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Title: Strangeness chemical equilibration in a quark-gluon plasma

Abstract

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.

Authors:
;  [1];  [2]
  1. Laboratoire de Physique Theorique et Hautes Energies, Universite Paris 7, 2 place Jussieu, F-75251 Cedex 05 (France)
  2. (United States)
Publication Date:
OSTI Identifier:
20990968
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 75; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevC.75.014905; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; BROOKHAVEN RHIC; CERN LHC; ENTROPY; HEAVY ION REACTIONS; QUANTUM CHROMODYNAMICS; QUARK MATTER; STRANGENESS

Citation Formats

Letessier, Jean, Rafelski, Johann, and Department of Physics, University of Arizona, Tucson, Arizona 85721. Strangeness chemical equilibration in a quark-gluon plasma. United States: N. p., 2007. Web. doi:10.1103/PHYSREVC.75.014905.
Letessier, Jean, Rafelski, Johann, & Department of Physics, University of Arizona, Tucson, Arizona 85721. Strangeness chemical equilibration in a quark-gluon plasma. United States. doi:10.1103/PHYSREVC.75.014905.
Letessier, Jean, Rafelski, Johann, and Department of Physics, University of Arizona, Tucson, Arizona 85721. Mon . "Strangeness chemical equilibration in a quark-gluon plasma". United States. doi:10.1103/PHYSREVC.75.014905.
@article{osti_20990968,
title = {Strangeness chemical equilibration in a quark-gluon plasma},
author = {Letessier, Jean and Rafelski, Johann and Department of Physics, University of Arizona, Tucson, Arizona 85721},
abstractNote = {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.},
doi = {10.1103/PHYSREVC.75.014905},
journal = {Physical Review. C, Nuclear Physics},
number = 1,
volume = 75,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • We develop a kinetic theory of chemical reactions in a quark-gluon plasma in order to study the evolution of flavor composition in ultrarelativistic nucleus-nucleus collisions. The rates of production and annihilation of strange-quark pairs are computed in lowest order in perturbation theory assuming local equilibrium with respect to other, more frequent collision processes. Quantum-statistical effects are taken into account. The hydrodynamic equations coupled to the rate equation are derived and solved numerically in a homogeneous plasma, simulating the approach toward complete chemical equilibrium. The corresponding relaxation times are computed.
  • A calculation of thermal gluon decay shows that this process contributes significantly to strangeness production in a quark-gluon plasma. Our analysis does not support recent claims that this is the dominant process. In our calculations we take into account the resummed form of the transverse and longitudinal parts of the gluon propagator following the Braaten-Pisarski method. The estimate of the damping rate entering the effective gluon propagator subjects our results to uncertainty.
  • We investigate the chemical equilibration of the parton distributions in collisions of two heavy nuclei. We use initial conditions obtained from a self-screened parton cascade calculation and, for comparison, from the HIJING model. We consider a one-dimensional as well as a three-dimensional expansion of the parton plasma and find that the onset of the transverse expansion impedes the chemical equilibration. At energies of 100 GeV/nucleon, the results for one-dimensional and three-dimensional expansions are quite similar except at large values of the transverse radius. At energies of several TeV/nucleon, the plasma initially approaches chemical equilibrium, but then is driven away frommore » it, when the transverse velocity gradients develop. We find that the total parton multiplicity density remains essentially unaffected by the flow, but the individual concentrations of quarks, antiquarks, and gluons are sensitive to the transverse flow. The consequences of the flow are also discernible in the transverse momenta of the partons and in the lepton pair spectra, where the flow causes a violation of the so-called M{sub T} scaling. {copyright} {ital 1997} {ital The American Physical Society}« less
  • A dynamical model has been developed to study the evolution of a quark-gluon system towards equilibrium with the gluons equilibrating prior to the quarks and the quarks executing random Brownian motion in the gluonic heat bath. We estimate the thermalization times for various quark flavors and heavy flavor production rates within this model.
  • We consider the production of strange particles in relativistic nucleus-nucleus collisions. We employ a quark-gluon plasma (QGP) formalism, incorporating the production of the (anti)quarks in the plasma during equilibration by the gluon field. We assume generally accepted [ital T]([mu][sub [ital q]]=0) and [mu][sub [ital q]]([ital T]=0) values to construct a phase curve, defining an approximate lower limit of the ideal QGP phase. We express the strange particle ratios as function of [mu][sub [ital q]] and [ital T] along this curve and predict quantitatively their minimum QGP values. We analyze the NA36 and WA85 CERN experiments and obtain the quarkchemical potentials,more » [mu][sub [ital q]], [mu][sub [ital s]] and the chemical equilibration, [gamma][sub [ital s]]. The gluon sector, providing the [bar q]'s, is necessary for the correct and consistent estimation of these quantities and prediction of all strange particle ratios. We put forward that the values of [ital T], [mu][sub [ital q]], [mu][sub [ital s]], and [gamma][sub [ital s]] are the only significant quantities determining a possible phase transition, not the magnitude of any strange particle ratio, as previously proclaimed. We find that the 200 GeV/nucleon [sup 32]S-induced interactions at midrapidity may have approached the ideal QGP phase to within about 60%.« less