Constraining the hadronic spectrum and repulsive interactions in a hadron resonance gas via fluctuations of conserved charges

TL;DR

This paper enhances the hadron resonance gas model by adding unconfirmed resonances and repulsive interactions, using conserved charge fluctuations to constrain these features, improving agreement with lattice QCD data and aiding heavy-ion collision analysis.

Contribution

It introduces a combined extension of the hadron resonance gas model with unconfirmed states and repulsive interactions, constrained by charge fluctuation ratios, to better match lattice QCD results.

Findings

Evidence for extra baryon states from lattice data

Indications of repulsive interactions among baryons

Hyperons may have weaker repulsive cores than non-strange baryons

Abstract

We simultaneously incorporate two common extensions of the hadron resonance gas model, namely the addition of extra, unconfirmed resonances to the particle list and the excluded volume repulsive interactions. We emphasize the complementary nature of these two extensions and identify combinations of conserved charge susceptibilities that allow to constrain them separately. In particular, ratios of second-order susceptibilities like $\chi_{11}^{BQ}/\chi_2^B$ and $\chi_{11}^{BS}/\chi_2^B$ are sensitive only to the baryon spectrum, while fourth-to-second order ratios like $\chi_4^B/\chi_2^B$, $\chi_{31}^{BS}/\chi_{11}^{BS}$, or $\chi_{31}^{BQ}/\chi_{11}^{BQ}$ are mainly determined by repulsive interactions. Analysis of the available lattice results suggests the presence of both the extra states in the baryon-strangeness sector and the repulsive baryonic interaction, with indications that hyperons have a smaller repulsive core than non-strange baryons. The modified hadron resonance gas model presented here significantly improves the description of lattice QCD susceptibilities at chemical freeze-out and can be used for the analysis of event-by-event fluctuations in heavy-ion collisions.