Chiral QCD phase in equilibrium with Hadron Gas and the location of the critical point

Abstract

We develop a description of the equation of state of QCD matter with restored chiral symmetry, which is in thermal and chemical equilibrium with the hadronic phase. The hadron gas is described with thermodynamically consistent volume corrections. The chiral phase is composed of a set of few quark condensates, each of which corresponds to a family of hadrons with specific quark content. On the boundary between the two phases we apply the requirement of conservation of particle numbers per family. We use lattice calculations for temperatures below the transition curve to determine hadronic volumes. We find that the pion system plays decisive role in the shift of the transition from higher order (crossover) to first order. For four volume models we calculate the location of the critical point as function of critical temperature $T_c$ at vanishing baryon density. Particularly, if we additionally impose the equality between the densities of quarks contained in mesons and baryons, we find a critical point residing in the interval of baryon chemical potential $\mu_B \simeq$ 233-267 MeV and of temperature $T \simeq$ 153-158 MeV.