Rivet analyses

title: ATLAS_2013_I1219109

W + b production at 7 TeV

Experiment: ATLAS (LHC)

Inspire ID: 1219109

Status: VALIDATED

Authors: - Christian Gutschow

References: - Expt page: ATLAS-STDM-2012-11 - JHEP 1306 (2013) 084 - DOI: 10.1007/JHEP06(2013)084 - arXiv: 1302.2929

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - W+b in the electron channel

Measurements of the W+b-jets ($W+b+X$ and $W+b\bar{b}+X$) production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These results are based on data corresponding to an integrated luminosity of 4.6~$fb^{-1}$, collected with the ATLAS detector. Cross-sections are presented as a function of jet multiplicity and of the transverse momentum of the leading b-jet for both the combined muon and electron decay modes of the W boson. The default routine will consider the average of electron and muon decay channel of the W boson. Use LMODE=EL and LMODE=MU to specify the decay channel directly.

Source code:ATLAS_2013_I1219109.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/HeavyHadrons.hh"

include "Rivet/Projections/LeptonFinder.hh"

include "Rivet/Projections/MissingMomentum.hh"

include "Rivet/Projections/PromptFinalState.hh"

include "Rivet/Projections/VetoedFinalState.hh"

namespace Rivet {

/// @brief ATLAS W+b measurement class ATLAS_2013_I1219109 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2013_I1219109);


void init() {

  // Get options from the option system
  _mode = 0;
  if (getOption("LMODE") == "EL") _mode = 1;
  if (getOption("LMODE") == "MU") _mode = 2;


  // Initialise and register projections
  declare("MET", MissingMomentum());
  Cut cuts = Cuts::abseta < 2.5 && Cuts::pT > 25 * GeV;
  LeptonFinder ef(0.1, cuts && Cuts::abspid == PID::ELECTRON);
  declare(ef, "Elecs");
  LeptonFinder mf(0.1, cuts && Cuts::abspid == PID::MUON);
  declare(mf, "Muons");

  // Jets
  VetoedFinalState jet_fs;
  jet_fs.addVetoOnThisFinalState(ef);
  jet_fs.addVetoOnThisFinalState(mf);
  FastJets fj(jet_fs, JetAlg::ANTIKT, 0.4);
  fj.useInvisibles();
  declare(fj, "Jets");
  declare(HeavyHadrons(Cuts::abseta < 2.5 && Cuts::pT > 5 * GeV), "BHadrons");

  // Book histograms
  book(_njet, 1, 1, 1);     // dSigma / dNjet
  book(_jet1_bPt, 3, 1, 1); // dSigma / dBjetPt for Njet = 1
  book(_jet2_bPt, 8, 1, 1); // dSigma / dBjetPt for Njet = 2
}


void analyze(const Event& event) {

  // MET cut
  const P4& pmiss = apply<MissingMom>(event, "MET").missingMom();
  if (pmiss.pT() < 25 * GeV) vetoEvent;

  // Retrieve W boson candidate
  const Particles& es = apply<LeptonFinder>(event, "Elecs").particles();
  const int iefound = closestMatchIndex(es, pmiss, Kin::mass, 80.4 * GeV);
  const Particles& mus = apply<LeptonFinder>(event, "Muons").particles();
  const int imfound = closestMatchIndex(mus, pmiss, Kin::mass, 80.4 * GeV);

  // Event selection and identify W lepton
  size_t nWel = (iefound >= 0);
  size_t nWmu = (imfound >= 0);
  if (_mode == 0 && !((nWmu == 1 && !nWel) || (!nWmu && nWel == 1)))
    vetoEvent;                                        // one W->munu OR W->elnu candidate, otherwise veto
  if (_mode == 1 && !(!nWmu && nWel == 1)) vetoEvent; // one W->elnu candidate, otherwise veto
  if (_mode == 2 && !(nWmu == 1 && !nWel)) vetoEvent; // one W->munu candidate, otherwise veto
  const Particle& lepton = (nWel > 0) ? es[iefound] : mus[imfound];

  // mT cut
  /// @todo Shouldn't this go earlier, in the lepton filtering?
  if (mT(lepton, pmiss) < 60 * GeV) vetoEvent;

  // Count good jets, check if good jet contains B hadron
  const Particles& bHadrons = apply<HeavyHadrons>(event, "BHadrons").bHadrons();
  const Jets& jets = apply<JetFinder>(event, "Jets").jetsByPt(Cuts::pT > 25 * GeV);
  int goodjets = 0, bjets = 0;
  double bPt = 0.;
  for (const Jet& j : jets) {
    if ((j.abseta() < 2.1) && (deltaR(lepton, j) > 0.5)) {
      // this jet passes the selection!
      ++goodjets;
      // Perform manual dR matching
      for (const Particle& b : bHadrons) {
        if (deltaR(j, b) < 0.3) {
          // jet matched to B hadron!
          if (!bPt) bPt = j.pT() / GeV; // leading b-jet pT
          ++bjets;                      // count number of b-jets
          break;
        }
      }
    }
  }
  if (goodjets > 2) vetoEvent; // at most two jets
  if (!bjets) vetoEvent;       // at least one of them b-tagged

  const double ncomb = 3.0; //< ?
  _njet->fill(goodjets);
  _njet->fill(ncomb);

  if (goodjets == 1)
    _jet1_bPt->fill(bPt);
  else if (goodjets == 2)
    _jet2_bPt->fill(bPt);
}


void finalize() {
  const double sf = _mode ? 1.0 : 0.5;
  const double xs_pb = sf * crossSection() / picobarn / sumOfWeights();
  const double xs_fb = sf * crossSection() / femtobarn / sumOfWeights();
  scale(_njet, xs_pb);
  scale(_jet1_bPt, xs_fb);
  scale(_jet2_bPt, xs_fb);
}

private:

size_t _mode;

Histo1DPtr _njet;
Histo1DPtr _jet1_bPt;
Histo1DPtr _jet2_bPt;

};

RIVET_DECLARE_PLUGIN(ATLAS_2013_I1219109);

} ```