Rivet analyses

title: LHCB_2018_I1662483

Measurement of the forward top pair production cross-section in the dilepton channel

Experiment: LHCB (LHC)

Inspire ID: 1662483

Status: VALIDATED

Authors: - Stephen Farry

References: - JHEP 08 (2018) 174 - arXiv: hep-ex/1803.05188 - LHCB-PAPER-2017-050, CERN-EP-2018-022

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - Proton-proton collisions at c.o.m. energy of 13 TeV producing hard QCD events containing a top--anti-top quark pair decaying into dilepton channel accompanied by a b-jet in the final state.

Measurement of the top pair cross-section in the dilepton channel, where a muon, electron and one $b$-jet are required to be present in the event. A fiducial cross-section is measuremed where the leptons and jets are required to be within the pseudorapidity acceptance of the LHCb acceptance ($2<\eta<4.5$), and to have a transverse momentum greater than 20 GeV. Additionally leptons are required to be separated from each other by a radial distance ($\Delta R$) of 0.1, and from the $b$-jet by a distance of 0.5.

Source code:LHCB_2018_I1662483.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalPartons.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/LeptonFinder.hh"

include "Rivet/Projections/MissingMomentum.hh"

include "Rivet/Projections/PromptFinalState.hh"

namespace Rivet {

/// @brief Measurement of forward top pair production in the mu e channel at LHCb /// /// Both leptons with pt > 20 GeV and in pseudorapidity range 2.0 - 4.5. /// Leptons are separated from each other by a dR of 0.1. /// Leading jet is required to be a b-jet with pt > 20 GeV and pseudorapidity in range 2.2 - 4.2. /// The jet is separated from both leptons by dR of 0.5. /// class LHCB_2018_I1662483 : public Analysis { public:

/// Default constructor
RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2018_I1662483);


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

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

  // Initialise and register projections

  // the basic final-state projection:
  // all final-state particles
  const FinalState fs;

  //get the final state b quarks for b-tagging
  FinalPartons bquarks(Cuts::abspid == 5 && Cuts::pT > 5 * GeV);
  declare(bquarks, "bquarks");

  // the final-state particles declared above are clustered using FastJet with
  // the anti-kT algorithm and a jet-radius parameter 0.5
  // muons and neutrinos are excluded from the clustering
  FastJets jetfs(fs, JetAlg::ANTIKT, 0.5, JetMuons::NONE, JetInvisibles::NONE);
  declare(jetfs, "jets");

  // FinalState of bare muons and electrons in the event
  Cut lepton_cuts = Cuts::pT >= 20 * GeV && Cuts::etaIn(2.0, 4.5);
  FinalState fsmuons(Cuts::abspid == PID::MUON && lepton_cuts);
  FinalState fselectrons(Cuts::abspid == PID::ELECTRON && lepton_cuts);

  declare(fsmuons, "muons");
  declare(fselectrons, "electrons");

  // Inclusive cross-section measurement
  book(_h_fiducial_xsect, 1, 1, 1);
}


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

  // retrieve leptons, sorted by pT
  const FinalState& muons = apply<FinalState>(event, "muons");
  const FinalState& electrons = apply<FinalState>(event, "electrons");
  const FinalPartons& bquarks = apply<FinalPartons>(event, "bquarks");

  // retrieve clustered jets, sorted by pT, with a minimum pT cut
  Jets jets = apply<FastJets>(event, "jets").jetsByPt(Cuts::pT > 20 * GeV && Cuts::etaIn(2.2, 4.2));

  if (jets.empty()) vetoEvent;
  bool pass = false;
  for (const auto& m : muons.particles()) {
    for (const auto& e : electrons.particles()) {
      if (deltaR(m.momentum(), e.momentum()) < 0.1) continue;
      vector<Jet> lepton_jets;
      for (const auto& j : jets) {
        if (deltaR(j.momentum(), m.momentum()) > 0.5 && deltaR(j.momentum(), e.momentum()) > 0.5)
          lepton_jets.push_back(j);
        if (lepton_jets.size() > 0) {
          for (const auto& b : bquarks.particles()) {
            if (deltaR(b.momentum(), lepton_jets.at(0).momentum()) < 0.5) {
              pass = true;
            }
          }
        }
      }
    }
  }

  // veto event if it doesn't pass our selection
  if (!pass) vetoEvent;
  // append to cross-section
  _h_fiducial_xsect->fill(13000);
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_fiducial_xsect, crossSection() / femtobarn / sumOfWeights()); // norm to cross section
}


/// Histogram
BinnedHistoPtr<int> _h_fiducial_xsect;

};

RIVET_DECLARE_PLUGIN(LHCB_2018_I1662483);

} ```