Charged-particle multiplicity measurement in proton-proton collisions at √s 0.9 and 2.36 TeV with ALICE at LHC

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.