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

Aad, G and Abbott, B. and Abdallah, J. and Abdelalim, A .A. and Abdesselam, A. and Abdinov, O. and Abi, B. and Abolins, M. and Bell, William, The ATLAS collaboration (2011) Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC. New Journal of Physics, 13 (053033). 053033. ISSN 1367-2630 (https://doi.org/10.1088/1367-2630/13/5/053033)

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Abstract

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 .

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