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ATLAS_2020_I1803608

Electroweak Zjj at 13 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1803608
Status: VALIDATED
Authors:
  • Stephen Weber
  • Dag Gillberg
References: Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
  • pp -> Z [-> ee and mumu] + jets production at 13 TeV

Differential cross-section measurements are presented for the electroweak production of two jets in association with a $ZZ$ boson. These measurements are sensitive to the vector-boson fusion production mechanism and provide a fundamental test of the gauge structure of the Standard Model. The analysis is performed using proton-proton collision data collected by ATLAS at $\sqrt{s} = 13$ TeV and with an integrated luminosity of 139 fb$^{-1}$. The differential cross-sections are measured in the $Z\rightarrow \ell^+\ell^-$ decay channel ($\ell=e,\mu$) as a function of four observables: the dijet invariant mass, the rapidity interval spanned by the two jets, the signed azimuthal angle between the two jets, and the transverse momentum of the dilepton pair. The data are corrected for the effects of detector inefficiency and resolution and are sufficiently precise to distinguish between different state-of-the-art theoretical predictions calculated using Powheg+Pythia8, Herwig7+Vbfnlo and Sherpa 2.2. The differential cross-sections are used to search for anomalous weak-boson self-interactions using a dimension-six effective field theory. The measurement of the signed azimuthal angle between the two jets is found to be particularly sensitive to the interference between the Standard Model and dimension-six scattering amplitudes and provides a direct test of charge-conjugation and parity invariance in the weak-boson self-interactions. Note that the default entry point is for the inclusive Z+2jet selections. For the EW-only measurement use the option TYPE=EW_ONLY. In both cases, electron and muon channels are to be summed.

