Charged-particle multiplicity measurement in proton-proton collisions at $\sqrt{s}$ = 0.9 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 |$\eta$| < 1.4. In the central region (|$\eta$| < 0.5), at 0.9 TeV, we measure charged-particle pseudorapidity density dNch/deta = 3.02 $\pm$ 0.01 (stat.) ${}_{-0.05}^{+0.08}$ (syst.) for inelastic interactions, and dNch/deta = 3.58 $\pm$ 0.01 (stat.) ${}_{-0.12}^{+0.12}$ (syst.) for non-single-diffractive interactions. At 2.36 TeV, we find dNch/deta = 3.77 $\pm$ 0.01 (stat.) ${}_{-0.12}^{+0.25}$ (syst.) for inelastic, and dNch/deta = 4.43 $\pm$ 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% $\pm$ 0.5% (stat.) ${}_{-2.8}^{+5.7}$% (syst.) for inelastic and 23.7% $\pm$ 0.5% (stat.) ${}_{-1.1}^{+4.6}$% (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.

20 pages, 12 captioned figures, 4 tables, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/3903

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