, 2011:79,
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Date: 19 Jan 2011

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


Measurements of primary charged hadron multiplicity distributions are presented for non-single-diffractive events in proton-proton collisions at centre-of-mass energies of \( \sqrt {s} = 0.9 \), 2.36, and 7 TeV, in five pseudorapidity ranges from |η| < 0.5 to |η| < 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 \( \sqrt {s} = 0.9\;{\text{TeV}} \) is in agreement with previous measurements. At higher energies the increase of the mean multiplicity with \( \sqrt {s} \) 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.