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Bochum 1998 – scientific programme

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HK: Hadronen und Kerne

HK 34: Heavy Ion Reactions IV, Relativistic Energies

HK 34.1: Group Report

Tuesday, March 17, 1998, 17:00–17:30, P

Thermodynamic evolution in heavy ion reactions — •T. Gaitanos, M. Rempter, and H. H. Wolter — Sektion Physik, Univ. München, 85748 Garching

The determination of temperatures in heavy ion reactions is of particular interest with respect to the investigation of the caloric equation of state and of liquid-gas phase transitions. In this work we attempt to determine the thermodynamical evolution of the nuclear medium in a heavy ion collision directly from the phase space distribution of a transport theoretical calculation. We use a relativistic treatment with gaussian test particles which yields smooth phase space distributions and allows to determine locally density, pressure, collective velocity and temperature. For the latter we describe the local momentum distributions in terms of an antisymmetrized superposition of two finite temperature Fermi distributions [1]. Thus non-equilibrium effects are taken into account and are not interpreted as temperature. In this way the thermodynamical state of nuclear matter is characterized locally and temporally.
We applied this approach to central and peripheral Au+Au reactions which were also extensively investigated by the FOPI collaboration [2]. We discuss the evolution in the spectator and in the participant region. By discussing the effective incompressibility from the pressure-density relation we determine regions of thermodynamical instability. The temperature and density conditions found in the spectator matter are consistent with experimental indications for the occurence of phase transitions. We also determine radial flow for non-central points and compare with blast szenarios. In our approach fragments are described in an qualitative fashion in a coalescence model. We investigate the temperature at which fragments are formed, which is of relevance to the question of comparing different isotope thermometers.

[1] C. Fuchs, P. Essler, T. Gaitanos, H. H. Wolter,
Nucl. Phys. A in press.

[2] W. Reisdorf (FOPI Collaboration), Nucl. Phys. A 612 (1997) 493 supported by aggrant of BMBW, 06LM363.

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