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ATLAS_2019_I1718132

Control region measurements for leptoquark search at 13 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1718132
Status: VALIDATED
Authors:
  • Louie Corpe
  • Christian Gutschow
References: Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
  • pp -> Z + jets at 13 TeV, pp -> ttbar at 13 TeV,

Searches for scalar leptoquarks pair-produced in proton-proton collisions at $\sqrt{s} = 13$ TeV at the Large Hadron Collider are performed by the ATLAS experiment. A data set corresponding to an integrated luminosity of 36.1 fb${}^{-1}$ is used. Final states containing two electrons or two muons and two or more jets are studied, as are states with one electron or muon, missing transverse momentum and two or more jets. No statistically significant excess above the Standard Model expectation is observed. The observed and expected lower limits on the leptoquark mass at 95% confidence level extend up to 1.25 TeV for first- and second-generation leptoquarks, as postulated in the minimal Buchmuller-Ruckl-Wyler model, assuming a branching ratio into a charged lepton and a quark of 50%. In addition, measurements of particle-level fiducial and differential cross sections are presented for the $Z\to ee$, $Z\to\mu\mu$ and $t\bar{t}$ processes in several regions related to the search control regions. Predictions from a range of generators are compared with the measurements, and good agreement is seen for many of the observables. However, the predictions for the $Z\to\ell\ell$ measurements in observables sensitive to jet energies disagree with the data.

Source code: ATLAS_2019_I1718132.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/DressedLeptons.hh"


namespace Rivet {

  /// @brief leptoquark search at 13 TeV 
  /// @note This base class contains a "mode" variable to specify lepton channel
  class ATLAS_2019_I1718132 : public Analysis {
    public:

      /// Constructor
      DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2019_I1718132);
      //@}

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

        // default to widest cut, electrons and muons.
        _mode = 3;      
        if ( getOption("LMODE") == "ELEL" )  _mode = 1;
        if ( getOption("LMODE") == "MUMU" )  _mode = 2;
        if ( getOption("LMODE") == "ELMU" )  _mode = 3;

        // Lepton cuts
        Cut baseline_lep_cuts = Cuts::abseta < 2.5 && Cuts::pT >=  40*GeV;

        // All final state particles
        const FinalState fs;

        // Get photons to dress leptons
        FinalState photons(Cuts::abspid == PID::PHOTON);

        // Find and dress the electrons and muons
        PromptFinalState bare_leps(Cuts::abspid == PID::ELECTRON || Cuts::abspid == PID::MUON);
        DressedLeptons dressed_leps(photons, bare_leps, 0.1, baseline_lep_cuts, true);
        declare(dressed_leps, "leptons");

        //and finally the jets:
        FastJets jets(fs, FastJets::ANTIKT, 0.4, JetAlg::Muons::NONE);
        declare(jets, "jets");

        size_t offset = _mode;
        book(_h["JetPt_leading"],     1 + offset, 1, 1);
        book(_h["JetPt_subleading"],  7 + offset, 1, 1); 
        book(_h["minDeltaPhiJ0_L"],  13 + offset, 1, 1);
        book(_h["minDeltaPhiJ1_L"],  19 + offset, 1, 1);
        book(_h["DeltaEtaJJ"],       25 + offset, 1, 1);
        book(_h["DeltaPhiJJ"],       31 + offset, 1, 1);
        book(_h["DeltaPhiLL"],       37 + offset, 1, 1);
        book(_h["DiJetMass"],        43 + offset, 1, 1);
        book(_h["DiLepPt"],          49 + offset, 1, 1);
        book(_h["Ht"],               55 + offset, 1, 1);
        book(_h["St"],               61 + offset, 1, 1);

        offset = _mode + 3;
        book(_hST["JetPt_leading"],     1 + offset, 1, 1);
        book(_hST["JetPt_subleading"],  7 + offset, 1, 1); 
        book(_hST["minDeltaPhiJ0_L"],  13 + offset, 1, 1);
        book(_hST["minDeltaPhiJ1_L"],  19 + offset, 1, 1);
        book(_hST["DeltaEtaJJ"],       25 + offset, 1, 1);
        book(_hST["DeltaPhiJJ"],       31 + offset, 1, 1);
        book(_hST["DeltaPhiLL"],       37 + offset, 1, 1);
        book(_hST["DiJetMass"],        43 + offset, 1, 1);
        book(_hST["DiLepPt"],          49 + offset, 1, 1);
        book(_hST["Ht"],               55 + offset, 1, 1);
        book(_hST["St"],               61 + offset, 1, 1);

      }

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

        // Get the selected leptons:
        vector<DressedLepton> leptons = apply<DressedLeptons>(event, "leptons").dressedLeptons();

        // get the selected jets:
        Jets jets = apply<JetAlg>(event, "jets").jetsByPt(Cuts::pT > 60*GeV && Cuts::absrap < 2.5);

