Centrality Dependence of Chemical Freeze-Out Parameters and Strangeness Equilibration in RHIC and LHC Energies

Abstract

We have estimated centrality variation of chemical freeze-out parameters from yield data at midrapidity of π ± , K ± and p , p ¯ for collision energies of RHIC (Relativistic Heavy Ion Collider), Beam Energy Scan (RHIC-BES) program, and LHC (Large Hadron Collider). We have considered a simple hadron resonance gas model and employed a formalism involving conserved charges ( B , Q , S ) of QCD for parameterization. Along with temperature and three chemical potentials ( T , μ B , μ Q , μ S ), a strangeness undersaturation factor ( γ S ) has been used to incorporate the partial equilibration in the strange sector. Our obtained freeze-out temperature does not vary much with centrality, whereas chemical potentials and γ S seem to have a significant dependence. The strange hadrons are found to deviate from a complete chemical equilibrium at freeze-out at the peripheral collisions. This deviation appears to be more prominent as the collision energy decreases at lower RHIC-BES energies. We have also shown that this departure from equilibrium reduces towards central collisions, and strange particle equilibration may happen after a threshold number of participants in A - A collision.

Fixed point behavior of cumulants in the three-dimensional Ising universality class

“…[39,40], the chemical freeze-out temperature and net-baryon chemical potential could change as the centrality in the relativistic heavy-ion collisions. Although the temperature does not vary much, the net-baryon chemical potential increases from peripheral to central collisions [40]. For simplicity, we move the freeze-out curve described by Eq.…”

“…In fact, the centrality dependence of the chemical freeze-out temperature and baryon chemical potential have been studied in Refs. [63,64]. Although the chemical freeze-out temperature does not vary much with centralities, the temperature interval between the three different freeze-out curves can be very small.…”