.36 using a technique based on the colour singlet model. An arbitrary normalisation factor is required to obtain a reasonable integral of the gluon distribution. Some comments are made on the use of J/ψ production by virtual photons to extract the gluon distribution at HERA. (orig.)
J/ψ-production mechanisms and determination of the gluon density at HERA
International Nuclear Information System (INIS)
Jung, H.; Schuler, G.A.; Terron, J.
1992-02-01
We discuss photo- and leptoproduction of J/ψ-mesons at energies ranging from fixed-target experiments up to HERA. Elastic and diffractive production as well as various inelastic processes are studied. We investigate the range in which J/ψ-production is described by photon-gluon fusion in the colour-singlet model. We show how inelastic J/ψ production at HERA can be used to extract the gluon density. We estimate an accessible range of 3 x 10 -4 < x < 0.1 and discuss sources of errors in the reconstruction of the gluon density at HERA. (orig.)
The gluon Sivers asymmetry measurements at COMPASS
Szabelski, Adam
2018-01-01
The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. As such, a nonzero Sivers effect for gluons could be a signature of their nonzero orbital angular momentum inside the nucleon. COMPASS has collected data of semi-inclusive deep inelastic scattering by impinging 160 GeV/$c$ muons on transversely polarised proton and deuteron targets. The gluon Sivers asymmetry is extracted from a high-$p_T$ hadron pair sample with the use of monte carlo simulations and the a neural network approach. The results of a similar analysis for a Collins-like asymmetry for gluons will also be given.
The gluon Sivers asymmetry measurements at COMPASS
Szabelski, Adam
2017-01-01
The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. As such, a nonzero Sivers effect for gluons could be a signature of their nonzero orbital angular momentum inside the nucleon. COMPASS has collected data of semi-inclusive deep inelastic scattering by impinging 160 GeV/$c$ muons on transversely polarised proton and deuteron targets. The gluon Sivers asymmetry is extracted from a high-$p_T$ hadron pair sample with the use of monte carlo simulations and the a neural network approach. The results of a similar analysis for a Collins-like asymmetry for gluons will also be given.
Gluon structure function of a color dipole in the light-cone limit of lattice QCD
International Nuclear Information System (INIS)
Gruenewald, D.; Ilgenfritz, E.-M.; Pirner, H. J.
2009-01-01
We calculate the gluon structure function of a color dipole in near-light-cone SU(2) lattice QCD as a function of x B . The quark and antiquark are external nondynamical degrees of freedom which act as sources of the gluon string configuration defining the dipole. We compute the color dipole matrix element of transversal chromo-electric and chromo-magnetic field operators separated along a direction close to the light cone, the Fourier transform of which is the gluon structure function. As vacuum state in the pure glue sector, we use a variational ground state of the near-light-cone Hamiltonian. We derive a recursion relation for the gluon structure function on the lattice similar to the perturbative Dokshitzer-Gribov-Lipatov-Altarelli-Parisi equation. It depends on the number of transversal links assembling the Schwinger string of the dipole. Fixing the mean momentum fraction of the gluons to the 'experimental value' in a proton, we compare our gluon structure function for a dipole state with four links with the next-to-leading-order MRST 2002 and the CTEQ AB-0 parametrizations at Q 2 =1.5 GeV 2 . Within the systematic uncertainty we find rather good agreement. We also discuss the low x B behavior of the gluon structure function in our model calculation.
Gluon saturation in a saturated environment
International Nuclear Information System (INIS)
Kopeliovich, B. Z.; Potashnikova, I. K.; Schmidt, Ivan
2011-01-01
A bootstrap equation for self-quenched gluon shadowing leads to a reduced magnitude of broadening for partons propagating through a nucleus. Saturation of small-x gluons in a nucleus, which has the form of transverse momentum broadening of projectile gluons in pA collisions in the nuclear rest frame, leads to a modification of the parton distribution functions in the beam compared with pp collisions. In nucleus-nucleus collisions all participating nucleons acquire enhanced gluon density at small x, which boosts further the saturation scale. Solution of the reciprocity equations for central collisions of two heavy nuclei demonstrate a significant, up to several times, enhancement of Q sA 2 , in AA compared with pA collisions.
Charmed quark production as a gluon probe
International Nuclear Information System (INIS)
Phillips, R.J.N.
1980-09-01
The lowest-order QCD mechanisms for producing cc or other heavy quarks depend on the gluon distributions in hadrons; hence the latter can be extracted directly from experiment. Recent results are described. (author)
International Nuclear Information System (INIS)
Koller, K.; Zerwas, P.M.; Walsh, T.F.
1978-12-01
We show how the Q 2 evolution of gluon jets can be used to provide indirect but strong evidence for the 3 gluon vertex of QCD. We propose looking for this evolution in the QantiQ → 3G → hadrons decay of successive 1 3 S 1 quarkonium states. The results apply to other processes if G jets can be isolated. (orig.) [de
The structure of the gluon propagator
Energy Technology Data Exchange (ETDEWEB)
Leinweber, D.B.; Parrinello, C.; Skullerud, J.I.; Williams, A.G
1999-03-01
The gluon propagator has been calculated for quenched QCD in the Landau gauge at {beta} = 6.0 for volumes 16{sup 3} x 48 and 32{sup 3} x 64, and at {beta} 6.2 for volume 24{sup 3} x 48. The large volume and different lattice spacings allow us to identify and minimise finite volume and finite lattice spacing artefacts. We also study the tensor structure of the gluon propagator, confirming that it obeys the lattice Landau gauge condition.
Describing gluons at zero and finite temperature
International Nuclear Information System (INIS)
Maas, A.
2010-01-01
Any description of gluons requires a well-defined gauge. This is complicated non-perturbatively by Gribov copies. A possible method-independent gauge definition to resolve this problem is presented and afterwards used to study the properties of gluons at any temperature. It is found that only chromo-electric properties reflect the phase transition. From these the gauge-invariant phase transition temperature is determined for SU(2) and SU(3) Yang-Mills theory independently. (author)
Identified particles in quark and gluon jets
Abreu, P; Adye, T; Ajinenko, I; Alekseev, G D; Alemany, R; Allport, P P; Almehed, S; Amaldi, Ugo; Amato, S; Andreazza, A; Andrieux, M L; Antilogus, P; Apel, W D; Åsman, B; Augustin, J E; Augustinus, A; Baillon, Paul; Bambade, P; Barão, F; Barbi, M S; Barbiellini, Guido; Bardin, Dimitri Yuri; Barker, G; Baroncelli, A; Bärring, O; Barrio, J A; Bartl, Walter; Bates, M J; Battaglia, Marco; Baubillier, M; Baudot, J; Becks, K H; Begalli, M; Beillière, P; Belokopytov, Yu A; Benvenuti, Alberto C; Berggren, M; Bertini, D; Bertrand, D; Besançon, M; Bianchi, F; Bigi, M; Bilenky, S M; Billoir, P; Bizouard, M A; Bloch, D; Blume, M; Bolognese, T; Bonesini, M; Bonivento, W; Booth, P S L; Bosio, C; Botner, O; Boudinov, E; Bouquet, B; Bourdarios, C; Bowcock, T J V; Bozzo, M; Branchini, P; Brand, K D; Brenke, T; Brenner, R A; Bricman, C; Brown, R C A; Brückman, P; Brunet, J M; Bugge, L; Buran, T; Burgsmüller, T; Buschmann, P; Cabrera, S; Caccia, M; Calvi, M; Camacho-Rozas, A J; Camporesi, T; Canale, V; Canepa, M; Cankocak, K; Cao, F; Carena, F; Carroll, L; Caso, Carlo; Castillo-Gimenez, M V; Cattai, A; Cavallo, F R; Chabaud, V; Charpentier, P; Chaussard, L; Checchia, P; Chelkov, G A; Chen, M; Chierici, R; Chliapnikov, P V; Chochula, P; Chorowicz, V; Chudoba, J; Cindro, V; Collins, P; Contri, R; Cortina, E; Cosme, G; Cossutti, F; Cowell, J H; Crawley, H B; Crennell, D J; Crosetti, G; Cuevas-Maestro, J; Czellar, S; Dahl-Jensen, Erik; Dahm, J; D'Almagne, B; Dam, M; Damgaard, G; Dauncey, P D; Davenport, Martyn; Da Silva, W; Defoix, C; Deghorain, A; Della Ricca, G; Delpierre, P A; Demaria, N; De Angelis, A; de Boer, Wim; De Brabandere, S; De Clercq, C; La Vaissière, C de; De Lotto, B; De Min, A; De Paula, L S; De Saint-Jean, C; Dijkstra, H; Di Ciaccio, Lucia; Di Diodato, A; Djama, F; Djannati, A; Dolbeau, J; Doroba, K; Dracos, M; Drees, J; Drees, K A; Dris, M; Durand, J D; Edsall, D M; Ehret, R; Eigen, G; Ekelöf, T J C; Ekspong, Gösta; Elsing, M; Engel, J P; Erzen, B; Espirito-Santo, M C; Falk, E; Fassouliotis, D; Feindt, Michael; Ferrer, A; Fichet, S; Filippas-Tassos, A; Firestone, A; Fischer, P A; Föth, H; Fokitis, E; Fontanelli, F; Formenti, F; Franek, B J; Frenkiel, P; Fries, D E C; Frodesen, A G; Frühwirth, R; Fulda-Quenzer, F; Fuster, J A; Galloni, A; Gamba, D; Gandelman, M; García, C; García, J; Gaspar, C; Gasparini, U; Gavillet, P; Gazis, E N; Gelé, D; Gerber, J P; Gerdyukov, L N; Gokieli, R; Golob, B; Gopal, Gian P; Gorn, L; Górski, M; Guz, Yu; Gracco, Valerio; Graziani, E; Green, C; Grefrath, A; Gris, P; Grosdidier, G; Grzelak, K; Gumenyuk, S A; Gunnarsson, P; Günther, M; Guy, J; Hahn, F; Hahn, S; Hajduk, Z; Hallgren, A; Hamacher, K; Harris, F J; Hedberg, V; Henriques, R P; Hernández, J J; Herquet, P; Herr, H; Hessing, T L; Heuser, J M; Higón, E; Hilke, Hans Jürgen; Hill, T S; Holmgren, S O; Holt, P J; Holthuizen, D J; Hoorelbeke, S; Houlden, M A; Hrubec, Josef; Huet, K; Hultqvist, K; Jackson, J N; Jacobsson, R; Jalocha, P; Janik, R; Jarlskog, C; Jarlskog, G; Jarry, P; Jean-Marie, B; Johansson, E K; Jönsson, L B; Jönsson, P E; Joram, Christian; Juillot, P; Kaiser, M; Kapusta, F; Karafasoulis, K; Karlsson, M; Karvelas, E; Katargin, A; Katsanevas, S; Katsoufis, E C; Keränen, R; Khokhlov, Yu A; Khomenko, B A; Khovanskii, N N; King, B J; Kjaer, N J; Klapp, O; Klein, H; Klovning, A; Kluit, P M; Köne, B; Kokkinias, P; Koratzinos, M; Korcyl, K; Kostyukhin, V; Kourkoumelis, C; Kuznetsov, O; Krammer, Manfred; Kreuter, C; Kronkvist, I J; Krumshtein, Z; Krupinski, W; Kubinec, P; Kucewicz, W; Kurvinen, K L; Lacasta, C; Laktineh, I; Lamsa, J; Lanceri, L; Lane, D W; Langefeld, P; Lapin, V; Laugier, J P; Lauhakangas, R; Leder, Gerhard; Ledroit, F; Lefébure, V; Legan, C K; Leitner, R; Lemonne, J; Lenzen, Georg; Lepeltier, V; Lesiak, T; Libby, J; Liko, D; Lindner, R; Lipniacka, A; Lippi, I; Lörstad, B; Loken, J G; López, J M; Loukas, D; Lutz, P; Lyons, L; MacNaughton, J N; Maehlum, G; Mahon, J R; Malmgren, T G M; Malychev, V; Mandl, F; Marco, J; Marco, R P; Maréchal, B; Margoni, M; Marin, J C; Mariotti, C; Markou, A; Martínez-Rivero, C; Martínez-Vidal, F; Martí i García, S; Masik, J; Matorras, F; Matteuzzi, C; Matthiae, Giorgio; Mazzucato, M; McCubbin, M L; McKay, R; McNulty, R; Medbo, J; Merk, M; Meroni, C; Meyer, S; Meyer, W T; Michelotto, M; Migliore, E; Mirabito, L; Mitaroff, Winfried A; Mjörnmark, U; Moa, T; Møller, R; Mönig, K; Monge, M R; Morettini, P; Müller, H; Münich, K; Mulders, M; Mundim, L M; Murray, W J; Muryn, B; Myatt, Gerald; Naraghi, F; Navarria, Francesco Luigi; Navas, S; Nawrocki, K; Negri, P; Neumann, W; Neumeister, N; Nicolaidou, R; Nielsen, B S; Nieuwenhuizen, M; Nikolaenko, V; Niss, P; Nomerotski, A; Normand, Ainsley; Novák, M; Oberschulte-Beckmann, W; Obraztsov, V F; Olshevskii, A G; Onofre, A; Orava, Risto; Österberg, K; Ouraou, A; Paganini, P; Paganoni, M; Pagès, P; Pain, R; Palka, H; Papadopoulou, T D; Papageorgiou, K; Pape, L; Parkes, C; Parodi, F; Passeri, A; Pegoraro, M; Peralta, L; Pernicka, Manfred; Perrotta, A; Petridou, C; Petrolini, A; Petrovykh, M; Phillips, H T; Piana, G; Pierre, F; Pimenta, M; Podobnik, T; Podobrin, O; Pol, M E; Polok, G; Poropat, P; Pozdnyakov, V; Privitera, P; Pukhaeva, N; Pullia, Antonio; Radojicic, D; Ragazzi, S; Rahmani, H; Rames, J; Ratoff, P N; Read, A L; Reale, M; Rebecchi, P; Redaelli, N G; Regler, Meinhard; Reid, D; Reinhardt, R; Renton, P B; Resvanis, L K; Richard, F; Richardson, J; Rídky, J; Rinaudo, G; Ripp, I; Romero, A; Roncagliolo, I; Ronchese, P; Roos, L; Rosenberg, E I; Roudeau, Patrick; Rovelli, T; Rückstuhl, W; Ruhlmann-Kleider, V; Ruiz, A; Rybicki, K; Rybin, A; Saarikko, H; Sacquin, Yu; Sadovskii, A; Sahr, O; Sajot, G; Salt, J; Sánchez, J; Sannino, M; Schimmelpfennig, M; Schneider, H; Schwickerath, U; Schyns, M A E; Sciolla, G; Scuri, F; Seager, P; Sedykh, Yu; Segar, A M; Seitz, A; Sekulin, R L; Serbelloni, L; Shellard, R C; Siegrist, P; Silvestre, R; Simonetti, S; Simonetto, F; Sissakian, A N; Sitár, B; Skaali, T B; Smadja, G; Smirnov, N; Smirnova, O G; Smith, G R; Sosnowski, R; Souza-Santos, D; Spassoff, Tz; Spiriti, E; Sponholz, P; Squarcia, S; Stampfer, D; Stanescu, C; Stanic, S; Stapnes, Steinar; Stavitski, I; Stevenson, K; Stocchi, A; Strauss, J; Strub, R; Stugu, B; Szczekowski, M; Szeptycka, M; Tabarelli de Fatis, T; Tavernet, J P; Chikilev, O G; Thomas, J; Tilquin, A; Timmermans, J; Tkatchev, L G; Todorov, T; Todorova, S; Toet, D Z; Tomaradze, A G; Tomé, B; Tonazzo, A; Tortora, L; Tranströmer, G; Treille, D; Tristram, G; Trombini, A; Troncon, C; Tsirou, A L; Turluer, M L; Tyapkin, I A; Tyndel, M; Tzamarias, S; Überschär, B; Ullaland, O; Uvarov, V; Valenti, G; Vallazza, E; Van der Velde, C; van Apeldoorn, G W; van Dam, P; Van Doninck, W K; Van Eldik, J; Van Lysebetten, A; Vassilopoulos, N; Vegni, G; Ventura, L; Venus, W A; Verbeure, F; Verlato, M; Vertogradov, L S; Vilanova, D; Vincent, P; Vitale, L; Vlasov, E; Vodopyanov, A S; Vrba, V; Wahlen, H; Walck, C; Weierstall, M; Weilhammer, Peter; Weiser, C; Wetherell, Alan M; Wicke, D; Wickens, J H; Wielers, M; Wilkinson, G R; Williams, W S C; Winter, M; Witek, M; Wlodek, T; Woschnagg, K; Yip, K; Yushchenko, O P; Zach, F; Zaitsev, A; Zalewska-Bak, A; Zalewski, Piotr; Zavrtanik, D; Zevgolatakos, E; Zimin, N I; Zito, M; Zontar, D; Zucchelli, G C; Zumerle, G
1997-01-01
A sample of about 1.4 million hadronic \\z decays, selected among the data recorded by the DELPHI detector at LEP during 1994, was used to measure for the first time the momentum spectra of \\kp, \\ko, \\p, \\l and their antiparticles in gluon and quark jets. As observed for inclusive charged particles, the production spectra of identified particles were found to be softer in gluon jets than in quark jets, with a higher total multiplicity.
Quarks and gluons in nuclear and particle physics
International Nuclear Information System (INIS)
Van Hove, L.
1988-01-01
This paper provides a broad overview of strong interactions, or nuclear forces, as ones understanding has expanded over the past 25 years. The major particles and models are briefly touched upon. The author expands upon the field theories which have evolved to explain the experimental work, and the present model of quarks and gluons which form the components of hadrons. The standard model has been very successful in explaining much of the newly acquired experimental data. But the property of confinement, where the partons, (quarks and gluons), are not observed seperately has precluded observation of these particles. He touches on the manifestation of these particles in high energy physics, where they model the observed particles and resonances, and are responsible for the production of hadronic jets. However in nuclear physics, one does not need to postulate the existance of these particles to explain the properties of nuclei, until one deals with interaction energies in the range of GeV. The author then touches on the area of ultra-relativistic nuclear physics, where the partons must play a role in the effects which are observed. In particular he discusses deep inelastic lepton scattering on nuclei, the Drell-Yan process in nuclei, and ultra-relativistic nuclear collisions. Finally he gives a brief discussion of the quark-gluon plasma, which is postulated to form during very high energy collisions, manifesting itself as a brief deconfinement of the partons into an equilibrium plasma
Non-perturbative inputs for gluon distributions in the hadrons
Energy Technology Data Exchange (ETDEWEB)
Ermolaev, B.I. [Ioffe Physico-Technical Institute, Saint Petersburg (Russian Federation); Troyan, S.I. [St. Petersburg Institute of Nuclear Physics, Gatchina (Russian Federation)
2017-03-15
Description of hadronic reactions at high energies is conventionally done in the framework of QCD factorization. All factorization convolutions comprise non-perturbative inputs mimicking non-perturbative contributions and perturbative evolution of those inputs. We construct inputs for the gluon-hadron scattering amplitudes in the forward kinematics and, using the optical theorem, convert them into inputs for gluon distributions in the hadrons, embracing the cases of polarized and unpolarized hadrons. In the first place, we formulate mathematical criteria which any model for the inputs should obey and then suggest a model satisfying those criteria. This model is based on a simple reasoning: after emitting an active parton off the hadron, the remaining set of spectators becomes unstable and therefore it can be described through factors of the resonance type, so we call it the resonance model. We use it to obtain non-perturbative inputs for gluon distributions in unpolarized and polarized hadrons for all available types of QCD factorization: basic, K{sub T}-and collinear factorizations. (orig.)
Non-perturbative inputs for gluon distributions in the hadrons
International Nuclear Information System (INIS)
Ermolaev, B.I.; Troyan, S.I.
2017-01-01
Description of hadronic reactions at high energies is conventionally done in the framework of QCD factorization. All factorization convolutions comprise non-perturbative inputs mimicking non-perturbative contributions and perturbative evolution of those inputs. We construct inputs for the gluon-hadron scattering amplitudes in the forward kinematics and, using the optical theorem, convert them into inputs for gluon distributions in the hadrons, embracing the cases of polarized and unpolarized hadrons. In the first place, we formulate mathematical criteria which any model for the inputs should obey and then suggest a model satisfying those criteria. This model is based on a simple reasoning: after emitting an active parton off the hadron, the remaining set of spectators becomes unstable and therefore it can be described through factors of the resonance type, so we call it the resonance model. We use it to obtain non-perturbative inputs for gluon distributions in unpolarized and polarized hadrons for all available types of QCD factorization: basic, K_T-and collinear factorizations. (orig.)
Gluon and charm content of the η' meson and instantons
International Nuclear Information System (INIS)
Shuryak, E.V.; Zhitnitsky, A.R.
1998-01-01
Motivated by recent CLEO measurements of the B→η ' 'K decay, we evaluate the gluon and charm content of the η ' ' meson using the interacting instanton liquid model of the QCD vacuum. Our main result is left-angle 0|g 3 f abc G μν a G να b G αμ c |η ' 'right-angle=-(2
Q2 evolution of a soft gluon distribution function
International Nuclear Information System (INIS)
Enkovskij, L.L.; Kotikov, A.V.; Pakkanoni, F.
1992-01-01
Model parameter dependence refferring to the function of gluon distribution linked with the exchange of a dipole pomeron from Q 2 is calculated within the framework of the Gribov-Lipatov-Altarelli-Parisi evolution equation (GLAP) both in the leading logarithm approximation and in the double logarithmic approximation. The behaviour of logarithmic parametrization ∼ (ln(1/x)) b appears to be unstable in relation to perturbative calculations
Dilepton as a signature for the baryon-rich quark-gluon matter
International Nuclear Information System (INIS)
Zejun He; Jiaju Zhang
1995-01-01
From the full stopping scenario, we study dilepton production in a baryon rich quark-gluon fireball on the basis of a relativistic hydrodynamic model, and find that with increasing initial baryon density a characteristic valley and a subsequent peak, which more uniquely signal the formation of the baryon-rich quark-gluon matter, appear in the total dilepton yield. Such characteristics can be tested in future experiments at CERN and Brookhaven. (author). Letter-to-the-editor
Study of high-transverse momentum quark and gluon jet fragmentation
International Nuclear Information System (INIS)
Ghez, P.
1986-09-01
The fragmentation properties of high-transverse momentum jets are investigated using new data from the ISR and the SPS collider. Effects from gluon radiation are clearly demonstrated by comparison with a state-of-the-art model including QCD parton cascade evolution and string hadronization, which gives in general good agreement with the data. Differences between quark and gluon jets are discussed as well as Q 2 -dependent scaling violation effects
Ultra relativistic heavy ions collisions or the search for quark-gluon plasmas
International Nuclear Information System (INIS)
Blaizot, J.P.
1985-03-01
This paper reviews some aspects of the physics of ultra-relativistic heavy ion collisions. The qualitative changes expected in the properties of hadronic matter at high temperature and/or large baryon density are described in terms of simple models. We discuss a scenario giving the space-time evolution of a quark-gluon plasma. Finally we address the difficult question of the possible signatures of the formation of a quark-gluon plasma in heavy ion collisions
Hadronic total cross-sections through soft gluon summation in impact parameter space
International Nuclear Information System (INIS)
Grau, A.
1999-01-01
IThe Bloch-Nordsieck model for the parton distribution of hadrons in impact parameter space, constructed using soft gluon summation, is investigated in detail. Its dependence upon the infrared structure of the strong coupling constant α s is discussed, both for finite as well as singular, but integrable, α s . The formalism is applied to the prediction of total proton-proton and proton-antiproton cross-sections, where screening, due to soft gluon emission from the initial valence quarks, becomes evident
Two-Loop Gluon to Gluon-Gluon Splitting Amplitudes in QCD
International Nuclear Information System (INIS)
Bern, Z.
2004-01-01
Splitting amplitudes are universal functions governing the collinear behavior of scattering amplitudes for massless particles. We compute the two-loop g → gg splitting amplitudes in QCD, N = 1, and N = 4 super-Yang-Mills theories, which describe the limits of two-loop n-point amplitudes where two gluon momenta become parallel. They also represent an ingredient in a direct x-space computation of DGLAP evolution kernels at next-to-next-to-leading order. To obtain the splitting amplitudes, we use the unitarity sewing method. In contrast to the usual light-cone gauge treatment, our calculation does not rely on the principal-value or Mandelstam-Leibbrandt prescriptions, even though the loop integrals contain some of the denominators typically encountered in light-cone gauge. We reduce the integrals to a set of 13 master integrals using integration-by-parts and Lorentz invariance identities. The master integrals are computed with the aid of differential equations in the splitting momentum fraction z. The ε-poles of the splitting amplitudes are consistent with a formula due to Catani for the infrared singularities of two-loop scattering amplitudes. This consistency essentially provides an inductive proof of Catani's formula, as well as an ansatz for previously-unknown 1/ε pole terms having non-trivial color structure. Finite terms in the splitting amplitudes determine the collinear behavior of finite remainders in this formula
Soft gluon resummation in the infrared region and the Froissart bound
Pancheri, Giulia; Godbole, Rohini M; Srivastava, Yogendra N
2010-01-01
We describe the taming effect induced by soft gluon $k_t$-resummation on the rapid rise of QCD mini-jet contributions to the total cross-sections.This results from an eikonal model in which the rise of the total cross-section is due to mini-jet contribution. We perform the calculation with current Parton Density Functions (PDFs). The impact parameter distribution we use is obtained as the Fourier transform of the resummed $k_t$-distribution of soft gluons emitted from the initial state during the collision.The emission, which is energy dependent, destroys the initial collinearity of partons.In this model, the strong power-like rise due to the increasing number of low-x gluon collisions is tamed by the acollinearity induced by soft gluon kt-resummation down to zero gluon momenta. It explicitly links a singular soft gluon coupling in the infrared region to the behaviour dictated by the Froissart bound for the total cross-section. The model describes well both proton and photon processes at present accelerator e...
Quark/gluon jet discrimination: a reproducible analysis using R
CERN. Geneva
2017-01-01
The power to discriminate between light-quark jets and gluon jets would have a huge impact on many searches for new physics at CERN and beyond. This talk will present a walk-through of the development of a prototype machine learning classifier for differentiating between quark and gluon jets at experiments like those at the Large Hadron Collider at CERN. A new fast feature selection method that combines information theory and graph analytics will be outlined. This method has found new variables that promise significant improvements in discrimination power. The prototype jet tagger is simple, interpretable, parsimonious, and computationally extremely cheap, and therefore might be suitable for use in trigger systems for real-time data processing. Nested stratified k-fold cross validation was used to generate robust estimates of model performance. The data analysis was performed entirely in the R statistical programming language, and is fully reproducible. The entire analysis workflow is data-driven, automated a...
Quark-gluon plasma in strong magnetic fields
International Nuclear Information System (INIS)
Kalaydzhyan, Tigran
2013-04-01
One of the fundamental problems in subatomic physics is the determination of properties of matter at extreme temperatures, densities and electromagnetic fields. The modern ultrarelativistic heavy-ion experiments are able to study such states (the quark-gluon plasma) and indicate that the physics at extreme conditions differs drastically from what is known from the conventional observations. Also the theoretical methods developed mostly within the perturbative framework face various conceptual problems and need to be replaced by a nonperturbative approach. In this thesis we study the physics of the strongly-coupled quark-gluon plasma in external magnetic fields as well as general electromagnetic and topological properties of the QCD and QCD-like systems. We develop and apply various nonperturbative techniques, based on e.g. gauge-gravity correspondence, lattice QCD simulations, relativistic hydrodynamics and condensed-matter-inspired models.
Quark-gluon plasma in strong magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Kalaydzhyan, Tigran
2013-04-15
One of the fundamental problems in subatomic physics is the determination of properties of matter at extreme temperatures, densities and electromagnetic fields. The modern ultrarelativistic heavy-ion experiments are able to study such states (the quark-gluon plasma) and indicate that the physics at extreme conditions differs drastically from what is known from the conventional observations. Also the theoretical methods developed mostly within the perturbative framework face various conceptual problems and need to be replaced by a nonperturbative approach. In this thesis we study the physics of the strongly-coupled quark-gluon plasma in external magnetic fields as well as general electromagnetic and topological properties of the QCD and QCD-like systems. We develop and apply various nonperturbative techniques, based on e.g. gauge-gravity correspondence, lattice QCD simulations, relativistic hydrodynamics and condensed-matter-inspired models.
Inclusive gluon production in the dipole approach: Abramovskii-Gribov-Kancheli (AGK) cutting rules
International Nuclear Information System (INIS)
Levin, Eugene; Prygarin, Alex
2008-01-01
We consider single gluon production in the dipole model and reproduce the result of Kovchegov and Tuchin for the adjoint (gluonic) dipole structure of the inclusive cross section. We show the validity of the adjoint dipole structure to any order of evolution by deriving and solving the nonlinear evolution for the nondiagonal cross section of a dipole scattering off the target. The form of the solution to this equation restores the dipole interpretation for nondiagonal cross sections that appear in gluon production. Using this formalism, we analyze the single inclusive production cross section in terms of the contributions of different multiplicities, and we derive the Abramovskii-Gribov-Kancheli (AGK) cutting rules for two-Pomeron exchange. The cutting rules, which were found in this formalism, fully reproduce the original AGK rules for the total cross section. However, for the case of gluon production, the AGK rules are violated already for one-gluon emission from the vertex
Experimental study of rapidity gaps in gluon jets
Gary, J W
2003-01-01
Gluon jets are selected from hadronic Z/sup 0/ decay events produced in e/sup +/e/sup -/ annihilations, collected with the OPAL detector at LEP. A subsample of these jets is identified which exhibit a large gap in the rapidity distribution of particles within the jet. These jets are observed to demonstrate a high degree of sensitivity to the presence of color reconnection, i.e. higher order QCD processes affecting the underlying color structure. We test two QCD Monte Carlo programs which implement color reconnection: one in the Ariadne Monte Carlo and the other by Rathsman in the Pythia Monte Carlo. We find these models can describe our gluon jet measurements only if very large values are used for the cutoff parameters which serve to terminate the parton showers, and conclude that color reconnection as implemented in these models is disfavored. Further, we use our data on gluon jets with a rapidity gap to search for glueball-like objects in the leading part of those jets. We do not find any clear evidence for...
The gluon structure of hadrons and nuclei from lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Shanahan, Phiala A. [College of William and Mary, Williamsburg, VA (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
2018-04-01
I discuss recent lattice QCD studies of the gluon structure of hadrons and light nuclei. After very briefly highlighting new determinations of the gluon contributions to the nucleon's momentum and spin, presented by several collaborations over the last year, I describe first calculations of gluon generalised form factors. The generalised transversity gluon distributions are of particular interest since they are purely gluonic; they do not mix with quark distributions at leading twist. In light nuclei they moreover provide a clean signature of non-nucleonic gluon degrees of freedom, and I present the first evidence for such effects, based on lattice QCD calculations. The planned Electron-Ion Collider, designed to access gluon structure quantities, will have the capability to test this prediction, and measure a range of gluon observables including generalised gluon distributions and transverse momentum dependent gluon distributions, within the next decade.
The gluon structure of hadrons and nuclei from lattice QCD
Shanahan, Phiala
2018-03-01
I discuss recent lattice QCD studies of the gluon structure of hadrons and light nuclei. After very briefly highlighting new determinations of the gluon contributions to the nucleon's momentum and spin, presented by several collaborations over the last year, I describe first calculations of gluon generalised form factors. The generalised transversity gluon distributions are of particular interest since they are purely gluonic; they do not mix with quark distributions at leading twist. In light nuclei they moreover provide a clean signature of non-nucleonic gluon degrees of freedom, and I present the first evidence for such effects, based on lattice QCD calculations. The planned Electron-Ion Collider, designed to access gluon structure quantities, will have the capability to test this prediction, and measure a range of gluon observables including generalised gluon distributions and transverse momentum dependent gluon distributions, within the next decade.
Gluon quasidistribution function at one loop
Energy Technology Data Exchange (ETDEWEB)
Wang, Wei; Zhao, Shuai [Shanghai Jiao Tong University, INPAC, Shanghai Key Laboratory for Particle Physics and Cosmology, School of Physics and Astronomy, Shanghai (China); Zhu, Ruilin [Shanghai Jiao Tong University, INPAC, Shanghai Key Laboratory for Particle Physics and Cosmology, School of Physics and Astronomy, Shanghai (China); Nanjing Normal University, Department of Physics and Institute of Theoretical Physics, Nanjing, Jiangsu (China)
2018-02-15
We study the unpolarized gluon quasidistribution function in the nucleon at one loop level in the large momentum effective theory. For the quark quasidistribution, power law ultraviolet divergences arise in the cut-off scheme and an important observation is that they all are subjected to Wilson lines. However for the gluon quasidistribution function, we first point out that the linear ultraviolet divergences also exist in the real diagram which is not connected to any Wilson line. We then study the one loop corrections to parton distribution functions in both cut-off scheme and dimensional regularization to deal with the ultraviolet divergences. In addition to the ordinary quark and gluon distributions, we also include the quark to gluon and gluon to quark splitting diagrams. The complete one-loop matching factors between the quasi and light cone parton distribution functions are presented in the cut-off scheme. We derive the P{sup z} evolution equation for quasi parton distribution functions, and find that the P{sup z} evolution kernels are identical to the DGLAP evolution kernels. (orig.)
Soft probes of the quark gluon plasma in ATLAS
Wozniak, K W; The ATLAS collaboration
2014-01-01
Measurements of low-$p_{T}$ (< 5 GeV) particle production have provided valuable insight on the production and evolution of the quark-gluon plasma in Pb+Pb collisions at the LHC. In particular, measurements of elliptic and higher order collective flow imprinted on the azimuthal angle distributions of low-$p_{T}$ particles directly probe the strongly-coupled dynamics of the quark gluon plasma and test hydrodynamic model descriptions of its evolution. The large acceptance of detectors like ATLAS have made it possible to measure flow event-by-event and to determine the correlations between different harmonics. Recent measurements of low-$p_{T}$ particle production and multi-particle correlations in proton-lead collisions have shown features similar to the collective flow observed in Pb+Pb collisions. Results will be presented from a variety of single and multi-particle measurements in Pb+Pb and proton-Pb collisions that probe the collective dynamics of the quark gluon plasma and possibly provide evidence for ...
Gluon density determination from open charm events at HERA
International Nuclear Information System (INIS)
Woudenberg, R. van; Ould-Saada, F.; Eisenberg, Y.; Glasman, C.; Karshon, U.; Montag, A.; Egli, S.
1992-01-01
We study some prospects of measuring the gluon density in the proton using charm events at HERA for the ep center of mass energy √s = 314 GeV. We invoke the QCD-improved boson-gluon fusion model and find the following cross-section: σ(ep → ecanti cX) ≅ O(0.6 μb). This cross-section would provide O(10 8 ) events/year, for an integrated luminosity of 100 pb -1 . We have investigated two traditional methods for tagging of charm, namely, D *± reconstruction using the process D *± → D 0 π ± → (K -+ π ± )π ± , and dileptonic decays of charmed hadrons (canti c → l + l - X). The inclusive cross-sections after full detector simulation are 10 3 pb and 10 2 pb, respectively. In both cases the background was strongly reduced. By using these events, the gluon distribution in the proton can be measured in the range 10 -3 ≤ x g ≤ 10 -1 . We conclude that an adequate discrimination among the present theoretical parametrizations can be achieved at HERA. (orig.)
Gluon Bremsstrahlung in Weakly-Coupled Plasmas
International Nuclear Information System (INIS)
Arnold, Peter
2009-01-01
I report on some theoretical progress concerning the calculation of gluon bremsstrahlung for very high energy particles crossing a weakly-coupled quark-gluon plasma. (i) I advertise that two of the several formalisms used to study this problem, the BDMPS-Zakharov formalism and the AMY formalism (the latter used only for infinite, uniform media), can be made equivalent when appropriately formulated. (ii) A standard technique to simplify calculations is to expand in inverse powers of logarithms ln(E/T). I give an example where such expansions are found to work well for ω/T≥10 where ω is the bremsstrahlung gluon energy. (iii) Finally, I report on perturbative calculations of q.
Constituent gluons and the static quark potential
Energy Technology Data Exchange (ETDEWEB)
Greensite, Jeff [San Francisco State Univ., CA (United States); Szczepaniak, Adam P. [Indiana Univ., Bloomington, IN (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
2016-04-01
We suggest that Hamiltonian matrix elements between physical states in QCD might be approximated, in Coulomb gauge, by "lattice-improved" tree diagrams; i.e. tree diagram contributions with dressed ghost, transverse gluon, and Coulomb propagators obtained from lattice simulations. Such matrix elements can be applied to a variational treatment of hadronic states which include constituent gluons. As an illustration and first application of this hybrid approach, we derive a variational estimate of the heavy quark potential for distances up to 2.5 fm. The Coulomb string tension in SU(3) gauge theory is about a factor of four times greater than the asymptotic string tension. In our variational approach, using for simplicity a single variational parameter, we can reduce this overshoot by nearly the factor required. The building blocks of our approach are Coulomb gauge propagators, and in this connection we present new lattice results for the ghost and transverse gluon propagators in position space.
Quark vs Gluon Jet Tagging at ATLAS
Rubbo, Francesco; The ATLAS collaboration
2017-01-01
Distinguishing quark-initiated from gluon-initiated jets is useful for many measurements and searches at the LHC. We present a quark-initiated versus gluon-initiated jet tagger from the ATLAS experiment using the number of reconstructed charged particles inside the jet. The measurement of the charged-particle multiplicity inside jets from Run 1 is used to derive uncertainties on the tagger performance for Run 2. With an efficiency of 60% to select quark-initiated jets, the efficiency to select gluon-initiated jets is between 10 and 20% across a wide range in jet pT up to 1.5 TeV with about an absolute 5% systematic uncertainty on the efficiencies. In addition, we also present preliminary studies on a tagger for the ATLAS experiment using the full radiation pattern inside a jet processed as images in deep neural network classifiers.
Quantum Simulations of Strongly Coupled Quark-Gluon Plasma
International Nuclear Information System (INIS)
Filinov, V.S.; Bonitz, M.; Ivanov, Yu.B.
2013-01-01
In recent years, there has been an increasing interest in dynamics and thermodynamics of non-Abelian plasmas at both very high temperature and density. It is expected that a specific state of matter with unconfined quarks and gluons - the so called quark - gluon plasma (QGP) - can exist. The most fundamental way to compute properties of the strongly interacting matter is provided by the lattice QCD. Interpretation of these very complicated computations requires application of various QCD motivated, albeit schematic, models simulating various aspects of the full theory. Moreover, such models are needed in cases when the lattice QCD fails, e.g. at large baryon chemical potentials and out of equilibrium. A semi-classical approximation, based on a point like quasi-particle picture has been recently introduced in literature. It is expected that it allows to treat soft processes in the QGP which are not accessible by the perturbative means and the main features of non-Abelian plasmas can be understood in simple semi-classical terms without the difficulties inherent to a full quantum field theoretical analysis. Here we propose stochastic simulation of thermodynamics and kinetic properties for QGP in semi-classical approximation in the wide region of temperature, density and quasi-particles masses. We extend previous classical nonrelativistic simulations based on a color Coulomb interaction to the quantum regime and take into account the Fermi (Bose) statistics of quarks (gluons) and quantum degeneracy self-consistently. In grand canonical ensemble for finite and zero baryon chemical potential we use the direct quantum path integral Monte Carlo method (PIMC) developed for finite temperature within Feynman formulation of quantum mechanics to do calculations of internal energy, pressure and pair correlation functions. The QGP quasi-particles representing dressed quarks, antiquarks and gluons interact via color quantum Kelbg pseudopotential rigorously derived in for Coulomb
Gluon fragmentation in T(1S) decays
International Nuclear Information System (INIS)
Bienlein, J.K.
1983-05-01
In T(1S) decays most observables (sphericity, charged multiplicity, photonic energy fraction, inclusive spectra) can be understood assuming that gluons fragment like quarks. New results from LENA use the (axis-independent) Fox-Wolfram moments for the photonic energy deposition. Continuum reactions show 'standard' Field-Feynman fragmentation. T(1S) decays show a significant difference in the photonic energy topology. It is more isotropic than with the Field-Feynman fragmentation scheme. Gluon fragmentation into isoscalar mesons (a la Peterson and Walsh) is excluded. But if one forces the leading particle to be isoscalar, one gets good agreement with the data. (orig.)
Gluon amplitudes as 2 d conformal correlators
Pasterski, Sabrina; Shao, Shu-Heng; Strominger, Andrew
2017-10-01
Recently, spin-one wave functions in four dimensions that are conformal primaries of the Lorentz group S L (2 ,C ) were constructed. We compute low-point, tree-level gluon scattering amplitudes in the space of these conformal primary wave functions. The answers have the same conformal covariance as correlators of spin-one primaries in a 2 d CFT. The Britto-Cachazo-Feng-Witten (BCFW) recursion relation between three- and four-point gluon amplitudes is recast into this conformal basis.
High energy multi-gluon exchange amplitudes
International Nuclear Information System (INIS)
Jaroszewicz, T.
1980-11-01
We examine perturbative high energy n-gluon exchange amplitudes calculated in the Coulomb gauge. If n exceeds the minimum required by the t-channel quantum numbers, such amplitudes are non-leading in lns. We derive a closed system of coupled integral equations for the corresponding two-particle n-gluon vertices, obtained by summing the leading powers of ln(N μ psup(μ)), where psup(μ) is the incident momentum and Nsup(μ) the gauge-defining vector. Our equations are infra-red finite, provided the external particles are colour singlets. (author)
Squeezed colour states in gluon jet
Kilin, S. YA.; Kuvshinov, V. I.; Firago, S. A.
1993-01-01
The possibility of the formation of squeezed states of gluon fields in quantum chromodynamics due to nonlinear nonperturbative self interaction during jet evolution in the process of e(+)e(-) annihilation into hadrons, which are analogous to the quantum photon squeezed states in quantum electrodynamics, is demonstrated. Additionally, the squeezing parameters are calculated.
Phenomenology of gluon TMDs at NNLL
Garcia, M.
2015-01-01
All the leading-Twist (un)polarized gluon transverse momentum dependent parton distribution functions have the same evolution, once they are properly defined in order to cancel spurious rapidity divergences. Currently known perturbative ingredients can be used to resum large logarithms up to
Electromagnetic signals of quark gluon plasma
Indian Academy of Sciences (India)
Successive equilibration of quark degrees of freedom and its effects on electromagnetic signals of quark gluon plasma are discussed. The effects of the variation of vector meson masses and decay widths on photon production from hot strongly interacting matter formed after Pb + Pb and S + Au collisions at CERN SPS ...
Polarized photons from quark-gluon plasma
International Nuclear Information System (INIS)
Goloviznin, V.V.; Snigirev, A.M.; Zinov'ev, G.M.
1988-01-01
The degree of polarization of magnetic bremsstrahlung radiation resulting from the interaction of escaping quarks with a collective confining color field is calculated. For a wide rapidity interval the angle at which the photon is registered and constitutes about 25%. This could signal about quark-gluon plasma formation
Soft gluon contributions to hard processes
International Nuclear Information System (INIS)
Ciafaloni, M.
1981-10-01
The main concern of this paper is in trying to elucidate the origin of large QCD perturbative corrections and explain how to deal with them to all orders. They come essentially from the phase space regions close to the kinematical boundary of a hard process, in which one or many gluons become soft
Searching for the quarks and gluons plasma
International Nuclear Information System (INIS)
Gerschel, C.; Kluberg, L.
1989-01-01
Some investigations involving quark matter, at CERN, are discussed. The CERN available oxygen and sulfur beams, with energy about 200 GeV/nuclei, allow the obtention of high energy densities, never reached before. The possibilities of investigating (at CERN) the quarks and gluons plasma are considered. The first and unexpected results obtained from the NA38 experiment are overviewed [fr
Gluon 2- and 3-Point Correlation Functions on the Lattice
Parrinello, Claudio
1993-01-01
I present some preliminary results, obtained in collaboration with C. Bernard and A. Soni, for the lattice evaluation of 2- and 3-point gluon correlation functions in momentum space, with emphasis on the amputated 3-gluon vertex function. The final goal of this approach is the study of the running QCD coupling constant as defined from the amputated 3-gluon vertex.
2- and 3-point gluon correlation functions on the lattice
Energy Technology Data Exchange (ETDEWEB)
Parrinello, C. (Dept. of Physics, Univ. of Edinburgh (United Kingdom))
1994-04-01
I present some preliminary results, obtained in collaboration with C. Bernard and A. Soni, for the lattice evaluation of 2- and 3-point gluon correlation functions in momentum space, with emphasis on the amputated 3-gluon vertex function. The final goal of this approach is the study of the running QCD coupling constant as defined from the amputated 3-gluon vertex. (orig.)
Jagiellonian University Colour Reconnections in Quark and Gluon Jets in Herwig 7
Reichelt, Daniel; Siódmok, Andrzej
2017-01-01
Major event generators deviate significantly in their description of quark and gluon initiated jets. The modelling of these is particularly sensitive to the colour reconnection model used in the cluster hadronization model in the event generator Herwig. However, up to now, observables sensitive to the light flavour of jets have not been widely used in the construction and tuning of event generators. The scheme used in Herwig and changes within it are investigated using observables in $e^+ e^−$ and pp collisions, which are expected to discriminate quark and gluon jets.
Axial-vector gluons and the fine structure of heavy quark--antiquark systems
International Nuclear Information System (INIS)
Feinberg, G.; Lynn, B.; Sucher, J.
1979-01-01
We point out that two models of the origin of spin-dependent forces in heavy quark systems make very different predictions about the relative size of these forces in c-barc and b-barb. The model in which these forces are relativistic corrections to vector or scalar gluon exchange predicts smaller spin-dependent effects in b-barb than in c-barc while a model in which these forces are due to exchange of axial-vector gluons predicts a similar size for spin-dependent splittings in the two systems
Event-by-Event Simulations of Early Gluon Fields in High Energy Nuclear Collisions
Nickel, Matthew; Rose, Steven; Fries, Rainer
2017-09-01
Collisions of heavy ions are carried out at ultra relativistic speeds at the Relativistic Heavy Ion Collider and the Large Hadron Collider to create Quark Gluon Plasma. The earliest stages of such collisions are dominated by the dynamics of classical gluon fields. The McLerran-Venugopalan (MV) model of color glass condensate provides a model for this process. Previous research has provided an analytic solution for event averaged observables in the MV model. Using the High Performance Research Computing Center (HPRC) at Texas A&M, we have developed a C++ code to explicitly calculate the initial gluon fields and energy momentum tensor event by event using the analytic recursive solution. The code has been tested against previously known analytic results up to fourth order. We have also have been able to test the convergence of the recursive solution at high orders in time and studied the time evolution of color glass condensate.
Compound quarks and gluons and parton confinement (proposal of a different approach)
International Nuclear Information System (INIS)
Krolikowski, W.
1978-01-01
The author develops further the compound model proposed in 1971, where coloured quarks are factorized into elementary constituents carrying separately the flavour and colour quantum numbers and obeying the 'compensating' wrong statistics. An 'effective quantum chromodynamics' is conjectured, where both coloured quarks and vector gluons (which obey good statistics) are factorized into elementary constituents obeying wrong statistics. Then the Pauli connection of spin and statistics confines these elementary constituents within bound states obeying good statistics. In the parton model approximation with these elementary constituents as partons it prevents also coloured quarks and vector gluons from appearing as free particles. The expected confinement violation for coloured quarks and vector gluons and the observed scaling violation have here a common origin, namely the clustering of elementary constituents inside hadrons. The basic difference between leptons and quarks is related in this model to wrong statistics of elementary constituents involved in the quark structure. (Auth.)
Quarks and gluons in the nucleon: Proceedings. Volume 6
Energy Technology Data Exchange (ETDEWEB)
NONE
1997-12-31
The purpose of the symposium was to discuss the quark and gluon structure of the nucleon as probed experimentally by hard processes with lepton and hadron beams and studied theoretically by perturbative QCD, lattice QCD and effective models on the one hand and to stimulate research activities in the fields related to RHIC and RHIC-SPIN projects on the other hand. There were 18 talks and 2 discussion sessions. About 50, including 5 from abroad participated in the symposium. An excellent summary in the form of 5 most important transparencies and a one-page explanation is included for each of the invited talks.
