CMS_2015_I1346843.cc

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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/ChargedLeptons.hh"
#include "Rivet/Projections/NeutralFinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"

namespace Rivet {


  /// Differential cross-section of FSR photons in Z decays
  class CMS_2015_I1346843 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(CMS_2015_I1346843);

    /// Book histograms and initialise projections before the run
    void init() {

      Cut c_photons = Cuts::pT >= 5.0*GeV && (Cuts::etaIn(-2.5, 1.4) || Cuts::etaIn(1.6, 2.5));
      IdentifiedFinalState photons(c_photons);
      photons.acceptId(PID::PHOTON);
      declare(photons, "PHOTFS");

      Cut c_muons   = Cuts::pT > 9*GeV && Cuts::abseta < 2.4;
      IdentifiedFinalState muons(c_muons);
      muons.acceptIdPair(PID::MUON);
      declare(muons, "MUFS");


      _hist_pho_et           = bookHisto1D(1, 1, 1);  // photon transverse energy
      _hist_pho_et_wide      = bookHisto1D(1, 2, 1);  // photon transverse energy (0.5 < dr < 3.0)
      _hist_pho_et_close     = bookHisto1D(1, 3, 1);  // photon transverse energy (0.05 < dr < 0.5)
      _hist_pho_et_lqt       = bookHisto1D(1, 4, 1);  // photon transverse energy (q_T < 10)
      _hist_pho_et_hqt       = bookHisto1D(1, 5, 1);  // photon transverse energy (q_T > 50)
      _hist_pho_dr           = bookHisto1D(2, 1, 1);  // delta_R
      _hist_pho_dr_lqt       = bookHisto1D(2, 2, 1);  // delta_R (q_T < 10)
      _hist_pho_dr_hqt       = bookHisto1D(2, 3, 1);  // delta_R  (q_T > 50)
    }


    // Perform the per-event analysis
    void analyze(const Event& event) {

      const Particles muons = apply<IdentifiedFinalState>(event, "MUFS").particlesByPt();

      if (muons.size() < 2) vetoEvent;
      if (muons[0].pT()/GeV < 31) vetoEvent;
      if (muons[0].charge()*muons[1].charge() > 0) vetoEvent;
      const double mZ = (muons[0].momentum() + muons[1].momentum()).mass();
      if (!inRange(mZ, 30*GeV, 87*GeV)) vetoEvent;

      const Particles photons = apply<IdentifiedFinalState>(event, "PHOTFS").particlesByPt();
      // We want the photon with the highest pT that does not come from a decay
      foreach(const Particle& p, photons) {
        if (p.fromDecay() || !p.isStable()) continue;

        const double dR = std::min(deltaR(p, muons[0]), deltaR(p, muons[1]) );
        if (!inRange(dR, 0.05, 3.0)) continue;

        // Calculate the three-body (mu,mu,gamma) transverse momentum
        const double qT = (muons[0].mom() + muons[1].mom() + p.mom()).pT();

        // Fill the analysis histograms
        _hist_pho_et->fill(p.pT()/GeV, event.weight());
        _hist_pho_dr->fill(dR, event.weight());

        (dR <= 0.5 ? _hist_pho_et_close : _hist_pho_et_wide)->fill(p.pT()/GeV, event.weight());

        if (qT / GeV < 10.) {
          _hist_pho_et_lqt->fill(p.pT()/GeV, event.weight());
          _hist_pho_dr_lqt->fill(dR, event.weight());
        }

        if (qT / GeV > 50.) {
          _hist_pho_et_hqt->fill(p.pT()/GeV, event.weight());
          _hist_pho_dr_hqt->fill(dR, event.weight());
        }

        break; // Exit the loop since we found the highest pT lepton already
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_hist_pho_et,       crossSection() / sumOfWeights());
      scale(_hist_pho_et_wide,  crossSection() / sumOfWeights());
      scale(_hist_pho_et_close, crossSection() / sumOfWeights());
      scale(_hist_pho_et_lqt,   crossSection() / sumOfWeights());
      scale(_hist_pho_et_hqt,   crossSection() / sumOfWeights());
      scale(_hist_pho_dr,       crossSection() / sumOfWeights());
      scale(_hist_pho_dr_lqt,   crossSection() / sumOfWeights());
      scale(_hist_pho_dr_hqt,   crossSection() / sumOfWeights());
    }


  private:

    Histo1DPtr _hist_pho_et;
    Histo1DPtr _hist_pho_et_wide, _hist_pho_et_close;
    Histo1DPtr _hist_pho_et_lqt,  _hist_pho_et_hqt;
    Histo1DPtr _hist_pho_dr;
    Histo1DPtr _hist_pho_dr_lqt, _hist_pho_dr_hqt;

  };


  DECLARE_RIVET_PLUGIN(CMS_2015_I1346843);

}