J/Psi and Psi ' Suppression in P-A Collisions at 800 Gev/C

We calculate excitation functions for various dynamical quantities as well as experimental observables from SIS to RHIC energies within the HSD transport approach which is based on string, quark, diquark ( q , q̄ , qq , q̄q̄ ) and hadronic degrees of freedom without including any explicit phase transition to a quark–gluon plasma (QGP). It is argued that the failure of this more `conventional' approach in comparison to experimental data should indicate the presence of a different phase which might be either attributed to space–time regions of vanishing scalar quark condensate ( 〈qq̄〉 = 0) or to the presence of a QGP phase with strongly interacting partons. We study the K/π ratio, the low mass dilepton enhancement in the invariant mass regime from 0.2–1.2 GeV as well as charmonium suppression for central Au + Au collisions as a function of the bombarding energy and present predictions for these observables as well as hadron rapidity distributions at RHIC energies. Whereas all observables studied within HSD show smooth increasing/decreasing excitation functions, the experimental K+/π+ ratio indicates a maximum at 11 A GeV (or above) which is interpreted as a signature for a chirally restored phase in the course of the reaction.