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ATLAS_2017_I1627873

EW Zjj using early Run-2 data
Experiment: ATLAS (LHC)
Inspire ID: 1627873
Status: VALIDATED
Authors:
  • Christian Johnson
  • Deepak Kar
  • Christian Gutschow
References: Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
  • Inclusive Z+jets events at 13 TeV, with Z decaying to muons or electrons

The cross-section for the production of two jets in association with a leptonically decaying Z boson ($Zjj$) is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV, using data recorded with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 3.2 fb$^{-1}$. The electroweak $Zjj$ cross-section is extracted in a fiducial region chosen to enhance the electroweak contribution relative to the dominant Drell-Yan $Zjj$ process, which is constrained using a data-driven approach. The measured fiducial electroweak cross-section is $\sigma_{EWZjj}$ = 119$\pm$16(stat.)$\pm$20(syst.)$\pm$2(lumi.) fb for dijet invariant mass greater than 250 GeV, and 34.2$\pm$5.8(stat.)$\pm$5.5(syst.)$\pm$0.7(lumi.) fb for dijet invariant mass greater than 1 TeV. Standard Model predictions are in agreement with the measurements. The inclusive $Zjj$ cross-section is also measured in six different fiducial regions with varying contributions from electroweak and Drell-Yan $Zjj$ production.

