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ATLAS_2012_CONF_2012_153

4 or more lepton plus missing transverse energy SUSY search
Experiment: ATLAS (LHC)
Status: PRELIMINARY
Authors:
  • Peter Richardson
References:
  • ATLAS-CONF-2012-153
Beams: p+ p+
Beam energies: (4000.0, 4000.0) GeV
Run details:
  • BSM signal events at 8000 GeV.

Search for SUSY using events with 4 or more leptons in association with missing transverse energy in proton-proton collisions at a centre-of-mass energy of 8 TeV. The data sample has a total integrated luminosity of 13.0 fb$^{-1}$. There is no reference data and in addition to the control plots from the paper the number of events in the two signal regions, correctly normalized to an integrated luminosity 13.0 fb$^{-1}$, are calculated.

Source code: ATLAS_2012_CONF_2012_153.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Tools/BinnedHistogram.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Projections/VisibleFinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Tools/RivetMT2.hh"

namespace Rivet {


  class ATLAS_2012_CONF_2012_153 : public Analysis {
  public:

    /// @name Constructors etc.
    //@{

    /// Constructor
    ATLAS_2012_CONF_2012_153()
      : Analysis("ATLAS_2012_CONF_2012_153")
    {    }

    //@}



  public:

    /// @name Analysis methods
    //@{

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

      // projection to find the electrons
      IdentifiedFinalState elecs(Cuts::abseta < 2.47 && Cuts::pT > 10*GeV);
      elecs.acceptIdPair(PID::ELECTRON);
      declare(elecs, "elecs");


      // projection to find the muons
      IdentifiedFinalState muons(Cuts::abseta < 2.4 && Cuts::pT > 10*GeV);
      muons.acceptIdPair(PID::MUON);
      declare(muons, "muons");

      // for pTmiss
      declare(VisibleFinalState(Cuts::abseta < 4.9), "vfs");

      VetoedFinalState vfs;
      vfs.addVetoPairId(PID::MUON);

      /// Jet finder
      declare(FastJets(vfs, FastJets::ANTIKT, 0.4), "AntiKtJets04");

      // all tracks (to do deltaR with leptons)
      declare(ChargedFinalState(Cuts::abseta < 3.0), "cfs");

      vector<double> edges_meff;
      edges_meff.push_back(   0);
      edges_meff.push_back( 150);
      edges_meff.push_back( 300);
      edges_meff.push_back( 500);
      edges_meff.push_back(1000);
      edges_meff.push_back(1500);

      vector<double> edges_eT;
      edges_eT.push_back(0);
      edges_eT.push_back(50);
      edges_eT.push_back(150);
      edges_eT.push_back(300);
      edges_eT.push_back(500);

      // Book histograms
      _hist_electrons = bookHisto1D("hist_electrons_before", 11, -0.5,10.5);
      _hist_muons     = bookHisto1D("hist_muons_before"    , 11, -0.5,10.5);
      _hist_leptons   = bookHisto1D("hist_leptons_before"  , 11, -0.5,10.5);
      _hist_4leptons  = bookHisto1D("hist_4leptons", 1, 0.,1.);
      _hist_veto      = bookHisto1D("hist_veto", 1, 0., 1.);
      _hist_etmiss    = bookHisto1D("hist_etmiss",edges_eT);
      _hist_meff      = bookHisto1D("hist_m_eff",edges_meff);
      _count_SR1      = bookHisto1D("count_SR1", 1, 0., 1.);
      _count_SR2      = bookHisto1D("count_SR2", 1, 0., 1.);

    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const double weight = event.weight();
      // get the jet candidates
      Jets cand_jets;
      foreach (const Jet& jet, apply<FastJets>(event, "AntiKtJets04").jetsByPt(20.0*GeV) ) {
        if (jet.abseta() < 2.5) cand_jets.push_back(jet);
      }

      // candidate muons
      Particles cand_mu = apply<IdentifiedFinalState>(event, "muons").particlesByPt();

