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ATLAS_2012_CONF_2012_104

Search for supersymmetry at 8 TeV in final states with jets, missing transverse momentum and one lepton with the ATLAS detector.
Experiment: ATLAS (LHC)
Status: OBSOLETE
Authors:
  • Peter Richardson
References:
  • ATLAS-CONF-2012-104
Beams: p+ p+
Beam energies: (4000.0, 4000.0) GeV
Run details:
  • BSM signal events at 8000 GeV.

One lepton search for supersymmmetric particles by ATLAS at 8 TeV with $5.8\,\text{fb}^{-1}$ integrated luminosity. Event counts in the signal regions are implemented as one-bin histograms. Histograms for effective mass are implemented for the two signal hard lepton signal regions and the ratio of missing transverse energy to effective mass for the soft lepton region.

Source code: ATLAS_2012_CONF_2012_104.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/IdentifiedFinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/FastJets.hh"

namespace Rivet {


  class ATLAS_2012_CONF_2012_104 : public Analysis {
  public:

    /// Constructor
    ATLAS_2012_CONF_2012_104()
      : Analysis("ATLAS_2012_CONF_2012_104")
    {    }


    /// @name Analysis methods
    //@{

    /// Book histograms and initialize 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");

      // Jet finder
      VetoedFinalState vfs;
      vfs.addVetoPairId(PID::MUON);
      declare(FastJets(vfs, FastJets::ANTIKT, 0.4), "AntiKtJets04");

      // all tracks (to do deltaR with leptons)
      declare(ChargedFinalState(Cuts::abseta < 3 && Cuts::pT > 0.5*GeV), "cfs");

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

      // Book histograms
      _count_e  = bookHisto1D("count_e" , 1, 0., 1.);
      _count_mu = bookHisto1D("count_mu", 1, 0., 1.);

      _hist_eTmiss_e  = bookHisto1D("hist_eTmiss_e"  , 25, 0., 1000.);
      _hist_eTmiss_mu = bookHisto1D("hist_eTmiss_mu" , 25, 0., 1000.);

    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const double weight = event.weight();

      // get the candiate jets
      Jets cand_jets;
      foreach ( const Jet& jet,
                apply<FastJets>(event, "AntiKtJets04").jetsByPt(20.0*GeV) ) {
        if ( fabs( jet.eta() ) < 2.8 ) {
          cand_jets.push_back(jet);
        }
      }

      // get the candidate "medium" leptons without isolation
      Particles cand_e;
      foreach( const Particle & e,
               apply<IdentifiedFinalState>(event, "elecs").particlesByPt()) {
        // remove any leptons within 0.4 of any candidate jets
        bool e_near_jet = false;
        foreach ( const Jet& jet, cand_jets ) {
          double dR = deltaR(e.momentum(),jet.momentum());
          if ( dR < 0.4 && dR > 0.2 ) {
            e_near_jet = true;
            break;
          }
        }
        if ( ! e_near_jet ) cand_e.push_back(e);
      }
      Particles cand_mu;
      foreach( const Particle & mu,
               apply<IdentifiedFinalState>(event, "muons").particlesByPt()) {
        // remove any leptons within 0.4 of any candidate jets
        bool mu_near_jet = false;
        foreach ( const Jet& jet, cand_jets ) {
          if ( deltaR(mu.momentum(),jet.momentum()) < 0.4 ) {
            mu_near_jet = true;
            break;
          }
        }
        if ( ! mu_near_jet ) cand_mu.push_back(mu);
      }
      // apply the isolation
      Particles chg_tracks =
        apply<ChargedFinalState>(event, "cfs").particles();
      // pTcone around muon track (hard)
      Particles recon_mu;
      foreach ( const Particle & mu, cand_mu ) {
        double pTinCone = -mu.pT();
        if(-pTinCone<25.) continue;
        foreach ( const Particle & track, chg_tracks ) {
          if ( deltaR(mu.momentum(),track.momentum()) < 0.2 )
            pTinCone += track.pT();
        }
        if ( pTinCone < 1.8*GeV ) recon_mu.push_back(mu);
      }
      // pTcone around electron track (hard)
      Particles recon_e;
      foreach ( const Particle & e, cand_e ) {
        double pTinCone = -e.pT();
        if(-pTinCone<25.) continue;
        foreach ( const Particle & track, chg_tracks ) {
          if ( deltaR(e.momentum(),track.momentum()) < 0.2 )
            pTinCone += track.pT();
        }
        if ( pTinCone < 0.1 * e.pT() ) recon_e.push_back(e);
      }

      // discard jets that overlap with electrons
      Jets recon_jets;
      foreach ( const Jet& jet, cand_jets ) {
        if(jet.abseta()>2.5||
           jet.perp()<25.) continue;
        bool away_from_e = true;
        foreach ( const Particle & e, cand_e ) {
          if ( deltaR(e.momentum(),jet.momentum()) < 0.2 ) {
            away_from_e = false;
            break;
          }
        }
        if ( away_from_e ) recon_jets.push_back( jet );
      }

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

      // at least 4 jets with pT>80.
      if(recon_jets.size()<4 || recon_jets[3].perp()<80.) vetoEvent;

      // only 1 signal lepton
      if( recon_e.size() + recon_mu.size() != 1 )
        vetoEvent;
      if( cand_e .size() + cand_mu .size() != 1 )
        vetoEvent;

      // start of meff calculation
      double HT=0.;
      foreach( const Jet & jet, recon_jets) {
        double pT = jet.perp();
        if(pT>40.) HT += pT;
      }

      // get the lepton
      Particle lepton = recon_e.empty() ? recon_mu[0] : recon_e[0];

      // lepton variables
      double pT = lepton.perp();

      double mT  = 2.*(pT*eTmiss -
                       lepton.px()*pTmiss.px() -
                       lepton.py()*pTmiss.py());
      mT = sqrt(mT);
      HT += pT;
      double m_eff_inc  = HT + eTmiss + pT;
      double m_eff_4 = eTmiss + pT;
      for(unsigned int ix=0;ix<4;++ix)
        m_eff_4 +=  recon_jets[ix].perp();

      // four jet selecton
      if(mT>100.&& eTmiss/m_eff_4>0.2 &&
         m_eff_inc > 800.) {
        if( eTmiss > 250. ) {
          if(lepton.abspid()==PID::ELECTRON)
            _count_e->fill(0.5,weight);
          else if(lepton.abspid()==PID::MUON)
            _count_mu->fill(0.5,weight);
        }
        if(lepton.abspid()==PID::ELECTRON)
          _hist_eTmiss_e ->fill(eTmiss,weight);
        else if(lepton.abspid()==PID::MUON)
          _hist_eTmiss_mu->fill(eTmiss,weight);
      }
    }
    //@}


    void finalize() {

      double norm = 5.8* crossSection()/sumOfWeights()/femtobarn;
      scale(_count_e ,norm);
      scale(_count_mu,norm);
      scale(_hist_eTmiss_e  ,40.*norm);
      scale(_hist_eTmiss_mu ,40.*norm);

    }

  private:

    /// @name Histograms
    //@{
    Histo1DPtr _count_e ;
    Histo1DPtr _count_mu;

    Histo1DPtr _hist_eTmiss_e ;
    Histo1DPtr _hist_eTmiss_mu;
    //@}

  };

  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2012_CONF_2012_104);

}