Source code: ATLAS_2017_I1627873.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FastJets.hh"
  4#include "Rivet/Projections/FinalState.hh"
  5#include "Rivet/Projections/PromptFinalState.hh"
  6#include "Rivet/Projections/VetoedFinalState.hh"
  7#include "Rivet/Projections/LeptonFinder.hh"
  8
  9namespace Rivet {
 10
 11
 12  /// @brief EW Zjj using early Run-2 data
 13  class ATLAS_2017_I1627873 : public Analysis {
 14  public:
 15
 16    /// Constructor
 17    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2017_I1627873);
 18
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22
 23      _mode = 0;
 24      if ( getOption("TYPE") == "EW_ONLY" ) _mode = 1;
 25
 26      FinalState fs(Cuts::abseta < 5.0);
 27
 28      FinalState photon_fs(Cuts::abspid == PID::PHOTON);
 29
 30      PromptFinalState electron_fs(Cuts::abspid == PID::ELECTRON);
 31      PromptFinalState muon_fs(Cuts::abspid == PID::MUON);
 32
 33      LeptonFinder dressed_electrons(electron_fs, photon_fs, 0.1, Cuts::abseta < 2.47 && Cuts::pT > 25*GeV);
 34      declare(dressed_electrons, "DressedElectrons");
 35
 36      LeptonFinder dressed_muons(muon_fs, photon_fs, 0.1, Cuts::abseta < 2.47 && Cuts::pT > 25*GeV);
 37      declare(dressed_muons, "DressedMuons");
 38
 39      VetoedFinalState remfs(fs);
 40      remfs.addVetoOnThisFinalState(dressed_electrons);
 41      remfs.addVetoOnThisFinalState(dressed_muons);
 42
 43      FastJets jets(remfs, JetAlg::ANTIKT, 0.4, JetMuons::ALL, JetInvisibles::ALL);
 44      declare(jets, "Jets");
 45
 46      if (_mode)  book(_h, 3, 1, 1);
 47      else        book(_h, 2, 1, 1);
 48    }
 49
 50
 51    /// Perform the per-event analysis
 52    void analyze(const Event& event) {
 53
 54      const Jets& jets = apply<FastJets>(event, "Jets").jetsByPt(Cuts::pT > 25*GeV && Cuts::abseta < 4.4);
 55	    DressedLeptons electrons = apply<LeptonFinder>(event, "DressedElectrons").dressedLeptons();
 56	    DressedLeptons muons = apply<LeptonFinder>(event, "DressedMuons").dressedLeptons();
 57
 58	   	// Overlap Removal
 59      idiscardIfAnyDeltaRLess(electrons, jets, 0.4);
 60      idiscardIfAnyDeltaRLess(muons,     jets, 0.4);
 61
 62      Particle lep1, lep2;
 63      if (electrons.size() == 2 && muons.empty()) {
 64				lep1 = electrons[0]; lep2 = electrons[1];
 65				if ( lep1.charge3() == lep2.charge3() )  vetoEvent;
 66			}
 67      else if (electrons.empty() && muons.size() == 2) {
 68				lep1 = muons[0]; lep2 = muons[1];
 69				if (lep1.charge3() == lep2.charge3())  vetoEvent;
 70			}
 71      else  vetoEvent;
 72
 73      if (jets.size() < 2) vetoEvent;
 74
 75      const FourMomentum dilepton = lep1.mom()+lep2.mom();
 76      if ( !inRange(dilepton.mass(), 81.0*GeV, 101.0*GeV) ) vetoEvent;
 77
 78      const double jet1pt = jets[0].pT();
 79      const double jet2pt = jets[1].pT();
 80      const double  mjj = (jets[0].mom() + jets[1].mom()).mass();
 81      const double  zpt = (lep1.mom() + lep2.mom()).pT();
 82
 83      size_t ngapjets = 0;
 84      Jet thirdjet;
 85      for (size_t i = 2; i < jets.size(); ++i) {
 86        const Jet j = jets[i];
 87        if (_isBetween(j, jets[0], jets[1])) {
 88          if (!ngapjets)  thirdjet = j;
 89          ++ngapjets;
 90        }
 91      }
 92
 93      const double ptbal_vec = (jets[0].mom() + jets[1].mom() + lep1.mom() + lep2.mom()).pT();
 94      const double ptbal_sc = jets[0].pT() + jets[1].pT() + lep1.pT() + lep2.pT();
 95      const double ptbalance2 = ptbal_vec / ptbal_sc;
 96
 97      const double ptbal3_vec = (jets[0].mom() + jets[1].mom() + thirdjet.mom() + lep1.mom() + lep2.mom()).pT();
 98      const double ptbal3_sc = jets[0].pT() + jets[1].pT() + thirdjet.pT() + lep1.pT() + lep2.pT();
 99      const double ptbalance3 = ptbal3_vec / ptbal3_sc;
100
101
102
103      //categories: baseline, high-PT, EW-enriched, QCD-enriched, high-mass, EW-enriched and high-mass
104      if(!(jet1pt > 55*GeV && jet2pt > 45*GeV))  vetoEvent;
105
106      if (_mode) {
107        if (zpt > 20.0*GeV && !ngapjets && ptbalance2 < 0.15 && mjj >  250.0*GeV) {
108          _h->fill(_h->bin(1).xEdge());
109        }
110        if (zpt > 20.0*GeV && !ngapjets && ptbalance2 < 0.15 && mjj > 1000.0*GeV) {
111          _h->fill(_h->bin(2).xEdge());
112        }
113      }
114      else {
115        _h->fill(_h->bin(1).xEdge());
116        if (jet1pt > 85.0*GeV && jet2pt > 75.0*GeV)  _h->fill(_h->bin(2).xEdge());
117        if (zpt > 20.0*GeV && ngapjets == 0 && ptbalance2 < 0.15 && mjj > 250.0*GeV)  _h->fill(_h->bin(3).xEdge());
118        if (zpt > 20.0*GeV && ngapjets && ptbalance3 < 0.15 && mjj > 250.0*GeV)  _h->fill(_h->bin(4).xEdge());
119        if (mjj > 1000.0*GeV)  _h->fill(_h->bin(5).xEdge());
120        if (zpt > 20.0*GeV && !ngapjets && ptbalance2 < 0.15 && mjj > 1000.0*GeV)  _h->fill(_h->bin(3).xEdge());
121      }
122
123    }
124
125
126
127     /// Normalise histograms etc., after the run
128    void finalize() {
129
130      const double factor = crossSection()/(_mode? femtobarn : picobarn)/sumOfWeights();
131      scale(_h, factor);
132    }
133
134    bool _isBetween(const Jet probe, const Jet boundary1, const Jet boundary2) {
135      double y_p = probe.rapidity();
136      double y_b1 = boundary1.rapidity();
137      double y_b2 = boundary2.rapidity();
138
139      double y_min = std::min(y_b1, y_b2);
140      double y_max = std::max(y_b1, y_b2);
141
142      if (y_p > y_min && y_p < y_max) return true;
143      else return false;
144    }
145
146    ///@}
147
148  private:
149
150    size_t _mode;
151
152    /// @name Histograms
153    ///@{
154     BinnedHistoPtr<string> _h;
155    ///@}
156
157  };
158
159
160  RIVET_DECLARE_PLUGIN(ATLAS_2017_I1627873);
161
162}