Charged-particle multiplicity measurement in proton-proton collitions at sqrt(s)=7TeV 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 s√=7 TeV, were measured in the central pseudorapidity region |η|<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 |η|<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.