Effects of magnetic fields on the quark–gluon plasma
Energy Technology Data Exchange (ETDEWEB)
Bali, G.S. [Institute for Theoretical Physics, Universität Regensburg, D-93040 Regensburg (Germany); Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India); Bruckmann, F. [Institute for Theoretical Physics, Universität Regensburg, D-93040 Regensburg (Germany); Endrődi, G., E-mail: gergely.endrodi@physik.uni-r.de [Institute for Theoretical Physics, Universität Regensburg, D-93040 Regensburg (Germany); Fodor, Z. [Eötvös University, Theoretical Physics, Pázmány P. s 1/A, H-1117, Budapest (Hungary); Bergische Universität Wuppertal, Theoretical Physics, 42119 Wuppertal (Germany); Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52425 Jülich (Germany); Katz, S.D. [Eötvös University, Theoretical Physics, Pázmány P. s 1/A, H-1117, Budapest (Hungary); MTA-ELTE Lendület Lattice Gauge Theory Research Group (Hungary); Schäfer, A. [Institute for Theoretical Physics, Universität Regensburg, D-93040 Regensburg (Germany)
2014-11-15
In this talk, the response of the thermal QCD medium to external (electro)magnetic fields is studied using continuum extrapolated lattice results at physical quark masses. The magnetic susceptibility of QCD is calculated, revealing a strong paramagnetic response at high temperatures. This paramagnetism is shown to result in an anisotropic squeezing of the quark–gluon plasma in non-central heavy-ion collisions, implying a sizeable contribution to the elliptic flow. Another aspect is the magnetic response of topologically non-trivial domains to the magnetic field. We quantify this effect on the lattice and compare the results to a simple model estimate.
Quarks and gluons in the nucleon: Proceedings. Volume 6
International Nuclear Information System (INIS)
1997-01-01
The purpose of the symposium was to discuss the quark and gluon structure of the nucleon as probed experimentally by hard processes with lepton and hadron beams and studied theoretically by perturbative QCD, lattice QCD and effective models on the one hand and to stimulate research activities in the fields related to RHIC and RHIC-SPIN projects on the other hand. There were 18 talks and 2 discussion sessions. About 50, including 5 from abroad participated in the symposium. An excellent summary in the form of 5 most important transparencies and a one-page explanation is included for each of the invited talks
Meson interferometry and the quest for quark-gluon matter
International Nuclear Information System (INIS)
Soff, Sven
2001-01-01
We point out what we may learn from the investigation of identical two-particle interferometry in ultrarelativistic heavy ion collisions if we assume a particular model scenario by the formation of a thermalized quark-gluon plasma hadronizing via a first-order phase transition to an interacting hadron gas. The bulk properties of the two-pion correlation functions are dominated by these late and soft resonance gas rescattering processes. However, we show that kaons at large transverse momenta have several advantages and a bigger sensitivity to the QCD phase transition parameters
Quarkonium states in an anisotropic quark-gluon plasma
Energy Technology Data Exchange (ETDEWEB)
Guo Yun
2009-09-10
In this work we study the properties of quarkonium states in a quark-gluon plasma which, due to expansion and non-zero viscosity, exhibits a local anisotropy in momentum space. We determine the hard-loop resummed gluon propagator in an anisotropic QCD plasma in general linear gauges and define a potential between heavy quarks from the Fourier transform of its static limit. This potential which arises due to one-gluon exchange describes the force between a quark and anti-quark at short distances. It is closer to the vacuum potential as compared to the isotropic Debye screened potential which indicates the reduced screening in an anisotropic QCD plasma. In addition, angular dependence appears in the potential; we find that there is stronger attraction on distance scales on the order of the inverse Debye mass for quark pairs aligned along the direction of anisotropy than for transverse alignment. The potential at long distances, however, is non-perturbative and modeled as a QCD string which is screened at the same scale as the Coulomb field. At asymptotic separation the potential energy is non-zero and inversely proportional to the temperature. With a phenomenological potential model which incorporates the different behaviors at short and long distances, we solve the three-dimensional Schroedinger equation. Our numerical results show that quarkonium binding is stronger at non-vanishing viscosity and expansion rate, and that the anisotropy leads to polarization of the P-wave states. Furthermore, we determine viscosity corrections to the imaginary part of the heavy-quark potential in the weak-coupling hard-loop approximation. The imaginary part is found to be smaller (in magnitude) than at vanishing viscosity. This implies a smaller decay width of quarkonium bound states in an anisotropic plasma. (orig.)
Quarkonium states in an anisotropic quark-gluon plasma
International Nuclear Information System (INIS)
Guo Yun
2009-01-01
In this work we study the properties of quarkonium states in a quark-gluon plasma which, due to expansion and non-zero viscosity, exhibits a local anisotropy in momentum space. We determine the hard-loop resummed gluon propagator in an anisotropic QCD plasma in general linear gauges and define a potential between heavy quarks from the Fourier transform of its static limit. This potential which arises due to one-gluon exchange describes the force between a quark and anti-quark at short distances. It is closer to the vacuum potential as compared to the isotropic Debye screened potential which indicates the reduced screening in an anisotropic QCD plasma. In addition, angular dependence appears in the potential; we find that there is stronger attraction on distance scales on the order of the inverse Debye mass for quark pairs aligned along the direction of anisotropy than for transverse alignment. The potential at long distances, however, is non-perturbative and modeled as a QCD string which is screened at the same scale as the Coulomb field. At asymptotic separation the potential energy is non-zero and inversely proportional to the temperature. With a phenomenological potential model which incorporates the different behaviors at short and long distances, we solve the three-dimensional Schroedinger equation. Our numerical results show that quarkonium binding is stronger at non-vanishing viscosity and expansion rate, and that the anisotropy leads to polarization of the P-wave states. Furthermore, we determine viscosity corrections to the imaginary part of the heavy-quark potential in the weak-coupling hard-loop approximation. The imaginary part is found to be smaller (in magnitude) than at vanishing viscosity. This implies a smaller decay width of quarkonium bound states in an anisotropic plasma. (orig.)
Higgs production in gluon fusion beyond NNLO
Energy Technology Data Exchange (ETDEWEB)
Ball, Richard D. [Edinburgh Univ. (United Kingdom). Tait Inst.; Bonvini, Marco [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Forte, Stefano [Milano Univ. (Italy). Dipt. di Fisica; INFN, Sezione di Milano (Italy); Marzani, Simone [Durham Univ. (United Kingdom). Inst. for Particle Physics Phenomenology; Ridolfi, Giovanni [Genova Univ. (Italy). Dipt. di Fisica; INFN, Sezione di Genova (Italy)
2013-03-15
We construct an approximate expression for the cross section for Higgs production in gluon fusion at next-to-next-to-next-to-leading order (N{sup 3}LO) in {alpha}{sub s} with finite top mass. We argue that an accurate approximation can be constructed by exploiting the analiticity of the Mellin space cross section, and the information on its singularity structure coming from large N (soft gluon, Sudakov) and small N (high energy, BFKL) all order resummation. We support our argument with an explicit comparison of the approximate and the exact expressions up to the highest (NNLO) order at which the latter are available. We find that the approximate N{sup 3}LO result amounts to a correction of 17% to the NNLO QCD cross section for production of a 125 GeV Higgs at the LHC (8 TeV), larger than previously estimated, and it significantly reduces the scale dependence of the NNLO result.
Higgs production in gluon fusion beyond NNLO
International Nuclear Information System (INIS)
Ball, Richard D.; Bonvini, Marco; Forte, Stefano; Marzani, Simone; Ridolfi, Giovanni
2013-01-01
We construct an approximate expression for the cross section for Higgs production in gluon fusion at next-to-next-to-next-to-leading order (N 3 LO) in α s with finite top mass. We argue that an accurate approximation can be constructed by exploiting the analyticity of the Mellin space cross section, and the information on its singularity structure coming from large N (soft gluon, Sudakov) and small N (high energy, BFKL) all order resummation. We support our argument with an explicit comparison of the approximate and the exact expressions up to the highest (NNLO) order at which the latter are available. We find that the approximate N 3 LO result amounts to a correction of 17% to the NNLO QCD cross section for production of a 125 GeV Higgs at the LHC (8 TeV), larger than previously estimated, and it significantly reduces the scale dependence of the NNLO result
Higgs production in gluon fusion beyond NNLO
Energy Technology Data Exchange (ETDEWEB)
Ball, Richard D. [Tait Institute, University of Edinburgh, Edinburgh EH9 3JZ, Scotland (United Kingdom); Bonvini, Marco [Deutsches Elektronen-Synchroton, DESY, Notkestraße 85, D-22603 Hamburg (Germany); Forte, Stefano, E-mail: forte@mi.infn.it [Dipartimento di Fisica, Università di Milano and INFN, Sezione di Milano, Via Celoria 16, I-20133 Milano (Italy); Marzani, Simone [Institute for Particle Physics Phenomenology, Durham University, Durham DH1 3LE, England (United Kingdom); Ridolfi, Giovanni [Dipartimento di Fisica, Università di Genova and INFN, Sezione di Genova, Via Dodecaneso 33, I-16146 Genova (Italy)
2013-09-21
We construct an approximate expression for the cross section for Higgs production in gluon fusion at next-to-next-to-next-to-leading order (N{sup 3}LO) in α{sub s} with finite top mass. We argue that an accurate approximation can be constructed by exploiting the analyticity of the Mellin space cross section, and the information on its singularity structure coming from large N (soft gluon, Sudakov) and small N (high energy, BFKL) all order resummation. We support our argument with an explicit comparison of the approximate and the exact expressions up to the highest (NNLO) order at which the latter are available. We find that the approximate N{sup 3}LO result amounts to a correction of 17% to the NNLO QCD cross section for production of a 125 GeV Higgs at the LHC (8 TeV), larger than previously estimated, and it significantly reduces the scale dependence of the NNLO result.
Higgs production in gluon fusion beyond NNLO
International Nuclear Information System (INIS)
Ball, Richard D.; Forte, Stefano; Marzani, Simone
2013-03-01
We construct an approximate expression for the cross section for Higgs production in gluon fusion at next-to-next-to-next-to-leading order (N 3 LO) in α s with finite top mass. We argue that an accurate approximation can be constructed by exploiting the analiticity of the Mellin space cross section, and the information on its singularity structure coming from large N (soft gluon, Sudakov) and small N (high energy, BFKL) all order resummation. We support our argument with an explicit comparison of the approximate and the exact expressions up to the highest (NNLO) order at which the latter are available. We find that the approximate N 3 LO result amounts to a correction of 17% to the NNLO QCD cross section for production of a 125 GeV Higgs at the LHC (8 TeV), larger than previously estimated, and it significantly reduces the scale dependence of the NNLO result.
The structure of gluon radiation in QCD
International Nuclear Information System (INIS)
Parke, S.; Mangano, M.
1989-08-01
For massless QCD the hard scattering amplitudes are naturally written in terms of the dual color expansion. here I present this expansion for purely gluonic processes and processes involving quark-antiquark pairs and gluons. The properties of the sub-amplitudes as well as explicit algebraic expressions are given for a number of these processes. Also, I demonstrate how to recover massless QED amplitudes from the dual expansion of massless QCD. 16 refs., 3 figs., 1 tab
Effective gluon interactions from superstring disk amplitudes
Energy Technology Data Exchange (ETDEWEB)
Oprisa, D.
2006-05-15
In this thesis an efficient method for the calculation of the N-point tree-level string amplitudes is presented. Furthermore it is shown that the six-gluon open-superstring disk amplitude can be expressed by a basis of six triple hypergeometric functions, which encode the full {alpha}' dependence. In this connection material for obtaining the {alpha}' expansion of these functions is derived. Hereby many Euler-Zagier sums are calculated including multiple harmonic series. (HSI)
Gluon saturation beyond (naive) leading logs
Energy Technology Data Exchange (ETDEWEB)
Beuf, Guillaume
2014-12-15
An improved version of the Balitsky–Kovchegov equation is presented, with a consistent treatment of kinematics. That improvement allows to resum the most severe of the large higher order corrections which plague the conventional versions of high-energy evolution equations, with approximate kinematics. This result represents a further step towards having high-energy QCD scattering processes under control beyond strict Leading Logarithmic accuracy and with gluon saturation effects.
The gluon propagator in momentum space
Energy Technology Data Exchange (ETDEWEB)
Bernard, C. [Washington Univ., St. Louis, MO (United States). Dept. of Physics; Parrinello, C. [New York Univ., NY (United States). Dept. of Physics]|[Brookhaven National Lab., Upton, NY (United States); Soni, A. [Brookhaven National Lab., Upton, NY (United States)
1992-12-31
We consider quenched QCD on a 16{sup 3}{times}40 lattice at {beta}=6.0. We give preliminary numerical results for the lattice gluon propagator evaluated both in coordinate and momentum space. Our findings are compared with earlier results in the literature at zero momentum. In addition, by considering nonzero momenta we attempt to extract the form of the propagator and compare it to continuum predictions formulated by Gribov and others.
The gluon propagator in momentum space
Energy Technology Data Exchange (ETDEWEB)
Bernard, C. (Washington Univ., St. Louis, MO (United States). Dept. of Physics); Parrinello, C. (New York Univ., NY (United States). Dept. of Physics Brookhaven National Lab., Upton, NY (United States)); Soni, A. (Brookhaven National Lab., Upton, NY (United States))
1992-01-01
We consider quenched QCD on a 16[sup 3][times]40 lattice at [beta]=6.0. We give preliminary numerical results for the lattice gluon propagator evaluated both in coordinate and momentum space. Our findings are compared with earlier results in the literature at zero momentum. In addition, by considering nonzero momenta we attempt to extract the form of the propagator and compare it to continuum predictions formulated by Gribov and others.
The gluon propagator in momentum space
Energy Technology Data Exchange (ETDEWEB)
Bernard, C. (Dept. of Physics, Washington Univ., St. Louis, MO (United States)); Parrinello, C. (Physics Dept., New York Univ., NY (United States) Physics Dept., Brookhaven National Lab., Upton, NY (United States)); Soni, A. (Physics Dept., Brookhaven National Lab., Upton, NY (United States))
1993-03-01
We consider quenched QCD on a 16[sup 3] x 40 lattice at [beta] = 6.0. We give preliminary numerical results for the lattice gluon propagator evaluated both in coordinate and momentum space. Our findings are compared with earlier results in the literature at zero momentum. In addition, by considering nonzero momenta we attempt to extract the form of the propagator and compare it to continuum predictions formulated by Gribov and others. (orig.)
Physics of the quark-gluon plasma
International Nuclear Information System (INIS)
Polonyi, J.; Institut National de Physique Nucleaire et de Physique des Particules; Lorand Eoetvoes Univ., Budapest
1995-01-01
Some features of the high temperature gluonic matter, such as the breakdown of the fundamental group symmetry by the kinetic energy, the screening of test quarks by some unusual gluon states and the explanation of the absence of isolated quarks in the vacuum without the help of infinities are presented in this talk. Special attention is paid to separate the dynamical input inferred from the numerical results of lattice gauge theory from the kinematics. (author)
The structure of gluon radiation in QCD
International Nuclear Information System (INIS)
Parke, S.; Mangano, M.
1990-01-01
For massless QCD the hard scattering amplitudes are naturally written in terms of the dual color expansion. Here I present this expansion for purely gluonic processes and processes involving quark-antiquark pairs and gluons. The properties of the sub-amplitudes as well as explicit algebraic expressions are given for a number of these processess. Finally, I demonstrate how to recover massless QED amplitudes from the dual expansion of massless QCD
Soft gluon emission in coloured quark scattering
International Nuclear Information System (INIS)
Frenkel, J.; Meuldemans, R.; Mohammad, I.; Taylor, J.C.
1977-01-01
In order to investigate the infrared behaviour of non-Abelian gauge theories the leading logarithms in the bremsstrahlung of two soft gluons by a coloured quark scattered in an external colourless potential have been calculated. In the calculations only diagrams containing exactly one Yang-Mills vertex have been used alongside with the dimensional infrared regularization. An expression is obtained exhibiting a crucial difference between QCD and QED
Effective gluon interactions from superstring disk amplitudes
International Nuclear Information System (INIS)
Oprisa, D.
2006-05-01
In this thesis an efficient method for the calculation of the N-point tree-level string amplitudes is presented. Furthermore it is shown that the six-gluon open-superstring disk amplitude can be expressed by a basis of six triple hypergeometric functions, which encode the full α' dependence. In this connection material for obtaining the α' expansion of these functions is derived. Hereby many Euler-Zagier sums are calculated including multiple harmonic series. (HSI)
Signatures of quark-gluon plasma production
International Nuclear Information System (INIS)
Gyulassy, M.
1985-01-01
A critical analysis of a variety of proposed signatures for quark-gluon formation in ultrarelativistic nuclear collisions is given. The authors emphasize that longitudinal growth rather than the nuclear radius controls the time scales for expansion. The author pointed out the qualitative difference of the evolution of the plasma produced in the stopping regime E approx. 10 GeV/nucleon and the scaling regime E > 1 TeV/nucleon. This difference reflects itself in the the rmal profile function
The gluon propagator in momentum space
International Nuclear Information System (INIS)
Bernard, C.; Soni, A.
1992-01-01
We consider quenched QCD on a 16 3 x40 lattice at β=6.0. We give preliminary numerical results for the lattice gluon propagator evaluated both in coordinate and momentum space. Our findings are compared with earlier results in the literature at zero momentum. In addition, by considering nonzero momenta we attempt to extract the form of the propagator and compare it to continuum predictions formulated by Gribov and others
New signals of quark-gluon-hadron mixed phase formation
Energy Technology Data Exchange (ETDEWEB)
Bugaev, K.A.; Sagun, V.V.; Ivanytskyi, A.I.; Zinovjev, G.M. [Bogolyubov Institute for Theoretical Physics, Kiev (Ukraine); Oliinychenko, D.R. [Bogolyubov Institute for Theoretical Physics, Kiev (Ukraine); Goethe University, FIAS, Frankfurt am Main (Germany); Ilgenfritz, E.M. [JINR, Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation); Nikonov, E.G. [JINR, Laboratory for Information Technologies, Dubna (Russian Federation); Taranenko, A.V. [Moscow Engineering Physics Institute, National Research Nuclear University ' ' MEPhI' ' , Moscow (Russian Federation)
2016-08-15
Here we present several remarkable irregularities at chemical freeze-out which are found using an advanced version of the hadron resonance gas model. The most prominent of them are the sharp peak of the trace anomaly existing at chemical freeze-out at the center-of-mass energy 4.9 GeV and two sets of highly correlated quasi-plateaus in the collision energy dependence of the entropy per baryon, total pion number per baryon, and thermal pion number per baryon which we found at the center-of-mass energies 3.8-4.9 GeV and 7.6-10 GeV. The low-energy set of quasi-plateaus was predicted a long time ago. On the basis of the generalized shock-adiabat model we demonstrate that the low-energy correlated quasi-plateaus give evidence for the anomalous thermodynamic properties inside the quark-gluon-hadron mixed phase. It is also shown that the trace anomaly sharp peak at chemical freeze-out corresponds to the trace anomaly peak at the boundary between the mixed phase and quark gluon plasma. We argue that the high-energy correlated quasi-plateaus may correspond to a second phase transition and discuss its possible origin and location. Besides we suggest two new observables which may serve as clear signals of these phase transformations. (orig.)
The Gluon Sivers Distribution: Status and Future Prospects
International Nuclear Information System (INIS)
Zhou, Jian; Boer, Daniël; Pisano, Cristian; Lorcé, Cédric
2015-01-01
We review what is currently known about the gluon Sivers distribution and what are the opportunities to learn more about it. Because single transverse spin asymmetries in p"↑p→πX provide only indirect information about the gluon Sivers function through the relation with the quark-gluon and tri-gluon Qiu-Sterman functions, current data from hadronic collisions at RHIC have not yet been translated into a solid constraint on the gluon Sivers function. SIDIS data, including the COMPASS deuteron data, allow for a gluon Sivers contribution of natural size expected from large N_c arguments, which is O(1/N_c) times the nonsinglet quark Sivers contribution. Several very promising processes to measure the gluon Sivers effect directly have been suggested, which besides RHIC investigations, would strongly favor experiments at AFTER@LHC and a possible future Electron-Ion Collider. Due to the inherent process dependence of TMDs, the gluon Sivers TMD probed in the various processes are different linear combinations of two universal gluon Sivers functions that have different behavior under charge conjugation and that therefore satisfy different theoretical constraints. For this reason both hadronic and DIS type of collisions are essential in the study of the role of gluons in transversely polarized protons.
Eleven lectures on the physics of the quark-gluon plasma
International Nuclear Information System (INIS)
McLerran, L.
1984-10-01
These lectures are intended to be an introduction to the physics of the quark-gluon plasma, and were presented at a workshop on The Physics of the Quark-Gluon Plasma held at Hua-Zhong Normal University in Wuhan, People's Republic of China in September, 1983. The lectures cover perturbation theory of the plasma at high temperature as well as the non-perturbative methods and results of lattice gauge theory computations. Physical models of the confinement-deconfinement phase transition and the modes of chiral symmetry breaking are presented. The possibility that a quark-gluon plasma might be produced in ultra-relativistic nuclear collisions is analyzed. Separate entries were prepared for the data base for the eleven lectures
The role of three-gluon correlation functions in the single spin asymmetry
Directory of Open Access Journals (Sweden)
Beppu Hiroo
2015-01-01
Full Text Available We study the twist-3 three-gluon contribution to the single spin asymmetry in the light-hadron production in pp collision in the framework of the collinear factorization. We derive the corresponding cross section formula in the leading order with respect to the QCD coupling constant. We also present a numerical calculation of the asymmetry at the RHIC energy, using a model for the three-gluon correlation functions suggested by the asymmetry for the D-meson production at RHIC. We found that the asymmetries for the light-hadron and the jet productions are very useful to constrain the magnitude and form of the correlation functions. Since the three-gluon correlation functions shift the asymmetry for all kinds of hadrons in the same direction, it is unlikely that they become a main source of the asymmetry.
Soft gluon approach for diffractive photoproduction of J/ψ
International Nuclear Information System (INIS)
Ma, J.P.; Xu Jiasheng
2002-01-01
We study diffractive photoproduction of J/ψ by taking the charm quark as a heavy quark. A description of nonperturbative effect related to J/ψ can be made by using NRQCD. In the forward region of the kinematics, the interaction between the cc-bar-pair and the initial hadron is due to exchange of soft gluons. The effect of the exchange can be studied by using the expansion in the inverse of the quark mass m c . At the leading order we find that the nonperturbative effect related to the initial hadron is represented by a matrix element of field strength operators, which are separated in the moving direction of J/ψ in the spacetime. The S-matrix element is then obtained without using perturbative QCD and the results are not based on any model. Corrections to the results can be systematically added. Keeping the dominant contribution of the S-matrix element in the large energy limit we find that the imaginary part of the S-matrix element is related to the gluon distribution for x→0 with a reasonable assumption, the real part can be obtained with another approximation or with dispersion relation. Our approach is different than previous approaches and also our results are different than those in these approaches. The differences are discussed in detail. A comparison with experiment is also made and a qualitative agreement is found. (author)
Three gluon jets as a test of QCD
International Nuclear Information System (INIS)
Koller, K.; Walsh, T.F.
1977-10-01
As a test of quantum chromodynamics (QCD), we suggest looking for gluon jets in the decay of a heavy quark-antiquark bound state produced in e + e - -annihilation, Q anti Q → 3 gluons → 3 gluon jets. In particular, we point out that these events form a jet Dalitz plot, and we calculate the gluon or jet distributions (including the effect of polarized e + e - -beams). This process affords a test of the gluon spin. It is the analogue of two-jet angular distributions in e + e - %→ q anti q → 2 quark jets. We also estimate multiplicities and momentum distributions of hadrons in Q anti Q → 3 gluons → hadrons, using the recently discovered UPSILON (9.4) as an example. (orig.) [de
Experimental properties of gluon and quark jets from a point source
International Nuclear Information System (INIS)
Abbiendi, G.; Ackerstaff, K.; Alexander, G.
1999-01-01
Gluon jets are identified in hadronic Z 0 decays as all the particles in a hemisphere opposite to a hemisphere containing two tagged quark jets. Gluon jets defined in this manner are equivalent to gluon jets produced from a color singlet point source and thus correspond to the definition employed for most theoretical calculations. In a separate stage of the analysis, we select quark jets in a manner to correspond to calculations, as the particles in hemispheres of flavor tagged light quark (uds) events. We present the distributions of rapidity, scaled energy, the logarithm of the momentum, and transverse momentum with respect to the jet axes, for charged particles in these gluon and quark jets. We also examine the charged particle multiplicity distributions of the jets in restricted intervals of rapidity. For soft particles at large p T , we observe the charged particle multiplicity ratio of gluon to quark jets to be 2.29±0.09(stat.)±0.15(syst.), in agreement with the prediction that this ratio should approximately equal the ratio of QCD color factors, C A /C F =2.25. The intervals used to define soft particles and large p T for this result, p T < 3.0 GeV/c, are motivated by the predictions of the Herwig Monte Carlo multihadronic event generator. Additionally, our gluon jet data allow a sensitive test of the phenomenon of non-leading QCD terms known as color reconnection. We test the model of color reconnection implemented in the Ariadne Monte Carlo multihadronic event generator and find it to be disfavored by our data. (orig.)
From the multifragmentation to the quark-gluon plasma
International Nuclear Information System (INIS)
Boisgard, R.
1988-01-01
Multifragmentation and quark de-confinement phenomena are discussed. A scenario for studying the stability of a hot and compressed nuclei is developed. The thermalization of the nuclei generated in heavy ion reactions is described by a pre-equilibrium model. A hydrodynamical approach and a percolation model are applied for determining the stability of the nucleus. The conditions for the nuclear fragmentation process and the cross sections for various systems at different energies are calculated. The experiments were carried out in ultrarelativistic interactions at CERN. The results are different from those obtained at lower energies and in proton reactions. The formation of a quark-gluon plasma is described by means of an aggregation model. The results are similar to those obtained with sophisticated methods. The differences between the macroscopical systems and the studied one (small number of particles) are stressed [fr
Roles of quarks and gluons in the spin structure of nucleons
International Nuclear Information System (INIS)
Modarres, M.; Amir-Kabir Univ., Teheran; Ghafoori-Tabrizi, K.; Shahid-Beheshti Univ., Teheran
1992-01-01
The spin structure of protons will be discussed by using MIT-bag model and considering constituent quarks to be combined from current quarks and gluons. It will be shown that the gluonic degrees of freedom play an important role in prediction of the recent EMC results. (orig.)
Remark on the Ansatz for IR behaviour of gluon propagator in QCD
International Nuclear Information System (INIS)
Tran Huu Phat; Nguyen Tuan Anh.
1996-10-01
It is shown that if in the IR region the gluon propagator of QCD behaves like D(k) = μ 2 δ(k) then the minimum of effective potential would correspond to the vanishing value of μ in the global color symmetry model (GCS) of QCD. (author). 10 refs, 1 fig
The impact of PDF and alphas uncertainties on Higgs Production in gluon fusion at hadron colliders
Demartin, Federico; Forte, Stefano; Mariani, Elisa; Rojo, Juan; Vicini, Alessandro
2010-01-01
We present a systematic study of uncertainties due to parton distributions and the strong coupling on the gluon-fusion production cross section of the Standard Model Higgs at the Tevatron and LHC colliders. We compare procedures and results when three recent sets of PDFs are used, CTEQ6.6, MSTW08
Soft Gluon Radiation off Heavy Quarks beyond Eikonal Approximation
International Nuclear Information System (INIS)
Mazumder, Surasree; Bhattacharyya, Trambak; Abir, Raktim
2016-01-01
We calculate the soft gluon radiation spectrum off heavy quarks (HQs) interacting with light quarks (LQs) beyond small angle scattering (eikonality) approximation and thus generalize the dead-cone formula of heavy quarks extensively used in the literatures of Quark-Gluon Plasma (QGP) phenomenology to the large scattering angle regime which may be important in the energy loss of energetic heavy quarks in the deconfined Quark-Gluon Plasma medium. In the proper limits, we reproduce all the relevant existing formulae for the gluon radiation distribution off energetic quarks, heavy or light, used in the QGP phenomenology.
The Theory of Quark and Gluon Interactions
Ynduráin, Francisco J
2006-01-01
F. J. Ynduráin's book on Quantum Chromodynamics has become a classic among advanced textbooks. First published in 1983, and translated into Russian in 1986, it now sees its fourth edition. It addresses readers with basic knowledge of field theory and particle phenomenology. The author presents the basic facts of quark and gluon physics in pedagogical form. Theory is always confronted with experimental findings. The reader will learn enough to be able to follow modern research articles. This fourth edition presents a new section on heavy quark effective theories, more material on lattice QCD and on chiral perturbation theory.
A new prescription for soft gluon resummation
International Nuclear Information System (INIS)
Abbate, Riccardo; Forte, Stefano; Ridolfi, Giovanni
2007-01-01
We present a new prescription for the resummation of the divergent series of perturbative corrections, due to soft gluon emission, to hard processes near threshold in perturbative QCD (threshold resummation). This prescription is based on Borel resummation, and contrary to the commonly used minimal prescription, it does not introduce a dependence of resummed physical observables on the kinematically unaccessible x→0 region of parton distributions. We compare results for resummed deep-inelastic scattering obtained using the Borel prescription and the minimal prescription and exploit the comparison to discuss the ambiguities related to the resummation procedure
Gluon fragmentation into 3 PJ quarkonium
International Nuclear Information System (INIS)
Ma, J.P.
1995-01-01
The functions of the gluon fragmentation into 3 P j quarkonium are calculated to order α 2 s . With the recent progress in analysing quarkonium systems in QCD it is possible show how the so called divergence in the limit of the zero-binding energy, which is related to P-wave quarkonia, is treated correctly in the case of fragmentation functions. The obtained fragmentation functions satisfy explicitly at the order of α 2 s the Altarelli-Parisi equation and when z → 0 they behave as z -1 as expected. 19 refs., 7 figs
Hydrodynamics of quark-gluon plasmas
International Nuclear Information System (INIS)
Blaizot, J.P.
1986-06-01
This paper reviews some aspects of the hydrodynamics of quark-gluon plasmas. Various stages of ultra-relativistic heavy ion collisions are described. Several estimates of the maximum energy density expected to be achieved in these collisions are compared. Discontinuities which may be induced in the hydrodynamic flow by a phase transition are described and a convenient numerical method designed to deal with such discontinuous flows is briefly presented. Finally, the correlations between particle transverse momenta and multiplicities are analyzed and one discusses to which extent these correlations could signal the occurrence of a phase transition in heavy ion collisions
Electric and magnetic properties of hot gluons
International Nuclear Information System (INIS)
Hansson, T.H.; Zahed, I.
1987-01-01
The dielectric constant ε and magnetic permeability μ for gluon plasma are calculated from the one-loop gauge-invariant effective action. The real parts are gauge-fixing independent and agree with earlier work. The imaginary part of μ/sup -1/ is zero in any covariant background-field gauge, while the imaginary part of ε is gauge-fixing dependent and negative definite. This result indicates that there is no consistent perturbative description of gluonic plasmons on scale ≥(g 2 T)/sup -1/
The quark gluon plasma; Le plasma de quarks et de gluons
Energy Technology Data Exchange (ETDEWEB)
Granier de Cassagnac, R. [Ecole Polytechnique, Lab. Leprince-Ringuet, 91 - Palaiseau (France)
2010-05-15
The quark-gluon plasma (QGP) is a state of matter in which the universe was expected to be a few micro-seconds after the big-bang. Violent collisions of heavy ions are supposed to re-create this state in particle accelerators. Numerous signatures of this fugacious state have already been observed at the RHIC (relativistic heavy ion collider). The first evidence of the violence of collisions is the number of generated particles: about 6000 per collision, mostly hadrons. This figure seems high but in fact is less than theoretically expected and is the first sign of the formation of a QGP that saturates the density of gluons. Another sign, observed at the RHIC is the damping of the particle jets that are produced in the collision. This damping is consistent with the crossing of a medium whose density is so high that it can not be made of hadrons but of partons. In the RHIC experiments the collective behaviour of quarks and gluons shows that they are strongly interacting with one another. This fact supports the idea that the QGP is more a perfect liquid rather than an ideal gas in which quarks and gluons move freely. (A.C.)
Surface emission of quark gluon plasma at RHIC and LHC
International Nuclear Information System (INIS)
Xiang Wenchang; Wan Renzhou; Zhou Daicui
2008-01-01
Within the framework of a factorization model, we study the behaviour of nuclear modification factor in Au-Au collisions at RHIC and Pb-Pb collisions at LHC. We find that the nuclear modification factor is inversely proportional to the radius of the quark-gluon plasma and is dominated by the surface emission of hard jets. We predict the nuclear modification factor P AALHS ∼0.15 in central Pb-Pb collisions at LHC. The study shows that the factorization model can be used to describe the centrality dependence of nuclear modification factor of the high transverse momentum particles produced in heavy ion collisions at both RHIC and LHC. (authors)
Muoproduction of J/ψ-mesons and the gluon distribution in nucleons
International Nuclear Information System (INIS)
Jong, Maarten de.
1991-01-01
The cross sections for production of J/ψ-mesons in muon-scattering at hydrogen and deuterium have been measured at a muon-energy of 280 GeV in order to extract from these the momentum distribution of gluons in the nucleon. These cross sections turned out to be equal for protons and neutrons within the experimental error. In the framework of the colour singlet model the gluon distribution has been determined from the cross section for the inelastic production of J/ψ mesons. At small gluon impulses the distribution obtained resembles a brems-strahlung spectrum. This distribution decreases, according to a simple description (counting rules) at larger impulses. The same model however underestimates the cross section for elastic production of J/ψ-mesons seriously. It is found that in inelastic production of J/ψ-mesons both helicities of the meson occur equally. Also a correlation has been observed between the scattering plane and the plane in which the J/ψ meson decays. The production of J/ψ-mesons and ψ'-mesons has been investigated in muon scattering at concrete at the same incoming energy. The measured ratio of their cross sections agrees with the colour singlet model but disagrees with the simplified description which characterizes the 'photon-gluon fusion model'. The possible nuclear-mass dependence of the cross section for J/ψ-meson production has been investigated in interactions of muons with tin and carbon at an energy of 280 GeV. This possible dependence turns out to be absent which means that on the basis of the colour singlet model the distributions of the gluons in the nucleon are equal in tin and carbon. (author). 103 refs.; 60 figs.; 19 tabs
χc charmonium - a tool to investigate gluon polarization
International Nuclear Information System (INIS)
Batunin, A.V.; Slabospitskij, S.R.
1986-01-01
Production of particles with a hidden charm Χ C in polarized parton beams (quarks or gluons) is studied. Parton polarization is shown to cause the changes of angular distributions of Χ C meson decay products, which allows one to investigate possible gluon polarization in hadrons
Accessing the distribution of linearly polarized gluons in unpolarized hadrons
Boer, Daniël; Brodsky, Stanley J.; Mulders, Piet J.; Pisano, Cristian
2011-01-01
Gluons inside unpolarized hadrons can be linearly polarized provided they have a nonzero transverse momentum. The simplest and theoretically safest way to probe this distribution of linearly polarized gluons is through cos(2 phi) asymmetries in heavy quark pair or dijet production in electron-hadron
Differences between quark and gluon jets as seen at LEP
International Nuclear Information System (INIS)
Tasevsky, M.
2001-01-01
The differences between quark and gluon jets are studied using LEP results on jet widths, scale dependent multiplicities, ratios of multiplicities, slopes and curvatures and fragmentation functions. It is emphasized that the observed differences stem primarily from the different quark and gluon colour factors
Differences between Quark and Gluon jets as seen at LEP
Tasevsky, Marek
2001-01-01
The differences between quark and gluon jets are studied using LEP results on jet widths, scale dependent multiplicities, ratios of multiplicities, slopes and curvatures and fragmentation functions. It is emphasized that the observed differences stem primarily from the different quark and gluon colour factors.
EXPLORING THE POLARIZATION OF GLUONS IN THE NUCLEON.
Energy Technology Data Exchange (ETDEWEB)
STRATMANN,M.; VOGELSANG,W.
2007-10-22
We give an overview of the current status of investigations of the polarization of gluons in the nucleon. We describe some of the physics of the spin-dependent gluon parton distribution and its phenomenology in high-energy polarized hadronic scattering. We also review the recent experimental results.
Regge behaviour of distribution functions and evolution of gluon ...
Indian Academy of Sciences (India)
work we solved DGLAP evolution equation for gluon distribution function at low-x in next-to-leading order (NLO) and the t and x-evolutions of gluon distribution function thus obtained have been compared with global MRST2004 and GRV98 parametrizations. In PQCD, since the higher-order terms in the leading logarithmic.
Dynamical instabilities in quark-gluon plasma with hard jet
International Nuclear Information System (INIS)
Pavlenko, O.P.
1990-01-01
The dynamical instabilities, whose development can be expected under the hard jet propagating through the quark-gluon plasma, are analyzed. The possible signals of the quark-gluon plasma formation in ultrarelativistic nuclear collisions connected with the development of the plasma-jet instabilities are discussed. 10 refs
Linearly Polarized Gluons and the Higgs Transverse Momentum Distribution
Boer, Daniel; den Dunnen, Wilco J.; Pisano, Cristian; Schlegel, Marc; Vogelsang, Werner
2012-01-01
We study how gluons carrying linear polarization inside an unpolarized hadron contribute to the transverse momentum distribution of Higgs bosons produced in hadronic collisions. They modify the distribution produced by unpolarized gluons in a characteristic way that could be used to determine
Gluon condensate from lattice caculations: SU(3) pure gauge theory
International Nuclear Information System (INIS)
Kripfganz, J.
1981-01-01
A short distance expansion of Wilson loops is used to define and isolate vacuum expectation values of composite gluon operators. It is applied to available lattice Monte Carlo data for SU(3) pure gauge theory. The value obtained for the gluon condensate is consistent with the ITEP estimate. (author)
Dynamical quark and gluon condensates from a modified perturbative QCD
International Nuclear Information System (INIS)
Cabo Montes de Oca, A.; Martinez Pedrera, D.
2004-12-01
As it was suggested by previous works on a modified perturbation expansion for QCD, the possibility for the generation of large quark condensates in the massless version of the theory is explored. For this purpose, it is firstly presented a way to well define the Feynman diagrams at any number of loops by just employing dimensional regularization. After that, the calculated zero and one loop corrections to the effective potential indicate a strong instability of the system under the generation of quark condensates even in the absence of the gluon one. The quark condensate dependence of particular two loop terms does not modify the instability picture arising at one loop. The results suggest a possible mechanism for a sort of Top Condensate Model to be a dynamically fixed effective action for massless QCD. The inability of lattice calculations in detecting this possibility could be related to the current limitations in treating the fermion determinants. (author)
Anomalous quark and gluon contents of light hadrons
Energy Technology Data Exchange (ETDEWEB)
Hatsuda, T. (Washington Univ., Seattle, WA (United States). Inst. for Nuclear Theory); Kunihiro, T. (Ryukoku Univ., Otsu-City (Japan). Faculty of Science and Technology)
1992-09-14
The sea-quark contents such as anti ss, anti cc, anti bb... of the low-lying baryons in the octet and decuplet are calculated with a combined use of the trace anomaly of QCD and a chiral quark model. We find (i) the empirical value of the [pi]-N sigma term ([proportional to] 45 MeV) can be reproduced with a rather small anti ss content of nucleon consistently with the Gell-Mann-Okubo mass formula, (ii) the probability to find a charm quark in nucleon is found to be 0.5% which is consistent with the experimental analysis of the charm structure function of the proton and is necessary to account for the J/[psi]-production in proton-nucleous collisions and (iii) both strange and heavy quarks are equally important for the Higgs-nucleon coupling. The heavy-quark and gluon contents of pion and kaon are briefly mentioned. (orig.).
Equation of state of quasi-free gluon gas
International Nuclear Information System (INIS)
Chakrabarty, Somenath; Syam, Debapriyo
1993-01-01
The object of this work is to derive an equation of state for a system of gluons beyond the deconfining temperature (∼200 MeV) with phenomenological applications in mind. Our starting point is the relativistic virial theorem. We assume that the non-Abelian nature of QCD (especially the confirming gluon-gluon interaction), as far as the gluon gas is concerned, can be accounted for by postulating a bag pressure (B), while the residual interaction among the gluons can be treated as if the problem is Abelian. Near the 'critical' temperature the residual interactions are seen to play an important role. Also the Stefan-Boltzmann constant is required to be replaced by an effective constant having a somewhat smaller value. (Author)
Selection of Photon Gluon Fusion Events in DIS
International Nuclear Information System (INIS)
Kowalik, K.; Rondio, E.; Sulej, R.; Zaremba, K.
2001-01-01
A selection of the Photon Gluon Fusion (PGF) process with light quarks for deep inelastic scattering events is presented. This process is directly sensitive to gluon polarization and our goal is to find out the most effective selection on a sample of events simulated for the SMC experiment. We compare two general multi-class classification methods - Bayes method and neural network with a conventional selection procedure. The neural network algorithm presented here is a modification of method belonging to the family of directional minimization algorithms. This method is convenient and effective for photon gluon fusion selection and determination of gluon polarization. Finally we present the estimation for precision of gluon polarization for neural network method. (author)
Bound states of quarks and gluons and hadronic transitions
International Nuclear Information System (INIS)
Castro, Antonio Soares de.
1990-05-01
A potential which incorporates the concepts of confinement and asymptotic freedom, previously utilized in the description of the spectroscopy of mesons and baryons, is extended to the gluon sector. The mass spectroscopy of glueballs and hybrids is analyzed considering only pairwise potentials and massive constituent gluons. The mass spectrum of the color octet two-gluon system is adopted as a suitable description of the intermediate states of hadronic transitions, within the framework of the multipole expansion for quantum chromodynamics. The spin-dependent effects in the gluonium spectrum, associated with the Coulombian potential, are calculated through the inverted first Born approximation for the gluon-gluon scattering. (author). 102 refs, 1 fig, 13 tabs
Production of $K^{0}_{S}$ and $\\Lambda$ in Quark and Gluon Jets from $Z^{0}$ Decay
Ackerstaff, K.; Allison, John; Altekamp, N.; Anderson, K.J.; Anderson, S.; Arcelli, S.; Asai, S.; Ashby, S.F.; Axen, D.; Azuelos, G.; Ball, A.H.; Barberio, E.; Barlow, Roger J.; Bartoldus, R.; Batley, J.R.; Baumann, S.; Bechtluft, J.; Behnke, T.; Bell, Kenneth Watson; Bella, G.; Bentvelsen, S.; Bethke, S.; Betts, S.; Biebel, O.; Biguzzi, A.; Bird, S.D.; Blobel, V.; Bloodworth, I.J.; Bobinski, M.; Bock, P.; Bohme, J.; Boutemeur, M.; Braibant, S.; Bright-Thomas, P.; Brown, Robert M.; Burckhart, H.J.; Burgard, C.; Burgin, R.; Capiluppi, P.; Carnegie, R.K.; Carter, A.A.; Carter, J.R.; Chang, C.Y.; Charlton, David G.; Chrisman, D.; Ciocca, C.; Clarke, P.E.L.; Clay, E.; Cohen, I.; Conboy, J.E.; Cooke, O.C.; Couyoumtzelis, C.; Coxe, R.L.; Cuffiani, M.; Dado, S.; Dallavalle, G.Marco; Davis, R.; De Jong, S.; del Pozo, L.A.; de Roeck, A.; Desch, K.; Dienes, B.; Dixit, M.S.; Doucet, M.; Dubbert, J.; Duchovni, E.; Duckeck, G.; Duerdoth, I.P.; Eatough, D.; Estabrooks, P.G.; Evans, H.G.; Fabbri, F.; Fanfani, A.; Fanti, M.; Faust, A.A.; Fiedler, F.; Fierro, M.; Fischer, H.M.; Fleck, I.; Folman, R.; Furtjes, A.; Futyan, D.I.; Gagnon, P.; Gary, J.W.; Gascon, J.; Gascon-Shotkin, S.M.; Geich-Gimbel, C.; Geralis, T.; Giacomelli, G.; Giacomelli, P.; Gibson, V.; Gibson, W.R.; Gingrich, D.M.; Glenzinski, D.; Goldberg, J.; Gorn, W.; Grandi, C.; Gross, E.; Grunhaus, J.; Gruwe, M.; Hanson, G.G.; Hansroul, M.; Hapke, M.; Hargrove, C.K.; Hartmann, C.; Hauschild, M.; Hawkes, C.M.; Hawkings, R.; Hemingway, R.J.; Herndon, M.; Herten, G.; Heuer, R.D.; Hildreth, M.D.; Hill, J.C.; Hillier, S.J.; Hobson, P.R.; Hocker, James Andrew; Homer, R.J.; Honma, A.K.; Horvath, D.; Hossain, K.R.; Howard, R.; Huntemeyer, P.; Igo-Kemenes, P.; Imrie, D.C.; Ishii, K.; Jacob, F.R.; Jawahery, A.; Jeremie, H.; Jimack, M.; Joly, A.; Jones, C.R.; Jovanovic, P.; Junk, T.R.; Karlen, D.; Kartvelishvili, V.; Kawagoe, K.; Kawamoto, T.; Kayal, P.I.; Keeler, R.K.; Kellogg, R.G.; Kennedy, B.W.; Klier, A.; Kluth, S.; Kobayashi, T.; Kobel, M.; Koetke, D.S.; Kokott, T.P.; Kolrep, M.; Komamiya, S.; Kowalewski, Robert V.; Kress, T.; Krieger, P.; von Krogh, J.; Kyberd, P.; Lafferty, G.D.; Lanske, D.; Lauber, J.; Lautenschlager, S.R.; Lawson, I.; Layter, J.G.; Lazic, D.; Lee, A.M.; Lefebvre, E.; Lellouch, D.; Letts, J.; Levinson, L.; Liebisch, R.; List, B.; Littlewood, C.; Lloyd, A.W.; Lloyd, S.L.; Loebinger, F.K.; Long, G.D.; Losty, M.J.; Ludwig, J.; Lui, D.; Macchiolo, A.; Macpherson, A.; Mannelli, M.; Marcellini, S.; Markopoulos, C.; Martin, A.J.; Martin, J.P.; Martinez, G.; Mashimo, T.; Mattig, Peter; McDonald, W.John; McKenna, J.A.; Mckigney, E.A.; McMahon, T.J.; McPherson, R.A.; Meijers, F.; Menke, S.; Merritt, F.S.; Mes, H.; Meyer, J.; Michelini, A.; Mihara, S.; Mikenberg, G.; Miller, D.J.; Mir, R.; Mohr, W.; Montanari, A.; Mori, T.; Nagai, K.; Nakamura, I.; Neal, H.A.; Nellen, B.; Nisius, R.; O'Neale, S.W.; Oakham, F.G.; Odorici, F.; Ogren, H.O.; Oreglia, M.J.; Orito, S.; Palinkas, J.; Pasztor, G.; Pater, J.R.; Patrick, G.N.; Patt, J.; Perez-Ochoa, R.; Petzold, S.; Pfeifenschneider, P.; Pilcher, J.E.; Pinfold, J.; Plane, David E.; Poffenberger, P.; Poli, B.; Polok, J.; Przybycien, M.; Rembser, C.; Rick, H.; Robertson, S.; Robins, S.A.; Rodning, N.; Roney, J.M.; Roscoe, K.; Rossi, A.M.; Rozen, Y.; Runge, K.; Runolfsson, O.; Rust, D.R.; Sachs, K.; Saeki, T.; Sahr, O.; Sang, W.M.; Sarkisian, E.K.G.; Sbarra, C.; Schaile, A.D.; Schaile, O.; Scharf, F.; Scharff-Hansen, P.; Schieck, J.; Schmitt, B.; Schmitt, S.; Schoning, A.; Schorner, T.; Schroder, Matthias; Schumacher, M.; Schwick, C.; Scott, W.G.; Seuster, R.; Shears, T.G.; Shen, B.C.; Shepherd-Themistocleous, C.H.; Sherwood, P.; Siroli, G.P.; Sittler, A.; Skuja, A.; Smith, A.M.; Snow, G.A.; Sobie, R.; Soldner-Rembold, S.; Sproston, M.; Stahl, A.; Stephens, K.; Steuerer, J.; Stoll, K.; Strom, David M.; Strohmer, R.; Tafirout, R.; Talbot, S.D.; Tanaka, S.; Taras, P.; Tarem, S.; Teuscher, R.; Thiergen, M.; Thomson, M.A.; von Torne, E.; Torrence, E.; Towers, S.; Trigger, I.; Trocsanyi, Z.; Tsur, E.; Turcot, A.S.; Turner-Watson, M.F.; Van Kooten, Rick J.; Vannerem, P.; Verzocchi, M.; Vikas, P.; Voss, H.; Wackerle, F.; Wagner, A.; Ward, C.P.; Ward, D.R.; Watkins, P.M.; Watson, A.T.; Watson, N.K.; Wells, P.S.; Wermes, N.; White, J.S.; Wilson, G.W.; Wilson, J.A.; Wyatt, T.R.; Yamashita, S.; Yekutieli, G.; Zacek, V.; Zer-Zion, D.
