Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC

The ATLAS collaboration, G Aad, B. Abbott, J. Abdallah, A .A. Abdelalim, A. Abdesselam, O. Abdinov, B. Abi, M. Abolins, William Bell

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Measurements are presented from proton–proton collisions at centre-of-mass energies of , 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimum-bias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared to each other and to various Monte Carlo (MC) models, including a new AMBT1 pythia6 tune. In all the kinematic regions considered, the particle multiplicities are higher than predicted by the MC models. The central charged-particle multiplicity per event and unit of pseudorapidity, for tracks with pT>100 MeV, is measured to be 3.483±0.009 (stat)±0.106 (syst) at and 5.630±0.003 (stat)±0.169 (syst) at .
Original languageEnglish
Article number053033
Number of pages68
JournalNew Journal of Physics
Issue number053033
Publication statusPublished - 19 May 2011


  • ATLAS detector
  • LHC
  • charged-particle multiplicities
  • proton–proton collisions


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