Equation of state at FAIR energies and the role of resonances

TL;DR

This study uses microscopic models to analyze the equation of state of nuclear matter in heavy-ion collisions at FAIR energies, revealing linear dependencies and the influence of resonances on the system's thermodynamic properties.

Contribution

It provides a detailed analysis of the effective equation of state at FAIR energies using UrQMD and QGSM models, highlighting the role of resonances and inelastic freeze-out.

Findings

EOS exhibits a linear P/e = c_s^2 with 0.12 < c_s^2 < 0.145

Resonances cause deviations from linear behavior in c_s^2(T) and c_s^2(μ_B)

Kinks in the EOS are linked to inelastic freeze-out, not deconfinement transition

Abstract

Two microscopic models, UrQMD and QGSM, are used to extract the effective equation of state (EOS) of locally equilibrated nuclear matter produced in heavy-ion collisions at energies from 11.6 AGeV to 160 AGeV. Analysis is performed for the fixed central cubic cell of volume V = 125 fm**3 and for the expanding cell that followed the growth of the central area with uniformly distributed energy. For all reactions the state of local equilibrium is nearly approached in both models after a certain relaxation period. The EOS has a simple linear dependence P/e = c_s**2 with 0.12 < c_s**2 < 0.145. Heavy resonances are shown to be responsible for deviations of the c_s**2(T) and c_s**2(mu_B) from linear behavior. In the T-mu_B and T-mu_S planes the EOS has also almost linear dependence and demonstrates kinks related not to the deconfinement phase transition but to inelastic freeze-out in the system.