Excitation Function of Energy Density and Partonic Degrees of Freedom in Relativistic Heavy Ion Collisions

H. Weber, C. Ernst, M. Bleicher, L. Bravina, H. Stoecker, W. Greiner, C. Spieles, S. A. Bass

Published 1998-08-10, updated 1998-08-11Version 2

We estimate the energy density pile-up at mid-rapidity in central Pb+Pb collisions from 2 - 200 GeV/nucleon. The energy density is decomposed into hadronic and partonic contributions. A detailed analysis of the collision dynamics in the framework of a microscopic transport model shows the importance of partonic degrees of freedom and rescattering of leading (di)quarks in the early phase of the reaction for lab-energies > 30 GeV/nucleon. In Pb+Pb collisions at 160 GeV/nucleon the energy density reaches up to 4 GeV/fm^3, 95% of which are contained in partonic degrees of freedom.