Particle yields in pp interactions at $\sqrt{s}=17.3$ GeV interpreted in the statistical hadronization model

TL;DR

This study evaluates particle yields in proton-proton collisions at 17.3 GeV using the statistical hadronization model, revealing limitations in fit quality and suggesting independent variation of strangeness and non-strange volumes.

Contribution

It demonstrates that allowing separate canonical volumes for strange and non-strange hadrons improves fit quality and provides predictions for unmeasured particle yields.

Findings

High chi-squared values indicate poor fit quality.

Excluding the phi meson yield improves the fit.

Strangeness volume exceeds non-strange volume, aligning with femtoscopy measurements.

Abstract

The unified set of yields of particles produced in proton-proton collisions at $\sqrt{s}$ = 17.3 GeV (laboratory beam momentum 158 GeV/c) is evaluated, combining the experimental results of the NA49 and NA61/SHINE collaborations at the CERN SPS. With the statistical hadronization code Thermal-Fist we confirm the unacceptably high value of $\chi^2$, both in the canonical and grand canonical - strangeness canonical approach, and the common volume for all the hadrons. The use of the energy-dependent width of the Breit-Wigner parametrization for the mass distributions of unstable particles improves the quality of the description of particle yields only slightly. We confirm the observation that exclusion of the $\phi$ meson yield makes the fit result acceptable. The complete experimental data set of particle yields can be reasonably fitted if the canonical volumes of hadrons without and with open strangeness are allowed to vary independently. The canonical volume of strangeness was found larger than that for non-strange hadrons, which is compatible with the femtoscopy measurements of p+p system at $\sqrt{s} = $ 27.4 MeV and 900 MeV. The model with the best-fit parameters allows to predict the yields of several not yet measured particles emitted from p+p at $\sqrt{s}$ = 17.3 GeV.