      // candidate electrons
      // Discard if two electrons are within R=0.1
      Particles temp = apply<IdentifiedFinalState>(event, "elecs").particles(cmpMomByE);
      vector<bool> vetoed(temp.size(),false);
      Particles cand_e;
      for (size_t ix = 0; ix < temp.size(); ++ix) {
        if (vetoed[ix]) continue;
        for (size_t iy = ix+1; iy < temp.size(); ++iy) {
          if ( deltaR(temp[ix], temp[iy]) < 0.1 ) vetoed[iy] = true;
        }
        if (!vetoed[ix]) cand_e.push_back(temp[ix]);
      }

      // Sort by transverse momentum
      sortByPt(cand_e);

      // resolve jet/lepton ambiguity
      Jets recon_jets;
      foreach ( const Jet& jet, cand_jets ) {
        bool away_from_e = true;
        foreach ( const Particle& e, cand_e ) {
          if (deltaR(e, jet) <= 0.2) {
            away_from_e = false;
            break;
          }
        }
        if (away_from_e) recon_jets.push_back( jet );
      }

      // only keep electrons more than R=0.4 from jets
      Particles cand2_e;
      foreach (const Particle& e, cand_e) {
        // at least 0.4 from any jets
        bool away = true;
        foreach ( const Jet& jet, recon_jets ) {
          if ( deltaR(e, jet) < 0.4 ) {
            away = false;
            break;
          }
        }
        // if isolated keep it
        if ( away )
          cand2_e.push_back( e );
      }

      // only keep muons more than R=0.4 from jets
      Particles cand2_mu;
      foreach(const Particle & mu, cand_mu ) {
        bool away = true;
        // at least 0.4 from any jets
        foreach ( const Jet& jet, recon_jets ) {
          if ( deltaR(mu, jet) < 0.4 ) {
            away = false;
            break;
          }
        }
        if (away) cand2_mu.push_back( mu );
      }

      // electron and muon more than 0.1 apart
      Particles cand3_e;
      foreach ( const Particle & e, cand2_e ) {
        bool away = true;
        foreach( const Particle & mu, cand2_mu ) {
          if( deltaR(e, mu) < 0.1) {
            away = false;
            break;
          }
        }
        if (away) cand3_e.push_back(e);
      }
      Particles cand3_mu;
      foreach( const Particle & mu, cand2_mu ) {
        bool away = true;
        foreach ( const Particle & e, cand2_e ) {
          if( deltaR(e, mu) < 0.1) {
            away = false;
            break;
          }
        }
        if (away) cand3_mu.push_back(mu);
      }

      // pTmiss
      Particles vfs_particles =
        apply<VisibleFinalState>(event, "vfs").particles();
      FourMomentum pTmiss;
      foreach ( const Particle & p, vfs_particles ) {
        pTmiss -= p.momentum();
      }
      double eTmiss = pTmiss.pT();

      // apply electron isolation
      Particles chg_tracks =
        apply<ChargedFinalState>(event, "cfs").particles();
      Particles cand4_e;
      foreach (const Particle& e, cand3_e) {
        // charge isolation
        double pTinCone = -e.pT();
        foreach (const Particle& track, chg_tracks) {
          if (track.pT() > 0.4*GeV && deltaR(e, track) <= 0.3 )
            pTinCone += track.pT();
        }
        if (pTinCone/e.pT() > 0.16) continue;
        // all particles isolation
        pTinCone = -e.pT();
        foreach (const Particle& p, vfs_particles) {
          if (p.abspid() != PID::MUON && deltaR(e, p) <= 0.3 )
            pTinCone += p.pT();
        }
        if (pTinCone/e.pT() < 0.18) cand4_e.push_back(e);
      }

