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PScalarPScalarVectorDecayer.h
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PScalarPScalarVectorDecayer.h
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// -*- C++ -*-
//
// PScalarPScalarVectorDecayer.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_PScalarPScalarVectorDecayer_H
#define HERWIG_PScalarPScalarVectorDecayer_H
//
// This is the declaration of the PScalarPScalarVectorDecayer class.
//
#include "Herwig/Decay/DecayIntegrator.h"
#include "Herwig/Decay/PhaseSpaceMode.h"
#include "ThePEG/Helicity/LorentzPolarizationVector.h"
namespace Herwig {
using namespace ThePEG;
/** \ingroup Decay
*
* The <code>PScalarPScalarVectorDecayer</code> class is designed to perform the decay
* of a pseudoscalar meson to another pseudoscalar meson and a vector meson.
* In this case the matrix element has the
* form
* \f[\mathcal{M} = g\epsilon_2^\mu(p_0+p_1)_\mu,\f]
* where
* - \f$p_0\f$ is the momentum of the incoming pseudoscalar meson.
* - \f$p_1\f$ is the momentum of the outgoing pseudoscalar meson.
* - \f$\epsilon_2\f$ is the polarization vector of the vector meson.
* - \f$g\f$ is the coupling for the decay.
*
* The same Lorentz structure is also valid, and used for Scalar to Scalar Vector, Scalar to PseudoScalar PseudoVector, or PseudoScalar to PseudoVector Scalar decays.
* @see DecayIntegrator
*
* \author Peter Richardson
*
*/
class PScalarPScalarVectorDecayer: public DecayIntegrator {
public:
/**
* 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;
/**
* Specify the \f$1\to2\f$ matrix element to be used in the running width calculation.
* @param dm The DecayMode
* @param mecode The code for the matrix element as described
* in the GenericWidthGenerator class, in this case 10.
* @param coupling The coupling for the matrix element.
* @return True or False if this mode can be handled.
*/
bool twoBodyMEcode(const DecayMode & dm, int & mecode, double & coupling) 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();
/**
* 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;
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.
*/
PScalarPScalarVectorDecayer & operator=(const PScalarPScalarVectorDecayer &) = delete;
private:
/**
* the PDG code for the incoming particle
*/
vector<int> incoming_;
/**
* the PDG code for the outgoing particles pseudoscalar, then vector
*/
vector<pair<int,int> > outgoing_;
/**
* the coupling for the decay
*/
vector<double> coupling_;
/**
* the maximum weight for the decay
*/
vector<double> maxWeight_;
/**
* Spin density matrix
*/
mutable RhoDMatrix rho_;
/**
* Polarization vectors for the decay products
*/
mutable vector<Helicity::LorentzPolarizationVector> vectors_;
};
}
#endif /* HERWIG_PScalarPScalarVectorDecayer_H */

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