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

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          Abstract

          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 |eta|<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 eta = 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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          Most cited references5

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          Parton Distributions for LO Generators

          We present a study of the results obtained combining LO partonic matrix elements with either LO or NLO partons distributions. These are compared to the best prediction using NLO for both matrix elements and parton distributions. The aim is to determine which parton distributions are most appropriate to use in those cases where only LO matrix elements are available, e.g. as in many Monte Carlo generators. Both LO and NLO parton distributions have flaws, sometimes serious, for some processes, so a modified optimal LO set is suggested. We investigate a wide variety of process, and the LO* pdf works at least as well as, and often better than, both LO and NLO pdfs in nearly all cases.The LO* pdf set is now available in the LHAPDF package.
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            Photoproduction within the two-component Dual Parton Model: Amplitudes and cross sections

            R. Engel (1995)
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              Non-perturbative QCD Effects and the Top Mass at the Tevatron

              We present a new, universally applicable toy model of colour reconnections in hadronic final states. The model is based on hadronising strings and has one free parameter. We next present an implementation of this model in the Pythia event generator and provide several parameter sets ("tunes"), constrained by fits to Tevatron minimum-bias data. Finally, we consider the sensitivity of a simplified top mass analysis to these effects, in exclusive semi-leptonic top events at the Tevatron. A first attempt at isolating the genuine non-perturbative effects gives an estimate of order delta(m_top) ~ 0.5 GeV from non-perturbative uncertainties, and a further delta(m_top) ~ 1 GeV from shower effects.
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                Author and article information

                Journal
                16 March 2010
                2010-04-29
                Article
                10.1016/j.physletb.2010.03.064
                1003.3124
                615cdab9-2b0d-483e-a681-cd87f52a281c

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

                History
                Custom metadata
                CERN-PH-EP/2010-004
                Phys.Lett.B688:21-42,2010
                40 pages (pages 24-40 appendix with ATLAS collaboration author list), 4 figures. The data points are in the HEP-data database at: http://hepdata.cedar.ac.uk/View/8591806
                hep-ex

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