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

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.

Mott Dissociation and Kaon to Pion Ratio in the EPNJL Model

“…After finding the error bar of the maximal value of the pion nonequilibrium chemical potential due to overall normalization to the large-x points (with almost zero chemical potential) the other parameters is fitted. The detailed description of the fit and error bar estimation of all parameters procedure has been given in [19].…”

“…At zero chemical potential both the BW and the BU approach show the degeneracy of positive and negative charged meson masses, as for light quarks m u = m d was chosen. At nonzero chemical potential and low T, the splitting of mass in charged multiplets appears due to excitation of the Dirac sea modified by the presence of the medium (see [17][18][19]). In BU approach an anomalous mode appears after T Mott for positively charged kaons.…”

Strangeness thermodynamic instabilities in hot and dense nuclear matter

“…At high temperature regime, various QCD inspired theoretical models indicate a region with a rapid cross-over of thermodynamic observable and a formation of a critical endpoint, beyond which the system shows a first order phase transition from confined to deconfined matter [2,3,4,5,6]. The existence and the location of such phase transition at finite baryon chemical potential is still a matter of debate and can be in principle detected in the planned high-energy compressed nuclear matter experiments [7,8,9,10,11,12].…”

Strangeness thermodynamic instabilities in hot and dense nuclear matter

“…At high temperature regime, various QCD inspired theoretical models indicate a region with a rapid cross-over of thermodynamic observable and a formation of a critical endpoint, beyond which the system shows a first order phase a e-mail: andrea.lavagno@polito.it (corresponding author) transition from confined to deconfined matter [2][3][4][5][6]. The existence and the location of such phase transition at finite baryon chemical potential is still a matter of debate and can be in principle detected in the planned high-energy compressed nuclear matter experiments [7][8][9][10][11][12].…”

“…Fig 4. Phase diagrams for two values of the coupling: x σ Δ = 1.2 (upper panel) and x σ Δ = 1.0 (lower panel).…”