Rivet analyses

title: CMS_2016_PAS_TOP_15_006

Jet multiplicity in the top-quark pair lepton+jets final state at $\sqrt{s} = 8~\TeV$

Experiment: CMS (LHC)

Inspire ID: 1476015

Status: VALIDATED

Authors: - Alexis Descroix - Frederik Schaaf - Markus Seidel

References: - Expt page: CMS-PAS-TOP-15-006

Beams: p+ p+

Beam energies: (4000.0, 4000.0)GeV

Run details: - ttbar events at sqrt(s) = 8 TeV (inclusive decay modes)

The top-quark pair differential production cross section in $pp$ collisions at $\sqrt{s}=8~\TeV$ as a function of the number of jets is measured in the lepton+jets (e/mu+jets) final state for an integrated luminosity of 19.7/fb. The cross section is presented in the visible phase space of the measurement.

Source code:CMS_2016_PAS_TOP_15_006.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/IdentifiedFinalState.hh"

include "Rivet/Projections/LeptonFinder.hh"

include "Rivet/Projections/VetoedFinalState.hh"

namespace Rivet {

/// Jet multiplicity in lepton+jets ttbar at 8 TeV class CMS_2016_PAS_TOP_15_006 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2016_PAS_TOP_15_006);


/// @name Analysis methods
/// @{

/// Set up projections and book histograms
void init() {

  // Complete final state
  FinalState fs;
  Cut superLooseLeptonCuts = Cuts::pt > 5 * GeV;
  SpecialLeptonFinder dressedleptons(fs, superLooseLeptonCuts);
  declare(dressedleptons, "LeptonFinder");

  // Projection for jets
  VetoedFinalState fsForJets(fs);
  fsForJets.addVetoOnThisFinalState(dressedleptons);
  declare(FastJets(fsForJets, JetAlg::ANTIKT, 0.5), "Jets");

  // Booking of histograms
  book(_normedElectronMuonHisto, "normedElectronMuonHisto", 7, 3.5, 10.5);
  book(_absXSElectronMuonHisto, "absXSElectronMuonHisto", 7, 3.5, 10.5);
}


/// Per-event analysis
void analyze(const Event& event) {
  // Select ttbar -> lepton+jets
  const SpecialLeptonFinder& dressedleptons = apply<SpecialLeptonFinder>(event, "LeptonFinder");
  vector<FourMomentum> selleptons;
  for (const DressedLepton& dressedlepton : dressedleptons.dressedLeptons()) {
    // Select good leptons
    if (dressedlepton.pT() > 30 * GeV && dressedlepton.abseta() < 2.4) selleptons += dressedlepton.mom();
    // Veto loose leptons
    else if (dressedlepton.pT() > 15 * GeV && dressedlepton.abseta() < 2.5)
      vetoEvent;
  }
  if (selleptons.size() != 1) vetoEvent;
  // Identify hardest tight lepton
  const FourMomentum lepton = selleptons[0];

  // Jets
  const FastJets& jets = apply<FastJets>(event, "Jets");
  const Jets jets30 = jets.jetsByPt(Cuts::pT > 30 * GeV);
  int nJets = 0, nBJets = 0;
  for (const Jet& jet : jets30) {
    if (jet.abseta() > 2.5) continue;
    if (deltaR(jet.momentum(), lepton) < 0.5) continue;
    nJets += 1;
    if (jet.bTagged(Cuts::pT > 5 * GeV)) nBJets += 1;
  }
  // Require >= 4 resolved jets, of which two must be b-tagged
  if (nJets < 4 || nBJets < 2) vetoEvent;

  // Fill histograms
  _normedElectronMuonHisto->fill(min(nJets, 10));
  _absXSElectronMuonHisto->fill(min(nJets, 10));
}


void finalize() {
  const double ttbarXS = !std::isnan(crossSectionPerEvent()) ? crossSection() : 252.89 * picobarn;
  if (std::isnan(crossSectionPerEvent()))
    MSG_INFO("No valid cross-section given, using NNLO (arXiv:1303.6254; sqrt(s)=8 TeV, m_t=172.5 GeV): "
             << ttbarXS / picobarn << " pb");

  const double xsPerWeight = ttbarXS / picobarn / sumOfWeights();
  scale(_absXSElectronMuonHisto, xsPerWeight);

  normalize(_normedElectronMuonHisto);
}

/// @}


/// @brief Special dressed lepton finder
///
/// Find dressed leptons by clustering all leptons and photons
class SpecialLeptonFinder : public FinalState {
public:

  /// Constructor
  SpecialLeptonFinder(const FinalState& fs, const Cut& cut)
      : FinalState(cut) {
    setName("CMS_2016_PAS_TOP_15_006::SpecialLeptonFinder");
    IdentifiedFinalState ifs(fs);
    ifs.acceptIdPair(PID::PHOTON);
    ifs.acceptIdPair(PID::ELECTRON);
    ifs.acceptIdPair(PID::MUON);
    declare(FastJets(ifs, JetAlg::ANTIKT, 0.1), "LeptonJets");
  }

  /// Clone on the heap
  RIVET_DEFAULT_PROJ_CLONE(SpecialLeptonFinder);

  /// Import to avoid warnings about overload-hiding
  using Projection::operator=;

  /// Retrieve the dressed leptons
  const DressedLeptons& dressedLeptons() const {
    return _clusteredLeptons;
  }

  /// Compare projections
  CmpState compare(const Projection& p) const {
    const PCmp fscmp = mkNamedPCmp(p, "LeptonJets");
    if (fscmp != CmpState::EQ) return fscmp;
    const SpecialLeptonFinder& other = dynamic_cast<const SpecialLeptonFinder&>(p);
    const bool cutcmp = _cuts == other._cuts;
    if (!cutcmp) return CmpState::NEQ;
    return CmpState::EQ;
  }

  /// Perform the calculation
  void project(const Event& e) {
    _theParticles.clear();
    _clusteredLeptons.clear();

    DressedLeptons allClusteredLeptons;
    const Jets jets = apply<FastJets>(e, "LeptonJets").jetsByPt(Cuts::pT > 5 * GeV);
    for (const Jet& jet : jets) {
      Particle lepCand;
      for (const Particle& cand : jet.particles()) {
        const int absPdgId = cand.abspid();
        if (absPdgId == PID::ELECTRON || absPdgId == PID::MUON) {
          if (cand.pt() > lepCand.pt()) lepCand = cand;
        }
      }
      // Central lepton must be the major component
      if ((lepCand.pt() < jet.pt() / 2.) || (!lepCand.isChargedLepton())) continue;

      DressedLepton lepton = DressedLepton(lepCand);
      for (const Particle& cand : jet.particles()) {
        if (isSame(cand, lepCand)) continue;
        lepton.addConstituent(cand, true);
      }
      allClusteredLeptons.push_back(lepton);
    }

    for (const DressedLepton& lepton : allClusteredLeptons) {
      if (_cuts->accept(static_cast<const Particle&>(lepton))) {
        _clusteredLeptons.push_back(lepton);
        _theParticles.push_back(lepton.bareLepton());
        _theParticles += lepton.photons();
      }
    }
  }

protected:

  /// Container which stores the clustered lepton objects
  DressedLeptons _clusteredLeptons;
};

private:

/// Histograms
Histo1DPtr _normedElectronMuonHisto, _absXSElectronMuonHisto;

};

RIVET_DECLARE_PLUGIN(CMS_2016_PAS_TOP_15_006);

} ```