1999-01-01
The production of K^0_S mesons and Lambda baryons in quark and gluon jets has been investigated using two complementary techniques. In the first approach, which provides high statistical accuracy, jets were selected using different jet finding algorithms and ordered according to their energy. Production rates were determined taking into account the dependences of quark and gluon compositions as a function of jet energy as predicted by Monte Carlo models. Selecting three-jet events with the k_perp (Durham) jet finder (y_cut = 0.005), the ratios of K^0_S and Lambda production rates in gluon and quark jets relative to the mean charged particle multiplicity were found to be 1.10 +/- 0.02 +/- 0.02 and 1.41 +/- 0.04 +/- 0.04, respectively, where the first uncertainty is statistical and the second is systematic. In the second approach, a new method of identifying quark jets based on the collimation of energy flow around the jet axis is introduced and was used to anti-tag gluon jets in symmetric (Y-shaped) three-jet ...
Quarkonium decays: Testing the 3-gluon vertex
International Nuclear Information System (INIS)
Koller, K.; Walsh, T.F.; Zerwas, P.M.; Technische Hochschule Aachen
1980-12-01
We study the 3-jet decays of S and P-wave quarkonia with C = +. If observed, some of these will offer a way of seeing the 3G vertex of QCD via 1 Ssub(o), 3 Psub(o), 3 P 2 (Qanti Q) → GGG + Gqanti q → 3 jets. (As is well-known, cancellations reduce 3 P 1 (anti Q) → GGG.) We elaborate in detail the S-wave decay as it is expected to show all the characteristic features of orthoquarkonium decays into 4 jets, 3 S 1 (Qanti Q) → GGGG + GGqanti q → 4 jets which we will comment upon. These quarkonium decays offer a very clear signal for QCD as a non-abelian local gauge field theory with color-charged gluons. (orig.)
Quark-gluon plasma: experimental signatures
International Nuclear Information System (INIS)
Drapier, O.
1995-01-01
The existence of a deconfining phase transition of nuclear matter is a clear prediction of lattice quantum chromodynamics calculations. The signatures of this quark-gluon plasma (QGP) have been searched for, since the first high energy ion beams became available at BNL and CERN in 1986, and gold and lead beams are now accelerated at 11 and 160 GeV per nucleon by the AGS and SPS. An overview of the main signatures expected in case of QGP formation is presented here. Although some recent results have been found in agreement with the predictions of the QGP scenario, no clear evidence for its formation has been observed at present. Nevertheless, new high statistics results are expected from CERN lead beams. In addition, future experiments are being prepared at RHIC and LHCC, providing an increase by two orders of magnitude of the c.m.s. energy within a few years. (author). 66 refs., 28 figs
Soft gluons and superleading logarithms in QCD
Forshaw, J R
2009-01-01
After a brief introduction to the physics of soft gluons in QCD we present a surprising prediction. Dijet production in hadron-hadron collisions provides the paradigm, i.e. h_1 +h_2 \\to jj+X. In particular, we look at the case where there is a restriction placed on the emission of any further jets in the region in between the primary (highest p_T) dijets. Logarithms in the ratio of the jet scale to the veto scale can be summed to all orders in the strong coupling. Surprisingly, factorization of collinear emissions fails at scales above the veto scale and triggers the appearance of double logarithms in the hard sub-process. The effect appears first at fourth order relative to the leading order prediction and is subleading in the number of colours.
Gluon Green functions free of quantum fluctuations
Directory of Open Access Journals (Sweden)
A. Athenodorou
2016-09-01
Full Text Available This letter reports on how the Wilson flow technique can efficaciously kill the short-distance quantum fluctuations of 2- and 3-gluon Green functions, remove the ΛQCD scale and destroy the transition from the confining non-perturbative to the asymptotically-free perturbative sector. After the Wilson flow, the behavior of the Green functions with momenta can be described in terms of the quasi-classical instanton background. The same behavior also occurs, before the Wilson flow, at low-momenta. This last result permits applications as, for instance, the detection of instanton phenomenological properties or a determination of the lattice spacing only from the gauge sector of the theory.
Energy Technology Data Exchange (ETDEWEB)
Castro, Antonio Soares de
1990-05-01
A potential which incorporates the concepts of confinement and asymptotic freedom, previously utilized in the description of the spectroscopy of mesons and baryons, is extended to the gluon sector. The mass spectroscopy of glueballs and hybrids is analyzed considering only pairwise potentials and massive constituent gluons. The mass spectrum of the color octet two-gluon system is adopted as a suitable description of the intermediate states of hadronic transitions, within the framework of the multipole expansion for quantum chromodynamics. The spin-dependent effects in the gluonium spectrum, associated with the Coulombian potential, are calculated through the inverted first Born approximation for the gluon-gluon scattering. (author). 102 refs, 1 fig, 13 tabs.
Baryonic hybrids: Gluons as beads on strings between quarks
International Nuclear Information System (INIS)
Cornwall, John M.
2005-01-01
In this paper we analyze the ground state of the heavy-quark qqqG system using standard principles of quark confinement and massive constituent gluons as established in the center-vortex picture. The known string tension K F and approximately-known gluon mass M lead to a precise specification of the long-range nonrelativistic part of the potential binding the gluon to the quarks with no undetermined phenomenological parameters, in the limit of large interquark separation R. Our major tool (also used earlier by Simonov) is the use of proper-time methods to describe gluon propagation within the quark system, along with some elementary group theory describing the gluon Wilson-line as a composite of colocated q and q lines. We show that (aside from color-Coulomb and similar terms) the gluon potential energy in the presence of quarks is accurately described (for small gluon fluctuations) via attaching these three strings to the gluon, which in equilibrium sits at the Steiner point of the Y-shaped string network joining the three quarks. The gluon undergoes small harmonic fluctuations that slightly stretch these strings and quasiconfine the gluon to the neighborhood of the Steiner point. To describe nonrelativistic ground-state gluonic fluctuations at large R we use the Schroedinger equation, ignoring mixing with l=2 states. Available lattice data and real-world hybrids require consideration of R values small enough for significant relativistic corrections, which we apply using a variational principle for the relativistic harmonic-oscillator. We also consider the role of color-Coulomb contributions. In terms of interquark separations R, we find leading nonrelativistic large-R terms in the gluon excitation energy of the form ε(R)→M+ξ[K F /(MR)] 1/2 -ζα c /R where ξ,ζ are calculable numerical coefficients and α c ≅ 0.15 is the color-Coulomb qq coupling. When the gluon is relativistic, ε∼(K F /R) 1/3 . We get an acceptable fit to lattice data with M=500 Me
Quarks and gluons in the phase diagram of quantum chromodynamics
Energy Technology Data Exchange (ETDEWEB)
Welzbacher, Christian Andreas
2016-07-14
that a dynamical charm quark has no influence on the phase structure. An open question about the phase diagram of quantum chromodynamics is the importance of hadronic degrees of freedom. These are subject to an exploratory study in Ch. 5, where we perform a two flavour calculation and include the nucleon as a degree of freedom in the well-known quark-diquark approximation. Due to the lack of explicit knowledge of in-medium properties of the nucleon, we refer to vacuum results and test their influence by variation. The results show that in this truncation baryons have only very little influence on the phase diagram. This is followed by an approach for a systematic investigation of the quark-gluon vertex Dyson-Schwinger equation at finite temperature. The presented work features an internal model vertex. Calculations taking an unquenched gluon as input are presented, where we compare the quark mass function to results from lattice calculations. We give details about the regularised condensate and study the impact of the different quark flavours and the dependence of the calculation on the chosen internal properties. In the last chapter we perform an investigation of the analytical properties of the quark. The Schwinger function, as the Fourier transform of the Euclidean quark propagator with respect to (imaginary) time, is studied in the vacuum as well as the medium. The spectral function, obtained from correlator data by solving an ill-defined inverse problem, is introduced together with the Rothkopf-Burnier Bayesian reconstruction algorithm, which returns the Bayesian answer to the given inverse problem. The status of the reconstruction for test data is presented and an outline given.
Baryon scattering at high energies. Wave function, impact factor, and gluon radiation
International Nuclear Information System (INIS)
Bartels, J.; Motyka, L.; Jagellonian Univ., Krakow
2007-11-01
The scattering of a baryon consisting of three massive quarks is investigated in the high energy limit of perturbative QCD. A model of a relativistic proton-like wave function, dependent on valence quark longitudinal and transverse momenta and on quark helicities, is proposed, and we derive the baryon impact factors for two, three and four t-channel gluons. We find that the baryonic impact factor can be written as a sum of three pieces: in the first one a subsystem consisting of two of the three quarks behaves very much like the quark-antiquark pair in γ * scattering, whereas the third quark acts as a spectator. The second term belongs to the odderon, whereas in the third (C-even) piece all three quarks participate in the scattering. This term is new and has no analogue in γ * scattering. We also study the small x evolution of gluon radiation for each of these three terms. The first term follows the same pattern of gluon radiation as the γ * -initiated quark-antiquark dipole, and, in particular, it contains the BFKL evolution followed by the 2→4 transition vertex (triple Pomeron vertex). The odderon-term is described by the standard BKP evolution, and the baryon couples to both known odderon solutions, the Janik-Wosiek solution and the BLV solution. Finally, the t-channel evolution of the third term starts with a three reggeized gluon state which then, via a new 3→4 transition vertex, couples to the four gluon (two-Pomeron) state. We briefly discuss a few consequences of these findings, in particular the pattern of unitarization of high energy baryon scattering amplitudes. (orig.)
Baryon scattering at high energies. Wave function, impact factor, and gluon radiation
Energy Technology Data Exchange (ETDEWEB)
Bartels, J. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Motyka, L. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik]|[Jagellonian Univ., Krakow (Poland). Inst. of Physics
2007-11-15
The scattering of a baryon consisting of three massive quarks is investigated in the high energy limit of perturbative QCD. A model of a relativistic proton-like wave function, dependent on valence quark longitudinal and transverse momenta and on quark helicities, is proposed, and we derive the baryon impact factors for two, three and four t-channel gluons. We find that the baryonic impact factor can be written as a sum of three pieces: in the first one a subsystem consisting of two of the three quarks behaves very much like the quark-antiquark pair in {gamma}{sup *} scattering, whereas the third quark acts as a spectator. The second term belongs to the odderon, whereas in the third (C-even) piece all three quarks participate in the scattering. This term is new and has no analogue in {gamma}{sup *} scattering. We also study the small x evolution of gluon radiation for each of these three terms. The first term follows the same pattern of gluon radiation as the {gamma}{sup *}-initiated quark-antiquark dipole, and, in particular, it contains the BFKL evolution followed by the 2{yields}4 transition vertex (triple Pomeron vertex). The odderon-term is described by the standard BKP evolution, and the baryon couples to both known odderon solutions, the Janik-Wosiek solution and the BLV solution. Finally, the t-channel evolution of the third term starts with a three reggeized gluon state which then, via a new 3{yields}4 transition vertex, couples to the four gluon (two-Pomeron) state. We briefly discuss a few consequences of these findings, in particular the pattern of unitarization of high energy baryon scattering amplitudes. (orig.)
Shear and bulk viscosity of high-temperature gluon plasma
Zhang, Le; Hou, De-Fu
2018-05-01
We calculate the shear viscosity (η) and bulk viscosity (ζ) to entropy density (s) ratios η/s and ζ/s of a gluon plasma system in kinetic theory, including both the elastic {gg}≤ftrightarrow {gg} forward scattering and the inelastic soft gluon bremsstrahlung {gg}≤ftrightarrow {ggg} processes. Due to the suppressed contribution to η and ζ in the {gg}≤ftrightarrow {gg} forward scattering and the effective g≤ftrightarrow {gg} gluon splitting, Arnold, Moore and Yaffe (AMY) and Arnold, Dogan and Moore (ADM) have got the leading order computations for η and ζ in high-temperature QCD matter. In this paper, we calculate the correction to η and ζ in the soft gluon bremsstrahlung {gg}≤ftrightarrow {ggg} process with an analytic method. We find that the contribution of the collision term from the {gg}≤ftrightarrow {ggg} soft gluon bremsstrahlung process is just a small perturbation to the {gg}≤ftrightarrow {gg} scattering process and that the correction is at ∼5% level. Then, we obtain the bulk viscosity of the gluon plasma for the number-changing process. Furthermore, our leading-order result for bulk viscosity is the formula \\zeta \\propto \\tfrac{{α }s2{T}3}{ln}{α }s-1} in high-temperature gluon plasma. Supported by Ministry of Science and Technology of China (MSTC) under the “973” Project (2015CB856904(4)) and National Natural Science Foundation of China (11735007, 11521064)
Charmonia enhancement in quark-gluon plasma with improved description of c-quarks phase distribution
International Nuclear Information System (INIS)
Gossiaux, Pol Bernard; Guiho, Vincent; Aichelin, Joerg
2005-01-01
We present a dynamical model of heavy quark evolution in the quark-gluon plasma (QGP) based on the Fokker-Planck equation. We then apply this model to the case of central ultra-relativistic nucleus-nucleus collisions performed at RHIC and estimate the component of J/ψ production (integrated and differential) stemming from c-c-bar pairs that are initially uncorrelated
The SU(3) running coupling from lattice gluons
Energy Technology Data Exchange (ETDEWEB)
Parrinello, C. [Edinburgh Univ. (United Kingdom). Dept. of Phys. and Astron.; UKQCD Collaboration
1995-04-01
We provide numerical results for the running coupling in SU(3) Yang-Mills theory as determined from an analysis of lattice two and three-point gluon correlation functions. The coupling is evaluated directly, from first principles, by defining suitable renormalisation constants from the lattice triple gluon vertex and gluon propagator. For momenta larger than 2GeV, the coupling is found to run according to the 2-loop asymptotic formula. The influence of lattice artifacts on the results appears negligible within the precision of our measurements, although further work on this point is in progress. ((orig.)).
Infra-red ghost contribution to the gluon Green's functions
International Nuclear Information System (INIS)
Paccanoni, F.
1985-01-01
The Schwinger-Dyson equations for the ghost propagator and the ghost-ghost-gluon vertex function are studied in the Landau gauge. A confining infra-red singularity is assumed for the gluon propagator and a suitable approximation is devised for the solution of the integral equations. It is found that the bare values of the ghost propagator and coupling cannot be a consistent solution of either equation. It is determined a possible behaviour of the correction factor for the ghost propagator in the small-momentum limit and discussed the consistency of the approximation schemes for the gluon propagator that neglet Faddeev-Popov ghost
The gluon distribution at small x - a phenomenological analysis
International Nuclear Information System (INIS)
Harriman, P.N.; Martin, A.D.; Stirling, W.J.; Roberts, R.G.
1990-03-01
The size of the gluon distribution at small χ has important implications for phenomenology at future high energy hadron-hadron and lepton-hadron colliders. We extend a recent global parton distribution fit to investigate the constraints on the gluon from deep inelastic and prompt photon data. In particular, we estimate a band of allowed gluon distributions with qualitatively small-χ behaviour and study the implications of these on a variety of cross sections at high energy pp and ep colliders. (author)
Rapidity evolution of gluon TMD from low to moderate x
International Nuclear Information System (INIS)
Balitsky, I.
2016-01-01
I discuss how the rapidity evolution of gluon transverse momentum dependent distribution (TMD) changes from nonlinear evolution at small x << 1 to linear evolution at moderate x ∼ 1. I have described the rapidity evolution of gluon TMD in the whole range of Bjorken x B and the whole range of transverse momentum. It should be emphasized that with our definition of rapidity cutoff the leading-order matrix elements of TMD operators are UV-finite so the rapidity evolution is the only evolution and it describes all the dynamics of gluon TMDs in the leading-log approximation
Quark charges and colour gluon mass from deep-inelastic bremsstrahlung
International Nuclear Information System (INIS)
Pandita, P.N.
1978-01-01
Sum rules are derived for the structure function V(x) for the 'three-photon' process e +- + p →e +- + γ +X which can distinguish between various colour models below colour threshold, independently of the quark and gluon distributions. A careful study of the sum rule for V(x) in the broken colour gauge theory model can in principle be used to determine the colour gluon mass. Invoking the specific assumptions of the dominance of p-type quarks and neglecting the sea of quark-antiquark pairs, bounds for V(x) are obtained in terms of νW 2 (x) which can distinguish between various colour models below colour threshold. (author)
The very hot soup of quarks and gluons; La tres chaude soupe de quarks et de gluons
Energy Technology Data Exchange (ETDEWEB)
Ter Minassian, V.
2010-05-15
The Phenix collaboration at the RHIC collider (Usa) has measured directly, for the first time, the temperature just after 2 gold nuclei have collided. All the experimental conditions were taken to assure that the temperature measured was that of the quark-gluon plasma. The value of this temperature is 4000*10{sup 9} K, which is 1.20 as high as the theoretical temperature threshold for the existence of the quark-gluon plasma. It is a proof that the quark-gluon plasma can be created within the operating conditions of the RHIC. (A.C.)
Role of the QCD induced gluon-gluon coupling to gauge boson pairs in the multitev region
International Nuclear Information System (INIS)
Ametller, L.; Gava, E.; Paver, N.; Treleani, D.
1985-02-01
We discuss the production of γγ and Zsup(O)γ pairs induced by the gluon-gluon fusion mechanism at typical supercollider energies. Due to the large flux of gluons with small fractional momenta, it is found that in certain kinematical configurations that subprocess, although of order (αsub(S)/π) 2 with respect to the leading quark annihilation, can give an appreciable contribution to the cross-section for Zsup(O)γ and even a larger one for the γγ production. (author)
Strangeness and the quark-gluon plasma: An experimenter's perspective
International Nuclear Information System (INIS)
Odyniec, G.
1994-02-01
Current status of experimental results on strange particle production in relativistic nucleus-nucleus collisions is reviewed. Emphasis is placed on the relevance to the hypothetical quark-gluon plasma formation and the origin of the Universe
The LPM effect in sequential bremsstrahlung: 4-gluon vertices
Energy Technology Data Exchange (ETDEWEB)
Arnold, Peter; Chang, Han-Chih [Department of Physics, University of Virginia,382 McCormick Road, Charlottesville, Virginia 22904-4714 (United States); Iqbal, Shahin [National Centre for Physics, Quaid-i-Azam University Campus, Islamabad, 45320 (Pakistan)
2016-10-24
The splitting processes of bremsstrahlung and pair production in a medium are coherent over large distances in the very high energy limit, which leads to a suppression known as the Landau-Pomeranchuk-Migdal (LPM) effect. In this paper, we continue study of the case when the coherence lengths of two consecutive splitting processes overlap (which is important for understanding corrections to standard treatments of the LPM effect in QCD), avoiding soft-gluon approximations. In particular, this paper completes the calculation of the rate for real double gluon bremsstrahlung from an initial gluon with various simplifying assumptions (thick media; q̂ approximation; and large N{sub c}) by now including processes involving 4-gluon vertices.
Resummation and the gluon damping rate in hot QCD
International Nuclear Information System (INIS)
Pisarski, R.D.
1990-08-01
At high temperature a consistent perturbative expansion requires the resummation of an infinite subset of loop corrections into an effective expansion. This effective exansion is used to compute the gluon damping rate at leading order. 25 refs
Differences between quark and gluon jets at LEP1
Boutemeur, Madjid
1997-01-01
A report is ven here on the differences between quark and gluon initiated jets as measured in LEPl. Various measurements, agree qualitatively on the differences between quark and gluon jets. However a direct quantitative comparison among the measurements as well as comparisons between the measurements and analytical calculations are difficult. This is due to the dependence of the results on the selected event topologies and used jet finding algorithms. Topology dependence of the charged particle multiplicity in quark and gluon jets is studied by ALEPH and transverse momentum-like scales are proposed to account for it. OPAL produced the first quantitative test of QCD analytic prediction for the ratio of the mean particle multiplicity between gluon and quark jets valid, at least, for 39 GeV jets.
A new method for computing the quark-gluon vertex
International Nuclear Information System (INIS)
Aguilar, A C
2015-01-01
In this talk we present a new method for determining the nonperturbative quark-gluon vertex, which constitutes a crucial ingredient for a variety of theoretical and phenomenological studies. This new method relies heavily on the exact all-order relation connecting the conventional quark-gluon vertex with the corresponding vertex of the background field method, which is Abelian-like. The longitudinal part of this latter quantity is fixed using the standard gauge technique, whereas the transverse is estimated with the help of the so-called transverse Ward identities. This method allows the approximate determination of the nonperturbative behavior of all twelve form factors comprising the quark-gluon vertex, for arbitrary values of the momenta. Numerical results are presented for the form factors in three special kinematical configurations (soft gluon and quark symmetric limit, zero quark momentum), and compared with the corresponding lattice data. (paper)
On the application of gluon to heavy quarkonium fragmentation function
International Nuclear Information System (INIS)
Qi Wei; Wang Jianxiong
2007-01-01
We analyze the uncertainties induced by different definitions of the momentum fraction z in the application of gluon to heavy quarkonium fragmentation function. We numerically calculate the initial g→J/ψ fragmentation functions by using the non-covariant definitions of z with finite gluon momentum and find that these fragmentation functions have strong dependence on the gluon momentum k. As |k|→∞, these fragmentation functions approach to the fragmentation function in the light-cone definition. We find that when |k| is small (for instance in the typical energy scale (about 4-20GeV) of the gluon production at the hadron colliders, such as Tevatron and LHC), large uncertainty remains while the in-covariant definitions of z are employed in the application of the fragmentation functions. (authors)
Energy Technology Data Exchange (ETDEWEB)
Goncalves, V.P. [Lund University, Department of Astronomy and Theoretical Physics, Lund (Sweden); Universidade Federal de Pelotas, Instituto de Fisica e Matematica, Pelotas, RS (Brazil); Martins, L.A.S.; Sauter, W.K. [Universidade Federal de Pelotas, Instituto de Fisica e Matematica, Pelotas, RS (Brazil)
2016-02-15
The current uncertainty on the gluon density extracted from the global parton analysis is large in the kinematical range of small values of the Bjorken-x variable and low values of the hard scale Q{sup 2}. An alternative to reduces this uncertainty is the analysis of the exclusive vector meson photoproduction in photon-hadron and hadron-hadron collisions. This process offers a unique opportunity to constrain the gluon density of the proton, since its cross section is proportional to the gluon density squared. In this paper we consider current parametrisations for the gluon distribution and estimate the exclusive vector meson photoproduction cross section at HERA and LHC using the leading logarithmic formalism. We perform a fit of the normalisation of the γh cross section and the value of the hard scale for the process and demonstrate that the current LHCb experimental data are better described by models that assume a slow increasing of the gluon distribution at small x and low Q{sup 2}. (orig.)
Calculation of parton fragmentation functions from jet calculus: gluon applications
International Nuclear Information System (INIS)
Lassila, K.E.; Ng, A.
1985-01-01
A method is presented for calculation of general parton fragmentation functions based on jet calculus plus meson and baryon wave functions. Results for gluon fragmentation into mesons and baryons are discussed and related to recent information on upsilon decay into gluons. The expressions derived can be used directly in e + e - cross section predictions and will need to be folded in with baryon parton distribution functions when used in p-barp collisions. (author)
Strangeness Production in a Chemically Equilibrating Quark-Gluon Plasma
Institute of Scientific and Technical Information of China (English)
HE Ze-Jun; LONG Jia-Li; MA Yu-Gang; MA Guo-Liang
2004-01-01
@@ We study the strangeness of a chemically equilibrating quark-gluon plasma at finite baryon density based on the and will accelerate with the change of the initial system from a chemically non-equilibrated to an equilibrated system. We also find that the calculated strangeness is very different from the one in the thermodynamic equilibrium system. This study may be helpful to understand the formation of quark-gluon plasma via a chemically non-equilibrated evolution framework.
Phenomenological Evidence for Gluon Depletion in pA Collisions
Hwa, R. C.; Pisut, J.; Pisutova, N.
2000-01-01
The data of J/psi suppression at large x_F in pA collisions are used to infer the existence of gluon depletion as the projectile proton traverses the nucleus. The modification of the gluon distribution is studied by use of a convolution equation whose non-perturbative splitting function is determined phenomenologically. The depletion factor at x_1=0.8 is found to be about 25% at A=100.
Gluon asymmetries in the leptoproduction of J/Ψ
International Nuclear Information System (INIS)
Godbole, R.M.; Gupta, S.; Sridhar, K.
1990-07-01
We study J/Ψ production, in deep inelastic scattering experiments with polarised beams and polarised targets. The spin asymmetries are seen to depend strongly on the particular form of the spin dependent gluon distributions used. Therefore, it should be possible in these experiments, to discriminate between different parametrizations of polarised gluon distributions, and hence between the distinctly different physical pictures of the proton spin underlying these parametrizations. (author). 18 refs, 4 figs, 1 tab
The five-gluon amplitude and one-loop integrals
International Nuclear Information System (INIS)
Bern, Z.; Dixon, L.; Kosower, D.A.
1992-12-01
We review the conventional field theory description of the string motivated technique. This technique is applied to the one-loop five-gluon amplitude. To evaluate the amplitude a general method for computing dimensionally regulated one-loop integrals is outlined including results for one-loop integrals required for the pentagon diagram and beyond. Finally, two five-gluon helicity amplitudes are given
TMD splitting functions in kT factorization. The real contribution to the gluon-to-gluon splitting
International Nuclear Information System (INIS)
Hentschinski, M.; Kusina, A.; Kutak, K.; Serino, M.
2018-01-01
We calculate the transverse momentum dependent gluon-to-gluon splitting function within k T -factorization, generalizing the framework employed in the calculation of the quark splitting functions in Hautmann et al. (Nucl Phys B 865:54-66, arXiv:1205.1759, 2012), Gituliar et al. (JHEP 01:181, arXiv:1511.08439, 2016), Hentschinski et al. (Phys Rev D 94(11):114013, arXiv:1607.01507, 2016) and demonstrate at the same time the consistency of the extended formalism with previous results. While existing versions of k T factorized evolution equations contain already a gluon-to-gluon splitting function i.e. the leading order Balitsky-Fadin-Kuraev-Lipatov (BFKL) kernel or the Ciafaloni-Catani-Fiorani-Marchesini (CCFM) kernel, the obtained splitting function has the important property that it reduces both to the leading order BFKL kernel in the high energy limit, to the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) gluon-to-gluon splitting function in the collinear limit as well as to the CCFM kernel in the soft limit. At the same time we demonstrate that this splitting kernel can be obtained from a direct calculation of the QCD Feynman diagrams, based on a combined implementation of the Curci-Furmanski-Petronzio formalism for the calculation of the collinear splitting functions and the framework of high energy factorization. (orig.)
Gluon distributions in nucleons and pions at a low resolution scale
International Nuclear Information System (INIS)
Christiansen, H.R.
2000-10-01
In this paper we study the gluon distribution functions in nucleons and pions at a low resolution Q 2 scale. This is an important issue since parton densities at low Q 2 have always been taken as an external input which is adjusted through DGLAP evolution to fit the experimental data at higher scales. Here, in the framework of a model recently developed, it is shown that the hypothetical cloud of neutral pions surrounding nucleons and pions appears to be responsible for the characteristic valence-like gluon distributions needed at the initial low scale. As an additional result, we get the remarkable prediction that neutral and charged ions have different intrinsic sea flavor contents. (author)
CP-even scalar boson production via gluon fusion at the LHC
Anastasiou, Charalampos; Dulat, Falko; Furlan, Elisabetta; Gehrmann, Thomas; Herzog, Franz; Lazopoulos, Achilleas; Mistlberger, Bernhard
2016-09-07
In view of the searches at the LHC for scalar particle resonances in addition to the 125 GeV Higgs boson, we present the cross section for a CP-even scalar produced via gluon fusion at N3LO in perturbative QCD assuming that it couples directly to gluons in an effective theory approach. We refine our prediction by taking into account the possibility that the scalar couples to the top-quark and computing the corresponding contributions through NLO in perturbative QCD. We assess the theoretical uncertainties of the cross section due to missing higher-order QCD effects and we provide the necessary information for obtaining the cross section value and uncertainty from our results in specific scenarios beyond the Standard Model. We also give detailed results for the case of a 750 GeV scalar, which will be the subject of intense experimental studies.
Searching for gluon number fluctuations effects in eA collisions
Energy Technology Data Exchange (ETDEWEB)
Kugeratski, M. S. [Universidade Federal de Santa Catarina, Campus Joinville, Rua Presidente Prudente de Moraes, 406, CEP 89218-000, Joinville, SC (Brazil); Gonçalves, V. P.; Santana Amaral, J. T. de [Instituto de Física e Matemática, Universidade Federal de Pelotas, Caixa Postal 354, CEP 96010-900, Pelotas, RS (Brazil)
2014-11-11
We propose to investigate the gluon number fluctuations effects in deep inelastic electron-ion scattering at high energies. We estimate the nuclear structure function F{sub 2}{sup A}(x,Q{sup 2}), as well the longitudinal and charm contributions, using a generalization for nuclear targets of the Golec-Biernat-Wusthoff (GBW) model which describes the electron proton HERA data. Here we consider that the nucleus at high energies acts as an amplifier of the physics of high parton densities. For a first investigation we study the scattering with Ca and Pb nuclei. Our preliminary results predict that the effects of gluon number fluctuations are small in the region of the future electron ion collider.
Probing gluon number fluctuation effects in future electron–hadron colliders
Energy Technology Data Exchange (ETDEWEB)
Amaral, J.T.; Gonçalves, V.P. [Instituto de Física e Matemática, Universidade Federal de Pelotas, Caixa Postal 354, CEP 96010-900, Pelotas, RS (Brazil); Kugeratski, M.S. [Universidade Federal de Santa Catarina, Campus Joinville, Rua Presidente Prudente de Moraes, 406, CEP 89218-000, Joinville, SC (Brazil)
2014-10-15
The description of the QCD dynamics in the kinematical range which will be probed in the future electron–hadron colliders is still an open question. Although phenomenological studies indicate that the gluon number fluctuations, which are related to discreteness in the QCD evolution, are negligible at HERA, the magnitude of these effects for the next generation of colliders still should be estimated. In this paper we investigate inclusive and diffractive ep observables considering a model for the physical scattering amplitude which describes the HERA data. Moreover, we estimate, for the first time, the contribution of the fluctuation effects for the nuclear structure functions. Our results indicate that the study of these observables in the future colliders can be useful to constrain the presence of gluon number fluctuations.
Phenomenological aspects of an anisotropic quark-gluon plasma
International Nuclear Information System (INIS)
Martinez Guerrero, Mauricio
2010-01-01
In this work we investigate phenomenological aspects of an anisotropic quark-gluon plasma. In the first part of this thesis, we formulate phenomenologicalmodels that take into account the momentumspace anisotropy of the system developed during the expansion of the fireball at early-times. By including the proper-time dependence of the parton hard momentum scale, p hard (τ), and the plasma anisotropy parameter, ξ(τ), the proposed models allow us to interpolate from 0+1 pre-equilibrated expansion at early-times to 0+1 ideal hydrodynamics at late times. We study dilepton production as a valuable observable to experimentally determine the isotropization time of the system as well as the degree of anisotropy developed at early-times. We generalize our interpolating models to include the rapidity dependence of p hard and consider its impact on forward dileptons. Next, we discuss how to constrain the onset of hydrodynamics by demanding two requirements of the solutions to the equations of motion of viscous hydrodynamics. We show this explicitly for 0+1 dimensional 2nd-order conformal viscous hydrodynamics and find that the initial conditions are non-trivially constrained. Finally, we demonstrate how to match the initial conditions for 0+1 dimensional viscous hydrodynamics from pre-equilibrated expansion. We analyze the dependence of the entropy production on the pre-equilibrium phase and discuss limitations of the standard definitions of the non-equilibrium entropy in kinetic theory. (orig.)
Phenomenological aspects of an anisotropic quark-gluon plasma
Energy Technology Data Exchange (ETDEWEB)
Martinez Guerrero, Mauricio
2010-04-30
In this work we investigate phenomenological aspects of an anisotropic quark-gluon plasma. In the first part of this thesis, we formulate phenomenologicalmodels that take into account the momentumspace anisotropy of the system developed during the expansion of the fireball at early-times. By including the proper-time dependence of the parton hard momentum scale, p{sub hard}({tau}), and the plasma anisotropy parameter, {xi}({tau}), the proposed models allow us to interpolate from 0+1 pre-equilibrated expansion at early-times to 0+1 ideal hydrodynamics at late times. We study dilepton production as a valuable observable to experimentally determine the isotropization time of the system as well as the degree of anisotropy developed at early-times. We generalize our interpolating models to include the rapidity dependence of p{sub hard} and consider its impact on forward dileptons. Next, we discuss how to constrain the onset of hydrodynamics by demanding two requirements of the solutions to the equations of motion of viscous hydrodynamics. We show this explicitly for 0+1 dimensional 2nd-order conformal viscous hydrodynamics and find that the initial conditions are non-trivially constrained. Finally, we demonstrate how to match the initial conditions for 0+1 dimensional viscous hydrodynamics from pre-equilibrated expansion. We analyze the dependence of the entropy production on the pre-equilibrium phase and discuss limitations of the standard definitions of the non-equilibrium entropy in kinetic theory. (orig.)
Exploring the Quark-Gluon Content of Hadrons: From Mesons to Nuclear Matter
International Nuclear Information System (INIS)
Hrayr Matevosyan
2007-01-01
Even though Quantum Chromodynamics (QCD) was formulated over three decades ago, it poses enormous challenges for describing the properties of hadrons from the underlying quark-gluon degrees of freedom. Moreover, the problem of describing the nuclear force from its quark-gluon origin is still open. While a direct solution of QCD to describe the hadrons and nuclear force is not possible at this time, we explore a variety of developed approaches ranging from phenomenology to first principle calculations at one or other level of approximation in linking the nuclear force to QCD. The Dyson Schwinger formulation (DSE) of coupled integral equations for the QCD Green's functions allows a non-perturbative approach to describe hadronic properties, starting from the level of QCD n-point functions. A significant approximation in this method is the employment of a finite truncation of the system of DSEs, that might distort the physical picture. In this work we explore the effects of including a more complete truncation of the quark-gluon vertex function on the resulting solutions for the quark 2-point functions as well as the pseudoscalar and vector meson masses. The exploration showed strong indications of possibly large contributions from the explicit inclusion of the gluon 3- and 4-point functions that are omitted in this and previous analyses. We then explore the possibility of extrapolating state of the art lattice QCD calculations of nucleon form factors to the physical regime using phenomenological models of nucleon structure. Finally, we further developed the Quark Meson Coupling model for describing atomic nuclei and nuclear matter, where the quark-gluon structure of nucleons is modeled by the MIT bag model and the nucleon many body interaction is mediated by the exchange of scalar and vector mesons. This approach allows us to formulate a fully relativistic theory, which can be expanded in the nonrelativistic limit to reproduce the well known phenomenological Skyrme
What (if anything) can few-body strange systems teach us about quark-gluon hadronic substructure?
International Nuclear Information System (INIS)
Maltman, K.
1990-01-01
We discuss expectation, relevant to the proposed (π,K) program at PILAC, for the effects of hadronic quark-gluon substructure on the physics of few-body strangeness -1 systems, in the context of QCD-inspired models used previously to describe the hadron spectrum and short distance nucleon-nucleon scattering. 50 refs., 2 tabs
Lattice study of the gluon propagator in momentum space
Energy Technology Data Exchange (ETDEWEB)
Bernard, C. (Department of Physics, Washington University, St. Louis, Missouri 63130 (United States)); Parrinello, C. (Physics Department, New York University, 4 Washington Place, New York, New York 10003 (United States) Physics Department, Brookhaven National Laboratory, Upton, New York 11973 (United States)); Soni, A. (Physics Department, Brookhaven National Laboratory, Upton, New York 11973 (United States))
1994-02-01
We consider pure glue QCD at [beta]=5.7, [beta]=6.0, and [beta]=6.3. We evaluate the gluon propagator both in time at zero three-momentum and in momentum space. From the former quantity we obtain evidence for a dynamically generated effective mass, which at [beta]=6.0 and [beta]=6.3 increases with the time separation of the sources, in agreement with earlier results. The momentum space propagator [ital G]([ital k]) provides further evidence for mass generation. In particular, at [beta]=6.0, for 300 MeV[approx lt][ital k][approx lt]1 GeV, the propagator [ital G]([ital k]) can be fit to a continuum formula proposed by Gribov and others, which contains a mass scale [ital b], presumably related to the hadronization mass scale. For higher momenta Gribov's model no longer provides a good fit, as [ital G]([ital k]) tends rather to follow an inverse power law [approx]1/[ital k][sup 2+[gamma
Chiral superfluidity of the quark-gluon plasma
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Kalaydzhyan, Tigran [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Institute for Theoretical and Experimental Physics ITEP, Moscow (Russian Federation)
2012-08-15
In this paper we argue that the strongly coupled quark-gluon plasma can be considered as a chiral superfluid. The ''normal'' component of the fluid is the thermalized matter in common sense, while the ''superfluid'' part consists of long wavelength (chiral) fermionic states moving independently. We use several nonperturbative techniques to demonstrate that. First, we analyze the fermionic spectrum in the deconfinement phase (T{sub c}
Pion radiation by hot quark-gluon plasma
International Nuclear Information System (INIS)
Rafelski, J.; Danos, M.; Universitaet Frankfurt, Germany; National Bureau of Standards, Washington, DC)
1983-01-01
We consider here an approximately spherical region of the perturbative QCD vacuum, filled with quarks, antiquarks and gluons. For an impenetrable surface between the perturbative and true vacuum states, the inside thermal and degeneracy pressure would lead to an expansion until either pressure equilibrium or a phase transition into individual hadrons is reached. However, if the surface is penetrable, i.e., if it allows transmission of momentum and energy (but not colour) from the inside, then this can lead to a substantial internal energy and pressure loss by radiation - the pressure acting on the surface is reduced, as not all the momentum impinging on the surface has to be reflected. On first thought, the microscopic mechanism for this transmission arises in the following manner: when a fast quark or antiquark hits the boundary, a jet-like structure filled with colour field flux, i.e., a fluxtube might be formed. For sufficiently high quark momentum, this tube, instead of retracting, splits by q anti q pair creation. The leading particle associates with the antiparticle of the pair to form a meson, while the remaining pair particle may retract into the plasma. Difficulties with this model are discussed
Chiral superfluidity of the quark-gluon plasma
International Nuclear Information System (INIS)
Kalaydzhyan, Tigran
2012-08-01
In this paper we argue that the strongly coupled quark-gluon plasma can be considered as a chiral superfluid. The ''normal'' component of the fluid is the thermalized matter in common sense, while the ''superfluid'' part consists of long wavelength (chiral) fermionic states moving independently. We use several nonperturbative techniques to demonstrate that. First, we analyze the fermionic spectrum in the deconfinement phase (T c c ) using lattice (overlap) fermions and observe a gap between near-zero modes and the bulk of the spectrum. Second, we use the bosonization procedure with a finite cut-off and obtain a dynamical axion-like field out of the chiral fermionic modes. Third, we use relativistic hydrodynamics for macroscopic description of the effective theory obtained after the bosonization. Finally, solving the hydrodynamic equations in gradient expansion, we find that in the presence of external electromagnetic fields the motion of the ''superfluid'' component gives rise to the chiral magnetic, chiral electric and dipole wave effects. Latter two effects are specific for a two-component fluid, which provides us with crucial experimental tests of the model.
Evidence of ghost suppression in gluon mass scale dynamics
Aguilar, A. C.; Binosi, D.; Figueiredo, C. T.; Papavassiliou, J.
2018-03-01
In this work we study the impact that the ghost sector of pure Yang-Mills theories may have on the generation of a dynamical gauge boson mass scale, which hinges on the appearance of massless poles in the fundamental vertices of the theory, and the subsequent realization of the well-known Schwinger mechanism. The process responsible for the formation of such structures is itself dynamical in nature, and is governed by a set of Bethe-Salpeter type of integral equations. While in previous studies the presence of massless poles was assumed to be exclusively associated with the background-gauge three-gluon vertex, in the present analysis we allow them to appear also in the corresponding ghost-gluon vertex. The full analysis of the resulting Bethe-Salpeter system reveals that the contribution of the poles associated with the ghost-gluon vertex are particularly suppressed, their sole discernible effect being a slight modification in the running of the gluon mass scale, for momenta larger than a few GeV. In addition, we examine the behavior of the (background-gauge) ghost-gluon vertex in the limit of vanishing ghost momentum, and derive the corresponding version of Taylor's theorem. These considerations, together with a suitable Ansatz, permit us the full reconstruction of the pole sector of the two vertices involved.
The gluon contribution to polarised nucleon structure functions
International Nuclear Information System (INIS)
Ross, G.G.; Roberts, R.G.
1990-08-01
As with all parton distributions in quantum chromodynamics (QCD) the separation of polarised nucleon structure functions into gluon and quark contributions must be specified. We consider a definition of the gluon contribution to polarised nucleon structure functions based on exclusive processes which is explicitly gauge invariant, has no regularisation ambiguities, is insensitive to infrared singularities and can be related to other polarised scattering processes. We discuss the relationship of this gluon definition to others that have recently been used and to the estimates that have been made of the gluon contribution using current algebra and other methods. A quantitative analysis of the structure function g 1 (x,Q 2 ) for polarised deep inelastic scattering is carried out, with the aim of examining the importance of the gluon contribution. Using the positivity of parton distributions the magnitude of Δg(x,Q 2 ) is constrained by a realistic estimate of the unpolarised glue. With the appropriate choice of the hard scattering cross-section, Δσ γg , we find that even with a maximally polarised glue (for x > 0.1), some polarised strange quark contribution is still needed by the data of the EMC. (author)
Measurement of gluon polarization through spin asymmetry in the production of charmed mesons
International Nuclear Information System (INIS)
Panebianco, St.
2005-09-01
The main aim of the COMPASS experiment is the measurement of the gluon polarization in the nucleon, which can be accessed by the spin asymmetry in the scattering of a polarized muon beam on a polarized nucleon target. The process sensitive to the gluon polarization is the photon-gluon fusion, which can be tagged in the cleanest way by looking at the production of D 0 mesons. At COMPASS, D 0 mesons are reconstructed from the invariant mass of their decay products. However, it is a rare process, dominated by a large combinatorial background. This thesis presents some studies devoted to the improvement of the charmed mesons reconstruction. The measurement of the efficiency and the space resolution of the 3 drift chamber stations of the COMPASS spectrometer is a necessary step in understanding the performances of the reconstruction of particle trajectories. The hadron identification, which is fundamental in the reconstruction of charmed meson decay, is performed by a RICH detector. A statistical treatment of signal and background, together with an upgrade project to replace the present front-end electronics, have been developed in order to improve the particle identification performances. The second part of this work concerns the spin asymmetry measurement, which requires the application of event selection criteria in order to minimize the noise over signal ratio in the D 0 invariant mass, and the development of event-weighting methods to reduce the statistical error. This work presents a preliminary result, based on 2002-2004 statistics, which is the ΔG/G measurement from open charm production. Although the error bars are large, the measured gluon polarization is compatible with zero. Given the present accuracy, this result is compatible with the existing direct measurements from other channels. However, it does not allow to distinguish between different theoretical models. (author)
Quark-gluon vertex dressing and meson masses beyond ladder-rainbow truncation
International Nuclear Information System (INIS)
Matevosyan, Hrayr H.; Thomas, Anthony W.; Tandy, Peter C.
2007-01-01
We include a generalized infinite class of quark-gluon vertex dressing diagrams in a study of how dynamics beyond the ladder-rainbow truncation influences the Bethe-Salpeter description of light-quark pseudoscalar and vector mesons. The diagrammatic specification of the vertex is mapped into a corresponding specification of the Bethe-Salpeter kernel, which preserves chiral symmetry. This study adopts the algebraic format afforded by the simple interaction kernel used in previous work on this topic. The new feature of the present work is that in every diagram summed for the vertex and the corresponding Bethe-Salpeter kernel, each quark-gluon vertex is required to be the self-consistent vertex solution. We also adopt from previous work the effective accounting for the role of the explicitly non-Abelian three-gluon coupling in a global manner through one parameter determined from recent lattice-QCD data for the vertex. Within the current model, the more consistent dressed vertex limits the ladder-rainbow truncation error for vector mesons to be never more than 10% as the current quark mass is varied from the u/d region to the b region
Quark and gluon production from a boost-invariantly expanding color electric field
Taya, Hidetoshi
2017-07-01
Particle production from an expanding classical color electromagnetic field is extensively studied, motivated by the early stage dynamics of ultrarelativistic heavy ion collisions. We develop a formalism at one-loop order to compute the particle spectra by canonically quantizing quark, gluon, and ghost fluctuations under the presence of such an expanding classical color background field; the canonical quantization is done in the τ -η coordinates in order to take into account manifestly the expanding geometry. As a demonstration, we model the expanding classical color background field by a boost-invariantly expanding homogeneous color electric field with lifetime T , for which we obtain analytically the quark and gluon production spectra by solving the equations of motion of QCD nonperturbatively with respect to the color electric field. In this paper we study (i) the finite lifetime effect, which is found to modify significantly the particle spectra from those expected from the Schwinger formula; (ii) the difference between the quark and gluon production; and (iii) the quark mass dependence of the production spectra. Implications of these results to ultrarelativistic heavy ion collisions are also discussed.
Study on the coherent emission of gluons in QCD jets from electron-positron annihilation
International Nuclear Information System (INIS)
Kreutzmann, H.
1990-11-01
The inclusive momentum distribution of charged particles is studied with the OPAL detector at LEP in multihadronic events produced in e + e - -annihilations at E cm ≅ M(Z 0 ). Agreement is found with analytical formulae for gluon production that include the phenomena of soft gluon interference. Using data from c.m. energies between 14 GeV and 91 GeV, the dependence of the inclusive momentum distribution on the centre of momentum energy E cm is investigated. The analytic predictions derived from perturbative energy E cm ≅ M(Z 0 ) and its change with E cm are also described by QCD shower Monte Carlo programs which include either coherent gluon branchings or string fragmentation. Simple incoherent models with independent fragmentation fail to reproduce the energy dependence and the momentum spectra. A detailed simulation of the OPAL Jet Chamber and a reconstruction program for jet chamber tracks were developed and applied in this analysis. The essential features of both programs are presented. (orig.) [de
Diffractive hard photoproduction at HERA and evidence for the gluon content of the pomeron
International Nuclear Information System (INIS)
Derrick, M.; Krakauer, D.; Magill, S.
1995-01-01
Inclusive jet cross sections for events with a large rapidity gap with respect to the proton direction from the reaction ep→jet+X with quasi-real photons have been measured with the ZEUS detector. The cross sections refer to jets with transverse energies E T jet >8 GeV. The data show the characteristics of a diffractive process mediated by pomeron exchange. Assuming that the events are due to the exchange of a pomeron with partonic structure, the quark and gluon content of the pomeron is probed at a scale ∼(E T jet ) 2 . A comparison of the measurements with model predictions based on QCD plus Regge phenomenology requires a contribution of partons with a hard momentum density in the pomeron. A combined analysis of the jet cross sections and recent ZEUS measurements of the diffractive structure function in deep inelastic scattering gives the first experimental evidence for the gluon content of the pomeron in diffractive hard scattering processes. The data indicate that between 30% and 80% of the momentum of the pomeron carried by partons is due to hard gluons. (orig.)
Determination of the gluon polarisation from open charm production at COMPASS
Energy Technology Data Exchange (ETDEWEB)
Koblitz, Susanne
2009-01-27
background. This method results in an average value of the gluon polarisation in the x-range covered by the data. For the COMPASS data from 2002-2004, the resulting value of the gluon polarisation is left angle {delta}g/g right angle =0.47{+-}0.44(stat.){+-}0.15(syst.), at an average x=0.11{sup +0.11}{sub -0.05} and a scale of {mu}{sup 2}=13 GeV{sup 2}. This result points to small or negative values of {delta}G/G(x) around a value of x {proportional_to} 0.1, which could point to a small gluon polarisation in the nucleon. The result is statistically compatible with the existing measurements of left angle {delta}g/g right angle in the high-p{sub t} channel. Compared to these, the open charm measurement has the advantage of a considerably smaller model dependence. (orig.)
