A Study of the Thermodynamical Properties of a Hot, Dense Hadron Gas Using an Event Generator - Hadro-Molecular-Dynamical Calculation -

Abstract

We investigate the equilibration and the equation of state of a hot hadron gas at finite baryon density using an event generator which is designed to approximately satisfy detailed balance at finite temperatures and finite baryon densities of the hadronic scale (80 MeV < T < 170 MeV and 0.157 fm^-3 < n_B < 0.315 fm^-3). Molecular-dynamical simulations were performed for a system of hadrons in a box with periodic boundary conditions. Starting from an initial state composed of only nucleons with a uniform phase-space distribution, the evolution takes place through interactions such as collisions, productions and absorptions. The system approaches a stationary state of baryons, mesons and their resonances, which is characterized by the value of the exponent in the energy distribution common to the different particles, i.e., the temperature. After the equilibration, thermodynamic quantities, such as the energy density, particle density, entropy and pressure are calculated. Above T - m_pi, the obtained equation of state exhibits a significant deviation from the naive mixed free gas model. Large values of the entropy per baryon are also notable. In our system, the excitation of heavy baryon resonances and meson production are enhanced simultaneously, and the increase of the temperature becomes moderate, but a Hagedorn-type artificial temperature saturation does not occur. The pressure exhibits a linear dependence on the energy density.