Rivet analyses

title: CDF_2008_I768451

Measurement of differential Z/$\gamma^*$ + jet + X cross sections

Experiment: CDF (Tevatron Run 2)

Inspire ID: 768451

Status: VALIDATED

Authors: - Frank Siegert

References: - Phys.Rev.Lett.100:102001,2008 - arXiv: 0711.3717

Beams: p- p+

Beam energies: (980.0, 980.0)GeV

Run details: - $p \bar{p} \to e^+ e^-$ + jets at 1960 GeV. Needs mass cut on lepton pair to avoid photon singularity, looser than $66 < m_{ee} < 116$

Cross sections as a function of jet transverse momentum in 1 and 2 jet events, and jet multiplicity in $p \bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV, based on an integrated luminosity of $1.7~\text{fb}^{-1}$. The measurements cover the rapidity region $|y_\text{jet}| < 2.1$ and the transverse momentum range $\pT^\text{jet} > 30~\GeV/c$.

Source code:CDF_2008_I768451.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/VetoedFinalState.hh"

namespace Rivet {

/// @brief Measurement differential Z/\f$ \gamma^* \f$ + jet + \f$ X \f$ cross sections /// /// @author Frank Siegert class CDF_2008_I768451 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(CDF_2008_I768451);


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

/// Book histograms
void init() {
  // Full final state
  FinalState fs((Cuts::etaIn(-5.0, 5.0)));
  declare(fs, "FS");

  // Leading electrons in tracking acceptance
  IdentifiedFinalState elfs(Cuts::abseta < 5 && Cuts::pT > 25 * GeV);
  elfs.acceptIdPair(PID::ELECTRON);
  declare(elfs, "LeadingElectrons");

  book(_h_jet_multiplicity, 1, 1, 1);
  book(_h_jet_pT_cross_section_incl_1jet, 2, 1, 1);
  book(_h_jet_pT_cross_section_incl_2jet, 3, 1, 1);
}


/// Do the analysis
void analyze(const Event& event) {
  // Skip if the event is empty
  const FinalState& fs = apply<FinalState>(event, "FS");
  if (fs.empty()) {
    MSG_DEBUG("Skipping event " << numEvents() << " because no final state pair found");
    vetoEvent;
  }

  // Find the Z candidates
  const FinalState& electronfs = apply<FinalState>(event, "LeadingElectrons");
  std::vector<std::pair<Particle, Particle>> Z_candidates;
  Particles all_els = electronfs.particles();
  for (size_t i = 0; i < all_els.size(); ++i) {
    for (size_t j = i + 1; j < all_els.size(); ++j) {
      bool candidate = true;
      double mZ = FourMomentum(all_els[i].momentum() + all_els[j].momentum()).mass() / GeV;
      if (mZ < 66.0 || mZ > 116.0) {
        candidate = false;
      }
      double abs_eta_0 = fabs(all_els[i].eta());
      double abs_eta_1 = fabs(all_els[j].eta());
      if (abs_eta_1 < abs_eta_0) {
        double tmp = abs_eta_0;
        abs_eta_0 = abs_eta_1;
        abs_eta_1 = tmp;
      }
      if (abs_eta_0 > 1.0) {
        candidate = false;
      }
      if (!(abs_eta_1 < 1.0 || (inRange(abs_eta_1, 1.2, 2.8)))) {
        candidate = false;
      }
      if (candidate) {
        Z_candidates.push_back(make_pair(all_els[i], all_els[j]));
      }
    }
  }
  if (Z_candidates.size() != 1) {
    MSG_DEBUG("Skipping event " << numEvents() << " because no unique electron pair found ");
    vetoEvent;
  }

  // Now build the jets on a FS without the electrons from the Z (including QED radiation)
  Particles jetparts;
  for (const Particle& p : fs.particles()) {
    bool copy = true;
    if (p.pid() == PID::PHOTON) {
      FourMomentum p_e0 = Z_candidates[0].first.momentum();
      FourMomentum p_e1 = Z_candidates[0].second.momentum();
      FourMomentum p_P = p.momentum();
      if (deltaR(p_e0, p_P) < 0.2) copy = false;
      if (deltaR(p_e1, p_P) < 0.2) copy = false;
    }
    else {
      if (HepMCUtils::uniqueId(p.genParticle())
          == HepMCUtils::uniqueId(Z_candidates[0].first.genParticle()))
        copy = false;
      if (HepMCUtils::uniqueId(p.genParticle())
          == HepMCUtils::uniqueId(Z_candidates[0].second.genParticle()))
        copy = false;
    }
    if (copy) jetparts.push_back(p);
  }

  // Proceed to lepton dressing
  const PseudoJets pjs = mkPseudoJets(jetparts);
  const auto jplugin = make_shared<fastjet::CDFMidPointPlugin>(0.7, 0.5, 1.0);
  const Jets jets_all = mkJets(fastjet::ClusterSequence(pjs, jplugin.get()).inclusive_jets());
  const Jets jets_cut = sortByPt(select(jets_all, Cuts::pT > 30 * GeV && Cuts::abseta < 2.1));
  // FastJets jetpro(JetAlg::CDFMIDPOINT, 0.7);
  // jetpro.calc(jetparts);
  // // Take jets with pt > 30, |eta| < 2.1:
  // const Jets& jets = jetpro.jets();
  // Jets jets_cut;
  // for (const Jet& j, jets) {
  //   if (j.pT()/GeV > 30.0 && j.abseta() < 2.1) {
  //     jets_cut.push_back(j);
  //   }
  // }
  // // Sort by pT:
  // sort(jets_cut.begin(), jets_cut.end(), cmpMomByPt);

  // Return if there are no jets:
  MSG_DEBUG("Num jets above 30 GeV = " << jets_cut.size());
  if (jets_cut.empty()) {
    MSG_DEBUG("No jets pass cuts ");
    vetoEvent;
  }

  // Cut on Delta R between Z electrons and *all* jets
  for (const Jet& j : jets_cut) {
    if (deltaR(Z_candidates[0].first, j) < 0.7) vetoEvent;
    if (deltaR(Z_candidates[0].second, j) < 0.7) vetoEvent;
  }

  // Fill histograms
  for (size_t njet = 1; njet <= jets_cut.size(); ++njet) {
    _h_jet_multiplicity->fill(njet);
  }
  for (const Jet& j : jets_cut) {
    if (jets_cut.size() > 0) {
      _h_jet_pT_cross_section_incl_1jet->fill(j.pT());
    }
    if (jets_cut.size() > 1) {
      _h_jet_pT_cross_section_incl_2jet->fill(j.pT());
    }
  }
}


/// Rescale histos
void finalize() {
  const double invlumi = crossSection() / femtobarn / sumOfWeights();
  scale(_h_jet_multiplicity, invlumi);
  scale(_h_jet_pT_cross_section_incl_1jet, invlumi);
  scale(_h_jet_pT_cross_section_incl_2jet, invlumi);
}

/// @}

private:

/// @name Histograms
/// @{
Histo1DPtr _h_jet_multiplicity;
Histo1DPtr _h_jet_pT_cross_section_incl_1jet;
Histo1DPtr _h_jet_pT_cross_section_incl_2jet;
/// @}

};

RIVET_DECLARE_ALIASED_PLUGIN(CDF_2008_I768451, CDF_2008_S7540469);

} ```

Aliases: - CDF_2008_S7540469