Determination of the gluon polarisation from open charm production at COMPASS
International Nuclear Information System (INIS)
Koblitz, Susanne
2009-01-01
in the x-range covered by the data. For the COMPASS data from 2002-2004, the resulting value of the gluon polarisation is left angle Δg/g right angle =0.47±0.44(stat.)±0.15(syst.), at an average x=0.11 +0.11 -0.05 and a scale of μ 2 =13 GeV 2 . This result points to small or negative values of ΔG/G(x) around a value of x ∝ 0.1, which could point to a small gluon polarisation in the nucleon. The result is statistically compatible with the existing measurements of left angle Δg/g right angle in the high-p t channel. Compared to these, the open charm measurement has the advantage of a considerably smaller model dependence. (orig.)
Infrared Behavior of Gluon and Ghost Propagators in Landau Gauge QCD
International Nuclear Information System (INIS)
von Smekal, L.; Hauck, A.; Alkofer, R.
1997-01-01
A truncation scheme for the Dyson-Schwinger equations of Euclidean QCD in Landau gauge is presented. It implements the Slavnov-Taylor identities for the three-gluon and ghost-gluon vertices, whereas irreducible four-gluon couplings as well as the gluon-ghost and ghost-ghost scattering kernels are neglected. The infrared behavior of gluon and ghost propagators is obtained analytically: The gluon propagator vanishes for small momenta, whereas the ghost propagator diverges strongly. The numerical solutions are compared with recent lattice results. The running coupling approaches a fixed point, α c ≅9.5 , in the infrared. copyright 1997 The American Physical Society
Transport quasiparticles and transverse interactions in quark-gluon plasmas
International Nuclear Information System (INIS)
Baym, Gordon
1996-01-01
Calculations of the properties of interacting quark-gluon plasmas are beset by infrared divergences associated with the fact that magnetic interactions, i.e., those occurring through exchange of transverse gluons, are, in the absence of a 'magnetic mass''in QCD, not screened. In this lecture we discuss the effects of magnetic interactions on the transport coefficients and the quasiparticle structure of quark-gluon plasmas. We describe how inclusion of dynamical screening effects - corresponding to Landau damping of the virtual quanta exchanged - leads to finite transport scattering rates. In the weak coupling limit, dynamical screening effects dominate over a magnetic mass. We illustrate the breakdown of the quasi particle structure of degenerate plasmas caused by long-ranged magnetic interactions, describe the structure of fermion quasiparticles in hot relativistic plasmas, and touch briefly on the problem of the lifetime of quasiparticle in the presence of long-ranged magnetic interactions. (author)
Worldline calculation of the three-gluon vertex
International Nuclear Information System (INIS)
Ahmadiniaz, N.; Schubert, C.
2012-01-01
The three-gluon vertex is a basic object of interest in nonabelian gauge theory. At the one-loop level, it has been calculated and analyzed by a number of authors. Here we use the worldline formalism to unify the calculations of the scalar, spinor and gluon loop contributions to the one-loop vertex, leading to an extremely compact representation in terms of field strength tensors. We verify its equivalence with previously obtained representations, and explain the relation of its structure to the low-energy effective action. The sum rule found by Binger and Brodsky for the scalar, spinor and gluon loop contributions in the present approach relates to worldline supersymmetry.
Neural network classification of quark and gluon jets
International Nuclear Information System (INIS)
Graham, M.A.; Jones, L.M.; Herbin, S.
1995-01-01
We demonstrate that there are characteristics common to quark jets and to gluon jets regardless of the interaction that produced them. The classification technique we use depends on the mass of the jet as well as the center-of-mass energy of the hard subprocess that produces the jet. In addition, we present the quark-gluon separability results of an artificial neural network trained on three-jet e + e - events at the Z 0 mass, using a back-propagation algorithm. The inputs to the network are the longitudinal momenta of the leading hadrons in the jet. We tested the network with quark and gluon jets from both e + e - →3 jets and bar pp→2 jets. Finally, we compare the performance of the artificial neural network with the results of making well chosen physical cuts
The gluon Reggeization in perturbative QCD at NLO
Energy Technology Data Exchange (ETDEWEB)
Fadin, V.S. [Novosibirsk State Univ., Institute for Nuclear Physics (Russian Federation)
2005-07-01
The gluon Reggeization is one of the outstanding properties of QCD. It is extremely important for description of high energy processes. In particular, it appears as the basis of the BFKL approach to summation of the terms strengthened by powers of log(1/x). The hypothesis is extremely powerful, since all scattering amplitudes are expressed in terms of the gluon trajectory and several Reggeon vertices. Now the hypothesis is proved in NLA (next-to leading approximation). The proof is based on bootstrap relations. It is shown that an infinite number of these relations is reduced to several bootstrap conditions on the gluon trajectory and the Reggeon vertices. It is shown that fulfillment of these conditions means a proof of the Reggeization hypothesis. All bootstraps conditions are formulated explicitly and are proved to be fulfilled.
Study of gluon condensates using the Bogolyubov transformation
International Nuclear Information System (INIS)
Iracane, Daniel
1985-01-01
We describe the ground state of non-perturbative QCD as a gluon condensate. In the framework of the Coulomb gauge Hamiltonian, we introduce an effective interaction between infrared gluons by removing high-momentum gluons. The Bogoliubov transformation provides us with our variational space. The minimisation over this Fock subspace leads to a non-perturbative vacuum and its excitations. The minimum functional space for a boson dynamic is a distribution set. We find two kinds of condensation. The first one occurs only for zero-momentum states and looks like the Bose Condensation. In the second one, the quasiparticle spectrum shows a finite gap and the vacuum is a superconducting state. We give constraints on the interaction so that the superconducting phase is more bounded than the Bose one. (author) [fr
Non-perturbative power corrections to ghost and gluon propagators
International Nuclear Information System (INIS)
Boucaud, Philippe; Leroy, Jean-Pierre; Yaouanc, Alain Le; Lokhov, Alexey; Micheli, Jacques; Pene, Olivier; RodrIguez-Quintero, Jose; Roiesnel, Claude
2006-01-01
We study the dominant non-perturbative power corrections to the ghost and gluon propagators in Landau gauge pure Yang-Mills theory using OPE and lattice simulations. The leading order Wilson coefficients are proven to be the same for both propagators. The ratio of the ghost and gluon propagators is thus free from this dominant power correction. Indeed, a purely perturbative fit of this ratio gives smaller value ( ≅ 270MeV) of Λ M-barS-bar than the one obtained from the propagators separately( ≅ 320MeV). This argues in favour of significant non-perturbative ∼ 1/q 2 power corrections in the ghost and gluon propagators. We check the self-consistency of the method
Transverse momentum of gluons in ep-scattering at HERA
International Nuclear Information System (INIS)
Cholewa, A.
2005-11-01
A Monte Carlo analysis of the phase space of hard interacting gluons in ep-scattering is presented. The event generator CASCADE is used in combination with the program HZTOOL to identify the accessible regions of phase space of present HERA measurements. A map of the k t -x g -plane is presented to show that in the region -3≤log g ≤-1 transverse gluon momenta of up to k t >or sim 20 GeV are accessible to HERA measurements. Furthermore the observables x γ and the transverse jet energy E T are found to be highly sensitive to the transverse momentum and the longitudinal momentum fraction of gluons. (orig.) (orig.)
In search of the quark-gluon plasma
International Nuclear Information System (INIS)
Schutz, Y.; Delagrange, H.
2002-01-01
This article describes in a very pedagogical manner the ultimate state of matter when quarks are no longer confined in hadrons. This state is called quark and gluon plasma, its existence is suspected through 4 facts: 1) a quark and gluon plasma that has just been created from a high energy ion-collision is mainly made up of light quarks (up and down), then this plasma should evolve towards other quarks (particularly strange quarks) because of the Pauli exclusion principle. This fact has been experimentally confirmed: at the CERN accelerator physicists have detected a higher production of strange hadrons when the energy of the collision increases; 2) some particles like ρ 0 mesons, that are made up of 2 quarks, are massively produced in ion collisions, their mass has been measured at the moment of the collision and later in the quark and gluon plasma, 2 different values have been found so it confirms the theory that predicts that free quarks have a mass that decreases as energy increases; 3) J/Ψ mesons are made up of a charmed quark combined with its anti-quark, physicists have noticed that less J/Ψ mesons are detected when the energy of the collision rises, this result agrees with the fact that in quark gluon plasma where quarks are free and of different colours and flavors, it is highly unlikely that a charmed quark combines with its anti-quark to form a J/Ψ meson; and 4) the theory of the formation of quark gluon plasma predicts that its electromagnetic radiation has a thermal radiation specificity, physicists have studied the radiation spectra emitted in the core of a ion collision, they have shown that it is a thermal radiation and that the temperature of the emitter corresponds to the temperature of a quark gluon plasma. (A.C.)
A gauge quantum field theory of confined quarks and gluons
International Nuclear Information System (INIS)
Voelkel, A.H.
1983-01-01
A SU(3)-gauge quantum field theory with a quark triplet, an antiquark triplet and a self-conjugate gluon octet as basic fields is investigated. In virtue of a non trivial coupling between the representation of the translation group and the SU(3)-colour charge of the basic fields it is proved: (i) The basic quark, antiquark and gluon fields are confined. (ii) Every statevector of the physical Hilbert space is a SU(3)-colour singlet state. (iii) Poincare invariance holds in the physical Hilbert space. (orig.)
Evidence for a spin 1 gluon in three jet events
International Nuclear Information System (INIS)
Brandelik, R.; Braunschweig, W.; Gather, K.; Kadansky, V.; Kirschfink, F.J.; Luebelsmeyer, K.; Martyn, H.U.; Peise, G.; Rimkus, J.; Sander, H.G.
1980-08-01
High energy e + e - annihilation events obtained in the TASSO detector at PETRA have been used to determine the spin of the gluon in the reaction e + e - → q anti qg. We analyzed angular correlations between the 3 jet axes. While vector gluons are consistent with the data (55% confidence limit), scalar fluons are disfavored by 3.8 standard deviations, corresponding to a confidence level of about 10 -4 . Our conclusion is free of possible biases due to uncertainties in the fragmentation process or in determining the q anti qg kinematic from the observed hadrons. (orig.)
A gluon cluster solution of effective Yang-Mills theory
Pavlovsky, O V
2001-01-01
A classical solution of the effective Yang-Mills (YM) theory with a finite energy and nonstandard Lagrangian was obtained. Influence of vacuum polarization on gluon cluster formation was discussed. Appearance of cluster solutions in the theory of non-Abelian fields can take place only if the result goes beyond the framework of pure YM theory. It is shown that account of quantum effects of polarized vacuum in the presence of a classical gluon field can also result in formation of the solutions. Solutions with the finite intrinsic energy are provided. Besides, fields of colour groups SU(2) were studied
Check of the bootstrap conditions for the gluon Reggeization
International Nuclear Information System (INIS)
Papa, A.
2000-01-01
The property of gluon Reggeization plays an essential role in the derivation of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation for the cross sections at high energy √s in perturbative QCD. This property has been proved to all orders of perturbation theory in the leading logarithmic approximation and it is assumed to be valid also in the next-to-leading logarithmic approximation, where it has been checked only to the first three orders of perturbation theory. From s-channel unitarity, however, very stringent 'bootstrap' conditions can be derived which, if fulfilled, leave no doubts that gluon Reggeization holds
Plaquette expectation value and gluon condensate in three dimensions
International Nuclear Information System (INIS)
Hietanen, Ari; Kajantie, Keijo; Schroeder, York; Laine, Mikko; Rummukainen, Kari
2005-01-01
In three dimensions, the gluon condensate of pure SU(3) gauge theory has ultraviolet divergences up to 4-loop level only. By subtracting the corresponding terms from lattice measurements of the plaquette expectation value and extrapolating to the continuum limit, we extract the finite part of the gluon condensate in lattice regularization. Through a change of regularization scheme to MS-bar and (inverse) dimensional reduction, this result would determine the first non-perturbative coefficient in the weak-coupling expansion of hot QCD pressure. (author)
Nielsen's identity and gluon condensation at finite temperature
International Nuclear Information System (INIS)
Skalozub, V.V.
1992-11-01
The gauge dependence problem of the gluon field zero component condensate, A 0 =const, is investigated in finite temperature SU(3) gluodynamics. The two-loop effective action W(A 0 ,ξ) is recalculated in the background R ξ gauge. The obtained result somewhat differs from that of other authors. By straightforward calculation it is shown that W(A 0 ,ξ) satisfies the Nielsen (the Ward type) identity. Thus, the gauge invariance of the gluon condensation phenomenon is proved. (author). 14 refs
Plaquette expectation value and gluon condensate in three dimensions
Hietanen, A; Laine, Mikko; Rummukainen, K; Schröder, Y
2005-01-01
In three dimensions, the gluon condensate of pure SU(3) gauge theory has ultraviolet divergences up to 4-loop level only. By subtracting the corresponding terms from lattice measurements of the plaquette expectation value and extrapolating to the continuum limit, we extract the finite part of the gluon condensate in lattice regularization. Through a change of regularization scheme to MSbar and (inverse) dimensional reduction, this result would determine the first non-perturbative coefficient in the weak-coupling expansion of hot QCD pressure.
Mechanism of J/PSI production: determining gluon distributions
International Nuclear Information System (INIS)
Nandi, S.; Schneider, H.R.
1978-01-01
Assuming a generalised Drell-Yan type mechanism for hadronic PSI-production, the relative importance of the different possible contributions is estimated from the data. We find that about 80% of the pp → PSI X cross-section is due to gluons. Therefore, these data give some information on the gluon distribution G(x) in the proton. Assuming xG(x) approximately (1-x)sup(n), data restrict n to 4... 6, in agreement with dimensional counting rules. The energy dependence of sigma(anti p p → PSI X)/sigma(pp → PSIX) is predicted. (orig.) [de
Kovchegov, Yuri V.; Skokov, Vladimir V.
2018-05-01
We show that, in the saturation/color glass condensate framework, odd azimuthal harmonics of the two-gluon correlation function with a long-range separation in rapidity are generated by the higher-order saturation corrections in the interactions with the projectile and the target. At the very least, the odd harmonics require three scatterings in the projectile and three scatterings in the target. We derive the leading-order expression for the two-gluon production cross section which generates odd harmonics: the expression includes all-order interactions with the target and three interactions with the projectile. We evaluate the obtained expression both analytically and numerically, confirming that the odd-harmonics contribution to the two-gluon production in the saturation framework is nonzero.
The unitary mechanism of infrared freezing in QCD with massive gluons
International Nuclear Information System (INIS)
Shirkov, D.V.
1999-01-01
A 'natural' model for the QCD invariant (running) coupling, free of the IR singularity, is proposed. It is based upon the hypothesis of finite gluon mass m gl existence and, technically, uses an accurate treating of threshold behaviour of Feynman diagram contribution. The model correlates with the unitarity condition. Quantitative estimate, performed in the one-loop approximation yields a reasonable lower bound for this mass m gl > 150 MeV and a smooth IR freezing at the level α s (Q 2 ) < or ∼ 1
Virtual photoproduction of hadrons at large p/sub T/ as a probe for gluon bremsstrahlung
Floratos, Emmanuel G
1978-01-01
In a SU/sub 3, colour/ x SU/sub 3, flavour/ invariant interaction of quarks and gluons, where the colour degree of freedom is locally gauged, first-order corrections of the naive parton model are calculated for the one-hadron inclusive virtual photoproduction. The high p/sub T/ distribution of hadrons is studied and the kinetical region in which the prediction of the model dominates over the fall- off approximately exp(-bp/sub T//sup 2/) which seems to be supported by the low-p/sub T/ available experimental data is determined. (29 refs).
A study of quark and gluon jets and of the long distance QCD force field at the Z0
International Nuclear Information System (INIS)
Gary, J.W.
1993-10-01
Quantum Chromodynamics (QCD) is widely accepted as the correct theory of the strong nuclear force in elementary particle physics. The precision to which QCD has been tested is relatively limited, however, compared to the precision to which other interactions such as the electro-weak one have been tested. In part, this is because the large value of the QCD coupling constant, α s , renders theoretical calculations based on perturbation theory relatively imprecise. The confinement of quarks and gluons inside hadrons also leads to uncertainty because the theoretical predictions cannot, in general, be tested directly against the experimental measurements but are subject to hadronization corrections. From an experimental standpoint, it has proven difficult to isolate gluon jets inside multi-jet events in an unbiased manner so as to determine gluon jet properties using model independent methods. Basic quark-gluon interactions such as the four-jet matrix element in e + e - annihilations have been relatively untested due to the lack of a data sample with sufficient statistics. Perturbation theory has essentially nothing to say about the properties of the hadronization process itself. It is for these reasons that QCD has remained relatively untested
Infrared behaviour of three and four gluon vertices in Yang-Mills theory
International Nuclear Information System (INIS)
Brandt, F.T.; Frenkel, J.
1985-01-01
The structure of the 3-point function with one and two external gluons on-shell is studied in a general covariant gauge. The contributions which result in one loop approximation are expressed in terms of simple functions containing collinear and soft singularities. Furthermore, the contributions associated with the 4-point vertex when all external gluons are on-shell are analysed. As an application of these results, the infrared structure of gluon-gluon scattering amplitude is studied. (Author) [pt
Measurements of gluon spin-sensitive quantities at the Z0 resonance
International Nuclear Information System (INIS)
Fan, C.G.
1993-10-01
Measurements have been made of the scaled jet energies (x 1 , x 2 , x 3 ) and the Ellis-Karliner angle (cosθ EK ), which are sensitive to the spill of the gluon, in the 3-jet hadronic events from the e + e - annihilation at the Z 0 resonance. The experiment is performed with the SLD detector at the Stanford Linear Accelerator Center (SLAC). The data used in this analysis was collected during the 1992 physics run, which includes 10,252 hadronic Z 0 events that have CDC information written out. Only charged tracks measured in the central drift chamber are used for the measurements of the above variables. The raw data are found to be in good agreement with the Monte Carlo simulations passing the same set of track and event selection cuts. A bin-to-bin correction is done for the distributions of x 1 , x 2 , x 3 , and cosθ EK to account for the effects of hadronization, detector acceptance and resolution. The corrected data is compared to the parton level distributions of x 1 , x 2 , x 3 , and cosθ EK simulated from the vector QCD model and the scalar gluon model respectively. The systematic errors, calculated for all the bins in these distributions, are obtained by comparing the results from different sets of track and event selection cuts, from different hadronization models and from different Monte Carlo programs. Good agreement is found between data and the vector QCD model. The scalar gluon model strongly disagrees with the data
Measurements of gluon spin-sensitive quantities at the Z^{0} resonance
Energy Technology Data Exchange (ETDEWEB)
Fan, Cheng -Gang [Stanford Univ., CA (United States)
1993-10-01
Measurements have been made of the scaled jet energies (x_{1}, x_{2}, x_{3}) and the Ellis-Karliner angle (cosθ_{EK}), which are sensitive to the spill of the gluon, in the 3-jet hadronic events from the e^{+}e^{-} annihilation at the Z^{0} resonance. The experiment is performed with the SLD detector at the Stanford Linear Accelerator Center (SLAC). The data used in this analysis was collected during the 1992 physics run, which includes 10,252 hadronic Z^{0} events that have CDC information written out. Only charged tracks measured in the central drift chamber are used for the measurements of the above variables. The raw data are found to be in good agreement with the Monte Carlo simulations passing the same set of track and event selection cuts. A bin-to-bin correction is done for the distributions of x_{1}, x_{2}, x_{3}, and cosθ_{EK} to account for the effects of hadronization, detector acceptance and resolution. The corrected data is compared to the parton level distributions of x_{1}, x_{2}, x_{3}, and cosθ_{EK} simulated from the vector QCD model and the scalar gluon model respectively. The systematic errors, calculated for all the bins in these distributions, are obtained by comparing the results from different sets of track and event selection cuts, from different hadronization models and from different Monte Carlo programs. Good agreement is found between data and the vector QCD model. The scalar gluon model strongly disagrees with the data.
Quark-gluon plasma and the little bang
International Nuclear Information System (INIS)
McLerran, L.
1981-06-01
A space-time picture of the fragmentation and central regions is presented for extremely high energy head-on heavy nucleus collisions. The energy densities of the matter produced in such collisions are estimated. Speculations concerning the possible formation of a quark-gluon plasma are discussed, as are possible experimental signals for analyzing such a plasma
Universal Regge slope α' from QCD gluon propagator
International Nuclear Information System (INIS)
Nielsen, H.B.; Ninomiya, M.
1980-02-01
An effective gluon propagator is estimated in the presence of a fluctuating color magnetic field in vacuum. Using the dual honeycomb diagram tlhe universal slope is estimated to yield Λsub(p) = 0.34 GeV when corrected by instanton, for α' = 0.88 GeV -2 . (Auth.)
Direct Probes of Linearly Polarized Gluons inside Unpolarized Hadrons
Boer, D.; Brodsky, S. J.; Mulders, P.J.G.; Pisano, C.
2011-01-01
We show that linearly polarized gluons inside unpolarized hadrons can be directly probed in jet or heavy quark pair production in electron-hadron collisions. We discuss the simplest cos2 asymmetries and estimate their maximal value, concluding that measurements of the unknown linearly polarized
The quark gluon plasma: Lattice computations put to experimental test
Indian Academy of Sciences (India)
I describe how lattice computations are being used to extract experimentally relevant features of the quark gluon plasma. I deal speciﬁcally with relaxation times, photon emissivity, strangeness yields, event-by-event ﬂuctuations of conserved quantities and hydrodynamic ﬂow. Finally I give evidence that the plasma is rather ...
The angular ordering in soft-gluon emission
International Nuclear Information System (INIS)
Tesima, K.
1987-01-01
The way to evaluate multi-parton cross-sections systematically is discussed. In the leading-double-log approximation in QCD, the successive emission of soft gluons is at successively smaller angles. The angular ordering, however, is violated in the next-to-leading order
Experiments to measure the gluon helicity distribution in protons
International Nuclear Information System (INIS)
Spinka, H.; Beddo, M.E.; Underwood, D.G.
1993-01-01
Several experiments are described that could obtain information about the gluon helicity distribution in protons. These experiments include inclusive direct-γ, direct-γ + jet, jet, and jet + jet production with colliding beams of longitudinally-polarized protons. Some rates and kinematics are also discussed
How Resummation Depresses the Gluon at Small x
Forte, Stefano; Ball, Richard D.; Forte, Stefano; Altarelli, Guido; Ball, Richard D.
2006-01-01
We summarize recent progress in the resummation of perturbative evolution at small x. We show that the problem of incorporating BFKL small x logs in GLAP evolution is now completely solved, and that the main effect of small x resummation is to reduce the growth of the gluon at small x in the HERA and LHC regions.
Nonperturbative quark-gluon thermodynamics at finite density
Andreichikov, M. A.; Lukashov, M. S.; Simonov, Yu. A.
2018-03-01
Thermodynamics of the quark-gluon plasma at finite density is studied in the framework of the Field Correlator Method, where thermodynamical effects of Polyakov loops and color magnetic confinement are taken into account. Having found good agreement with numerical lattice data for zero density, we calculate pressure P(T,μ), for 0 confinement.
Strangeness and quark gluon plasma: Aspects of theory and experiment
International Nuclear Information System (INIS)
Eggers, H.C.; Rafelski, J.
1990-07-01
A survey of our current understanding of the strange particle signature of quark gluon plasma is presented. Emphasis is placed on the theory of strangeness production in the plasma and recent pertinent experimental results. Useful results on spectra of thermal particles are given. (orig.)
Two theoretical treatments of the quark-gluon plasma
International Nuclear Information System (INIS)
Carrington, M.E.
1989-01-01
The study of the quark-gluon plasma is of direct relevance to questions about the confinement properties of QCD and the validity of the standard theory of QCD in a different physical regime. Part 1 of this work contains a brief discussion of the theoretical and numerical evidence for the existence of the quark-gluon plasma. In the next two sections, two different approaches are discussed. In Part 2, the problem is presented in the general framework of kinetic theory. A definition of the Wigner distribution operator is introduced for quarks and a set of kinetic equations are derived for the momentum moments of this operator. A Wigner distribution operator is defined for gluons and the momentum of this operator are calculated and related to physical quantities. In Part 3, a calculation of linear response functions in a hot gluon plasma is presented. Problems related to gauge invariance and to the definition of a thermal ensemble in the presence of unphysical degrees of freedom are discussed. Results in different gauges and with different ensembles are compared, and the implications of the results for plasma oscillations are discussed
Quark-gluon plasma: Status of heavy ion physics
Indian Academy of Sciences (India)
Lattice quantum chromodynamics (QCD), deﬁned on a discrete space–time lattice, leads to a spectacular non-perturbative prediction of a new state of matter, called quark-gluon plasma (QGP), at sufﬁciently high temperatures or equivalently large energy densities. The experimental programs of CERN, Geneva and BNL, ...
Properties of the quark gluon plasma from lattice QCD
International Nuclear Information System (INIS)
Mages, Simon Wolfgang
2015-01-01
Quantum Chromodynamics (QCD) is the theory of the strong interaction, the theory of the interaction between the constituents of composite elementary particles (hadrons). In the low energy regime of the theory, standard methods of theoretical physics like perturbative approaches break down due to a large value of the coupling constant. However, this is the region of most interest, where the degrees of freedom of QCD, the color charges, form color-neutral composite elementary particles, like protons and neutrons. Also the transition to more energetic states of matter like the quark gluon plasma (QGP), is difficult to investigate with perturbative approaches. A QGP is a state of strongly interacting matter, which existed shortly after the Big Bang and can be created with heavy ion collisions for example at the LHC at CERN. In a QGP the color charges of QCD are deconfined. This thesis explores ways how to use the non-perturbative approach of lattice QCD to determine properties of the QGP. It focuses mostly on observables which are derived from the energy momentum tensor, like two point correlation functions. In principle these contain information on low energy properties of the QGP like the shear and bulk viscosity and other transport coefficients. The thesis describes the lattice QCD simulations which are necessary to measure the correlation functions and proposes new methods to extract these low energy properties. The thesis also tries to make contact to another non-perturbative approach which is Improved Holographic QCD. The aim of this approach is to use the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence to make statements about QCD with calculations of a five dimensional theory of gravity. This thesis contributes to that work by constraining the parameters of the model action by comparing the predictions with those of measurements with lattice QCD.
Schenke, Björn; Tribedy, Prithwish; Venugopalan, Raju
2012-09-01
The event-by-event multiplicity distribution, the energy densities and energy density weighted eccentricity moments ɛn (up to n=6) at early times in heavy-ion collisions at both the BNL Relativistic Heavy Ion Collider (RHIC) (s=200GeV) and the CERN Large Hardron Collider (LHC) (s=2.76TeV) are computed in the IP-Glasma model. This framework combines the impact parameter dependent saturation model (IP-Sat) for nucleon parton distributions (constrained by HERA deeply inelastic scattering data) with an event-by-event classical Yang-Mills description of early-time gluon fields in heavy-ion collisions. The model produces multiplicity distributions that are convolutions of negative binomial distributions without further assumptions or parameters. In the limit of large dense systems, the n-particle gluon distribution predicted by the Glasma-flux tube model is demonstrated to be nonperturbatively robust. In the general case, the effect of additional geometrical fluctuations is quantified. The eccentricity moments are compared to the MC-KLN model; a noteworthy feature is that fluctuation dominated odd moments are consistently larger than in the MC-KLN model.
International Nuclear Information System (INIS)
Kaempfer, B.; Technische Univ. Dresden; Pavlenko, O.P.; AN Ukrainskoj SSR, Kiev; Gorenstein, M.I.; Peshier, A.; Soff, G.
1994-07-01
The influence of a non-vanishing baryon charge on the rapidity distribution of dileptons produced in ultrarelativistic heavy-ion collisions is studied. We employ a frozen motion model with scaling invariant expansion of the hadronizing quark-gluon plasma as well as a realistic rapidity distribution of secondary particles (i.e., pions and baryons) expected for RHIC energies. We find a considerable suppression of the dilepton production yield at large rapidities due to the finite baryon density. To discriminate the thermal dileptons from Drell-Yan background we propose to utilize the dilepton yield scaled suitably by the pion multiplicity as function of rapidity. (orig.)
Search for gluons in e/sup +/e/sup -/ annihilation
Ellis, Jonathan Richard; Ross, Graham G
1976-01-01
The authors study the deviations to be expected at high energies from the recently observed two jet structure of hadronic final states in e /sup +/e/sup -/ annihilation. Motivated by the approximate validity of the naive parton model and by asymptotic freedom they suggest that hard gluon bremsstrahlung may be the dominant source of hadrons with large momenta transverse to the main jet axes. This process should give rise to three-jet final states. These may be observable at the highest SPEAR or DORIS energies, and should be important at the higher PETRA or PEP energies. (15 refs).
Finding the 3-gluon vertex from 4-jet events in e+e- annihilation
International Nuclear Information System (INIS)
Bengtsson, M.
1988-05-01
Although the 3-gluon coupling is a necessary ingredient for QCD to be asymptotically free, conclusive experimental evidence is still lacking. We make here a comprehensive and systematic study of the possibilities of finding it in e + e - annihilation at the Z 0 resonance. Emphasis is put on observables of 4-jet events which are sensitive to the specific helicity structure of the processes g → gg and g → qanti q. These observables give a quantitative and qualitative difference between QCD and abelian models, making it straightforward to confirm the nonabelian nature of the theory of strong interactions. (orig.)
Quark and gluon jet properties in symmetric three-jet events
Buskulic, Damir; De Bonis, I; Décamp, D; Ghez, P; Goy, C; Lees, J P; Lucotte, A; Minard, M N; Odier, P; Pietrzyk, B; Chmeissani, M; Crespo, J M; Efthymiopoulos, I; Fernández, E; Fernández-Bosman, M; Garrido, L; Juste, A; Martínez, M; Orteu, S; Pacheco, A; Padilla, C; Palla, Fabrizio; Pascual, A; Perlas, J A; Riu, I; Sánchez, F; Teubert, F; Colaleo, A; Creanza, D; De Palma, M; Farilla, A; Gelao, G; Girone, M; Iaselli, Giuseppe; Maggi, G; Maggi, M; Marinelli, N; Natali, S; Nuzzo, S; Ranieri, A; Raso, G; Romano, F; Ruggieri, F; Selvaggi, G; Silvestris, L; Tempesta, P; Zito, G; Huang, X; Lin, J; Ouyang, Q; Wang, T; Xie, Y; Xu, R; Xue, S; Zhang, J; Zhang, L; Zhao, W; Alemany, R; Bazarko, A O; Bonvicini, G; Cattaneo, M; Comas, P; Coyle, P; Drevermann, H; Forty, Roger W; Frank, M; Hagelberg, R; Harvey, J; Jacobsen, R; Janot, P; Jost, B; Kneringer, E; Knobloch, J; Lehraus, Ivan; Martin, E B; Mato, P; Minten, Adolf G; Miquel, R; Mir, L M; Moneta, L; Oest, T; Palazzi, P; Pater, J R; Pusztaszeri, J F; Ranjard, F; Rensing, P E; Rolandi, Luigi; Schlatter, W D; Schmelling, M; Schneider, O; Tejessy, W; Tomalin, I R; Venturi, A; Wachsmuth, H W; Wildish, T; Witzeling, W; Wotschack, J; Ajaltouni, Ziad J; Barrès, A; Boyer, C; Falvard, A; Gay, P; Guicheney, C; Henrard, P; Jousset, J; Michel, B; Monteil, S; Montret, J C; Pallin, D; Perret, P; Podlyski, F; Proriol, J; Rossignol, J M; Fearnley, Tom; Hansen, J B; Hansen, J D; Hansen, J R; Hansen, P H; Nilsson, B S; Wäänänen, A; Kyriakis, A; Markou, C; Simopoulou, Errietta; Siotis, I; Vayaki, Anna; Zachariadou, K; Blondel, A; Bonneaud, G R; Brient, J C; Bourdon, P; Rougé, A; Rumpf, M; Tanaka, R; Valassi, Andrea; Verderi, M; Videau, H L; Candlin, D J; Parsons, M I; Focardi, E; Parrini, G; Corden, M; Delfino, M C; Georgiopoulos, C H; Jaffe, D E; Antonelli, A; Bencivenni, G; Bologna, G; Bossi, F; Campana, P; Capon, G; Chiarella, V; Felici, G; Laurelli, P; Mannocchi, G; Murtas, F; Murtas, G P; Passalacqua, L; Pepé-Altarelli, M; Curtis, L; Dorris, S J; Halley, A W; Knowles, I G; Lynch, J G; O'Shea, V; Raine, C; Reeves, P; Scarr, J M; Smith, K; Thompson, A S; Thomson, F; Thorn, S; Turnbull, R M; Becker, U; Braun, O; Geweniger, C; Graefe, G; Hanke, P; Hepp, V; Kluge, E E; Putzer, A; Rensch, B; Schmidt, M; Sommer, J; Stenzel, H; Tittel, K; Werner, S; Wunsch, M; Abbaneo, D; Beuselinck, R; Binnie, David M; Cameron, W; Colling, D J; Dornan, Peter J; Moutoussi, A; Nash, J; San Martin, G; Sedgbeer, J K; Stacey, A M; Dissertori, G; Girtler, P; Kuhn, D; Rudolph, G; Bowdery, C K; Brodbeck, T J; Colrain, P; Crawford, G; Finch, A J; Foster, F; Hughes, G; Sloan, Terence; Whelan, E P; Williams, M I; Galla, A; Greene, A M; Kleinknecht, K; Quast, G; Renk, B; Rohne, E; Sander, H G; Van Gemmeren, P; Zeitnitz, C; Aubert, Jean-Jacques; Bencheikh, A M; Benchouk, C; Bonissent, A; Bujosa, G; Calvet, D; Carr, J; Diaconu, C A; Etienne, F; Konstantinidis, N P; Nicod, D; Payre, P; Rousseau, D; Talby, M; Sadouki, A; Thulasidas, M; Trabelsi, K; Abt, I; Assmann, R W; Bauer, C; Blum, Walter; Brown, D; Dietl, H; Dydak, Friedrich; Ganis, G; Gotzhein, C; Jakobs, K; Kroha, H; Lütjens, G; Lutz, Gerhard; Männer, W; Moser, H G; Richter, R H; Rosado-Schlosser, A; Schael, S; Settles, Ronald; Seywerd, H C J; Saint-Denis, R; Wiedenmann, W; Wolf, G; Boucrot, J; Callot, O; Cordier, A; Davier, M; Duflot, L; Grivaz, J F; Heusse, P; Jacquet, M; Kim, D W; Le Diberder, F R; Lefrançois, J; Lutz, A M; Nikolic, I A; Park, H J; Park, I C; Schune, M H; Simion, S; Veillet, J J; Videau, I; Azzurri, P; Bagliesi, G; Batignani, G; Bettarini, S; Bozzi, C; Calderini, G; Carpinelli, M; Ciocci, M A; Ciulli, V; Dell'Orso, R; Fantechi, R; Ferrante, I; Foà, L; Forti, F; Giassi, A; Giorgi, M A; Gregorio, A; Ligabue, F; Lusiani, A; Marrocchesi, P S; Messineo, A; Rizzo, G; Sanguinetti, G; Sciabà, A; Spagnolo, P; Steinberger, Jack; Tenchini, Roberto; Tonelli, G; Vannini, C; Verdini, P G; Walsh, J; Betteridge, A P; Blair, G A; Bryant, L M; Cerutti, F; Chambers, J T; Gao, Y; Green, M G; Johnson, D L; Medcalf, T; Perrodo, P; Strong, J A; Von Wimmersperg-Töller, J H; Botterill, David R; Clifft, R W; Edgecock, T R; Haywood, S; Edwards, M; Maley, P; Norton, P R; Thompson, J C; Bloch-Devaux, B; Colas, P; Emery, S; Kozanecki, Witold; Lançon, E; Lemaire, M C; Locci, E; Marx, B; Pérez, P; Rander, J; Renardy, J F; Roussarie, A; Schuller, J P; Schwindling, J; Trabelsi, A; Vallage, B; Johnson, R P; Kim, H Y; Litke, A M; McNeil, M A; Taylor, G; Beddall, A; Booth, C N; Boswell, R; Brew, C A J; Cartwright, S L; Combley, F; Köksal, A; Letho, M; Newton, W M; Rankin, C; Reeve, J; Thompson, L F; Böhrer, A; Brandt, S; Cowan, G D; Feigl, E; Grupen, Claus; Lutters, G; Minguet-Rodríguez, J A; Rivera, F; Saraiva, P; Smolik, L; Stephan, F; Apollonio, M; Bosisio, L; Della Marina, R; Giannini, G; Gobbo, B; Musolino, G; Ragusa, F; Rothberg, J E; Wasserbaech, S R; Armstrong, S R; Bellantoni, L; Elmer, P; Feng, Z; Ferguson, D P S; Gao, Y S; González, S; Grahl, J; Greening, T C; Harton, J L; Hayes, O J; Hu, H; McNamara, P A; Nachtman, J M; Orejudos, W; Pan, Y B; Saadi, Y; Schmitt, M; Scott, I J; Sharma, V; Turk, J; Walsh, A M; Wu Sau Lan; Wu, X; Yamartino, J M; Zheng, M; Zobernig, G
1996-01-01
Quark and gluon jets with the same energy, 24GeV, are compared in symmetric three-jet configurations from hadronic Z decays observed by the ALEPH detector. Jets are defined using the Durham algorithm. Gluon jets are identified using an anti-tag on b jets, based on either a track impact parameter method or a high transverse momentum lepton tag. The comparison of gluon and mixed flavour quark jets shows that gluon jets have a softer fragmentation function, a larger angular width and a higher particle multiplicity. Evidence is also presented which shows that the corresponding differences between gluon and heavy flavour jets are significantly smaller.
The Higgs transverse momentum distribution in gluon fusion as multiscale problem
International Nuclear Information System (INIS)
Bagnaschi, E.; Vicini, A.
2015-05-01
We consider Higgs production in gluon fusion and in particular the prediction of the Higgs transverse momentum distribution. We discuss the ambiguities affecting the matching procedure between fixed order matrix elements and the resummation to all orders of the terms enhanced by log(p H T /m H ) factors. Following a recent proposal (Grazzini et al., hep-ph/1306.4581), we argue that the gluon fusion process, computed considering two active quark flavors, is a multiscale problem from the point of view of the resummation of the collinear singular terms. We perform an analysis at parton level of the collinear behavior of the real emission amplitudes and we derive an upper limit to the range of transverse momenta where the collinear approximation is valid. This scale is then used as the value of the resummation scale in the analytic resummation framework or as the value of the h parameter in the POWHEG-BOX code. Finally, we provide a phenomenological analysis in the Standard Model, in the Two Higgs Doublet Model and in the Minimal Supersymmetric Standard Model. In the two latter cases, we provide an ansatz for the central value of the matching parameters not only for a Standard Model-like Higgs boson, but also for heavy scalars and in scenarios where the bottom quark may play the dominant role.
Kaluza-Klein gluon + jets associated production at the Large Hadron Collider
Iyer, A.M.; Manglani, N.; Sridhar, K.
2016-08-10
The Kaluza-Klein excitations of gluons offer the exciting possibility of probing bulk Randall-Sundrum (RS) models. In these bulk models either a custodial symmetry or a deformation of the metric away from AdS is invoked in order to deal with electroweak precision tests. Addressing both these models, we suggest a new channel in which to study the production of KK-gluons ($g_{KK}$): one where it is produced in association with one or more hard jets. The cross-section for the $g_{KK}+$ jets channel is significant because of several contributing sub-processes. In particular, the 1-jet and the 2-jet associated processes are important because at these orders in QCD the $qg$ and the $gg$ initial states respectively come into play. We have performed a hadron-level simulation of the signal and present strategies to effectively extract the signal from what could potentially be a huge background. We present results for the kinematic reach of the LHC Run-II for different $g_{KK}$ masses in bulk-RS models.
Medium-induced gluon radiation beyond the eikonal approximation
Apolinário, Liliana; Milhano, Guilherme; Salgado, Carlos A
2014-01-01
In this work we improve existing calculations of radiative energy loss by computing corrections that implement energy-momentum conservation, previously only implemented a posteriori, in a rigorous way. Using the path-integral formalism, we compute in-medium splittings allowing transverse motion of all particles in the emission process, thus relaxing the assumption that only the softest particle is permitted such movement. This work constitutes the extension of the computation carried out for x$\\rightarrow$1 in Phys. Lett. B718 (2012) 160-168, to all values of x, the momentum fraction of the energy of the parent parton carried by the emitted gluon. In order to accomplish a general description of the whole in-medium showering process, in this work we allow for arbitrary formation times for the emitted gluon. We provide general expressions and their realisation in the path integral formalism within the harmonic oscillator approximation.
Quark-Gluon Soup -- The Perfectly Liquid Phase of QCD
Heinz, Ulrich
2015-03-01
At temperatures above about 150 MeV and energy densities exceeding 500 MeV/fm3, quarks and gluons exist in the form of a plasma of free color charges that is about 1000 times hotter and a billion times denser than any other plasma ever created in the laboratory. This quark-gluon plasma (QGP) turns out to be strongly coupled, flowing like a liquid. About 35 years ago, the nuclear physics community started a program of relativistic heavy-ion collisions with the goal of producing and studying QGP under controlled laboratory conditions. This article recounts the story of its successful creation in collider experiments at Brookhaven National Laboratory and CERN and the subsequent discovery of its almost perfectly liquid nature, and reports on the recent quantitatively precise determination of its thermodynamic and transport properties.
Singular gauge potentials and the gluon condensate at zero temperature
International Nuclear Information System (INIS)
Langfeld, K.; Ilgenfritz, E.-M.; Reinhardt, H.; Schaefke, A.
2002-01-01
We consider a new cooling procedure which separates gluon degrees of freedom from singular center vortices in SU(2) LGT in a gauge invariant way. Restricted by a cooling scale κ 4 /σ 2 fixing the residual SO(3) gluonic action relative to the string tension, the procedure is RG invariant. In the limit κ → 0 a pure Z(2) vortex texture is left. This minimal vortex content does not contribute to the string tension. It reproduces, however, the lowest glueball states. With an action density scaling like a 4 with β, it defines a finite contribution to the action density at T = 0 in the continuum limit. We propose to interpret this a mass dimension 4 condensate related to the gluon condensate. Similarly, this vortex texture is revealed in the Landau gauge
Recursive Neural Networks in Quark/Gluon Tagging
CERN. Geneva
2018-01-01
Vidyo contribution Based on the natural tree-like structure of jet sequential clustering, the recursive neural networks (RecNNs) embed jet clustering history recursively as in natural language processing. We explore the performance of RecNN in quark/gluon discrimination. The results show that RecNNs work better than the baseline BDT by a few percent in gluon rejection at the working point of 50\\% quark acceptance. We also experimented on some relevant aspects which might influence the performance of networks. It shows that even only particle flow identification as input feature without any extra information on momentum or angular position is already giving a fairly good result, which indicates that most of the information for q/g discrimination is already included in the tree-structure itself.
Running coupling corrections to high energy inclusive gluon production
International Nuclear Information System (INIS)
Horowitz, W.A.; Kovchegov, Yuri V.
2011-01-01
We calculate running coupling corrections for the lowest-order gluon production cross section in high energy hadronic and nuclear scattering using the BLM scale-setting prescription. In the final answer for the cross section the three powers of fixed coupling are replaced by seven factors of running coupling, five in the numerator and two in the denominator, forming a 'septumvirate' of running couplings, analogous to the 'triumvirate' of running couplings found earlier for the small-x BFKL/BK/JIMWLK evolution equations. It is interesting to note that the two running couplings in the denominator of the 'septumvirate' run with complex-valued momentum scales, which are complex conjugates of each other, such that the production cross section is indeed real. We use our lowest-order result to conjecture how running coupling corrections may enter the full fixed-coupling k T -factorization formula for gluon production which includes nonlinear small-x evolution.
The soft-gluon current at one-loop order
Catani, S
2000-01-01
We study the soft limit of one-loop QCD amplitudes and we derive the process-independent factorization formula that controls the singular behaviour in this limit. This is obtained from the customary eikonal factorization formula valid at tree (classical) level by introducing a generalized soft-gluon current that embodies the quantum corrections. We compute the explicit expression of the soft-gluon current at one-loop order. It contains purely non-abelian correlations between the colour charges of each pair of hard-momentum partons in the matrix element. This leads to colour correlations between (two and) three hard partons in the matrix element squared. Exploiting colour conservation, we recover QED-like factorization for the square of the matrix elements with two and three hard partons.
The strongly coupled quark-gluon plasma created at RHIC
Heinz, Ulrich W
2009-01-01
The Relativistic Heavy Ion Collider (RHIC) was built to re-create and study in the laboratory the extremely hot and dense matter that filled our entire universe during its first few microseconds. Its operation since June 2000 has been extremely successful, and the four large RHIC experiments have produced an impressive body of data which indeed provide compelling evidence for the formation of thermally equilibrated matter at unprecedented temperatures and energy densities -- a "quark-gluon plasma (QGP)". A surprise has been the discovery that this plasma behaves like an almost perfect fluid, with extremely low viscosity. Theorists had expected a weakly interacting gas of quarks and gluons, but instead we seem to have created a strongly coupled plasma liquid. The experimental evidence strongly relies on a feature called "elliptic flow" in off-central collisions, with additional support from other observations. This article explains how we probe the strongly coupled QGP, describes the ideas and measurements whi...
On the zero crossing of the three-gluon vertex
Energy Technology Data Exchange (ETDEWEB)
Athenodorou, A. [Department of Physics, University of Cyprus, POB 20537, 1678 Nicosia (Cyprus); Binosi, D., E-mail: binosi@ectstar.eu [European Centre for Theoretical Studies in Nuclear Physics and Related Areas - ECT* and Fondazione Bruno Kessler, Villa Tambosi, Strada delle Tabarelle 286, I-38050 Villazzano (Italy); Boucaud, Ph. [Laboratoire de Physique Théorique (UMR8627), CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay (France); De Soto, F. [Dpto. Sistemas Físicos, Químicos y Naturales, Univ. Pablo de Olavide, 41013 Sevilla (Spain); Papavassiliou, J. [Department of Theoretical Physics and IFIC, University of Valencia-CSIC, E-46100, Valencia (Spain); Rodríguez-Quintero, J. [Department of Integrated Sciences, University of Huelva, E-21071 Huelva (Spain); Zafeiropoulos, S. [Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Str. 1, 60438 Frankfurt am Main (Germany)
2016-10-10
We report on new results on the infrared behavior of the three-gluon vertex in quenched Quantum Chromodynamics, obtained from large-volume lattice simulations. The main focus of our study is the appearance of the characteristic infrared feature known as ‘zero crossing’, the origin of which is intimately connected with the nonperturbative masslessness of the Faddeev–Popov ghost. The appearance of this effect is clearly visible in one of the two kinematic configurations analyzed, and its theoretical origin is discussed in the framework of Schwinger–Dyson equations. The effective coupling in the momentum subtraction scheme that corresponds to the three-gluon vertex is constructed, revealing the vanishing of the effective interaction at the exact location of the zero crossing.
Baryonic decay of the J/psi and gluon spin
International Nuclear Information System (INIS)
Pallin, D.
1985-04-01
A study of the J/psi state of the charmomium (c antic state) was performed at the D.C.I. collider in Orsay with the DM2 detector. 9 millions of J/psi have been produced, corresponding to more than one half of the actual world statistics. The very simple mecanism of the e +- annihilation into baryon-antibaryon via the J/psi state, allows measurements of the gluon spin through the emitted baryon angular distribution. The analyse of the channels J/psi → p antip and Λ antiΛ, permits to obtain parameters for the angular distributions. These experimental values favour very clearly a vectorial gluon hypothesis, as postulated by the quantum Chromodynamics [fr
RHIC and the pursuit of the quark-gluon plasma
International Nuclear Information System (INIS)
Mitchell, J.T.
