Rivet analyses

title: ATLAS_2015_I1390114

$tt+b(b)$ at 8 TeV

Experiment: ATLAS (LHC)

Inspire ID: 1390114

Status: VALIDATED

Authors: - Matthias Danninger - Christian Gutschow

References: - Expt page: ATLAS-TOPQ-2014-10 - Eur.Phys.J. C76 (2016) no.1, 11 - DOI: 10.1140/epjc/s10052-015-3852-4 - arXiv: 1508.06868

Beams: p+ p+

Beam energies: (4000.0, 4000.0)GeV

Run details: - Top-antitop production

Fiducial cross-sections for $t\bar{t}$ production with one or two additional $b$-jets are presented, using an integrated luminosity of 20.3 fb${}^{-1}$ of proton-proton collisions at a centre-of-mass energy of 8 TeV at the Large Hadron Collider, collected with the ATLAS detector. The cross-section times branching ratio for $t\bar{t}$ events with at least one additional $b$-jet is measured to be 950 $\pm$ 70 (stat.)~${}^{+240}{-190}$ (syst.)~fb in the lepton-plus-jets channel and 50 $\pm$ 10 (stat.) ${}^{+15}{-10}$ (syst.) fb in the $e\mu$ channel. The cross-section times branching ratio for events with at least two additional $b$-jets is measured to be 19.3 $\pm$ 3.5 (stat.) $\pm$ 5.7 (syst.) fb in the dilepton channel ($e\mu$, $\mu\mu$, $ee$) using a method based on tight selection criteria, and 13.5 $\pm$ 3.3 (stat.) $\pm$ 3.6 (syst.) fb using a looser selection that allows the background normalisation to be extracted from data. The latter method also measures a value of 1.30 $\pm$ 0.33 (stat.) $\pm$ 0.28 (syst.)$\%$ for the ratio of $t\bar{t}$ production with two additional $b$-jets to $t\bar{t}$ production with any two additional jets. NB: When merging several output YODA files, the ratio (d02-x01-y01) needs to be reconstructed in a post-processing step.

Source code:ATLAS_2015_I1390114.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/IdentifiedFinalState.hh"

include "Rivet/Projections/LeptonFinder.hh"

include "Rivet/Projections/PromptFinalState.hh"

include "Rivet/Projections/VetoedFinalState.hh"

namespace Rivet {

// ATLAS $tt+b(b)$ at 8~TeV class ATLAS_2015_I1390114 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2015_I1390114);


void init() {

  // Eta ranges
  Cut eta_full = Cuts::abseta < 5.0 && Cuts::pT >= 1.0 * MeV;
  Cut eta_lep = Cuts::abseta < 2.5;

  // All final state particles
  FinalState fs(eta_full);

  // Get photons to dress leptons
  IdentifiedFinalState photons(fs);
  photons.acceptIdPair(PID::PHOTON);

  // Projection to find the electrons
  IdentifiedFinalState el_id(fs);
  el_id.acceptIdPair(PID::ELECTRON);
  PromptFinalState electrons(el_id);
  electrons.acceptTauDecays(true);
  declare(electrons, "electrons");
  LeptonFinder dressedelectrons(electrons, photons, 0.1, eta_lep && Cuts::pT > 25 * GeV);
  declare(dressedelectrons, "dressedelectrons");
  LeptonFinder ewdressedelectrons(electrons, photons, 0.1, eta_full);

  // Projection to find the muons
  IdentifiedFinalState mu_id(fs);
  mu_id.acceptIdPair(PID::MUON);
  PromptFinalState muons(mu_id);
  muons.acceptTauDecays(true);
  declare(muons, "muons");
  LeptonFinder dressedmuons(muons, photons, 0.1, eta_lep && Cuts::pT > 25 * GeV);
  declare(dressedmuons, "dressedmuons");
  LeptonFinder ewdressedmuons(muons, photons, 0.1, eta_full);

  // Projection to find neutrinos and produce MET
  IdentifiedFinalState nu_id;
  nu_id.acceptNeutrinos();
  PromptFinalState neutrinos(nu_id);
  neutrinos.acceptTauDecays(true);

