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ATLAS_2016_I1492320_2l2j

WWW production at 8 TeV, 2L2J mode
Experiment: ATLAS (LHC)
Inspire ID: 1492320
Status: VALIDATED
Authors:
  • Alex Long
  • Ismet Siral
  • Louis Helary
  • Christian Gutschow
References: Beams: p+ p+
Beam energies: (4000.0, 4000.0) GeV
Run details:
  • pp -> WWW production at 8 TeV

This paper reports a search for triboson $W^\pm W^\pm W^\mp$ production in two decay channels ($W^\pm W^\pm W^\mp \to \ell^\pm\nu \ell^\pm\nu \ell^\mp\nu$) and ($W^\pm W^\pm W^\mp \to \ell^\pm\nu \ell^\pm\nu jj$ with $\ell = e,\mu$) in proton-proton collision data corresponding to an integrated luminosity of 20.3 fb${}^{-1}$ at a centre-of-mass energy of 8 TeV with the ATLAS detector at the Large Hadron Collider. Events with exactly three charged leptons, or two leptons with the same electric charge in association with two jets, are selected. The total number of events observed in data is consistent with the Standard Model (SM) predictions. The observed 95 % confidence level upper limit on the SM $W^\pm W^\pm W^\mp$ production cross section is found to be 730 fb with an expected limit of 560 fb in the absence of SM $W^\pm W^\pm W^\mp$ production. Limits are also set on $WWWW$ anomalous quartic gauge couplings.

Source code: ATLAS_2016_I1492320_2l2j.cc
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// -*- C++ -*
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/HeavyHadrons.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/MissingMomentum.hh"
#include "Rivet/Projections/DressedLeptons.hh"
#include "Rivet/Projections/PromptFinalState.hh"

namespace Rivet {


  /// @brief WWW cross-section at 8 TeV, 2L2J mode
  class ATLAS_2016_I1492320_2l2j : public Analysis {
  public:

    // Default constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2016_I1492320_2l2j);


    /// @name Analysis methods
    //@{

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

      // Charged leptons within acceptance
      const PromptFinalState chLep_fid = PromptFinalState(Cuts::abspid == PID::ELECTRON || Cuts::abspid == PID::MUON);
      const PromptFinalState photon_fs = PromptFinalState(Cuts::abspid == PID::PHOTON);
      const DressedLeptons dressed_leps(photon_fs, chLep_fid, 0.1, Cuts::pT > 10*GeV);
      declare(dressed_leps, "DressedLeptons");

      // Jets, anti-kt 0.4
      VetoedFinalState fsJets(FinalState(Cuts::abseta < 7.0)); //final state for jet finding: veto leptons and neutrinos
      fsJets.vetoNeutrinos();
      fsJets.addVetoOnThisFinalState(photon_fs);
      fsJets.addVetoOnThisFinalState(chLep_fid);
      declare(FastJets(fsJets, FastJets::ANTIKT, 0.4), "Jets");

      // b hadrons for b-tagging
      declare(HeavyHadrons(Cuts::abseta < 2.5 && Cuts::pT > 5*GeV), "Bhadrons");

      // Missing momentum
      declare(MissingMomentum(), "MET");

      // Histograms
      _h_2l2j = bookCounter("d01-x01-y02");
    }


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

      // Get leptons
      vector<DressedLepton> leps = apply<DressedLeptons>(event, "DressedLeptons").dressedLeptons();
      if (leps.size() < 2) vetoEvent;
      // Sort the dressed leptons by pt of their constituent lepton (bare lepton pt)
      std::sort(leps.begin(), leps.end() ,
                [](const DressedLepton& l1, const DressedLepton& l2) {
                  return (l1.constituentLepton().pT() > l2.constituentLepton().pT()); });
      if (leps[0].pT() < 30*GeV || leps[0].abseta() > 2.5)  vetoEvent;
      if (leps[1].pT() < 30*GeV || leps[1].abseta() > 2.5)  vetoEvent;

      // Get jets
      const Jets& jets = apply<FastJets>(event, "Jets").jetsByPt(Cuts::pT > 15*GeV);

      // Find min dilepton DR and mass
      double minDRll = DBL_MAX, mll = DBL_MAX;
      for (size_t i = 0; i < leps.size(); ++i) {
        for (size_t j = i + 1; j < leps.size(); ++j) {
          minDRll = min(minDRll, deltaR(leps[i], leps[j]));
          mll = min(mll, (leps[i].momentum() + leps[j].momentum()).mass());
        }
      }
      if (minDRll < 0.1) vetoEvent;
      if (mll < 40*GeV) vetoEvent;

      // Require same-sign leading leptons
      if (leps[0].charge()*leps[0].charge() < 0) vetoEvent;

      // Veto di-electron combinations within 10 GeV of the Z mass
      if (fabs(mll - 91.188*GeV) < 10*GeV && leps[0].abspid() == PID::ELECTRON && leps[1].abspid() == PID::ELECTRON) vetoEvent;

      // Now jet cuts
      if (jets.size() < 2) vetoEvent;
      if (jets[0].pT() < 30*GeV || jets[0].abseta() > 2.5) vetoEvent;
      if (jets[1].pT() < 20*GeV || jets[1].abseta() > 2.5) vetoEvent;

      // Find closest jet/lepton pair and veto if too close in phi or too far in eta
      double minDRLepJets = DBL_MAX;
      for (const Jet& jet : jets) {
        for (const Particle& lep : leps) minDRLepJets = min(minDRLepJets, deltaR(lep, jet));
      }
      if (minDRLepJets < 0.3) vetoEvent;
      if (fabs(deltaEta(jets[0], jets[1])) > 1.5) vetoEvent;

      // Dijet mass requirement
      double mjj = (jets[0].momentum() + jets[1].momentum()).mass();
      if (mjj < 65 || mjj > 105)  vetoEvent;
      if (!inRange(mjj, 65*GeV, 105*GeV)) vetoEvent;

      // Veto if any good jets are b-jets
      const Particles& bhadrons = apply<HeavyHadrons>(event, "Bhadrons").bHadrons();
      for (const Jet& j : jets) {
        if (j.abseta() > 2.5) continue; // outside acceptance of b-tagging
        const bool isbJet = any(bhadrons, deltaRLess(j, 0.3));
        if (isbJet) vetoEvent;
      }

      // MET vetoing for non-muon events
      const MissingMomentum& met = apply<MissingMomentum>(event, "MET");
      if (met.vectorEt().mod() < 55*GeV && (leps[0].abspid() != PID::MUON || leps[1].abspid() != PID::MUON)) vetoEvent;

      // Fill counter
      _h_2l2j->fill(event.weight());
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_h_2l2j, crossSection()/sumOfWeights()/femtobarn);
    }

    //@}


  private:

    /// @name Histograms
    //@{
    CounterPtr _h_2l2j;
    //@}

  };


  // Hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2016_I1492320_2l2j);

}