Relativistic transport approach for nucleus-nucleus collisions from SIS to SPS energies

Abstract

We formulate a covariant transport approach for high-energy nucleus-nucleus collisions where the real part of the nucleon self-energies is fitted to nuclear-matter properties which are evaluated on the basis of a NJL-type Lagrangian for the quark degrees of freedom. The parameters of the quark-model Lagrangian are fixed by the Gell-Mann, Oakes and Renner relation, the pion-nucleon Σ-term, the nucleon energy as well as the nuclear binding energy at saturation density ϱ0. We find the resulting scalar and vector self-energies for nucleons to be well in line with either Dirac-Brueckner computations for ϱ ⩽ 2ϱ0 or those from the phenomenological optical potential when accounting for a swelling of the nucleon at finite nuclear-matter density. The meson-baryon interaction density is modeled to describe a decrease of the meson mass with baryon density. The imaginary part of the hadron self-energies is determined by a string fragmentation model which accounts for the in-medium mass of hadrons in line with the ‘chiral’ dynamics employed. The applicability of the transport approach is demonstrated in comparison with experimental data from SIS to SPS energie The enhancement of the K+π+ ratio in A + A collisions compared to p + A reactions at AGS energies is reproduced within the ‘chiral’ dynamics. Furthermore, detailed predictions for the stopping in Pb + Pb collisions at 158 GeVA are presented.