Rivet analyses

title: CDF_2006_I717572

b-jet cross section in Z + jets events

Experiment: CDF (Tevatron Run 2)

Inspire ID: 717572

Status: VALIDATED

Authors: - Lars Sonnenschein - Steffen Schumann

References: - Phys.Rev.D.74:032008,2006 - DOI: 10.1103/PhysRevD.74.032008 - arXiv: hep-ex/0605099

Beams: p- p+

Beam energies: (980.0, 980.0)GeV

Run details: - Z + jets events at $\sqrt{s} = 1960$ GeV. Jets min $\pT$ cut = 20~GeV, leptons min $\pT$ cut = 10~GeV

Measurement of the $b$-jet cross section in events with $Z$ boson in $p\bar{p}$ collisions at center-of-mass energy $\sqrt{s} = 1.96$ TeV. The data cover jet transverse momenta above 20 GeV and jet pseudorapidities in the range -1.5 to 1.5. $Z$ bosons are identified in their electron and muon decay modes in an invariant dilepton mass range between 66 and 116 GeV.

Source code:CDF_2006_I717572.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/ChargedFinalState.hh"

include "Rivet/Projections/ChargedLeptons.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/InvMassFinalState.hh"

include "Rivet/Projections/VetoedFinalState.hh"

namespace Rivet {

/// @brief CDF Run II analysis: jet \f$ p_T \f$ and \f$ \eta \f$ /// distributions in Z + (b) jet production /// /// @author Lars Sonnenschein /// /// This CDF analysis provides \f$ p_T \f$ and \f$ \eta \f$ distributions of /// jets in Z + (b) jet production, before and after tagging. class CDF_2006_I717572 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CDF_2006_I717572);


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

void init() {
  const FinalState fs(Cuts::abseta < 3.6);
  declare(fs, "FS");

  // Create a final state with any e+e- or mu+mu- pair with
  // invariant mass 76 -> 106 GeV and ET > 20 (Z decay products)
  vector<pair<PdgId, PdgId>> vids;
  vids.push_back(make_pair(PID::ELECTRON, PID::POSITRON));
  vids.push_back(make_pair(PID::MUON, PID::ANTIMUON));
  FinalState fs2((Cuts::etaIn(-3.6, 3.6)));
  InvMassFinalState invfs(fs2, vids, 66 * GeV, 116 * GeV);
  declare(invfs, "INVFS");

  // Make a final state without the Z decay products for jet clustering
  VetoedFinalState vfs(fs);
  vfs.addVetoOnThisFinalState(invfs);
  declare(vfs, "VFS");
  declare(FastJets(vfs, JetAlg::CDFMIDPOINT, 0.7), "Jets");

  // Book histograms
  book(_sigmaBJet, 1, 1, 1);
  book(_ratioBJetToZ, 2, 1, 1);
  book(_ratioBJetToJet, 3, 1, 1);
  book(_sumWeightsWithZ, "sumWeightsWithZ");
  book(_sumWeightsWithZJet, "sumWeightsWithZJet");
}


/// Do the analysis
void analyze(const Event& event) {
  // Check we have an l+l- pair that passes the kinematic cuts
  // Get the Z decay products (mu+mu- or e+e- pair)
  const InvMassFinalState& invMassFinalState = apply<InvMassFinalState>(event, "INVFS");
  const Particles& ZDecayProducts = invMassFinalState.particles();

  // Make sure we have at least 2 Z decay products (mumu or ee)
  if (ZDecayProducts.size() < 2) vetoEvent;
  //
  double Lep1Pt = ZDecayProducts[0].pT();
  double Lep2Pt = ZDecayProducts[1].pT();
  double Lep1Eta = ZDecayProducts[0].absrap(); ///< @todo This is y... should be abseta()?
  double Lep2Eta = ZDecayProducts[1].absrap(); ///< @todo This is y... should be abseta()?

