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 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.

Study of Strange Particle Production in Central Pb–Pb Collisions at

We study here the transverse momentum spectra of Ks 0 – mesons, A − hyperons and multi–strange (Ξ–, Ω–) particles in the most central Pb–Pb collisions at √SNN = 2.76 TeV for the mid rapidity interval |y| < 0.5 by using two different Monte Carlo simulation models: EPOS–1.99 and EPOS–LHC. The validity of simulation codes of these models is checked for Pb–Pb collisions at √SNN = 2.76 TeV by comparing the simulation data with ALICE experimental data for the same collisions at √SNN = 2.76 TeV. Strange particles ratio i.e. and nuclear modification factors for multi–strange particles have been constructed as function of pT to study these strange particle production and their energy loss mechanism. The simulation models show suppression for the multi–strange particles in the transverse momentum range of 3–7 GeV/c. The outcome agrees with a recent finding by ALICE collaboration where it suggested a possibility that the kinetic freeze–out conditions for strange particles are different from those for non–strange particles

Strange particle effective temperatures in relativistic nuclear collisions

The energy dependence of the effective temperatures of charged kaons, [Formula: see text] and [Formula: see text] produced in Au[Formula: see text]Au collisions at the Relativistic Heavy Ion Collider (RHIC) Beam Energy Scan (BES) energies are presented. At energies around [Formula: see text][Formula: see text]GeV, there is a sudden change in the energy dependence of [Formula: see text] and [Formula: see text] effective temperatures, while at higher energies a slower, continuous rise up to [Formula: see text][Formula: see text]TeV is observed. This behavior is similar with previous SPS results and could indicate the onset of deconfinement in this energy range. The [Formula: see text] effective temperatures increase with energy and no plateau-like behavior is evidenced by the data.