  Net-baryon rapidity distributions in central Au+Au collisions at 200 GeV per
nucleon are shown to consist of three components. The nonequilibrium
contributions are accounted for in a Relativistic Diffusion Model. Near
midrapidity, a third fraction containing approximately 22 protons reaches local
statistical equilibrium in a discontinuous transition. It may be associated
with a deconfinement of the participant partons and thus, serve as a signature
for Quark-Gluon Matter formation.
