Thermodynamics of a Gas of Hadrons with Interaction Using S-Matrix Formalism

Abstract

Ideal hadron resonance gas (HRG) is a popular model to study the late stage of QCD matter formed in heavy-ion collisions at finite temperature and chemical potential. An extension of the HRG model is constructed to include attractive interactions using the relativistic virial expansion of partition function. The virial coefficients are related to the phase shifts which are calculated using K-matrix formalism. We calculate various thermodynamics quantities like pressure, energy density, and entropy density of the system. A comparison of thermodynamic quantities with non-interacting HRG model, calculated using the same number of hadrons, shows that the values of thermodynamic quantities from the above formalism are larger. A good agreement between equation of state calculated in K-matrix formalism and lattice QCD simulations is observed. Further, we report the effect of including repulsive interactions on various thermodynamic observables calculated using a S-matrix based HRG model to already available corresponding results with only attractive interactions.