Equilibration Of Quark-gluon Plasma Research Articles

Strangeness enhancement

t. Highly effective conversion of kinetic energy into abundant particle multiplicity is the remarkable feature discovered in high energy heavy ion collisions. This short and pedagogic review addresses topical issues related to the understanding of this phenomenon, originating in the creation of the deconfined quark-gluon plasma phase. I consider in depth the apparently simple, yet sometimes misunderstood, intricate issues: a) statistical hadro-chemistry, chemical parameters, b) strange flavor chemical equilibration in quark-gluon plasma, and c) particle yields and sudden hadronization, in the historic perspective of work and competition with my friend Jozsef Zimanyi.

Strangeness chemical equilibration in a quark-gluon plasma

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.

Production and equilibration of the quark-gluon plasma with chromoelectric field and minijets

Production and equilibration of quark-gluon plasma are studied within the color flux-tube model, at the Relativistic Heavy-Ion Collider (RHIC) and Large Hadron Collider (LHC) energies. Non-Abelian relativistic transport equations for quarks, antiquarks, and gluons, are solved in the extended phase space which includes coordinates, momenta, and color. Before the chromoelectric field is formed, hard and semihard partons are produced via minijets which provide the initial conditions necessary to solve the transport equations. The model predicts that in spite of the vast difference between the RHIC and LHC incident energies, once the local equilibrium is reached, the energy densities, the number densities, and the temperatures at the two machines may not be very different from each other. The minijet input significantly alters the evolution of the deconfined matter, unless the color field is too strong. For the input parameters used here the equilibration time is estimated to be $\ensuremath{\sim}1 \mathrm{fm}$ at RHIC and $\ensuremath{\sim}0.5 \mathrm{fm}$ at LHC, measured from the instant when the two colliding nuclei have just passed through each other. The temperature at equilibration is found to be $\ensuremath{\sim}250 \mathrm{MeV}$ at RHIC and $\ensuremath{\sim}300 \mathrm{MeV}$ at LHC.

Time evolution of strange-particle densities in hot hadronic matter

The kinetic equations for production in hot nuclear matter of rare, strange antibaryons are studied numerically. Strange antibaryons are confirmed as viable characteristic signatures of the quark-gluon plasma. We find four orders of magnitude enhancement in the abundance of Ω multiply-strange antibaryons. Strange antibaryon production in the hadronic gas phase is shown to have a relatively slow characteristic time constant of ∼ 10 −21 sec to be compared with the 100 times faster equilibration in quark-gluon plasma.