ϕ-Enhancement andJ/ψ-suppression in nuclear collisions—does the combination signal quark-gluon plasma formation?

We point out that recent indications from the NA38 collaboration at CERN for an increase of theΦ(ω+ρ0) ratio in central 200A GeVO+U andS+U collisions give evidence for an appr chemical equilibrium in these collisions. We different mechanisms for such a behavior, the hypothetical formation of a transient plasma (QGP) phase and a hadronic rescattering scenario. Theoretical uncertainties in the hadronic rescattering calculation are eliminated by linking the ϕ enhancement to the suppression ofJ/ψ mesons observed in the same experiment. We find that the data are most easily “explained” by postulating QGP formation in a fraction of the central collisions, but that a simultaneous quantitative description of both phenomena can also be obtained via hadronic rescattering. Even though in the latter case very high particle densities in the collision zone are required, a purely hadronic mechanism for the observations can thus presently not be excluded.