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ATLAS_2012_CONF_2012_001

4 or more lepton plus missing transverse energy SUSY search
Experiment: ATLAS (LHC)
Status: PRELIMINARY
Authors:
  • Peter Richardson
References:
  • ATLAS-CONF-2012-001
  • ATLAS-CONF-2012-035
Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • BSM signal events at 7000 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 7 TeV. The data sample has a total integrated luminosity of 2.06 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 2.06 fb$^{-1}$, are calculated.

Source code: ATLAS_2012_CONF_2012_001.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 {


  /// @author Peter Richardson
  class ATLAS_2012_CONF_2012_001 : public Analysis {
  public:

    /// Constructor
    ATLAS_2012_CONF_2012_001()
      : Analysis("ATLAS_2012_CONF_2012_001")
    {    }


    /// @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");

      // Book histograms
      _hist_leptonpT.push_back(bookHisto1D(1,1,1));
      _hist_leptonpT.push_back(bookHisto1D(2,1,1));
      _hist_leptonpT.push_back(bookHisto1D(3,1,1));
      _hist_leptonpT.push_back(bookHisto1D(4,1,1));
      _hist_njet   = bookHisto1D(5,1,1);
      _hist_etmiss = bookHisto1D(6,1,1);
      _hist_mSFOS  = bookHisto1D(7,1,1);
      _hist_meff   = bookHisto1D(8,1,1);

      _hist_leptonpT_MC.push_back(bookHisto1D("hist_lepton_pT_1", 26, 0., 260));
      _hist_leptonpT_MC.push_back(bookHisto1D("hist_lepton_pT_2", 15, 0., 150));
      _hist_leptonpT_MC.push_back(bookHisto1D("hist_lepton_pT_3", 20, 0., 100));
      _hist_leptonpT_MC.push_back(bookHisto1D("hist_lepton_pT_4", 20, 0., 100));
      _hist_njet_MC   = bookHisto1D("hist_njet", 7, -0.5, 6.5);
      _hist_etmiss_MC = bookHisto1D("hist_etmiss",11,0.,220.);
      _hist_mSFOS_MC  = bookHisto1D("hist_m_SFOS",13,0.,260.);
      _hist_meff_MC   = bookHisto1D("hist_m_eff",19,0.,950.);

      _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 ( fabs( jet.eta() ) < 2.8 ) {
          cand_jets.push_back(jet);
        }
      }

      // candidate muons
      Particles cand_mu;
      Particles chg_tracks =
        apply<ChargedFinalState>(event, "cfs").particles();
      foreach ( const Particle & mu,
                apply<IdentifiedFinalState>(event, "muons").particlesByPt() ) {
        double pTinCone = -mu.pT();
        foreach ( const Particle & track, chg_tracks ) {
          if ( deltaR(mu.momentum(),track.momentum()) <= 0.2 )
            pTinCone += track.pT();
        }
        if ( pTinCone < 1.8*GeV )
          cand_mu.push_back(mu);
      }

      // candidate electrons
      Particles cand_e;
      foreach ( const Particle & e,
                apply<IdentifiedFinalState>(event, "elecs").particlesByPt() ) {
        double eta = e.eta();
        // remove electrons with pT<15 in old veto region
        if( fabs(eta)>1.37 && fabs(eta) < 1.52 && e.perp()< 15.*GeV)
          continue;
        double pTinCone = -e.perp();
        foreach ( const Particle & track, chg_tracks ) {
          if ( deltaR(e.momentum(),track.momentum()) <= 0.2 )
            pTinCone += track.pT();
        }
        if (pTinCone/e.perp()<0.1) {
          cand_e.push_back(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.momentum(),jet.momentum()) <= 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;
      for(unsigned int ie=0;ie<cand_e.size();++ie) {
        const Particle & e = cand_e[ie];
        // at least 0.4 from any jets
        bool away = true;
        foreach ( const Jet& jet, recon_jets ) {
          if ( deltaR(e.momentum(),jet.momentum()) < 0.4 ) {
            away = false;
            break;
          }
        }
        // and 0.1 from any muons
        if ( away ) {
          foreach ( const Particle & mu, cand_mu ) {
            if ( deltaR(mu.momentum(),e.momentum()) < 0.1 ) {
              away = false;
              break;
            }
          }
        }
        // and 0.1 from electrons
        for(unsigned int ie2=0;ie2<cand_e.size();++ie2) {
          if(ie==ie2) continue;
          if ( deltaR(e.momentum(),cand_e[ie2].momentum()) < 0.1 ) {
            away = false;
            break;
          }
        }
        // if isolated keep it
        if ( away ) cand2_e.push_back( e );
      }
      // remove e+e- pairs with mass < 20.
      Particles recon_e;
      for(unsigned int ie=0;ie<cand2_e.size();++ie) {
	bool pass = true;
	for(unsigned int ie2=0;ie2<cand2_e.size();++ie2) {
	  if(cand2_e[ie].pid()*cand2_e[ie2].pid()>0) continue;
	  double mtest = (cand2_e[ie].momentum()+cand2_e[ie2].momentum()).mass();
	  if(mtest<=20.) {
	    pass = false;
	    break;
	  }
	}
	if(pass) recon_e.push_back(cand2_e[ie]);
      }

