Centrality dependence of chemical freeze-out parameters from net-proton and net-charge fluctuations using a hadron resonance gas model
AbstractWe estimate chemical freeze-out parameters in Hadron Resonance Gas (HRG) and Excluded Volume HRG (EVHRG) models by fitting the experimental information of net-proton and net-charge fluctuations measured in Au + Au collisions by the STAR Collaboration at the BNL Relativistic Heavy Ion Collider (RHIC). We observe that chemical freeze-out parameters obtained from lower and higher order fluctuations are almost the same for sNN>27 GeV, but tend to deviate from each other at lower sNN. Moreover, these separations increase with decrease of sNN, and for a fixed sNN increase towards central collisions. Furthermore, we observe an approximate scaling behavior of (μB/T)/(μB/T)central with (Npart)/(Npart)central for the parameters estimated from lower order fluctuations for 11.5≤sNN≤200 GeV. Scaling is violated for the parameters estimated from higher order fluctuations for sNN=11.5 and 19.6 GeV. It is observed that the chemical freeze-out parameter, which can describe σ2/M of net protons very well in all energies and centralities, cannot describe the sσ equally well, and vice versa.