How much strangeness production is there in ultrarelativistic nucleus-nucleus collisions?

Strangeness production has been proposed as a signal for the formation of a quark-gluon plasma in ultrarelativistic nucleus-nucleus collisions. We address this problem in the framework of Bjorkens model for the longitudinal hydrodynamic expansion of baryon-free matter. Different scenarios are considered for the assumed first-order phase transition from QCD plasma into hadrons, including a slow transition via the Maxwell construction of coexisting phases, and a rapid transition from supercooling followed by reheating. The rate equations for strange-quark and kaon abundances are solved numerically. With the most likely set of parameters, the K-/- ratio is about three times larger than in p»p collisions at the same energy. This results primarily from the large rate constant in the hadron phase and from the long time spent in this phase. Thus, the K-/- ratio may not be a direct signal for the formation of quark-gluon plasma; however, it may be an indirect signal, since the system would not live nearly as long if the quark-gluon plasma had not been formed initially.