Freiburg 1999 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 6: Physik mit schweren Ionen I
HK 6.5: Vortrag
Montag, 22. März 1999, 15:45–16:00, D
Does Quark-Gluon Plasma-formation lead to observable threshold effects in excitation functions? — •M. Reiter1, A. Dumitru2, J. Brachmann1, J.A. Maruhn1, H. Stöcker1, and W. Greiner1 — 1Institut für theoretische Physik, Universität Frankfurt — 2Physics Department, Yale University, USA
Entropy production in the compression stage of heavy ion collisions is discussed within three distinct macroscopic models (i.e. generalized RHTA, geometrical overlap model and three-fluid hydrodynamics). We find that within these models ∼80% or more of the experimentally observed final-state entropy is created in the early stage. It is thus likely followed by a nearly isentropic expansion. We employ an equation of state with a first-order phase transition. For low net baryon density, the entropy density exhibits a jump at the phase boundary. However, the excitation function of the specific entropy per net baryon, S/A, does not reflect this jump. This is due to the fact that for final states (of the compression) in the mixed phase, the baryon density ρB increases with √s, but not the temperature T. Calculations within the three-fluid model show that a large fraction of the entropy is produced by nuclear shockwaves in the projectile and target. With increasing beam energy, this fraction of S/A decreases. At √s=20 AGeV it is on the order of the entropy of the newly produced particles around midrapidity. Hadron ratios are calculated for the entropy values produced initially at beam energies from 2 to 200 AGeV.