Thermodynamical description of heavy ion collisions

We analyze the thermodynamical state of nuclear matter in transport descriptions of heavy ion reactions. We determine thermodynamical variables from an analysis of local momentum space distributions and compare to blast model parameters from an analysis of fragment energy spectra. These descriptions are applied to spectator and fireball matter in semi-central and central Au+Au collisions at SIS-energies, respectively.Comment: 4 pages, 2 postscript-figures, to be published in the proceedings of Bologna2000: Structure of the Nucleus at the Dawn of the Century, Bologna, Italy, 29 May - 3 Jun 200

Relativistic heavy ion collisions with realistic non-equilibrium mean fields

We study the influence of non-equilibrium phase space effects on the dynamics of heavy ion reactions within the relativistic BUU approach. We use realistic Dirac-Brueckner-Hartree-Fock (DBHF) mean fields determined for two-Fermi-ellipsoid configurations, i.e. for colliding nuclear matter, in a local phase space configuration approximation (LCA). We compare to DBHF mean fields in the local density approximation (LDA) and to the non-linear Walecka model. The results are further compared to flow data of the reaction $Au$ on $Au$ at 400 MeV per nucleon measured by the FOPI collaboration. We find that the DBHF fields reproduce the experiment if the configuration dependence is taken into account. This has also implications on the determination of the equation of state from heavy ion collisions.Comment: Physics Letters B in press; 10 pages, Postscript file replaced by Latex file and 3 Postscript figure

Testing Dirac-Brueckner models in collective flow of heavy-ion collisions

We investigate differential in-plane and out-of-plane flow observables in heavy ion reactions at intermediate energies from $0.2\div 2$ AGeV within the framework of relativistic BUU transport calculations. The mean field is based on microscopic Dirac-Brueckner-Hartree-Fock (DBHF) calculations. We apply two different sets of DBHF predictions, those of ter Haar and Malfliet and more recent ones from the T\"ubingen group, which are similar in general but differ in details. The latter DBHF calculations exclude spurious contributions from the negative energy sector to the mean field which results in a slightly softer equation of state and a less repulsive momentum dependence of the nucleon-nucleus potential at high densities and high momenta. For the application to heavy ion collisions in both cases non-equilibrium features of the phase space are taken into account on the level of the effective interaction. The systematic comparison to experimental data favours the less repulsive and softer model. Relative to non-relativistic approaches one obtains larger values of the effective nucleon mass. This produces a sufficient amount of repulsion to describe the differential flow data reasonably well.Comment: 14 pages Revtex, 19 figures, discussion extended and two figures added, accepted for publication in EPJ