Source code: ATLAS_2020_I1803608.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/PromptFinalState.hh"
  5#include "Rivet/Projections/DressedLeptons.hh"
  6#include "Rivet/Projections/FastJets.hh"
  7
  8namespace Rivet {
  9  
 10
 11  /// VBFZ in pp at 13 TeV
 12  class ATLAS_2020_I1803608 : public Analysis {
 13  public:
 14
 15    /// Constructor
 16    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2020_I1803608);
 17
 18
 19    /// @name Analysis methods
 20    /// @{
 21
 22    /// Book histograms and initialise projections before the run
 23    void init() {
 24      FinalState fs(Cuts::abseta < 5.0);
 25
 26      PromptFinalState photons(Cuts::abspid == PID::PHOTON);
 27      PromptFinalState electrons(Cuts::abspid == PID::ELECTRON);
 28      PromptFinalState muons(Cuts::abspid == PID::MUON);
 29
 30      Cut cuts_el = (Cuts::pT > 25*GeV) && ( Cuts::abseta < 1.37 || (Cuts::abseta > 1.52 && Cuts::abseta < 2.47) );
 31      Cut cuts_mu = (Cuts::pT > 25*GeV) && (Cuts::abseta < 2.4);
 32
 33      DressedLeptons dressed_electrons(photons, electrons, 0.1, cuts_el);
 34      declare(dressed_electrons, "DressedElectrons");
 35
 36      DressedLeptons dressed_muons(photons, muons, 0.1, cuts_mu);
 37      declare(dressed_muons, "DressedMuons");
 38
 39      FastJets jets(fs, FastJets::ANTIKT, 0.4, JetAlg::Muons::NONE, JetAlg::Invisibles::NONE);
 40      declare(jets, "Jets");
 41
 42      _doControl = bool(getOption("TYPE") != "EW_ONLY");
 43      if (_doControl) {
 44        initialisePlots(SRplots, "SR");
 45        initialisePlots(CRAplots, "CRA");
 46        initialisePlots(CRBplots, "CRB");
 47        initialisePlots(CRCplots, "CRC");
 48      } else {
 49        initialisePlots(SRplots, "EW");
 50      }
 51    }
 52
 53
 54    /// Perform the per-event analysis
 55    void analyze(const Event& event) {
 56
 57      // Access fiducial electrons and muons
 58      const Particle *l1 = nullptr, *l2 = nullptr;
 59      Particles muons = apply<DressedLeptons>(event, "DressedMuons").particles();
 60      Particles elecs = apply<DressedLeptons>(event, "DressedElectrons").particles();
 61
 62      // Dilepton selection 1: =2 leptons of the same kind
 63      if (muons.size()+elecs.size() != 2) vetoEvent;
 64      if      (muons.size()==2) { l1=&muons[0]; l2=&muons[1]; }
 65      else if (elecs.size()==2) { l1=&elecs[0]; l2=&elecs[1]; }
 66      else vetoEvent;
 67
 68      // Dilepton selection 2: oppostie-charge and in mass range
 69      if ( !oppCharge(*l1, *l2) )  vetoEvent;
 70      if ( !inRange((l1->mom()+l2->mom()).mass()/GeV, 81.0, 101.0) ) vetoEvent;
 71
 72      // Electron-jet overlap removal (note: muons are not included in jet finding)
 73      // make sure jets do not overlap with an electron within DR<0.2
 74      Jets jets;
 75      for (const Jet& j : apply<FastJets>(event, "Jets").jetsByPt(Cuts::pT > 25*GeV && Cuts::absrap < 4.4)) {
 76        if (elecs.size() == 2 && (deltaR(j, *l1, RAPIDITY) < 0.2 || deltaR(j, *l2, RAPIDITY) < 0.2 )) {
 77          continue;
 78        }
 79        jets += j;
 80      }
 81
 82      // Require 2 jets with pT > 85 and 80 GeV
 83      if (jets.size() < 2) vetoEvent;
 84
 85      // Calculate the observables
 86      Variables vars(jets, l1, l2);
 87
 88      // make sure neither lepton overlaps with a jet within 0.4
 89      for (const Jet& j : jets) {
 90        if (deltaR(j, *l1, RAPIDITY) < 0.4 || deltaR(j, *l2, RAPIDITY) < 0.4)  vetoEvent;
 91      }
 92
 93      if (jets[0].pt() < 85*GeV || jets[1].pt() < 80*GeV ) vetoEvent;
 94
 95      bool pass_VBFZtopo = (vars.mjj > 250*GeV && vars.Dyjj > 2.0 && vars.pTll > 20*GeV && vars.Zcent < 1.0 && vars.pTbal < 0.15);
 96
 97      if (pass_VBFZtopo) {
 98        if      (_doControl && vars.Ngj  > 0 && vars.Zcent <  0.5) fillPlots(vars, CRAplots);
 99        else if (_doControl && vars.Ngj  > 0 && vars.Zcent >= 0.5) fillPlots(vars, CRBplots);
100        else if (_doControl && vars.Ngj == 0 && vars.Zcent >= 0.5) fillPlots(vars, CRCplots);
101
102        if ( vars.Ngj == 0 && vars.Zcent < 0.5 ) {
103          fillPlots(vars, SRplots);
104        }
105      }
106    }
107
108
109    void finalize() {
110      const double xsec = crossSectionPerEvent()/femtobarn;
111      scalePlots(SRplots, xsec);
112      scalePlots(CRAplots, xsec);
113      scalePlots(CRBplots, xsec);
114      scalePlots(CRCplots, xsec);
115    }
116
117    /// @}
118
119
120    /// @name Analysis helpers
121    /// @{
122
123    struct Variables {
124      Variables(const vector<Jet>& jets, const Particle* l1, const Particle* l2) {
125        // get the jets
126        assert(jets.size()>=2);
127        FourMomentum j1 = jets[0].mom(), j2 = jets[1].mom();
128        pTj1 = j1.pT()/GeV; pTj2 = j2.pT()/GeV;
129        assert(pTj1 >= pTj2);
130        
131        // build dilepton system
132        FourMomentum ll = (l1->mom() + l2->mom());
133        pTll = ll.pT(); mll = ll.mass();
134        
135        Nj = jets.size();
136        Dyjj = std::abs(j1.rap() - j2.rap());
137        mjj = (j1 + j2).mass();
138        Dphijj = ( j1.rap() > j2.rap() ) ? mapAngleMPiToPi(j1.phi() - j2.phi()) : mapAngleMPiToPi(j2.phi() - j1.phi());
139        
140        Jets gjets = getGapJets(jets);
141        Ngj = gjets.size();
142        pTgj = Ngj? gjets[0].pT()/GeV : 0;
143        
144        FourMomentum vecSum = (j1 + j2 + l1->mom() + l2->mom());
145        double HT = j1.pT() + j2.pT() + l1->pT() + l2->pT();
146        if (Ngj) { 
147          vecSum += gjets[0].mom(); 
148          HT += pTgj;
149        }
150        pTbal = vecSum.pT() / HT;
151        
152        Zcent = std::abs(ll.rap() - (j1.rap() + j2.rap())/2) / Dyjj;
153      }
154      
155      double Zcent, pTj1, pTj2, pTgj, pTll, mll, Dyjj, mjj, Dphijj, pTbal;
156      size_t Nj, Ngj;
157
158      Jets getGapJets(const Jets& jets) {
159        Jets gjets;
160        if (jets.size() <= 2)  return gjets;
161        FourMomentum j1 = jets[0].mom(), j2 = jets[1].mom();
162        double yFwd = j1.rap(), yBwd = j2.rap();
163        if (yFwd < yBwd) std::swap(yFwd,yBwd);
164        for (size_t i = 2; i < jets.size(); ++i)
165         if (inRange(jets[i].rap(), yBwd, yFwd)) gjets += jets[i];
166        return gjets;
167      }
168
169    }; // struct variables
170
171
172    struct Plots {
173      string label;
174      Histo1DPtr m_jj, Dphi_jj, Dy_jj, pT_ll;
175    };
176
177
178    void initialisePlots(Plots& plots, const string& phase_space) {
179      plots.label   = phase_space;
180      size_t region = 0;
181      if (phase_space == "SR")   region = 4;
182      if (phase_space == "CRA")  region = 8;
183      if (phase_space == "CRB")  region = 12;
184      if (phase_space == "CRC")  region = 16;
185      book(plots.m_jj,    1 + region, 1, 1);
186      book(plots.Dy_jj,   2 + region, 1, 1);
187      book(plots.pT_ll,   3 + region, 1, 1);
188      book(plots.Dphi_jj, 4 + region, 1, 1);
189    }
190
191
192    void fillPlots(const Variables& vars, Plots& plots) {
193      // The mjj plot extends down to 250 GeV
194      plots.m_jj->fill(vars.mjj/GeV);
195      if (vars.mjj > 1000*GeV) {
196        plots.Dy_jj->fill(vars.Dyjj);
197        plots.Dphi_jj->fill(vars.Dphijj);
198        plots.pT_ll->fill(vars.pTll/GeV);
199      }
200    }
201
202
203    void scalePlots(Plots& plots, const double xsec) {
204      scale(plots.m_jj, xsec);
205      scale(plots.Dy_jj, xsec);
206      scale(plots.Dphi_jj, xsec);
207      scale(plots.pT_ll, xsec);
208    }
209
210    /// @}
211
212
213    private:
214
215      Plots SRplots, CRAplots, CRBplots, CRCplots;
216      bool _doControl;
217
218  };
219
220
221  
222  RIVET_DECLARE_PLUGIN(ATLAS_2020_I1803608);
223
224}