HADRONIC SIGNATURES OF DECONFINEMENT IN RELATIVISTIC NUCLEAR COLLISIONS

We describe the remarkable accomplishments of the current heavy ion Pb -Pb collision experiments involving strange particle production, carri ed out at 158A GeV at CERN-SPS. Together with earlier 200A GeV S-induc ed reactions, these results imply that, at central rapidity, a novel m echanism of strangeness production arises, accompanied by excess entro py formation. We argue that: these results are consistent with the for mation of a space-time localized, highly excited, dense state of matte r; the freeze-out properties of strange hadrons are suggestive of the formation of a color-deconfined, thermally and nearly chemically equil ibrated phase, which provides at present the only comprehensive framew ork to describe all experimental data; the matter fireball is undergoi ng a transverse expansion with nearly the velocity of sound of relativ istic matter; longitudinal expansion is not in the scaling regime. We present a first analysis of the recent Pb-Pb results and discuss sever al alternative reaction scenarios. We evaluate quantitatively strangen ess production in the deconfined quark-gluon phase and obtain yields i n agreement with the experimental observations made in 200A GeV S-W an d 158A GeV Pb-Pb interactions. We also present a qualitative discussio n of J/Psi results consistent with our understanding of strange partic le results.