Static quark anti-quark interactions at zero and finite temperature QCD. II.Quark anti-quark internal energy and entropy

TL;DR

This paper investigates how the free energy, internal energy, and entropy related to a heavy quark-antiquark pair change in a QCD thermal environment, revealing signals of phase transition and mechanisms of quarkonium dissociation.

Contribution

It introduces and analyzes internal energy and entropy as new observables derived from thermal derivatives of the QCD partition function with static sources, highlighting their role in phase transition signals.

Findings

Internal energy and entropy signal the confinement-deconfinement transition.

String breaking and color screening are reflected in the energy behaviors.

Some quarkonium states may survive the phase transition, dissolving only at higher temperatures.

Abstract

We analyze the change in free energy, internal energy and entropy due to the presence of a heavy quark anti-quark pair in a QCD heat bath. The internal energies and entropies are introduced as intensive observables calculated through thermal derivatives of the QCD partition function containing additional static color sources. The quark anti-quark internal energy and, in particular, the entropy clearly signal the phase change from quark confinement below and deconfinement above the transition and both observables are introduced such that they survive the continuum limit. The intermediate and large distance behavior of the energies reflect string breaking and color screening phenomena. This is used to characterize the energies which are needed to dissolve heavy quarkonium states in a thermal medium. Our discussion supports recent findings which suggest that parts of the quarkonium systems may survive the phase transition and dissolve only at higher temperatures.