Excitation functions of hadronic observables from SIS to RHIC energies

We calculate excitation functions for various dynamical quantities as well as experimental observables from SIS to RHIC energies within the HSD transp ort approach which is based on string, quark, diquark (q, (q) over bar, qq, (q) over bar (q) over bar) and hadronic degrees of freedom without includi ng any explicit phase transition to a quark-gluon plasma (QGP). It is argue d that the failure of this more 'conventional' approach in comparison to ex perimental data should indicate the presence of a different phase which mig ht be either attributed to space-time legions of vanishing scalar quark con densate ((q (q) over bar) = 0) or to the presence of a QGP phase with stron gly interacting partons. We study the K/pi ratio, the low mass dilepton enh ancement in the invariant mass regime from 0.2-1.2 GeV as well as charmoniu m suppression for central Au + Au collisions as a function of the bombardin g energy and present predictions for these observables as well as hadron ra pidity distributions at RHIC energies. Whereas all observables studied with in HSD show smooth increasing/decreasing excitation functions, the experime ntal K+/pi(+) ratio indicates a maximum at 11 A GeV (or above) which is int erpreted as a signature for a chirally restored phase in the course of the reaction. (C) 2000 Elsevier Science B.V. All rights reserved.