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HK: Physik der Hadronen und Kerne

HK 6: Physik mit schweren Ionen I

HK 6.1: Gruppenbericht

Montag, 17. März 2003, 15:45–16:15, E

Nuclear Stopping from 90A to 1500A GeV and its Correlation to Flow — •Willibrord Reisdorf — Gesellschaft für Schwerionenforschung, D-64291,Darmstadt,Germany

The pressure gradients established in the early phase of heavy ion collisions create flow which can be measured and used to infer information on the nuclear equation of state. However, in the non-equilibrium situation relevant for reactions with finite-size nuclei, the pressure (and density) actually established is heavily influenced by the acchieved degree of nuclear stopping and as a consequence by velocity dependent interactions. For central collisions, we present a systematics of measured ratios of the variances of the transverse and longitudinal rapidities obtained for complete events (i.e. integrated over 4π and over all major emitted particle species). This observable, dubbed VARTL, is one for spherical momentum space topologies. For central collisions hydrodynamics assuming full stopping predicts values well above one (’squeeze out’). Experimentally, for Au on Au, we find that VARTL, measured with a relative accuracy of 5%, goes thru a maximum of 0.82 at 400A MeV, decreasing to 0.65 at 90A MeV and 0.60 at 1500A MeV. For lighter systems a similar pattern is found, except that VARTL is systematically smaller. This behaviour is shown to correlate strongly with global flow observables.