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 wi thin 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 th e small-x region of the parton distributions entering the cross sections. T herefore, shadowing effects, previously more or less unimportant, will lead to new effects on variables such as particle multiplicities dN/dy, transve rse 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 e mploying different parametrizations for the shadowing effect for valence qu arks, sea quarks, and gluons. Since the cross sections at midrapidity are d ominated by processes involving gluons the amount of their depletion is par ticularly important. We will therefore take a closer look at the results fo r dN/dy, d (E) over bar(Y)/dy, and T-i by using two different gluon shadowi ng ratios, differing strongly in size. As a matter of fact, the calculated quantities differ significantly.