Rivet analyses

title: MC_PHOTONJETS

Monte Carlo validation observables for photon + jets production

Experiment: ()

Status: VALIDATED

Authors: - Frank Siegert

References: none listed

Beams: * *

Beam energies: ANY

Run details: - Tevatron Run II ppbar -> gamma + jets.

Different observables related to the photon and extra jets.

Source code:MC_PHOTONJETS.cc

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

include "Rivet/Analyses/MC_JETS_BASE.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/LeadingParticlesFinalState.hh"

include "Rivet/Projections/VetoedFinalState.hh"

namespace Rivet {

/// @brief MC validation analysis for photon + jets events class MC_PHOTONJETS : public MC_JETS_BASE { public:

/// Default constructor
MC_PHOTONJETS()
    : MC_JETS_BASE("MC_PHOTONJETS", 4, "Jets") { }


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

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

  // set ptcut from input option
  const double jetptcut = getOption<double>("PTJMIN", 20.0);
  _jetptcut = jetptcut * GeV;

  // set clustering radius from input option
  const double R = getOption<double>("R", 0.4);

  // set clustering algorithm from input option
  JetAlg clusterAlgo;
  const string algoopt = getOption("ALGO", "ANTIKT");
  if (algoopt == "KT") {
    clusterAlgo = JetAlg::KT;
  }
  else if (algoopt == "CA") {
    clusterAlgo = JetAlg::CA;
  }
  else if (algoopt == "ANTIKT") {
    clusterAlgo = JetAlg::ANTIKT;
  }
  else {
    MSG_WARNING("Unknown jet clustering algorithm option " + algoopt + ". Defaulting to anti-kT");
    clusterAlgo = JetAlg::ANTIKT;
  }

  // set photon cuts from input options
  const double etacut = getOption<double>("ABSETAGAMMAX", 2.5);
  const double ptcut = getOption<double>("PTGAMMIN", 30.);

  // Get leading photon
  LeadingParticlesFinalState photonfs(FinalState(Cuts::abseta < etacut && Cuts::pT >= ptcut * GeV));
  photonfs.addParticleId(PID::PHOTON);
  declare(photonfs, "LeadingPhoton");

  // FS for jets excludes the leading photon
  VetoedFinalState vfs(fs);
  vfs.addVetoOnThisFinalState(photonfs);
  declare(vfs, "JetFS");
  FastJets jetpro(vfs, clusterAlgo, R);
  declare(jetpro, "Jets");

  book(_h_photon_jet1_deta, "photon_jet1_deta", 50, -5.0, 5.0);
  book(_h_photon_jet1_dphi, "photon_jet1_dphi", 20, 0.0, M_PI);
  book(_h_photon_jet1_dR, "photon_jet1_dR", 25, 0.5, 7.0);

  MC_JETS_BASE::init();
}


/// Do the analysis
void analyze(const Event& e) {
  // Get the photon
  /// @todo share IsolatedPhoton projection between all MC_*PHOTON* analyses
  const Particles photons = apply<FinalState>(e, "LeadingPhoton").particles();
  if (photons.size() != 1) {
    vetoEvent;
  }
  const FourMomentum photon = photons.front().momentum();

  // Get all charged particles
  const FinalState& fs = apply<FinalState>(e, "JetFS");
  if (fs.empty()) {
    vetoEvent;
  }

  // Passed cuts, so get the weight

  // Isolate photon by ensuring that a 0.4 cone around it contains less than 7% of the photon's energy
  const double egamma = photon.E();
  double econe = 0.0;
  for (const Particle& p : fs.particles()) {
    if (deltaR(photon, p.momentum()) < 0.4) {
      econe += p.E();
      // Veto as soon as E_cone gets larger
      if (econe / egamma > 0.07) {
        vetoEvent;
      }
    }
  }

  const Jets& jets = apply<FastJets>(e, "Jets").jetsByPt(Cuts::pT > _jetptcut);
  if (jets.size() > 0) {
    _h_photon_jet1_deta->fill(photon.eta() - jets[0].eta());
    _h_photon_jet1_dphi->fill(mapAngle0ToPi(photon.phi() - jets[0].phi()));
    _h_photon_jet1_dR->fill(deltaR(photon, jets[0].momentum()));
  }

  MC_JETS_BASE::analyze(e);
}


// Finalize
void finalize() {
  scale(_h_photon_jet1_deta, crossSectionPerEvent());
  scale(_h_photon_jet1_dphi, crossSectionPerEvent());
  scale(_h_photon_jet1_dR, crossSectionPerEvent());

  MC_JETS_BASE::finalize();
}

/// @}

private:

/// @name Histograms
/// @{
Histo1DPtr _h_photon_jet1_deta;
Histo1DPtr _h_photon_jet1_dphi;
Histo1DPtr _h_photon_jet1_dR;
/// @}

};

RIVET_DECLARE_PLUGIN(MC_PHOTONJETS);

} ```