  if (Lep1Eta > _LepEtaCut && Lep2Eta > _LepEtaCut) vetoEvent;
  if (ZDecayProducts[0].abspid() == 13 && Lep1Eta > 1. && Lep2Eta > 1.) vetoEvent;
  if (Lep1Pt < _Lep1PtCut && Lep2Pt < _Lep2PtCut) vetoEvent;

  _sumWeightsWithZ->fill();

  /// @todo Write out a warning if there are more than two decay products
  FourMomentum Zmom = ZDecayProducts[0].momentum() + ZDecayProducts[1].momentum();

  // Put all b-quarks in a vector
  /// @todo Use jet contents rather than accessing quarks directly
  Particles bquarks;
  /// @todo is this HepMC wrangling necessary?
  for (ConstGenParticlePtr p : HepMCUtils::particles(event.genEvent())) {
    if (std::abs(p->pdg_id()) == PID::BQUARK) {
      bquarks.push_back(Particle(*p));
    }
  }

  // Get jets
  const FastJets& jetpro = apply<FastJets>(event, "Jets");
  MSG_DEBUG("Jet multiplicity before any pT cut = " << jetpro.size());

  const PseudoJets& jets = jetpro.pseudojetsByPt();
  MSG_DEBUG("jetlist size = " << jets.size());

  int numBJet = 0;
  int numJet = 0;
  // for each b-jet plot the ET and the eta of the jet, normalise to the total cross section at the end
  // for each event plot N jet and pT(Z), normalise to the total cross section at the end
  for (PseudoJets::const_iterator jt = jets.begin(); jt != jets.end(); ++jt) {
    // select jets that pass the kinematic cuts
    if (jt->perp() > _JetPtCut && fabs(jt->rapidity()) <= _JetEtaCut) {
      ++numJet;
      // Does the jet contain a b-quark?
      /// @todo Use jet contents rather than accessing quarks directly
      bool bjet = false;
      for (const Particle& bquark : bquarks) {
        if (deltaR(jt->rapidity(), jt->phi(), bquark.rapidity(), bquark.phi()) <= _Rjet) {
          bjet = true;
          break;
        }
      } // end loop around b-jets
      if (bjet) {
        numBJet++;
      }
    }
  } // end loop around jets

  if (numJet > 0) _sumWeightsWithZJet->fill();
  if (numBJet > 0) {
    _sigmaBJet->fill(1960);
    _ratioBJetToZ->fill(1960);
    _ratioBJetToJet->fill(1960);
  }
}


/// Finalize
void finalize() {
  MSG_DEBUG("Total sum of weights = " << sumOfWeights());
  MSG_DEBUG("Sum of weights for Z production in mass range = " << dbl(*_sumWeightsWithZ));
  MSG_DEBUG("Sum of weights for Z+jet production in mass range = " << dbl(*_sumWeightsWithZJet));

  scale(_sigmaBJet, crossSection() / picobarn / sumOfWeights());
  scale(_ratioBJetToZ, 1.0 / *_sumWeightsWithZ);
  scale(_ratioBJetToJet, 1.0 / *_sumWeightsWithZJet);
}

/// @}

private:

/// @name Cuts and counters
/// @{
const double _Rjet = 0.7;
const double _JetPtCut = 20.;
const double _JetEtaCut = 1.5;
const double _Lep1PtCut = 18.;
const double _Lep2PtCut = 10.;
const double _LepEtaCut = 1.1;
/// @}

/// @name Cuts and counters
/// @{
CounterPtr _sumWeightsWithZ;
CounterPtr _sumWeightsWithZJet;
/// @}

/// @name Histograms
/// @{
BinnedHistoPtr<int> _sigmaBJet, _ratioBJetToZ, _ratioBJetToJet;
/// @}

};

RIVET_DECLARE_ALIASED_PLUGIN(CDF_2006_I717572, CDF_2006_S6653332);

} ```

Aliases: - CDF_2006_S6653332