rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

ATLAS_2012_I1094568

Measurement of ttbar production with a veto on additional central jet activity
Experiment: ATLAS (LHC)
Inspire ID: 1094568
Status: VALIDATED
Authors:
  • Kiran Joshi
References:
  • arXiv: 1203.5015
  • Eur.Phys.J. C72 (2012) 2043
Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • Require dileptonic ttbar events at 7TeV. It is important to not include semileptonic decay channels in the runs, as they can not be vetoed in the analysis in a generator-independent fashion but have been subtracted from the particle level measurement. The tau decay channels also count as leptonic.

A measurement of the additional jet activity in dileptonic ttbar events. The fraction of events passing a veto requirement are shown as a function the veto scale for four central rapidity intervals. Two veto definitions are used: events are vetoed if they contain an additional jet in the rapidity interval with transverse momentum above a threshold, or alternatively, if the scalar transverse momentum sum of all additional jets in the rapidity interval is above a threshold.

Source code: ATLAS_2012_I1094568.cc
  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/HeavyHadrons.hh"

namespace Rivet {

  /// Top pair production with central jet veto
  class ATLAS_2012_I1094568 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2012_I1094568);

    struct Plots {
      // Track which veto region this is, to match the autobooked histograms
      int region_index;

      // Lower rapidity boundary or veto region
      double y_low;
      // Upper rapidity boundary or veto region
      double y_high;

      double veto_Q0;
      double veto_Qsum;

      // Histograms to store the veto jet pT and sum(veto jet pT) histograms.
      Histo1DPtr h_veto_Q0;
      Histo1DPtr h_veto_Qsum;

      // Scatter2Ds for the gap fractions
      Scatter2DPtr gapFrac_Q0;
      Scatter2DPtr gapFrac_Qsum;
    };

    /// Book histograms and initialise projections before the run
    void init() {

      const FinalState fs(Cuts::abseta < 4.5);

      /// Get electrons from truth record
      FinalState elec_fs(Cuts::abspid == PID::ELECTRON && Cuts::abseta < 2.47 && Cuts::pT > 25*GeV);
      declare(elec_fs, "ELEC_FS");

      /// Get muons which pass the initial kinematic cuts:
      FinalState muon_fs(Cuts::abspid == PID::MUON && Cuts::abseta < 2.5 && Cuts::pT > 20*GeV);
      declare(muon_fs, "MUON_FS");

      /// Get all neutrinos. These will not be used to form jets.
      /// We'll use the highest 2 pT neutrinos to calculate the MET
      IdentifiedFinalState neutrino_fs(Cuts::abseta < 4.5);
      neutrino_fs.acceptNeutrinos();
      declare(neutrino_fs, "NEUTRINO_FS");

      // Get the jets
      FastJets jets(fs, FastJets::ANTIKT, 0.4, JetAlg::Muons::NONE, JetAlg::Invisibles::NONE);
      declare(fs, "jet_input");
      declare(jets, "JETS");

      // get b-hadrons
      declare(HeavyHadrons(Cuts::pT > 5*GeV), "BHadrons");

      // Initialise weight counter
      book(m_total_weight, "_total_weight");

      // Init histogramming for the various regions
      m_plots[0].region_index = 1;
      m_plots[0].y_low = 0.0;
      m_plots[0].y_high = 0.8;
      initializePlots(m_plots[0]);
      //
      m_plots[1].region_index = 2;
      m_plots[1].y_low = 0.8;
      m_plots[1].y_high = 1.5;
      initializePlots(m_plots[1]);
      //
      m_plots[2].region_index = 3;
      m_plots[2].y_low = 1.5;
      m_plots[2].y_high = 2.1;
      initializePlots(m_plots[2]);
      //
      m_plots[3].region_index = 4;
      m_plots[3].y_low = 0.0;
      m_plots[3].y_high = 2.1;
      initializePlots(m_plots[3]);
    }


