Charged-particle multiplicity measurement in proton-proton collisions at 1as = 7 TeV with ALICE at LHC

The pseudorapidity density and multiplicity distribution of charged particles produced in proton-proton collisions at the LHC, at a centre-of-mass energy 1as= 7 TeV, were measured in the central pseudorapidity region {pipe}\u3b7{pipe} < 1. Comparisons are made with previous measurements at 1as = 0.9 TeV and 2.36 TeV. At 1as = 7 TeV, for events with at least one charged particle in {pipe}\u3b7{pipe} < 1, we obtain dNch/d\u3b7 = 6.01 \ub1 0.01(stat.)+0.20-0.12(syst.). This corresponds to an increase of 57.6% \ub1 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