Scaling properties in bulk and pT-dependent particle production near midrapidity in relativistic heavy ion collisions

The centrality dependence of the midrapidity charged-particle multiplicity density (|η|<1) is presented for Au+Au and Cu+Cu collisions at RHIC over a broad range of collision energies. The multiplicity measured in the Cu+Cu system is found to be similar to that measured in the Au+Au system, for an equivalent Npart, with the observed factorization in energy and centrality still persistent in the smaller Cu+Cu system. The extent of the similarities observed for bulk particle production is tested by a comparative analysis of the inclusive transverse momentum distributions for Au+Au and Cu+Cu collisions near midrapidity. It is found that, within the uncertainties of the data, the ratio of yields between the various energies for both Au+Au and Cu+Cu systems are similar and constant with centrality, both in the bulk yields and as a function of pT, up to at least 4 GeV/c. The effects of multiple nucleon collisions that strongly increase with centrality and energy appear to only play a minor role in bulk and intermediate transverse momentum particle production.