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

We investigate the equilibration and the equation of state of a hot hadrongas at finite baryon density using an event generator which is designed toapproximately satisfy detailed balance at finite temperatures and finite baryondensities 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 ofhadrons in a box with periodic boundary conditions. Starting from an initialstate composed of only nucleons with a uniform phase-space distribution, theevolution takes place through interactions such as collisions, productions andabsorptions. The system approaches a stationary state of baryons, mesons andtheir resonances, which is characterized by the value of the exponent in theenergy 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, theobtained equation of state exhibits a significant deviation from the naivemixed free gas model. Large values of the entropy per baryon are also notable.In our system, the excitation of heavy baryon resonances and meson productionare enhanced simultaneously, and the increase of the temperature becomesmoderate, but a Hagedorn-type artificial temperature saturation does not occur.The pressure exhibits a linear dependence on the energy density.Comment: 23 pages, 20 figure