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ALICE_2010_I880049

Centrality dependence of the charged-particle multiplicity density at mid-rapidity in Pb--Pb collisions at $\sqrt{s_{\rm{NN}}} = 2.76$ TeV
Experiment: ALICE (LHC)
Inspire ID: 880049
Status: VALIDATED
Authors:
  • Przemyslaw Karczmarczyk
  • Jan Fiete Grosse-Oetringhaus
  • Jochen Klein
References: Beams: 1000822080 1000822080
Beam energies: (287040.0, 287040.0) GeV
    No run details listed

The centrality dependence of the charged-particle multiplicity density at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor 2 from peripheral (70-80%) to central (0-5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions.

Source code: ALICE_2010_I880049.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/ChargedFinalState.hh"
  4#include "Rivet/Tools/Cuts.hh"
  5#include "Rivet/Projections/SingleValueProjection.hh"
  6#include "Rivet/Tools/AliceCommon.hh"
  7#include "Rivet/Projections/AliceCommon.hh"
  8#include "Rivet/Projections/HepMCHeavyIon.hh"
  9
 10namespace Rivet {
 11
 12  /// @brief ALICE PbPb at 2.76 TeV multiplicity at mid-rapidity
 13  class ALICE_2010_I880049 : public Analysis {    
 14  public:
 15
 16    /// Constructor
 17    RIVET_DEFAULT_ANALYSIS_CTOR(ALICE_2010_I880049);
 18
 19    /// @name Analysis methods
 20    //@{
 21
 22    /// Book histograms and initialise projections before the run
 23    void init() {
 24
 25      // Declare centrality projection
 26      declareCentrality(ALICE::V0MMultiplicity(),
 27        "ALICE_2015_PBPBCentrality", "V0M", "V0M");
 28
 29      // Trigger projections
 30      declare(ChargedFinalState((Cuts::eta > 2.8 && Cuts::eta < 5.1) &&
 31        Cuts::pT > 0.1*GeV), "VZERO1");
 32      declare(ChargedFinalState((Cuts::eta > -3.7 && Cuts::eta < -1.7) &&
 33        Cuts::pT > 0.1*GeV), "VZERO2");
 34      declare(ChargedFinalState(Cuts::abseta < 1. && Cuts::pT > 0.15*GeV),
 35        "SPD");
 36
 37      // Charged, primary particles with |eta| < 0.5 and pT > 50 MeV
 38      declare(ALICE::PrimaryParticles(Cuts::abseta < 0.5 &&
 39        Cuts::pT > 50*MeV && Cuts::abscharge > 0), "APRIM");
 40
 41      // Access the HepMC heavy ion info
 42      declare(HepMCHeavyIon(), "HepMC");
 43
 44      // Histograms and variables initialization
 45      book(_histNchVsCentr, 1, 1, 1);
 46      book(_histNpartVsCentr, 1, 1, 2);
 47
 48    }
 49
 50
 51    /// Perform the per-event analysis
 52    void analyze(const Event& event) {
 53
 54      // Charged, primary particles with at least pT = 50 MeV
 55      // in eta range of |eta| < 0.5
 56      Particles chargedParticles =
 57        applyProjection<ALICE::PrimaryParticles>(event,"APRIM").particles();
 58
 59      // Trigger projections
 60      const ChargedFinalState& vz1 =
 61        applyProjection<ChargedFinalState>(event,"VZERO1");
 62      const ChargedFinalState& vz2 =
 63        applyProjection<ChargedFinalState>(event,"VZERO2");
 64      const ChargedFinalState& spd =
 65        applyProjection<ChargedFinalState>(event,"SPD");
 66      int fwdTrig = (vz1.particles().size() > 0 ? 1 : 0);
 67      int bwdTrig = (vz2.particles().size() > 0 ? 1 : 0);
 68      int cTrig = (spd.particles().size() > 0 ? 1 : 0);
 69
 70      if (fwdTrig + bwdTrig + cTrig < 2) vetoEvent;
 71
 72      const CentralityProjection& centrProj =
 73        apply<CentralityProjection>(event, "V0M");
 74      double centr = centrProj();
 75      if (centr > 80) vetoEvent;
 76      // Calculate number of charged particles and fill histogram
 77      double nch = chargedParticles.size();
 78      _histNchVsCentr->fill(centr, nch);
 79
 80      // Attempt to extract Npart form GenEvent.
 81      if (event.genEvent()->heavy_ion()) {
 82        const HepMCHeavyIon & hi = apply<HepMCHeavyIon>(event, "HepMC");
 83        _histNpartVsCentr->fill(centr, hi.Npart_proj() + hi.Npart_targ());
 84      }
 85    }
 86
 87    
 88    /// Normalise histograms etc., after the run
 89    //void finalize() {   }
 90
 91    //@}
 92
 93
 94  private:
 95
 96    /// @name Histograms
 97    //@{
 98    Profile1DPtr _histNchVsCentr;
 99    Profile1DPtr _histNpartVsCentr;
100    //@}
101
102  };
103
104
105  // The hook for the plugin system
106  RIVET_DECLARE_PLUGIN(ALICE_2010_I880049);
107
108}