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 // -*- C++ -*-
 //
 // TwoPionRhoCurrent.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_TwoPionRhoCurrent_H
 #define HERWIG_TwoPionRhoCurrent_H
 // This is the declaration of the TwoPionRhoCurrent class.
 
 #include "WeakCurrent.h"
 #include "ThePEG/PDT/EnumParticles.h"
 #include "Herwig/Utilities/Kinematics.h"
 #include "ThePEG/StandardModel/StandardModelBase.h"
 #include "Herwig/Decay/ResonanceHelpers.h"
 
 namespace Herwig {
 using namespace ThePEG;
 
 /**  \ingroup Decay
  *
  *  Weak current for the production of two mesons via the \f$\rho\f$ or \f$K^*\f$
  *  resonances.
  *  These currents are taken from tau decays.
  *
  *  The current takes the form
  *
  *  \f[J^\mu = \frac{\sqrt{2}}{\sum_k\alpha_k}\left((p_1-p_2)^\mu-\frac{(p_1-p_2)\cdot q}{q^2}q^\mu))\right)
  *   \sum_k \alpha_k B_{R_k}(q^2)
  *  \f]
  *  where
  *  - \f$p_{1,2}\f$ are the momenta of the outgoing mesons,
  *  - \f$q=p_1+p_2\f$,
  *  - \f$B_{R_k}(q^2)\f$ is the Breit-Wigner distribution for the intermediate vector
  *    meson \f$R_k\f$.
  *  - \f$\alpha_k\f$ is the weight for the resonance.
  *
  *   The Breit-Wigner term is summed over the \f$\rho\f$ or \f$K^*\f$ resonances that
  *   can contribute to a given decay.
  *
  *  The models of either Kuhn and Santamaria (Z. Phys. C48, 445 (1990))
  *  or Gounaris and Sakurai Phys. Rev. Lett. 21, 244 (1968) are supported for the
  *  shape of the Breit-Wigner distribution. The mixing parameters
  *  are taken from Phys.Rev.D61:112002,2000 (CLEO) for the decay \f$\pi^\pm\pi^0\f$ and
  *  the CLEO version of TAUOLA for the \f$K\pi\f$ decays.
  *
  * @see WeakCurrent.
  * 
  *  \author Peter Richardson
  *
  */
 class TwoPionRhoCurrent: public WeakCurrent {
 
 public:
 
   /**
    * Default constructor
    */
   TwoPionRhoCurrent();
 
   /** @name Methods for the construction of the phase space integrator. */
   //@{
   /**
    * Complete the construction of the decay mode for integration.classes inheriting
    * from this one.
    * This method is purely virtual and must be implemented in the classes inheriting
    * from WeakCurrent.
    * @param icharge   The total charge of the outgoing particles in the current.
    * @param resonance If specified only include terms with this particle
    * @param flavour Information on the required flavours of the quarks
    * @param imode     The mode in the current being asked for.
    * @param mode      The phase space mode for the integration
    * @param iloc      The location of the of the first particle from the current in
    *                  the list of outgoing particles.
    * @param ires      The location of the first intermediate for the current.
    * @param phase     The prototype phase space channel for the integration.
    * @param upp       The maximum possible mass the particles in the current are
    *                  allowed to have.
    * @return Whether the current was sucessfully constructed.
    */
   virtual bool createMode(int icharge, tcPDPtr resonance,
               FlavourInfo flavour,
               unsigned int imode,PhaseSpaceModePtr mode,
               unsigned int iloc,int ires,
               PhaseSpaceChannel phase, Energy upp );
 
   /**
    * The particles produced by the current. This just returns the two pseudoscalar
    * mesons and the photon.
    * @param icharge The total charge of the particles in the current.
    * @param imode The mode for which the particles are being requested
    * @param iq The PDG code for the quark
    * @param ia The PDG code for the antiquark
    * @return The external particles for the current.
    */
   virtual tPDVector particles(int icharge, unsigned int imode, int iq, int ia);
   //@}
 