      // apply muon isolation
      Particles cand4_mu;
      foreach ( const Particle & mu, cand3_mu ) {
        double pTinCone = -mu.perp();
        foreach ( const Particle & track, chg_tracks ) {
          if (track.pT() > 1*GeV && deltaR(mu, track) <= 0.3)
            pTinCone += track.pT();
        }
        if (pTinCone/mu.pT() < 0.12) cand4_mu.push_back(mu);
      }

      // same SOSF pairs m>12.
      Particles recon_e;
      foreach(const Particle& e, cand4_e) {
        bool veto = false;
        foreach(const Particle& e2, cand4_e) {
          if (e.pid()*e2.pid() < 0 && (e.momentum()+e2.momentum()).mass() < 12*GeV) {
            veto = true;
            break;
          }
        }
        if (!veto) recon_e.push_back(e);
      }
      Particles recon_mu;
      foreach(const Particle& mu, cand4_mu) {
        bool veto = false;
        foreach(const Particle& mu2, cand4_mu) {
          if (mu.pid()*mu2.pid() < 0 && (mu.momentum()+mu2.momentum()).mass() < 12*GeV) {
            veto = true;
            break;
          }
        }
        if (!veto) recon_mu.push_back(mu);
      }

      // now only use recon_jets, recon_mu, recon_e
      _hist_electrons->fill(recon_e.size(), weight);
      _hist_muons->fill(recon_mu.size(), weight);
      _hist_leptons->fill(recon_mu.size() + recon_e.size(), weight);
      if (recon_mu.size() + recon_e.size() > 3) {
        _hist_4leptons->fill(0.5, weight);
      }

      // reject events with less than 4 electrons and muons
      if (recon_mu.size() + recon_e.size() < 4) {
        MSG_DEBUG("To few charged leptons left after selection");
        vetoEvent;
      }


      // or two lepton trigger
      bool passDouble =
        (recon_mu.size()>=2 && ( (recon_mu[1].pT()>14*GeV) ||
                                 (recon_mu[0].pT()>18*GeV && recon_mu[1].perp() > 10*GeV) )) ||
        (recon_e.size() >=2 && ( (recon_e [1].pT()>14*GeV) ||
                                 (recon_e [0].pT()>25*GeV && recon_e [1].perp() > 10*GeV) )) ||
        (!recon_e.empty() && !recon_mu.empty() &&
         ( (recon_e[0].pT() > 14*GeV && recon_mu[0].pT() > 10*GeV)||
           (recon_e[0].pT() > 10*GeV && recon_mu[0].pT() > 18*GeV) ));

      // must pass a trigger
      if (!passDouble ) {
        MSG_DEBUG("Hardest lepton fails trigger");
        _hist_veto->fill(0.5, weight);
        vetoEvent;
      }

      // calculate meff
      double meff = eTmiss;
      foreach ( const Particle & e , recon_e  ) meff += e.perp();
      foreach ( const Particle & mu, recon_mu ) meff += mu.perp();
      foreach ( const Jet & jet, recon_jets ) {
        const double pT = jet.pT();
        if (pT > 40*GeV) meff += pT;
      }

      // 2/3 leptons --> find 1 SFOS pair in range and veto event
      // 4+  leptons --> find 2 SFOS pairs and in range veto event
      for (size_t ix = 0; ix < recon_e.size(); ++ix) {
        for (size_t iy = ix+1; iy < recon_e.size(); ++iy) {
          if (recon_e[ix].pid()*recon_e[iy].pid() > 0) continue;
          const FourMomentum ppair = recon_e[ix].momentum() + recon_e[iy].momentum();
          if (inRange(ppair.mass(), 81.2*GeV, 101.2*GeV)) vetoEvent;

          // check triplets with electron
          for (size_t iz = 0; iz < recon_e.size(); ++iz) {
            if (iz == ix || iz == iy) continue;
            if (inRange((ppair+recon_e[iz].momentum()).mass(), 81.2*GeV, 101.2*GeV)) vetoEvent;
          }

