The Relativistic BUU Approach — Analysis of Retardation Effects and Thermal Properties

Abstract

The study of the nuclear equation of state (EOS) is one of the major goals in high energy heavy-ion collisions. However, it has turned out that the extraction of reliable information about the EOS is a nontrival task. Theoretical investigations, like simulations of the Boltzmann-Uehling-Uhlenbeck (BUU) equation have to include the momentum dependence of the mean-field potential [1] and should also study the sensitivity of the observables on the medium modifications of the nucleon-nucelon cross section [2]. Therefore, at bombarding energies in the order of 1 GeV/nucleon a relativistic treatment, which consistently includes these features, is necessary. In this spirit, a relativistic transport approach has been proposed and investigated [3,4,5,6]. Together with a relativistic generalization of the BUU transport equation one obtains equations of motion for the meson-fields which mediate interactions. In the first part of this contribution we present results which include the full solution of these field-equations and compare to different approximations. In particular we address the question of possible retardation effects in the case of fast moving nucleon sources. In the second part we investigate to which extend thermodynamic approaches are suited for the description of heavy-ion collisions at the considered energies and masses. We therefore calculate the pressures reached during the simulation in our microscopic approach and extract the size and the temperature of the equilibrated regions.

Supported by BMFT and Darmstadt