Rivet analyses

title: ATLAS_2010_I882463

Inclusive isolated prompt photon analysis

Experiment: ATLAS (LHC 7TeV)

Inspire ID: 882463

Status: VALIDATED

Authors: - Mike Hance

References: - Expt page: ATLAS-STDM-2010-08 - arXiv: 1012.4389

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - Inclusive photon+X events (primary gamma+jet events) at $\sqrt{s} = 7$~TeV.

A measurement of the cross section for inclusive isolated photon production at $\sqrt{s} = 7$ TeV. The measurement covers three ranges in $|\eta|$: [0.00,0.60), [0.60,1.37), and [1.52,1.81), for $E_T^\gamma>15$~GeV. The measurement uses 880~nb$^{-1}$ of integrated luminosity collected with the ATLAS detector.

Source code:ATLAS_2010_I882463.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/LeadingParticlesFinalState.hh"

namespace Rivet {

class ATLAS_2010_I882463 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2010_I882463);


/// Book histograms and initialise projections before the run
void init() {
  FinalState fs;
  declare(fs, "FS");

  FastJets fj(fs, JetAlg::KT, 0.5);
  fj.useJetArea(new fastjet::AreaDefinition(fastjet::VoronoiAreaSpec()));
  declare(fj, "KtJetsD05");

  LeadingParticlesFinalState photonfs(FinalState(Cuts::abseta < 1.81 && Cuts::pT > 15 * GeV));
  photonfs.addParticleId(PID::PHOTON);
  declare(photonfs, "LeadingPhoton");

  size_t hist_bin = 0;
  for (size_t i = 0; i < _eta_bins.size() - 1; ++i) {
    if (fabs(_eta_bins[i] - 1.37) < .0001) continue;
    book(_h_Et_photon[i], 1 + hist_bin, 1, 1);
    hist_bin += 1;
  }
}


size_t getEtaBin(double eta, bool area_eta) const {
  return (!area_eta) ? binIndex(fabs(eta), _eta_bins) : binIndex(fabs(eta), _eta_bins_areaoffset);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  Particles photons = apply<LeadingParticlesFinalState>(event, "LeadingPhoton").particles();
  if (photons.size() != 1) vetoEvent;

  const Particle& leadingPhoton = photons[0];
  if (inRange(leadingPhoton.abseta(), 1.37, 1.52)) vetoEvent;
  const int eta_bin = getEtaBin(leadingPhoton.abseta(), false);

  const Particles& fs = apply<FinalState>(event, "FS").particles();
  FourMomentum mom_in_EtCone;
  for (const Particle& p : fs) {
    // Check if it's in the cone of .4
    if (deltaR(leadingPhoton, p) >= 0.4) continue;
    // Check if it's in the 5x7 central core
    if (fabs(deltaEta(leadingPhoton, p)) < .025 * 5.0 * 0.5
        && fabs(deltaPhi(leadingPhoton, p)) < (PI / 128.) * 7.0 * 0.5)
      continue;
    // Increment
    mom_in_EtCone += p.momentum();
  }
  MSG_DEBUG("Done with initial Et cone");

  // Get the jet pT densities
  vector<vector<double>> ptDensities(_eta_bins_areaoffset.size() - 1);
  FastJets fastjets = apply<FastJets>(event, "KtJetsD05");
  const shared_ptr<fastjet::ClusterSequenceArea> clust_seq_area = fastjets.clusterSeqArea();
  for (const Jet& jet : fastjets.jets()) {
    const double area = clust_seq_area->area(jet); //< Implicit call to pseudojet()
    if (area > 1e-4 && jet.abseta() < _eta_bins_areaoffset.back()) {
      ptDensities.at(getEtaBin(jet.abseta(), true)) += jet.pT() / area;
    }
  }

  // Now compute the median energy densities
  vector<double> ptDensity;
  for (size_t b = 0; b < _eta_bins_areaoffset.size() - 1; ++b) {
    ptDensity += ptDensities[b].empty() ? 0 : median(ptDensities[b]);
  }

  // Now figure out the correction
  const double ETCONE_AREA = PI * .4 * .4 - (7.0 * .025) * (5.0 * PI / 128.);
  const double correction = ptDensity[getEtaBin(leadingPhoton.abseta(), true)] * ETCONE_AREA;
  MSG_DEBUG("Jet area correction done");

  // Shouldn't need to subtract photon
  // NB. Using expected cut at hadron/particle level, not cut at reco level
  if (mom_in_EtCone.Et() - correction /*-leadingPhoton.Et()*/ > 4.0 * GeV) vetoEvent;
  MSG_DEBUG("Passed isolation cut");

  // Fill histogram
  _h_Et_photon[eta_bin]->fill(leadingPhoton.Et() / GeV);
}


/// Normalise histograms etc., after the run
void finalize() {
  for (size_t i = 0; i < _eta_bins.size() - 1; ++i) {
    if (fabs(_eta_bins[i] - 1.37) < .0001) continue;
    scale(_h_Et_photon[i], crossSection() / nanobarn / sumOfWeights());
  }
}

private:

Histo1DPtr _h_Et_photon[6];

const vector<double> _eta_bins = {0.00, 0.60, 1.37, 1.52, 1.81};
const vector<double> _eta_bins_areaoffset = {0.0, 1.5, 3.0};

};

RIVET_DECLARE_ALIASED_PLUGIN(ATLAS_2010_I882463, ATLAS_2010_S8914702);

} ```

Aliases: - ATLAS_2010_S8914702