    void initializePlots(Plots& plots) {
      plots.veto_Q0 = 0.0;
      const string veto_Q0_name = "TMP/vetoJetPt_Q0_" + to_str(plots.region_index);
      book(plots.h_veto_Q0, veto_Q0_name, 200, 0.0, 1000.0);
      book(plots.gapFrac_Q0, plots.region_index, 1, 1, true);

      plots.veto_Qsum = 0.0;
      const string veto_Qsum_name = "TMP/vetoJetPt_Qsum_" + to_str(plots.region_index);
      book(plots.h_veto_Qsum, veto_Qsum_name, 200, 0.0, 1000.0);
      book(plots.gapFrac_Qsum, plots.region_index, 2, 1, true);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {

      /// Get the various sets of final state particles
      const Particles& elecFS = apply<FinalState>(event, "ELEC_FS").particlesByPt();
      const Particles& muonFS = apply<FinalState>(event, "MUON_FS").particlesByPt();
      const Particles& neutrinoFS = apply<IdentifiedFinalState>(event, "NEUTRINO_FS").particlesByPt();

      // Get all jets with pT > 25 GeV and |y| < 2.4
      Jets jets = apply<FastJets>(event, "JETS").jetsByPt(Cuts::pT > 25*GeV && Cuts::absrap < 2.4);

      // For each of the jets that pass the rapidity cut, only keep those that are not
      // too close to any leptons
      idiscardIfAnyDeltaRLess(jets, elecFS, 0.4);
      idiscardIfAnyDeltaRLess(jets, muonFS, 0.4);

      // Get b hadrons with pT > 5 GeV
      const Particles& bHadrons = apply<HeavyHadrons>(event, "BHadrons").bHadrons();

      // For each of the good jets, check whether any are b-jets (via dR matching)
      size_t nMatches = 0;
      Jets bJets, vetoJets;
      for (const Jet& jet : jets) {
        bool isBjet = any(bHadrons, DeltaRLess(jet, 0.3));
        if (isBjet) { ++nMatches; bJets += jet; }
        if (!isBjet || nMatches > 2)  vetoJets += jet;
      }

      // Get the MET by taking the vector sum of all neutrinos
      /// @todo Use MissingMomentum instead?
      double MET = 0;
      FourMomentum p_MET;
      for(const Particle& p: neutrinoFS) {
        p_MET = p_MET + p.momentum();
      }
      MET = p_MET.pT();

      // Now we have everything we need to start doing the event selections
      bool passed_ee = false;

      // We want exactly 2 electrons...
      if (elecFS.size() == 2) {
        // ... with opposite sign charges.
        if (charge(elecFS[0]) != charge(elecFS[1])) {
          // Check the MET
          if (MET >= 40*GeV) {
            // Do some dilepton mass cuts
            const double dilepton_mass = (elecFS[0].momentum() + elecFS[1].momentum()).mass();
            if (dilepton_mass >= 15*GeV) {
              if (fabs(dilepton_mass - 91.0*GeV) >= 10.0*GeV) {
                // We need at least 2 b-jets
                passed_ee = bJets.size() > 1;
              }
            }
          }
        }
      }

      bool passed_mumu = false;
      // Now do the same checks for the mumu channel
      // So we now want 2 good muons...
      if (muonFS.size() == 2) {
        // ...with opposite sign charges.
        if (charge(muonFS[0]) != charge(muonFS[1])) {
          // Check the MET
          if (MET >= 40*GeV) {
            // and do some di-muon mass cuts
            const double dilepton_mass = (muonFS.at(0).momentum() + muonFS.at(1).momentum()).mass();
            if (dilepton_mass >= 15*GeV) {
              if (fabs(dilepton_mass - 91.0*GeV) >= 10.0*GeV) {
                // Need at least 2 b-jets
                passed_mumu = bJets.size() > 1;
              }
            }
          }
        }
      }

