New results on the multiplicity and centre-of-mass energy dependence of identified particle production in pp collisions with ALICE

TL;DR

This paper presents new measurements of identified particle production in proton-proton collisions at various energies, revealing energy-independent multiplicity patterns and highlighting limitations of current models in describing yield ratios.

Contribution

It provides comprehensive data on particle yields and spectra across energies and multiplicities, showing similarities between small and large systems and challenging existing Monte Carlo models.

Findings

Strange hadron production increases more than non-strange with multiplicity.

Yield ratios are similar across different collision systems at comparable multiplicities.

Monte Carlo models fail to accurately predict the evolution of yield ratios.

Abstract

The study of identified particle production in proton-proton (pp) collisions as a function of center-of-mass energy ($\sqrt{s}$) and event charged-particle multiplicity is a key tool for understanding similarities and differences between small and large collision systems. We report on new measurements of the production of identified particles and their dependence on multiplicity and $\sqrt{s}$. Latest results for light flavor hadrons, comprising $\pi^{\pm}$, $\mathrm{K}^{\pm}$, ${\rm p}(\rm \bar{p})$, single-strange ($\mathrm{K_{S}^{0}}$, $\bar{\Lambda}$, and $\Lambda$), multi-strange ($\Xi^{-}$, $\overline{\Xi}^{+}$, $\Omega^{-}$, and $\overline{\Omega}^{+}$) particles as well as resonances ($\mathrm{K^{*0}}$, $\mathrm{\overline{K}^{*0}}$, $\phi$), are presented for $\sqrt{s}~=~5.02, 7$, and 13 TeV. The measured minimum bias $p_{\rm T}$ spectra and yields were complemented with multiplicity-dependent measurements for single- and multi-strange hadrons at $\sqrt{s}~=~7$ and $\sqrt{s}~=~13$ TeV. Results are compared to measurements at lower $\sqrt{s}$ as well as to those in proton-lead and lead-lead (Pb-Pb) collisions, respectively at $\sqrt{s}_{\rm NN}~=~5.02$ TeV and $\sqrt{s}_{\rm NN}~=~2.76$ TeV. The results unveil intriguing similarities among collision systems at different $\sqrt{s}$. The production rates of strange hadrons are found to increase more than those of non-strange particles, showing an enhancement pattern with multiplicity which does not depend on the collision energy. These yield ratios take values which are alike for small systems at comparable multiplicities and show smooth evolution with multiplicity across all collision systems. Although the multiplicity dependence of spectral shapes can be qualitatively described by general-purpose Monte Carlo (MC) event generators, the evolution of yield ratios is barely (or not) captured by MC model predictions.