Eur. Phys. J. Special Topics 229, 3517–3536 (2020)
https://doi.org/10.1140/epjst/e2020-000218-1

Regular Article

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

¹ Joint Institute for Nuclear Research, 141980 Dubna, Russia
² Institute for Theoretical Physics, University of Wrocław, 50-204 Wrocław, Poland
³ National Research Nuclear University (MEPhI), 115409 Moscow, Russia
⁴ Dubna State University, 141982 Dubna, Russia
⁵ Matrosov Institute for System Dynamics and Control Theory, 664033 Irkutsk, Russia
⁶ Irkutsk State University, Karl Marx str. 1, 664003 Irkutsk, Russia

^a e-mail: david.blaschke@gmail.com

Received: 7 September 2020
Accepted: 28 October 2020
Published online: 21 December 2020

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 μ_B. 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 − μ_B plane as a proxy for the chemical freezeout line, whereby the variable x = T∕μ_B 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 √s_NN=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.