      // only keep muons more than R=0.4 from jets
      Particles cand2_mu;
      for(unsigned int imu=0;imu<cand_mu.size();++imu) {
        const Particle & mu = cand_mu[imu];
        bool away = true;
        // at least 0.4 from any jets
        foreach ( const Jet& jet, recon_jets ) {
          if ( deltaR(mu.momentum(),jet.momentum()) < 0.4 ) {
            away = false;
            break;
          }
        }
        // and 0.1 from any electrona
        if ( away ) {
          foreach ( const Particle & e, cand_e ) {
            if ( deltaR(mu.momentum(),e.momentum()) < 0.1 ) {
              away = false;
              break;
            }
          }
        }
        // and 0.1 from muons
        for(unsigned int imu2=0;imu2<cand_mu.size();++imu2) {
          if(imu==imu2) continue;
          if ( deltaR(mu.momentum(),cand_mu[imu2].momentum()) < 0.1 ) {
            away = false;
            break;
          }
        }
        if ( away )
          cand2_mu.push_back( mu );
      }

      // remove mu+mu- pairs with mass < 20.
      Particles recon_mu;
      for(unsigned int imu=0;imu<cand2_mu.size();++imu) {
	bool pass = true;
	for(unsigned int imu2=0;imu2<cand2_mu.size();++imu2) {
	  if(cand2_mu[imu].pid()*cand2_mu[imu2].pid()>0) continue;
	  double mtest = (cand2_mu[imu].momentum()+cand2_mu[imu2].momentum()).mass();
	  if(mtest<=20.) {
	    pass = false;
	    break;
	  }
	}
	if(pass) recon_mu.push_back(cand2_mu[imu]);
      }

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

      // now only use recon_jets, recon_mu, recon_e

      // 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;
      }

      // ATLAS calo problem
      if(rand()/static_cast<double>(RAND_MAX)<=0.42) {
        foreach ( const Particle & e, recon_e ) {
          double eta = e.eta();
          double phi = e.azimuthalAngle(MINUSPI_PLUSPI);
          if(eta>-0.1&&eta<1.5&&phi>-0.9&&phi<-0.5)
            vetoEvent;
        }
        foreach ( const Jet & jet, recon_jets ) {
          double eta = jet.rapidity();
          double phi = jet.azimuthalAngle(MINUSPI_PLUSPI);
          if(jet.perp()>40 && eta>-0.1&&eta<1.5&&phi>-0.9&&phi<-0.5)
            vetoEvent;
        }
      }

      // check at least one e/mu passing trigger
      if( !( !recon_e .empty() && recon_e[0] .perp()>25.)  &&
          !( !recon_mu.empty() && recon_mu[0].perp()>20.) ) {
        MSG_DEBUG("Hardest lepton fails trigger");
        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 ) {
        double pT = jet.perp();
        if(pT>40.) meff += pT;
      }

      double mSFOS=1e30, mdiff=1e30;
      // mass of SFOS pairs closest to the Z mass
      for(unsigned int ix=0;ix<recon_e.size();++ix) {
        for(unsigned int iy=ix+1;iy<recon_e.size();++iy) {
          if(recon_e[ix].pid()*recon_e[iy].pid()>0) continue;
          double mtest = (recon_e[ix].momentum()+recon_e[iy].momentum()).mass();
          if(fabs(mtest-90.)<mdiff) {
            mSFOS = mtest;
            mdiff = fabs(mtest-90.);
          }
        }
      }
      for(unsigned int ix=0;ix<recon_mu.size();++ix) {
        for(unsigned int iy=ix+1;iy<recon_mu.size();++iy) {
          if(recon_mu[ix].pid()*recon_mu[iy].pid()>0) continue;
          double mtest = (recon_mu[ix].momentum()+recon_mu[iy].momentum()).mass();
          if(fabs(mtest-91.118)<mdiff) {
            mSFOS = mtest;
            mdiff = fabs(mtest-91.118);
          }
        }
      }

