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

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.