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TwoBodyDecayMatrixElement.h
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TwoBodyDecayMatrixElement.h
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// -*- C++ -*-
//
// TwoBodyMatrixElement.h is a part of Herwig - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2011 The Herwig Collaboration
//
// Herwig is licenced under version 2 of the GPL, see COPYING for details.
// Please respect the MCnet academic guidelines, see GUIDELINES for details.
//
#ifndef HERWIG_TwoBodyDecayMatrixElement_H
#define HERWIG_TwoBodyDecayMatrixElement_H
//
// This is the declaration of the TwoBodyDecayMatrixElement class.
#include "DecayMatrixElement.h"
namespace Herwig {
using namespace ThePEG;
/** \ingroup Helicity
* \author Peter Richardson
*
* Implementation of the complex matrix element for a two-body decay
* a decay.
* An arbitary number of external particles are supported.
* @see RhoDMatrix
* @see ProductionMatrixElement
* @see DecayVertex
*/
class TwoBodyDecayMatrixElement: public DecayMatrixElement {
public:
/** @name Standard constructors and destructors. */
//@{
/**
* Default constructor.
*/
TwoBodyDecayMatrixElement() : DecayMatrixElement(2) {}
/**
* Constructor for two body decay.
* @param spinin \f$2S+1\f$ for the decaying particle
* @param outspin1 \f$2S+1\f$ for the first decay product.
* @param outspin2 \f$2S+1\f$ for the second decay product.
*/
TwoBodyDecayMatrixElement(PDT::Spin spinin,PDT::Spin outspin1,PDT::Spin outspin2)
: DecayMatrixElement(2,spinin) {
outspin().push_back(outspin1);
outspin().push_back(outspin2);
}
/**
* Constructor for arbitary body decay.
* @param inspin \f$2S+1\f$ for the decaying particle
* @param spinout \f$2S+1\f$ for the decay products.
*/
TwoBodyDecayMatrixElement(PDT::Spin inspin,vector<PDT::Spin> spinout)
: DecayMatrixElement(2,inspin) {
assert(spinout.size()==2);
outspin() = spinout;
}
/**
* Constructor for arbitary body decay.
* @param extspin \f$2S+1\f$ external particles.
*/
TwoBodyDecayMatrixElement(vector<PDT::Spin> extspin)
: DecayMatrixElement(2,extspin[0]) {
assert(extspin.size()==3);
outspin() = vector<PDT::Spin>(extspin.begin()+1,extspin.end());
}
//@}
public:
/**
* Spin Density matrices
*/
//@{
/**
* Calculate the decay matrix for this decay.
* @param rhoout The \f$D\f$ matrix for this decay.
*/
RhoDMatrix calculateDMatrix(const vector<RhoDMatrix> & rhoout) const;
/**
* Calculate the \f$\rho\f$ matrix for a given outgoing particle.
* @param ipart The outgoing particle the \f$\rho\f$ matrix is needed for
* @param rhoin The \f$\rho\f$ matrix for the decaying particle.
* @param rhoout he \f$D\f$ matrices for the other decay products.
*/
RhoDMatrix calculateRhoMatrix(int ipart,const RhoDMatrix & rhoin,
const vector<RhoDMatrix> & rhoout) const;
/**
* Contract the matrix element with the \f$\rho\f$ matrix of the
* incoming particle. The spins of the decay products are summed over.
* @param rhoin The \f$\rho\f$ matrix for the decaying particle.
*/
Complex contract(const RhoDMatrix & rhoin) const;
/**
* Contract the matrix element with the \f$\rho\f$ matrix of the
* incoming particle. The spins of the decay products are summed over.
* @param con The conjugate matrix elemetn for the contraction
* @param rhoin The \f$\rho\f$ matrix for the decaying particle.
*/
Complex contract(const TwoBodyDecayMatrixElement & con,
const RhoDMatrix & rhoin);
//@}
public:
/**
* Access to the individual helicity components.
