Charged-particle multiplicity measurement in proton–proton collisions at √s = 7 TeV with ALICE at LHC

Abstract

The pseudorapidity density and multiplicity distribution of charged particles produced in proton–proton collisions at the LHC, at a centre-of-mass energy Ös=7s=7 TeV, were measured in the central pseudorapidity region |η|<1. Comparisons are made with previous measurements at Ös=0.9s=09 TeV and 2.36 TeV. At Ös=7s=7 TeV, for events with at least one charged particle in |η|<1, we obtain dNch/dh = 6.01±0.01(stat.)+0.20-0.12(syst.)dNchd=601001(stat)+020−012(syst). This corresponds to an increase of 57.6%±0.4%(stat.)+3.6-1.8%(syst.)576%04%(stat)+36−18%(syst) relative to collisions at 0.9 TeV, significantly higher than calculations from commonly used models. The multiplicity distribution at 7 TeV is described fairly well by the negative binomial distribution.