CDF_2008_S7541902.cc

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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/RivetAIDA.hh"
#include "Rivet/Tools/Logging.hh"
#include "Rivet/Tools/ParticleIdUtils.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/InvMassFinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include <algorithm>

namespace Rivet {


  /// @brief CDF jet pT and multiplicity distributions in W + jets events
  ///
  /// This CDF analysis provides jet pT distributions for 4 jet multiplicity bins
  /// as well as the jet multiplicity distribution in W + jets events.
  /// e-Print: arXiv:0711.4044 [hep-ex]
  class CDF_2008_S7541902 : public Analysis {
  public:

    /// Constructor
    CDF_2008_S7541902()
      : Analysis("CDF_2008_S7541902"),
        _electronETCut(20.0*GeV), _electronETACut(1.1),
        _eTmissCut(30.0*GeV), _mTCut(20.0*GeV),
        _jetEtCutA(20.0*GeV),  _jetEtCutB(25.0*GeV), _jetETA(2.0),
        _xpoint(1960.)
    {    }


    /// @name Analysis methods
    //@{

    void init() {
      // Set up projections
      // Basic FS
      FinalState fs(-3.6, 3.6);
      addProjection(fs, "FS");

      // Create a final state with any e-nu pair with invariant mass 65 -> 95 GeV and ET > 20 (W decay products)
      vector<pair<PdgId,PdgId> > vids;
      vids += make_pair(ELECTRON, NU_EBAR);
      vids += make_pair(POSITRON, NU_E);
      FinalState fs2(-3.6, 3.6, 20*GeV);
      InvMassFinalState invfs(fs2, vids, 65*GeV, 95*GeV);
      addProjection(invfs, "INVFS");

      // Make a final state without the W decay products for jet clustering
      VetoedFinalState vfs(fs);
      vfs.addVetoOnThisFinalState(invfs);
      addProjection(vfs, "VFS");
      addProjection(FastJets(vfs, FastJets::CDFJETCLU, 0.4), "Jets");

      // Book histograms
      for (int i = 0 ; i < 4 ; ++i) {
        _histJetEt[i] = bookHistogram1D(i+1, 1, 1);
        _histJetMultRatio[i] = bookDataPointSet(5 , 1, i+1);
        _histJetMult[i]   = bookHistogram1D(i+6, 1, 1);
      }
      _histJetMultNorm = bookHistogram1D("norm", 1, _xpoint, _xpoint+1.);
    }


    /// Do the analysis
    void analyze(const Event& event) {
      // Get the W decay products (electron and neutrino)
      const InvMassFinalState& invMassFinalState = applyProjection<InvMassFinalState>(event, "INVFS");
      const ParticleVector&  wDecayProducts = invMassFinalState.particles();

      FourMomentum electronP, neutrinoP;
      bool gotElectron(false), gotNeutrino(false);
      foreach (const Particle& p, wDecayProducts) {
        FourMomentum p4 = p.momentum();
        if (p4.Et() > _electronETCut && fabs(p4.eta()) < _electronETACut && abs(p.pdgId()) == ELECTRON) {
          electronP = p4;
          gotElectron = true;
        }
        else if (p4.Et() > _eTmissCut && abs(p.pdgId()) == NU_E) {
          neutrinoP = p4;
          gotNeutrino = true;
        }
      }

      // Veto event if the electron or MET cuts fail
      if (!gotElectron || !gotNeutrino) vetoEvent;

      // Veto event if the MTR cut fails
      double mT2 = 2.0 * ( electronP.pT()*neutrinoP.pT() - electronP.px()*neutrinoP.px() - electronP.py()*neutrinoP.py() );
      if (sqrt(mT2) < _mTCut ) vetoEvent;

      // Get the jets
      const JetAlg& jetProj = applyProjection<FastJets>(event, "Jets");
      Jets theJets = jetProj.jetsByEt(_jetEtCutA);
      size_t njetsA(0), njetsB(0);
      foreach (const Jet& j, theJets) {
        const FourMomentum pj = j.momentum();
        if (fabs(pj.rapidity()) < _jetETA) {
          // Fill differential histograms for top 4 jets with Et > 20
          if (njetsA < 4 && pj.Et() > _jetEtCutA) {
            ++njetsA;
            _histJetEt[njetsA-1]->fill(pj.Et(), event.weight());
          }
          // Count number of jets with Et > 25 (for multiplicity histograms)
          if (pj.Et() > _jetEtCutB) ++njetsB;
        }
      }

