Hadron production from quark-gluon plasma via mixed phase

Abstract

Well-controlled hadronization of the quark-gluon plasma via a mixed phase is described by a set of rate equations supplemented with the one-dimensional scaling hydrodynamics. The reaction rates for the hadronization processes are constrained by the equilibrium condition for the static mixed phase using the fractional volume formalism. As an example, two models of hadronization of baryon-free quark-gluon plasma are constructed according to different choices of the constituents of the free hadron gas: the meson-baryon model and the pseudoscalar-vector model. Time evolution of the flavor composition and hadron multiplicity is studied in detail. It was found that (i) the abundance of strange hadrons at the final stage of the phase transition is insensitive to the strangeness abundance in the initial stage, (ii) the K π ratio in the final stage is essentially given by the equilibrium value for the hadronic phase, (iii) the baryon/meson ratio is sensitive to the transition temperature, (iv) the entropy is approximately conserved or increases slightly, and (v) the period of the mixed phase era depends on both the critical temperature and the effective number of hadronic degrees of freedom. The time-integrated ratio of the vector meson yields 〈 φ>/<ρ 0 + ω〉 is found to be twice as large as the maximum enhancement observed by the NA38 experiment on muon pair production. It is suggested that suppression of resonance production relative to direct pseudoscalar meson production may serve as a signature of thermal equilibrium in the hadronic phase.