2001-01-01
There is a fugitive on the loose. Its name is Quark-Gluon Plasma, alias the QGP. The QGP is a known informant with knowledge about the fundamental building blocks of nature that we wish to extract. This briefing will outline the status of the pursuit of the elusive QGP. We will cover what makes the QGP tick, its modus operandi, details on how we plan to hunt the fugitive down, and our level of success thus far
Superconvergent gluon propagator and the quark-antiquark potential
International Nuclear Information System (INIS)
Oehme, R.; Chicago Univ., IL; Chicago Univ., IL
1989-01-01
Superconvergence of the gluon propagator, together with the asymptotically negative sign of the discontinuity, imply that the structure function has a representation which corresponds to an approximately linear quark-antiquark potential, provided the number of flavors is less than ten. For more than ten flavors, there is no indication for a linear potential within this framework. The connection with metric confinement is emphasized. Possible dipole terms are considered briefly. (orig.)
On the scattering of gluons in the GKP string
International Nuclear Information System (INIS)
Bianchi, Lorenzo; Hamburg Univ.; Bianchi, Marco S.
2015-11-01
We compute the one-loop S-matrix for the light bosonic excitations of the GKP string at strong coupling. These correspond, on the gauge theory side, to gluon insertions in the GKP vacuum. We perform the calculation by Feynman diagrams in the worldsheet theory and we compare the result to the integrability prediction, finding perfect agreement for the scheme independent part. For scheme dependent rational terms we test different schemes and find that a recent proposal reproduces exactly the integrability prediction.
Cold quark-gluon plasma. Theoretical and experimental perspectives
Energy Technology Data Exchange (ETDEWEB)
Mandzhavidze, I [Institute of Physics, Tbilisi (Georgia); Sisakyan, A N [Bogolyubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna (Russian Federation)
1998-12-01
The arguments that extremely high-multiplicity hadron interactions at high energies are the source of cold, dense quark-gluon plasma (CQGP) created by the QCD heavy jets are offered. The possibility of calorimetric triggering and measurements of CQGP is considered. The space-time local thermodynamical formalism is adopted for field-theoretical description of such measurements. The valid phenomena in the CQGP are discussed (qualitatively) from theoretical and experimental points of view 62 refs.
Enhanced J/psi suppression due to gluon depletion
Hwa, R. C.; Pisut, J.; Pisutova, N.
1997-01-01
The nonlinear effect of gluon depletion in the collision of large nuclei can be large. It is due to multiple scatterings among comoving partons initiated by primary scattering of partons in the colliding nuclei. The effect can give rise to substantial suppression of $J/\\psi$ production in very large nuclei, even if the linear depletion effect is insignificant for the collisions of nuclei of smaller sizes. This mechanism offers a natural explanation of the enhanced suppression in the Pb-Pb dat...
Tree-level gluon amplitudes on the celestial sphere
Schreiber, Anders Ø.; Volovich, Anastasia; Zlotnikov, Michael
2018-06-01
Pasterski, Shao and Strominger have recently proposed that massless scattering amplitudes can be mapped to correlators on the celestial sphere at infinity via a Mellin transform. We apply this prescription to arbitrary n-point tree-level gluon amplitudes. The Mellin transforms of MHV amplitudes are given by generalized hypergeometric functions on the Grassmannian Gr (4 , n), while generic non-MHV amplitudes are given by more complicated Gelfand A-hypergeometric functions.
Debye's length in expanding quark-gluon plasma
International Nuclear Information System (INIS)
Bialas, A.
1988-06-01
The screening properties of an abelian quark-gluon plasma and boost invariantly expanding in a given direction, are discussed. The expansion results in anisotropic screening. At early stages of the process, the Debye length along the direction of the expansion is reduced by a factor of about 2, relative to static calculations. This may have important consequences for the J/ψ production rate. 12 refs., 2 figs., 1 tab. (author)
Phenomenological Review on Quark-Gluon Plasma: Concepts vs. Observations
Czech Academy of Sciences Publication Activity Database
Pasechnik, R.; Šumbera, Michal
2017-01-01
Roč. 3, č. 1 (2017), č. článku 7. ISSN 2218-1997 R&D Projects: GA MŠk(CZ) LG13031; GA ČR GA13-20841S Institutional support: RVO:61389005 Keywords : extreme states of matter * heavy ion collisions * QCD critical point * quark-gluon plasma * saturation phenomena * QCD vacuum Subject RIV: BF - Elementary Particles and High Energy Physics OBOR OECD: Particles and field physics
Evolution of gluon TMDs from small to moderate x
Energy Technology Data Exchange (ETDEWEB)
Tarasov, Andrey [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
2016-05-01
Recently we obtained an evolution equation of gluon TMDs, which addresses a problem of unification of different kinematic regimes. It describes evolution in the whole range of Bjorken $x_B$ and the whole range of transverse momentum $k_\\perp$. In this notes I study different limits of this evolution equation and show how it yields several well-known and some previously unknown results.
From quarks and gluons to baryon form factors.
Eichmann, Gernot
2012-04-01
I briefly summarize recent results for nucleon and [Formula: see text] electromagnetic, axial and transition form factors in the Dyson-Schwinger approach. The calculation of the current diagrams from the quark-gluon level enables a transparent discussion of common features such as: the implications of dynamical chiral symmetry breaking and quark orbital angular momentum, the timelike structure of the form factors, and their interpretation in terms of missing pion-cloud effects.
Dynamical gluon masses in perturbative calculations at the loop level
International Nuclear Information System (INIS)
Machado, Fatima A.; Natale, Adriano A.
2013-01-01
Full text: In the phenomenology of strong interactions one always has to deal at some extent with the interplay between perturbative and non-perturbative QCD. On one hand, the former has quite developed tools, yielded by asymptotic freedom. On the other, concerning the latter, we nowadays envisage the following scenario: 1) There are strong evidences for a dynamically massive gluon propagator and infrared finite coupling constant; 2) There is an extensive and successful use of an infrared finite coupling constant in phenomenological calculations at tree level; 3) The infrared finite coupling improves the perturbative series convergence; 4) The dynamical gluon mass provides a natural infrared cutoff in the physical processes at the tree level. Considering this scenario it is natural to ask how these non-perturbative results can be used in perturbative calculations of physical observables at the loop level. Recent papers discuss how off-shell gauge and renormalization group invariant Green functions can be computed with the use of the Pinch Technique (PT), with IR divergences removed by the dynamical gluon mass, and using a well defined effective charge. In this work we improve the former results by the authors, which evaluate 1-loop corrections to some two- and three-point functions of SU(3) pure Yang-Mills, investigating the dressing of quantities that could account for an extension of loop calculations to the infrared domain of the theory, in a way applicable to phenomenological calculations. One of these improvements is maintaining the gluon propagator transverse in such a scheme. (author)
The gluon momentum fraction of the nucleon from lattice QCD
International Nuclear Information System (INIS)
Alexandrou, Constantia; Hadjiyiannakou, Kyriakos; Constantinou, Martha; Jansen, Karl; Wiese, Christian; Panagopoulos, Haralambos
2016-01-01
We perform a direct calculation of the gluon momentum fraction of the nucleon using maximally twisted mass fermion ensembles with N_f=2+1+1 flavors at a pion mass of about 370 MeV and a lattice spacing of a∼0.082 fm and with N_f=2 flavors at the physical pion mass and a lattice spacing of a∼0.093 fm. In the definition of the gluon operator we employ stout smearing to obtain a statistically significant result for the bare matrix elements. In addition, we perform a lattice perturbative calculation including 2 levels of stout smearing to carry out the mixing and the renormalization of the quark and gluon operators. We find, after conversion to the MS scheme at a scale of 2 GeV: left angle x right angle "R_g=0.284(23)(23) for pion mass of about 370 MeV and left angle x right angle "R_g=0.283(23)(15) for the physical pion mass.
Physics and astrophysics of quark-gluon plasma
Energy Technology Data Exchange (ETDEWEB)
Anon.
1993-06-15
The quark gluon plasma - matter too hot or dense for quarks to crystallize into particles - played a vital role in the formation of the Universe. Efforts to recreate and understand this type of matter are forefront physics and astrophysics, and progress was highlighted in the Second International Conference on Physics and Astrophysics of Quark Gluon Plasma (ICPA-QGP 93), held in Calcutta from 19-23 January. (The first conference in the series was held in Bombay in February 1988). Although primarily motivated towards enlightening the Indian physics community in this new and rapidly evolving area, in which India now plays an important role, the conference also catered for an international audience. Particular emphasis was placed on the role of quark gluon plasma in astrophysics and cosmology. While Charles Alcock of Lawrence Livermore looked at a less conventional picture giving inhomogeneous ('clumpy') nucleosynthesis, David Schramm (Chicago) covered standard big bang nucleosynthesis. The abundances of very light elements do not differ appreciably for these contrasting scenarios; the crucial difference between them shows up for heavier elements like lithium-7 and -8 and boron-11. Richard Boyd (Ohio State) highlighted the importance of accurate measurements of the primordial abundances of these elements for clues to the cosmic quark hadron phase transition. B. Banerjee (Bombay) argued, on the basis of lattice calculations, for only slight supercooling in the cosmic quark phase transition - an assertion which runs counter to the inhomogeneous nucleosynthesis scenario.
Physics and astrophysics of quark-gluon plasma
International Nuclear Information System (INIS)
Anon.
1993-01-01
The quark gluon plasma - matter too hot or dense for quarks to crystallize into particles - played a vital role in the formation of the Universe. Efforts to recreate and understand this type of matter are forefront physics and astrophysics, and progress was highlighted in the Second International Conference on Physics and Astrophysics of Quark Gluon Plasma (ICPA-QGP 93), held in Calcutta from 19-23 January. (The first conference in the series was held in Bombay in February 1988). Although primarily motivated towards enlightening the Indian physics community in this new and rapidly evolving area, in which India now plays an important role, the conference also catered for an international audience. Particular emphasis was placed on the role of quark gluon plasma in astrophysics and cosmology. While Charles Alcock of Lawrence Livermore looked at a less conventional picture giving inhomogeneous ('clumpy') nucleosynthesis, David Schramm (Chicago) covered standard big bang nucleosynthesis. The abundances of very light elements do not differ appreciably for these contrasting scenarios; the crucial difference between them shows up for heavier elements like lithium-7 and -8 and boron-11. Richard Boyd (Ohio State) highlighted the importance of accurate measurements of the primordial abundances of these elements for clues to the cosmic quark hadron phase transition. B. Banerjee (Bombay) argued, on the basis of lattice calculations, for only slight supercooling in the cosmic quark phase transition - an assertion which runs counter to the inhomogeneous nucleosynthesis scenario
Electromagnetic signals of quark gluon plasma
Indian Academy of Sciences (India)
dsm@vecaxp2.veccal.ernet.in (D.S.Mukherjee)
tate our understanding of the quark-hadron phase transition although, I do not think I ... Our energetic friends [7] who deal with Parton cascade model (PCM) seem to have ..... in QHD is untenable, these are solved in mean field approximation.
Rapidity distribution of photons from an anisotropic quark-gluon plasma
International Nuclear Information System (INIS)
Bhattacharya, Lusaka; Roy, Pradip
2010-01-01
We calculate rapidity distribution of photons due to Compton and annihilation processes from quark gluon plasma with pre-equilibrium momentum-space anisotropy. We also include contributions from hadronic matter with late-stage transverse expansion. A phenomenological model has been used for the time evolution of hard momentum scale, p hard (τ), and anisotropy parameter, ξ(τ). As a result of pre-equilibrium momentum-space anisotropy, we find significant modification of photons rapidity distribution. For example, with the fixed initial condition (FIC) free-streaming (δ=2) interpolating model we observe significant enhancement of photon rapidity distribution at fixed p T , where as for FIC collisionally broadened (δ=2/3) interpolating model the yield increases till y∼1. Beyond that suppression is observed. With fixed final multiplicity (FFM) free-streaming interpolating model we predict enhancement of photon yield which is less than the case of FIC. Suppression is always observed for FFM collisionally broadened interpolating model.
International Nuclear Information System (INIS)
Safronov, A.N.
1983-01-01
A system of nonsingular integral equations is formulated for the calculation of hadron-hadron partial amplitudes in the low-and intermediate-energy range taking into account meson and quark-gluon degrees of freedom. The quark-gluon degrees of freedom are included in the framework of the composite-quark-bag model, and the meson degrees of freedom are treated by the methods of the relativistic quantum field theory. It is shown that including the quark-gluon degrees of freedom leads to suppression of meson exchange effects, mostly of heavy meson (rho, ω) exchanges. The method has been applied to the calculation of the 3 S 1 , 1 S 0 , 3 P 0 , 3 P 1 , and 1 P 1 phase shifts for the nucleon-nucleon scattering at the incident nucleon energies T=0-1050 MeV, as well as to the S-wave scattering lengths and effective radii
Quarks and gluons in hadrons and nuclei
International Nuclear Information System (INIS)
Close, F.E.
1989-01-01
These lectures discuss the particle-nuclear interface -- a general introduction to the ideas and application of colored quarks in nuclear physics, color, the Pauli principle, and spin flavor correlations -- this lecture shows how the magnetic moments of hadrons relate to the underlying color degree of freedom, and the proton's spin -- a quark model perspective. This lecture reviews recent excitement which has led some to claim that in deep inelastic polarized lepton scattering very little of the spin of a polarized proton is due to its quarks. 38 refs
Holographic quark gluon plasma with flavor
Energy Technology Data Exchange (ETDEWEB)
Kaminski, M. [Max-Planck-Institut fuer Physik (Werner-Heisenberg-Institut), Muenchen (Germany)
2009-01-15
In this work I explore theoretical and phenomenological implications of chemical potentials and charge densities inside a strongly coupled thermal plasma, using the gauge/gravity correspondence. Strong coupling effects discovered in this model theory are interpreted geometrically and may be taken as qualitative predictions for heavy ion collisions at RHIC and LHC. In particular I examine the thermodynamics, spectral functions, transport coefficients and the phase diagram of the strongly coupled plasma. For example stable mesons, which are the analogs of the QCD Rho-mesons, are found to survive beyond the deconfinement transition. A phase transition resembling 2-flavor QCD is discovered. The momentum diffusion rate of charmonium at strong coupling is significantly reduced compared to the weak coupling result, in reminiscence of the universal viscosity bound. This paper is based on partly unpublished work performed in the context of my PhD thesis. New results and ideas extending significantly beyond those published until now are stressed. (Abstract Copyright [2009], Wiley Periodicals, Inc.)
Ghost-gluon vertex in the presence of the Gribov horizon
Mintz, B. W.; Palhares, L. F.; Sorella, S. P.; Pereira, A. D.
2018-02-01
We consider Yang-Mills theories quantized in the Landau gauge in the presence of the Gribov horizon via the refined Gribov-Zwanziger (RGZ) framework. As the restriction of the gauge path integral to the Gribov region is taken into account, the resulting gauge field propagators display a nontrivial infrared behavior, being very close to the ones observed in lattice gauge field theory simulations. In this work, we explore a higher correlation function in the refined Gribov-Zwanziger theory: the ghost-gluon interaction vertex, at one-loop level. We show explicit compatibility with kinematical constraints, as required by the Ward identities of the theory, and obtain analytical expressions in the limit of vanishing gluon momentum. We find that the RGZ results are nontrivial in the infrared regime, being compatible with lattice Yang-Mills simulations in both SU(2) and SU(3), as well as with solutions from Schwinger-Dyson equations in different truncation schemes, Functional Renormalization Group analysis, and the renormalization group-improved Curci-Ferrari model.
Phenomenological analysis of Higgs boson production through gluon fusion in association with jets
International Nuclear Information System (INIS)
Greiner, Nicolas; Luisoni, Gionata; Winter, Jan-Christopher; Yundin, Valery; Schoenherr, Marek
2015-06-01
We present a detailed phenomenological analysis of the production of a Standard Model Higgs boson in association with up to three jets. We consider the gluon fusion channel using an effective theory in the large top-quark mass limit. Higgs boson production in gluon fusion constitutes an irreducible background to the vector boson fusion (VBF) process; hence the precise knowledge of its characteristics is a prerequisite for any measurement in the VBF channel. The calculation is carried out at next-to-leading order (NLO) in QCD in a fully automated way by combining the two programs GoSam and Sherpa. We present numerical results for a large variety of observables for both standard cuts and VBF selection cuts. We find that for all jet multiplicities the NLO corrections are sizeable. This is particularly true in the presence of kinematic selections enhancing the VBF topology, which are based on vetoing additional jet activity. In this case, precise predictions for the background can be made using our calculation by taking the difference between the inclusive H+2 jets and the inclusive H+3 jets result.
Inclusive observables and hard gluon emission in neutrino deep inelastic scattering
International Nuclear Information System (INIS)
Bouchiat, C.; Meyer, P.; Mezard, M.
1980-01-01
We derive the predictions of perturbative QCD together with non-perturbative corrections for a set of inclusive observables connected with the angular distribution of light-cone energy in deep inelastic neutrino scattering. Our particular choice of observables has been made in order to meet important physical requirements besides the necessary condition of infrared regularity. Our inclusive observables receive their dominant contribution from the quark fragmentation region. The non-perturbative contribution is calculable in a rather model-independent way and stays at an acceptable level in realistic experimental conditions. The QCD perturbative contribution, which takes the simple form of a convolution product, exhibits a strongly decreasing behaviour as a function of the Bjorken scaling variable x, superimposed on a constant background associated with the non-perturbative terms, allowing a rather clean separation of the two effects. The perturbative term being dominated by the process of hard-gluon emission, an experimental investigation of the observables discussed here may be a good way to detect the effect of gluon emission in deep inelastic neutrino scattering. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Kang, Hyejoo
2002-01-30
We present production measurements of the charged hadrons {pi}{sup {+-}}, K{sup {+-}} and p/{bar p} in e{sup +}e{sup -} interactions at the Z{sup 0} pole. The excellent particle identification capability of the SLC Large Detector (SLD) at the Stanford Linear Collider (SLC) are used. In addition to studies over a wide momentum range in hadronic Z{sup 0} events of all five flavors, we have made the most precise measurements in light (uds), c and b flavor events separately. Unambiguous flavor dependencies have been observed, and the results have been compared with the predictions of several QCD fragmentation models. We have also exploited the unique feature of electron beam polarization in our experiment to compare hadron production separately in quark and antiquark jets. Direct evidence that higher momentum hadrons are more likely to contain the primary quark and antiquark is seen, with precision sufficient to provide new model tests. Finally, we have studied hard gluon jets in detail. We have confirmed that gluon jets have a higher multiplicity of softer particles than light quark jets, and found this enhancement to be the same for {pi}{sup {+-}}, K{sup {+-}} and p/{bar p} at the few percent level at all momenta. Any overall difference in the hadron fractions is limited to 0.018 at the 95% confidence level, indicating that there are no differences at the hadronization stage in jet formation between gluons and quarks.
Numerical estimates of the evolution of quark and gluon populations inside QCD jets
International Nuclear Information System (INIS)
Garetto, M.
1980-01-01
The system of first order differential equations for the probabilities of producing nsub(g) gluons and nsub(q) quarks in a single gluon or quark jet are solved numerically for a convenient choice of the parameters A, A-tilde, B. Relevant branching ratios as the evolution parameter Y increases are shown. The different behaviour of the distributions in the quark- and in the gluon-jet is discussed. (author)
Structure functions and pair correlations of the quark-gluon plasma
International Nuclear Information System (INIS)
Thoma, Markus H.
2005-01-01
Recent experiments at RHIC and theoretical considerations indicate that the quark-gluon plasma, present in the fireball of relativistic heavy-ion collisions, might be in a liquid phase. The liquid state can be identified by characteristic correlation and structure functions. Here definitions of the structure functions and pair correlations of the quark-gluon plasma are presented as well as perturbative results. These definitions might be useful for verifying the quark-gluon-plasma liquid in QCD lattice calculations
Regge behaviour of structure function and gluon distribution at low-x in leading order
International Nuclear Information System (INIS)
Sarma, J.K.
2000-01-01
We present a method to find the gluon distribution from the F 2 proton structure function data at low-x assuming the Regge behaviour of the gluon distribution function at this limit. We use the leading order (LO) Altarelli-Parisi (AP) evolution equation in our analysis and compare our result with those of other authors. We also discuss the limitations of the Taylor expansion method in extracting the gluon distribution from the F 2 structure function used by those authors. (orig.)
Transverse gluon contributions to the thermal static potential of heavy quarkonium
International Nuclear Information System (INIS)
Zhu, Jia-Qing; Li, Yun-De
2015-01-01
The transverse gluon contributions to the thermal static potentials of heavy quarkonia in isotropic medium are studied. Using the resummation of the damping rates method developed by Hou and Li, the infrared divergence that appeared in the effective potential calculations of transverse gluon is avoided. The comparisons between the transverse and the longitudinal contributions for heavy quarkonia are discussed. The results show that the dissociation scales of quarkonia in thermal medium are decreased by the transverse gluon contributions
Energy Technology Data Exchange (ETDEWEB)
Panebianco, St
2005-09-15
The main aim of the COMPASS experiment is the measurement of the gluon polarization in the nucleon, which can be accessed by the spin asymmetry in the scattering of a polarized muon beam on a polarized nucleon target. The process sensitive to the gluon polarization is the photon-gluon fusion, which can be tagged in the cleanest way by looking at the production of D{sup 0} mesons. At COMPASS, D{sup 0} mesons are reconstructed from the invariant mass of their decay products. However, it is a rare process, dominated by a large combinatorial background. This thesis presents some studies devoted to the improvement of the charmed mesons reconstruction. The measurement of the efficiency and the space resolution of the 3 drift chamber stations of the COMPASS spectrometer is a necessary step in understanding the performances of the reconstruction of particle trajectories. The hadron identification, which is fundamental in the reconstruction of charmed meson decay, is performed by a RICH detector. A statistical treatment of signal and background, together with an upgrade project to replace the present front-end electronics, have been developed in order to improve the particle identification performances. The second part of this work concerns the spin asymmetry measurement, which requires the application of event selection criteria in order to minimize the noise over signal ratio in the D{sup 0} invariant mass, and the development of event-weighting methods to reduce the statistical error. This work presents a preliminary result, based on 2002-2004 statistics, which is the {delta}G/G measurement from open charm production. Although the error bars are large, the measured gluon polarization is compatible with zero. Given the present accuracy, this result is compatible with the existing direct measurements from other channels. However, it does not allow to distinguish between different theoretical models. (author)
A perturbative treatment of double gluon exchange in γ*-proton DIS
International Nuclear Information System (INIS)
Kharraziha, H.
2000-04-01
A new model for the exchange of two gluons between the virtual photon and the proton, in non-diffractive deeply inelastic electron-proton scattering, is developed and studied. This model relies on a perturbative calculation, previously applied to diffraction, and a general result from Regge theory. As a first application of the model, we study corrections to the momentum transfer to the quark-anti-quark pair, at the photon-vertex. We find a significant enhancement of the cross-section at ∝Q 2 momentum transfers, and large negative corrections for small momentum transfers. The implication of this result for jet-distributions measured at HERA, is discussed. (orig.)
Inclusive gluon production in deep inelastic scattering at high parton density
International Nuclear Information System (INIS)
Kovchegov, Yuri V.; Tuchin, Kirill
2002-01-01
We calculate the cross section of single inclusive gluon production in deep inelastic scattering at very high energies in the saturation regime, where the parton densities inside hadrons and nuclei are large and the evolution of structure functions with energy is nonlinear. The expression we obtain for the inclusive gluon production cross section is generated by this nonlinear evolution. We analyze the rapidity distribution of the produced gluons as well as their transverse momentum spectrum given by the derived expression for the inclusive cross section. We propose an ansatz for the multiplicity distribution of gluons produced in nuclear collisions which includes the effects of nonlinear evolution in both colliding nuclei
Vertex of three and four gluons in the Yang-Mills theory
International Nuclear Information System (INIS)
Brandt, F.T.C.
1986-01-01
In a general covariant gauge, the structure of the three-point function with one and two external gluons on shell is studied. The contributions which result in the one-loop approximation are expressed in terms of simple functions containing collinear and soft singularities. Furthermore, the contributions asociated with the four-point vertex when all external gluons are on-sheel, are analysed. As an application of these results, the infrared structure of the gluon-gluon scattering amplitude, is studied. (author) [pt
High energy production of gluons in a quasi-multi-Regge kinematics
International Nuclear Information System (INIS)
Fadin, V.S.; Lipatov, L.N.
1989-01-01
Inelastic gluon-gluon scattering amplitudes in the Born approximation for the quasi-multi-Regge kinematics are calculated, starting with the Veneziano-type expression for the inelastic amplitude of the gluon-tachyon scattering with its subsequent simplification in the region of large energies and the Regge slope α'→0. Results obtained allow one to determine the high order corrections to the gluon Regge trajectory, the reggeon-particle vertices and to the integral kernel of the Bethe-Salpeter equation for the vacuum t-channel partial waves. 10 refs.; 7 figs
Analysis of the proton longitudinal structure function from the gluon distribution function
International Nuclear Information System (INIS)
Boroun, G.R.; Rezaei, B.
2012-01-01
We make a critical, next-to-leading order, study of the relationship between the longitudinal structure function F L and the gluon distribution proposed in Cooper-Sarkar et al. (Z. Phys. C 39:281, 1988; Acta Phys. Pol. B 34:2911 2003), which is frequently used to extract the gluon distribution from the proton longitudinal structure function at small x. The gluon density is obtained by expanding at particular choices of the point of expansion and compared with the hard Pomeron behavior for the gluon density. Comparisons with H1 data are made and predictions for the proposed best approach are also provided. (orig.)
Looking at the gluon moment of the nucleon with dynamical twisted mass fermions
International Nuclear Information System (INIS)
Alexandrou, Constantia; Cyprus Institute, Nicosia; Drach, Vincent; Wiese, Christian; Hadjiyiannakou, Kyriakos; Jansen, Karl; Deutsches Elektronen-Synchrotron; Kostrzewa, Bartosz
2013-11-01
To understand the structure of hadrons it is important to know the PDF of their constituents, the quarks and gluons. In our work we aim to compute the first moment of the gluon PDF left angle x right angle g for the nucleon. We follow two possible approaches in order to extract the gluon moment: the Feynman-Hellmann theorem and a direct method with smearing of the gluon operator. We present preliminary results computed on 24 3 x 48 lattices for the case where the Feynman-Hellman theorem is used and 32 3 x 64 lattices for the direct method, employing N f =2+1+1 maximally twisted mass fermions.
Heavy ion collisions, the quark-gluon plasma and antinucleon annihilation
International Nuclear Information System (INIS)
Sarma, Nataraja
1985-01-01
Studies in high energy physics have indicated that nucleon and mesons are composed of quarks confined in bags by the strong colours mediated by gluons. It is reasonably expected that at suitably high baryon density and temperature of the nucleus, these bags of nucleon and mesons fuse into a big bag of quarks or gluons i.e. hadronic matter undergoes transition to a quark-gluon phase. Two techniques to achieve this transition in a laboratory are: (1) collision of two heavy nuclei, and (2) annihilation of antinucleons and antinuclei in nuclear matter. Theoretical studies as well as experimental studies associated with the transition to quark-gluon phase are reviewed. (author)
Threshold region for Higgs boson production in gluon fusion.
Bonvini, Marco; Forte, Stefano; Ridolfi, Giovanni
2012-09-07
We provide a quantitative determination of the effective partonic kinematics for Higgs boson production in gluon fusion in terms of the collider energy at the LHC. We use the result to assess, as a function of the Higgs boson mass, whether the large m(t) approximation is adequate and Sudakov resummation advantageous. We argue that our results hold to all perturbative orders. Based on our results, we conclude that the full inclusion of finite top mass corrections is likely to be important for accurate phenomenology for a light Higgs boson with m(H)~125 GeV at the LHC with √s=14 TeV.
Probing Quark-Gluon Interactions with Transverse Polarized Scattering
International Nuclear Information System (INIS)
Rondon, Oscar A.
2011-01-01
Transverse polarized inelastic scattering extends the power of the electromagnetic interaction as a probe of nucleon dynamics beyond the leading order regime explored with longitudinally polarized DIS. In transverse polarized scattering, the twist-3 g 2 spin structure function contributes at the same order as the longitudinal, twist-2, g 1 , so interactions between quarks and gluons can be studied, opening a window on the mechanisms of confinement. This talk reports the results of Jefferson Lab's Resonances Spin Structure experiment measurement of g 2 and the d 2 twist-3 quark matrix element at a four-momentum transfer of 1.3 GeV 2 .
Singular gauge potentials and the gluon condensate at zero temperature
Langfeld, K.; Ilgenfritz, E. -M.; Reinhardt, H.; Schäfke, A.
2001-01-01
We consider a new cooling procedure which separates gluon degrees of freedom from singular center vortices in SU(2) LGT in a gauge invariant way. Restricted by a cooling scale $\\kappa^4/\\sigma^2$ fixing the residual SO(3) gluonic action relative to the string tension, the procedure is RG invariant. In the limit $\\kappa \\to 0$ a pure Z(2) vortex texture is left. This {\\it minimal} vortex content does not contribute to the string tension. It reproduces, however, the lowest glueball states. With...
Very high energy probes of the quark-gluon plasma
International Nuclear Information System (INIS)
Ludlam, T.; Paige, F.; Madansky, L.
1984-01-01
Among the penetrating probes of nuclear matter the most frequently discussed have been those which involve the detection of photons or leptons with m/sub T/ approx. = P/sub T/ < 3 GeV. This is the expected range of emission from a hot, thermalized plasma of quarks and gluons. The suggestion has been made that in very high energy collisions of nuclei the properties of high P/sub T/ jets may also reflect the characteristics of the nuclear medium through which the parent partons have propagated just after the collision. In this note we expand on the possible uses of such a probe
Finite size effects in quark-gluon plasma formation
International Nuclear Information System (INIS)
Gopie, Andy; Ogilvie, Michael C.
1999-01-01
Using lattice simulations of quenched QCD we estimate the finite size effects present when a gluon plasma equilibrates in a slab geometry, i.e., finite width but large transverse dimensions. Significant differences are observed in the free energy density for the slab when compared with bulk behavior. A small shift in the critical temperature is also seen. The free energy required to liberate heavy quarks relative to bulk is measured using Polyakov loops; the additional free energy required is on the order of 30 - 40 MeV at 2 - 3 T c
Quark-gluon plasma searches: today and tomorrow
International Nuclear Information System (INIS)
Geist, W.M.
1991-01-01
Selected recent data from ion collisions at high energy are discussed in the frame-work of Quark-Gluon Plasma (QGP) searches. The purpose of these experiments is to measure the volume where a high temperature QGP may have been formed, determine its characteristic temperature, verify chemical equilibrium, establish deconfinement of this phase of matter, and/or find anything that differs from natural extrapolations from pp and pA collisions. Refined methods and new theoretical ideas for future experiments with heavier beams and/or at higher energies are briefly outlined. (G.P.) 49 refs., 28 figs
Gluon ladders in pp (pp-bar) collisions
International Nuclear Information System (INIS)
Machado, Magno Valerio Trindade; Ducati, Maria Beatriz Gay
2000-01-01
Full text follows: We study the contribution of a finite sum of gluon ladders to the hadronic processes showing that a reliable description is obtained using two order on perturbation theory. The pp(pp-bar) total cross sections are described with good agreement, consistent with unitarity bound. We also calculate the elastic scattering amplitude at non zero momentum transfer t, introducing two distinct Ansatz for the proton impact factor. As a by product the elastic differential cross section is obtained at small t approximation and compared with the data. (author)
Interactions of quarks and gluons with nuclei at intermediate energies
Energy Technology Data Exchange (ETDEWEB)
Mueller, A.H. [Columbia Univ., New York, NY (United States)
1994-04-01
Some processes involving the interaction of medium energy quarks and gluons with nuclear matter are described. Possible mechanisms for the A-dependence of the energy loss of leading protons produced in proton-nucleus collisions are given, and an experiment which may help to distinguish these mechanisms is described. A possible color transparency experiment at CEBAF is described. Experiments to measure energy loss of quarks in nuclear matter and the formation time of hadrons are discussed along with the possibilities of measuring {sigma}{sub J}/{psi} and {sigma}{sub {psi}{prime}} at CEBAF.
Gluon cascades and amplitudes in light-front perturbation theory
International Nuclear Information System (INIS)
Cruz-Santiago, C.A.; Staśto, A.M.
2013-01-01
We construct the gluon wave functions, fragmentation functions and scattering amplitudes within the light-front perturbation theory. Recursion relations on the light-front are constructed for the wave functions and fragmentation functions, which in the latter case are the light-front analogs of the Berends–Giele recursion relations. Using general relations between wave functions and scattering amplitudes it is demonstrated how to obtain the maximally-helicity violating amplitudes, and explicit verification of the results is based on simple examples.
Astrophysical Aspects of Neutrino Dynamics in Ultradegenerate Quark Gluon Plasma
Directory of Open Access Journals (Sweden)
Souvik Priyam Adhya
2017-01-01
Full Text Available The cardinal focus of the present review is to explore the role of neutrinos originating from the ultradense core of neutron stars composed of quark gluon plasma in the astrophysical scenario. The collective excitations of the quarks involving the neutrinos through the different kinematical processes have been studied. The cooling of the neutron stars as well as pulsar kicks due to asymmetric neutrino emission has been discussed in detail. Results involving calculation of relevant physical quantities like neutrino mean free path and emissivity have been presented in the framework of non-Fermi liquid behavior as applicable to ultradegenerate plasma.
Heavy quarks and squarks from W-gluon fusion
International Nuclear Information System (INIS)
Lindfors, J.
1986-05-01
We discuss Wg-fusion as a source of heavy quark and squark pairs at very high energy hadron colliders. Effective W approximation is used to calculate the cross-sections analytically in the forward scattering configuration; good agreement is obtained with exact numerical calculations. W-gluon fusion is found to be not nearly as important a production mechanism of heavy squarks as it is of heavy quarks. This is especially true when the mass-splitting within the SU(2) L doublet is small
Recent Results on Soft Probes of the Quark-Gluon Plasma from the ATLAS Experiment at the LHC
Przybycien, M; The ATLAS collaboration
2014-01-01
Measurements of low-pT (< 5 GeV) particle production have provided valuable insight on the production and evolution of the quark-gluon plasma in Pb+Pb collisions at the LHC. In particular, measurements of elliptic and higher order collective flow imprinted on the azimuthal angle distributions of low-pT particles directly probe the strongly-coupled dynamics of the quark-gluon plasma and test hydrodynamic model descriptions of its evolution. The large acceptance of detectors like ATLAS has made it possible to measure flow event-by-event and to determine the correlations between different harmonics. Recent measurements of low-pT particle production and multi-particle correlations in proton-lead collisions have shown features similar to the collective flow observed in Pb+Pb collisions. Results will be presented from a variety of single and multi-particle measurements in Pb+Pb and proton-Pb collisions that probe the collective dynamics of the quark-gluon plasma and possibly provide evidence for collectivity in ...
International Nuclear Information System (INIS)
Greiner, M.; Hofmann, C.; Schaefer, A.; Soff, G.
1994-08-01
The photon-gluon fusion process into a pair of heavy quarks is studied for peripheral Pb+Pb collisions at LHC energies. The double differential cross section with respect to the invariant mass and the rapidity of the produced quark pair at zero rapidity is directly proportional to the gluon distribution in the nuclear medium. Differential cross sections for the b-quark production lie well in the μbarn/GeV regime which will allow the deduction of the gluon distribution at low x. Rapidity cuts for the actual detectors are also considered. (orig.)
In-medium effects in the holographic quark-gluon plasma
International Nuclear Information System (INIS)
Rust, Felix Christian
2009-01-01
In this dissertation we use the gauge/gravity duality to investigate various properties of strongly coupled gauge theories, which we interpret as models for the quark-gluon plasma (QGP). In particular, we use variants of the D3/D7 setup as an implementation of the top-down approach of connecting string theory with phenomenologically relevant gauge theories. We focus on the effects of finite temperature and finite density on fundamental matter in the holographic quark-gluon plasma, which we model as the N = 2 hypermultiplet in addition to the N=4 gauge multiplet of supersymmetric Yang-Mills theory. As a key ingredient we develop a setup in which we can describe vector meson spectra in the holographic plasma at finite temperature and either baryon or isospin density. The description of vector meson excitations allows for a demonstration of the splitting of their spectrum at finite isospin chemical potential. In the effort to better understand transport processes in the QGP, we then study various diffusion coefficients in the quark-gluon plasma, including their dependence on temperature and particle density. In particular, we perform a simple calculation to obtain the diffusion coefficient of baryon charge and we derive expressions to obtain the isospin diffusion coefficient. Furthermore, we make use of an effective model to study the diffusion behavior of mesons in the plasma by setting up a kinetic model. Finally, we observe the implications of finite temperature and finite baryon or isospin density on the phase structure of fundamental matter in the holographic plasma. As one consequence we find a phase transition in the baryon diffusion coefficient which vanishes at a critical value of the particle density. The critical density we quantify matches the values of the according critical densities previously found in the phase transitions of other quantities. More important, we observe a new phase transition occurring when the isospin chemical potential excesses a
In-medium effects in the holographic quark-gluon plasma
Energy Technology Data Exchange (ETDEWEB)
Rust, Felix Christian
2009-08-05
In this dissertation we use the gauge/gravity duality to investigate various properties of strongly coupled gauge theories, which we interpret as models for the quark-gluon plasma (QGP). In particular, we use variants of the D3/D7 setup as an implementation of the top-down approach of connecting string theory with phenomenologically relevant gauge theories. We focus on the effects of finite temperature and finite density on fundamental matter in the holographic quark-gluon plasma, which we model as the N = 2 hypermultiplet in addition to the N=4 gauge multiplet of supersymmetric Yang-Mills theory. As a key ingredient we develop a setup in which we can describe vector meson spectra in the holographic plasma at finite temperature and either baryon or isospin density. The description of vector meson excitations allows for a demonstration of the splitting of their spectrum at finite isospin chemical potential. In the effort to better understand transport processes in the QGP, we then study various diffusion coefficients in the quark-gluon plasma, including their dependence on temperature and particle density. In particular, we perform a simple calculation to obtain the diffusion coefficient of baryon charge and we derive expressions to obtain the isospin diffusion coefficient. Furthermore, we make use of an effective model to study the diffusion behavior of mesons in the plasma by setting up a kinetic model. Finally, we observe the implications of finite temperature and finite baryon or isospin density on the phase structure of fundamental matter in the holographic plasma. As one consequence we find a phase transition in the baryon diffusion coefficient which vanishes at a critical value of the particle density. The critical density we quantify matches the values of the according critical densities previously found in the phase transitions of other quantities. More important, we observe a new phase transition occurring when the isospin chemical potential excesses a
Gluons and the Quark Sea at High Energies: Distributions, Polarization, Tomography
Energy Technology Data Exchange (ETDEWEB)
Boer, Daniel; /Groningen U.; Diehl, Markus; /DESY; Milner, Richard; /MIT; Venugopalan, Raju; /Brookhaven; Vogelsang, Werner; /Tubingen U.; Kaplan, David; /Washington U., Seattle; Montgomery, Hugh; /Jefferson Lab; Vigdor, Steven; /Brookhaven; Accardi, A.; /Jefferson Lab; Aschenauer, E.C.; /Brookhaven; Burkardt, M.; /New Mexico State U.; Ent, R.; /Jefferson Lab; Guzey, V.; /Jefferson Lab; Hasch, D.; /Frascati; Kumar, K.; /Massachusetts U., Amherst; Lamont, M.A.C.; /Brookhaven; Li, Ying-chuan; /Brookhaven; Marciano, W.; /Brookhaven; Marquet, C.; /CERN; Sabatie, F.; /IRFU, SPhN, Saclay; Stratmann, M.; /Brookhaven /LBL, Berkeley /Buenos Aires U. /Antwerp U. /Pelotas U. /Moncton U. /Santa Maria U., Valparaiso /CCTVal, Valparaiso /Hefei, CUST /Shandong U., Weihai /Boskovic Inst., Zagreb /Zagreb U., Phys. Dept. /Jyvaskyla U. /Orsay, LPT /Paris U., VI-VII /Ecole Polytechnique, CPHT /IRFU, SPhN, Saclay /Saclay, SPhT /Ruhr U., Bochum /Giessen U. /DESY /Hamburg U., Inst. Theor. Phys. II /Heidelberg U. /Mainz U., Inst. Kernphys. /Mainz U., Inst. Phys. /Regensburg U. /Tubingen U. /Wuppertal U. /DESY /Cagliari U. /INFN, Cagliari /Frascati /Milan U. /INFN, Milan /INFN, Pavia /Pavia U. /INFN, Perugia /Perugia U.; /more authors..
2012-06-07
the brightest femtoscope scale lepton-collider ever, exceeding the intensity of the HERA collider a thousand fold. HERA, with its center-of-mass (CM) energy of 320 GeV, was built to search for quark substructure. An EIC, with its scientific focus on studying QCD in the regime where the sea quarks and gluons dominate, would have a lower CM energy. In a staged EIC design, the CM energy will range from 50-70 GeV in stage I to approximately twice that for the full design. In addition to being the first lepton collider exploring the structure of polarized protons, an EIC will also be the first electron-nucleus collider, probing the gluon and sea quark structure of nuclei for the first time. Following the same structure as the scientific discussions at the INT, this report is organized around the following four major themes: (1) The spin and flavor structure of the proton; (2) Three dimensional structure of nucleons and nuclei in momentum and configuration space; (3) QCD matter in nuclei; and (4) Electroweak physics and the search for physics beyond the Standard Model. In this executive summary, we will briefly outline the outstanding physics questions in these areas and the suite of measurements that are available with an EIC to address these. The status of accelerator and detector designs is addressed at the end of the summary. Tables of golden measurements for each of the key science areas outlined are presented on page 12. In addition, each chapter in the report contains a comprehensive overview of the science topic addressed. Interested readers are encouraged to read these and the individual contributions for more details on the present status of EIC science.
Resummation improved rapidity spectrum for gluon fusion Higgs production
International Nuclear Information System (INIS)
Ebert, Markus A.; Tackmann, Frank J.; Michel, Johannes K.L.; Muenster Univ.
2017-02-01
Gluon-induced processes such as Higgs production typically exhibit large perturbative corrections. These partially arise from large virtual corrections to the gluon form factor, which at timelike momentum transfer contains Sudakov logarithms evaluated at negative arguments ln 2 (-1)=-π 2 . It has been observed that resumming these terms in the timelike form factor leads to a much improved perturbative convergence for the total cross section. We discuss how to consistently incorporate the resummed form factor into the perturbative predictions for generic cross sections differential in the Born kinematics, including in particular the Higgs rapidity spectrum. We verify that this indeed improves the perturbative convergence, leading to smaller and more reliable perturbative uncertainties, and that this is not affected by cancellations between resummed and unresummed contributions. Combining both fixed-order and resummation uncertainties, the perturbative uncertainty for the total cross section at N 3 LO+N 3 LL φ ' is about a factor of two smaller than at N 3 LO. The perturbative uncertainty of the rapidity spectrum at NNLO+NNLL φ ' is similarly reduced compared to NNLO. We also study the analogous resummation for quark-induced processes, namely Higgs production through bottom quark annihilation and the Drell-Yan rapidity spectrum. For the former the resummation leads to a small improvement, while for the latter it confirms the already small uncertainties of the fixed-order predictions.
Soft gluon resummation formulae for hard proton processes in QCD
International Nuclear Information System (INIS)
Craigie, N.S.; Jones, H.F.
1980-01-01
We briefly review the treatment of leading logarithmic behaviour of the parton distributions in QCD within the Bethe-Salpeter framework by analysing directly parton hadron Green functions in the limit of parton four-momentum k 2 → - infinitely in a special light-like gauge involving a spectator vector. This technique allows us to derive the factorization of parton probabilities in leading logarithmic order in QCD in the various inclusive processes involving a single short-distance scale. The proof requires us to show that the use of planar gauges eta = psub(A) + psub(B) + ..., where psub(A), psub(B)... are the observed hadron momenta, reduces to choosing the appropriate light-like gauge for each hadron-parton BS channel, after demonstrating a Bloch-Nordsieck cancellation of the real and virtual soft left-over gluons. In the case where two large momentum scales appear, by restricting the transverse phase space into which the gluons are radiated, we derive the double logarithmic eikonal renormalization of the hard scattering formula of the type proposed recently by Parisi and Petronzio. (orig.)
Two-gluon correlations in heavy–light ion collisions
International Nuclear Information System (INIS)
Wertepny, Douglas E.
2014-01-01
We derive the cross-section for two-gluon production in heavy–light ion collisions in the saturation/Color Glass Condensate framework. This calculation includes saturation effects to all orders in one of the nuclei (heavy ion) along with a single saturation correction in the projectile (light ion). The calculation of the correlation function predicts (qualitatively) two identical ridge-like correlations, near- and away-side. This prediction was later supported by experimental findings in p + A collisions at the LHC. Concentrating on the energy and geometry dependence of the correlation functions we find that the correlation function is nearly center-of-mass energy independent. The geometry dependence of the correlation function leads to an enhancement of near- and away-side correlations for the tip-on-tip U + U collisions when compared with side-on-side U + U collisions, an exactly opposite behavior from the correlations generated by the elliptic flow of the quark–gluon plasma
The strongly coupled quark-gluon plasma created at RHIC
International Nuclear Information System (INIS)
Heinz, Ulrich
2009-01-01
The relativistic heavy-ion collider (RHIC) was built to re-create and study in the laboratory the extremely hot and dense matter that filled our entire universe during its first few microseconds. Its operation since June 2000 has been extremely successful, and the four large RHIC experiments have produced an impressive body of data which indeed provide compelling evidence for the formation of thermally equilibrated matter at unprecedented temperatures and energy densities-a 'quark-gluon plasma (QGP)'. A surprise has been the discovery that this plasma behaves like an almost perfect fluid, with extremely low viscosity. Theorists had expected a weakly interacting gas of quarks and gluons, but instead we seem to have created a strongly coupled plasma liquid. The experimental evidence strongly relies on a feature called 'elliptic flow' in off-central collisions, with additional support from other observations. This paper explains how we probe the strongly coupled QGP, describes the ideas and measurements which led to the conclusion that the QGP is an almost perfect liquid, and shows how they tie relativistic heavy-ion physics into other burgeoning fields of modern physics, such as strongly coupled Coulomb plasmas, ultracold systems of trapped atoms and superstring theory
Chemical Evolution of Strongly Interacting Quark-Gluon Plasma
International Nuclear Information System (INIS)
Pan, Ying-Hua; Zhang, Wei-Ning
2014-01-01
At very initial stage of relativistic heavy ion collisions a wave of quark-gluon matter is produced from the break-up of the strong color electric field and then thermalizes at a short time scale (~1 fm/c). However, the quark-gluon plasma (QGP) system is far out of chemical equilibrium, especially for the heavy quarks which are supposed to reach chemical equilibrium much late. In this paper a continuing quark production picture for strongly interacting QGP system is derived, using the quark number susceptibilities and the equation of state; both of them are from the results calculated by the Wuppertal-Budapest lattice QCD collaboration. We find that the densities of light quarks increase by 75% from the temperature T=400 MeV to T=150 MeV, while the density of strange quark annihilates by 18% in the temperature region. We also offer a discussion on how this late production of quarks affects the final charge-charge correlations
Certain exclusive processes in QCD taking into account two-gluon states
International Nuclear Information System (INIS)
Baier, V.N.; Grozin, A.G.
1982-01-01
The wave functions and evolution equations for mesons are classified completely taking into account two-gluon states and then are compared to the Altarelli-Parisi evolution equations. The form factors of completely neutral mesons and the probabilities for exclusive decays of quarkonium states are found taking into account two-gluon states
Multiplicity distributions of gluon and quark jets and a test of QCD analytic calculations
International Nuclear Information System (INIS)
Gary, J. William
1999-01-01
Gluon jets are identified in e + e - hadronic annihilation events by tagging two quark jets in the same hemisphere of an event. The gluon jet is defined inclusively as all the particles in the opposite hemisphere. Gluon jets defined in this manner have a close correspondence to gluon jets as they are defined for analytic calculations, and are almost independent of a jet finding algorithm. The mean and first few higher moments of the gluon jet charged particle multiplicity distribution are compared to the analogous results found for light quark (uds) jets, also defined inclusively. Large differences are observed between the mean, skew and curtosis values of the gluon and quark jets, but not between their dispersions. The cumulant factorial moments of the distributions are also measured, and are used to test the predictions of QCD analytic calculations. A calculation which includes next-to-next-to-leading order corrections and energy conservation is observed to provide a much improved description of the separated gluon and quark jet cumulant moments compared to a next-to-leading order calculation without energy conservation. There is good quantitative agreement between the data and calculations for the ratios of the cumulant moments between gluon and quark jets. The data sample used is the LEP-1 sample of the OPAL experiment at LEP
Multiplicity distributions of gluon and quark jets and a test of QCD analytic calculations
Energy Technology Data Exchange (ETDEWEB)
Gary, J. William
1999-03-01
Gluon jets are identified in e{sup +}e{sup -} hadronic annihilation events by tagging two quark jets in the same hemisphere of an event. The gluon jet is defined inclusively as all the particles in the opposite hemisphere. Gluon jets defined in this manner have a close correspondence to gluon jets as they are defined for analytic calculations, and are almost independent of a jet finding algorithm. The mean and first few higher moments of the gluon jet charged particle multiplicity distribution are compared to the analogous results found for light quark (uds) jets, also defined inclusively. Large differences are observed between the mean, skew and curtosis values of the gluon and quark jets, but not between their dispersions. The cumulant factorial moments of the distributions are also measured, and are used to test the predictions of QCD analytic calculations. A calculation which includes next-to-next-to-leading order corrections and energy conservation is observed to provide a much improved description of the separated gluon and quark jet cumulant moments compared to a next-to-leading order calculation without energy conservation. There is good quantitative agreement between the data and calculations for the ratios of the cumulant moments between gluon and quark jets. The data sample used is the LEP-1 sample of the OPAL experiment at LEP.