*/
//@{
/**
* Get the helicity components for a two body decay
* @param inhel The helicity of the decaying particle.
* @param outhel1 The helicity of the first decay product.
* @param outhel2 The helicity of the second decay product.
*/
Complex operator () (unsigned int inhel, unsigned int outhel1,
unsigned int outhel2) const {
return matrixElement_[inhel][outhel1][outhel2];
}
/**
* Set the helicity components for a two body decay
* @param inhel The helicity of the decaying particle.
* @param outhel1 The helicity of the first decay product.
* @param outhel2 The helicity of the second decay product.
*/
Complex & operator () (unsigned int inhel, unsigned int outhel1,
unsigned int outhel2) {
return matrixElement_[inhel][outhel1][outhel2];
}
/**
* Get the helicity components for a three body decay
*/
Complex operator () (unsigned int , unsigned int ,
unsigned int , unsigned int ) const {
assert(false);
static const Complex out = 0.;
return out;
}
/**
* Set the helicity components for a three body decay
*/
Complex & operator () (unsigned int , unsigned int ,
unsigned int , unsigned int ) {
assert(false);
static Complex out = 0.;
return out;
}
/**
* Get the helicity components for a four body decay
*/
Complex operator () (unsigned int , unsigned int ,
unsigned int , unsigned int ,
unsigned int ) const {
assert(false);
static const Complex out = 0.;
return out;
}
/**
* Set the helicity components for a four body decay
*/
Complex & operator () (unsigned int , unsigned int ,
unsigned int , unsigned int ,
unsigned int ) {
assert(false);
static Complex out = 0.;
return out;
}
/**
* Get the helicity components for a five body decay
* @param inhel The helicity of the decaying particle.
* @param outhel1 The helicity of the first decay product.
* @param outhel2 The helicity of the second decay product.
* @param outhel3 The helicity of the third decay product.
* @param outhel4 The helicity of the fourth decay product.
* @param outhel5 The helicity of the fifth decay product.
*/
Complex operator () (unsigned int , unsigned int ,
unsigned int , unsigned int ,
unsigned int , unsigned int ) const {
assert(false);
static const Complex out = 0.;
return out;
}
/**
* Set the helicity components for a five body decay
*/
Complex & operator () (unsigned int , unsigned int ,
unsigned int , unsigned int ,
unsigned int , unsigned int ) {
assert(false);
static Complex out = 0.;
return out;
}
/**
* Get the helicity components for a six body decay
*/
Complex operator () (unsigned int ,unsigned int ,
unsigned int ,unsigned int ,
unsigned int ,unsigned int ,
unsigned int ) const {
assert(false);
static const Complex out = 0.;
return out;
}
/**
* Set the helicity components for a six body decay
*/
Complex & operator () (unsigned int , unsigned int ,
unsigned int , unsigned int ,
unsigned int , unsigned int ,
unsigned int ) {
assert(false);
static Complex out = 0.;
return out;
}
/**
* Get the helicity components for an \f$n\f$-body decay.
* @param in The helicities of the external particles.
*/
Complex operator () (const vector<unsigned int> & in) const {
assert(in.size()==3);
return matrixElement_[in[0]][in[1]][in[2]];
}
/**
* Set the helicity components for an \f$n\f$-body decay.
* @param in The helicities of the external particles.
*/
Complex & operator () (const vector<unsigned int> & in) {
assert(in.size()==3);
return matrixElement_[in[0]][in[1]][in[2]];
}
//@}
/**
* Member to zero all the elements for the matrix element
*/
void zero() {
for(unsigned int ix=0;ix<5;++ix) {
for(unsigned int iy=0;iy<5;++iy) {
for(unsigned int iz=0;iz<5;++iz) {
matrixElement_[ix][iy][iz]=0.;
}
}
}
}
private:
/**
* Storage of the matrix element, a vector is better for memory usage.
*/
Complex matrixElement_[5][5][5];
};
}
#endif /* HERWIG_TwoBodyDecayMatrixElement_H */

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