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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
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FastJets.hh"
  4#include "Rivet/Projections/ChargedFinalState.hh"
  5#include "Rivet/Particle.hh"
  6
  7namespace Rivet {
  8
  9
 10  class ATLAS_2012_I1188891 : public Analysis {
 11  public:
 12
 13
 14    ATLAS_2012_I1188891()
 15      : Analysis("ATLAS_2012_I1188891")
 16    {    }
 17
 18
 19    void init() {
 20
 21      const FinalState fs;
 22      FastJets fj04(fs,  FastJets::ANTIKT, 0.4);
 23      declare(fj04, "AntiKT04");
 24
 25      string histotitle[7]={"BBfraction","BCfraction","CCfraction","BUfraction","CUfraction","UUfraction","Total"};
 26      for (int i = 0 ; i < 7 ; i++){
 27        book(_h_temp[i] ,"TMP/"+histotitle[i],refData(1,1,1));
 28        if (i < 6) {
 29          book(_h_results[i], i+1, 1, 1);
 30        }
 31      }
 32    }
 33
 34
 35    void analyze(const Event& event) {
 36
 37      double weight    = 1.0;
 38      double weight100 = 1.0 * 100.;  //to get results in %
 39
 40      //keeps jets with pt>20 geV and ordered in decreasing pt
 41      Jets jetAr = apply<FastJets>(event, "AntiKT04").jetsByPt(20*GeV);
 42
 43      int flav[2]={1,1};
 44      vector<FourMomentum> leadjets;
 45
 46      //get b/c-hadrons
 47      vector<ConstGenParticlePtr> B_hadrons, C_hadrons;
 48      vector<ConstGenParticlePtr> allParticles = HepMCUtils::particles(event.genEvent());
 49      for (size_t i = 0; i < allParticles.size(); i++) {
 50        ConstGenParticlePtr p = allParticles.at(i);
 51        if(p->momentum().perp()*GeV < 5) continue;
 52        if ( (Rivet::PID::isHadron ( p->pdg_id() ) &&
 53              Rivet::PID::hasBottom( p->pdg_id() )    ) ) {
 54          B_hadrons.push_back(p);
 55        }
 56        if ( (Rivet::PID::isHadron( p->pdg_id() ) &&
 57              Rivet::PID::hasCharm( p->pdg_id() )    ) ) {
 58          C_hadrons.push_back(p);
 59        }
 60      }
 61
 62      //select dijet
 63      for (const Jet& jet : jetAr) {
 64
 65        const double pT   = jet.pT();
 66        const double absy = jet.absrap();
 67
 68        bool isBjet = jet.bTagged();
 69        bool isCjet = jet.cTagged();
 70
 71        int jetflav=1;
 72        if      (isBjet)jetflav=5;
 73        else if (isCjet)jetflav=4;
 74
 75        if (absy <= 2.1 && leadjets.size() < 2) {
 76
 77          if (pT > 500*GeV) continue;
 78          if ((leadjets.empty() && pT < 40*GeV) || pT < 20*GeV) continue;
 79
 80          leadjets.push_back(jet.momentum());
 81
 82          if (leadjets.size()==1) flav[0] = jetflav;
 83          if (leadjets.size()==2) flav[1] = jetflav;
 84        }
 85      }
 86
 87      if (leadjets.size() < 2) vetoEvent;
 88
 89
 90      double pBinsLJ[7] = {40.,60.,80.,120.,160.,250.,500.};
 91      int    iPBinLJ = -1;
 92
 93      for (int k = 0 ; k < 7 ; k++) {
 94        if (leadjets[0].pT() > pBinsLJ[k]*GeV) iPBinLJ=k;
 95        else break;
 96      }
 97
 98      bool c_ljpt  = (iPBinLJ != -1);
 99      bool c_nljpt = leadjets[1].pT() > 20*GeV;
100      bool c_dphi  = fabs( deltaPhi(leadjets[0],leadjets[1]) ) > 2.1;
101      bool isDijet = c_ljpt & c_nljpt & c_dphi;
102      if (!isDijet) vetoEvent;
103
104      _h_temp[6]->fill(leadjets[0].pT(), weight);
105
106      if (flav[0]==5 && flav[1]==5)                                  // BB dijet
107        _h_temp[0]->fill(leadjets[0].pT(), weight100);
108
109      if ((flav[0]==5 && flav[1]==4) || (flav[0]==4 && flav[1]==5))  // BC dijet
110        _h_temp[1]->fill(leadjets[0].pT(), weight100);
111
112      if (flav[0]==4 && flav[1]==4)                                  // CC dijet
113        _h_temp[2]->fill(leadjets[0].pT(), weight100);
114
115      if ((flav[0]==5 && flav[1]==1) || (flav[0]==1 && flav[1]==5))  // B-light dijet
116        _h_temp[3]->fill(leadjets[0].pT(), weight100);
117
118      if ((flav[0]==4 && flav[1]==1) || (flav[0]==1 && flav[1]==4))  // C-light dijet
119        _h_temp[4]->fill(leadjets[0].pT(), weight100);
120
121      if (flav[0]==1 && flav[1]==1)                                  // light-light dijet
122        _h_temp[5]->fill(leadjets[0].pT(), weight100);
123    }
124
125
126    void finalize() {
127      divide(_h_temp[0], _h_temp[6], _h_results[0]);
128      divide(_h_temp[1], _h_temp[6], _h_results[1]);
129      divide(_h_temp[2], _h_temp[6], _h_results[2]);
130      divide(_h_temp[3], _h_temp[6], _h_results[3]);
131      divide(_h_temp[4], _h_temp[6], _h_results[4]);
132      divide(_h_temp[5], _h_temp[6], _h_results[5]);
133    }
134
135  private:
136
137    Histo1DPtr   _h_temp[7];
138    Scatter2DPtr _h_results[6];
139  };
140
141
142  RIVET_DECLARE_PLUGIN(ATLAS_2012_I1188891);
143
144
145}