Rivet analyses

title: MC_DIPHOTON

Monte Carlo validation observables for diphoton production at LHC

Experiment: ()

Status: VALIDATED

Authors: - Frank Siegert

References: none listed

Beams: * *

Beam energies: ANY

Run details: - LHC pp -> jet+jet, photon+jet, photon+photon, all with EW+QCD shower

Different observables related to the two photons

Source code:MC_DIPHOTON.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/IdentifiedFinalState.hh"

namespace Rivet {

/// @brief MC validation analysis for isolated di-photon events class MC_DIPHOTON : public Analysis { public:

/// Constructor
MC_DIPHOTON()
    : Analysis("MC_DIPHOTON") { }


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

void init() {
  FinalState fs;
  declare(fs, "FS");

  // set photon cuts from input options
  const double etacut = getOption<double>("ABSETAGAMMAX", 2.);
  const double ptcut = getOption<double>("PTGAMMIN", 20.);

  IdentifiedFinalState ifs(Cuts::abseta < etacut && Cuts::pT > ptcut * GeV);
  ifs.acceptId(PID::PHOTON);
  declare(ifs, "IFS");

  book(_h_m_PP, "m_PP", logspace(50, 1.0, 0.25 * (sqrtS() > 0. ? sqrtS() : 14000.)));
  book(_h_pT_PP, "pT_PP", logspace(50, 1.0, 0.25 * (sqrtS() > 0. ? sqrtS() : 14000.)));
  book(_h_pT_P1, "pT_P1", 50, 0.0, 70.0);
  book(_h_pT_P2, "pT_P2", 50, 0.0, 70.0);
  book(_h_dphi_PP, "dphi_PP", 20, 0.0, M_PI);
}


void analyze(const Event& event) {

  const Particles& photons = apply<IdentifiedFinalState>(event, "IFS").particlesByPt();

  if (photons.size() < 2) {
    vetoEvent;
  }

  // Isolate photons with ET_sum in cone
  Particles isolated_photons;
  const Particles& fs = apply<FinalState>(event, "FS").particlesByPt();
  for (const Particle& photon : photons) {
    FourMomentum mom_in_cone;
    double eta_P = photon.eta();
    double phi_P = photon.phi();
    for (const Particle& p : fs) {
      if (deltaR(eta_P, phi_P, p.eta(), p.phi()) < 0.4) {
        mom_in_cone += p.momentum();
      }
    }
    if (mom_in_cone.Et() - photon.Et() < 4.0 * GeV) {
      isolated_photons.push_back(photon);
    }
  }

  if (isolated_photons.size() != 2) {
    vetoEvent;
  }

  _h_pT_P1->fill(isolated_photons[0].pT());
  _h_pT_P2->fill(isolated_photons[1].pT());
  FourMomentum mom_PP = isolated_photons[0].momentum() + isolated_photons[1].momentum();
  _h_m_PP->fill(mom_PP.mass());
  _h_pT_PP->fill(mom_PP.pT());
  _h_dphi_PP->fill(deltaPhi(isolated_photons[0].phi(), isolated_photons[1].phi()));
}


void finalize() {
  scale(_h_m_PP, crossSection() / picobarn / sumOfWeights());
  scale(_h_pT_PP, crossSection() / picobarn / sumOfWeights());
  scale(_h_pT_P1, crossSection() / picobarn / sumOfWeights());
  scale(_h_pT_P2, crossSection() / picobarn / sumOfWeights());
  scale(_h_dphi_PP, crossSection() / picobarn / sumOfWeights());
}

/// @}

private:

/// @name Histograms
/// @{
Histo1DPtr _h_m_PP;
Histo1DPtr _h_pT_PP;
Histo1DPtr _h_pT_P1;
Histo1DPtr _h_pT_P2;
Histo1DPtr _h_dphi_PP;
/// @}

};

RIVET_DECLARE_PLUGIN(MC_DIPHOTON);

} ```