Centrality dependence of the pseudorapidity density distribution for charged particles in Pb–Pb collisions at √sNN=5.02TeV

Abstract

We present the charged-particle pseudorapidity density in Pb–Pb collisions at √sNN=5.02TeVin centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from −3.5to 5, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0–5%) collisions we find 21 400 ±1 300, while for the most peripheral (80–90%) we find 230 ±38. This corresponds to an increase of (27 ±4)%over the results at √sNN=2.76TeVpreviously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations — none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies.