ATLAS_2011_I945498.cc

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// -*- C++ -*-
#include "Rivet/Analysis.hh"

#include "Rivet/Projections/ZFinder.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/LeadingParticlesFinalState.hh"
#include "Rivet/Projections/ClusteredPhotons.hh"


namespace Rivet {


  class ATLAS_2011_I945498 : public Analysis {
  public:

    /// @name Constructors etc.
    //@{

    /// Constructor
    ATLAS_2011_I945498()
      : Analysis("ATLAS_2011_I945498")
    {
      setNeedsCrossSection(true);
      for (size_t chn = 0; chn < 3; ++chn) {
        weights_nj0[chn] = 0.0;
        weights_nj1[chn] = 0.0;
        weights_nj2[chn] = 0.0;
        weights_nj3[chn] = 0.0;
        weights_nj4[chn] = 0.0;
      }
    }

    //@}


  public:

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

      // Set up projections
      ZFinder zfinder_mu(-2.4, 2.4, 20, PID::MUON, 66.0*GeV, 116.0*GeV, 0.1, true, false);
      addProjection(zfinder_mu, "ZFinder_mu");

      std::vector<std::pair<double, double> > eta_e;
      eta_e.push_back(make_pair(-2.47, -1.52));
      eta_e.push_back(make_pair(-1.37, 1.37));
      eta_e.push_back(make_pair(1.52, 2.47));
      ZFinder zfinder_el(eta_e, 20, PID::ELECTRON, 66.0*GeV, 116.0*GeV, 0.1, true, false);
      addProjection(zfinder_el, "ZFinder_el");

      // Define veto FS in order to prevent Z-decay products entering the jet algorithm
      VetoedFinalState remfs;
      remfs.addVetoOnThisFinalState(zfinder_el);
      remfs.addVetoOnThisFinalState(zfinder_mu);

      FastJets jets(remfs, FastJets::ANTIKT, 0.4);
      jets.useInvisibles();
      addProjection(jets, "jets");

      // 0=el, 1=mu, 2=comb
      for (size_t chn = 0; chn < 3; ++chn) {
        _h_njet_incl[chn]  = bookHisto1D(1, 1, chn+1);
        _h_njet_ratio[chn] = bookScatter2D(2, 1, chn+1);
        _h_ptjet[chn]      = bookHisto1D(3, 1, chn+1);
        _h_ptlead[chn]     = bookHisto1D(4, 1, chn+1);
        _h_ptseclead[chn]  = bookHisto1D(5, 1, chn+1);
        _h_yjet[chn]       = bookHisto1D(6, 1, chn+1);
        _h_ylead[chn]      = bookHisto1D(7, 1, chn+1);
        _h_yseclead[chn]   = bookHisto1D(8, 1, chn+1);
        _h_mass[chn]       = bookHisto1D(9, 1, chn+1);
        _h_deltay[chn]     = bookHisto1D(10, 1, chn+1);
        _h_deltaphi[chn]   = bookHisto1D(11, 1, chn+1);
        _h_deltaR[chn]     = bookHisto1D(12, 1, chn+1);
      }
    }


    // Jet selection criteria universal for electron and muon channel
    /// @todo Replace with a Cut passed to jetsByPt
    Jets selectJets(const ZFinder* zf, const Event& event) {
      FourMomentum l1 = zf->constituents()[0].momentum();
      FourMomentum l2 = zf->constituents()[1].momentum();
      Jets jets;
      foreach (const Jet& jet, applyProjection<FastJets>(event, "jets").jetsByPt(30.0*GeV)) {
        FourMomentum jmom = jet.momentum();
        if (fabs(jmom.rapidity()) < 4.4 && deltaR(l1, jmom) > 0.5  && deltaR(l2, jmom) > 0.5) {
          jets.push_back(jet);
        }
      }
      return jets;
    }


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

      const double weight = event.weight();

      vector<const ZFinder*> zfs;
      zfs.push_back(& (applyProjection<ZFinder>(event, "ZFinder_el")));
      zfs.push_back(& (applyProjection<ZFinder>(event, "ZFinder_mu")));

