WFinder.hh

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// -*- C++ -*-
#ifndef RIVET_WFinder_HH
#define RIVET_WFinder_HH

#include "Rivet/Projections/FinalState.hh"

namespace Rivet {


  /// @brief Convenience finder of leptonically decaying Ws
  ///
  /// Chain together different projections as convenience for finding W's
  /// from two leptons in the final state, including photon clustering.
  ///
  /// @todo Inherit directly from ParticleFinder, not FinalState
  class WFinder : public FinalState {
  public:

    enum ClusterPhotons { NOCLUSTER=0, CLUSTERNODECAY=1, CLUSTERALL };
    enum PhotonTracking { NOTRACK=0, TRACK=1 };
    enum MassWindow { MASS=0, TRANSMASS=1 };

    /// @name Constructors
    //@{

    /// Constructor taking cuts object
    /// @param inputfs Input final state
    /// @param cuts charged lepton cuts
    /// @param pid type of the charged lepton
    /// @param minmass,maxmass (transverse) mass window
    /// @param missingET minimal amount of missing ET (neutrinos) required
    /// @param dRmax maximum dR of photons around charged lepton to take into account
    ///  for W reconstruction (only relevant if one of the following are true)
    /// @param clusterPhotons whether such photons are supposed to be
    ///  clustered to the lepton object and thus W mom
    /// @param trackPhotons whether such photons should be added to _theParticles
    /// @param masstype whether mass window should be applied using m or mT
    WFinder(const FinalState& inputfs,
            Cut cuts,
            PdgId pid,
            double minmass, double maxmass,
            double missingET,
            double dRmax=0.1, 
            ClusterPhotons clusterPhotons=CLUSTERNODECAY,
            PhotonTracking trackPhotons=NOTRACK,
            MassWindow masstype=MASS,
            double masstarget=80.4*GeV);

    /// Clone on the heap.
    virtual const Projection* clone() const {
      return new WFinder(*this);
    }

    //@}


    /// Access to the found bosons
    ///
    /// @note Currently either 0 or 1 boson can be found.
    const Particles& bosons() const { return _bosons; }

    /// Access to the found boson (assuming it exists)
    const Particle& boson() const { return _bosons[0]; }


    /// Access to the W constituent clustered leptons
    ///
    /// @note Either size 0 if no boson was found or 1 if one boson was found
    const Particles& constituentLeptons() const { return _constituentLeptons; }

    /// Access to the W constituent clustered lepton (assuming it exists)
    const Particle& constituentLepton() const { return _constituentLeptons[0]; }


    /// Access to the W constituent neutrinos
    ///
    /// @note Either size 0 if no boson was found or 1 if one boson was found
    const Particles& constituentNeutrinos() const { return _constituentNeutrinos; }

    /// Access to the W constituent neutrinos
    const Particle& constituentNeutrino() const { return _constituentNeutrinos[0]; }


    /// Access to the particles other than the W leptons and clustered photons
    ///
    /// Useful for e.g. input to a jet finder
    const FinalState& remainingFinalState() const;

    /// @brief Calculate the transverse mass of the W, from the charged lepton and neutrino
    ///
    /// Defined as sqrt(2 pT_l pT_nu (1.0 - cos(dphi_lnu))). Return -1 if no boson found.
    double mT() const {
      if (bosons().empty()) return -1;
      const FourMomentum& l = constituentLeptons()[0].momentum();
      const FourMomentum& nu = constituentNeutrinos()[0].momentum();
      return sqrt( 2 * l.pT() * nu.pT() * (1 - cos(deltaPhi(l, nu))) );
    }


  protected:

    /// Apply the projection on the supplied event.
    void project(const Event& e);

    /// Compare projections.
    int compare(const Projection& p) const;


  public:

    /// Clear the projection
    void clear() {
      _theParticles.clear();
      _bosons.clear();
      _constituentLeptons.clear();
      _constituentNeutrinos.clear();
    }

  private:

    /// Transverse mass cuts
    double _minmass, _maxmass, _masstarget;
    bool _useTransverseMass;

    /// Missing ET cut
    double _etMiss;

    /// Switch for tracking of photons (whether to add them to _theParticles)
    /// This is relevant when the ZFinder::_theParticles are to be excluded
    /// from e.g. the input to a jet finder, to specify whether the clustered
    /// photons are to be excluded as well.
    /// (Yes, some experiments make a difference between clusterPhotons and
    /// trackPhotons!)
    PhotonTracking _trackPhotons;

    /// Lepton flavour
    PdgId _pid;

    /// Neutrino flavour
    PdgId _nu_pid;

    /// list of found bosons (currently either 0 or 1)
    Particles _bosons;

    /// Constituent leptons (currently either 0 or 1)
    Particles _constituentLeptons;

    /// Constituent neutrinos (currently either 0 or 1)
    Particles _constituentNeutrinos;

  };


}


#endif