Particle yields in pp interactions at GeV interpreted in the statistical hadronization model

Abstract

Following the recent measurement of several hadron yields by NA61/SHINE collaboration, the unified set of yields of particles produced in proton–proton collisions at = 17.3 GeV (laboratory beam momentum 158 GeV/c) is evaluated, combining the 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 χ 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 ϕ meson yield makes the fit result more reasonable. The complete experimental data set of particle yields can be also 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 to be larger than that for non-strange hadrons. The femtoscopy measurements with kaon pairs and pion pairs at 27.4, 63 and 900 GeV are not precise enough to confirm or reject this observation. The model with the best-fit parameters allows to predict the yields of several not yet measured particles emitted from p + p at = 17.3 GeV.