   /**
    * Hadronic current. This method is purely virtual and must be implemented in
    * all classes inheriting from this one.
    * @param resonance If specified only include terms with this particle
    * @param flavour Information on the required flavours of the quarks
    * @param imode The mode
    * @param ichan The phase-space channel the current is needed for.
    * @param scale The invariant mass of the particles in the current.
    * @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 current. 
    */
   virtual vector<LorentzPolarizationVectorE> 
   current(tcPDPtr resonance,
       FlavourInfo flavour,
       const int imode, const int ichan,Energy & scale,
       const tPDVector & outgoing,
       const vector<Lorentz5Momentum> & momenta,
       DecayIntegrator::MEOption meopt) const;
 
   /**
    * Accept the decay. Checks the particles are the allowed mode.
    * @param id The id's of the particles in the current.
    * @return Can this current have the external particles specified.
    */
   virtual bool accept(vector<int> id);
 
   /**
    * Return the decay mode number for a given set of particles in the current. 
    * @param id The id's of the particles in the current.
    * @return The number of the mode
    */
   virtual unsigned int decayMode(vector<int> id);
 
   /**
    * 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
    * @param create Whether or not to add a statement creating the object
    */
   virtual void dataBaseOutput(ofstream & os,bool header,bool create) 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();
   //@}
 
 private:
 
   /**
    * Private and non-existent assignment operator.
    */
   TwoPionRhoCurrent & operator=(const TwoPionRhoCurrent &) = delete;
 
 private:
 
   /**
    * \f$p\f$-wave breit wigner for form-factors
    * @param q2 The scale \f$q^2\f$ for the Breit-Wigner
    * @param imodel Which of the two models for the Breit-Wigner shape to use.
    * @param ires   Which of the different multiplets to use.
    * @return The value of the Breit-Wigner distribution.
    */
   Complex BreitWigner(Energy2 q2, unsigned int imodel,
               unsigned int ires) const {
     // calculate the BW
     if(imodel==0) {
       return Resonance::BreitWignerPWave(q2,_mass[ires],_width[ires],
                      _massa[ires],_massb[ires]);
     }
     else if(imodel==1) {
       return Resonance::BreitWignerGS(q2,_mass[ires],_width[ires],
                       _massa[ires],_massb[ires],
                       _h0[ires],_dh[ires],_hres[ires]);
     }
     else
       assert(false);
   }
 
 private:
 
   /**
    * Weights for the different \f$\rho\f$ resonances in the current, \f$\alpha_k\f$.
    */
   //@{
   /**
    *  The Complex weight used in the calculation
    */
   vector<Complex> _piwgt;
 
   /**
    *  The magnitude for input
    */
   vector<double> _pimag;
 
   /**
    *  The phase for input
    */
   vector<double> _piphase;
   //@}
 
   /**
    * Model to use for the \f$\rho\f$ propagator.
    */
   int _pimodel;
 
   /**
    * Option not to use the physical masses and widths for the \f$\rho\f$.
    */
   bool _rhoparameters;
 
   /**
    * The masses of the \f$\rho\f$ resonances.
    */
   vector<Energy> _rhomasses;
 
   /**
    * The widths of the \f$\rho\f$ resonances.
    */
   vector<Energy> _rhowidths;
 
   /**
    * Parameters for the Breit-Wigners
    */
   //@{
   /**
    * The masses of the resonances
    */
   vector<Energy> _mass;
 
   /**
    * The widths of the resonances
    */
   vector<Energy> _width;
 
   /**
    * Masses of the decay products for the momentum calculation.
    */
   vector<Energy> _massa,_massb;
 
   /**
    * The function \f$\frac{\\hat{H}}{dq^2}\f$ at \f$q^2=m^2\f$ for the GS form of the
    *  Breit-Wigner
    */
   vector<double> _dh;
 
   /**
    * The function \f$\\hat{H}\f$ at \f$q^2=m^2\f$ for the GS form of the
    *  Breit-Wigner
    */
   vector<Energy2> _hres;
 
   /**
    * The \f$H(0)\f$ parameter  for the GS form of the
    *  Breit-Wigner
    */
   vector<Energy2> _h0;
   //@}
 };
 
 }
 
 
 #endif /* HERWIG_TwoPionRhoCurrent_H */

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