Statistical hadron-gas treatment of systems created in proton-proton interactions at CERN SPS

TL;DR

This study applies a statistical hadron-gas model to analyze proton-proton collision data at CERN SPS, revealing limitations in describing multiplicity fluctuations and the role of the $\

Contribution

It demonstrates that a canonical ensemble HRG model cannot fully explain p+p collision data, highlighting the need for alternative approaches to understand these systems.

Findings

Inclusion of $\

Large multiplicity fluctuations are observed that the model cannot explain.

Canonical ensemble does not outperform grand canonical in fitting p+p data.

Abstract

We analyze the newest data from the NA61/SHINE collaboration which, in addition to previous results on pions and kaons, include mean multiplicities of $p$, $\Lambda$, and $\phi$-mesons produced in inelastic proton-proton (p+p) interactions at $\sqrt{s_{NN}}=6.3-17.3$~GeV. The canonical ensemble formulation of the ideal hadron resonance gas (HRG) model is used with exact conservation of net baryon number $B=2$, electric charge $Q=2$, and strangeness $S=0$. The chemical freeze-out parameters in p+p interactions are obtained and compared to those in central nucleus-nucleus collisions. Several features of p+p interactions at the CERN SPS within a statistical model are studied: 1) the inclusion of the $\phi$-meson yields in thermal fits worsens significantly the fit quality; 2) the data show large event-by-event multiplicity fluctuations in inelastic p+p interactions which can not be explained by a single fireball described by a statistical model; 3) the fits within the canonical ensemble formulation of HRG do not give any improvement over the fits within the grand canonical ensemble formulation, i.e., there are no indications for existence of a single statistical system in p+p inelastic interactions in the considered energy range.