The pseudorapidity density and multiplicity distribution of charged particles produced in proton-proton collisions at the LHC, at a centre-of-mass energy √s= 7 TeV, were measured in the central pseudorapidity region {pipe}η{pipe} < 1. Comparisons are made with previous measurements at √s = 0.9 TeV and 2.36 TeV. At √s = 7 TeV, for events with at least one charged particle in {pipe}η{pipe} < 1, we obtain dNch/dη = 6.01 ± 0.01(stat.)+0.20-0.12(syst.). This corresponds to an increase of 57.6% ± 0.4%(stat.)+3.6-1.8%(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. © 2010 CERN for the benefit of the ALICE collaboration.

Charged-particle production was studied in proton-proton collisions collected at the LHC with the ALICE detector at centre-of-mass energies 0.9 TeV and 2.36 TeV in the pseudorapidity range {pipe}η{pipe}<1.4. In the central region ({pipe}η{pipe}<0.5), at 0.9 TeV, we measure charged-particle pseudorapidity density dNch/dη= 3.02 ± 0.01 (stat.)-0.05+0.08(syst.) for inelastic interactions, and dNch/dη = 3.58 ± 0.01 (stat.)-0.12+0.12(syst.) for non-single-diffractive interactions. At 2.36 TeV, we find dNch/dη = 3.77 ± 0.01 (stat.)-0.12+0.25(syst.) for inelastic, and dNch/dη = 4.43 ± 0.01(stat.)-0.12+0.17(syst.) for non-single-diffractive collisions. The relative increase in charged-particle multiplicity from the lower to higher energy is 24.7% ± 0.5%(stat.)-2.8+5.7(syst.) for inelastic and 23.7% ± 0.5%(stat.)-1.1+4.6% 1.1%(syst.) for non-single-diffractive interactions. This increase is consistent with that reported by the CMS collaboration for non-single-diffractive events and larger than that found by a number of commonly used models. The multiplicity distribution was measured in different pseudorapidity intervals and studied in terms of KNO variables at both energies. The results are compared to proton-antiproton data and to model predictions. © 2010 CERN for the benefit of the ALICE collaboration.