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 // -*- C++ -*-
 //
 // PScalarVectorFermionsDecayer.h is a part of Herwig - A multi-purpose Monte Carlo event generator
 // Copyright (C) 2002-2019 The Herwig Collaboration
 //
 // Herwig is licenced under version 3 of the GPL, see COPYING for details.
 // Please respect the MCnet academic guidelines, see GUIDELINES for details.
 //
 #ifndef THEPEG_PScalarVectorFermionsDecayer_H
 #define THEPEG_PScalarVectorFermionsDecayer_H
 //
 // This is the declaration of the PScalarVectorFermionsDecayer class.
 //
 #include "Herwig/Decay/DecayIntegrator.h"
 #include "Herwig/Decay/PhaseSpaceMode.h"
 #include "ThePEG/Helicity/LorentzPolarizationVector.h"
 #include "ThePEG/Helicity/LorentzSpinorBar.h"
 
 namespace Herwig {
 using namespace ThePEG;
 
 /**  \ingroup Decay
  *
  * The <code>PScalarVectorFermionsDecayer</code> class is designed for the decay of a 
  * pseudoscalar meson to a spin-1 particle and a fermion-antifermion pair. In practice
  * these decays are of the form \f$\gamma\ell^+\ell^-\f$ and the propagator of
  * the off-shell boson is taken to be \f$\frac1{m^2_{f\bar{f}}}\f$.
  * There is also the option of including a vector meson dominance
  * form-factor.
  *
  *  In this case the matrix element is
  *  \f[\mathcal{M} = \frac{g}{m^2_{f\bar{f}}}
  *                   \epsilon^{\mu\nu\alpha\beta}p_{V\mu}\epsilon_{V\nu}
  *                   \bar{u}(p_f)\gamma_\alpha v(p_{\bar{f}}) p_{f\bar{f}\beta}
  *  \f]
  *  It includes the option of a vector meson dominance (VMD) type form factor  
  *  \f$\frac{-M^2+i\Gamma M}{(m^2_{f\bar{f}}-M^2+i\Gamma M)}\f$.
  *    
  *  The incoming pseudoscalar meson, the outgoing vector, the fermion and antifermion
  *  and the coupling can be specified using the relevant interfaces.
  *
  * @see DecayIntegrator
  * @see PScalarVectorVectorDecayer
  * @see PScalar4FermionsDecayer
  * 
  *  \author Peter Richardson
  *
  */
 class PScalarVectorFermionsDecayer: public DecayIntegrator {
 
 public:
 
   /**
    * Default constructor.
    */
   PScalarVectorFermionsDecayer();
   
   /**
    * Which of the possible decays is required
    * @param cc Is this mode the charge conjugate
    * @param parent The decaying particle
    * @param children The decay products
    */
   virtual int modeNumber(bool & cc, tcPDPtr parent, 
              const tPDVector & children) const;
 
   /**
    * Return the matrix element squared for a given mode and phase-space channel.
    * @param ichan The channel we are calculating the matrix element for. 
    * @param part The decaying Particle.
    * @param outgoing The particles produced in the decay
    * @param momenta  The momenta of the particles produced in the decay
    * @param meopt Option for the calculation of the matrix element
    * @return The matrix element squared for the phase-space configuration.
    */
   double me2(const int ichan,const Particle & part,
          const tPDVector & outgoing,
          const vector<Lorentz5Momentum> & momenta,
          MEOption meopt) const;
 
   /**
    *   Construct the SpinInfos for the particles produced in the decay
    */
   virtual void constructSpinInfo(const Particle & part,
                  ParticleVector outgoing) const;
 
   /**
    * Method to return an object to calculate the 3 body partial width.
    * @param dm The DecayMode
    * @return A pointer to a WidthCalculatorBase object capable of calculating the width
    */
   virtual WidthCalculatorBasePtr threeBodyMEIntegrator(const DecayMode & dm) const;
   
