# Universal descriptions of chemical freeze-out based on pressure and specific heat

## TL;DR

This paper introduces universal descriptions of chemical freeze-out parameters in heavy ion collisions based on pressure and specific heat, using lattice QCD data and the EVHRG model, revealing consistent thermodynamic properties.

## Contribution

It presents new universal relations for chemical freeze-out based on pressure and specific heat, derived from lattice QCD data within the EVHRG model.

## Key findings

- Chemical freeze-out parameters correspond to P/T^4= 0.88 and C_V/T^3= 47.
- The hadronic radius parameter R_h= 0.15 fm fits lattice QCD data well.
- Universal freeze-out lines are insensitive to repulsive interactions for optimal radii.

## Abstract

The lattice QCD data of pressure and the energy density have been used to extract the hadronic radius parameter of the excluded volume hadron resonance gas (EVHRG) model. The equation of state can be described well with the extracted radius parameter $R_h= 0.15$ fm. Specific heat is also calculated in the EVHRG model. Further, two new universal descriptions of chemical freeze-out parameters have been introduced based on pressure and specific heat respectively. It is shown that the chemical freeze-out parameters obtained at various $\sqrt{s_{NN}}$ in ideal HRG model approximately correspond to $P/T^4= 0.88$ and $C_V/T^3= 47$ respectively. These two quantities are important to describe the thermodynamic properties of the hadronic matter created in heavy ion collision experiment. The sensitivity of universal chemical freeze-out lines on repulsive interaction is also studied. It has been observed that the behaviors of chemical freeze-out lines for $P/T^4$ and $C_V/T^3$ in EVHRG model remain similar to ideal HRG model for the best fit value of hadronic radii.