Strangeness Production in Heavy-Ion Collisions

Abstract

Strangeness has been proposed as a signal for quark-gluon plasma formation in relativistic ion collisions [1,2]. It has also been proposed on a variety of occasions that stable multi-strange states could exist in nature, viz. strange matter or strangelets [3,4,5,6]. Subsequent to the original proposal several papers appeared which considerably weakened the early claims made for strangeness production in heavy ion collisions [7,8,9,10]. Representative of many I quote a statement taken from Lee et al. [10]: “... we conclude that there is no natural large difference in flavor composition between the (...) quark-gluon plasma and an equilibrium hadron gas.”. It thus became clear that if both the hadronic system and the quark-gluon plasma phase are in chemical equilibrium then the amount of strangeness in both phases is similar. However, it was pointed out that, due to non-equilibrium effects one could still expect a large enhancement of strangeness. In the quark-gluon plasma phase the equilibration rate for strange quarks is fast because the strange quark mass is not very large compared to the typical strong interaction scale. In the hadronic phase however the equilibration rate for strange mesons is expected to be slower because the masses involved are higher [11]. Since estimates of non-equilibrium behaviour are much more model dependent it becomes unclear what to expect.

Talk presented by J. Cleymans at the Summer School in Theoretical Physics “Phase Structure of Strongly Interacting Matter.”, Cape Town, January 8–19,1990