Entropy production in chemically non-equilibrium quark-gluon plasma created in central Pb+Pb collisions at LHC energies

TL;DR

This paper investigates entropy production in a chemically non-equilibrium quark-gluon plasma created in central Pb+Pb collisions at LHC energies, highlighting how entropy increases during evolution due to delayed quark production.

Contribution

It introduces a hydrodynamic model with time-dependent quark fugacity to describe non-equilibrium evolution, showing entropy generation and its impact on particle ratios.

Findings

Entropy increases by about 25% during evolution.

Delayed quark production affects baryon-to-meson ratios.

Non-equilibrium scenario explains reduced (anti)baryon to meson ratios.

Abstract

We study the possibility that partonic matter produced at early stage of ultrarelativistic heavy-ion collisions is out of chemical equilibrium. It is assumed that initially this matter is mostly composed of gluons, but quarks and antiquarks are produced at later times. The dynamical evolution of partonic system is described by the Bjorken-like ideal hydrodynamics with a time dependent quark fugacity. The results of this model are compared with those obtained by assuming the complete chemical equilibrium of partons already at the initial stage. It is shown that in a chemically non-equilibrium scenario the entropy gradually increases, and about 25% of the total final entropy is generated during the hydrodynamic evolution of deconfined matter. We argue that the (anti)quark suppression included in this approach may be responsible for reduced (anti)baryon to meson ratios observed in heavy-ion collisions at LHC energies.