The strange degrees of freedom in QCD at high temperature

TL;DR

This paper investigates the behavior of strange degrees of freedom in QCD across different temperature regimes, using fluctuations of conserved charges to compare with hadron resonance gas and quark gas models.

Contribution

It provides a detailed analysis of strange charge fluctuations and their correlations, proposing observables to test the validity of hadronic versus quark degrees of freedom at various temperatures.

Findings

Strange degrees of freedom match hadron resonance gas predictions below 160 MeV.

At temperatures above twice the crossover temperature, a quasi-particle model describes the data.

Partial pressures from strangeness sectors align with HRG model expectations.

Abstract

We discuss recent results on fluctuations of conserved charges, and their approach to the hadron resonance gas at temperatures below the chiral crossover (Tc) as well as to a gas of free quarks at very high temperatures. We will focus on the strange degrees of freedom and verify that they are consistent with those of an uncorrelated gas of hadrons for temperatures of T<160 MeV and that they can be described by a quasi particle model at best for T>2Tc. To extract this information we use all cumulants of net baryon number and net strangeness fluctuations and their correlations up to the fourth order. In particular we propose observables that serve as indicator for the validity of the hadronic degrees of freedom and show that the partial pressures from different strangeness sectors agree separately with HRG model predictions.