Charged-particle multiplicity measurement in proton-proton collisions at √s=09 and 2.36 TeV with ALICE at LHC

Abstract

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 |η| < 1.4. In the central region (|η| < 0.5), at 0.9 TeV, we measure charged-particle pseudorapidity density dN_ch/d_η=3.02±0 01 (stat. )^+0.08_−0.05 (syst.) for inelastic interactions, and dN_ch/d_η=3.58±0.01(stat.)^+0.12_−0.12(syst.) for non-single-diffractive interactions. At 2.36 TeV, we find dN_chd_η=3.77±0.01(stat.) ^+0.25_−0.12(syst.) for inelastic, and dN_ch/d_η=4.43±0.01(stat.)^+0.17_−0.12(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.)^+5.7_−2.8%(syst.) for inelastic and 23.7%±0.5%(stat.)^+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.