Multiplicity distributions of gluon and quark jets and a test of QCD analytic calculations
Energy Technology Data Exchange (ETDEWEB)
Gary, J.W. [California Univ., Riverside, CA (United States). Dept. of Physics
1999-03-01
Gluon jets are identified in e{sup +}e{sup -} hadronic annihilation events by tagging two quark jets in the same hemisphere of an event. The gluon jet is defined inclusively as all the particles in the opposite hemisphere. Gluon jets defined in this manner have a close correspondence to gluon jets as they are defined for analytic calculations, and are almost independent of a jet finding algorithm. The mean and first few higher moments of the gluon jet charged particle multiplicity distribution are compared to the analogous results found for light quark (uds) jets, also defined inclusively. Large differences are observed between the mean, skew and curtosis values of the gluon and quark jets, but not between their dispersions. The cumulant factorial moments of the distributions are also measured, and are used to test the predictions of QCD analytic calculations. A calculation which includes next-to-next-to-leading order corrections and energy conservation is observed to provide a much improved description of the separated gluon and quark jet cumulant moments compared to a next-to-leading order calculation without energy conservation. There is good quantitative agreement between the data and calculations for the ratios of the cumulant moments between gluon and quark jets. The data sample used is the LEP-1 sample of the OPAL experiment at LEP. (orig.) 6 refs.
Multiplicity distributions of gluon and quark jets and a test of QCD analytic calculations
International Nuclear Information System (INIS)
Gary, J.W.
1999-01-01
Gluon jets are identified in e + e - hadronic annihilation events by tagging two quark jets in the same hemisphere of an event. The gluon jet is defined inclusively as all the particles in the opposite hemisphere. Gluon jets defined in this manner have a close correspondence to gluon jets as they are defined for analytic calculations, and are almost independent of a jet finding algorithm. The mean and first few higher moments of the gluon jet charged particle multiplicity distribution are compared to the analogous results found for light quark (uds) jets, also defined inclusively. Large differences are observed between the mean, skew and curtosis values of the gluon and quark jets, but not between their dispersions. The cumulant factorial moments of the distributions are also measured, and are used to test the predictions of QCD analytic calculations. A calculation which includes next-to-next-to-leading order corrections and energy conservation is observed to provide a much improved description of the separated gluon and quark jet cumulant moments compared to a next-to-leading order calculation without energy conservation. There is good quantitative agreement between the data and calculations for the ratios of the cumulant moments between gluon and quark jets. The data sample used is the LEP-1 sample of the OPAL experiment at LEP. (orig.)
Multiplicity distributions of gluon and quark jets and a test of QCD analytic calculations
Gary, J. William
1999-03-01
Gluon jets are identified in e +e - hadronic annihilation events by tagging two quark jets in the same hemisphere of an event. The gluon jet is defined inclusively as all the particles in the opposite hemisphere. Gluon hets defined in this manner have a close correspondence to gluon jets as they are defined for analytic calculations, and are almost independent of a jet finding algorithm. The mean and first few higher moments of the gluon jet charged particle multiplicity distribution are compared to the analogous results found for light quark (uds) jets, also defined inclusively. Large differences are observed between the mean, skew and curtosis values of the gluon and quark jets, but not between their dispersions. The cumulant factorial moments of the distributions are also measured, and are used to test the predictions of QCD analytic calculations. A calculation which includes next-to-next-to-leading order corrections and energy conservation is observed to provide a much improved description of the separated gluon and quark jet cumulant moments compared to a next-to-leading order calculation without energy conservation. There is good quantitative agreement between the data and calculations for the ratios of the cumulant moments between gluon and quark jets. The data sample used is the LEP-1 sample of the OPAL experiment at LEP.
A solution of the DGLAP equation for gluon at low x
Indian Academy of Sciences (India)
We obtain a solution of the DGLAP equation for the gluon at low ﬁrst by expanding the gluon in a Taylor series and then using the method of characteristics. We test its validity by comparing it with that of Glück, Reya and Vogt. The convergence criteria of the approximation used are also discussed. We also calculate ...
A solution of the DGLAP equation for gluon at low x
Indian Academy of Sciences (India)
Using (43) we will estimate the logarithmic slope of the structure function from the proposed gluon distribution at several points of expansion and compare with data [19] at. Q2 =20 GeV2 where the data on the slope are available. 3. Results and discussion. In the present paper, we have obtained a new description of gluon ...
Low-energy behavior of gluons and gravitons from gauge invariance
DEFF Research Database (Denmark)
di Vecchia, Paolo; Bern, Zvi; Davies, Scott
2014-01-01
We show that at tree level, on-shell gauge invariance can be used to fully determine the first subleading soft-gluon behavior and the first two subleading soft-graviton behaviors. Our proofs of the behaviors for n-gluon and n-graviton tree amplitudes are valid in D dimensions and are similar to Low...
Gluon structure function for deeply inelastic scattering with nucleus in QCD
Energy Technology Data Exchange (ETDEWEB)
Ayala Filho, Alvaro L; Ducati, M.B. Gay [Rio Grande do Sul Univ., Porto Alegre, RS (Brazil). Inst. de Fisica; Levin, Eugene [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); [Petersburg Nuclear Physics Institute, Gatchina (Russian Federation). Theory Dept.
1995-06-01
In this talk we present the first calculation of the gluon structure function for nucleus in QCD. We discuss the Glauber formula for the gluon structure function and the violation of this simple approach that we anticipate in QCD. (author). 10 refs, 4 figs.
A two-loop four-gluon helicity amplitude in QCD
Energy Technology Data Exchange (ETDEWEB)
Dixon, L.
2000-01-06
The authors present the two-loop pure gauge contribution to the gluon-gluon scattering amplitude with maximal helicity violation. The construction of the amplitude does not rely directly on Feynman diagrams, but instead uses its analytic properties 4--2{epsilon} dimensions. The authors evaluate the loop integrals appearing in the amplitude through order({epsilon}{sup 0})in terms of polylogarithms.
Dilepton production from quark gluon plasma using non-equilibrium thermodynamics
International Nuclear Information System (INIS)
Sinha, B.
1984-01-01
The importance of the approach phase to the thermodynamic equilibrium has been investigated for dilepton production from quark-gluon plasma - an effective temperature for the quarks as Brounian particle in a heat bath of gluons has been suggested. The spectrum for low invariant mass is, as a consequence, sharper
Introduction to quantum chromo transport theory for quark-gluon plasmas
International Nuclear Information System (INIS)
Gyulassy, M.; Elze, H.Th.; Iwazaki, A.; Vasak, D.
1986-08-01
Upcoming heavy ion experiments at the AGS and SPS are aimed at producing and diagnosing a primordial form of matter, the quark-gluon plasma. In these lectures some recent developments on formulating a quantum transport theory for quark-gluon plasmas are introduced. 46 refs
Flavour equilibration studies of quark-gluon plasma with non-zero ...
Indian Academy of Sciences (India)
Abstract. Flavour equilibration for a thermally equilibrated but chemically non- equilibrated quark-gluon plasma is presented. Flavour equilibration is studied enforcing baryon number conservation. In addition to the usual processes like single additional gluon production gg ⇌ ggg and its reverse and quark–antiquark pair ...
QCD sum rules for the gluon component of the U(1)sub(A) pseudoscalar meson
International Nuclear Information System (INIS)
Narison, S.; Centre National de la Recherche Scientifique, 13 - Marseille
1981-01-01
Using sum rules based on the positivity and the analyticity of the U(1)sub(A) spectral functions, and within the framework of QCD (quantum chromodynamics), we derive an upper bound Msub(p) approximately less than (0.6 approximately 0.75) GeV to the gluon component of the U(1)sub(A) meson mass. Such a bound could be identified as the exact value of Msub(p) if one accepts a QCD model for the ''continuum'' contribution to the U(1)sub(A) spectral functions. Comparing our result to the observed mass Msub(eta)' approximately equal to 0.96GeV, one could expect an important gluonic contribution to the eta'-mass. This experimental result could be reproduced, if one adds to our result, the quark contribution known to be Msub(q) approximately equal to root(3)msub(π). (author)
The quark gluon plasma equation of state and the expansion of the early Universe
International Nuclear Information System (INIS)
Sanches, S.M.; Navarra, F.S.; Fogaça, D.A.
2015-01-01
Our knowledge of the equation of state of the quark gluon plasma has been continuously growing due to the experimental results from heavy ion collisions, due to recent astrophysical measurements and also due to the advances in lattice QCD calculations. The new findings about this state may have consequences on the time evolution of the early Universe, which can be estimated by solving the Friedmann equations. The solutions of these equations give the time evolution of the energy density and also of the temperature in the beginning of the Universe. In this work we compute the time evolution of the QGP in the early Universe, comparing several equations of state, some of them based on the MIT bag model (and on its variants) and some of them based on lattice QCD calculations. Among other things, we investigate the effects of a finite baryon chemical potential in the evolution of the early Universe
Towards the dynamical study of heavy-flavor quarks in the Quark-Gluon-Plasma
International Nuclear Information System (INIS)
Berrehrah, H; Bratkovskaya, E; Cassing, W; Gossiaux, P B; Aichelin, J
2014-01-01
Within the aim of a dynamical study of on- and off-shell heavy quarks Q in the quark gluon plasma (QGP) – as produced in relativistic nucleus-nucleus collisions – we study the heavy quark collisional scattering on partons of the QGP. The elastic cross sections σ q,g−Q are evaluated for perturbative partons (massless on-shell particles) and for dynamical quasi-particles (massive off-shell particles as described by the dynamical quasi-particles model D QPM ) using the leading order Born diagrams. We demonstrate that the finite width of the quasi-particles in the DQPM has little influence on the cross sections σ q,g−Q except close to thresholds. We, furthermore, calculate the heavy quark relaxation time as a function of temperature T within the different approaches using these cross sections
Measurements of the structure of quark and gluon jets in hadronic Z decays
Barate, R; Décamp, D; Ghez, P; Goy, C; Lees, J P; Lucotte, A; Merle, E; Minard, M N; Nief, J Y; Pietrzyk, B; Alemany, R; Boix, G; Casado, M P; Chmeissani, M; Crespo, J M; Delfino, M C; Fernández, E; Fernández-Bosman, M; Garrido, L; Graugès-Pous, E; Juste, A; Martínez, M; Merino, G; Miquel, R; Mir, L M; Park, I C; Pascual, A; Perlas, J A; Riu, I; Sánchez, F; Colaleo, A; Creanza, D; De Palma, M; Gelao, G; Iaselli, Giuseppe; Maggi, G; Maggi, M; Nuzzo, S; Ranieri, A; Raso, G; Ruggieri, F; Selvaggi, G; Silvestris, L; Tempesta, P; Tricomi, A; Zito, G; Huang, X; Lin, J; Ouyang, Q; Wang, T; Xie, Y; Xu, R; Xue, S; Zhang, J; Zhang, L; Zhao, W; Abbaneo, D; Becker, U; Bright-Thomas, P G; Casper, David William; Cattaneo, M; Ciulli, V; Dissertori, G; Drevermann, H; Forty, Roger W; Frank, M; Hagelberg, R; Hansen, J B; Harvey, J; Janot, P; Jost, B; Lehraus, Ivan; Mato, P; Minten, Adolf G; Moneta, L; Pacheco, A; Pusztaszeri, J F; Ranjard, F; Rolandi, Luigi; Rousseau, D; Schlatter, W D; Schmitt, M; Schneider, O; Tejessy, W; Teubert, F; Tomalin, I R; Wachsmuth, H W; Wagner, A; Ajaltouni, Ziad J; Badaud, F; Chazelle, G; Deschamps, O; Falvard, A; Ferdi, C; Gay, P; Guicheney, C; Henrard, P; Jousset, J; Michel, B; Monteil, S; Montret, J C; Pallin, D; Perret, P; Podlyski, F; Proriol, J; Rosnet, P; Hansen, J D; Hansen, J R; Hansen, P H; Nilsson, B S; Rensch, B; Wäänänen, A; Daskalakis, G; Kyriakis, A; Markou, C; Simopoulou, Errietta; Siotis, I; Vayaki, Anna; Blondel, A; Bonneaud, G R; Brient, J C; Bourdon, P; Rougé, A; Rumpf, M; Valassi, Andrea; Verderi, M; Videau, H L; Focardi, E; Parrini, G; Zachariadou, K; Corden, M; Georgiopoulos, C H; Jaffe, D E; Antonelli, A; Bencivenni, G; Bologna, G; Bossi, F; Campana, P; Capon, G; Cerutti, F; Chiarella, V; Felici, G; Laurelli, P; Mannocchi, G; Murtas, F; Murtas, G P; Passalacqua, L; Pepé-Altarelli, M; Curtis, L; Halley, A W; Lynch, J G; Negus, P; O'Shea, V; Raine, C; Scarr, J M; Smith, K; Teixeira-Dias, P; Thompson, A S; Thomson, E; Buchmüller, O L; Dhamotharan, S; Geweniger, C; Graefe, G; Hanke, P; Hansper, G; Hepp, V; Kluge, E E; Putzer, A; Sommer, J; Tittel, K; Werner, S; Wunsch, M; Beuselinck, R; Binnie, David M; Cameron, W; Dornan, Peter J; Girone, M; Goodsir, S M; Martin, E B; Marinelli, N; Moutoussi, A; Nash, J; Sedgbeer, J K; Spagnolo, P; Williams, M D; Ghete, V M; Girtler, P; Kneringer, E; Kuhn, D; Rudolph, G; Betteridge, A P; Bowdery, C K; Buck, P G; Colrain, P; Crawford, G; Finch, A J; Foster, F; Hughes, G; Jones, R W L; Williams, M I; Giehl, I; Greene, A M; Hoffmann, C; Jakobs, K; Kleinknecht, K; Quast, G; Renk, B; Rohne, E; Sander, H G; Van Gemmeren, P; Zeitnitz, C; Aubert, Jean-Jacques; Benchouk, C; Bonissent, A; Bujosa, G; Carr, J; Coyle, P; Etienne, F; Leroy, O; Motsch, F; Payre, P; Talby, M; Sadouki, A; Thulasidas, M; Trabelsi, K; Aleppo, M; Antonelli, M; Ragusa, F; Berlich, R; Blum, Walter; Büscher, V; Dietl, H; Ganis, G; Kroha, H; Lütjens, G; Mannert, C; Männer, W; Moser, H G; Schael, S; Settles, Ronald; Seywerd, H C J; Stenzel, H; Wiedenmann, W; Wolf, G; Boucrot, J; Callot, O; Chen, S; Cordier, A; Davier, M; Duflot, L; Grivaz, J F; Heusse, P; Höcker, A; Jacholkowska, A; Kim, D W; Le Diberder, F R; Lefrançois, J; Lutz, A M; Schune, M H; Tournefier, E; Veillet, J J; Videau, I; Zerwas, D; Azzurri, P; Bagliesi, G; Batignani, G; Bettarini, S; Boccali, T; Bozzi, C; Calderini, G; Carpinelli, M; Ciocci, M A; Dell'Orso, R; Fantechi, R; Ferrante, I; Foà, L; Forti, F; Giassi, A; Giorgi, M A; Gregorio, A; Ligabue, F; Lusiani, A; Marrocchesi, P S; Messineo, A; Palla, Fabrizio; Rizzo, G; Sanguinetti, G; Sciabà, A; Tenchini, Roberto; Tonelli, G; Vannini, C; Venturi, A; Verdini, P G; Blair, G A; Bryant, L M; Chambers, J T; Green, M G; Medcalf, T; Perrodo, P; Strong, J A; Von Wimmersperg-Töller, J H; Botterill, David R; Clifft, R W; Edgecock, T R; Haywood, S; Norton, P R; Thompson, J C; Wright, A E; Bloch-Devaux, B; Colas, P; Emery, S; Kozanecki, Witold; Lançon, E; Lemaire, M C; Locci, E; Pérez, P; Rander, J; Renardy, J F; Roussarie, A; Schuller, J P; Schwindling, J; Trabelsi, A; Vallage, B; Black, S N; Dann, J H; Johnson, R P; Kim, H Y; Konstantinidis, N P; Litke, A M; McNeil, M A; Taylor, G; Booth, C N; Brew, C A J; Cartwright, S L; Combley, F; Kelly, M S; Lehto, M H; Reeve, J; Thompson, L F; Affholderbach, K; Böhrer, A; Brandt, S; Cowan, G D; Grupen, Claus; Saraiva, P; Smolik, L; Stephan, F; Apollonio, M; Bosisio, L; Della Marina, R; Giannini, G; Gobbo, B; Musolino, G; Rothberg, J E; Wasserbaech, S R; Armstrong, S R; Charles, E; Elmer, P; Ferguson, D P S; Gao, Y; González, S; Greening, T C; Hayes, O J; Hu, H; Jin, S; McNamara, P A; Nachtman, J M; Nielsen, J; Orejudos, W; Pan, Y B; Saadi, Y; Scott, I J; Walsh, J; Wu Sau Lan; Wu, X; Zobernig, G
2000-01-01
An experimental investigation of the structure of identified quark and gluon jets is presented. Observables related to both the global and internal structure of jets are measured; this allows for tests of QCD over a wide range of transverse momentum scales. The observables include distributions of jet-shape variables, the mean and standard deviation of the subjet multiplicity distribution and the fragmentation function for charged particles. The data are compared with predictions of perturbative QCD as well as QCD-based Monte Carlo models. In certain kinematic regions the measurements are sensitive mainly to perturbatively calculable effects, allowing for a test of QCD. The comparisons are also extended into regions where nonperturbative effects become large, and in this way the transition from hard to soft QCD is investigated. It is found that by including leading and next-to-leading logarithmic contributions in the QCD predictions, the agreement with the data can be extended to lower transverse momentum sca...
Gluon bremstrahlung effects in large P/sub perpendicular/ hadron-hadron scattering
International Nuclear Information System (INIS)
Fox, G.C.; Kelly, R.L.
1982-02-01
We consider effects of parton (primarily gluon) bremstrahlung in the initial and final states of high transverse momentum hadron-hadron scattering. Monte Carlo calculations based on conventional QCD parton branching and scattering processes are presented. The calculations are carried only to the parton level in the final state. We apply the model to the Drell-Yan process and to high transverse momentum hadron-hadron scattering triggered with a large aperture calorimeter. We show that the latter triggers are biased in that they select events with unusually large bremstrahlung effects. We suggest that this trigger bias explains the large cross section and non-coplanar events observed in the NA5 experiment at the SPS
Equation of state and viscosities from a gravity dual of the gluon plasma
Directory of Open Access Journals (Sweden)
R. Yaresko
2015-07-01
Full Text Available Employing new precision data of the equation of state of the SU(3 Yang–Mills theory (gluon plasma the dilaton potential of a gravity-dual model is adjusted in the temperature range (1–10Tc within a bottom-up approach. The ratio of bulk viscosity to shear viscosity follows then as ζ/η≈πΔvs2 for Δvs2<0.2 and achieves a maximum value of 0.94 at Δvs2≈0.3, where Δvs2≡1/3−vs2 is the non-conformality measure and vs2 is the velocity of sound squared, while the ratio of shear viscosity to entropy density is known as (4π−1 for the considered set-up with Hilbert action on the gravity side.
Regularization of the light-cone gauge gluon propagator singularities using sub-gauge conditions
Energy Technology Data Exchange (ETDEWEB)
Chirilli, Giovanni A.; Kovchegov, Yuri V.; Wertepny, Douglas E. [Department of Physics, The Ohio State University,191 W Woodruff Ave, Columbus, OH 43210 (United States)
2015-12-21
Perturbative QCD calculations in the light-cone gauge have long suffered from the ambiguity associated with the regularization of the poles in the gluon propagator. In this work we study sub-gauge conditions within the light-cone gauge corresponding to several known ways of regulating the gluon propagator. Using the functional integral calculation of the gluon propagator, we rederive the known sub-gauge conditions for the θ-function gauges and identify the sub-gauge condition for the principal value (PV) regularization of the gluon propagator’s light-cone poles. The obtained sub-gauge condition for the PV case is further verified by a sample calculation of the classical Yang-Mills field of two collinear ultrarelativistic point color charges. Our method does not allow one to construct a sub-gauge condition corresponding to the well-known Mandelstam-Leibbrandt prescription for regulating the gluon propagator poles.
Forward gluon production in hadron-hadron scattering with Pomeron loops
International Nuclear Information System (INIS)
Iancu, E.
2006-01-01
We discuss new physical phenomena expected in particle production in hadron-hadron collisions at high energy, as a consequence of Pomerons loop effects in the evolution equations for the Color Glass Condensate. We focus on gluon production in asymmetric, 'dilute-dense', collisions: a dilute projectile scatters off a dense hadronic target, whose gluon distribution is highly evolved. This situation is representative for particle production in proton-proton collisions at forward rapidities (say, at LHC) and admits a dipole factorization similar to that of deep inelastic scattering (DIS). We show that at sufficiently large forward rapidities, where the Pomerons loop effects become important in the evolution of the target wavefunction, gluon production is dominated by 'black spots' (saturated gluon configurations) up to very large values of the transverse momentum, well above the average saturation momentum in the target. In this regime, the produced gluon spectrum exhibits diffusive scaling, so like DIS at sufficiently high energy. (authors)
Quark and gluon jet properties in symmetric three-jet events
Buskulic, D.; Casper, D.; de Bonis, I.; Decamp, D.; Ghez, P.; Goy, C.; Lees, J.-P.; Lucotte, A.; Minard, M.-N.; Odier, P.; Pietrzyk, B.; Chmeissani, M.; Crespo, J. M.; Efthymiopoulos, I.; Fernandez, E.; Fernandez-Bosman, M.; Garrido, Ll.; Juste, A.; Martinez, M.; Orteu, S.; Pacheco, A.; Padilla, C.; Palla, F.; Pascual, A.; Perlas, J. A.; Riu, I.; Sanchez, F.; Teubert, F.; Colaleo, A.; Creanza, D.; de Palma, M.; Farilla, A.; Gelao, G.; Girone, M.; Iaselli, G.; Maggi, G.; Maggi, M.; Marinelli, N.; Natali, S.; Nuzzo, S.; Ranieri, A.; Raso, G.; Romano, F.; Ruggieri, F.; Selvaggi, G.; Silvestris, L.; Tempesta, P.; Zito, G.; Huang, X.; Lin, J.; Ouyang, Q.; Wang, T.; Xie, Y.; Xu, R.; Xue, S.; Zhang, J.; Zhang, L.; Zhao, W.; Alemany, R.; Bazarko, A. O.; Bonvicini, G.; Cattaneo, M.; Comas, P.; Coyle, P.; Drevermann, H.; Forty, R. W.; Frank, M.; Hagelberg, R.; Harvey, J.; Jacobsen, R.; Janot, P.; Jost, B.; Kneringer, E.; Knobloch, J.; Lehraus, I.; Martin, E. B.; Mato, P.; Minten, A.; Miquel, R.; Mir, Ll. M.; Moneta, L.; Oest, T.; Palazzi, P.; Pater, J. R.; Pusztaszeri, J.-F.; Ranjard, F.; Rensing, P.; Rolandi, L.; Schlatter, D.; Schmelling, M.; Schneider, O.; Tejessy, W.; Tomalin, I. R.; Venturi, A.; Wachsmuth, H.; Wildish, T.; Witzeling, W.; Wotschack, J.; Ajaltouni, Z.; Barrès, A.; Boyer, C.; Falvard, A.; Gay, P.; Guicheney, C.; Henrard, P.; Jousset, J.; Michel, B.; Monteil, S.; Montret, J.-C.; Pallin, D.; Perret, P.; Podlyski, F.; Proriol, J.; Rossignol, J.-M.; Fearnley, T.; Hansen, J. B.; Hansen, J. D.; Hansen, J. R.; Hansen, P. H.; Nilsson, B. S.; Wäänänen, A.; Kyriakis, A.; Markou, C.; Simopoulou, E.; Siotis, I.; Vayaki, A.; Zachariadou, K.; Blondel, A.; Bonneaud, G.; Brient, J. C.; Bourdon, P.; Rougé, A.; Rumpf, M.; Tanaka, R.; Valassi, A.; Verderi, M.; Videau, H.; Candlin, D. J.; Parsons, M. I.; Focardi, E.; Parrini, G.; Corden, M.; Delfino, M.; Georgiopoulos, C.; Jaffe, D. E.; Antonelli, A.; Bencivenni, G.; Bologna, G.; Bossi, F.; Campana, P.; Capon, G.; Chiarella, V.; Felici, G.; Laurelli, P.; Mannocchi, G.; Murtas, F.; Murtas, G. P.; Passalacqua, L.; Pepe-Altarelli, M.; Curtis, L.; Dorris, S. J.; Halley, A. W.; Knowles, I. G.; Lynch, J. G.; O'Shea, V.; Raine, C.; Reeves, P.; Scarr, J. M.; Smith, K.; Thompson, A. S.; Thomson, F.; Thorn, S.; Turnbull, R. M.; Becker, U.; Braun, O.; Geweniger, C.; Graefe, G.; Hanke, P.; Hepp, V.; Kluge, E. E.; Putzer, A.; Rensch, B.; Schmidt, M.; Sommer, J.; Stenzel, H.; Tittel, K.; Werner, S.; Wunsch, M.; Abbaneo, D.; Beuselinck, R.; Binnie, D. M.; Cameron, W.; Colling, D. J.; Dornan, P. J.; Moutoussi, A.; Nash, J.; San Martin, G.; Sedgbeer, J. K.; Stacey, A. M.; Dissertori, G.; Girtler, P.; Kuhn, D.; Rudolph, G.; Bowdery, C. K.; Brodbeck, T. J.; Colrain, P.; Crawford, G.; Finch, A. J.; Foster, F.; Hughes, G.; Sloan, T.; Whelan, E. P.; Williams, M. I.; Galla, A.; Greene, A. M.; Kleinknecht, K.; Quast, G.; Renk, B.; Rohne, E.; Sander, H.-G.; van Gemmeren, P.; Zeitnitz, C.; Aubert, J. J.; Bencheikh, A. M.; Benchouk, C.; Bonissent, A.; Bujosa, G.; Calvet, D.; Carr, J.; Diaconu, C.; Etienne, F.; Konstantinidis, N.; Nicod, D.; Payre, P.; Rousseau, D.; Talby, M.; Sadouki, A.; Thulasidas, M.; Trabelsi, K.; Abt, I.; Assmann, R.; Bauer, C.; Blum, W.; Brown, D.; Dietl, H.; Dydak, F.; Ganis, G.; Gotzhein, C.; Jakobs, K.; Kroha, H.; Lütjens, G.; Lutz, G.; Männer, W.; Moser, H.-G.; Richter, R.; Rosado-Schlosser, A.; Schael, S.; Settles, R.; Seywerd, H.; Denis, R. St.; Wiedenmann, W.; Wolf, G.; Boucrot, J.; Callot, O.; Cordier, A.; Davier, M.; Duflot, L.; Grivaz, J.-F.; Heusse, Ph.; Jacquet, M.; Kim, D. W.; Le Diberder, F.; Lefrançois, J.; Lutz, A.-M.; Nikolic, I.; Park, H. J.; Park, I. C.; Schune, M.-H.; Simion, S.; Veillet, J.-J.; Videau, I.; Azzurri, P.; Bagliesi, G.; Batignani, G.; Bettarini, S.; Bozzi, C.; Calderini, G.; Carpinelli, M.; Ciocci, M. A.; Ciulli, V.; Dell'Orso, R.; Fantechi, R.; Ferrante, I.; Foà, L.; Forti, F.; Giassi, A.; Giorgi, M. A.; Gregorio, A.; Ligabue, F.; Lusiani, A.; Marrocchesi, P. S.; Messineo, A.; Rizzo, G.; Sanguinetti, G.; Sciabà, A.; Spagnolo, P.; Steinberger, J.; Tenchini, R.; Tonelli, G.; Vannini, C.; Verdini, P. G.; Walsh, J.; Betteridge, A. P.; Blair, G. A.; Bryant, L. M.; Cerutti, F.; Chambers, J. T.; Gao, Y.; Green, M. G.; Johnson, D. L.; Medcalf, T.; Perrodo, P.; Strong, J. A.; von Wimmersperg-Toeller, J. H.; Botterill, D. R.; Clifft, R. W.; Edgecock, T. R.; Haywood, S.; Edwards, M.; Maley, P.; Norton, P. R.; Thompson, J. C.; Bloch-Devaux, B.; Colas, P.; Emery, S.; Kozanecki, W.; Lançon, E.; Lemaire, M. C.; Locci, E.; Marx, B.; Perez, P.; Rander, J.; Renardy, J.-F.; Roussarie, A.; Schuller, J.-P.; Schwindling, J.; Trabelsi, A.; Vallage, B.; Johnson, R. P.; Kim, H. Y.; Litke, A. M.; McNeil, M. A.; Taylor, G.; Beddall, A.; Booth, C. N.; Boswell, R.; Brew, C. A. J.; Cartwright, S.; Combley, F.; Koksal, A.; Letho, M.; Newton, W. M.; Rankin, C.; Reeve, J.; Thompson, L. F.; Böhrer, A.; Brandt, S.; Cowan, G.; Feigl, E.; Grupen, C.; Lutters, G.; Minguet-Rodriguez, J.; Rivera, F.; Saraiva, P.; Smolik, L.; Stephan, F.; Apollonio, M.; Bosisio, L.; Della Marina, R.; Giannini, G.; Gobbo, B.; Musolino, G.; Ragusa, F.; Rothberg, J.; Wasserbaech, S.; Armstrong, S. R.; Bellantoni, L.; Elmer, P.; Feng, Z.; Ferguson, D. P. S.; Gao, Y. S.; González, S.; Grahl, J.; Greening, T. C.; Harton, J. L.; Hayes, O. J.; Hu, H.; McNamara, P. A.; Nachtman, J. M.; Orejudos, W.; Pan, Y. B.; Saadi, Y.; Schmitt, M.; Scott, I. J.; Sharma, V.; Turk, J. D.; Walsh, A. M.; Wu, Sau Lan; Wu, X.; Yamartino, J. M.; Zheng, M.; Zobernig, G.; Aleph Collaboration
1996-02-01
Quark and gluon jets with the same energy, 24 GeV, are compared in symmetric three-jet configurations from hadronic Z decays observed by the ALEPH detector. Jets are defined using the Durham algorithm. Gluon jets are identified using an anti-tag on b jets, based on a track impact parameter method. The comparison of gluon and mixed flavour quark jets shows that gluon jets have a softer fragmentation function, a larger angular width and a higher particle multiplicity, Evidence is presented which shows that the corresponding differences between gluon and b jets are significantly smaller. In a statistically limited comparison the multiplicity in c jets was found to be comparable with that observed for the jets of mixed quark flavour.
Godbole, Rohini M.; Kaushik, Abhiram; Misra, Anuradha
2018-04-01
We study the low-virtuality inclusive leptoproduction of open charm, p↑l →D0+X as a probe of the gluon Sivers function. We perform the analysis in a generalized parton model framework. At leading order, this process is sensitive only to the gluon content of the proton. Hence any detection of a transverse single-spin asymmetry in this process would be clear indication of a non-zero gluon Sivers function (GSF). Considering COMPASS and a future Electron-Ion Collider (EIC), we present predictions for asymmetry using fits for the GSF available in literature. Predictions for peak asymmetry values lie in the range of 0.8% to 13%. We also present estimates of the upper bound on the asymmetry as obtained with a maximal gluon Sivers function. Further, for the case of the Electron-Ion Collider, we evaluate the asymmetry in the muons decaying from the D -meson and find that the asymmetry is well preserved in the kinematics of the muons. Peak values of the muon asymmetry are close to those obtained for the D -meson and lie in the range 0.75% to 11%.
Thermal radiation from an evolving viscous quark gluon plasma
International Nuclear Information System (INIS)
Mitra, Sukanya; Mohanty, Payal; Sarkar, Sourav; Alam, Jan-E
2013-01-01
The effects of viscosity on the space-time evolution of quark gluon plasma produced in nuclear collisions at relativistic heavy ion collider energies have been studied. The entropy generated due to the viscous motion of the fluid has been taken into account in constraining the initial temperature by the final multiplicity (measured at the freeze-out point). The viscous effects on the photon spectra has been introduced consistently through the evolution dynamics and phase space factors of all the participating partons/hadrons in the production process. In contrast to some of the recent calculations the present work includes the contribution from the hadronic phase. A small change in the transverse momentum (p T ) distribution of photons is observed due to viscous effects. (author)
Hadronic interactions from effective chiral Lagrangians of quarks and gluons
International Nuclear Information System (INIS)
Krein, G.
1996-06-01
We discuss the combined used of the techniques of effective chiral field theory and the field theoretic method known as Fock-Tani representation to derive effective hadron interactions. The Fock-Tani method is based on a change of representation by means of a unitary transformation such that the composite hadrons are redescribed by elementary-particle field operators. Application of the unitary transformation on the microscopic quark-quark interaction derived from a chiral effective Lagrangian leads to chiral effective interactions describing all possible processes involving hadrons and their constituents. The formalism is illustrated by deriving the one-pion-exchange potential between the nucleons using the quark-gluon effective chiral Lagrangian of Manohar and Georgi. We also present the results of a study of the saturation properties of the nuclear matter using this formalism. (author). 9 refs., 2 figs
Magnetic field in expanding quark-gluon plasma
Stewart, Evan; Tuchin, Kirill
2018-04-01
Intense electromagnetic fields are created in the quark-gluon plasma by the external ultrarelativistic valence charges. The time evolution and the strength of this field are strongly affected by the electrical conductivity of the plasma. Yet, it has recently been observed that the effect of the magnetic field on the plasma flow is small. We compute the effect of plasma flow on magnetic field and demonstrate that it is less than 10%. These observations indicate that the plasma hydrodynamics and the dynamics of electromagnetic field decouple. Thus, it is a very good approximation, on the one hand, to study QGP in the background electromagnetic field generated by external sources and, on the other hand, to investigate the dynamics of magnetic field in the background plasma. We also argue that the wake induced by the magnetic field in plasma is negligible.
Strangeness chemical equilibration in a quark-gluon plasma
International Nuclear Information System (INIS)
Letessier, Jean; Rafelski, Johann
2007-01-01
We study, in the dynamically evolving quark-gluon plasma (QGP) fireball formed in relativistic heavy ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC), the growth of strangeness yield toward and beyond the chemical equilibrium. We account for the contribution of the direct strangeness production and evaluate the thermal-QCD strangeness production mechanisms. The specific yield of strangeness per entropy, s/S, is the primary target variable. We explore the effect of collision impact parameter, i.e., fireball size, on kinetic strangeness chemical equilibration in QGP. Insights gained in studying the RHIC data with regard to the dynamics of the fireball are applied to the study of strangeness production at the LHC. We use these results and consider the strange hadron relative particle yields at RHIC and LHC in a systematic fashion. We consider both the dependence on s/S and the direct dependence on the participant number
The search for quark-gluon plasma at E735
International Nuclear Information System (INIS)
Findeisen, Ch.
1989-01-01
The experiment E735 was designed to measure soft p t physics in proton-antiproton interactions at √s=1.8 TeV performed at Fermilab's Tevatron collider. Some ideas related to Quark Gluon Plasma (QGP) are recalled with emphasis on their applications to E735. The experiment E735 measures minimum-bias soft p t events in proton-antiproton interactions at √s=1.8 TeV. One goal of E735 is to search for signs of a deconfined hadronic phase produced in the central region. Some results including particle identified spectra are presented from the first run in 1987. (R.P.) 25 refs.; 13 figs
Collective phenomena in the non-equilibrium quark-gluon plasma
Energy Technology Data Exchange (ETDEWEB)
Schenke, Bjoern Peter
2008-07-03
In this work we study the non-equilibrium dynamics of a quark-gluon plasma, as created in heavy-ion collisions. We investigate how big of a role plasma instabilities can play in the isotropization and equilibration of a quark-gluon plasma. In particular, we determine, among other things, how much collisions between the particles can reduce the growth rate of unstable modes. This is done both in a model calculation using the hard-loop approximation, as well as in a real-time lattice simulation combining both classical Yang-Mills-fields as well as inter-particle collisions. The new extended version of the simulation is also used to investigate jet transport in isotropic media, leading to a cutoff-independent result for the transport coefficient q. The precise determination of such transport coefficients is essential, since they can provide important information about the medium created in heavy ion collisions. In anisotropic media, the effect of instabilities on jet transport is studied, leading to a possible explanation for the experimental observation that high-energy jets traversing the plasma perpendicular to the beam axis experience much stronger broadening in rapidity than in azimuth. The investigation of collective modes in the hard-loop limit is extended to fermionic modes, which are shown to be all stable. Finally, we study the possibility of using high energy photon production as a tool to experimentally determine the anisotropy of the created system. Knowledge of the degree of local momentum-space anisotropy reached in a heavy-ion collision is essential for the study of instabilities and their role for isotropization and thermalization, because their growth rate depends strongly on the anisotropy. (orig.)
Multiplicity distributions of gluon and quark jets and tests of QCD analytic predictions
OPAL Collaboration; Ackerstaff, K.; et al.
Gluon jets are identified in e+e^- hadronic annihilation events by tagging two quark jets in the same hemisphere of an event. The gluon jet is defined inclusively as all the particles in the opposite hemisphere. Gluon jets defined in this manner have a close correspondence to gluon jets as they are defined for analytic calculations, and are almost independent of a jet finding algorithm. The charged particle multiplicity distribution of the gluon jets is presented, and is analyzed for its mean, dispersion, skew, and curtosis values, and for its factorial and cumulant moments. The results are compared to the analogous results found for a sample of light quark (uds) jets, also defined inclusively. We observe differences between the mean, skew and curtosis values of gluon and quark jets, but not between their dispersions. The cumulant moment results are compared to the predictions of QCD analytic calculations. A calculation which includes next-to-next-to-leading order corrections and energy conservation is observed to provide a much improved description of the data compared to a next-to-leading order calculation without energy conservation. There is agreement between the data and calculations for the ratios of the cumulant moments between gluon and quark jets.
Energy Technology Data Exchange (ETDEWEB)
Bondarenko, S.; Prygarin, A. [Ariel University, Physics Department, Ariel (Israel); Lipatov, L. [St. Petersburg Nuclear Physics Institute, Saint Petersburg (Russian Federation); Hamburg University, II Institute of Theoretical Physics, Hamburg (Germany)
2017-08-15
We discuss application of formalism of small-x effective action for reggeized gluons (Gribov, Sov. Phys. JETP 26:414, 1968; Lipatov, Nucl. Phys. B 452:369, 1995; Lipatov, Phys. Rep. 286:131, 1997; Lipatov, Subnucl. Ser. 49:131, 2013; Lipatov, Int. J. Mod. Phys. Conf. Ser. 39:1560082, 2015; Lipatov, Int. J. Mod. Phys. A 31(28/29):1645011, 2016; Lipatov, EPJ Web Conf. 125:01010, 2016; Lipatov, Sov. J. Nucl. Phys. 23:338, 1976; Kuraev et al., Sov. Phys. JETP 45:199, 1977; Kuraev et al., Zh Eksp, Teor. Fiz. 72:377, 1977; Balitsky and Lipatov, Sov. J. Nucl. Phys. 28:822, 1978; Balitsky and Lipatov, Yad. Fiz. 28:1597 1978), for the calculation of classical gluon field of relativistic color charge, similarly to that done in CGC approach of McLerran and Venugopalan, Phys. Rev. D 49:2233 (1994), Jalilian-Marian et al., Phys. Rev. D 55:5414 (1997), Jalilian-Marian et al., Nucl. Phys. B 504:415 (1997), Jalilian-Marian et al., Phys. Rev. D 59:014014 (1998), Jalilian-Marian et al., Phys. Rev. D 59:014015 (1998), Iancu et al., Nucl. Phys. A 692:583 (2001), Iancu et al., Phys. Lett. B 510:133 (2001), Ferreiro et al., Nucl. Phys. A 703:489 (2002). The equations of motion with the reggeon fields are solved in LO and NLO approximations and new solutions are found. The results are compared to the calculations performed in the CGC framework and it is demonstrated that the LO CGC results for the classical field are reproduced in our calculations. Possible applications of the NLO solution in the effective action and CGC frameworks are discussed as well. (orig.)
Two-gluon emission and interference in a thin QCD medium: insights into jet formation
International Nuclear Information System (INIS)
Casalderrey-Solana, Jorge; Pablos, Daniel; Tywoniuk, Konrad
2016-01-01
In heavy-ion collisions, an abundant production of high-energy QCD jets allows to study how these multiparticle sprays are modified as they pass through the quark-gluon plasma. In order to shed new light on this process, we compute the inclusive two-gluon rate off a hard quark propagating through a color deconfined medium at first order in medium opacity. We explicitly impose an energy ordering of the two emitted gluons, such that the “hard” gluon can be thought of as belonging to the jet substructure while the other is a “soft” emission (which can be collinear or medium-induced). Our analysis focusses on two specific limits that clarify the modification of the additional angle- and formation time-ordering of splittings. In one limit, the formation time of the “hard” gluon is short compared to the “soft” gluon formation time, leading to a probabilistic formula for production of and subsequent radiation off a quark-gluon antenna. In the other limit, the ordering of formation is reverted, which automatically leads to the fact that the jet substructure is resolved by the medium. We observe in this case a characteristic delay: the jet radiates as one color current (quark) up to the formation of the “hard” gluon, at which point we observe the onset of radiation of the new color current (gluon). Within our kinematic constraints, our computation supports a picture in which the in-medium jet dynamics are described as a collection of subsequent antennas which are resolved by the medium according to their transverse extent.
Unintegrated gluon distributions in D*± and dijet associated photoproduction at HERA
International Nuclear Information System (INIS)
Lipatov, A.V.; Zotov, N.P.
2006-01-01
We consider the photoproduction of D *± mesons associated with two hadron jets at HERA collider in the framework of the k T -factorization approach. The unintegrated gluon densities in a proton are obtained from the full CCFM, from unified BFKL-DGLAP evolution equations as well as from the Kimber-Martin-Ryskin prescription. Resolved photon contributions are reproduced by the initial-state gluon radiation. We investigate different production rates and make a comparison with the recent experimental data taken by the ZEUS collaboration. Special attention is given to the specific dijet correlations which can provide unique information about non-collinear gluon evolution dynamics. (orig.)
Gluon transport equation with effective mass and dynamical onset of Bose–Einstein condensation
International Nuclear Information System (INIS)
Blaizot, Jean-Paul; Jiang, Yin; Liao, Jinfeng
2016-01-01
We study the transport equation describing a dense system of gluons, in the small scattering angle approximation, taking into account medium-generated effective masses of the gluons. We focus on the case of overpopulated systems that are driven to Bose–Einstein condensation on their way to thermalization. The presence of a mass modifies the dispersion relation of the gluon, as compared to the massless case, but it is shown that this does not change qualitatively the scaling behavior in the vicinity of the onset.
An introduction to quark-gluon plasma and high energy heavy ion collisions
International Nuclear Information System (INIS)
McLerran, L.
1987-01-01
The quark-gluon plasma, and how it might be produced in ultra-relativistic nuclear collisions is reviewed. I briefly introduce the quark-gluon plasma, and what we might learn from studying it. I then discuss what has been learned from the recent results from the CERN oxygen run. I then attempt to address the issue of whether A = 16 and E = 200 GeV are sufficient to make a quark-gluon plasma. I discuss strangeness and charm production as well as electromagnetic probes of the plasma
Probing sea quarks and gluons: the electron-ion collider project
International Nuclear Information System (INIS)
Horn, T.
2014-01-01
A future Electron-Ion Collider (EIC) would be the world's first polarized electron-proton collider, and the world's first e-A collider, and would seek the QCD foundation of nucleons and nuclei in terms of the sea quarks and gluons, matching to these valence quark studies. The EIC will provide a versatile range of kinematics and beam polarization, as well as beam species, to allow for mapping the spin and spatial structure of the quark sea and gluons, to discover the collective effects of gluons in atomic nuclei, and to understand the emergence of hadronic matter from color charge. (authors)
Where and how the quark-gluon matter should be searched for?
International Nuclear Information System (INIS)
Strugalski, Z.
1997-01-01
The experimentally based answers are presented to the questions: 1) Where and how the quark-gluon matter should be searched for? 2) How to create objects of highly excited quark-gluon matter? 3) How to study the phase transitions in excited quark-gluon matter? In the argumentation, experimental information has been used about hadron passages through layers of intranuclear matter, about mechanisms of hadron-nucleus and nucleus-nucleus collisions, and about energy transfer from hadronic projectiles to target nuclei
Vacuum instabilities with a wrong-sign Higgs-gluon-gluon amplitude
Reece, Matthew
2013-04-01
The recently discovered 125 GeV boson appears very similar to a Standard Model (SM) Higgs, but with data favoring an enhanced h → γγ rate. A number of groups have found that fits would allow (or, less so after the latest updates, prefer) that the ht\\bar {t} coupling have the opposite sign. This can be given meaning in the context of an electroweak chiral Lagrangian, but it might also be interpreted to mean that a new colored and charged particle runs in loops and reinforces the W-loop contribution to hFF, while also producing the opposite-sign hGG amplitude to that generated by integrating out the top. Due to a correlation in sign of the new physics amplitudes, when the SM hFF coupling is enhanced the hGG coupling is decreased. Thus, in order to not suppress the rate of h → WW and h → ZZ, which appear to be approximately SM-like, one would need the loop to ‘overshoot’, not only canceling the top contribution but producing an opposite-sign hGG vertex of about the same magnitude as that in the SM. We argue that most such explanations have severe problems with fine-tuning and, more importantly, vacuum stability. In particular, the case of stop loops producing an opposite-sign hGG vertex of the same size as the SM one is ruled out by a combination of vacuum decay bounds and Large Electron-Positron Collider (LEP) constraints. We also show that scenarios with a sign flip from loops of color octet charged scalars or new fermionic states are highly constrained.
Thermalization of mini-jets in a quark–gluon plasma
Energy Technology Data Exchange (ETDEWEB)
Iancu, Edmond, E-mail: edmond.iancu@cea.fr; Wu, Bin, E-mail: bin.wu.phys@gmail.com [Institut de Physique Théorique, CEA Saclay, CNRS UMR 3681, F-91191 Gif-sur-Yvette (France); Department of Physics, The Ohio State University, Columbus, OH 43210 (United States)
2016-12-15
We present the complete physical picture for the evolution of a high-energy jet propagating through a weakly-coupled quark-gluon plasma (QGP) by analytical and numerical investigation of thermalization of the soft components of the jet. Our results support the following physical picture: the leading particle emits a significant number of mini-jets which promptly evolve via multiple branching and thus degrade into a myriad of soft gluons, with energies of the order of the medium temperature T. Via elastic collisions with the medium constituents, these soft gluons relax to local thermal equilibrium with the plasma over a time scale which is considerably shorter than the typical lifetime of the mini-jet. The thermalized gluons form a tail which lags behind the hard components of the jet. Together with the background QGP, they behave hydrodynamically.
Quark versus Gluon Jet Tagging Using Jet Images with the ATLAS Detector
The ATLAS collaboration
2017-01-01
Distinguishing quark-initiated from gluon-initiated jets is useful for many measurements and searches at the LHC. This note presents a jet tagger for distinguishing quark-initiated from gluon-initiated jets, which uses the full radiation pattern inside a jet processed as an image in a deep neural network classifier. The study is conducted using simulated dijet events in $\\sqrt{s}$=13 TeV pp collisions with the ATLAS detector. Across a wide range of quark jet identification efficiencies, the neural network tagger achieves a gluon jet rejection that is comparable to or better than the performance of the jet width and track multiplicity observables conventionally used for quark-versus-gluon jet tagging.
