Measurement of the charged-hadron multiplicity in proton-proton collisions at LHC with the CMS detector

Abstract

Charged-hadron pseudorapidity densities and multiplicity distributions in protonproton collisions at [the square root of sigma] = 0.9, 2.36, 7.0 TeV were measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield was obtained by counting the number of hit-pairs (tracklets). The charged-particle multiplicity per unit of pseudorapidity dNch/d[eta] [eta]<0.5 at [the square root of sigma] = 7.0 TeV is 5.78 i 0.01(stat.) i 0.23(syst.) for nonsingle- diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from [the square root of sigma] = 0.9 to 7 TeV is 66.1% ± 1.0%(stat.) ± 4.2%(syst.) and strong KNO violation is observed in the multiplicity distributions. Results are compared with low energy measurements.