Rapidity equilibration in d+Au and Au+Au systems

In a Relativistic Diffusion Model (RDM), the evolution of net-proton rapidity spectra with √(sNN) in heavy systems is proposed as an indicator for local equilibration and longitudinal expansion. The broad midrapidity valley recently discovered at RHIC in central Au+Au collisions at √(sNN)=200 GeV suggests rapid local equilibration which is most likely due to deconfinement, and fast longitudinal expansion. Rapidity spectra of produced charged hadrons in d+Au and Au+Au systems at RHIC energies and their centrality dependence are well described in a three-sources RDM. In central collisions, about 19% of the produced particles are in the equilibrated midrapidity region for d+Au. (orig.)