Finite resonance widths influence the thermal-model description of hadron yields

TL;DR

This paper investigates how different resonance modeling schemes, especially the energy dependent Breit-Wigner scheme, affect the thermal model's accuracy in describing hadron yields in heavy-ion collisions, potentially resolving the proton anomaly.

Contribution

It introduces the energy dependent Breit-Wigner scheme into thermal models, showing improved agreement with experimental data and highlighting systematic uncertainties from resonance modeling.

Findings

The eBW scheme suppresses proton yields due to threshold effects.

Applying eBW improves the fit to ALICE Pb-Pb collision data.

Resonance modeling significantly impacts thermal model predictions.

Abstract

Different scenarios for modeling resonances in a thermal model description of hadron yields measured in heavy-ion collisions are explored: the zero-width approximation, the energy independent Breit-Wigner scheme, and the energy dependent Breit-Wigner (eBW) scheme. Application of the eBW scheme leads to a notable suppression in the proton yields, stemming mainly from a reduced feeddown from $\Delta$ resonances because of the threshold effects. A significantly improved agreement of thermal model with hadron yields measured in Pb-Pb collisions at $\sqrt{s_{_{NN}}} = 2.76$ TeV by the ALICE collaboration is obtained in the eBW scheme at $T \simeq 155$ MeV, indicating a possible resolution of the so-called 'proton anomaly'. The results obtained show that there are significant systematic uncertainties in the thermal model due to the modeling of broad resonances.