   /**
    * The differential three body decay rate with one integral performed.
    * @param imode The mode for which the matrix element is needed.
    * @param q2 The scale, \e i.e. the mass squared of the decaying particle.
    * @param s  The invariant mass which still needs to be integrate over.
    * @param m1 The mass of the first  outgoing particle.
    * @param m2 The mass of the second outgoing particle.
    * @param m3 The mass of the third  outgoing particle.
    * @return The differential rate \f$\frac{d\Gamma}{ds}\f$
    */
   virtual InvEnergy threeBodydGammads(const int imode, const Energy2 q2, 
                       const Energy2 s,
                       const Energy m1, const Energy m2, 
                       const Energy m3) const;
 
   /**
    * Output the setup information for the particle database
    * @param os The stream to output the information to
    * @param header Whether or not to output the information for MySQL
    */
   virtual void dataBaseOutput(ofstream & os,bool header) const;
 
 public:
 
   /** @name Functions used by the persistent I/O system. */
   //@{
   /**
    * Function used to write out object persistently.
    * @param os the persistent output stream written to.
    */
   void persistentOutput(PersistentOStream & os) const;
 
   /**
    * Function used to read in object persistently.
    * @param is the persistent input stream read from.
    * @param version the version number of the object when written.
    */
   void persistentInput(PersistentIStream & is, int version);
   //@}
 
   /**
    * Standard Init function used to initialize the interfaces.
    */
   static void Init();
 
 protected:
 
   /** @name Clone Methods. */
   //@{
   /**
    * Make a simple clone of this object.
    * @return a pointer to the new object.
    */
   virtual IBPtr clone() const {return new_ptr(*this);}
 
   /** Make a clone of this object, possibly modifying the cloned object
    * to make it sane.
    * @return a pointer to the new object.
    */
   virtual IBPtr fullclone() const {return new_ptr(*this);}
   //@}
 
 protected:
 
   /** @name Standard Interfaced functions. */
   //@{
   /**
    * Initialize this object after the setup phase before saving and
    * EventGenerator to disk.
    * @throws InitException if object could not be initialized properly.
    */
   virtual void doinit();
 
   /**
    * Initialize this object to the begining of the run phase.
    */
   virtual void doinitrun();
   //@}
 
 private:
 
   /**
    * Private and non-existent assignment operator.
    */
   PScalarVectorFermionsDecayer & operator=(const PScalarVectorFermionsDecayer &) = delete;
 
 public:
 
   /**
    *   Set the parameters for a decay mode
    */
   string setUpDecayMode(string arg);
 
 private:
 
   /**
    * coupling for a decay
    */
   vector<InvEnergy> coupling_;
 
   /**
    * the PDG codes for the incoming particles
    */
   vector<int> incoming_;
 
   /**
    * the PDG codes for the outgoing vector
    */
   vector<pair<long,long> > outgoing_;
 
   /**
    * maximum weight for a decay
    */
   vector<double> maxweight_;
 
   /**
    * Include the VMD factor
    */
   vector<int> includeVMD_;
 
   /**
    * PDG code for thte particle to use in the VMD factor.
    */
   vector<int> VMDid_;
 
   /**
    * Mass to use in the VMD factor.
    */
   vector<Energy> VMDmass_;
 
   /**
    * Width to use in the VMD factor.
    */
   vector<Energy> VMDwidth_;
   /**
    *  Spin density matrix
    */
   mutable RhoDMatrix rho_;
 
   /**
    *  Polarization vectors for the decay product
    */
   mutable vector<Helicity::LorentzPolarizationVector> vectors_;
 
   /**
    *  Spinors for the fermions
    */
   mutable vector<Helicity::LorentzSpinor   <SqrtEnergy> > wave_;
 
   /**
    *  Barred spinors for the fermions 
    */
   mutable vector<Helicity::LorentzSpinorBar<SqrtEnergy> > wavebar_;
 };
 
 }
 
 
 #endif /* THEPEG_PScalarVectorFermionsDecayer_H */

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