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

TL;DR

This paper reports measurements of charged hadron multiplicity distributions in proton-proton collisions at various energies, revealing that higher-energy data show increased multiplicity not fully captured by existing models, and confirming KNO scaling violation.

Contribution

It provides new multiplicity distribution data at 0.9, 2.36, and 7 TeV, highlighting discrepancies with event generator predictions and confirming KNO scaling violation at high energies.

Findings

Mean multiplicity increases with energy but is underestimated by models.

Higher-order moments confirm KNO scaling violation.

Data extend previous measurements to higher energies.

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 sqrt(s) = 0.9, 2.36, and 7 TeV, in five pseudorapidity ranges from |eta|<0.5 to |eta|<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 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.