Adiabatic Chemical Freeze-out and Wide Resonance Modification in a Thermal Medium

TL;DR

This paper develops a model for the hadron resonance gas at chemical freeze-out, revealing a power-like mass spectrum and introducing effects like resonance sharpening and enhancement, with implications for understanding strongly interacting matter.

Contribution

The paper introduces a new model equation of state that explains the adiabatic chemical freeze-out criterion and demonstrates the impact of wide resonance effects in a thermal medium.

Findings

Hadronic mass spectrum at freeze-out is power-like, not exponential.

Resonance sharpening reduces sigma meson width to 50-70 MeV below 92 MeV temperature.

Wide quark-gluon bags may appear as narrow resonances with widths 50-150 MeV above 2.5 GeV.

Abstract

Here we develop a model equation of state which successfully parameterizes the thermodynamic functions of hadron resonance gas model at chemical freeze-out and which allows us to naturally explain the adiabatic chemical freeze-out criterion. The present model enables us to clearly demonstrate that at chemical freeze-out the resulting hadronic mass spectrum used in the hadron resonance gas model is not an exponential-like, but a power-like. We argue that such a property of hadronic mass spectrum at chemical freeze-out can be explained by the two new effects found here for wide resonances existing in a thermal environment: the near threshold thermal resonance enhancement and the near threshold resonance sharpening. The effect of resonance sharpening is studied for a sigma meson and our analysis shows that for the temperatures well below 92 MeV the effective width of sigma meson is about 50 to 70 MeV. Thus, the effect of resonance sharpening justifies the usage of the sigma-like field-theoretical models for the strongly interacting matter equation of state at such temperatures. Also we argue that the most optimistic hope to find the quark gluon bags experimentally may be related to their sharpening and enhancement in a thermal medium. In this case the wide quark gluon bags may appear directly or in decays as narrow resonances that are absent in the tables of elementary particles and that have the width about 50-150 MeV and the mass about or above 2.5 GeV.