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 // -*- C++ -*-
 //
 // EtaPiPiPiDecayer.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_EtaPiPiPiDecayer_H
 #define HERWIG_EtaPiPiPiDecayer_H
 // This is the declaration of the EtaPiPiPiDecayer class.
 
 #include "Herwig/Decay/DecayIntegrator.h"
 #include "Herwig/Decay/PhaseSpaceMode.h"
 
 namespace Herwig {
 using namespace ThePEG;
 
 /** \ingroup Decay
  *
  * The <code>EtaPiPiPiDecayer</code> class is designed for the simulation of
  * the decay of the \f$\eta\f$ or \f$\eta'\f$ to either \f$\pi^+\pi^-\pi^0\f$ 
  * or \f$\pi^0\pi^0\pi^0\f$ and the decay of the \f$\eta'\f$ to 
  * \f$\pi^+\pi^-\eta\f$ or \f$\pi^0\pi^0\eta\f$
  *
  *  The matrix element takes the form 
  * \f[ |\mathcal{M}|^2 = N\left[1+ay+by^2+cx^2\right],\f]
  *  where 
  * \f[x = \frac{\sqrt{3}(u-t)}{2M_0(M_0-m_1-m_2-m_3)},\f]
  * \f[y = \frac{(m_1+m_2+m_3)((M_0-m_3)^2-s)}{2M_0(m_1+m_2)(M_0-m_1-m_2-m_3)}-1,\f]
  *  where 
  * - \f$m_{1,2,3}\f$ are the masses of the outgoing mesons
  * - \f$u = (p_0-p_1)^2\f$,
  * - \f$t = (p_0-p_2)^2\f$,
  * - \f$s = (p_0-p_3)^2\f$.
  *
  *  This form is taken from hep-ph/0301058 as are the experimental results for 
  * the constants which are used where available and the theory results which are
  * used when there is no experimental data. 
  *
  * @see DecayIntegrator
  * 
  */
 class EtaPiPiPiDecayer: public DecayIntegrator {
 
 public:
 
   /**
    * Default constructor.
    */
   EtaPiPiPiDecayer() {
     // no intermediates
     generateIntermediates(false);
   }
  
   
   /**
    * 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.
    */
   EtaPiPiPiDecayer & operator=(const EtaPiPiPiDecayer &) = delete;
 
 public:
 
   /**
    *   Set the parameters for a decay mode
    */
   string setUpDecayMode(string arg);
 
 private:
 
   /**
    * the id of the incoming particle
    */
   vector<int> incoming_;
 
   /**
    * the id of the last neutral meson
    */
   vector<int> outgoing_;
 
   /**
    * whether the pions are charged or neutral
    */
   vector<bool> charged_;
 
   /**
    * the prefactor for the decay
    */
   vector<double> prefactor_;
 
   /**
    * The constants for the matrix elements
    */
   //*{
   /**
    * The \f$a\f$ constant
    */
   vector<double> a_;
 
   /**
    * The \f$a\f$ constant
    */
   vector<double> b_;
 
   /**
    * The \f$a\f$ constant
    */
   vector<double> c_;
   //@}
 
   /**
    * maximum weights
    */
   vector<double> maxWeight_;
 
   /**
    *  Spin density matrix
    */
   mutable RhoDMatrix rho_;
 };
 
 }
 
 
 #endif /* HERWIG_EtaPiPiPiDecayer_H */

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