Confined gluon from Minkowski space continuation of the PT-BFM SDE solution
Czech Academy of Sciences Publication Activity Database
Šauli, Vladimír
2012-01-01
Roč. 39, č. 3 (2012), 035003/1-035003/16 ISSN 0954-3899 Institutional support: RVO:61389005 Keywords : Minkowski pace * effective QCD * gluon mass generation Subject RIV: BE - Theoretical Physics Impact factor: 5.326, year: 2012
Color response and color transport in a quark-gluon plasma
International Nuclear Information System (INIS)
Heinz, U.
1986-01-01
Using color kinetic theory, we discuss color conduction and color response in a quark-gluon plasma. Collective color oscillations and their damping rates are investigated. An instability of the thermal equilibrium state in high T QCD is discovered
Bogoliubov condensation of gluons and spontaneous gauge symmetry breaking in QCD
International Nuclear Information System (INIS)
Pervushin, V.N.; Roepke, G.; Volkov, M.K.; Blaschke, D.; Pavel, H.P.; Litvin, A.
1995-08-01
The ''squeezed'' representation of commutation relations for gluon fields in QCD is formulated as the mathematical tool for the description of the gluon condensate. We first consider λφ 4 theory and show that the ''squeezed'' Bogoliubov condensate can lead to the spontaneous appearance of a mass. Using the ''squeezed'' representation, we show that in the non-Abelian theory spontaneous gauge symmetry breaking (SGSB) and the appearance of a constituent mass of gluons can be described. We construct a projector onto the oscillator - like variables, for which the ''squeezed'' representation is valid, by using the formal solution of the Gauss equation instead of fixing a gauge. We discuss the effects of the SGSB and present as an application of the approach the calculation of the gluon mass from the difference of the η' and the η - meson masses. (author). 27 refs
Color response and color transport in a quark-gluon plasma
International Nuclear Information System (INIS)
Heinz, U.
1986-01-01
Using color kinetic theory, the authors discuss color conduction and color response in a quark-gluon plasma. Collective color oscillations and their damping rates are investigated. An instability of the thermal equilibrium state in high T QCD is discovered
One-loop Higgs plus four gluon amplitudes. Full analytic results
International Nuclear Information System (INIS)
Badger, Simon; Nigel Glover, E.W.; Williams, Ciaran; Mastrolia, Pierpaolo
2009-10-01
We consider one-loop amplitudes of a Higgs boson coupled to gluons in the limit of a large top quark mass. We treat the Higgs as the real part of a complex field φ that couples to the self-dual field strengths and compute the one-loop corrections to the φ-NMHV amplitude, which contains one gluon of positive helicity whilst the remaining three have negative helicity. We use four-dimensional unitarity to construct the cut-containing contributions and a hybrid of Feynman diagram and recursive based techniques to determine the rational piece. Knowledge of the φ-NMHV contribution completes the analytic calculation of the Higgs plus four gluon amplitude. For completeness we also include expressions for the remaining helicity configurations which have been calculated elsewhere. These amplitudes are relevant for Higgs plus jet production via gluon fusion in the limit where the top quark is large compared to all other scales in the problem. (orig.)
Alekseev, M; Alexandrov, Yu; Alexeev, G D; Amoroso, A; Austregisilio, A; Badelek, B; Balestra, F; Ball, J; Barth, J; Baum, G; Bedfer, Y; Bernhard, J; Bertini, R; Bettinelli, M; Birsa, R; Bisplinghoff, J; Bordalo, P; Bradamante, F; Bravar, A; Bressan, A; Brona, G; Burtin, E; Bussa, M P; Chapiro, A; Chiosso, M; Chung, S U; Cicuttin, A; Colantoni, M; Crespo, M L; Dalla Torre, S; Dafni, T; Das, S; Dasgupta, S S; Denisov, O.Yu; Dhara, L; Diaz, V; Dinkelbach, A M; Donskov, S V; Doshita, N; Duic, V; Dunnweber, W; Efremov, A; El Alaoui, A; Eversheim, P D; Eyrich, W; Faessler, M; Ferrero, A; Finger, M; Finger, M., jr; Fischer, H; Franco, C; Friedrich, J M; Garfagnini, R; Gautheron, F; Gavrichtchouk, O P; Gazda, R; Gerassimov, S; Geyer, R; Giorgi, M; Gobbo, B; Goertz, S; Grabmuller, S; Grajek, O A; Grasso, A; Grube, B; Gushterski, R; Guskov, A; Haas, F; Hagemann, R; von Harrach, D; Hasegawa, T; Heckmann, J; Heinsius, F H; Hermann, R; Herrmann, F; Hess, C; Hinterberger, F; von Hodenberg, M; Horikawa, N; Hoppner, Ch; d'Hose, N; Ilgner, C; Ishimoto, S; Ivanov, O; Ivanshin, Yu; Iwata, T; Jahn, R; Jasinski, P; Jegou, G; Joosten, R; Kabuss, E; Kafer, W; Kang, D; Ketzer, B; Khaustov, G V; Khokhlov, Yu.A; Kiefer, J; Kisselev, Yu; Klein, F; Klimaszewski, K; Koblitz, S; Koivuniemi, J H; Kolosov, V N; Komissarov, E V; Kondo, K; Konigsmann, Kay; Konorov, I; Konstantinov, V F; Korzenev, A; Kotzinian, A M; Kouznetsov, O; Kowalik, K; Kramer, M; Kral, A; Kroumchtein, Z V; Kuhn, R; Kunne, F; Kurek, K; Le Goff, J M; Lednev, A A; Lehmann, A; Levorato, S; Lichtenstadt, J; Liska, T; Maggiora, A; Maggiora, M; Magnon, A; Mallot, G K; Mann, A; Marchand, C; Marroncle, J; Martin, A; Marzec, J; Massmann, F; Matsuda, T; Maximov, A N; Meyer, W; Michigami, T; Mikhailov, Yu.V; Moinester, M A; Mutter, A; Nagaytsev, A; Nagel, T; Nassalski, J; Negrini, S; Nerling, F; Neubert, S; Neyret, D; Nikolaenko, V I; Olshevsky, A G; Ostrick, M; Padee, A; Panknin, R; Panebianco, S; Panzieri, D; Parsamyan, B; Paul, S; Pawlukiewicz-Kaminska, B; Perevalova, E; Pesaro, G; Peshekhonov, D V; Piragino, G; Platchkov, S; Pochodzalla, J; Polak, J; Polyakov, V A; Pontecorvo, G; Pretz, J; Quintans, C; Rajotte, J.-F; Ramos, S; Rapatsky, V; Reicherz, G; Reggiani, D; Richter, A; Robinet, F; Rocco, E; Rondio, E; Ryabchikov, D I; Samoylenko, V D; Sandacz, A; Santos, H; Sapozhnikov, M G; Sarkar, S; Savin, Igor A; Sbrizza, G; Schiavon, P; Schill, C; Schmitt, L; Schroder, W; Shevchenko, O.Yu; Siebert, H.-W; Silva, L; Sinha, L; Sissakian, A N; Slunecka, M; Smirnov, G I; Sosio, S; Sozzi, F; Srnka, A; Stolarski, M; Sulc, M; Sulej, R; Takekawa, S; Tessaro, S; Tessarotto, F; Teufel, A; Tkatchev, L G; Venugopal, G; Virius, M; Vlassov, N V; Vossen, A; Weitzel, Q; Wenzl, K; Windmolders, R; Wislicki, W; Wollny, H; Zaremba, K; Zavertyaev, M; Zemlyanichkina, E; Ziembicki, M; Zhao, J; Zhuravlev, N; Zvyagin, A
2009-01-01
The gluon polarisation in the nucleon has been determined by detecting charm production via D0 meson decay to charged K and pi in polarised muon scattering off a longitudinally polarised deuteron target. The data were taken by the COMPASS Collaboration at CERN between 2002 and 2006 and corresponds to an integrated luminosity of 2.8 fb^-1. The dominant underlying process of charm production is the photon-gluon fusion to a cc-bar pair. A leading order QCD approach gives an average gluon polarisation of (Delta g/g)_x= -0.49 +- 0.27(stat) +- 0.11(syst) at a scale mu^2 ~ 13 (GeV/c)^2 and at an average gluon momentum fraction (x) ~ 0.11. The longitudinal cross-section asymmetry for D0 production is presented in bins of the transverse momentum and the energy of the D0 meson.
Thermalization of the quark-gluon plasma and dynamical formation of Bose-Einstein Condensate
Liao, Jinfeng
2012-01-01
We report recent progress on understanding the thermalization of the quark-gluon plasma during the early stage in a heavy ion collision. The initially high overpopulation in the pre-equilibrium gluonic matter (``glasma'') is shown to play a crucial role. The strongly interacting nature (and thus fast evolution) naturally arises as an {\\em emergent property} of this pre-equilibrium matter where the intrinsic coupling is weak but the highly occupied gluon states coherently amplify the scatterin...
K factor for Higgs boson production via gluon fusion process at hadron colliders
International Nuclear Information System (INIS)
Tanaka, H.
1992-01-01
In this paper soft gluon corrections for Higgs boson production at hadron colliders are calculated. It is found that the soft contributions for the Higgs boson production via gluon fusion process is large and it cannot be neglected even at SSC energy. Some qualitative discussions for the QCD corrections to the Higgs boson production at hadron colliders and their background processes are presented for various Higgs boson mass cases
Off-shell gluon production in interaction of a projectile with 2 or 3 targets
Energy Technology Data Exchange (ETDEWEB)
Braun, M.A.; Salykin, M.Yu. [Saint-Petersburg State University, Department of High Energy physics, Saint Petersburg (Russian Federation)
2017-07-15
Within the effective QCD action for the Regge kinematics, the amplitudes for virtual gluon emission are studied in collision of a projectile with two and three targets. It is demonstrated that all non-Feynman singularities cancel between induced vertices and rescattering contributions. Formulas simplify considerably in a special gauge, which is a straightforward generalization of the light-cone gauge for emission of real gluons. (orig.)
The strong running coupling from an approximate gluon Dyson-Schwinger equation
International Nuclear Information System (INIS)
Alkofer, R.; Hauck, A.
1996-01-01
Using Mandelstam's approximation to the gluon Dyson-Schwinger equation we calculate the gluon self-energy in a renormalisation group invariant fashion. We obtain a non-perturbative Β function. The scaling behavior near the ultraviolet stable fixed point is in good agreement with perturbative QCD. No further fixed point for positive values of the coupling is found: α S increases without bound in the infrared
Quark condensate contributions to the gluon self-energy and the ρ meson sum rule
International Nuclear Information System (INIS)
Steele, T.G.
1989-01-01
The operator-product expansion will be employed to obtain the lowest-order, quark condensate component of both the gluon self-energy and the ρ meson correlation function to all orders in the quark mass parameter. Field-theoretic aspects of the self-energy and correlation function will be considered, and physical effects to the quark condensate upon gluon mass generation will be examined. (orig.)
Gluons from logarithmic slopes of F2 in the NLL approximation
International Nuclear Information System (INIS)
Golec-Biernat, K.
1994-02-01
We make a critical, next-to-leading order, study of the accuracy of the ''Prytz'' relation, which is frequently used to extract the gluon distribution at small x from the logarithmic slopes of the structure function F 2 . We find that the simple relation is not generally valid in the HERA regime, but show that it is a reasonable approximation for gluons which are sufficiency singular at small x. (author). 9 refs, 3 figs
Initial conditions of non-equilibrium quark-gluon plasma evolution
International Nuclear Information System (INIS)
Shmatov, S.V.
2002-01-01
In accordance with the hydrodynamic Bjorken limit, the initial energy density and temperature for a chemical non-equilibrium quark-gluon system formed in the heavy ion collisions at the LHC are computed. The dependence of this value on the type of colliding nuclei and the collision impact parameter is studied. The principle possibility of the non-equilibrium quark-gluon plasma (QGP) formation in the light nuclei collisions is shown. The life time of QGP is calculated. (author)
Dilepton spectrum from quark-gluon plasma in second Born approximation
International Nuclear Information System (INIS)
Makhlin, A.N.
1989-01-01
The real time temperature Keldysh technique has been used to calculate the rate of dilepton emission from quark-gluon plasma in the first order with respect to strong coupling constant. This approximation us shown to be inconsistent. The radiative corrections turned to be of the same order as the contribution of real processes with gluons. Nevertheless the general properties inherent in dilepton emission from continuous media can be verified by measuring the lepton distribution inside the dilepton. 11 refs.; 2 figs
A Glimpse of Gluons through Deeply Virtual Compton Scattering on the Proton
Defurne, M.; Jiménez-Argüello, A. Martì; Ahmed, Z.; Albataineh, H.; Allada, K.; Aniol, K. A.; Bellini, V.; Benali, M.; Boeglin, W.; Bertin, P.; Brossard, M.; Camsonne, A.; Canan, M.; Chandavar, S.; Chen, C.
2017-01-01
The proton is composed of quarks and gluons, bound by the most elusive mechanism of strong interaction called confinement. In this work, the dynamics of quarks and gluons are investigated using deeply virtual Compton scattering (DVCS): produced by a multi-GeV electron, a highly virtual photon scatters off the proton which subsequently radiates a high energy photon. Similarly to holography, measuring not only the magnitude but also the phase of the DVCS amplitude allows to perform 3D images of...
Average gluon and quark jet multiplicities at higher orders
Energy Technology Data Exchange (ETDEWEB)
Bolzoni, Paolo; Kniehl, Bernd A. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Kotikov, Anatoly V. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Joint Institute of Nuclear Research, Moscow (Russian Federation). Bogoliubov Lab. of Theoretical Physics
2013-05-15
We develop a new formalism for computing and including both the perturbative and nonperturbative QCD contributions to the scale evolution of average gluon and quark jet multiplicities. The new method is motivated by recent progress in timelike small-x resummation obtained in the MS factorization scheme. We obtain next-to-next-to-leading-logarithmic (NNLL) resummed expressions, which represent generalizations of previous analytic results. Our expressions depend on two nonperturbative parameters with clear and simple physical interpretations. A global fit of these two quantities to all available experimental data sets that are compatible with regard to the jet algorithms demonstrates by its goodness how our results solve a longstanding problem of QCD. We show that the statistical and theoretical uncertainties both do not exceed 5% for scales above 10 GeV. We finally propose to use the jet multiplicity data as a new way to extract the strong-coupling constant. Including all the available theoretical input within our approach, we obtain {alpha}{sub s}{sup (5)}(M{sub Z})=0.1199{+-}0.0026 in the MS scheme in an approximation equivalent to next-to-next-to-leading order enhanced by the resummations of ln(x) terms through the NNLL level and of ln Q{sup 2} terms by the renormalization group, in excellent agreement with the present world average.
Dual QCD thermodynamics and quark–gluon plasma
International Nuclear Information System (INIS)
Chandola, H.C.; Punetha, Garima; Dehnen, H.
2016-01-01
Using grand canonical ensemble formulation of a multi-particle statistical system, the thermodynamical description of dual QCD based on magnetic symmetry has been presented and analyzed for the quark–gluon plasma phase of hadronic matter. The dual QCD based bag construction has been shown to lead to the radial pressure on bag surface in terms of the vector glueball masses of magnetically condensed QCD vacuum. Constructing the grand canonical partition function, the energy density and plasma pressure have been derived and used to compute the critical temperatures for QGP–hadron phase transition along with its dynamics. A comparison of the values of critical temperatures for QGP–hadron phase transition with those obtained for the deconfinement-phase transition, has been shown to lead to either the relaxation of the system via a mixed phase of QGP and hot hadron gas or go through a crossover. The associated profiles of the normalized energy density and specific heat have been shown to lead to a large latent heat generation and indicate the onset of a first-order QGP phase transition which turns into a rapid crossover for the case of temperature dependent bag parameter. The squared speed of sound has been shown to act as a physical measure of large thermodynamical fluctuations near transition point. The possible implications of trace anomaly and conformal measure on QGP formation have also been discussed.
Soft gluon evolution and non-global logarithms
Martínez, René Ángeles; De Angelis, Matthew; Forshaw, Jeffrey R.; Plätzer, Simon; Seymour, Michael H.
2018-05-01
We consider soft-gluon evolution at the amplitude level. Our evolution algorithm applies to generic hard-scattering processes involving any number of coloured partons and we present a reformulation of the algorithm in such a way as to make the cancellation of infrared divergences explicit. We also emphasise the special role played by a Lorentz-invariant evolution variable, which coincides with the transverse momentum of the latest emission in a suitably defined dipole zero-momentum frame. Handling large colour matrices presents the most significant challenge to numerical implementations and we present a means to expand systematically about the leading colour approximation. Specifically, we present a systematic procedure to calculate the resulting colour traces, which is based on the colour flow basis. Identifying the leading contribution leads us to re-derive the Banfi-Marchesini-Smye equation. However, our formalism is more general and can systematically perform resummation of contributions enhanced by the t'Hooft coupling α s N ˜ 1, along with successive perturbations that are parametrically suppressed by powers of 1 /N . We also discuss how our approach relates to earlier work.
T -matrix approach to quark-gluon plasma
Liu, Shuai Y. F.; Rapp, Ralf
2018-03-01
A self-consistent thermodynamic T -matrix approach is deployed to study the microscopic properties of the quark-gluon plasma (QGP), encompassing both light- and heavy-parton degrees of freedom in a unified framework. The starting point is a relativistic effective Hamiltonian with a universal color force. The input in-medium potential is quantitatively constrained by computing the heavy-quark (HQ) free energy from the static T -matrix and fitting it to pertinent lattice-QCD (lQCD) data. The corresponding T -matrix is then applied to compute the equation of state (EoS) of the QGP in a two-particle irreducible formalism, including the full off-shell properties of the selfconsistent single-parton spectral functions and their two-body interaction. In particular, the skeleton diagram functional is fully resummed to account for emerging bound and scattering states as the critical temperature is approached from above. We find that the solution satisfying three sets of lQCD data (EoS, HQ free energy, and quarkonium correlator ratios) is not unique. As limiting cases we discuss a weakly coupled solution, which features color potentials close to the free energy, relatively sharp quasiparticle spectral functions and weak hadronic resonances near Tc, and a strongly coupled solution with a strong color potential (much larger than the free energy), resulting in broad nonquasiparticle parton spectral functions and strong hadronic resonance states which dominate the EoS when approaching Tc.
Gluons and gravitons at one loop from ambitwistor strings
Geyer, Yvonne; Monteiro, Ricardo
2018-03-01
We present new and explicit formulae for the one-loop integrands of scattering amplitudes in non-supersymmetric gauge theory and gravity, valid for any number of particles. The results exhibit the colour-kinematics duality in gauge theory and the double-copy relation to gravity, in a form that was recently observed in supersymmetric theories. The new formulae are expressed in a particular representation of the loop integrand, with only one quadratic propagator, which arises naturally from the framework of the loop-level scattering equations. The starting point in our work are the expressions based on the scattering equations that were recently derived from ambitwistor string theory. We turn these expressions into explicit formulae depending only on the loop momentum, the external momenta and the external polarisations. These formulae are valid in any number of spacetime dimensions for pure Yang-Mills theory (gluon) and its natural double copy, NS-NS gravity (graviton, dilaton, B-field), and we also present formulae in four spacetime dimensions for pure gravity (graviton). We perform several tests of our results, such as checking gauge invariance and directly matching our four-particle formulae to previously known expressions. While these tests would be elaborate in a Feynman-type representation of the loop integrand, they become straightforward in the representation we use.
Multiplicities of $\\pi^{0}$, $\\eta$, $K^{0}$ and of charged particles in quark and gluon jets
Abbiendi, G.; Ainsley, C.; Akesson, P.F.; Alexander, G.; Allison, John; Anderson, K.J.; Arcelli, S.; Asai, S.; Ashby, S.F.; Axen, D.; Azuelos, G.; Bailey, I.; Ball, A.H.; Barberio, E.; Barlow, Roger J.; Batley, J.R.; Baumann, S.; Behnke, T.; Bell, Kenneth Watson; Bella, G.; Bellerive, A.; Bentvelsen, S.; Bethke, S.; Biebel, O.; Bloodworth, I.J.; Bock, P.; Bohme, J.; Boeriu, O.; Bonacorsi, D.; Boutemeur, M.; Braibant, S.; Bright-Thomas, P.; Brigliadori, L.; Brown, Robert M.; Burckhart, H.J.; Cammin, J.; Capiluppi, P.; Carnegie, R.K.; Carter, A.A.; Carter, J.R.; Chang, C.Y.; Charlton, David G.; Ciocca, C.; Clarke, P.E.L.; Clay, E.; Cohen, I.; Cooke, O.C.; Couchman, J.; Couyoumtzelis, C.; Coxe, R.L.; Cuffiani, M.; Dado, S.; Dallavalle, G.Marco; Dallison, S.; de Roeck, A.; Dervan, P.; Desch, K.; Dienes, B.; Dixit, M.S.; Donkers, M.; Dubbert, J.; Duchovni, E.; Duckeck, G.; Duerdoth, I.P.; Estabrooks, P.G.; Etzion, E.; Fabbri, F.; Fanti, M.; Feld, L.; Ferrari, P.; Fiedler, F.; Fleck, I.; Ford, M.; Frey, A.; Furtjes, A.; Futyan, D.I.; Gagnon, P.; Gary, J.W.; Gaycken, G.; Geich-Gimbel, C.; Giacomelli, G.; Giacomelli, P.; Glenzinski, D.; Goldberg, J.; Grandi, C.; Graham, K.; Gross, E.; Grunhaus, J.; Gruwe, M.; Gunther, P.O.; Hajdu, C.; Hanson, G.G.; Hansroul, M.; Hapke, M.; Harder, K.; Harel, A.; Hargrove, C.K.; Harin-Dirac, M.; Hauke, A.; Hauschild, M.; Hawkes, C.M.; Hawkings, R.; Hemingway, R.J.; Hensel, C.; Herten, G.; Heuer, R.D.; Hildreth, M.D.; Hill, J.C.; Hocker, James Andrew; Hoffman, Kara Dion; Homer, R.J.; Honma, A.K.; Horvath, D.; Hossain, K.R.; Howard, R.; Huntemeyer, P.; Igo-Kemenes, P.; Ishii, K.; Jacob, F.R.; Jawahery, A.; Jeremie, H.; Jones, C.R.; Jovanovic, P.; Junk, T.R.; Kanaya, N.; Kanzaki, J.; Karapetian, G.; Karlen, D.; Kartvelishvili, V.; Kawagoe, K.; Kawamoto, T.; Keeler, R.K.; Kellogg, R.G.; Kennedy, B.W.; Kim, D.H.; Klein, K.; Klier, A.; Kobayashi, T.; Kobel, M.; Kokott, T.P.; Komamiya, S.; Kowalewski, Robert V.; Kress, T.; Krieger, P.; von Krogh, J.; Kuhl, T.; Kupper, M.; Kyberd, P.; Lafferty, G.D.; Landsman, H.; Lanske, D.; Lawson, I.; Layter, J.G.; Leins, A.; Lellouch, D.; Letts, J.; Levinson, L.; Liebisch, R.; Lillich, J.; List, B.; Littlewood, C.; Lloyd, A.W.; Lloyd, S.L.; Loebinger, F.K.; Long, G.D.; Losty, M.J.; Lu, J.; Ludwig, J.; Macchiolo, A.; Macpherson, A.; Mader, W.; Mannelli, M.; Marcellini, S.; Marchant, T.E.; Martin, A.J.; Martin, J.P.; Martinez, G.; Mashimo, T.; Mattig, Peter; McDonald, W.John; McKenna, J.; McMahon, T.J.; McPherson, R.A.; Meijers, F.; Mendez-Lorenzo, P.; Merritt, F.S.; Mes, H.; Michelini, A.; Mihara, S.; Mikenberg, G.; Miller, D.J.; Mohr, W.; Montanari, A.; Mori, T.; Nagai, K.; Nakamura, I.; Neal, H.A.; Nisius, R.; O'Neale, S.W.; Oakham, F.G.; Odorici, F.; Ogren, H.O.; Oh, A.; Okpara, A.; Oreglia, M.J.; Orito, S.; Pasztor, G.; Pater, J.R.; Patrick, G.N.; Patt, J.; Pfeifenschneider, P.; Pilcher, J.E.; Pinfold, J.; Plane, David E.; Poli, B.; Polok, J.; Pooth, O.; Przybycien, M.; Quadt, A.; Rembser, C.; Rick, H.; Robins, S.A.; Rodning, N.; Roney, J.M.; Rosati, S.; Roscoe, K.; Rossi, A.M.; Rozen, Y.; Runge, K.; Runolfsson, O.; Rust, D.R.; Sachs, K.; Saeki, T.; Sahr, O.; Sarkisyan, E.K.G.; Sbarra, C.; Schaile, A.D.; Schaile, O.; Scharff-Hansen, P.; Schmitt, S.; Schroder, Matthias; Schumacher, M.; Schwick, C.; Scott, W.G.; Seuster, R.; Shears, T.G.; Shen, B.C.; Shepherd-Themistocleous, C.H.; Sherwood, P.; Siroli, G.P.; Skuja, A.; Smith, A.M.; Snow, G.A.; Sobie, R.; Soldner-Rembold, S.; Spagnolo, S.; Sproston, M.; Stahl, A.; Stephens, K.; Stoll, K.; Strom, David M.; Strohmer, R.; Surrow, B.; Talbot, S.D.; Tarem, S.; Taylor, R.J.; Teuscher, R.; Thiergen, M.; Thomas, J.; Thomson, M.A.; Torrence, E.; Towers, S.; Trefzger, T.; Trigger, I.; Trocsanyi, Z.; Tsur, E.; Turner-Watson, M.F.; Ueda, I.; Vannerem, P.; Verzocchi, M.; Voss, H.; Vossebeld, J.; Waller, D.; Ward, C.P.; Ward, D.R.; Watkins, P.M.; Watson, A.T.; Watson, N.K.; Wells, P.S.; Wengler, T.; Wermes, N.; Wetterling, D.; White, J.S.; Wilson, G.W.; Wilson, J.A.; Wyatt, T.R.; Yamashita, S.; Zacek, V.; Zer-Zion, D.
2000-01-01
We compared the multiplicities of pizero, eta, Kzero and of charged particles in quark and gluon jets in 3-jet events, as measured by the OPAL experiment at LEP. The comparisons were performed for distributions unfolded to 100% pure quark and gluon jets, at an effective scale Qjet which took into account topological dependences of the 3-jet environment. The ratio of particle multiplicity in gluon jets to that in quark jets as a function of Qjet for pizero, eta and Kzero was found to be independent of the particle species. This is consistent with the QCD prediction that the observed enhancement in the mean particle rate in gluon jets with respect to quark jets should be independent of particle species. In contrast to some theoretical predictions and previous observations, we observed no evidence for an enhancement of eta meson production in gluon jets with respect to quark jets, beyond that observed for charged particles. We measured the ratio of the slope of the average charged particle multiplicity in gluon ...
Gluon contribution to the Sivers effect. COMPASS results on deuteron target
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Szabelski Adam
2015-01-01
Full Text Available Sivers effect for gluons is connected to gluon orbital angular momentum which may be the missing part of the nucleon spin puzzle. We present a method of extraction of Sivers effect for gluons from COMPASS SIDIS data on transversely polarised target. In order to access the Sivers effect for gluons photon-gluon fusion (PGF process is used. To enhance the fraction of PGF in the sample high-pT hadron pair events are selected. The method is based on a assumption that there are 3 processes contributing to the muon-nucleon scattering: PGF, leading process and QCD Compton process. Then one performs a weighting procedure which enables to extract the asymmetries for the 3 contributing processes simultaneously. In order to do that a neural network trained by a Monte Carlo to assign to each event 3 probabilities corresponding to the 3 processes is needed. Finaly we show results of Sivers effect for gluons extraction on COMPASS data with transversely polarised deuteron target. APGFsinΦ2h–ΦS = −0.14 ± 0.15 (stat. at ‹XG› = 0.126.
Multiplicity distributions of gluon and quark jets and tests of QCD analytic predictions
Ackerstaff, K; Allison, J; Altekamp, N; Anderson, K J; Anderson, S; Arcelli, S; Asai, S; Axen, D A; Azuelos, Georges; Ball, A H; Barberio, E; Barlow, R J; Bartoldus, R; Batley, J Richard; Baumann, S; Bechtluft, J; Beeston, C; Behnke, T; Bell, A N; Bell, K W; Bella, G; Bentvelsen, Stanislaus Cornelius Maria; Bethke, Siegfried; Biebel, O; Biguzzi, A; Bird, S D; Blobel, Volker; Bloodworth, Ian J; Bloomer, J E; Bobinski, M; Bock, P; Bonacorsi, D; Boutemeur, M; Bouwens, B T; Braibant, S; Brigliadori, L; Brown, R M; Burckhart, Helfried J; Burgard, C; Bürgin, R; Capiluppi, P; Carnegie, R K; Carter, A A; Carter, J R; Chang, C Y; Charlton, D G; Chrisman, D; Clarke, P E L; Cohen, I; Conboy, J E; Cooke, O C; Cuffiani, M; Dado, S; Dallapiccola, C; Dallavalle, G M; Davis, R; De Jong, S; del Pozo, L A; Desch, Klaus; Dienes, B; Dixit, M S; do Couto e Silva, E; Doucet, M; Duchovni, E; Duckeck, G; Duerdoth, I P; Eatough, D; Edwards, J E G; Estabrooks, P G; Evans, H G; Evans, M; Fabbri, Franco Luigi; Fanti, M; Faust, A A; Fiedler, F; Fierro, M; Fischer, H M; Fleck, I; Folman, R; Fong, D G; Foucher, M; Fürtjes, A; Futyan, D I; Gagnon, P; Gary, J W; Gascon, J; Gascon-Shotkin, S M; Geddes, N I; Geich-Gimbel, C; Geralis, T; Giacomelli, G; Giacomelli, P; Giacomelli, R; Gibson, V; Gibson, W R; Gingrich, D M; Glenzinski, D A; Goldberg, J; Goodrick, M J; Gorn, W; Grandi, C; Gross, E; Grunhaus, Jacob; Gruwé, M; Hajdu, C; Hanson, G G; Hansroul, M; Hapke, M; Hargrove, C K; Hart, P A; Hartmann, C; Hauschild, M; Hawkes, C M; Hawkings, R; Hemingway, Richard J; Herndon, M; Herten, G; Heuer, R D; Hildreth, M D; Hill, J C; Hillier, S J; Hobson, P R; Homer, R James; Honma, A K; Horváth, D; Hossain, K R; Howard, R; Hüntemeyer, P; Hutchcroft, D E; Igo-Kemenes, P; Imrie, D C; Ingram, M R; Ishii, K; Jawahery, A; Jeffreys, P W; Jeremie, H; Jimack, Martin Paul; Joly, A; Jones, C R; Jones, G; Jones, M; Jost, U; Jovanovic, P; Junk, T R; Karlen, D A; Kartvelishvili, V G; Kawagoe, K; Kawamoto, T; Kayal, P I; Keeler, Richard K; Kellogg, R G; Kennedy, B W; Kirk, J; Klier, A; Kluth, S; Kobayashi, T; Kobel, M; Koetke, D S; Kokott, T P; Kolrep, M; Komamiya, S; Kress, T; Krieger, P; Von Krogh, J; Kyberd, P; Lafferty, G D; Lahmann, R; Lai, W P; Lanske, D; Lauber, J; Lautenschlager, S R; Layter, J G; Lazic, D; Lee, A M; Lefebvre, E; Lellouch, Daniel; Letts, J; Levinson, L; Lloyd, S L; Loebinger, F K; Long, G D; Losty, Michael J; Ludwig, J; Macchiolo, A; MacPherson, A L; Mannelli, M; Marcellini, S; Markus, C; Martin, A J; Martin, J P; Martínez, G; Mashimo, T; Mättig, P; McDonald, W J; McKenna, J A; McKigney, E A; McMahon, T J; McPherson, R A; Meijers, F; Menke, S; Merritt, F S; Mes, H; Meyer, J; Michelini, Aldo; Mikenberg, G; Miller, D J; Mincer, A; Mir, R; Mohr, W; Montanari, A; Mori, T; Morii, M; Müller, U; Mihara, S; Nagai, K; Nakamura, I; Neal, H A; Nellen, B; Nisius, R; O'Neale, S W; Oakham, F G; Odorici, F; Ögren, H O; Oh, A; Oldershaw, N J; Oreglia, M J; Orito, S; Pálinkás, J; Pásztor, G; Pater, J R; Patrick, G N; Patt, J; Pearce, M J; Pérez-Ochoa, R; Petzold, S; Pfeifenschneider, P; Pilcher, J E; Pinfold, J L; Plane, D E; Poffenberger, P R; Poli, B; Posthaus, A; Rees, D L; Rigby, D; Robertson, S; Robins, S A; Rodning, N L; Roney, J M; Rooke, A M; Ros, E; Rossi, A M; Routenburg, P; Rozen, Y; Runge, K; Runólfsson, O; Ruppel, U; Rust, D R; Rylko, R; Sachs, K; Saeki, T; Sarkisyan-Grinbaum, E; Sbarra, C; Schaile, A D; Schaile, O; Scharf, F; Scharff-Hansen, P; Schenk, P; Schieck, J; Schleper, P; Schmitt, B; Schmitt, S; Schöning, A; Schröder, M; Schultz-Coulon, H C; Schumacher, M; Schwick, C; Scott, W G; Shears, T G; Shen, B C; Shepherd-Themistocleous, C H; Sherwood, P; Siroli, G P; Sittler, A; Skillman, A; Skuja, A; Smith, A M; Snow, G A; Sobie, Randall J; Söldner-Rembold, S; Springer, R W; Sproston, M; Stephens, K; Steuerer, J; Stockhausen, B; Stoll, K; Strom, D; Szymanski, P; Tafirout, R; Talbot, S D; Tanaka, S; Taras, P; Tarem, S; Teuscher, R; Thiergen, M; Thomson, M A; Von Törne, E; Towers, S; Trigger, I; Trócsányi, Z L; Tsur, E; Turcot, A S; Turner-Watson, M F; Utzat, P; Van Kooten, R; Verzocchi, M; Vikas, P; Vokurka, E H; Voss, H; Wäckerle, F; Wagner, A; Ward, C P; Ward, D R; Watkins, P M; Watson, A T; Watson, N K; Wells, P S; Wermes, N; White, J S; Wilkens, B; Wilson, G W; Wilson, J A; Wolf, G; Wyatt, T R; Yamashita, S; Yekutieli, G; Zacek, V; Zer-Zion, D
1999-01-01
Gluon jets are identified in e+e- hadronic annihilation events by tagging two quark jets in the same hemisphere of an event. The gluon jet is defined inclusively as all the particles in the opposite hemisphere. Gluon jets defined in this manner have a close correspondence to gluon jets as they are defined for analytic calculations, and are almost independent of a jet finding algorithm. The charged particle multiplicity distribution of the gluon jets is presented, and is analyzed for its mean, dispersion, skew, and curtosis values, and for its factorial and cumulant moments. The results are compared to the analogous results found for a sample of light quark (uds) jets, also defined inclusively. We observe differences between the mean, skew and curtosis values of gluon and quark jets, but not between their dispersions. The cumulant moment results are compared to the predictions of QCD analytic calculations. A calculation which includes next-to-next-to-leading order corrections and energy conservation is observe...
Energy dependence of the differences between the quark and gluon jet fragmentation
Abreu, P; Adye, T; Agasi, E; Ajinenko, I; Aleksan, Roy; Alekseev, G D; Alemany, R; Allport, P P; Almehed, S; Alvsvaag, S J; Amaldi, Ugo; Amato, S; Andreazza, A; Andrieux, M L; Antilogus, P; Apel, W D; Arnoud, Y; Åsman, B; Augustin, J E; Augustinus, A; Baillon, Paul; Bambade, P; Barão, F; Barate, R; Bardin, Dimitri Yuri; Baroncelli, A; Bärring, O; Barrio, J A; Bartl, Walter; Bates, M J; Battaglia, Marco; Baubillier, M; Baudot, J; Becks, K H; Begalli, M; Beillière, P; Belokopytov, Yu A; Belous, K S; Benvenuti, Alberto C; Berggren, M; Bertrand, D; Bianchi, F; Bigi, M; Bilenky, S M; Billoir, P; Bloch, D; Blume, M; Blyth, S; Bolognese, T; Bonesini, M; Bonivento, W; Booth, P S L; Borisov, G; Bosio, C; Bosworth, S; Botner, O; Bouquet, B; Bourdarios, C; Bowcock, T J V; Bozzo, M; Branchini, P; Brand, K D; Brenke, T; Brenner, R A; Bricman, C; Brillault, L; Brown, R C A; Brückman, P; Brunet, J M; Bugge, L; Buran, T; Burgsmüller, T; Buschmann, P; Buys, A; Cabrera, S; Caccia, M; Calvi, M; Camacho-Rozas, A J; Camporesi, T; Canale, V; Canepa, M; Cankocak, K; Cao, F; Carena, F; Carrilho, P; Carroll, L; Caso, Carlo; Castillo-Gimenez, M V; Cattai, A; Cavallo, F R; Cerrito, L; Chabaud, V; Charpentier, P; Chaussard, L; Chauveau, J; Checchia, P; Chelkov, G A; Chen, M; Chierici, R; Chliapnikov, P V; Chochula, P; Chorowicz, V; Chudoba, J; Cindro, V; Collins, P; Contreras, J L; Contri, R; Cortina, E; Cosme, G; Cossutti, F; Crawley, H B; Crennell, D J; Crosetti, G; Cuevas-Maestro, J; Czellar, S; Dahl-Jensen, Erik; Dahm, J; D'Almagne, B; Dam, M; Damgaard, G; Dauncey, P D; Davenport, Martyn; Da Silva, W; Defoix, C; Deghorain, A; Della Ricca, G; Delpierre, P A; Demaria, N; De Angelis, A; de Boer, Wim; De Brabandere, S; De Clercq, C; La Vaissière, C de; De Lotto, B; De Min, A; De Paula, L S; De Saint-Jean, C; Dijkstra, H; Di Ciaccio, Lucia; Djama, F; Dolbeau, J; Dönszelmann, M; Doroba, K; Dracos, M; Drees, J; Drees, K A; Dris, M; Dufour, Y; Dupont, F; Edsall, D M; Ehret, R; Eigen, G; Ekelöf, T J C; Ekspong, Gösta; Elsing, M; Engel, J P; Ershaidat, N; Erzen, B; Espirito-Santo, M C; Falk, E; Fassouliotis, D; Feindt, Michael; Ferrer, A; Filippas-Tassos, A; Firestone, A; Fischer, P A; Föth, H; Fokitis, E; Fontanelli, F; Formenti, F; Franek, B J; Frenkiel, P; Fries, D E C; Frodesen, A G; Frühwirth, R; Fulda-Quenzer, F; Fuster, J A; Galloni, A; Gamba, D; Gandelman, M; García, C; García, J; Gaspar, C; Gasparini, U; Gavillet, P; Gazis, E N; Gelé, D; Gerber, J P; Gerdyukov, L N; Gibbs, M; Gokieli, R; Golob, B; Gopal, Gian P; Gorn, L; Górski, M; Guz, Yu; Gracco, Valerio; Graziani, E; Grosdidier, G; Grzelak, K; Gumenyuk, S A; Gunnarsson, P; Günther, M; Guy, J; Hahn, F; Hahn, S; Hallgren, A; Hamacher, K; Hao, W; Harris, F J; Hedberg, V; Henriques, R P; Hernández, J J; Herquet, P; Herr, H; Hessing, T L; Higón, E; Hilke, Hans Jürgen; Hill, T S; Holmgren, S O; Holt, P J; Holthuizen, D J; Hoorelbeke, S; Houlden, M A; Hrubec, Josef; Huet, K; Hultqvist, K; Jackson, J N; Jacobsson, R; Jalocha, P; Janik, R; Jarlskog, C; Jarlskog, G; Jarry, P; Jean-Marie, B; Johansson, E K; Jönsson, L B; Jönsson, P E; Joram, Christian; Juillot, P; Kaiser, M; Kapusta, F; Karafasoulis, K; Karlsson, M; Karvelas, E; Katsanevas, S; Katsoufis, E C; Keränen, R; Khomenko, B A; Khovanskii, N N; King, B J; Kjaer, N J; Klapp, O; Klein, H; Klovning, A; Kluit, P M; Köne, B; Kokkinias, P; Koratzinos, M; Korcyl, K; Kostyukhin, V; Kourkoumelis, C; Kuznetsov, O; Kramer, P H; Krammer, Manfred; Kreuter, C; Kronkvist, I J; Krumshtein, Z; Krupinski, W; Kubinec, P; Kucewicz, W; Kurvinen, K L; Lacasta, C; Laktineh, I; Lamblot, S; Lamsa, J; Lanceri, L; Lane, D W; Langefeld, P; Lapin, V; Last, I; Laugier, J P; Lauhakangas, R; Leder, Gerhard; Ledroit, F; Lefébure, V; Legan, C K; Leitner, R; Lemoigne, Y; Lemonne, J; Lenzen, Georg; Lepeltier, V; Lesiak, T; Lindner, R; Lipniacka, A; Lippi, I; Lörstad, B; Loken, J G; López, J M; López-Aguera, M A; Loukas, D; Lutz, P; Lyons, L; MacNaughton, J N; Maehlum, G; Malychev, V; Mandl, F; Marco, J; Maréchal, B; Margoni, M; Marin, J C; Mariotti, C; Markou, A; Maron, T; Martínez-Rivero, C; Martínez-Vidal, F; Martí i García, S; Masik, J; Matorras, F; Matteuzzi, C; Matthiae, Giorgio; Mazzucato, M; McCubbin, M L; McKay, R; McNulty, R; Medbo, J; Meroni, C; Meyer, S; Meyer, W T; Michelotto, M; Migliore, E; Mirabito, L; Mitaroff, Winfried A; Mjörnmark, U; Moa, T; Møller, R; Mönig, K; Monge, M R; Morettini, P; Müller, H; Mundim, L M; Murray, W J; Muryn, B; Myatt, Gerald; Naraghi, F; Navarria, Francesco Luigi; Navas, S; Nawrocki, K; Negri, P; Neumann, W; Neumeister, N; Nicolaidou, R; Nielsen, B S; Nieuwenhuizen, M; Nikolaenko, V; Niss, P; Nomerotski, A; Normand, Ainsley; Oberschulte-Beckmann, W; Obraztsov, V F; Olshevskii, A G; Onofre, A; Orava, Risto; Österberg, K; Ouraou, A; Paganini, P; Paganoni, M; Pagès, P; Palka, H; Papadopoulou, T D; Papageorgiou, K; Pape, L; Parkes, C; Parodi, F; Passeri, A; Pegoraro, M; Peralta, L; Pernegger, H; Pernicka, Manfred; Perrotta, A; Petridou, C; Petrolini, A; Petrovykh, M; Phillips, H T; Piana, G; Pierre, F; Pimenta, M; Pindo, M; Plaszczynski, S; Podobrin, O; Pol, M E; Polok, G; Poropat, P; Pozdnyakov, V; Prest, M; Privitera, P; Pukhaeva, N; Pullia, Antonio; Radojicic, D; Ragazzi, S; Rahmani, H; Rames, J; Ratoff, P N; Read, A L; Reale, M; Rebecchi, P; Redaelli, N G; Regler, Meinhard; Reid, D; Renton, P B; Resvanis, L K; Richard, F; Richardson, J; Rídky, J; Rinaudo, G; Ripp, I; Romero, A; Roncagliolo, I; Ronchese, P; Roos, L; Rosenberg, E I; Rosso, E; Roudeau, Patrick; Rovelli, T; Rückstuhl, W; Ruhlmann-Kleider, V; Ruiz, A; Saarikko, H; Sacquin, Yu; Sadovskii, A; Sajot, G; Salt, J; Sánchez, J; Sannino, M; Schimmelpfennig, M; Schneider, H; Schwickerath, U; Schyns, M A E; Sciolla, G; Scuri, F; Seager, P; Sedykh, Yu; Segar, A M; Seitz, A; Sekulin, R L; Shellard, R C; Siccama, I; Siegrist, P; Simonetti, S; Simonetto, F; Sissakian, A N; Sitár, B; Skaali, T B; Smadja, G; Smirnov, N; Smirnova, O G; Smith, G R; Sosnowski, R; Souza-Santos, D; Spassoff, Tz; Spiriti, E; Sponholz, P; Squarcia, S; Stanescu, C; Stapnes, Steinar; Stavitski, I; Stichelbaut, F; Stocchi, A; Strauss, J; Strub, R; Stugu, B; Szczekowski, M; Szeptycka, M; Tabarelli de Fatis, T; Tavernet, J P; Chikilev, O G; Tilquin, A; Timmermans, J; Tkatchev, L G; Todorov, T; Toet, D Z; Tomaradze, A G; Tomé, B; Tonazzo, A; Tortora, L; Tranströmer, G; Treille, D; Trischuk, W; Tristram, G; Trombini, A; Troncon, C; Tsirou, A L; Turluer, M L; Tyapkin, I A; Tyndel, M; Tzamarias, S; Überschär, B; Ullaland, O; Uvarov, V; Valenti, G; Vallazza, E; Van der Velde, C; van Apeldoorn, G W; van Dam, P; Van Doninck, W K; Van Eldik, J; Vassilopoulos, N; Vegni, G; Ventura, L; Venus, W A; Verbeure, F; Verlato, M; Vertogradov, L S; Vilanova, D; Vincent, P; Vitale, L; Vlasov, E; Vodopyanov, A S; Vrba, V; Wahlen, H; Walck, C; Waldner, F; Weierstall, M; Weilhammer, Peter; Weiser, C; Wetherell, Alan M; Wicke, D; Wickens, J H; Wielers, M; Wilkinson, G R; Williams, W S C; Winter, M; Witek, M; Woschnagg, K; Yip, K; Yushchenko, O P; Zach, F; Zaitsev, A; Zalewska-Bak, A; Zalewski, Piotr; Zavrtanik, D; Zevgolatakos, E; Zimin, N I; Zito, M; Zontar, D; Zuberi, R; Zucchelli, G C; Zumerle, G; Charpentier, Ph; Gavillet, Ph; Jarlskog, Ch; Papadopoulou, Th D
1996-01-01
Three jet events arising from decays of the Z boson, collected by the DELPHI detector, were used to measure differences in quark and gluon fragmentation. Gluon jets were anti-tagged by identifying b quark jets. Unbiased quark jets came from events with two jets plus one photon. Quark and gluon jet properties in different energy ranges were compared for the first time within the same detector. Quark and gluon jets of nearly the same energy in symmetric three jet event topologies were also compared. Using three independent methods, the average value of the ratio of the mean charged multiplicities of gluon and quark jets is \\[ =1.241\\pm 0.015\\ (stat.) \\pm 0.025\\ (syst.). \\] Gluon jets are broader and produce fragments with a softer energy spectrum than quark jets of equivalent energy. The string effect has been observed in fully symmetric three jet events. The measured ratio R_{\\gamma} of the charged particle flow in the q\\overline{q} inter-jet region of the q\\bar{q}g and q\\bar{q}\\gamma samples agrees with the p...
Search for scalar gluons with the ATLAS detector at the LHC
AUTHOR|(CDS)2079195; Zerwas, Dirk
This thesis describes the search for new color-octet scalar particles in the ATLAS experiment data at the Large Hadron Collider (LHC). For a wide range of mass, the decay of the scalar to two SM partons dominates. This motivates the search for these new scalars in multijet final states, where they would manifest as dijet resonances. As the new scalars are products in pairs, a final state containing at least four jets is used as a search environment. A method is developed to extract a possible scalar resonance from the multijet QCD background and is used to search for such scalar in the data from the ATLAS experiment collected in 2010 and 2011. The data are in agreement with the estimation of the background and limits are set on the scalar production cross section as a function of the scalar mass. Interpreting these limits in models of supersymmetry, the scalar gluon of the MRSSM and of the hybrid N=1/N=2 model is excluded at the 95 % CL between 100 and 287 GeV. Limits are also interpreted in a model of gauge ...
