Chiral phase transition and kaon-to-pion ratios in the entanglement SU(3) PNJL model

D Blaschke,A V Friesen,Yu L Kalinovsky,A Radzhabov

doi:10.1140/epjst/e2020-000218-1

Abstract

Within the three-flavor PNJL and EPNJL chiral quark models we have obtained pseudoscalar meson properties in quark matter at finite temperature T and baryochemical potential μB. We compare the meson pole (Breit-Wigner) approximation with the Beth-Uhlenbeck (BU) approach that takes into account the continuum of quark-antiquark scattering states when determining the partial densities of pions and kaons. We evaluate the kaon-to-pion ratios along the (pseudo-)critical line in the T − μB plane as a proxy for the chemical freezeout line, whereby the variable x = T∕μB is introduced that corresponds to the conserved entropy per baryon as initial condition for the heavy-ion collision experiments. We present a comparison with the experimental pattern of kaon-to-pion ratios within the BU approach and using x-dependent pion and strange quark potentials. A sharp “horn” effect in the energy dependence K+∕π+ ratio is explained by the enhanced pion production at energies above √sNN=8 GeV, when the system enters the regime of meson dominance. This effect is in line with the enhancement of low-momentum pion spectra that is discussed as a precursor of the pion Bose condensation and entails the occurrence of a nonequilibrium pion chemical potential of the order of the pion mass. We elucidate that the horn effect is not related to the existence of a critical endpoint in the QCD phase diagram.

Highlights

The European Physical Journal Special Topics finite temperatures and low chemical potentials only [1,2], so that the development of effective model descriptions is of importance.In the present work, we discuss the chiral phase transition and the in-medium behaviour of pseudoscalar mesons in the framework of the SU(3) NJL model extended by the coupling to the Polyakov loop, the PNJL model
We evaluate the kaon-to-pion ratios along thecritical line in the T − μB plane as a proxy for the chemical freezeout line, whereby the variable x = T /μB is introduced that corresponds to the conserved entropy per baryon as initial condition for the heavy-ion collision experiments
Despite the principal problem in explaining the phase structure of QCD within chiral quark models like PNJL and entanglement PNJL (EPNJL) at the mean field level we find by comparing with the lattice QCD data [1] that the result for the EPNJL model provides an acceptable proxy for the phase border where the hadronization transition shall take place in the dynamical evolution of the quark-gluon plasma (QGP)

Summary

Introduction

The European Physical Journal Special Topics finite temperatures and low chemical potentials only [1,2], so that the development of effective model descriptions is of importance. It is reassuring for the application of the EPNJL model to heavy-ion collisions at the end of this contribution that the parametrized line of the chemical freezeout [46] shown as a green line in the right panel of Figure 1 lies entirely in the confining phase with broken chiral symmetry, and sufficiently close to the hadronization transition The basis for such applications, in particular to the celebrated kaon-to-pion ratios and the horn effect for the energy dependence of K+/π+, is a field theoretical description of scalar and pseudoscalar meson bound states and their dissociation by the Mott effect which occurs under extreme conditions of temperature and density.

Mesons in hot and dense matter

Breit-Wigner approximation

Beth-Uhlenbeck approach

Findings

Conclusions