Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at \(\sqrt{s_{\rm NN}}=5.02\) TeV

Abstract

We present the charged-particle pseudorapidity density in Pb-Pb collisions at \(\sqrt{s_{\mathrm{NN}}}=5.02\,\mathrm{Te\kern-.25exV}\) in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from \(-3.5\) to \(5\), 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 \(21\,400\pm 1\,300\) while for the most peripheral (80-90%) we find \(230\pm 38\), This corresponds to an increase of \((27\pm4)%\) over the results at \(\sqrt{s_{\mathrm{NN}}}=2.76\,\mathrm{Te\kern-.25exV}\) previously 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.