Confronting particle emission scenarios with strangeness data

An enhancement of strangeness production in relativistic nuclear collisions (compared to, e.g., proton-proton collisions at the same energy) is a possible signature [1] of the much sought-after quark-gluon plasma. It is therefore particularly interesting that current data at AGS (Alternating Gradient Synchroton) and SPS (Super Proton Synchrotron) energies do show an increase in strangeness production (see, e.g., [2]). At SPS energies, this increase seems to imply that something new is happening: In microscopical models, one has to postulate some previously unseen reaction mechanism (color rope formation in the RQMD code [3], multiquark clusters in the VENUS code [4], etc.) while hydrodynamical models have their own problems (be it those with a rapidly hadronizing plasma [5] or those with an equilibrated hadronic phase, preceded or not by a plasma phase). In this paper, we examine the shortcomings of the latter class of hydrodynamical models and suggest that they might be due to a too rough description of particle emission. (The main problem for the former class of hydrodynamical models is the difficulty to yield enough entropy after hadronization.)