        // exclude jets which are actually electrons


        // This would be super-sweet, but unfortunately lxplus default gcc4.8 doesn't like it :(
        /*idiscardIfAny(jets, leptons, [](const Jet& jet, const DressedLepton& lep) { 
          return lep.abspid() == PID::ELECTRON and deltaR(jet, lep) < 0.2; 
        });*/

        for (const DressedLepton& lep : leptons) {
          ifilter_discard(jets, [&](const Jet& jet) { 
            return lep.abspid() == PID::ELECTRON and deltaR(jet, lep) < 0.2; 
          });
        }

        // remove cases where muons are too close to a jet 
        if (_mode == 3) { // el-mu case
          /*idiscardIfAny(leptons, jets, [](const DressedLepton& lep, const Jet& jet) { 
            return lep.abspid() == PID::MUON and deltaR(jet, lep) < 0.4;
          });*/
          for (const DressedLepton& lep : leptons) {
            ifilter_discard(jets, [&](const Jet& jet) { 
              return lep.abspid() == PID::MUON and deltaR(jet, lep) < 0.4;
            });
          }
        }

        // make sure we have the right number of jets
        if (jets.size() < 2)  vetoEvent;

        // make sure we have right number of leptons
        size_t requiredMuons = 0, requiredElecs = 0;
        if (_mode == 1)  requiredElecs = 2;
        if (_mode == 2)  requiredMuons = 2;
        if (_mode == 3)  requiredMuons = requiredElecs = 1;

        size_t nEl = count(leptons, [](const DressedLepton& lep) { return  lep.abspid() == PID::ELECTRON; });
        if (nEl != requiredElecs)   vetoEvent; 

        size_t nMu = count(leptons, [](const DressedLepton& lep) { return  lep.abspid() == PID::MUON; });
        if (nMu != requiredMuons)  vetoEvent;  

        // make sure leptons are in right order (should be OK byt better safe than sorry!)
        std::sort(leptons.begin(), leptons.end(), cmpMomByPt);

        // calculate all observables and store in dict
        const double jetpt_leading    = jets[0].pT()/GeV;
        const double jetpt_subleading = jets[1].pT()/GeV;
        const double mll              = (leptons[0].momentum() + leptons[1].momentum()).mass()/GeV;
        const double st               = (leptons[0].pT() + leptons[1].pT() + jets[0].pT() + jets[1].pT())/GeV;
        const double ht               = (jets[0].pT() + jets[1].pT())/GeV;
        const double dijetmass        = (jets[0].mom() + jets[1].mom()).mass()/GeV;
        const double dileppt          = (leptons[0].momentum() + leptons[1].momentum()).pT()/GeV;
        const double deltaphijj       = deltaPhi(jets[0], jets[1]);
        const double deltaetajj       = deltaEta(jets[0], jets[1]);
        const double deltaphill       = deltaPhi(leptons[0], leptons[1]);
        const double mindeltaphij0_l  = min(deltaPhi(jets[0], leptons[0]), deltaPhi(jets[0], leptons[1]));
        const double mindeltaphij1_l  = min(deltaPhi(jets[1], leptons[0]), deltaPhi(jets[1], leptons[1]));

        // add Z-mass window cut if needed
        bool addMllCut = _mode == 1 || _mode == 2;
        if (addMllCut && (mll < 70. || 110. < mll))  vetoEvent;

        // fill output histos
        _h["JetPt_leading"]->fill(jetpt_leading); 
        _h["JetPt_subleading"]->fill(jetpt_subleading); 
        _h["St"]->fill(st);
        _h["Ht"]->fill(ht);
        _h["DiJetMass"]->fill(dijetmass);
        _h["DiLepPt"]->fill(dileppt);
        _h["DeltaPhiJJ"]->fill(deltaphijj);
        _h["DeltaEtaJJ"]->fill(deltaetajj);
        _h["DeltaPhiLL"]->fill(deltaphill);
        _h["minDeltaPhiJ0_L"]->fill(mindeltaphij0_l);
        _h["minDeltaPhiJ1_L"]->fill(mindeltaphij1_l);

        // "extreme" ST cut 
        if (st > 600.) {
          // fill output histos
          _hST["JetPt_leading"]->fill(jetpt_leading); 
          _hST["JetPt_subleading"]->fill(jetpt_subleading); 
          _hST["St"]->fill(st);
          _hST["Ht"]->fill(ht);
          _hST["DiJetMass"]->fill(dijetmass);
          _hST["DiLepPt"]->fill(dileppt);
          _hST["DeltaPhiJJ"]->fill(deltaphijj);
          _hST["DeltaEtaJJ"]->fill(deltaetajj);
          _hST["DeltaPhiLL"]->fill(deltaphill);
          _hST["minDeltaPhiJ0_L"]->fill(mindeltaphij0_l);
          _hST["minDeltaPhiJ1_L"]->fill(mindeltaphij1_l);
        }

      }



      void finalize() {
        const double sf = crossSectionPerEvent();
        for (auto hist : _h) { scale(hist.second, sf); }
        for (auto hist : _hST) { scale(hist.second, sf); }
      }

      //@}


    protected:

      size_t _mode;

    private:

      map<string, Histo1DPtr> _h, _hST;

    };

  DECLARE_RIVET_PLUGIN(ATLAS_2019_I1718132);

}