      // Require exactly one electronic or muonic Z-decay in the event
      if (!( (zfs[0]->bosons().size() == 1 && zfs[1]->bosons().size() != 1) ||
             (zfs[1]->bosons().size() == 1 && zfs[0]->bosons().size() != 1) )) vetoEvent;
      int chn = zfs[0]->bosons().size() == 1 ? 0 : 1;

      Jets jets = selectJets(zfs[chn], event);

      /// @todo Holger wrote in his commit message that the njet_ratio
      /// histograms need fixing/checking, and therefore the analysis
      /// is marked unvalidated!

      // Some silly weight counters for the njet-ratio histo
      // --- not sure about the njet=0 case, the Figure caption says
      // that selected events require at least one jet with 20 GeV
      switch (jets.size()) {
      case 0:
        weights_nj0[chn] += weight;
        break;
      case 1:
        weights_nj0[chn] += weight;
        weights_nj1[chn] += weight;
        break;
      case 2:
        weights_nj0[chn] += weight;
        weights_nj1[chn] += weight;
        weights_nj2[chn] += weight;
        break;
      case 3:
        weights_nj0[chn] += weight;
        weights_nj1[chn] += weight;
        weights_nj2[chn] += weight;
        weights_nj3[chn] += weight;
        break;
      default: // >= 4
        weights_nj0[chn] += weight;
        weights_nj1[chn] += weight;
        weights_nj2[chn] += weight;
        weights_nj3[chn] += weight;
        weights_nj4[chn] += weight;
      }

      // Require at least one jet
      if (jets.size() < 1) vetoEvent;

      // Fill jet multiplicities
      _h_njet_incl[chn]->fill(jets.size(), weight);
      _h_njet_incl[2]->fill(jets.size(), weight);

      // Loop over selected jets, fill inclusive jet distributions
      for (size_t ijet = 0; ijet < jets.size(); ++ijet) {
        _h_ptjet[chn]->fill(jets[ijet].pT()/GeV, weight);
        _h_ptjet[2]  ->fill(jets[ijet].pT()/GeV, weight);
        _h_yjet[chn] ->fill(fabs(jets[ijet].rapidity()), weight);
        _h_yjet[2]   ->fill(fabs(jets[ijet].rapidity()), weight);
      }

      // Leading jet histos
      const double ptlead = jets[0].pT()/GeV;
      const double yabslead = fabs(jets[0].rapidity());
      _h_ptlead[chn]->fill(ptlead,   weight);
      _h_ptlead[2]  ->fill(ptlead,   weight);
      _h_ylead[chn] ->fill(yabslead, weight);
      _h_ylead[2]   ->fill(yabslead, weight);

      if (jets.size() >= 2) {
        // Second jet histos
        const double pt2ndlead   = jets[1].pT()/GeV;
        const double yabs2ndlead = fabs(jets[1].rapidity());
        _h_ptseclead[chn] ->fill(pt2ndlead,   weight);
        _h_ptseclead[2]   ->fill(pt2ndlead,   weight);
        _h_yseclead[chn]  ->fill(yabs2ndlead, weight);
        _h_yseclead[2]    ->fill(yabs2ndlead, weight);

        // Dijet histos
        const double deltaphi = fabs(deltaPhi(jets[1], jets[0]));
        const double deltarap = fabs(jets[0].rapidity() - jets[1].rapidity()) ;
        const double deltar   = fabs(deltaR(jets[0], jets[1], RAPIDITY));
        const double mass     = (jets[0].momentum() + jets[1].momentum()).mass();
        _h_mass[chn]    ->fill(mass,     weight);
        _h_mass[2]      ->fill(mass,     weight);
        _h_deltay[chn]  ->fill(deltarap, weight);
        _h_deltay[2]    ->fill(deltarap, weight);
        _h_deltaphi[chn]->fill(deltaphi, weight);
        _h_deltaphi[2]  ->fill(deltaphi, weight);
        _h_deltaR[chn]  ->fill(deltar,   weight);
        _h_deltaR[2]    ->fill(deltar,   weight);
      }