  // Jet clustering.
  VetoedFinalState vfs;
  vfs.addVetoOnThisFinalState(ewdressedelectrons);
  vfs.addVetoOnThisFinalState(ewdressedmuons);
  vfs.addVetoOnThisFinalState(neutrinos);
  FastJets jets(vfs, JetAlg::ANTIKT, 0.4);
  jets.useInvisibles();
  declare(jets, "jets");

  book(_histo, 1, 1, 1);
  book(_ratio, 2, 1, 1);
  book(_aux, "_aux");
}


void analyze(const Event& event) {

  // Get the selected objects, using the projections.
  DressedLeptons electrons = apply<LeptonFinder>(event, "dressedelectrons").dressedLeptons();
  DressedLeptons muons = apply<LeptonFinder>(event, "dressedmuons").dressedLeptons();
  if (electrons.empty() && muons.empty()) vetoEvent;

  Jets jets = apply<FastJets>(event, "jets")
                  .jets((Cuts::pT > 20 * GeV) && (Cuts::abseta < 2.5), cmpMomByPt);
  Jets bjets;

  // Check overlap of jets/leptons.
  for (Jet jet : jets) {
    // if dR(el,jet) < 0.4 skip the event
    for (DressedLepton el : electrons) {
      if (deltaR(jet, el) < 0.4) vetoEvent;
    }
    // if dR(mu,jet) < 0.4 skip the event
    for (DressedLepton mu : muons) {
      if (deltaR(jet, mu) < 0.4) vetoEvent;
    }
    // Count the number of b-tags
    // We have to check that the ghost-matched B hadrons have pT > 5 GeV
    // By default jet.bTags() returns all B hadrons without cuts
    bool btagged = jet.bTags(Cuts::pT >= 5 * GeV).size();
    if (btagged) bjets += jet;
  }

  // Evaluate basic event selection
  bool pass_1lep = (electrons.size() == 1 && muons.empty()) || (muons.size() == 1 && electrons.empty());
  if (pass_1lep && bjets.size() >= 3 && jets.size() >= 5) _histo->fill(1);

  if (muons.size() == 1 && electrons.size() == 1 && bjets.size() >= 3) {
    if (muons[0].charge() * electrons[0].charge() < 0.0) _histo->fill(2);
  }

  DressedLepton *lep1 = nullptr, *lep2 = nullptr;
  bool zveto = false;
  if (electrons.size() == 2 && muons.empty()) {
    lep1 = &electrons[0];
    lep2 = &electrons[1];
  }
  else if (muons.size() == 2 && electrons.empty()) {
    lep1 = &muons[0];
    lep2 = &muons[1];
  }
  else if (electrons.size() == 1 && muons.size() == 1) {
    lep1 = &electrons[0];
    lep2 = &muons[0];
    zveto = true;
  }
  if (lep1 && lep2 && lep1->charge() * lep2->charge() < 0.0 && bjets.size() >= 2) {
    double mass = (lep1->momentum() + lep2->momentum()).mass();
    bool pass_2lep = mass > 15 * GeV && (zveto || !(mass > 81 * GeV && mass < 101 * GeV));
    if (pass_2lep && bjets.size() >= 4) {
      _histo->fill(3);
      _histo->fill(4);
    }
    if (pass_2lep && jets.size() >= 4) {
      _aux->fill();
    }
  }
}


void finalize() {
  const double sf(crossSection() / sumOfWeights() / femtobarn);
  scale(_histo, sf);
  scale(_aux, sf);


  const double n = _histo->bin(4).sumW();
  const double dN = _histo->bin(4).sumW2();
  const double d = _aux->sumW();
  const double dD = _aux->sumW2();
  const double r = safediv(n, d);
  double e = sqrt(safediv(r * (1 - r), d));
  if (_aux->effNumEntries() != _aux->numEntries()) {
    // use F. James's approximation for weighted events:
    e = sqrt(safediv((1 - 2 * r) * dN + r * r * dD, d * d));
  }
  _ratio->bin(1).set(100.0 * r, 100.0 * e); // convert into percentage
}

private:

Histo1DPtr _histo;
CounterPtr _aux;
Estimate1DPtr _ratio;

};

RIVET_DECLARE_PLUGIN(ATLAS_2015_I1390114);

} ```