HADRON AND HADRON-CLUSTER PRODUCTION IN A HYDRODYNAMICAL MODEL INCLUDING PARTICLE EVAPORATION

We discuss the evolution of the mixed phase at RHIC and SPS within boo st-invariant hydrodynamics. In addition to the hydrodynamical expansio n, we also consider evaporation of particles off the surface of the fl uid. The back reaction of this evaporation process on the dynamics of the fluid shortens the lifetime of the mixed phase. In our model this lifetime of the mixed phase is less than or equal to 12 fm/c in Au+Au at RHIC and less than or equal to 8 fm/c in Pb+Pb at SPS, even in the limit of vanishing transverse expansion velocity. Strong separation of strangeness occurs. especially in events (or at rapidities) with rela tively high initial net baryon and strangeness number, enhancing the m ultiplicity of multiply strange nuclear clusters. If antiquarks and an tibaryons reach saturation in the course of the pure QGP or mixed phas e, we find that at RHIC the ratio of antideuterons to deuterons may ex ceed 0.3 and even He-4 /He-4>0.1. In S+Au at SPS we find only N/N appr oximate to 0.1. As a result of fluctuations, at RHIC even a negative b aryon number at midrapidity is possible in individual events, so that the antibaryon and antibaryon-cluster yields exceed those of the corre sponding baryons and clusters.