On the existence of a holographic description of the LHC quark–gluon plasmas
Energy Technology Data Exchange (ETDEWEB)
McInnes, Brett, E-mail: matmcinn@nus.edu.sg [Department of Mathematics, National University of Singapore, Singapore 119076 (Singapore); Ong, Yen Chin, E-mail: ongyenchin@sjtu.edu.cn [Center for Astronomy and Astrophysics, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China)
2017-04-15
Peripheral collisions of heavy ions can give rise to extremely intense magnetic fields. It has been suggested that these fields might invalidate the holographic description of the corresponding quark–gluon plasmas, assuming that these can be modelled by strongly coupled field theories. In the case of the plasmas produced in collisions at the RHIC facility (including in the beam energy scans), it is known how to deal with this problem: one has to take into account the large angular momenta generated in these plasmas, and the effects of the baryonic chemical potential. But this does not work for the plasmas produced in peripheral collisions at the LHC. However, these results neglect some (less significant) aspects of bulk physics; could it be that the problem is resolved by taking into account these lower-order effects? Here we use a bulk dilatonic field (fully compatible with boundary data, as well as with the asymptotically AdS character of the bulk geometry) as a model of these effects, and show that this is unlikely to be the solution. Thus, the existence of a consistent holographic description of the most extreme LHC plasmas remains open to question.
Quantum Wronskian approach to six-point gluon scattering amplitudes at strong coupling
International Nuclear Information System (INIS)
Hatsuda, Yasuyuki; Ito, Katsushi; Satoh, Yuji; Suzuki, Junji
2014-06-01
We study the six-point gluon scattering amplitudes in N=4 super Yang-Mills theory at strong coupling based on the twisted Z 4 -symmetric integrable model. The lattice regularization allows us to derive the associated thermodynamic Bethe ansatz (TBA) equations as well as the functional relations among the Q-/T-/Y-functions. The quantum Wronskian relation for the Q-/T-functions plays an important role in determining a series of the expansion coefficients of the T-/Y-functions around the UV limit, including the dependence on the twist parameter. Studying the CFT limit of the TBA equations, we derive the leading analytic expansion of the remainder function for the general kinematics around the limit where the dual Wilson loops become regular-polygonal. We also compare the rescaled remainder functions at strong coupling with those at two, three and four loops, and find that they are close to each other along the trajectories parameterized by the scale parameter of the integrable model.
Phase transition in a quark-gluon plasma and hydrodynamic theory
International Nuclear Information System (INIS)
Chernavskaya, O.D.; Chernavskij, D.S.
1988-01-01
A wide range of problem concerning the phase transition of a quark-gluon plasma to the hadron matter is considered in connection with the hardronization problem within the frame of the hydrodynamical theory of ultra-relativistic collisions. A short review of the present hadron models and possible mechanisms of thermalization is given. The character of the phase transition within the bag model is analysed, effects of the surface interaction result in a nontrivial character of the phase transition: the metastable states of matter become possible. The review of the possible scenaria of hadronization of the cooling hydrodynamical matter is given, the choice between them is determined by a kinetic analysis. The systems with the energy density near the critical point (∼ 4 GeV/Fm 3 ) are shown to be hadronized by the mechanism based on a strong plasma supercooling (with a considerable transverse momentum increase). The traditional hadronization mechanism (mixed phase) is preferable for more hot systems. Theoretical estimations are compared with the JACEE (cosmic rays) data
On the existence of a holographic description of the LHC quark–gluon plasmas
Directory of Open Access Journals (Sweden)
Brett McInnes
2017-04-01
Full Text Available Peripheral collisions of heavy ions can give rise to extremely intense magnetic fields. It has been suggested that these fields might invalidate the holographic description of the corresponding quark–gluon plasmas, assuming that these can be modelled by strongly coupled field theories. In the case of the plasmas produced in collisions at the RHIC facility (including in the beam energy scans, it is known how to deal with this problem: one has to take into account the large angular momenta generated in these plasmas, and the effects of the baryonic chemical potential. But this does not work for the plasmas produced in peripheral collisions at the LHC. However, these results neglect some (less significant aspects of bulk physics; could it be that the problem is resolved by taking into account these lower-order effects? Here we use a bulk dilatonic field (fully compatible with boundary data, as well as with the asymptotically AdS character of the bulk geometry as a model of these effects, and show that this is unlikely to be the solution. Thus, the existence of a consistent holographic description of the most extreme LHC plasmas remains open to question.
International Nuclear Information System (INIS)
Salmeron, R.A.
1992-01-01
The deconfinement of quarks, antiquarks and gluons, and the phase transition from a hadron phase to a quark-gluon plasma phase are presented after recalling some elementary notions about normal nuclear matter. Eight proposed signatures of the quark-gluon plasma are described and a summary is given of the experiments concerning three of them: Bose-Einstein interference, the suppression of the J/ψ production and strange particles production. (author)
Associated production of a KK-graviton with a Higgs boson via gluon fusion at the LHC
International Nuclear Information System (INIS)
Shivaji, Ambresh; Mitra, Subhadip; Agrawal, Pankaj
2012-01-01
In order to solve the hierarchy problem, several extra-dimensional models have received considerable attention. We have considered a process where a Higgs boson is produced in association with a KK-graviton (G KK ) at the LHC. At the leading order, this process occurs through the gluon fusion mechanism gg→hG KK via a quark loop. We compute the cross section and examine some features of this process in the ADD model. We find that the quark in the loop does not decouple in the large quark-mass limit just as in the case of gg→h process. We compute the cross section of this process for the case of the RS model also. We examine the feasibility of this process being observed at the LHC. (orig.)
Van Baal, Pierre; Korthals Altes, Chris P
2013-01-01
This volume is a collection of selected papers by Pierre van Baal on the subject of quark-gluon interactions. He concentrates on semi-perturbative phenomena that occur when these particles are confined to a box. He introduced in 1998 the notion of calorons to explain what happens in the high temperature phase of the quark-gluon plasma. Van Baal's discoveries of the mathematical intricacies of twisted gluon field configurations have left their mark on the field, opening new directions for numerical simulations. This reprint is intended to be a comprehensive introduction for all those who wish to have deeper understanding of quark-gluon dynamics.
Gluons and the quark sea at high energies: distributions, polarization, tomography
Energy Technology Data Exchange (ETDEWEB)
Boer, D.; Venugopalan, R.; Diehl, M.; Milner, R.; Vogelsang, W.; et al.
2011-09-30
This report is based on a ten-week program on Gluons and the quark sea at high-energies, which took place at the Institute for Nuclear Theory (INT) in Seattle in Fall 2010. The principal aim of the program was to develop and sharpen the science case for an Electron-Ion Collider (EIC), a facility that will be able to collide electrons and positrons with polarized protons and with light to heavy nuclei at high energies, offering unprecedented possibilities for in-depth studies of quantum chromodynamics (QCD). This report is organized around the following four major themes: (i) the spin and flavor structure of the proton, (ii) three dimensional structure of nucleons and nuclei in momentum and configuration space, (iii) QCD matter in nuclei, and (iv) Electroweak physics and the search for physics beyond the Standard Model. Beginning with an executive summary, the report contains tables of key measurements, chapter overviews for each of the major scientific themes, and detailed individual contributions on various aspects of the scientific opportunities presented by an EIC.
Gluons and the quark sea at high energies: distributions, polarization, tomography
Boer, D; Milner, Richard; Venugopalan, Raju; Vogelsang, Werner; Kaplan, David; Montgomery, Hugh; Vigdor, Steven; Accardi, A.; Aschenauer, E.C.; Burkardt, M.; Ent, R.; Guzey, V.; Hasch, D.; Kumar, K.; Lamont, M.A.C.; Li, Ying-chuan; Marciano, W.; Marquet, C.; Sabatie, F.; Stratmann, M.; Yuan, F.; Sassot, R.; Zurita, P.; Cherednikov, I.O.; Goncalves, V.P.; Sandapen, R.; Kopeliovich, B.Z.; Gao, J.-H.; Liang, Z.-T.; Passek-Kumericki, K.; Kumericki, K.; Lappi, T.; Wallon, S.; Pire, B.; Geraud, R.; Moutarde, H.; Gelis, F.; Soyez, G.; Meskauskas, M.; Mueller, Dieter; Stefanis, N.G.; Gallmeister, K.; Mosel, U.; Diehl, M.; Bartels, J.; Pirner, H.J.; Hagler, P.; Jager, B.; Spiesberger, H.; Lautenschlager, T.; Schafer, A.; Ringer, F.; Vogelsang, W.; Kroll, P.; Alekhin, S.; Blumlein, J; Moch, S.-O.; Pisano, C.; Rojo, J.; Bacchetta, A.; Pasquini, B.; Radici, M.; Ciofi degli Atti, C.; Mezzetti, C.B.; Kaptari, L.P.; Anselmino, M.; Tanaka, K.; Koike, Y.; Kumano, S.; Motyka, L.; Golec-Biernat, K.; Stasto, A.M.; Golec-Biernat, K.; Szymanowski, L.; Cherednikov, I.O.; Kaptari, L.P.; Radyushkin, A.; Alekhin, S.; Kondratenko, A.; Horowitz, W.A.; Schnell, G.; Chevtsov, P.; Mulders, P.J.; Rogers, T.C.; Boer, D.; Forshaw, J.R.; Cooper-Sarkar, A.; Chirilli, G.A.; Muller, D.; Wang, X.-N.; Yuan, F.; Qian, X.; Brodsky, S.J.; Schweitzer, P.; Horn, T.; Tuchin, K.; Dupre, R.; Erdelyi, B.; Manikonda, S.; Ostrumov, P.N.; Abeyratne, S.; Erdelyi, B.; Vossen, A.; Riordan, S.; Tsentalovich, E.; Goldstein, G.R.; Pozdeyev, E.; Huang, M.; Aidala, C.; Dumitru, A.; Dominguez, F.; Ben-Zvi, I.; Deshpande, A.; Faroughy, C.; Hammons, L.; Hao, Y.; Johnson, E.C.; Litvinenko, V.N.; Taneja, S.; Tsoupas, N.; Webb, S.; Beebe-Wang, J.; Belomestnykh, S.; Ben-Zvi, I.; Blaskiewicz, M.M.; Calaga, R.; Chang, X.; Fedotov, A.; Gassner, D.; Hahn, H.; Hammons, L.; Hao, Y.; He, P.; Jackson, W.; Jain, A.; Johnson, E.C.; Kayran, D.; Kewisch, J.; Litvinenko, V.N.; Luo, Y.; Mahler, G.; McIntyre, G.; Meng, W.; Minty, M.; Parker, B.; Pikin, A.; Ptitsyn, V.; Rao, T.; Roser, T.; Sheehy, B.; Skaritka, J.; Tepikian, S.; Than, Y.; Trbojevic, D.; Tsoupas, N.; Tuozzolo, J.; Wang, G.; Webb, S.; Wu, Q.; Xu, W.; Zelenski, A.; Beuf, G.; Burton, T.; Debbe, R.; Fazio, S.; Marciano, W.J.; Qiu, J.-W.; Toll, T.; Ullrich, T.; Deshpande, A.; Dumitru, A.; Kang, Z.-B.; Stasto, A.M.; Yuan, F.; Kovchegov, Y.V.; Majumder, A; Metz, A.; Zhou, J.; Gamberg, L.; Stasto, A.M.; Strikman, M.; Xiao, B.-W.; Guzzi, M.; Nadolsky, P.; Olness, F.; BC, H.; Liuti, S.; Ahmed, S.; Bogacz, A.; Derbenev, Ya.; Hutton, A.; Krafft, G.; Li, R.; Marhauser, F.; Morozov, V.; Pilat, F.; Rimmer, R.; Satogata, T.; Sullivan, M.; Spata, M.; Terzic, B.; Wang, H.; Yunn, B.; Zhang, Y.; Avakian, H.; Musch, B.; Nadel-Turonski, P.; Prokudin, A.; Radyushkin, A.; Weiss, C.; Krafft, G.; Radyushkin, A.; Sayed, H.; Gilfoyle, G.P.; Cloet, I.C.; Miller, G.; Gonderinger, M.
2011-01-01
This report is based on a ten-week program on "Gluons and the quark sea at high-energies", which took place at the Institute for Nuclear Theory in Seattle in Fall 2010. The principal aim of the program was to develop and sharpen the science case for an Electron-Ion Collider (EIC), a facility that will be able to collide electrons and positrons with polarized protons and with light to heavy nuclei at high energies, offering unprecedented possibilities for in-depth studies of quantum chromodynamics. This report is organized around four major themes: i) the spin and flavor structure of the proton, ii) three-dimensional structure of nucleons and nuclei in momentum and configuration space, iii) QCD matter in nuclei, and iv) Electroweak physics and the search for physics beyond the Standard Model. Beginning with an executive summary, the report contains tables of key measurements, chapter overviews for each of the major scientific themes, and detailed individual contributions on various aspects of the scientific op...
How does the Quark-Gluon Plasma know the collision energy?
McInnes, Brett
2018-02-01
Heavy ion collisions at the LHC facility generate a Quark-Gluon Plasma (QGP) which, for central collisions, has a higher energy density and temperature than the plasma generated in central collisions at the RHIC. But sufficiently peripheral LHC collisions give rise to plasmas which have the same energy density and temperature as the "central" RHIC plasmas. One might assume that the two versions of the QGP would have very similar properties (for example, with regard to jet quenching), but recent investigations have suggested that they do not: the plasma "knows" that the overall collision energy is different in the two cases. We argue, using a gauge-gravity analysis, that the strong magnetic fields arising in one case (peripheral collisions), but not the other, may be relevant here. If the residual magnetic field in peripheral LHC plasmas is of the order of at least eB ≈ 5mπ2, then the model predicts modifications of the relevant quenching parameter which approach those recently reported.
NLO QCD result for the gluon polarization from open charm $D^{0}$ meson production at COMPASS
Kurek, Krzysztof
2011-01-01
One of the main goals of the COMPASS experiment is the measurement of the gluon contribution to the nucleon spin. Among the processes studied by COMPASS, open- charm $D^{0}$ meson production seems to be the cleanest channel for probing gluons in the energy range covered by the experiment. The gluon polarisation is related to the measured asymmetry for charmed mesons production via the analyzing power (asymmetry at the partonic level) calculated in the perturbative QCD frame. The analyzing power for the "photon-gluon fusion" process corresponds to a LO QCD approximation. The signicant improvement of the statistical precision and the new, nal LO result are presented . The NLO QCD corrections to the partonic cross sections (unpolarised and polarized ones) are now also included into the analysis scheme since these higher order contributions are not negligible. The preliminary NLO QCD result on the gluon polarisation based on a set of measured $D^{0}$ meson asymmetries in kinematical bins of the $D^{0}$ energy amd...
Experimental properties of gluon and quark jets from a point source
Abbiendi, G.; Alexander, G.; Allison, John; Altekamp, N.; Anderson, K.J.; Anderson, S.; Arcelli, S.; Asai, S.; Ashby, S.F.; Axen, D.; Azuelos, G.; Ball, A.H.; Barberio, E.; Barlow, Roger J.; Batley, J.R.; Baumann, S.; Bechtluft, J.; Behnke, T.; Bell, Kenneth Watson; Bella, G.; Bellerive, A.; Bentvelsen, S.; Bethke, S.; Betts, S.; Biebel, O.; Biguzzi, A.; Blobel, V.; Bloodworth, I.J.; Bock, P.; Bohme, J.; Bonacorsi, D.; Boutemeur, M.; Braibant, S.; Bright-Thomas, P.; Brigliadori, L.; Brown, Robert M.; Burckhart, H.J.; Capiluppi, P.; Carnegie, R.K.; Carter, A.A.; Carter, J.R.; Chang, C.Y.; Charlton, David G.; Chrisman, D.; Ciocca, C.; Clarke, P.E.L.; Clay, E.; Cohen, I.; Conboy, J.E.; Cooke, O.C.; Couyoumtzelis, C.; Coxe, R.L.; Cuffiani, M.; Dado, S.; Dallavalle, G.Marco; Davis, R.; De Jong, S.; de Roeck, A.; Dervan, P.; Desch, K.; Dienes, B.; Dixit, M.S.; Dubbert, J.; Duchovni, E.; Duckeck, G.; Duerdoth, I.P.; Estabrooks, P.G.; Etzion, E.; Fabbri, F.; Fanfani, A.; Fanti, M.; Faust, A.A.; Fiedler, F.; Fierro, M.; Fleck, I.; Folman, R.; Frey, A.; Furtjes, A.; Futyan, D.I.; Gagnon, P.; Gary, J.W.; Gascon, J.; Gascon-Shotkin, S.M.; Gaycken, G.; Geich-Gimbel, C.; Giacomelli, G.; Giacomelli, P.; Gibson, V.; Gibson, W.R.; Gingrich, D.M.; Glenzinski, D.; Goldberg, J.; Gorn, W.; Grandi, C.; Graham, K.; Gross, E.; Grunhaus, J.; Gruwe, M.; Hanson, G.G.; Hansroul, M.; Hapke, M.; Harder, K.; Harel, A.; Hargrove, C.K.; Hauschild, M.; Hawkes, C.M.; Hawkings, R.; Hemingway, R.J.; Herndon, M.; Herten, G.; Heuer, R.D.; Hildreth, M.D.; Hill, J.C.; Hobson, P.R.; Hoch, M.; Hocker, James Andrew; Hoffman, Kara Dion; Homer, R.J.; Honma, A.K.; Horvath, D.; Hossain, K.R.; Howard, R.; Huntemeyer, P.; Igo-Kemenes, P.; Imrie, D.C.; Ishii, K.; Jacob, F.R.; Jawahery, A.; Jeremie, H.; Jimack, M.; Jones, C.R.; Jovanovic, P.; Junk, T.R.; Kanzaki, J.; Karlen, D.; Kartvelishvili, V.; Kawagoe, K.; Kawamoto, T.; Kayal, P.I.; Keeler, R.K.; Kellogg, R.G.; Kennedy, B.W.; Kim, D.H.; Klier, A.; Kobayashi, T.; Kobel, M.; Kokott, T.P.; Kolrep, M.; Komamiya, S.; Kowalewski, Robert V.; Kress, T.; Krieger, P.; von Krogh, J.; Kuhl, T.; Kyberd, P.; Lafferty, G.D.; Landsman, H.; Lanske, D.; Lauber, J.; Lautenschlager, S.R.; Lawson, I.; Layter, J.G.; Lee, A.M.; Lellouch, D.; Letts, J.; Levinson, L.; Liebisch, R.; List, B.; Littlewood, C.; Lloyd, A.W.; Lloyd, S.L.; Loebinger, F.K.; Long, G.D.; Losty, M.J.; Lu, J.; Ludwig, J.; Lui, D.; Macchiolo, A.; Macpherson, A.; Mader, W.; Mannelli, M.; Marcellini, S.; Markopoulos, C.; Martin, A.J.; Martin, J.P.; Martinez, G.; Mashimo, T.; Mattig, Peter; McDonald, W.John; McKenna, J.; Mckigney, E.A.; McMahon, T.J.; McPherson, R.A.; Meijers, F.; Menke, S.; Merritt, F.S.; Mes, H.; Meyer, J.; Michelini, A.; Mihara, S.; Mikenberg, G.; Miller, D.J.; Mir, R.; Mohr, W.; Montanari, A.; Mori, T.; Nagai, K.; Nakamura, I.; Neal, H.A.; Nisius, R.; O'Neale, S.W.; Oakham, F.G.; Odorici, F.; Ogren, H.O.; Oreglia, M.J.; Orito, S.; Palinkas, J.; Pasztor, G.; Pater, J.R.; Patrick, G.N.; Patt, J.; Perez-Ochoa, R.; Petzold, S.; Pfeifenschneider, P.; Pilcher, J.E.; Pinfold, J.; Plane, David E.; Poffenberger, P.; Poli, B.; Polok, J.; Przybycien, M.; Rembser, C.; Rick, H.; Robertson, S.; Robins, S.A.; Rodning, N.; Roney, J.M.; Rosati, S.; Roscoe, K.; Rossi, A.M.; Rozen, Y.; Runge, K.; Runolfsson, O.; Rust, D.R.; Sachs, K.; Saeki, T.; Sahr, O.; Sang, W.M.; Sarkisian, E.K.G.; Sbarra, C.; Schaile, A.D.; Schaile, O.; Scharff-Hansen, P.; Schieck, J.; Schmitt, S.; Schoning, A.; Schroder, Matthias; Schumacher, M.; Schwick, C.; Scott, W.G.; Seuster, R.; Shears, T.G.; Shen, B.C.; Shepherd-Themistocleous, C.H.; Sherwood, P.; Siroli, G.P.; Sittler, A.; Skuja, A.; Smith, A.M.; Snow, G.A.; Sobie, R.; Soldner-Rembold, S.; Spagnolo, S.; Sproston, M.; Stahl, A.; Stephens, K.; Steuerer, J.; Stoll, K.; Strom, David M.; Strohmer, R.; Surrow, B.; Talbot, S.D.; Taras, P.; Tarem, S.; Teuscher, R.; Thiergen, M.; Thomas, J.; Thomson, M.A.; Torrence, E.; Towers, S.; Trigger, I.; Trocsanyi, Z.; Tsur, E.; Turcot, A.S.; Turner-Watson, M.F.; Ueda, I.; Van Kooten, Rick J.; Vannerem, P.; Verzocchi, M.; Voss, H.; Wackerle, F.; Wagner, A.; Ward, C.P.; Ward, D.R.; Watkins, P.M.; Watson, A.T.; Watson, N.K.; Wells, P.S.; Wermes, N.; White, J.S.; Wilson, G.W.; Wilson, J.A.; Wyatt, T.R.; Yamashita, S.; Yekutieli, G.; Zacek, V.; Zer-Zion, D.
1999-01-01
Gluon jets are identified in hadronic Z0 decays as all the particles in a hemisphere opposite to a hemisphere containing two tagged quark jets. Gluon jets defined in this manner are equivalent to gluon jets produced from a color singlet point source and thus correspond to the definition employed for most theoretical calculations. In a separate stage of the analysis, we select quark jets in a manner to correspond to calculations, as the particles in hemispheres of flavor tagged light quark (uds) events. We present the distributions of rapidity, scaled energy, the logarithm of the momentum, and transverse momentum with respect to the jet axes, for charged particles in these gluon and quark jets. We also examine the charged particle multiplicity distributions of the jets in restricted intervals of rapidity. For soft particles at large transverse momentum, we observe the charged particle multiplicity ratio of gluon to quark jets to be 2.29 +- 0.09 +- 0.15 in agreement with the prediction that this ratio should ap...
Abbiendi, G.; Akesson, P.F.; Alexander, G.; Allison, John; Amaral, P.; Anagnostou, G.; Anderson, K.J.; Arcelli, S.; Asai, S.; Axen, D.; Azuelos, G.; Bailey, I.; Barberio, E.; Barlow, R.J.; Batley, R.J.; Bechtle, P.; Behnke, T.; Bell, Kenneth Watson; Bell, P.J.; Bella, G.; Bellerive, A.; Benelli, G.; Bethke, S.; Biebel, O.; Boeriu, O.; Bock, P.; Boutemeur, M.; Braibant, S.; Brigliadori, L.; Brown, Robert M.; Buesser, K.; Burckhart, H.J.; Campana, S.; Carnegie, R.K.; Caron, B.; Carter, A.A.; Carter, J.R.; Chang, C.Y.; Charlton, David G.; Csilling, A.; Cuffiani, M.; Dado, S.; De Roeck, A.; De Wolf, E.A.; Desch, K.; Dienes, B.; Donkers, M.; Dubbert, J.; Duchovni, E.; Duckeck, G.; Duerdoth, I.P.; Etzion, E.; Fabbri, F.; Feld, L.; Ferrari, P.; Fiedler, F.; Fleck, I.; Ford, M.; Frey, A.; Furtjes, A.; Gagnon, P.; Gary, John William; Gaycken, G.; Geich-Gimbel, C.; Giacomelli, G.; Giacomelli, P.; Giunta, Marina; Goldberg, J.; Gross, E.; Grunhaus, J.; Gruwe, M.; Gunther, P.O.; Gupta, A.; Hajdu, C.; Hamann, M.; Hanson, G.G.; Harder, K.; Harel, A.; Harin-Dirac, M.; Hauschild, M.; Hawkes, C.M.; Hawkings, R.; Hemingway, R.J.; Hensel, C.; Herten, G.; Heuer, R.D.; Hill, J.C.; Hoffman, Kara Dion; Horvath, D.; Igo-Kemenes, P.; Ishii, K.; Jeremie, H.; Jovanovic, P.; Junk, T.R.; Kanaya, N.; Kanzaki, J.; Karapetian, G.; Karlen, D.; Kawagoe, K.; Kawamoto, T.; Keeler, R.K.; Kellogg, R.G.; Kennedy, B.W.; Kim, D.H.; Klein, K.; Klier, A.; Kluth, S.; Kobayashi, T.; Kobel, M.; Komamiya, S.; Kormos, Laura L.; Kramer, T.; Krieger, P.; von Krogh, J.; Kruger, K.; Kuhl, T.; Kupper, M.; Lafferty, G.D.; Landsman, H.; Lanske, D.; Layter, J.G.; Leins, A.; Lellouch, D.; Letts, J.; Levinson, L.; Lillich, J.; Lloyd, S.L.; Loebinger, F.K.; Lu, J.; Ludwig, J.; Macpherson, A.; Mader, W.; Marcellini, S.; Martin, A.J.; Masetti, G.; Mashimo, T.; Mattig, Peter; McDonald, W.J.; McKenna, J.; McMahon, T.J.; McPherson, R.A.; Meijers, F.; Menges, W.; Merritt, F.S.; Mes, H.; Michelini, A.; Mihara, S.; Mikenberg, G.; Miller, D.J.; Moed, S.; Mohr, W.; Mori, T.; Mutter, A.; Nagai, K.; Nakamura, I.; Nanjo, H.; Neal, H.A.; Nisius, R.; O'Neale, S.W.; Oh, A.; Okpara, A.; Oreglia, M.J.; Orito, S.; Pahl, C.; Pasztor, G.; Pater, J.R.; Patrick, G.N.; Pilcher, J.E.; Pinfold, J.; Plane, David E.; Poli, B.; Polok, J.; Pooth, O.; Przybycien, M.; Quadt, A.; Rabbertz, K.; Rembser, C.; Renkel, P.; Rick, H.; Roney, J.M.; Rosati, S.; Rozen, Y.; Runge, K.; Sachs, K.; Saeki, T.; Sarkisyan, E.K.G.; Schaile, A.D.; Schaile, O.; Scharff-Hansen, P.; Schieck, J.; Schoerner-Sadenius, Thomas; Schroder, Matthias; Schumacher, M.; Schwick, C.; Scott, W.G.; Seuster, R.; Shears, T.G.; Shen, B.C.; Sherwood, P.; Siroli, G.; Skuja, A.; Smith, A.M.; Sobie, R.; Soldner-Rembold, S.; Spano, F.; Stahl, A.; Stephens, K.; Strom, David M.; Strohmer, R.; Tarem, S.; Tasevsky, M.; Taylor, R.J.; Teuscher, R.; Thomson, M.A.; Torrence, E.; Toya, D.; Tran, P.; Trigger, I.; Trocsanyi, Z.; Tsur, E.; Turner-Watson, M.F.; Ueda, I.; Ujvari, B.; Vollmer, C.F.; Vannerem, P.; Vertesi, R.; Verzocchi, M.; Voss, H.; Vossebeld, J.; Waller, D.; Ward, C.P.; Ward, D.R.; Warsinsky, M.; Watkins, P.M.; Watson, A.T.; Watson, N.K.; Wells, P.S.; Wengler, T.; Wermes, N.; Wetterling, D.; Wilson, G.W.; Wilson, J.A.; Wolf, G.; Wyatt, T.R.; Yamashita, S.; Zer-Zion, D.; Zivkovic, Lidija
2004-01-01
We present the first experimental results based on the jet boost algorithm, a technique to select unbiased samples of gluon jets in e+e- annihilations, i.e. gluon jets free of biases introduced by event selection or jet finding criteria. Our results are derived from hadronic Z0 decays observed with the OPAL detector at the LEP e+e- collider at CERN. First, we test the boost algorithm through studies with Herwig Monte Carlo events and find that it provides accurate measurements of the charged particle multiplicity distributions of unbiased gluon jets for jet energies larger than about 5 GeV, and of the jet particle energy spectra (fragmentation functions) for jet energies larger than about 14 GeV. Second, we apply the boost algorithm to our data to derive unbiased measurements of the gluon jet multiplicity distribution for energies between about 5 and 18 GeV, and of the gluon jet fragmentation function at 14 and 18 GeV. In conjunction with our earlier results at 40 GeV, we then test QCD calculations for the en...
First measurement of the Sivers asymmetry for gluons using SIDIS data
Directory of Open Access Journals (Sweden)
C. Adolph
2017-09-01
Full Text Available The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. For quarks, it was studied in previous measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive deep inelastic scattering of leptons off transversely polarised nucleon targets, and it was found to be non-zero. In this letter the evaluation of the Sivers asymmetry for gluons is presented. The contribution of the photon–gluon fusion subprocess is enhanced by requiring two high transverse-momentum hadrons. The analysis method is based on a Monte Carlo simulation that includes three hard processes: photon–gluon fusion, QCD Compton scattering and the leading-order virtual-photon absorption process. The Sivers asymmetries of the three processes are simultaneously extracted using the LEPTO event generator and a neural network approach. The method is applied to samples of events containing at least two hadrons with large transverse momentum from the COMPASS data taken with a 160 GeV/c muon beam scattered off transversely polarised deuterons and protons. With a significance of about two standard deviations, a negative value is obtained for the gluon Sivers asymmetry. The result of a similar analysis for a Collins-like asymmetry for gluons is consistent with zero.
Forward gluon production in hadron-hadron scattering with Pomeron loops
Energy Technology Data Exchange (ETDEWEB)
Iancu, E. [CEA Saclay, Service de Physique Th orique (DSM/SPhT), Unite de recherche associ e au CNRS (URA D2306), 91 - Gif-sur-Yvette (France). Direction des Sciences de la Matiere; Marquet, C.; Soyez, G. [CEA Saclay, Service de Physique Th orique (DSM/SPhT), Unite de recherche associ e au CNRS (URA D2306), 91 - Gif-sur-Yvette (France). Direction des Sciences de la Matiere; Liege Univ., Fundamental Theoretical Physics Group (Belgium)
2006-07-01
We discuss new physical phenomena expected in particle production in hadron-hadron collisions at high energy, as a consequence of Pomerons loop effects in the evolution equations for the Color Glass Condensate. We focus on gluon production in asymmetric, 'dilute-dense', collisions: a dilute projectile scatters off a dense hadronic target, whose gluon distribution is highly evolved. This situation is representative for particle production in proton-proton collisions at forward rapidities (say, at LHC) and admits a dipole factorization similar to that of deep inelastic scattering (DIS). We show that at sufficiently large forward rapidities, where the Pomerons loop effects become important in the evolution of the target wavefunction, gluon production is dominated by 'black spots' (saturated gluon configurations) up to very large values of the transverse momentum, well above the average saturation momentum in the target. In this regime, the produced gluon spectrum exhibits diffusive scaling, so like DIS at sufficiently high energy. (authors)
Monte Carlo study on the properties of gluon and quark jets
Kun Shi Zhang; Mei Ling Yu; Lian Shou Liu
2002-01-01
The 3-jet events produced in e/sup +/e/sup -/ collisions at 91.2 GeV have been studied using Monte Carlo method. After applying two angular cuts the three angles between the jets are used to identify the individual jet in 3-jet events. The energy distributions of the three jets, the mean particle multiplicities, mean transverse momenta of the three jets in equal energy bins and their distributions have been analyzed. Comparing with the corresponding results from the quark jets in 2-jet events, a simple method to select gluon and quark jets from 3-jet events is obtained. The properties of the gluon and quark jets being selected using the introduced method are in qualitative agreement with the expectations of perturbative QCD. The ratio of the mean multiplicity between quark and gluon jets, /sub gluon///sub quark/, has been calculated. The results, again, agree with the experimental results from SLD, OPAL, ALEPH, and DELPHI Collaborations, indicating that the method proposed to select gluon and quark jets from ...
International Nuclear Information System (INIS)
Safronov, A.N.
1983-01-01
A system of nonsingular integral equations is formulated for calculation of the partial-wave amplitudes of hadron-hadron scattering in the region of low and intermediate energies with allowance for the meson and quark-gluon degrees of freedom. The quark-gluon degrees of freedom are taken into account in the framework of the model of composite quark bags, and the meson degrees of freedom by the methods of relativistic quantum field theory. It is shown that inclusion of the quark-gluon degrees of freedom leads to suppression of meson exchange effects, for the most part exchanges of heavy mesons (rho,ω). The method is applied to the calculation of the 3 S 1 , 1 S 0 , 3 P 0 , 3 P 1 , and 1 P 1 phase shifts of nucleon-nucleon scattering in the range of incident-nucleon energies T = 0--1050 MeV, as well as the S-wave scattering lengths and effective ranges
Quark-gluon plasma tomography by vector mesons
International Nuclear Information System (INIS)
Lovas, I.
2001-01-01
Full text: The most important aim of relativistic heavy ion experiments is the observation f the quark-gluon plasma formation. In order to detect the transition into the plasma state it is desirable to map the density profile of the fireball formed in the collision. Here we investigate the possibility of this mapping by tomography. The fireball is characterized by the impact parameter vector b, which can be determined from the multiplicity and the angular distribution of the reaction products. By appropriate rotations the b vectors of each collision can be aligned into a fixed direction. Using the measured values of the momentum distributions independent integral equations can be formulated for the unknown emission densities (EM(r) and for the unknown absorption densities (Δ μ M (r)) of the different vector mesons M(≡ ω 0 , ρ 0 , φ 0 , ψ 0 , ψ 0' , Υ). At a fixed value of M and b the number of detected mesons N M (p,b) with momentum p, can be expressed by the following formula: N M (p,b) = ∫ V(b) dr EM(r) exp[-μ M (p)L(r,p o )] V(b) R(r, po)] exp[- ∫ from r until R(r,p 0 ) dl ' Δ μ M (r ' ,p)], where the average value of the absorption coefficient having no r dependence is denoted by μ(p), while Δ μM is defined as Δ μM = μ M - μ- M . The meson arrives to the surface of the fireball at R(r, p 0 ). The length of the path between r and R is denoted by L(r, po). The equation given above can be considered as an integral equation. Unfortunately it can not be transformed into an exact system of linear equations. However an iterative procedure can be constructed in such a way that in every iterative step a linear system of equations must be solved. N M (p,b) = ∫ V(b) dr exp[- μ M (p) L(r,p o )] [E M n (r) Σ from k=O until (n-1) (1/k !) (- ∫ from r until R (r, p 0 ) dl ' Δ μM n-1 (r ' , p) k + E M n-1 (r) (1/n !) (- ∫ from r until R(r, p 0 ) dl ' Δ μM n-1 (r ' , p)) (n-1) (- ∫ from r until R(r, p 0 ) dl ' Δ μM (n) (r ' , p))]. Since
Bergner, Georg; Piemonte, Stefano
2018-04-01
Non-Abelian gauge theories with fermions transforming in the adjoint representation of the gauge group (AdjQCD) are a fundamental ingredient of many models that describe the physics beyond the Standard Model. Two relevant examples are N =1 supersymmetric Yang-Mills (SYM) theory and minimal walking technicolor, which are gauge theories coupled to one adjoint Majorana and two adjoint Dirac fermions, respectively. While confinement is a property of N =1 SYM, minimal walking technicolor is expected to be infrared conformal. We study the propagators of ghost and gluon fields in the Landau gauge to compute the running coupling in the MiniMom scheme. We analyze several different ensembles of lattice Monte Carlo simulations for the SU(2) adjoint QCD with Nf=1 /2 ,1 ,3 /2 , and 2 Dirac fermions. We show how the running of the coupling changes as the number of interacting fermions is increased towards the conformal window.
Dynamical behavior connection of the gluon distribution and the proton structure function at small x
International Nuclear Information System (INIS)
Boroun, G.R.
2014-01-01
We make a critical study of the relationship between the singlet structure function F 2 S and the gluon distribution G(x,Q 2 ) proposed in the past two decades, which is frequently used to extract the gluon distribution from the proton structure function. We show that a simple relation is not generally valid in the simplest state. We complete this relation by using a Laplace transform method and hard-pomeron behavior at LO and NLO at small x. Our study shows that this relation is dependent on the splitting functions and initial conditions at Q 2 =Q 2 0 and running coupling constant at NLO. The resulting analytic expression allows us to predict the proton structure function with respect to the gluon distributions and to compare the results with H1 data and a QCD analysis fit. Comparisons with other results are made and predictions for the proposed best approach are also provided. (orig.)
International Nuclear Information System (INIS)
Chirilli, Giovanni A.; Kovchegov, Yuri V.; Wertepny, Douglas E.
2015-01-01
We calculate the classical single-gluon production amplitude in nucleus-nucleus collisions including the first saturation correction in one of the nuclei (the projectile) while keeping multiple-rescattering (saturation) corrections to all orders in the other nucleus (the target). In our approximation only two nucleons interact in the projectile nucleus: the single-gluon production amplitude we calculate is order-g"3 and is leading-order in the atomic number of the projectile, while resumming all order-one saturation corrections in the target nucleus. Our result is the first step towards obtaining an analytic expression for the first projectile saturation correction to the gluon production cross section in nucleus-nucleus collisions.
Experimental test of the flavor independence of the quark-gluon coupling constant
International Nuclear Information System (INIS)
Althoff, M.; Braunschweig, W.; Kirschfink, F.J.; Luebelsmeyer, K.; Martyn, H.U.; Rimkus, J.; Rosskamp, P.; Sander, H.G.; Schmitz, D.; Siebke, H.; Wallraff, W.; Duchovni, E.; Karshon, U.; Mikenberg, G.; Mir, R.; Revel, D.; Ronat, E.; Shapira, A.; Yekutieli, G.; Baranko, G.; Barklow, T.; Caldwell, A.; Cherney, M.; Izen, J.M.; Mermikides, M.; Rudolph, G.; Strom, D.; Takashima, M.; Venkataramania, H.; Wicklund, E.; Sau Lan Wu; Zobernig, G.; Eisenberg, Y.; Eskreys, A.; Gather, K.; Hultschig, H.; Joos, P.; Koetz, U.; Kowalski, H.; Ladage, A.; Loehr, B.; Lueke, D.; Maettig, P.; Maettig, P.; Notz, D.; Nowak, R.J.; Pyrlik, J.; Rushton, M.; Schuette, W.; Trines, D.; Wolf, G.; Xiao, C.
1984-01-01
Reconstruction of charged Dsup(*)'s produced inclusively in e + e - annhilations at c.m. energies near 34.4 GeV is accomplished in the decay modes Dsup(*+) -> D 0 π + -> K - π + π 0 π + and Dsup(*+) -> D 0 π + -> K - π + π - π + π + and their charge conjugates. Using these and previously reported Dsup(*+) -> D 0 π + -> K - π + π + and Dsup(*+) -> D 0 π + -> K - π + π + + missing π 0 channels we present evidence for hard gluon bremsstrahlung from charm quarks and show that the ratio of the quark-gluon coupling constant of charm quarks to the coupling constant obtained in the average hadronic event, αsub(s)sup(c)/αsub(s) = 1.00 +- 0.20 +- 0.20. Our result provides evidence that the quark-gluon coupling constant is independent of flavor. (orig.)
Infrared behavior of gluons and ghosts in ghost-antighost symmetric gauges
International Nuclear Information System (INIS)
Alkofer, R.; Fischer, C.S.; Reinhardt, H.; Smekal, L. von
2003-01-01
To investigate the possibility of a ghost-antighost condensate, the coupled Dyson-Schwinger equations for the gluon and ghost propagators in Yang-Mills theories are derived in general covariant gauges, including ghost-antighost symmetric gauges. The infrared behavior of these two-point functions is studied in a bare-vertex truncation scheme which has proven to be successful in the Landau gauge. In all linear covariant gauges the same infrared behavior as in the Landau gauge is found: The gluon propagator is infrared-suppressed whereas the ghost propagator is infrared-enhanced. This infrared singular behavior provides an indication against a ghost-antighost condensate. In the ghost-antighost symmetric gauges we find that the infrared behavior of the gluon and ghost propagators cannot be determined when replacing all dressed vertices by bare ones. The question of a BRS invariant dimension-2 condensate remains to be further studied
Resummation of soft gluon logarithms in the DGLAP evolution of fragmentation functions
International Nuclear Information System (INIS)
Albino, S.; Kniehl, B.A.; Kramer, G.; Ochs, W.
2005-10-01
We define a general scheme for the evolution of fragmentation functions which resums both soft gluon logarithms and mass singularities in a consistent manner and to any order, and requires no additional theoretical assumptions. Using the Double Logarithmic Approximation and the known perturbative results for the splitting functions, we present our scheme with the complete contribution from the double logarithms, being the largest soft gluon logarithms. We show that the resulting approximation is more complete than the Modified Leading Logarithm Approximation even with the fixed order contribution calculated to leading order only, and find, after using it to fit quark and gluon fragmentation functions to experimental data, that this approximation in our scheme gives a good description of the data from the largest χ p values to the peak region in ξ=ln(1/χ p ), in contrast to other approximations. In addition, we develop a treatment of hadron mass effects which gives additional improvements at large ξ. (orig.)
A T-matrix calculation for in-medium heavy-quark gluon scattering
International Nuclear Information System (INIS)
Huggins, K.; Rapp, R.
2012-01-01
The interactions of charm and bottom quarks in a quark-gluon plasma (QGP) are evaluated using a thermodynamic 2-body T-matrix. We specifically focus on heavy-quark (HQ) interactions with thermal gluons with an input potential motivated by lattice-QCD computations of the HQ free energy. The latter is implemented into a field-theoretic ansatz for color-Coulomb and (remnants of) confining interactions. This, in particular, enables to discuss corrections to the potential approach, specifically hard-thermal-loop corrections to the vertices, relativistic corrections deduced from pertinent Feynman diagrams, and a suitable projection on transverse thermal gluons. The resulting potentials are applied to compute scattering amplitudes in different color channels and utilized for a calculation of the corresponding HQ drag coefficient in the QGP. A factor of ∼2-3 enhancement over perturbative results is obtained, mainly driven by the resummation in the attractive color-channels.
Bound-state quark and gluon contributions to structure functions in QCD
International Nuclear Information System (INIS)
Brodsky, S.J.
1990-08-01
One can distinguish two types of contributions to the quark and gluon structure functions of hadrons in quantum chromodynamics: ''intrinsic'' contributions, which are due to the direct scattering on the bound-state constituents, and ''extrinsic'' contributions, which are derived from particles created in the collision. In this talk, I discussed several aspects of deep inelastic structure functions in which the bound-state structure of the proton plays a crucial role: the properties of the intrinsic gluon distribution associated with the proton bound-state wavefunction; the separation of the quark structure function of the proton onto intrinsic ''bound-valence'' and extrinsic ''non-valence'' components which takes into account the Pauli principle; the properties and identification of intrinsic heavy quark structure functions; and a theory of shadowing and anti-shadowing of nuclear structure functions, directly related to quark-nucleon interactions and the gluon saturation phenomenon. 49 refs., 5 figs
Bound-state quark and gluon contributions to structure functions in QCD
International Nuclear Information System (INIS)
Brodsky, S.J.
1991-01-01
One can distinguish two types of contributions to the quark and gluon structure functions of hadrons in quantum chromodynamics: 'intrinsic' contributions, which are due to the direct scattering on the bound-state constituents, and 'extrinsic' contributions, which are derived from particles created in the collision. In this talk, I discuss several aspects of deep inealstic structure functions in which the bound-state structure of the proton plays a crucial role: (1) the properties of the intrinsic gluon distribution associated with the proton bound-state wavefunction; (2) the separation of the quark structure function of the proton into intrinsic 'bound-valence' and extrinsic 'non-valence' components which takes into account the Pauli principle; (3) the properties and identification of intrinsic heavy quark structure functions; and (4) a theory of shadowing and anti-shadowing of nuclear structure functions, directly related to quark-nucleon interactions and the gluon saturation phenomenon. (orig.)
Different methods for quark/gluon jet classification on real data from the DELPHI detector
International Nuclear Information System (INIS)
Transtroemer, G.
1999-05-01
Different methods to separate quark jets from gluon jets have been investigated and tested on data from the DELPHI experiment. A test sample of gluon jets was selected from bb-barg threejet events where the two b-jets had been identified using a lifetime tag and quark jet sample was obtained from qq-barγ events where the photon was required to have a high energy and to be well separated from the two jets. Three types of tests were made. Firstly, the jet energy, which is the variable most frequently used for quark/gluon jet separation, was compared with methods based of the differences in the fragmentation of quark and gluon jets. It was found that the fragmentation based classification provides significantly better identification than the jet energy only in events where the jets all have approximately the same energy. In Monte Carlo generated symmetric e + e - → qq-barg threejet events, where the jet energy does not provide any identification at all, the gluon jet was correctly assigned in 58 % of the events. More important, however, is that the identification has been divided into two independent parts, the energy part and the fragmentation part. Secondly, two different sets of fragmentation sensitive variables were tested. It was found that a slightly better identification could be achieved using information from all the particles of the jet rather than using only the leading ones. Thirdly, three types of statistical discrimination methods were compared: a cut on a single fragmentation variable; a cut on the Fisher statistical discriminant calculated from one set of variables; a cut on the output from an Artificial Neural Networks (ANN) trained on different sets of variables. The three types of classifiers gave about the same performance and one conclusion from this study was that the use of ANNs or Fisher statistical discrimination do not seem to improve the results significantly in quark/gluon jet separation on a jet to jet basis
International Nuclear Information System (INIS)
Kondrashova, Nataliia
2016-04-01
A measurement of the differential cross-section of pp→Z/γ * (→e + e - )+jet production and a study of the jet quark-gluon decomposition are presented. The data of 21.3 fb -1 collected with the ATLAS detector at the Large Hadron Collider in 2012 at the centre-of-mass energy √(s)=8 TeV are used. The double-differential pp→Zγ * (→e + e - )+jet cross-section is measured as a function of the absolute rapidity and the transverse momentum of jets. The jet quark-gluon decomposition study is performed in bins of the transverse momentum and the absolute rapidity of the highest-p T jet. The possibility to distinguish between quark-initiated and gluon-initiated jets is especially important for beyond Standard Mode searches, where a lot of signal processes have quarks in the final states, while background processes in Quantum Chromodynamic have mostly gluons. The performance of the discrimination between these two types of jets using different jet properties is studied using data-driven techniques with purified quark-like and gluon-like jet samples. The pp→Z/γ * (→e + e - )+jet production provides an important test of perturbative Quantum Chromodynamics and is an important background for many Standard Model processes and beyond Standard Model searches. In addition, the measurement of the pp→Z/γ * (→e + e - )+jet cross section as a function of the absolute rapidity and the transverse momentum of inclusive jets provides constraints on the uncertainties on the parton distribution functions. The rapidity of jets provides the information on the fraction of the initial proton's momentum carried by the interacting partons, which provides the sensitivity to the parton distribution functions, while the transverse momentum of jets allows to probe different transfer momentum scales.The measured cross-section is compared to the predictions from Monte Carlo generators based on leading order matrix elements and supplemented by parton showers, where the predictions
Possibility of determining gluon polarization via polarized top pairs in gamma-proton scattering
International Nuclear Information System (INIS)
Atag, S.; Billur, A.A.
2009-01-01
We study the possibility for directly measuring the polarized gluon distribution in the process γp→t-bar t. It is shown that polarization asymmetry of the final top quarks is proportional to the gluon polarization. With available energy and luminosity, the collision of a polarized proton beam and a Compton backscattered photon beam can create polarized top quarks which carry the spin information of the process. Energy dependence and angular distributions of the polarization asymmetry of the top pairs has been discussed including statistical uncertainty.
Gluon and ghost correlation functions of 2-color QCD at finite density
Hajizadeh, Ouraman; Boz, Tamer; Maas, Axel; Skullerud, Jon-Ivar
2018-03-01
2-color QCD, i. e. QCD with the gauge group SU(2), is the simplest non-Abelian gauge theory without sign problem at finite quark density. Therefore its study on the lattice is a benchmark for other non-perturbative approaches at finite density. To provide such benchmarks we determine the minimal-Landau-gauge 2-point and 3-gluon correlation functions of the gauge sector and the running gauge coupling at finite density. We observe no significant effects, except for some low-momentum screening of the gluons at and above the supposed high-density phase transition.