      // make the control plots
      // lepton pT
      unsigned int ie=0,imu=0;
      for(unsigned int ix=0;ix<4;++ix) {
        double pTe  = ie <recon_e .size() ?
          recon_e [ie ].perp() : -1*GeV;
        double pTmu = imu<recon_mu.size() ?
          recon_mu[imu].perp() : -1*GeV;
        if(pTe>pTmu) {
          _hist_leptonpT   [ix]->fill(pTe ,weight);
          _hist_leptonpT_MC[ix]->fill(pTe ,weight);
          ++ie;
        }
        else {
          _hist_leptonpT   [ix]->fill(pTmu,weight);
          _hist_leptonpT_MC[ix]->fill(pTmu,weight);
          ++imu;
        }
      }
      // njet
      _hist_njet   ->fill(recon_jets.size(),weight);
      _hist_njet_MC->fill(recon_jets.size(),weight);
      // etmiss
      _hist_etmiss   ->fill(eTmiss,weight);
      _hist_etmiss_MC->fill(eTmiss,weight);
      if(mSFOS<1e30) {
        _hist_mSFOS   ->fill(mSFOS,weight);
        _hist_mSFOS_MC->fill(mSFOS,weight);
      }
      _hist_meff   ->fill(meff,weight);
      _hist_meff_MC->fill(meff,weight);

      // finally the counts
      if(eTmiss>50.) {
        _count_SR1->fill(0.5,weight);
        if(mdiff>10.) _count_SR2->fill(0.5,weight);
      }
    }

    //@}

    void finalize() {
      double norm = crossSection()/femtobarn*2.06/sumOfWeights();
      // these are number of events at 2.06fb^-1 per 10 GeV
      scale(_hist_leptonpT   [0],norm*10.);
      scale(_hist_leptonpT   [1],norm*10.);
      scale(_hist_leptonpT_MC[0],norm*10.);
      scale(_hist_leptonpT_MC[1],norm*10.);
      // these are number of events at 2.06fb^-1 per 5 GeV
      scale(_hist_leptonpT   [2],norm*5.);
      scale(_hist_leptonpT   [3],norm*5.);
      scale(_hist_leptonpT_MC[2],norm*5.);
      scale(_hist_leptonpT_MC[3],norm*5.);
      // these are number of events at 2.06fb^-1 per 20 GeV
      scale(_hist_etmiss      ,norm*20.);
      scale(_hist_mSFOS       ,norm*20.);
      scale(_hist_etmiss_MC   ,norm*20.);
      scale(_hist_mSFOS_MC    ,norm*20.);
      // these are number of events at 2.06fb^-1 per 50 GeV
      scale(_hist_meff        ,norm*50.);
      scale(_hist_meff_MC     ,norm*50.);
      // these are number of events at 2.06fb^-1
      scale(_hist_njet        ,norm);
      scale(_hist_njet_MC     ,norm);
      scale(_count_SR1,norm);
      scale(_count_SR2,norm);
    }

  private:

    /// @name Histograms
    //@{
    vector<Histo1DPtr> _hist_leptonpT,_hist_leptonpT_MC;
    Histo1DPtr _hist_njet;
    Histo1DPtr _hist_njet_MC;
    Histo1DPtr _hist_etmiss;
    Histo1DPtr _hist_etmiss_MC;
    Histo1DPtr _hist_mSFOS;
    Histo1DPtr _hist_mSFOS_MC;
    Histo1DPtr _hist_meff;
    Histo1DPtr _hist_meff_MC;
    Histo1DPtr _count_SR1;
    Histo1DPtr _count_SR2;
    //@}

  };

  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2012_CONF_2012_001);

}