Large Strangeness as a QGP Signal in an Isentropic Quark-Hadron Phase Transition

Lattice QCD results reveal that the critical parameters and the order of the quark-hadron phase transition are quite sensitive to the number of dynamical flavours and their masses included in the theory. Motivated by this result we develop a phenomenological equation of state for the quark-gluon plasma consisting of $n_f$ flavours retaining the entropy per baryon ratio continuous across the quark-hadron phase boundary. We thus obtain a generalised expression for the temperature and baryon chemical potential dependent bag constant. The results are shown for the realistic case, i.e., involving u, d and s quarks only. We then obtain a phase boundary for an isentropic quark-hadron phase transition using Gibbs' criteria. Similarly another phase boundary is obtained for the transition to an ideal QGP from the solution of the condition $B(\mu,T)=0$. The variation of critical temperature $T_c$ with the number of flavours included in the theory. Also the variation of ${(\epsilon-4P)}/T^4$ with temperature are studied and compared with lattice results. Finally the strange particle ratios $\frac{\bar{\Lambda}}{\Lambda}$, $\frac{\bar{\Xi}}{\Xi}$ and $\frac{K^+}{K^-}$ are obtained at both phase boundaries. We propose that their variations with the temperature and baryon chemical potential can be used in identifying the quark-gluon plasma in the recent as well as in future heavy-ion experiments.

B. K. Patra, K. K. Singh, C. P. Singh · 1998