rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

ATLAS_2018_I1705857

ttbb at 13 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1705857
Status: VALIDATED
Authors:
  • Stewart Swift
  • Tom Neep
  • Christian Gutschow
References: Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
  • ttbb production at 13 TeV in dilepton and lepton+jets channel

This paper presents measurements of $t\bar{t}$ production in association with additional $b$-jets in $pp$ collisions at the LHC at a centre-of-mass energy of 13 TeV. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb$^{-1}$. Fiducial cross-section measurements are performed in the dilepton and lepton-plus-jets $t\bar{t}$ decay channels. Results are presented at particle level in the form of inclusive cross-sections of $t\bar{t}$ final states with three and four $b$-jets as well as differential cross-sections as a function of global event properties and properties of $b$-jet pairs. The measured inclusive fiducial cross-sections generally exceed the $t\bar{t}b\bar{b}$ predictions from various next-to-leading-order matrix element calculations matched to a parton shower but are compatible within the total uncertainties. The experimental uncertainties are smaller than the uncertainties in the predictions. Comparisons of state-of-the-art theoretical predictions with the differential measurements are shown and good agreement with data is found for most of them.

Source code: ATLAS_2018_I1705857.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
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/DressedLeptons.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"

namespace Rivet {


class ATLAS_2018_I1705857 : public Analysis {
 public:
   /// Constructor
   /// @brief ttbb at 13 TeV
   DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2018_I1705857);

    void init() {
      // Eta ranges
      Cut eta_full = (Cuts::abseta < 5.0);
      // Lepton cuts
      Cut lep_cuts25 = (Cuts::abseta < 2.5) && (Cuts::pT >= 25*GeV);
      // All final state particles
      FinalState fs(eta_full);

      // Get photons to dress leptons
      PromptFinalState photons(eta_full && Cuts::abspid == PID::PHOTON, true);

      // Projection to find the electrons
      PromptFinalState electrons(eta_full && Cuts::abspid == PID::ELECTRON, true);

      // Projection to find the muons
      PromptFinalState muons(eta_full && Cuts::abspid == PID::MUON, true);

      DressedLeptons dressedelectrons25(photons, electrons, 0.1, lep_cuts25, true);
      DressedLeptons dressedmuons25(photons, muons, 0.1, lep_cuts25, true);

      declare(dressedelectrons25, "elecs");
      declare(dressedmuons25, "muons");

      // From here on we are just setting up the jet clustering
      IdentifiedFinalState nu_id;
      nu_id.acceptNeutrinos();
      PromptFinalState neutrinos(nu_id);
      neutrinos.acceptTauDecays(true);

      PromptFinalState jet_photons(eta_full && Cuts::abspid == PID::PHOTON, false);
      DressedLeptons all_dressed_electrons(jet_photons, electrons, 0.1, eta_full, true);
      DressedLeptons all_dressed_muons(jet_photons, muons, 0.1, eta_full, true);

      VetoedFinalState vfs(fs);
      vfs.addVetoOnThisFinalState(all_dressed_electrons);
      vfs.addVetoOnThisFinalState(all_dressed_muons);
      vfs.addVetoOnThisFinalState(neutrinos);

      FastJets jets(vfs, FastJets::ANTIKT, 0.4, JetAlg::DECAY_MUONS, JetAlg::DECAY_INVISIBLES);
      declare(jets, "jets");

      // fiducial cross-section histogram
      _histograms["fid_xsec"] = bookHisto1D(1, 1, 1);
      _histograms["fid_xsec_no_ttX"] = bookHisto1D(2, 1, 1);

      _histograms["nbjets_emu"] = bookHisto1D(3, 1, 1);
      _histograms["nbjets_emu_no_ttX"] = bookHisto1D(4, 1, 1);

      // HT
      book_hist("ht_emu", 3);
      book_hist("ht_had_emu", 4);

      book_hist("ht_ljets", 5);
      book_hist("ht_had_ljets", 6);

      // b-jet pTs
      book_hist("lead_bjet_pt_emu",    7);
      book_hist("sublead_bjet_pt_emu", 8);
      book_hist("third_bjet_pt_emu",   9);

      book_hist("lead_bjet_pt_ljets",    10);
      book_hist("sublead_bjet_pt_ljets", 11);
      book_hist("third_bjet_pt_ljets",   12);
      book_hist("fourth_bjet_pt_ljets",  13);

      // leading bb pair
      book_hist("m_bb_leading_emu",  14);
      book_hist("pt_bb_leading_emu", 15);
      book_hist("dR_bb_leading_emu", 16);

      book_hist("m_bb_leading_ljets",  17);
      book_hist("pt_bb_leading_ljets", 18);
      book_hist("dR_bb_leading_ljets", 19);

      // closest bb pair
      book_hist("m_bb_closest_emu",  20);
      book_hist("pt_bb_closest_emu", 21);
      book_hist("dR_bb_closest_emu", 22);

      book_hist("m_bb_closest_ljets",  23);
      book_hist("pt_bb_closest_ljets", 24);
      book_hist("dR_bb_closest_ljets", 25);
    }


    void analyze(const Event& event) {
      const double weight = event.weight();

      vector<DressedLepton> leptons;
      for (auto &lep : apply<DressedLeptons>(event, "muons").dressedLeptons()) { leptons.push_back(lep); }
      for (auto &lep : apply<DressedLeptons>(event, "elecs").dressedLeptons()) { leptons.push_back(lep); }

      const Jets jets = apply<FastJets>(event, "jets").jetsByPt(Cuts::pT > 25*GeV && Cuts::abseta < 2.5);
      for (const auto& jet : jets) {
        ifilter_discard(leptons, [&](const DressedLepton& lep) { return deltaR(jet, lep) < 0.4; });
      }