    }


    /// @name Ratio calculator util functions
    //@{

    /// Calculate the ratio, being careful about div-by-zero
    double ratio(double a, double b) {
      return (b != 0) ? a/b : 0;
    }

    /// Calculate the ratio error, being careful about div-by-zero
    double ratio_err(double a, double b) {
      return (b != 0) ? sqrt(a/sqr(b) + sqr(a)/(b*b*b)) : 0;
    }

    /// Calculate combined ratio from muon and electron channels
    double comb_ratio(double* as, double* bs) {
      return ratio(as[0]+as[1], bs[0]+bs[1]);
    }

    /// Calculate combined ratio error from muon and electron channels
    double comb_ratio_err(double* as, double* bs) {
      return ratio_err(as[0]+as[1], bs[0]+bs[1]);
    }

    //@}


    void finalize() {

      // Fill ratio histograms
      for (size_t chn = 0; chn < 2; ++chn) {
        _h_njet_ratio[chn]->addPoint(1, ratio(weights_nj1[chn], weights_nj0[chn]), 0, ratio_err(weights_nj1[chn], weights_nj0[chn]));
        _h_njet_ratio[chn]->addPoint(2, ratio(weights_nj2[chn], weights_nj1[chn]), 0, ratio_err(weights_nj2[chn], weights_nj1[chn]));
        _h_njet_ratio[chn]->addPoint(3, ratio(weights_nj3[chn], weights_nj2[chn]), 0, ratio_err(weights_nj3[chn], weights_nj2[chn]));
        _h_njet_ratio[chn]->addPoint(4, ratio(weights_nj4[chn], weights_nj3[chn]), 0, ratio_err(weights_nj4[chn], weights_nj3[chn]));
      }
      _h_njet_ratio[2]->addPoint(1, comb_ratio(weights_nj1, weights_nj0), 0, comb_ratio_err(weights_nj1, weights_nj0));
      _h_njet_ratio[2]->addPoint(2, comb_ratio(weights_nj2, weights_nj1), 0, comb_ratio_err(weights_nj2, weights_nj1));
      _h_njet_ratio[2]->addPoint(3, comb_ratio(weights_nj3, weights_nj2), 0, comb_ratio_err(weights_nj3, weights_nj2));
      _h_njet_ratio[2]->addPoint(4, comb_ratio(weights_nj4, weights_nj3), 0, comb_ratio_err(weights_nj4, weights_nj3));

      // Scale other histos
      const double xs = crossSectionPerEvent()/picobarn;
      for (size_t chn = 0; chn < 3; ++chn) {
        scale(_h_njet_incl[chn], xs);
        scale(_h_ptjet[chn]    , xs);
        scale(_h_ptlead[chn]   , xs);
        scale(_h_ptseclead[chn], xs);
        scale(_h_yjet[chn]     , xs);
        scale(_h_ylead[chn]    , xs);
        scale(_h_yseclead[chn] , xs);
        scale(_h_deltaphi[chn] , xs);
        scale(_h_deltay[chn]   , xs);
        scale(_h_deltaR[chn]   , xs);
        scale(_h_mass[chn]     , xs);
      }

    }

    //@}


  private:

    double weights_nj0[3];
    double weights_nj1[3];
    double weights_nj2[3];
    double weights_nj3[3];
    double weights_nj4[3];

    Scatter2DPtr _h_njet_ratio[3];
    Histo1DPtr _h_njet_incl[3];
    Histo1DPtr _h_ptjet[3];
    Histo1DPtr _h_ptlead[3];
    Histo1DPtr _h_ptseclead[3];
    Histo1DPtr _h_yjet[3];
    Histo1DPtr _h_ylead[3];
    Histo1DPtr _h_yseclead[3];
    Histo1DPtr _h_deltaphi[3];
    Histo1DPtr _h_deltay[3];
    Histo1DPtr _h_deltaR[3];
    Histo1DPtr _h_mass[3];

  };


  DECLARE_RIVET_PLUGIN(ATLAS_2011_I945498);


}