Charm degrees of freedom in hot matter from lattice QCD

TL;DR

This study uses lattice QCD to analyze charm degrees of freedom in hot matter, revealing that charmed hadrons dominate below the crossover temperature and charm quarks emerge as new degrees of freedom above it, up to 175 MeV.

Contribution

It provides a detailed lattice QCD analysis of charm fluctuations and their correlations, clarifying the transition from hadronic to quark degrees of freedom in hot matter.

Findings

Charmed hadrons dominate below the chiral crossover temperature.

Charm quarks appear as new degrees of freedom above the transition.

Charmed hadron-like excitations significantly contribute up to 175 MeV.

Abstract

We study the nature of charm degrees of freedom in hot strong interaction matter by performing lattice QCD calculations of the second and fourth-order cumulants of charm fluctuations, and their correlations with net baryon number, electric charge and strangeness fluctuations. We show that below the chiral crossover temperature thermodynamics of charm can be very well understood in terms of charmed hadrons. Above the chiral transition charm quarks show up as new degrees of freedom contributing to the partial charm pressure. However, up to temperatures as high as 175 MeV charmed hadron-like excitations provide a significant contribution to the partial charm pressure.