Rivet analyses

title: ATLAS_2012_I1186556

Search for a heavy top-quark partner in final states with two leptons.

Experiment: ATLAS (LHC)

Inspire ID: 1186556

Status: UNVALIDATED

Authors: - Peter Richardson

References: - Expt page: ATLAS-SUSY-2012-09 - arXiv: 1209.4186

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - BSM signal events at 7000 GeV.

Search for direct pair production of heavy top-quark partners with 4.7~fb$^{-1}$ integrated luminosity at $\sqrt{s} = 7 TeV$ by the ATLAS experiment. Heavy top-quark partners decaying into a top quark and a neutral non-interacting particle are searched for in events with two leptons in the final state.

Source code:ATLAS_2012_I1186556.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/ChargedFinalState.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/IdentifiedFinalState.hh"

include "Rivet/Projections/VetoedFinalState.hh"

include "Rivet/Projections/VisibleFinalState.hh"

include "Rivet/Tools/Random.hh"

namespace Rivet {

class ATLAS_2012_I1186556 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2012_I1186556);


/// @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 > 20 * 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, JetAlg::ANTIKT, 0.4), "AntiKtJets04");

  // all tracks (to do deltaR with leptons)
  declare(ChargedFinalState(Cuts::abseta < 3.0 && Cuts::pT > 1 * GeV), "cfs");

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

  // Book histograms
  book(_count_SR_SF, "count_SR_SF", 1, 0., 1.);
  book(_count_SR_OF, "count_SR_OF", 1, 0., 1.);

  book(_hist_mT2_SF_exp, "hist_mT2_SF_exp", 40, 0., 200.);
  book(_hist_mT2_OF_exp, "hist_mT2_OF_exp", 40, 0., 200.);
  book(_hist_mT2_SF_MC, "hist_mT2_SF_MC", 500, 0., 1000.);
  book(_hist_mT2_OF_MC, "hist_mT2_OF_MC", 500, 0., 1000.);
}

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

  // get the candiate jets
  Jets cand_jets;
  for (const Jet& jet :
       apply<FastJets>(event, "AntiKtJets04").jetsByPt(Cuts::pT > 20 * GeV && Cuts::abseta < 4.5)) {
    cand_jets.push_back(jet);
  }
  // charged tracks for isolation
  Particles chg_tracks = apply<ChargedFinalState>(event, "cfs").particles();
  // find the electrons
  Particles cand_e;
  for (const Particle& e : apply<IdentifiedFinalState>(event, "elecs").particlesByPt()) {
    // remove any leptons within 0.4 of any candidate jets
    bool e_near_jet = false;
    for (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) continue;
    cand_e.push_back(e);
  }
  Particles cand_mu;
  for (const Particle& mu : apply<IdentifiedFinalState>(event, "muons").particlesByPt()) {
    // remove any leptons within 0.4 of any candidate jets
    bool mu_near_jet = false;
    for (const Jet& jet : cand_jets) {
      if (deltaR(mu.momentum(), jet.momentum()) < 0.4) {
        mu_near_jet = true;
        break;
      }
    }
    if (mu_near_jet) continue;
    cand_mu.push_back(mu);
  }
  // pTcone around muon track
  Particles recon_mu;
  for (const Particle& mu : cand_mu) {
    double pTinCone = -mu.pT();
    for (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
  Particles recon_e;
  for (const Particle& e : cand_e) {
    double pTinCone = -e.pT();
    for (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);
  }

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

  // discard jets that overlap with electrons
  Jets recon_jets;
  for (const Jet& jet : cand_jets) {
    if (jet.abseta() > 2.5 || jet.perp() < 20.) continue;
    bool away_from_e = true;
    for (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);
  }

  // put leptons into 1 vector and order by pT
  Particles leptons(recon_e.begin(), recon_e.end());
  leptons.insert(leptons.begin(), recon_mu.begin(), recon_mu.end());
  sort(leptons.begin(), leptons.end(), cmpMomByPt);

  // exactly two leptons
  if (leptons.size() != 2) vetoEvent;

  // hardest lepton pT greater the 25 (20) e(mu)
  if ((leptons[0].abspid() == PID::ELECTRON && leptons[0].perp() < 25.)
      || (leptons[0].abspid() == PID::ELECTRON && leptons[0].perp() < 20.))
    vetoEvent;

  // require opposite sign
  if (leptons[0].pid() * leptons[1].pid() > 0) vetoEvent;

  // and invariant mass > 20
  double mll = (leptons[0].momentum() + leptons[1].momentum()).mass();
  if (mll < 20.) vetoEvent;

  // two jets 1st pT > 50 and second pT> 25
  if (recon_jets.size() < 2 || recon_jets[0].perp() < 50. || recon_jets[1].perp() < 25.) vetoEvent;

  // calculate mT2
  double m_T2 = mT2(leptons[0], leptons[1], pTmiss, 0.0); // zero mass invisibles

  // same flavour region
  if (leptons[0].pid() == -leptons[1].pid()) {
    // remove Z region
    if (mll > 71. && mll < 111.) vetoEvent;
    // require at least 1 b jet
    unsigned int n_b = 0;
    for (unsigned int ix = 0; ix < recon_jets.size(); ++ix) {
      if (recon_jets[ix].bTagged() && rand01() <= 0.60) ++n_b;
    }
    if (n_b == 0) vetoEvent;
    _hist_mT2_SF_exp->fill(m_T2);
    _hist_mT2_SF_MC->fill(m_T2);
    if (m_T2 > 120.) _count_SR_SF->fill(0.5);
  }
  // opposite flavour region
  else {
    _hist_mT2_OF_exp->fill(m_T2);
    _hist_mT2_OF_MC->fill(m_T2);
    if (m_T2 > 120.) _count_SR_OF->fill(0.5);
  }
}
/// @}


void finalize() {

  double norm = 4.7 * crossSection() / sumOfWeights() / femtobarn;
  scale(_count_SR_SF, norm);
  scale(_count_SR_OF, norm);
  scale(_hist_mT2_SF_exp, 5. * norm);
  scale(_hist_mT2_OF_exp, 5. * norm);
  scale(_hist_mT2_SF_MC, norm / 4.7);
  scale(_hist_mT2_OF_MC, norm / 4.7);
}

private:

/// @name Histograms
/// @{
Histo1DPtr _count_SR_SF;
Histo1DPtr _count_SR_OF;

Histo1DPtr _hist_mT2_SF_exp;
Histo1DPtr _hist_mT2_OF_exp;
Histo1DPtr _hist_mT2_SF_MC;
Histo1DPtr _hist_mT2_OF_MC;
/// @}

};

RIVET_DECLARE_PLUGIN(ATLAS_2012_I1186556);

} ```