EVIDENCE FOR A PHASE WITH HIGH SPECIFIC ENTROPY IN NUCLEAR COLLISIONS

We determine the entropy-per-baryon content of the central reaction re gion in terms of the charged particle multiplicity. We study the consi stency of our findings with recent data on strange antibaryon producti on at 200A GeV in S-A collisions (A approximately 200) assuming format ion of a central fireball. Hadron gas models which do not invoke stron g medium modifications of hadron masses do not provide enough entropy and are inconsistent with the combined experimental results. In contra st the quark-gluon plasma hypothesis explains them naturally.