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ATLAS_2010_CONF_2010_049

Cross-section and fragmentation function in anti-$k_t$ track jets
Experiment: ATLAS (LHC 7000GeV)
Spires ID: None
Status: OBSOLETE
Authors:
  • Hendrik Hoeth
References:
  • ATLAS-CONF-2010-049
Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • pp QCD interactions at 7000 GeV including diffractive events.

Jets are identified and their properties studied using tracks measured by the ATLAS Inner Detector. Events are selected using a minimum-bias trigger, allowing the emergence of jets at low transverse momentum to be observed and for jets to be studied independently of the calorimeter. Jets are reconstructed using the anti-kt algorithm applied to tracks with two parameter choices, 0.4 and 0.6. An inclusive jet transverse momentum cross section measurement from 4 GeV to 80 GeV is shown, integrated over $|\eta| < 0.57$ and corrected to charged particle-level truth jets. The probability that a particular particle carries a fixed fraction of the jet momentum (fragmentation function) is also measured. All data is corrected to the particle level. ATTENTION - Data read from plots!

Source code: ATLAS_2010_CONF_2010_049.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Projections/FastJets.hh"

namespace Rivet {


  class ATLAS_2010_CONF_2010_049 : public Analysis {
  public:

    ATLAS_2010_CONF_2010_049()
      : Analysis("ATLAS_2010_CONF_2010_049")
    {    }


    void init() {
      ChargedFinalState cfs(-1.5, 1.5, 0.5*GeV);
      declare(cfs, "CFS");

      FastJets jetsproj6(cfs, FastJets::ANTIKT, 0.6);
      declare(jetsproj6, "Jets6");

      FastJets jetsproj4(cfs, FastJets::ANTIKT, 0.4);
      declare(jetsproj4, "Jets4");

      for (size_t i=0 ; i<2 ; i++) {
        _h_xsec[i]       = bookHisto1D(1+i, 1, 1);
        _h_frag_04_06[i] = bookHisto1D(3+i, 1, 1);
        _h_frag_06_10[i] = bookHisto1D(3+i, 2, 1);
        _h_frag_10_15[i] = bookHisto1D(3+i, 3, 1);
        _h_frag_15_24[i] = bookHisto1D(3+i, 4, 1);
        _njets_04_06[i] = 0.0;
        _njets_06_10[i] = 0.0;
        _njets_10_15[i] = 0.0;
        _njets_15_24[i] = 0.0;
      }
    }


    void analyze(const Event& event) {
      const double weight = event.weight();

      const FastJets & jetsproj6 = apply<FastJets>(event, "Jets6");
      const FastJets & jetsproj4 = apply<FastJets>(event, "Jets4");
      Jets alljets[2];
      alljets[0] = jetsproj6.jetsByPt(4.0*GeV);
      alljets[1] = jetsproj4.jetsByPt(4.0*GeV);

      for (size_t i=0 ; i<2 ; i++) {
        Jets jets;

        // First we want to make sure that we only use jets within |eta|<0.57
        foreach (const Jet& jet, alljets[i]) {
          if (jet.abseta()<0.57) {
            jets.push_back(jet);
          }
        }
        foreach (const Jet& jet, jets) {
          const double pTjet = jet.pT();
          const double pjet = jet.p3().mod();
          _h_xsec[i]->fill(pTjet, weight);
          if (pTjet > 24*GeV) continue;
          foreach (const Particle& p, jet.particles()) {
            double z = p.p3().mod()/pjet;
            if (z >= 1) z = 0.9999; // Make sure that z=1 doesn't go into overflow
            if (pTjet > 15*GeV) {
              _h_frag_15_24[i]->fill(z, weight);
            }
            else if (pTjet > 10*GeV) {
              _h_frag_10_15[i]->fill(z, weight);
            }
            else if (pTjet > 6*GeV) {
              _h_frag_06_10[i]->fill(z, weight);
            }
            else {
              _h_frag_04_06[i]->fill(z, weight);
            }
          }
          if (pTjet > 15*GeV) {
            _njets_15_24[i] += weight;
          }
          else if (pTjet > 10*GeV) {
            _njets_10_15[i] += weight;
          }
          else if (pTjet > 6*GeV) {
            _njets_06_10[i] += weight;
          }
          else {
            _njets_04_06[i] += weight;
          }
        }
      }
    }

    void finalize() {
      for (size_t i=0 ; i<2 ; i++) {
        // deta = 2*0.57
        scale(_h_xsec[i], crossSection()/microbarn/sumOfWeights()/(2*0.57));
        scale(_h_frag_04_06[i], 1./_njets_04_06[i]);
        scale(_h_frag_06_10[i], 1./_njets_06_10[i]);
        scale(_h_frag_10_15[i], 1./_njets_10_15[i]);
        scale(_h_frag_15_24[i], 1./_njets_15_24[i]);
      }
    }


  private:

    Histo1DPtr _h_xsec[2];
    Histo1DPtr _h_frag_04_06[2];
    Histo1DPtr _h_frag_06_10[2];
    Histo1DPtr _h_frag_10_15[2];
    Histo1DPtr _h_frag_15_24[2];
    double _njets_04_06[2];
    double _njets_06_10[2];
    double _njets_10_15[2];
    double _njets_15_24[2];
  };



  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2010_CONF_2010_049);

}