Rivet analyses

Number of tracks in jets

Experiment: ATLAS (LHC)

Inspire ID: 1419070

Status: VALIDATED

Authors: - Ben Nachman - Christian Gutschow

References: - Expt page: ATLAS-STDM-2015-12 - arXiv: 1602.00988 - Eur.Phys.J. C76 (2016) no.6, 322 - DOI: 10.1140/epjc/s10052-016-4126-5

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_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`

#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() {

      declare(FastJets(FinalState(), JetAlg::ANTIKT, 0.4), "Jets");

      book(forward_500MeV ,1, 1, 1);
      book(forward_2GeV   ,2, 1, 1);
      book(forward_5GeV   ,3, 1, 1);

      book(central_500MeV ,4, 1, 1);
      book(central_2GeV   ,5, 1, 1);
      book(central_5GeV   ,6, 1, 1);

      book(diff_500MeV, "d07-x01-y01");
      book(diff_2GeV  , "d08-x01-y01");
      book(diff_5GeV  , "d09-x01-y01");

      book(sum_500MeV, "d10-x01-y01");
      book(sum_2GeV  , "d11-x01-y01");
      book(sum_5GeV  , "d12-x01-y01");

    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      Jets m_goodJets = apply<JetFinder>(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);
      forward_2GeV->fill(  pT_f, pt2GeV_f);
      forward_5GeV->fill(  pT_f, pt5GeV_f);

      central_500MeV->fill(pT_c, pt500MeV_c);
      central_2GeV->fill(  pT_c, pt2GeV_c);
      central_5GeV->fill(  pT_c, pt5GeV_c);
    }

    double CalculateNCharge(Jet& jet, double pTcut=0.5) {
      unsigned int ncharge = 0;
      for (const Particle& p : jet.particles()) {
        if (p.pT() < pTcut)  continue;
        if (p.charge3())  ++ncharge;
      }
      if (ncharge > 60)  ncharge = 60;
      return double(ncharge);
    }

    /// Normalise histograms etc., after the run
    void finalize() {

      if (numEvents() > 2) {
        for (unsigned int i = 1; i < forward_500MeV->numBins()+1; ++i) {
          const YODA::Dbn2D& bsum  = central_500MeV->bin(i) + forward_500MeV->bin(i);
          const YODA::Dbn2D& bsum2 = central_2GeV->bin(i) + forward_2GeV->bin(i);
          const YODA::Dbn2D& bsum5 = central_5GeV->bin(i) + forward_5GeV->bin(i);

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

          double yerr  = bsum.effNumEntries()  > 1.0 ?  bsum.yStdErr() : 0.0;
          double yerr2 = bsum2.effNumEntries() > 1.0 ? bsum2.yStdErr() : 0.0;
          double yerr5 = bsum5.effNumEntries() > 1.0 ? bsum5.yStdErr() : 0.0;

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

          sum_500MeV->bin(i).set(bsum.effNumEntries()? bsum.yMean() : 0.0, yerr);
          sum_2GeV->bin(i).set(bsum2.effNumEntries()? bsum2.yMean() : 0.0, yerr2);
          sum_5GeV->bin(i).set(bsum5.effNumEntries()? bsum5.yMean() : 0.0, yerr5);
        }
      }

    }


  private:

    Profile1DPtr forward_500MeV;
    Profile1DPtr forward_2GeV;
    Profile1DPtr forward_5GeV;

    Profile1DPtr central_500MeV;
    Profile1DPtr central_2GeV;
    Profile1DPtr central_5GeV;

    Estimate1DPtr sum_500MeV;
    Estimate1DPtr sum_2GeV;
    Estimate1DPtr sum_5GeV;

    Estimate1DPtr diff_500MeV;
    Estimate1DPtr diff_2GeV;
    Estimate1DPtr diff_5GeV;

  };

  RIVET_DECLARE_PLUGIN(ATLAS_2016_I1419070);
}

Rivet analyses

Number of tracks in jets

Source code:ATLAS_2016_I1419070.cc

Source code:`ATLAS_2016_I1419070.cc`