A hadron-quark hybrid model reliable for the EoS in $\mu_{B} \leq 400$ MeV

Abstract

We present a simple version of hadron-quark hybrid (HQH) model in the $\mu_B$--$T$ plain, where $T$ is temperature and $\mu_{B}$ is the baryon-number chemical potential. The model is composed of the independent-quark model for quark-gluon states and an improved version of excluded-volume hadron resonance gas (EV-HRG) model for hadronic states. In the improved version of EV-HRG, the pressure has charge conjugation and is obtained by a simple analytic form. The switching function from hadron states to quark-gluon states in the present model has no chemical potential dependence. The simple HQH model is successful in reproducing LQCD results on the transition region of chiral crossover and the EoS in $\mu_{B} \leq 400$ MeV. We then predict the chiral-crossover region in $400 \leq \mu_{B} \leq 800$ MeV. We also predict a transition line derived from isentropic trajectories in $0 \leq \mu_{B} \leq 800$ MeV and find that the effect of strangeness neutrality is small there.