Diffusion and local deconfinement in relativistic systems

The evolution of net-proton rapidity spectra with sNN is heavy relativistic systems is proposed as an indicator for local equilibration, longitudinal expansion, and deconfinement. Bell-shaped distributions in central collisions at AGS energies and double-humped nonequilibrium spectra at SPS ishow substantial collective expansion. The broad midrapidity valley appearing at RHIC indicates longitudinal collective expansion of a locally equilibrated subsystem. In central Au-Au collisions at sNN=200 GeV, fast local equilibration which is most likely due to deconfinement is estimated in a Relativistic Diffusion Model to occur for 14 per cent of the incoming baryons.