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 // -*- C++ -*-
 //
 // PScalarLeptonNeutrinoDecayer.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_PScalarLeptonNeutrinoDecayer_H
 #define HERWIG_PScalarLeptonNeutrinoDecayer_H
 // This is the declaration of the PScalarLeptonNeutrinoDecayer class.
 
 #include "Herwig/Decay/DecayIntegrator.h"
 #include "ThePEG/Helicity/LorentzSpinorBar.h"
 
 namespace Herwig {
 using namespace ThePEG;
 
 /**  \ingroup Decay
  *
  * The PScalarLeptonNeutrinoDecayer class is designed for the decay of 
  * pseudoscalar mesons to a lepton and a neutrino. Although it can be used
  * for charged pion and kaon decays it is mainly intended for the leptonic
  * decays of bottom and charm mesons.
  *
  *  The matrix element is given by 
  * \f[\mathcal{M} = \frac1{\sqrt{2}}f_PG_FV_{CKM}m_l\bar{u}(p_{\ell})(1-\gamma_5)v(p_\nu),\f]
  * where
  * - \f$f_P\f$ is the pseudoscalar decay constant.
  * - \f$G_F\f$ is the Fermi constant
  * - \f$V_{CKM}\f$ is the relevant CKM matrix element
  * - \f$p_\ell\f$ is the momentum of the charged lepton
  * - \f$p_\nu\f$ is the momentum of the neutrino
  *
  * @see DecayIntegrator
  * 
  */
 class PScalarLeptonNeutrinoDecayer: public DecayIntegrator {
   
   /**
    * 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;
 
   /**
    * 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();
   //@}
 
 public:
 
   /**
    *   Set the parameters for a decay mode
    */
   string setUpDecayMode(string arg);
 
 private:
 
   /**
    * Private and non-existent assignment operator.
    */
   PScalarLeptonNeutrinoDecayer & operator=(const PScalarLeptonNeutrinoDecayer &) = delete;
 
 private:
 
   /**
    * the PDG code for the incoming particle
    */
   vector<int> incoming_;
 
   /**
    * the meson decay constant for a particular particle multiplied by the CKM matrix
    * element, \e i.e. \f$f_pV_{CKM}\f$
    */
   vector<Energy> decayConstant_;
 
   /**
    * which outgoing leptons are allowed for a particular decay
    */
   vector<unsigned int> leptons_;
 
   /**
    * The maximum weight for the integration of decay to (\f$e\nu_e\f$, \f$\mu\nu_\mu\f$,\f$\tau\nu_\tau\f$).
    */
   vector<array<double,3> > maxWeight_;
 
   /**
    *  Spin density matrix
    */
   mutable RhoDMatrix rho_;
 
   /**
    *  Spinors for the decay products
    */
   mutable vector<Helicity::LorentzSpinor   <SqrtEnergy> > wave_;
 
   /**
    *  barred spinors for the decay products
    */
   mutable vector<Helicity::LorentzSpinorBar<SqrtEnergy> > wavebar_;
 
 };
 
 }
 
 
 #endif /* HERWIG_PScalarLeptonNeutrinoDecayer_H */

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