Charged particle's $p_T$ spectra and elliptic flow in $\sqrt{s_{NN}}$=200 GeV Au+Au collisions: QGP vs. hadronic resonance gas

TL;DR

This study compares the effects of a hadronic resonance gas and quark-gluon plasma on particle spectra and flow in high-energy gold-gold collisions, highlighting the challenge in distinguishing these states without precise lattice QCD data.

Contribution

It demonstrates that at certain temperatures, hadronic resonance gas can mimic QGP signatures, complicating the identification of the matter's true nature in heavy-ion collisions.

Findings

HRG with viscosity to entropy ratio ~0.24 can reproduce spectra and flow at T≈220 MeV

Distinguishing QGP from HRG requires demonstrating HRG is unphysical below 200 MeV

Precise lattice simulations are needed to clarify the matter's phase at these temperatures

Abstract

We show that if the hadronic resonance gas (HRG), with viscosity to entropy ratio $\eta/s\approx$0.24, is physical at temperature $T\approx$220 MeV, charged particles $p_T$ spectra and elliptic flow in Au+Au collisions at RHIC, over a wide range of collision centrality do not distinguish between initial QGP fluid and initial hadronic resonance gas. Unambiguous identification of bulk of the matter produced in Au+Au collisions require clear demonstration that HRG is unphysical at temperature $T<$200 MeV. It calls for precise lattice simulations with realistic boundary conditions.