Charged particle multiplicities in pp interactions at $ \sqrt {s} = 0.9 $ , 2.36, and 7 TeV

Abstract

Measurements of primary charged hadron multiplicity distributions are presented for non-single-diffractive events in proton-proton collisions at centre-of-mass energies of s = 0.9, 2.36, and 7 TeV, in five pseudorapidity ranges from || < 0.5 to || < 2.4. The data were collected with the minimum-bias trigger of the CMS experiment during the LHC commissioning runs in 2009 and the 7 TeV run in 2010. The multiplicity distribution at s = 0.9 TeV is in agreement with previous measurements. At higher energies the increase of the mean multiplicity with s is underestimated by most event generators. The average transverse momentum as a function of the multiplicity is also presented. The measurement of higher-order moments of the multiplicity distribution confirms the violation of Koba-Nielsen-Olesen scaling that has been observed at lower energies.