      // Jet multiplicity
      _histJetMultNorm->fill(_xpoint, event.weight());
      for (size_t i = 1; i <= njetsB; ++i) {
        _histJetMult[i-1]->fill(_xpoint, event.weight());
        if (i == 4) break;
      }
    }



    /// Finalize
    void finalize() {
      const double xsec = crossSection()/sumOfWeights();
      // Get the x-axis for the ratio plots
      /// @todo Replace with autobooking etc. once YODA in place
      std::vector<double> xval; xval.push_back(_xpoint);
      std::vector<double> xerr; xerr.push_back(.5);
      // Fill the first ratio histogram using the special normalisation histogram for the total cross section
      double ratio1to0 = 0.;
      if (_histJetMultNorm->binHeight(0) > 0.) ratio1to0 = _histJetMult[0]->binHeight(0)/_histJetMultNorm->binHeight(0);
      // Get the fractional error on the ratio histogram
      double frac_err1to0 = 0.;
      if (_histJetMult[0]->binHeight(0) > 0.)  frac_err1to0 = _histJetMult[0]->binError(0)/_histJetMult[0]->binHeight(0);
      if (_histJetMultNorm->binHeight(0) > 0.) {
        frac_err1to0 *= frac_err1to0;
        frac_err1to0 += pow(_histJetMultNorm->binError(0)/_histJetMultNorm->binHeight(0),2.);
        frac_err1to0 = sqrt(frac_err1to0);
      }

      /// @todo Replace with autobooking etc. once YODA in place
      vector<double> yval[4]; yval[0].push_back(ratio1to0);
      vector<double> yerr[4]; yerr[0].push_back(ratio1to0*frac_err1to0);
      _histJetMultRatio[0]->setCoordinate(0,xval,xerr);
      _histJetMultRatio[0]->setCoordinate(1,yval[0],yerr[0]);
      for (int i = 0; i < 4; ++i) {
        if (i < 3) {
          float ratio = 0.0;
          if (_histJetMult[i]->binHeight(0) > 0.0) ratio = _histJetMult[i+1]->binHeight(0)/_histJetMult[i]->binHeight(0);
          float frac_err = 0.0;
          if (_histJetMult[i]->binHeight(0) > 0.0) frac_err = _histJetMult[i]->binError(0)/_histJetMult[i]->binHeight(0);
          if (_histJetMult[i+1]->binHeight(0) > 0.0) {
            frac_err *= frac_err;
            frac_err += pow(_histJetMult[i+1]->binError(0)/_histJetMult[i+1]->binHeight(0),2.);
            frac_err = sqrt(frac_err);
          }
          yval[i+1].push_back(ratio);
          yerr[i+1].push_back(ratio*frac_err);
          _histJetMultRatio[i+1]->setCoordinate(0,xval,xerr);
          _histJetMultRatio[i+1]->setCoordinate(1,yval[i+1],yerr[i+1]);
        }
        _histJetEt[i]->scale(xsec);
        _histJetMult[i]->scale(xsec);
      }
      _histJetMultNorm->scale(xsec);
    }

    //@}


  private:

    /// @name Cuts
    //@{
    /// Cut on the electron ET:
    double _electronETCut;
    /// Cut on the electron ETA:
    double _electronETACut;
    /// Cut on the missing ET
    double _eTmissCut;
    /// Cut on the transverse mass squared
    double _mTCut;
    /// Cut on the jet ET for differential cross sections
    double _jetEtCutA;
    /// Cut on the jet ET for jet multiplicity
    double _jetEtCutB;
    /// Cut on the jet ETA
    double _jetETA;
    //@}

    double _xpoint;

    /// @name Histograms
    //@{
    AIDA::IHistogram1D* _histJetEt[4];
    AIDA::IHistogram1D* _histJetMultNorm;
    AIDA::IDataPointSet* _histJetMultRatio[4];
    AIDA::IHistogram1D* _histJetMult[4];
    //@}

  };



  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(CDF_2008_S7541902);

}