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DecayPhaseSpaceChannel.h
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DecayPhaseSpaceChannel.h
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// -*- C++ -*-
//
// DecayPhaseSpaceChannel.h is a part of Herwig - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2017 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_DecayPhaseSpaceChannel_H
#define HERWIG_DecayPhaseSpaceChannel_H
//
// This is the declaration of the DecayPhaseSpaceChannel class.
//
#include <ThePEG/Interface/Interfaced.h>
#include <ThePEG/PDT/ParticleData.h>
#include <ThePEG/EventRecord/Particle.h>
#include "DecayPhaseSpaceChannel.fh"
#include "DecayIntegrator.h"
#include "Herwig/Utilities/Kinematics.h"
#include "ThePEG/Repository/UseRandom.h"
#include "DecayPhaseSpaceMode.fh"
namespace Herwig {
using namespace ThePEG;
/** \ingroup Decay
*
* This class is designed to store the information needed for a given
* phase-space channel for use by the multi-channel phase space decayer
* and perform the generation of the phase space for that channel.
*
* The decay channel is specified as a series of \f$1\to2\f$ decays to either
* external particles or other intermediates. For each intermediate
* the Jacobian to be used can be either a Breit-Wigner(0) or a power-law
* (1).
*
* The class is then capable of generating a phase-space point using this
* channel and computing the weight of a given point for use in a multi-channel
* phase space integration using the <code>DecayPhaseSpaceMode</code> class.
*
* The class is designed so that the phase-space channels can either by specified
* using the addIntermediate method directly or via the repository.
* (In practice at the moment all the channels are constructed by the relevant decayers
* using the former method at the moment.)
*
* @see DecayPhaseSpaceMode
* @see DecayIntegrator
*
* @author Peter Richardson
*/
class DecayPhaseSpaceChannel: public Interfaced {
/**
* A friend output operator to allow the channel to be outputted for
* debugging purposes
*/
friend ostream & operator<<(ostream &, const DecayPhaseSpaceChannel &);
/**
* DecayPhaseSpaceMode is a friend to avoid making many of the phase space
* generation members public.
*/
friend class DecayPhaseSpaceMode;
public:
/** @name Standard constructors and destructors. */
//@{
/**
* Default constructor.
*/
DecayPhaseSpaceChannel() {}
/**
* Constructor with a pointer to a <code>DecayPhaseSpaceMode</code>. This
* is the constructor which should normally be used in decayers.
*/
DecayPhaseSpaceChannel(tcDecayPhaseSpaceModePtr);
//@}
public:
/** @name Set-up Members */
//@{
/**
* Add a new intermediate particle
* @param part A pointer to the particle data object for the intermediate.
* @param jac The jacobian to be used for the generation of the particle's mass
* 0 is a Breit-Wigner and 1 is a power-law
* @param power The power to beb used for the mass generation if a power law
* mass distribution is chosen.
* @param dau1 The first daughter. If this is postive it is the \f$dau1\f$ th
* outgoing particle (0 is the incoming particle), if it is negative it is the
* \f$|dau1|\f$ intermediate. The intermediates are specified in the order they
* are added with 0 being the incoming particle.
* @param dau2 The first daughter. If this is postive it is the \f$dau2\f$ th
* outgoing particle (0 is the incoming particle), if it is negative it is the
* \f$|dau2|\f$ intermediate. The intermediates are specified in the order they
* are added with 0 being the incoming particle.
*/
void addIntermediate(PDPtr part,int jac,double power,int dau1,int dau2) {
_intpart.push_back(part);
_jactype.push_back(jac);
_intpower.push_back(power);
_intdau1.push_back(dau1);
_intdau2.push_back(dau2);
}
/**
* Reset the properties of an intermediate particle. This member is used
* when a Decayer is used a different value for either the mass or width
* of a resonace to that in the ParticleData object. This improves the
* efficiency of the integration.
* @param part A pointer to the particle data object for the intermediate.
* @param mass The new mass of the intermediate
* @param width The new width of the intermediate.
