van der Waals Interactions in Hadron Resonance Gas: From Nuclear Matter to Lattice QCD

TL;DR

This paper extends the hadron resonance gas model by including van der Waals interactions between baryons, successfully reproducing nuclear matter properties and aligning with lattice QCD results, highlighting the importance of interactions in hadronic thermodynamics.

Contribution

It introduces a VDW-HRG model incorporating baryonic interactions, providing a more realistic description of nuclear matter and thermodynamic fluctuations compared to ideal models.

Findings

VDW-HRG reproduces nuclear liquid-gas transition.

Inclusion of VDW interactions alters fluctuation behavior to match lattice QCD.

Model predicts nontrivial net-baryon fluctuations relevant for heavy-ion collisions.

Abstract

An extension of the ideal hadron resonance gas (HRG) model is constructed which includes the attractive and repulsive van der Waals (VDW) interactions between baryons. This VDW-HRG model yields the nuclear liquid-gas transition at low temperatures and high baryon densities. The VDW parameters $a$ and $b$ are fixed by the ground state properties of nuclear matter, and the temperature dependence of various thermodynamic observables at zero chemical potential are calculated within VDW-HRG model. Compared to the ideal HRG model, the inclusion of VDW interactions between baryons leads to a qualitatively different behavior of second and higher moments of fluctuations of conserved charges, in particular in the so-called crossover region $T\sim 140 - 190$ MeV. For many observables this behavior resembles closely the results obtained from lattice QCD simulations. This hadronic model also predicts nontrivial behavior of net-baryon fluctuations in the region of phase diagram probed by heavy-ion collision experiments. These results imply that VDW interactions play a crucial role in thermodynamics of hadron gas. Thus, the commonly performed comparisons of the ideal HRG model with the lattice and heavy-ion data may lead to misconceptions and misleading conclusions.