          // check triplets with muon
          for (size_t iz = 0; iz < recon_mu.size(); ++iz) {
            if (inRange((ppair+recon_mu[iz].momentum()).mass(), 81.2*GeV, 101.2*GeV)) vetoEvent;
          }

          // check quadruplets with electrons
          for (size_t iz = 0; iz < recon_e.size(); ++iz) {
            for (size_t iw = iz+1; iw < recon_e.size(); ++iw) {
              if (iz==ix || iz==iy || iw==ix || iw==iy) continue;
              if (recon_e[iz].pid()*recon_e[iw].pid() > 0) continue;
              if (inRange((ppair+recon_e[iz].momentum()+recon_e[iw].momentum()).mass(), 81.2*GeV, 101.2*GeV)) vetoEvent;
            }
          }
          // check quadruplets with muons
          for (size_t iz = 0; iz < recon_mu.size(); ++iz) {
            for (size_t iw = iz+1; iw < recon_mu.size(); ++iw) {
              if (recon_mu[iz].pid()*recon_mu[iw].pid() > 0) continue;
              if (inRange((ppair+recon_mu[iz].momentum()+recon_mu[iw].momentum()).mass(), 81.2*GeV, 101.2*GeV)) vetoEvent;
            }
          }
        }
      }

      // Muon pairs
      for (size_t ix = 0; ix < recon_mu.size(); ++ix) {
        for (size_t iy = ix+1; iy < recon_mu.size(); ++iy) {
          if (recon_mu[ix].pid()*recon_mu[iy].pid()>0) continue;
          const FourMomentum ppair = recon_mu[ix].momentum()+recon_mu[iy].momentum();
          if (inRange(ppair.mass(), 81.2*GeV, 101.2*GeV)) vetoEvent;

          // check triplets with muon
          for (size_t iz = 0; iz < recon_mu.size(); ++iz) {
            if (iz==ix || iz==iy) continue;
            if (inRange((ppair+recon_mu[iz].momentum()).mass(), 81.2*GeV, 101.2*GeV)) vetoEvent;
          }

          // check triplets with electron
          for (size_t iz = 0; iz < recon_e.size(); ++iz) {
            if (inRange((ppair+recon_e[iz].momentum()).mass(), 81.2*GeV, 101.2*GeV)) vetoEvent;
          }

          // check muon quadruplets
          for (size_t iz = 0; iz < recon_mu.size(); ++iz) {
            for (size_t iw = iz+1; iy < recon_mu.size(); ++iy) {
              if (iz==ix || iz==iy || iw==ix || iw==iy) continue;
              if (recon_mu[iz].pid()*recon_mu[iw].pid() > 0) continue;
              if (inRange((ppair+recon_mu[iz].momentum()+recon_mu[iw].momentum()).mass(), 81.2*GeV, 101.2*GeV)) vetoEvent;
            }
          }
        }
      }

      // Make the control plots
      _hist_etmiss->fill(eTmiss,weight);
      _hist_meff  ->fill(meff  ,weight);
      // Finally the counts
      if (eTmiss > 50*GeV) _count_SR1->fill(0.5,weight);
      if (meff  >0*GeV) _count_SR2->fill(0.5,weight);

    }

    //@}

    void finalize() {
      double norm = crossSection()/femtobarn*13./sumOfWeights();
      scale(_hist_etmiss,norm*20.);
      scale(_hist_meff  ,norm*20.);
      scale(_count_SR1,norm);
      scale(_count_SR2,norm);
    }


  private:

    /// @name Histograms
    //@{
    Histo1DPtr _hist_electrons;
    Histo1DPtr _hist_muons;
    Histo1DPtr _hist_leptons;
    Histo1DPtr _hist_4leptons;
    Histo1DPtr _hist_veto;
    Histo1DPtr _hist_etmiss;
    Histo1DPtr _hist_meff;
    Histo1DPtr _count_SR1;
    Histo1DPtr _count_SR2;
    //@}

  };

  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2012_CONF_2012_153);

}