      bool passed_emu = false;
      // Finally, the same again with the emu channel
      // We want exactly 1 electron and 1 muon
      if (elecFS.size() == 1 && muonFS.size() == 1) {
        // With opposite sign charges
        if (charge(elecFS[0]) != charge(muonFS[0])) {
          // Calculate HT: scalar sum of the pTs of the leptons and all good jets
          double HT = sum(jets, pT, 0.);
          HT += elecFS[0].pT();
          HT += muonFS[0].pT();
          // Keep events with HT > 130 GeV
          if (HT > 130.0*GeV) {
            // And again we want 2 or more b-jets
            passed_emu = bJets.size() > 1;
          }
        }
      }

      if (passed_ee || passed_mumu || passed_emu) {
        // If the event passes the selection, we use it for all gap fractions
        m_total_weight->fill();

        // Loop over each veto jet
        for (const Jet& j : vetoJets) {
          const double pt = j.pT();
          const double rapidity = j.absrap();
          // Loop over each region
          for (size_t i = 0; i < 4; ++i) {
            // If the jet falls into this region, get its pT and increment sum(pT)
            if (inRange(rapidity, m_plots[i].y_low, m_plots[i].y_high)) {
              m_plots[i].veto_Qsum += pt;
              // If we've already got a veto jet, don't replace it
              if (m_plots[i].veto_Q0 == 0.0)  m_plots[i].veto_Q0 = pt;
            }
          }
        }
        for (size_t i = 0; i < 4; ++i) {
          m_plots[i].h_veto_Q0->fill(m_plots[i].veto_Q0);
          m_plots[i].h_veto_Qsum->fill(m_plots[i].veto_Qsum);
          m_plots[i].veto_Q0 = 0.0;
          m_plots[i].veto_Qsum = 0.0;
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      const double totalWeight = m_total_weight->val();
      for (size_t i = 0; i < 4; ++i) {
        finalizeGapFraction(totalWeight, m_plots[i].gapFrac_Q0,   m_plots[i].h_veto_Q0);
        finalizeGapFraction(totalWeight, m_plots[i].gapFrac_Qsum, m_plots[i].h_veto_Qsum);
      }
    }


    /// Convert temporary histos to cumulative efficiency scatters
    /// @todo Should be possible to replace this with a couple of YODA one-lines for diff -> integral and "efficiency division"
    void finalizeGapFraction(const double total_weight, Scatter2DPtr gapFrac, Histo1DPtr vetoPt) {
      // Stores the cumulative frequency of the veto jet pT histogram
      double vetoPtWeightSum = 0.0;

      // Keep track of which gap fraction point we're currently populating (#final_points != #tmp_bins)
      size_t fgap_point = 0;
      for (size_t i = 0; i < vetoPt->numBins(); ++i) {
        // If we've done the last "final" point, stop
        if (fgap_point == gapFrac->numPoints())  break;

        // Increment the cumulative vetoPt counter for this temp histo bin
        /// @todo Get rid of this and use vetoPt->integral(i+1) when points and bins line up?
        vetoPtWeightSum += vetoPt->bin(i).sumW();

        // If this temp histo bin's upper edge doesn't correspond to the reference point, don't finalise the scatter.
        // Note that points are ON the bin edges and have no width: they represent the integral up to exactly that point.
        if ( !fuzzyEquals(vetoPt->bin(i).xMax(), gapFrac->point(fgap_point).x()) )  continue;

        // Calculate the gap fraction and its uncertainty
        const double frac = (total_weight != 0.0) ? vetoPtWeightSum/total_weight : 0;
        const double fracErr = (total_weight != 0.0) ? sqrt(frac*(1-frac)/total_weight) : 0;
        gapFrac->point(fgap_point).setY(frac, fracErr);

        ++fgap_point;
      }
    }


  private:

    CounterPtr m_total_weight;
    Plots m_plots[4];

  };

  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2012_I1094568);
}