*/
void resetIntermediate(tcPDPtr part,Energy mass,Energy width) {
if(!part) return;
int idin=part->id();
for(unsigned int ix=0;ix<_intpart.size();++ix) {
if(_intpart[ix] && _intpart[ix]->id()==idin) {
_intmass[ix] =mass;_intwidth[ix]=width;
_intmass2[ix]=mass*mass;_intmwidth[ix]=mass*width;
}
}
}
/*
* Reset the one of the daughters
* @param oldp The id of the particle being reset
* @param newp The id of the particle replacing it
*/
void resetDaughter(int oldp, int newp) {
for(unsigned int ix=0;ix<_intdau1.size();++ix) {
if(_intdau1[ix]==oldp) _intdau1[ix]=newp;
}
for(unsigned int ix=0;ix<_intdau2.size();++ix) {
if(_intdau2[ix]==oldp) _intdau2[ix]=newp;
}
}
//@}
protected:
/** @name Phase-Space Generation Members */
//@{
/**
* Generate the momenta of the external particles. This member uses the masses
* of the external particles generated by the DecayPhaseMode class and the
* intermediates for the channel to generate the momenta of the decay products.
* @param pin The momenta of the decay products. This is outputed by the member.
* @param massext The masses of the particles. This is to allow inclusion of
* off-shell effects for the external particles.
*/
vector<Lorentz5Momentum> generateMomenta(const Lorentz5Momentum & pin,
const vector<Energy> & massext);
/**
* Generate the weight for this channel given a phase space configuration.
* This member generates the weight for a given phase space configuration
* and is used by the DecayPhaseSpaceMode class to compute the denominator
* of the weight in the multi-channel integration.
* @param output The momenta of the outgoing particles.
*/
double generateWeight(const vector<Lorentz5Momentum> & output);
/**
* Generate the final-state particles including the intermediate resonances.
* This method takes the outgoing particles and adds the intermediate particles
* specified by this phase-space channel. This is to allow a given set of
* intermediates to be specified even when there is interference between different
* intermediate states.
* @param cc Whether the particles are the mode specified or its charge conjugate.
* @param in The incoming particles.
* @param out The outgoing particles.
*
*/
void generateIntermediates(bool cc,const Particle & in, ParticleVector & out);
/**
* Calculate the momenta for a two body decay
* The return value indicates success or failure.
* @param p The momentum of the decaying particle
* @param m1 The mass of the first decay product
* @param m2 The mass of the second decay product
* @param p1 The momentum of the first decay product
* @param p2 The momentum of the second decay product
*/
void twoBodyDecay(const Lorentz5Momentum & p,
const Energy m1, const Energy m2,
Lorentz5Momentum & p1, Lorentz5Momentum & p2);
//@}
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. Called in the run phase just before
* a run begins.
*/
virtual void doinitrun();
//@}
private:
/**
* Private and non-existent assignment operator.
*/
DecayPhaseSpaceChannel & operator=(const DecayPhaseSpaceChannel &);
private:
/** @name Mass Generation Members */
//@{
/**
* Generate the mass of a resonance.
* @param ires The resonance to be generated.
* @param lower The lower limit on the particle's mass.
* @param upper The upper limit on the particle's mass.
*/
Energy generateMass(int ires,Energy lower,Energy upper);
/**
* Return the weight for a given resonance.
* @param ires The resonance to be generated.
* @param moff The mass of the resonance.
* @param lower The lower limit on the particle's mass.
* @param upper The upper limit on the particle's mass.
*/
InvEnergy2 massWeight(int ires, Energy moff,Energy lower,Energy upper);
//@}
private:
/**
* pointer to the mode
*/
tcDecayPhaseSpaceModePtr _mode;
/**
* Pointers to the particle data objects of the intermediate particles
*/
vector <PDPtr> _intpart;
/**
* The type of jacobian to be used for the intermediates.
*/
vector <int> _jactype;
/**
* The mass of the intermediates.
*/
vector<Energy> _intmass;
/**
* The width of the intermediates.
*/
vector<Energy> _intwidth;
/**
* The mass squared of the intermediate particles.
*/
vector<Energy2> _intmass2;
/**
* The mass times the width for the intermediate particles.
*/
vector<Energy2>_intmwidth;
/**
* The power for the intermediate resonance.
*/
vector<double> _intpower;
/**
* The first daughter of the intermediate resonance.
*/
vector<int> _intdau1;
/**
* The second daughter of the intermediate resonance.
*/
vector<int> _intdau2;
/**
* The external particles that an intermediate particle final decays to.
*/
vector< vector<int> > _intext;
/**
* Helper function for the weight calculation.
* @param ires The resonance to be generated.
* @param limit The limit on the particle's mass.
*/
double atanhelper_(int ires, Energy limit);
};
/**
* write the phase space channel to a stream
*/
ostream & operator<<(ostream &, const DecayPhaseSpaceChannel &);
/**
* exception for this class and those inheriting from it
*/
class DecayPhaseSpaceError: public Exception {};
}
#endif /* HERWIG_DecayPhaseSpaceChannel_H */

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