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Charged-particle multiplicities in pp interactions at √s = 900 GeV measured with the ATLAS detector at the LHC

Research output: Contribution to journalJournal article


  • ATLAS Collaboration
<mark>Journal publication date</mark>26/04/2010
<mark>Journal</mark>Physics Letters B
Issue number1
Number of pages22
Pages (from-to)21-42
<mark>Original language</mark>English


The first measurements from proton–proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged- particle multiplicity are measured for events with at least one charged particle in the kinematic range |η| < 2.5 and pT > 500 MeV. The measurements are compared to Monte Carlo models of proton–proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity at η = 0 is measured to be 1.333 ± 0.003(stat.) ± 0.040(syst.), which is 5–15% higher than the Monte Carlo models predict.

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