Centrality Dependence Of Chemical Freeze-Out Parameters And Strangeness Equilibration In Rhic And Lhc Energies

We have estimated centrality variation of chemical freeze-out parameters from yield data at midrapidity of pi(+/-), K-+/- and p, (p) over bar 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, mu(B), mu(Q), mu(S)), a strangeness undersaturation factor (gamma(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 gamma(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.