ALICE results on system-size dependence of charged-particle multiplicity density in p-Pb, Pb-Pb and Xe-Xe collisions

TL;DR

This paper presents ALICE experiment results on how charged-particle multiplicity density varies with system size and energy in p-Pb, Pb-Pb, and Xe-Xe collisions at the LHC, providing insights into particle production mechanisms.

Contribution

It provides new measurements of charged-particle pseudorapidity density for Xe-Xe and p-Pb collisions at high energies, comparing them to Pb-Pb results to study system-size dependence.

Findings

Charged-particle multiplicity increases with system size and energy.

Xe-Xe collisions show unique features compared to Pb-Pb.

Model comparisons help constrain particle production mechanisms.

Abstract

Particle production at LHC energies involves the interplay of hard (perturbative) and soft (non-perturbative) QCD processes. Global observables, such as the charged-particle multiplicity, are related to the initial geometry and the energy density produced in the collision. They are important to characterise relativistic heavy-ion collisions and to constrain model calculations. The LHC produced Xenon-Xenon collisions for the first time in October 2017. New results on the primary charged-particle pseudorapidity density, and its pseudorapidity and centrality dependence are presented for this lighter and deformed nucleus, and compared to measurements obtained for lead ions. New results will also be presented for p-Pb collisions at the highest energy of 8.16 TeV, as part of an overview of all the measurements at LHC Run 1 and 2 energies. These studies allow us to investigate the evolution of particle production with energy and system size and to compare models based on various particle production mechanisms and different initial conditions.