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ATLAS_2012_I1188891

Flavour composition of dijet events at 7 TeV
Experiment: ATLAS (LHC 7TeV)
Inspire ID: 1188891
Status: VALIDATED
Authors:
  • Cecile Lapoire
  • Roman Lysak
References: Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • pp di-jet events at 7 TeV

The measurement of the flavour composition of dijet events produced in pp collisions at $\sqrt{s}=7\;\text{TeV}$ using the ATLAS detector. Six possible combinations of light, charm and bottom jets are identified in the dijet events, where the jet flavour is defined by the presence of bottom, charm or solely light flavour hadrons in the jet. The fractions of these dijet flavour states as functions of the leading jet transverse momentum in the range 40 GeV to 500 GeV and jet rapidity $|y| < 2.1$ are measured.

Source code: ATLAS_2012_I1188891.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Tools/BinnedHistogram.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Particle.hh"

namespace Rivet {


  class ATLAS_2012_I1188891 : public Analysis {
  public:


    ATLAS_2012_I1188891()
      : Analysis("ATLAS_2012_I1188891")
    {    }


    void init() {

      const FinalState fs;
      FastJets fj04(fs,  FastJets::ANTIKT, 0.4);
      declare(fj04, "AntiKT04");

      string histotitle[7]={"BBfraction","BCfraction","CCfraction","BUfraction","CUfraction","UUfraction","Total"};
      for (int i = 0 ; i < 7 ; i++){
        _h_temp[i] = bookHisto1D("TMP/"+histotitle[i],refData(1,1,1));
        if (i < 6) {
          _h_results[i] = bookScatter2D(i+1, 1, 1);
        }
      }
    }


    void analyze(const Event& event) {

      double weight    = event.weight();
      double weight100 = event.weight() * 100.;  //to get results in %

      //keeps jets with pt>20 geV and ordered in decreasing pt
      Jets jetAr = apply<FastJets>(event, "AntiKT04").jetsByPt(20*GeV);

      int flav[2]={1,1};
      vector<FourMomentum> leadjets;

      //get b/c-hadrons
      vector<GenParticle const *> B_hadrons, C_hadrons;
      vector<GenParticle const *> allParticles = particles(event.genEvent());
      for (size_t i = 0; i < allParticles.size(); i++) {
        const GenParticle* p = allParticles.at(i);
        if(p->momentum().perp()*GeV < 5) continue;
        if ( (Rivet::PID::isHadron ( p->pdg_id() ) &&
              Rivet::PID::hasBottom( p->pdg_id() )    ) ) {
          B_hadrons.push_back(p);
        }
        if ( (Rivet::PID::isHadron( p->pdg_id() ) &&
              Rivet::PID::hasCharm( p->pdg_id() )    ) ) {
          C_hadrons.push_back(p);
        }
      }

      //select dijet
      foreach (const Jet& jet, jetAr) {

        const double pT   = jet.pT();
        const double absy = jet.absrap();

        bool isBjet = jet.bTagged();
        bool isCjet = jet.cTagged();

        int jetflav=1;
        if      (isBjet)jetflav=5;
        else if (isCjet)jetflav=4;

        if (absy <= 2.1 && leadjets.size() < 2) {

          if (pT > 500*GeV) continue;
          if ((leadjets.empty() && pT < 40*GeV) || pT < 20*GeV) continue;

          leadjets.push_back(jet.momentum());

          if (leadjets.size()==1) flav[0] = jetflav;
          if (leadjets.size()==2) flav[1] = jetflav;
        }
      }

      if (leadjets.size() < 2) vetoEvent;


      double pBinsLJ[7] = {40.,60.,80.,120.,160.,250.,500.};
      int    iPBinLJ = -1;

      for (int k = 0 ; k < 7 ; k++) {
        if (leadjets[0].pT() > pBinsLJ[k]*GeV) iPBinLJ=k;
        else break;
      }

      bool c_ljpt  = (iPBinLJ != -1);
      bool c_nljpt = leadjets[1].pT() > 20*GeV;
      bool c_dphi  = fabs( deltaPhi(leadjets[0],leadjets[1]) ) > 2.1;
      bool isDijet = c_ljpt & c_nljpt & c_dphi;
      if (!isDijet) vetoEvent;

      _h_temp[6]->fill(leadjets[0].pT(), weight);

      if (flav[0]==5 && flav[1]==5)                                  // BB dijet
        _h_temp[0]->fill(leadjets[0].pT(), weight100);

      if ((flav[0]==5 && flav[1]==4) || (flav[0]==4 && flav[1]==5))  // BC dijet
        _h_temp[1]->fill(leadjets[0].pT(), weight100);

      if (flav[0]==4 && flav[1]==4)                                  // CC dijet
        _h_temp[2]->fill(leadjets[0].pT(), weight100);

      if ((flav[0]==5 && flav[1]==1) || (flav[0]==1 && flav[1]==5))  // B-light dijet
        _h_temp[3]->fill(leadjets[0].pT(), weight100);

      if ((flav[0]==4 && flav[1]==1) || (flav[0]==1 && flav[1]==4))  // C-light dijet
        _h_temp[4]->fill(leadjets[0].pT(), weight100);

      if (flav[0]==1 && flav[1]==1)                                  // light-light dijet
        _h_temp[5]->fill(leadjets[0].pT(), weight100);
    }


    void finalize() {
      divide(_h_temp[0], _h_temp[6], _h_results[0]);
      divide(_h_temp[1], _h_temp[6], _h_results[1]);
      divide(_h_temp[2], _h_temp[6], _h_results[2]);
      divide(_h_temp[3], _h_temp[6], _h_results[3]);
      divide(_h_temp[4], _h_temp[6], _h_results[4]);
      divide(_h_temp[5], _h_temp[6], _h_results[5]);
    }

  private:

    Histo1DPtr   _h_temp[7];
    Scatter2DPtr _h_results[6];
  };


  DECLARE_RIVET_PLUGIN(ATLAS_2012_I1188891);


}