Excitation Function of Energy Density and Partonic Degrees of Freedom in   Relativistic Heavy Ion Collisions
  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. 
H. Weber, C. Ernst, M. Bleicher, L. Bravina, H. Stoecker, W. Greiner   (ITP, Frankfurt U.), C. Spieles (LBL Berkeley) and S....