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

  • Author(s): Aad, G;
  • Abbott, B;
  • Abdallah, J;
  • Abdelalim, AA;
  • Abdesselam, A;
  • Abdinov, O;
  • Abi, B;
  • Abolins, M;
  • Abramowicz, H;
  • Abreu, H;
  • Acerbi, E;
  • Acharya, BS;
  • Ackers, M;
  • Adams, DL;
  • Addy, TN;
  • Adelman, J;
  • Aderholz, M;
  • Adomeit, S;
  • Adragna, P;
  • Adye, T;
  • Aefsky, S;
  • Aguilar-Saavedra, JA;
  • Aharrouche, M;
  • Ahlen, SP;
  • Ahles, F;
  • Ahmad, A;
  • Ahsan, M;
  • Aielli, G;
  • Akdogan, T;
  • Åkesson, TPA;
  • Akimoto, G;
  • Akimov, AV;
  • Alam, MS;
  • Alam, MA;
  • Albrand, S;
  • Aleksa, M;
  • Aleksandrov, IN;
  • Aleppo, M;
  • Alessandria, F;
  • Alexa, C;
  • Alexander, G;
  • Alexandre, G;
  • Alexopoulos, T;
  • Alhroob, M;
  • Aliev, M;
  • Alimonti, G;
  • Alison, J;
  • Aliyev, M;
  • Allport, PP;
  • Allwood-Spiers, SE;
  • Almond, J;
  • Aloisio, A;
  • Alon, R;
  • Alonso, A;
  • Alonso, J;
  • Alviggi, MG;
  • Amako, K;
  • Amaral, P;
  • Amelung, C;
  • Ammosov, VV;
  • Amorim, A;
  • Amorós, G;
  • Amram, N;
  • Anastopoulos, C;
  • Andeen, T;
  • Anders, CF;
  • Anderson, KJ;
  • Andreazza, A;
  • Andrei, V;
  • Andrieux, ML;
  • Anduaga, XS;
  • Angerami, A;
  • Anghinolfi, F;
  • Anjos, N;
  • Annovi, A;
  • Antonaki, A;
  • Antonelli, M;
  • Antonelli, S;
  • Antos, J;
  • Anulli, F;
  • Aoun, S;
  • Aperio Bella, L;
  • Apolle, R;
  • Arabidze, G;
  • Aracena, I;
  • Arai, Y;
  • Arce, ATH;
  • Archambault, JP;
  • Arfaoui, S;
  • Arguin, JF;
  • Arik, E;
  • Arik, M;
  • Armbruster, AJ;
  • Arms, KE;
  • Armstrong, SR;
  • Arnaez, O;
  • Arnault, C;
  • Artamonov, A;
  • Artoni, G;
  • Arutinov, D
  • et al.
Abstract

Measurements are presented from proton-proton collisions at centre-of-mass energies of s = 0.9, 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimumbias 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 s = 0.9 TeV and 5.630±0.003 (stat)±0.169 (syst) at s = 7 TeV. © 2011 CERN for the benefit of the ATLAS Collaboration, published under licence by IOP Publishing Ltd for the Institute of Physics and Deutsche Physikalische Gesellschaft.

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