Specific heat of matter formed in relativistic nuclear collisions

Abstract

We report the excitation energy dependence of specific heat (${c}_{v}$) of hadronic matter at freeze-out in Au+Au and Cu+Cu collisions at the BNL Relativistic Heavy Ion Collider energies by analyzing the published data on event-by-event mean transverse momentum ($\ensuremath{\langle}{p}_{T}\ensuremath{\rangle}$) distributions. The $\ensuremath{\langle}{p}_{T}\ensuremath{\rangle}$ distributions in finite ${p}_{T}$ ranges are converted to distributions of effective temperatures, and dynamical fluctuations in temperature are extracted by subtracting widths of the corresponding mixed event distributions. The heat capacity per particle at the kinetic freeze-out surface is presented as a function of collision energy, which shows a sharp rise in ${c}_{v}$ below $\sqrt{{s}_{NN}}=62.4$ GeV. We employ the hadron resonance gas (HRG) model to estimate ${c}_{v}$ at the chemical and kinetic freeze-out surfaces. The experimental results are compared to the HRG and other theoretical model calculations. HRG results show good agreement with data. Model predictions for ${c}_{v}$ at the CERN Large Hadron Collider energy are presented.