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 // -*- C++ -*-
 //
 // a1SimpleDecayer.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 HERWIG_a1SimpleDecayer_H
 #define HERWIG_a1SimpleDecayer_H
 //
 // This is the declaration of the a1SimpleDecayer class.
 //
 
 #include "Herwig/Decay/DecayIntegrator.h"
 #include "Herwig/Decay/PhaseSpaceMode.h"
 #include "ThePEG/Helicity/LorentzPolarizationVector.h"
 #include "Herwig/Decay/ResonanceHelpers.h"
 
 namespace Herwig {
 
 using namespace ThePEG;
 
 /**
  * The a1SimpleDecayer class provides a simple model of the decay of the
  * \f$a_1\f$ meson to three pions including \f$\rho\f$ meson intermediate states.
  *
  * @see \ref a1SimpleDecayerInterfaces "The interfaces"
  * defined for a1SimpleDecayer.
  */
 class a1SimpleDecayer: public DecayIntegrator {
 
 public:
 
   /**
    * The default constructor.
    */
   a1SimpleDecayer();
 
   /**
    * 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 matrix element to be integrated for the three-body decays as a function
    * of the invariant masses of pairs of the outgoing particles.
    * @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 s3 The invariant mass squared of particles 1 and 2, \f$s_3=m^2_{12}\f$.
    * @param s2 The invariant mass squared of particles 1 and 3, \f$s_2=m^2_{13}\f$.
    * @param s1 The invariant mass squared of particles 2 and 3, \f$s_1=m^2_{23}\f$.
    * @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 matrix element
    */
   virtual double threeBodyMatrixElement(const int imode , const Energy2 q2,
                     const Energy2 s3, const Energy2 s2,
                     const Energy2 s1, 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);
   //@}
 
   /**
    * The standard Init function used to initialize the interfaces.
    * Called exactly once for each class by the class description system
    * before the main function starts or
    * when this class is dynamically loaded.
    */
   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 an
    * EventGenerator to disk.
    * @throws InitException if object could not be initialized properly.
    */
   virtual void doinit();
 
   /**
    * Initialize this object. Called in the run phase just before
    * a run begins.
    */
   virtual void doinitrun();
   //@}
 
 private:
   
   /**
    * The \f$\rho\f$ form factors
    * @param q2 The scale \f$q^2\f$ for the Breit-Wigner
    * @param ires Which \f$\rho\f$ multiplet
    * @return The form factor
    */
   Complex rhoFormFactor(Energy2 q2,int ires) const {
     Complex output(0.),norm(0.);
     for(unsigned int ix=0;ix<3;++ix) norm += _rhowgts[ix];
     if(ires<0) {
       for(unsigned int ix=0;ix<3;++ix)
     output+=_rhowgts[ix]*Resonance::BreitWignerPWave(q2,_rhomass[ix],_rhowidth[ix],_mpi,_mpi);
     }
     else {
       assert(ires<3);
       output=_rhowgts[ires]*Resonance::BreitWignerPWave(q2,_rhomass[ires],_rhowidth[ires],_mpi,_mpi);
     }
     return output/norm;
   }
 
 private:
 
   /**
    * The assignment operator is private and must never be called.
    * In fact, it should not even be implemented.
    */
   a1SimpleDecayer & operator=(const a1SimpleDecayer &) = delete;
 
 private:
 
   /**
    * The \f$\rho\f$ masses
    */
   vector<Energy> _rhomass;
   
   /**
    * The \f$\rho\f$ widths
    */
   vector<Energy> _rhowidth;
 
   /**
    * Weights for the different \f$\rho\f$ resonances 
    */
   vector<double> _rhowgts;
 
   /**
    *  Use local values of the parameters
    */
   bool _localparameters;
 
   /**
    *  The overall coupling for the decay
    */
   InvEnergy _coupling;
 
   /**
    * Maximum weight for the one charged pion channel.
    */
   double _onemax;
 
   /**
    * Maximum weight for the two charged pion channel.
    */
   double _twomax;
 
   /**
    * Maximum weight for the three charged pion channel.
    */
   double _threemax;
   
   /**
    * Weights for the channels for the one charged pion channel.
    */
   vector<double> _onewgts;
   
   /**
    * Weights for the channels for the two charged pion channel.
    */
   vector<double> _twowgts;
   
   /**
    * Weights for the channels for the three charged pion channel.
    */
   vector<double> _threewgts;
 
   /**
    * The pion mass
    */
   Energy _mpi;
 
   /**
    *  Spin Density matrix
    */
   mutable RhoDMatrix _rho;
 
   /**
    *  Polarization vectors
    */
   mutable vector<Helicity::LorentzPolarizationVector> _vectors;
 
 };
 
 }
 
 #endif /* HERWIG_a1SimpleDecayer_H */

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