Charged-particle production in pp collisions at $\sqrt{s}$ = 13.6 TeV and Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.36 TeV with ALICE

Abstract

This article presents the measurement of charged-particle pseudorapidity ($\eta$) density, $\mathrm{d}{N}_{\mathrm{ch}}/\mathrm{d}\eta$, in proton$-$proton (pp) collisions at a centre-of-mass energy $\sqrt{s}$ = 13.6 TeV, and in lead$-$lead (Pb$-$Pb) collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}$ = 5.36 TeV. The analysis is performed using the Run 3 data recorded during 2022 and 2023 by the upgraded ALICE detector. The charged-particle multiplicity is measured at midrapidity ($|\eta |<1$) using the new monolithic active pixel sensors-based Inner Tracking System and the Time Projection Chamber upgraded with Gas Electron Multiplier-based readout system. The measurements in pp collisions are reported for inelastic events with at least one charged particle having $|\eta |<1$ whereas for Pb$-$Pb collisions, the $\mathrm{d}{N}_{\mathrm{ch}}/\mathrm{d}\eta$ is obtained for different centrality classes, ranging from 0$-$5\% (most central) to 70$-$80\% (most peripheral). The energy dependence of average charged-particle pseudorapidity density ($⟨\mathrm{d}{N}_{\mathrm{ch}}/\mathrm{d}\eta ⟩$) measured in $|\eta |<0.5$ is studied and compared to earlier measurements at lower collision energies. In Pb$-$Pb collisions, the evolution of $⟨\mathrm{d}{N}_{\mathrm{ch}}/\mathrm{d}\eta ⟩$ as a function of the average number of participating nucleons, $⟨N_{\mathrm{part}}⟩$, determined with a Glauber model, is also studied and compared with predictions from theoretical models.

6 pages, 3 figures; proceedings of the 42nd International Conference on High Energy Physics (ICHEP2024)