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ATLAS_2016_I1419070

Number of tracks in jets
Experiment: ATLAS (LHC)
Inspire ID: 1419070
Status: VALIDATED
Authors:
  • Ben Nachman
  • Christian Gutschow
References: Beams: p+ p+
Beam energies: (4000.0, 4000.0) GeV
Run details:
  • dijet production

The number of charged particles inside jets is a widely used discriminant for identifying the quark or gluon nature of the initiating parton and is sensitive to both the perturbative and non-perturbative components of fragmentation. This analysis presents a measurement of the average number of charged particles with $p_\text{T}>500$ MeV inside high-momentum jets in dijet events using 20.3 fb${}^{-1}$ of data recorded with the ATLAS detector in $pp$ collisions at $\sqrt{s}=8$ TeV collisions at the LHC. The jets considered have transverse momenta from 50 GeV up to and beyond 1.5 TeV. The reconstructed charged-particle track multiplicity distribution is unfolded to remove distortions from detector effects.

Source code: ATLAS_2016_I1419070.cc
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#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.hh"

namespace Rivet {

  class ATLAS_2016_I1419070 : public Analysis {

  public:
  
    /// Constructor
    ATLAS_2016_I1419070() : Analysis("ATLAS_2016_I1419070")
    {  }
  
  public:

    void init() {

      addProjection(FastJets(FinalState(), FastJets::ANTIKT, 0.4), "Jets");

      forward_500MeV = bookProfile1D(1, 1, 1);
      forward_2GeV   = bookProfile1D(2, 1, 1);
      forward_5GeV   = bookProfile1D(3, 1, 1);

      central_500MeV = bookProfile1D(4, 1, 1);
      central_2GeV   = bookProfile1D(5, 1, 1);
      central_5GeV   = bookProfile1D(6, 1, 1);

      diff_500MeV = bookScatter2D("d07-x01-y01", true);
      diff_2GeV   = bookScatter2D("d08-x01-y01", true);
      diff_5GeV   = bookScatter2D("d09-x01-y01", true);

      sum_500MeV = bookScatter2D("d10-x01-y01", true);
      sum_2GeV   = bookScatter2D("d11-x01-y01", true);
      sum_5GeV   = bookScatter2D("d12-x01-y01", true);

    }
  
    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const double weight = event.weight();
      
      Jets m_goodJets = applyProjection<JetAlg>(event, "Jets").jetsByPt(Cuts::pT > 25*GeV && Cuts::abseta < 2.1);

      if (m_goodJets.size() < 2)        vetoEvent;
      if (m_goodJets[0].pT() < 50*GeV)  vetoEvent;
      if (m_goodJets[1].pT() < 50*GeV)  vetoEvent;
      if (fabs(1.0 - m_goodJets[0].pT()/m_goodJets[1].pT()) > 0.5)  vetoEvent;

      bool check = m_goodJets[0].abseta() < m_goodJets[1].abseta();
      int pos_f = int(check);
      int pos_c = int(!check);

      double pt500MeV_f = CalculateNCharge(m_goodJets[pos_f], 0.5);
      double pt2GeV_f   = CalculateNCharge(m_goodJets[pos_f], 2.0);
      double pt5GeV_f   = CalculateNCharge(m_goodJets[pos_f], 5.0);
      double pT_f = m_goodJets[pos_f].pT();
      
      double pt500MeV_c = CalculateNCharge(m_goodJets[pos_c], 0.5);
      double pt2GeV_c   = CalculateNCharge(m_goodJets[pos_c], 2.0);
      double pt5GeV_c   = CalculateNCharge(m_goodJets[pos_c], 5.0);
      double pT_c = m_goodJets[pos_c].pT();

      forward_500MeV->fill(pT_f, pt500MeV_f, weight);
      forward_2GeV->fill(  pT_f, pt2GeV_f,   weight);
      forward_5GeV->fill(  pT_f, pt5GeV_f,   weight);

      central_500MeV->fill(pT_c, pt500MeV_c, weight);
      central_2GeV->fill(  pT_c, pt2GeV_c,   weight);
      central_5GeV->fill(  pT_c, pt5GeV_c,   weight);
    }
  
    double CalculateNCharge(Jet& jet, double pTcut=0.5) {
      unsigned int ncharge = 0;
      foreach (const Particle& p, jet.particles()) {
        if (p.pT() < pTcut)  continue;
        if (p.threeCharge())  ++ncharge;
      }
      if (ncharge > 60)  ncharge = 60;
      return double(ncharge);
    }
  
    /// Normalise histograms etc., after the run
    void finalize() {
    
      if (numEvents() > 2) {
        for (unsigned int i = 0; i < forward_500MeV->numBins(); ++i) {
          ProfileBin1D bsum  = central_500MeV->bin(i) + forward_500MeV->bin(i);
          ProfileBin1D bsum2 = central_2GeV->bin(i) + forward_2GeV->bin(i);
          ProfileBin1D bsum5 = central_5GeV->bin(i) + forward_5GeV->bin(i);
          ProfileBin1D bdiff  = central_500MeV->bin(i) - forward_500MeV->bin(i);
          ProfileBin1D bdiff2 = central_2GeV->bin(i) - forward_2GeV->bin(i);
          ProfileBin1D bdiff5 = central_5GeV->bin(i) - forward_5GeV->bin(i);

          double ydiff  = central_500MeV->bin(i).numEntries()? central_500MeV->bin(i).mean() : 0.0;
          double ydiff2 = central_2GeV->bin(i).numEntries()?   central_2GeV->bin(i).mean()   : 0.0;
          double ydiff5 = central_5GeV->bin(i).numEntries()?   central_5GeV->bin(i).mean()   : 0.0;
          ydiff  -= forward_500MeV->bin(i).numEntries()? forward_500MeV->bin(i).mean() : 0.0;
          ydiff2 -= forward_2GeV->bin(i).numEntries()?   forward_2GeV->bin(i).mean()   : 0.0;
          ydiff5 -= forward_5GeV->bin(i).numEntries()?   forward_5GeV->bin(i).mean()   : 0.0;

          double yerr  = bsum.numEntries()?  bsum.stdErr()  : 0.0;
          double yerr2 = bsum2.numEntries()? bsum2.stdErr() : 0.0;
          double yerr5 = bsum5.numEntries()? bsum5.stdErr() : 0.0;

	        diff_500MeV->point(i).setY(ydiff, yerr);
          diff_2GeV->point(i).setY(ydiff2, yerr2);
          diff_5GeV->point(i).setY(ydiff5, yerr5);

          sum_500MeV->point(i).setY(bsum.numEntries()? bsum.mean() : 0.0, yerr);
          sum_2GeV->point(i).setY(bsum2.numEntries()? bsum2.mean() : 0.0, yerr2);
          sum_5GeV->point(i).setY(bsum5.numEntries()? bsum5.mean() : 0.0, yerr5);
        }
      }

    }


  private:
  
    Profile1DPtr forward_500MeV;
    Profile1DPtr forward_2GeV;
    Profile1DPtr forward_5GeV;

    Profile1DPtr central_500MeV;
    Profile1DPtr central_2GeV;
    Profile1DPtr central_5GeV;

    Scatter2DPtr sum_500MeV;
    Scatter2DPtr sum_2GeV;
    Scatter2DPtr sum_5GeV;

    Scatter2DPtr diff_500MeV;
    Scatter2DPtr diff_2GeV;
    Scatter2DPtr diff_5GeV;
  
  };

  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2016_I1419070);
}