      Jets bjets;
      for (const Jet& jet : jets) {
        if (jet.bTagged(Cuts::pT >= 5*GeV))  bjets += jet;
      }

      size_t njets = jets.size();
      size_t nbjets = bjets.size();

      // Evaluate basic event selection
      bool pass_ljets = (leptons.size() == 1 && leptons[0].pT() > 27*GeV);

      bool pass_emu =
        // 2 leptons > 27 GeV
        (leptons.size() == 2) &&
        (leptons[0].pT() > 27*GeV && leptons[1].pT() > 27*GeV) &&
        // emu events
        ((leptons[0].abspid() == 11 && leptons[1].abspid() == 13) ||
         (leptons[0].abspid() == 13 && leptons[1].abspid() == 11)) &&
        // opposite charge
        (leptons[0].charge() != leptons[1].charge());

      // If we don't have exactly 1 or 2 leptons then veto the event
      if (!pass_emu && !pass_ljets)  vetoEvent;

      if (pass_emu) {
        if (nbjets >= 2)  fill("nbjets_emu", nbjets - 1, weight);
        if (nbjets >= 3)  fill("fid_xsec", 1, weight);
        if (nbjets >= 4)  fill("fid_xsec", 2, weight);
      }

      if (pass_ljets) {
        if (nbjets >= 3 && njets >= 5)  fill("fid_xsec", 3, weight);
        if (nbjets >= 4 && njets >= 6)  fill("fid_xsec", 4, weight);
      }

      if (pass_emu && (nbjets < 3 || njets < 3))    vetoEvent;
      if (pass_ljets && (nbjets < 4 || njets < 6))  vetoEvent;

      double hthad = sum(jets, pT, 0.0);
      double ht = sum(leptons, pT, hthad);

      FourMomentum jsum = bjets[0].momentum() + bjets[1].momentum();
      double dr_leading = deltaR(bjets[0], bjets[1]);

      size_t ind1, ind2; double mindr = 999.;
      for (size_t i = 0; i < bjets.size(); ++i) {
        for (size_t j = 0; j < bjets.size(); ++j) {
          if (i == j)  continue;
          double dr = deltaR(bjets[i], bjets[j]);
          if (dr < mindr) {
            ind1 = i;
            ind2 = j;
            mindr = dr;
          }
        }
      }

      FourMomentum bb_closest = bjets[ind1].momentum() + bjets[ind2].momentum();
      double dr_closest = deltaR(bjets[ind1], bjets[ind2]);

      if (pass_ljets) {
        // b-jet pTs
        fill("lead_bjet_pt_ljets", bjets[0].pT()/GeV, weight);
        fill("sublead_bjet_pt_ljets", bjets[1].pT()/GeV, weight);
        fill("third_bjet_pt_ljets", bjets[2].pT()/GeV, weight);

        if (nbjets >= 4)  fill("fourth_bjet_pt_ljets", bjets[3].pT()/GeV, weight);

        // HT
        fill("ht_ljets", ht/GeV, weight);
        fill("ht_had_ljets", hthad/GeV, weight);

        // leading bb pair
        fill("m_bb_leading_ljets", jsum.mass()/GeV, weight);
        fill("pt_bb_leading_ljets", jsum.pT()/GeV, weight);
        fill("dR_bb_leading_ljets", dr_leading, weight);

        // closest bb pair
        fill("m_bb_closest_ljets", bb_closest.mass()/GeV, weight);
        fill("pt_bb_closest_ljets", bb_closest.pT()/GeV, weight);
        fill("dR_bb_closest_ljets", dr_closest, weight);
      }
      if (pass_emu) {
        // b-jet pTs
        fill("lead_bjet_pt_emu", bjets[0].pT()/GeV, weight);
        fill("sublead_bjet_pt_emu", bjets[1].pT()/GeV, weight);
        fill("third_bjet_pt_emu", bjets[2].pT()/GeV, weight);

        // HT
        fill("ht_emu", ht/GeV, weight);
        fill("ht_had_emu", hthad/GeV, weight);

        // leading bb pair
        fill("m_bb_leading_emu", jsum.mass()/GeV, weight);
        fill("pt_bb_leading_emu", jsum.pT()/GeV, weight);
        fill("dR_bb_leading_emu", dr_leading, weight);

        // closest bb pair
        fill("m_bb_closest_emu", bb_closest.mass()/GeV, weight);
        fill("pt_bb_closest_emu", bb_closest.pT()/GeV, weight);
        fill("dR_bb_closest_emu", dr_closest, weight);
      }
    }

    void finalize() {
      // Normalise all histograms
      const double sf = crossSection() / femtobarn / sumOfWeights();
      for (auto const& h : _histograms) {
        scale(h.second, sf);
        if (h.first.find("fid_xsec") != string::npos)  continue;
        normalize(h.second, 1.0);
      }
    }

    void fill(const string& name, const double value, const double weight) {
      _histograms[name]->fill(value, weight);
      _histograms[name + "_no_ttX"]->fill(value, weight);
    }

    void book_hist(const std::string& name, unsigned int d) {
      // ttX substracted histograms are even numbers
      _histograms[name] = bookHisto1D((d * 2) - 1, 1, 1);
      _histograms[name + "_no_ttX"] = bookHisto1D(d * 2, 1, 1);
    }

    private:
      map<std::string, Histo1DPtr> _histograms;

  };

  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2018_I1705857);
}