Nonequilibrium initial conditions from perturbative QCD for relativistic and ultrarelativistic heavy ion collisions -: art. no. 014901

We calculate the initial nonequilibrium conditions from perturbative QCD within Glauber multiple-scattering theory for root s=200A GeV and root s=5.5A TeV. At the soon available collider energies one will particularly test the small-x region of the parton distributions entering the cross sections. Therefore, shadowing effects, previously more or less unimportant, will lead to new effects on variables such as particle multiplicities dN/dy, transverse energy production d (E) over bar(T)/dy, and the initial temperature T-i. In this paper we will take a closer look at the effects of shadowing by employing different parametrizations for the shadowing effect for valence quarks, sea quarks, and gluons. Since the cross sections at midrapidity are dominated by processes involving gluons the amount of their depletion is particularly important. We will therefore take a closer look at the results for dN/dy, d (E) over bar(Y)/dy, and T-i by using two different gluon shadowing ratios, differing strongly in size. As a matter of fact, the calculated quantities differ significantly.