The thermal proton yield anomaly in Pb-Pb collisions at the LHC and its resolution

Anton Andronic,Peter Braun-Munzinger,Bengt Friman,Pok Man Lo,Krzysztof Redlich,Johanna Stachel

doi:10.1016/j.physletb.2019.03.052

Abstract

We propose a resolution of the discrepancy between the proton yield predicted by the statistical hadronization approach and data on hadron production in ultra-relativistic nuclear collisions at the LHC. Applying the S-matrix formulation of statistical mechanics to include pion-nucleon interactions, we reexamine their contribution to the proton yield, taking resonance widths and the presence of nonresonant correlations into account. The effect of multi-pion-nucleon interactions is estimated using lattice QCD results on the baryon-charge susceptibility. We show that a consistent implementation of these features in the statistical hadronization model, leads to a reduction of the predicted proton yield, which then quantitatively matches data of the ALICE collaboration for Pb-Pb collisions at the LHC.

Highlights

The thermal nature of particle production in high energy nucleus-nucleus collisions is one of the important findings in the phenomenological analysis of experimental data [1,2,3,4,5,6,7,8,9]
The thermal origin of particle production in heavy ion collisions is transparent at LHC energies, where the chemical freeze-out is quantified by only two parameters, the temperature and the volume of the produced fireball
We show that the answer to the above question is affirmative and demonstrate that the S-matrix treatment of pion-nucleon and multi-pion-nucleon interactions removes the discrepancy between experimental data and theoretical predictions within the statistical hadronization approach

Summary

Introduction

The thermal nature of particle production in high energy nucleus-nucleus collisions is one of the important findings in the phenomenological analysis of experimental data [1,2,3,4,5,6,7,8,9]. The proton yields predicted by statistical hadronization can be separated into two parts: a purely thermal yield from uncorrelated nucleons, which depends only on the freeze-out parameters, i.e., the freeze-out temperature T f and the freeze-out chemical potentials, and the contribution from multiparticle interactions involving nucleons The latter include baryon resonances, as well as nonresonant meson-baryon interactions. To describe the high-precision hadron yield data from ALICE at LHC, a more refined approach is required to properly account for the interaction contributions to particle multiplicities It is the purpose of this letter to employ a consistent theoretical framework to reliably describe resonant and nonresonant pion-nucleon interactions and their contributions to the proton yield. The resulting proton multiplicity is in good agreement with the ALICE data

S-matrix treatment of the π N system

The proton yield

Findings

Conclusions