Multiplicity dependence of identified particle production in proton-proton collisions with ALICE

Vytautas Vislavicius

doi:10.1016/j.nuclphysa.2017.05.088

Abstract

The study of identified particle production as a function of transverse momentum (pT) and event multiplicity in proton-proton (pp) collisions at different center-of-mass energies (s) is a key tool for understanding similarities and differences between small and large collisions systems. We report on the production of π±, K±, KS0, p(p‾), Λ(Λ‾), Ξ± and Ω± measured in pp collisions in a wide range of center-of-mass energies with ALICE [1]. The multiplicity dependence of identified particle yields is presented for s=7 and 13 TeV and discussed in the context of the results obtained in protonlead (p-Pb) and lead-lead (Pb-Pb) collisions, unveiling remarkable and intriguing similarities. The production rates of strange hadrons are observed to increase more than those of non-strange particles, showing an enhancement pattern with multiplicity which does not depend on the collision energy. Even if the multiplicity dependence of spectral shapes can be qualitatively described by commonly-used Monte Carlo (MC) event generators, the evolution of integrated yield ratios is poorly described by these models.

Highlights

The study of identified particle production as a function of√transverse momentum and event multiplicity in protonproton collisions at different center-of-mass energies ( s) is a key tool for understanding similarities and differences between small and large collisions systems
Revealed trends reminiscent to those observed in Pb-Pb collisions [2] and usually associated with the creation of a strongly interacting medium, the Quark-Gluon Plasma (QGP)
Features like baryonto-meson ratio enhancement at intermediate transverse momentum in Pb-Pb collisions are understood as a consequence of quark coalescence [4] or radial flow [5]. The latter is characteristic to hydrodynamical expansion of the system and its presence might require a fireball in local thermodynamical equilibrium

Summary

Introduction

√ Measurements of hadron yields as a function of multiplicity in p-Pb collisions at s. Features like baryonto-meson ratio enhancement at intermediate transverse momentum (pT) in Pb-Pb collisions are understood as a consequence of quark coalescence [4] or radial flow [5]. The latter is characteristic to hydrodynamical expansion of the system and its presence might require a fireball in local thermodynamical (kinetic) equilibrium. In statistical hadronization models [10] the observed strange particle abundances across collision systems can be explained as a canonical suppression of strange quark production in pp collisions, which gradually subsides for larger system sizes [11]. By comparing the most recent can isolate the center-of-mass energy dependence of hadrochemistry and kinematics

Analysis and results

Summary