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 // -*- C++ -*-
 //
 // SMTopDecayer.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_SMTopDecayer_H
 #define HERWIG_SMTopDecayer_H
 //
 // This is the declaration of the SMTopDecayer class.
 //
 
 #include "Herwig/Decay/PerturbativeDecayer.h"
 #include "ThePEG/Helicity/Vertex/AbstractFFVVertex.h"
 #include "ThePEG/Helicity/Vertex/AbstractVVVVertex.h"
 #include "Herwig/Decay/PhaseSpaceMode.h"
 #include "Herwig/Models/StandardModel/StandardModel.h"
 #include "Herwig/Shower/ShowerAlpha.fh"
 
 namespace Herwig {
   using namespace ThePEG;
   using namespace ThePEG::Helicity;
   
 /**
  * \ingroup Decay
  *
  * The SMTopDecayer performs decays of the top quark into
  * the bottom quark and qqbar pairs or to the bottom quark and lepton 
  * neutrino pairs via W boson exchange.
  */
 class SMTopDecayer: public PerturbativeDecayer {
 
 public:
 
   /**
    * The default constructor.
    */
   SMTopDecayer();
 
 public:
 
   /**
    *  Virtual members to be overridden by inheriting classes
    *  which implement hard corrections 
    */
   //@{
   /**
    *  Has an old fashioned ME correction
    */
   virtual bool hasMECorrection() {return true;}
 
   /**
    *  Initialize the ME correction
    */
   virtual void initializeMECorrection(RealEmissionProcessPtr , double & ,
                       double & );
   
   /**
    * Apply the soft matrix element correction
    * @param parent The initial particle in the current branching
    * @param progenitor The progenitor particle of the jet
    * @param fs Whether the emission is initial or final-state
    * @param highestpT The highest pT so far in the shower
    * @param ids ids of the particles produced in the branching
    * @param z The momentum fraction of the branching
    * @param scale the evolution scale of the branching
    * @param pT The transverse momentum of the branching
    * @return If true the emission should be vetoed
    */
   virtual bool softMatrixElementVeto(PPtr parent,
                      PPtr progenitor,
                      const bool & fs,
                      const Energy & highestpT,
                      const vector<tcPDPtr> & ids,
                      const double & z,
                      const Energy & scale,
                      const Energy & pT);
 
   /**
    *  Has a POWHEG style correction
    */
   virtual POWHEGType hasPOWHEGCorrection() {return FSR;}
   //@}
 
 public:
 
   /**
    * Which of the possible decays is required
    */
   virtual int modeNumber(bool & , tcPDPtr , const tPDVector & ) const {return -1;}
 
   /**
    * Check if this decayer can perfom the decay for a particular mode.
    * Uses the modeNumber member but can be overridden
    * @param parent The decaying particle
    * @param children The decay products
    */
   virtual bool accept(tcPDPtr parent, const tPDVector & children) const;
 
   /**
    * For a given decay mode and a given particle instance, perform the
    * decay and return the decay products. As this is the base class this
    * is not implemented.
    * @return The vector of particles produced in the decay.
    */
   virtual ParticleVector decay(const Particle & 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 (or higher 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);
   //@}
 
   /**
    * 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:
 
   /**
    *  The integrand for the integrate partial width
    */
   Energy6 dGammaIntegrand(Energy2 mffb2, Energy2 mbf2, Energy mt, Energy mb, 
               Energy mf, Energy mfb, Energy mw) const;
 
 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. Called in the run phase just before
    * a run begins.
    */
   virtual void doinitrun();
   //@}
 
 protected:
 
   /**
    *  This function determines the point (\f$x_{g}\f$) where the condition that 
    *  \f$x_{a}\f$ be real supersedes that due to the external input 
    *  \f$\tilde{\kappa}\f$ where, again, \f$\kappa\f$ pertains to emissions from the 
    *  b.
    */
   double xgbcut(double);
 
   /**
    *  Full matrix element with a factor of \f$\frac{\alpha_SC_F}{x_g^2\pi}\f$ removed.
    * @param xw The momentum fraction of the W boson
    * @param xg The momentum fraction of the gluon.
    */
   double me(double xw, double xg);
 
 protected:
 
   /**
    *  Calculate matrix element ratio R/B
    */
   virtual double matrixElementRatio(const Particle & inpart, const ParticleVector & decay2,
                     const ParticleVector & decay3, MEOption meopt,
                     ShowerInteraction inter);
 
   /**
    *  LO matrix element for \f$t\to b W^\pm\f$
    */
   double loME(const Particle & inpart, const ParticleVector & decay);
 
   /**
    *  LO matrix element for \f$t\to b W^\pm\f$
    */
   double realME(const Particle & inpart, const ParticleVector & decay,
         ShowerInteraction inter);
   
 private:
 
   /**
    * The assignment operator is private and must never be called.
    * In fact, it should not even be implemented.
    */
   SMTopDecayer & operator=(const SMTopDecayer &) = delete;
   
   /**
    * Pointer to the W vertex
    */
   AbstractFFVVertexPtr FFWVertex_;
   
   /**
    * Pointer to the gluon vertex
    */
   AbstractFFVVertexPtr FFGVertex_;
   
   /**
    * Pointer to the photon vertex
    */
   AbstractFFVVertexPtr FFPVertex_;
   
   /**
    * Pointer to the photon vertex
    */
   AbstractVVVVertexPtr WWWVertex_;
   
   /**
    * Max weight for integration
    */
   //@{   
   /**
    * Weight \f$W\to q\bar{q}'\f$
    */
   vector<double> _wquarkwgt;
   
   /**
    * Weight \f$W\to \ell \nu\f$
    */
   vector<double> _wleptonwgt;
   //@}
 
   /**
    *  Pointer to the \f$W^\pm\f$
    */
   PDPtr _wplus;
 
   /**
    *  Spin density matrix for the decay
    */
   mutable RhoDMatrix _rho;
 
   /**
    *  1st spinor for the decay
    */
   mutable vector<SpinorWaveFunction   >   _inHalf;
 
   /**
    *  2nd spinor for the decay
    */
   mutable vector<SpinorWaveFunction   >   _outHalf;
 
   /**
    *  1st barred spinor for the decay
    */
   mutable vector<SpinorBarWaveFunction>   _inHalfBar;
 
   /**
    *  2nd barred spinor for the decay
    */
   mutable vector<SpinorBarWaveFunction>   _outHalfBar;
 
   /**
    *  The mass of the W boson
    */
   Energy _ma;
 
   /**
    *  The mass of the bottom quark
    */
   Energy _mc;
 
   /**
    *  The top mass
    */
   Energy _mt;
 
   /**
    *  The gluon mass.
    */
   Energy _mg;
 
   /**
    *  The mass ratio for the W.
    */
   double _a;
 
   /**
    *  The mass ratio for the bottom.
    */
   double _c;
 
   /**
    *  The mass ratio for the gluon.
    */
   double _g;
 
   /**
    *  Two times the energy fraction of a.
    */
   double _ktb;
 
   /**
    *  Two times the energy fraction of the gluon.
    */
   double _ktc;
 
 
   /**
    *  This determines the hard matrix element importance 
    *  sampling in _xg. _xg_sampling=2.0 samples as 1/xg^2.
    */
   double _xg_sampling;
 
   /**
    *  The enhancement factor for initial-state radiation
    */
   double _initialenhance;
 
   /**
    *  The enhancement factor for final-state radiation
    */
   double _finalenhance;
 };
 
 }
 
 #endif /* HERWIG_SMTopDecayer_H */

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