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GeneralTwoBodyDecayer.cc
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// -*- C++ -*-
//
// GeneralTwoBodyDecayer.cc is a part of Herwig++ - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2007 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.
//
//
// This is the implementation of the non-inlined, non-templated member
// functions of the GeneralTwoBodyDecayer class.
//
#include "GeneralTwoBodyDecayer.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/Interface/Reference.h"
#include "ThePEG/Interface/Parameter.h"
#include "ThePEG/Interface/ParVector.h"
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
#include "ThePEG/PDT/DecayMode.h"
#include "ThePEG/Utilities/Exception.h"
using namespace Herwig;
ParticleVector GeneralTwoBodyDecayer::decay(const Particle & parent,
const tPDVector & children) const {
// return empty vector if products heavier than parent
Energy mout(ZERO);
for(tPDVector::const_iterator it=children.begin();
it!=children.end();++it) mout+=(**it).massMin();
if(mout>parent.mass()) return ParticleVector();
// generate the decay
bool cc;
int imode=modeNumber(cc,parent.dataPtr(),children);
// generate the kinematics
ParticleVector decay=generate(generateIntermediates(),cc,imode,parent);
// make the colour connections
colourConnections(parent, decay);
// return the answer
return decay;
}
void GeneralTwoBodyDecayer::doinit() {
DecayIntegrator::doinit();
assert( _theVertex );
_theVertex->init();
vector<double> wgt;
set<tPDPtr> parents = _theVertex->incoming();
for( set<tPDPtr>::const_iterator it = parents.begin();
it != parents.end(); ++it ) {
long pid = (*it)->id();
if( pid < 0 ) continue;
tcPDPtr inpart = *it;
Energy m1 = inpart->mass();
tPDVector decaylist;
for(unsigned int il = 0; il< _thelist.size(); ++il) {
tPDVector temp = _theVertex->search(_thelist[il], inpart);
decaylist.insert(decaylist.end(),temp.begin(),temp.end());
}
tPDVector::size_type ndec = decaylist.size();
for( tPDVector::size_type j = 0; j < ndec; j +=3 ) {
tPDPtr pa(decaylist[j]), pb(decaylist[j + 1]), pc(decaylist[j + 2]);
if( pb->id() == pid ) swap(pa, pb);
if( pc->id() == pid ) swap(pa, pc);
//allowed on-shell decay?
if( m1 <= pb->mass() + pc->mass() ) continue;
//vertices are defined with all particles incoming
if( pb->CC() ) pb = pb->CC();
if( pc->CC() ) pc = pc->CC();
//store ids so that the decayer knows what it is allowed to
//decay
_inpart.push_back(pid); _outparta.push_back(pb->id());
_outpartb.push_back(pc->id());
//create phase space mode
tPDVector extpart(3);
extpart[0] = pa;
extpart[1] = pb;
extpart[2] = pc;
addMode(new_ptr(DecayPhaseSpaceMode(extpart, this)),
_maxweight[0], wgt);
}
}
unsigned int isize(_inpart.size()), oasize(_outparta.size()),
obsize(_outpartb.size());
if( isize == 0 || oasize == 0 || obsize == 0 )
throw InitException()
<< "GeneralTwoBodyDecayer::doinit() - Atleast one of the particle "
<< "vectors has zero size, cannot continue."
<< isize << " " << oasize << " " << obsize
<< Exception::abortnow;
if( isize != oasize || isize != obsize )
throw InitException()
<< "GeneralTwoBodyDecayer::doinit() - The particle vectors have "
<< "different sizes. " << isize << " " << oasize << " " << obsize
<< Exception::abortnow;
}
int GeneralTwoBodyDecayer::modeNumber(bool & cc, tcPDPtr parent,
const tPDVector & children) const {
long parentID = parent->id();
long id1 = children[0]->id();
long id2 = children[1]->id();
int imode(-1);
unsigned ii(0), nipart(_inpart.size());
cc = false;
do {
long listpid(_inpart[ii]), listid1(_outparta[ii]),
listid2(_outpartb[ii]);
if( parentID == listpid &&
((id1 == listid1 && id2 == listid2) ||
(id1 == listid2 && id2 == listid1)) )
imode = ii;
//cc-mode
else if(parentID == -listpid) {
cc = true;
if((id1 == -listid1 && id2 == -listid2) ||
(id1 == -listid2 && id2 == -listid1) ||
(id1 == listid1 && id2 == -listid2) ||
(id1 == -listid1 && id2 == listid2) ||
(id1 == listid2 && id2 == -listid1) ||
(id1 == -listid2 && id2 == listid1) )
imode = ii;
else ++ii;
}
else ++ii;
}
while( imode < 0 && ii < nipart );
return imode;
}
void GeneralTwoBodyDecayer::
colourConnections(const Particle & parent,
const ParticleVector & out) const {
PDT::Colour incColour(parent.data().iColour());
PDT::Colour outaColour(out[0]->data().iColour());
PDT::Colour outbColour(out[1]->data().iColour());
//incoming colour singlet
if(incColour == PDT::Colour0) {
// colour triplet-colourantitriplet
if((outaColour == PDT::Colour3 && outbColour == PDT::Colour3bar) ||
(outaColour == PDT::Colour3bar && outbColour == PDT::Colour3)) {
bool ac(out[0]->id() < 0);
out[0]->colourNeighbour(out[1],!ac);
}
//colour octet
else if(outaColour == PDT::Colour8 && outbColour == PDT::Colour8) {
out[0]->colourNeighbour(out[1]);
out[0]->antiColourNeighbour(out[1]);
}
// colour singlets
else if(outaColour == PDT::Colour0 && outbColour == PDT::Colour0) {
}
// unknown
else
throw Exception() << "Unknown outgoing colours for decaying "
<< "colour singlet in "
<< "GeneralTwoBodyDecayer::colourConnections "
<< outaColour << " " << outbColour
<< Exception::runerror;
}
//incoming colour triplet
else if(incColour == PDT::Colour3) {
// colour triplet + singlet
if(outaColour == PDT::Colour3 && outbColour == PDT::Colour0) {
out[0]->incomingColour(const_ptr_cast<tPPtr>(&parent));
}
//opposite order
else if(outaColour == PDT::Colour0 && outbColour == PDT::Colour3) {
out[1]->incomingColour(const_ptr_cast<tPPtr>(&parent));
}
// octet + triplet
else if(outaColour == PDT::Colour8 && outbColour == PDT::Colour3) {
out[0]->incomingColour(const_ptr_cast<tPPtr>(&parent));
out[1]->antiColourNeighbour(out[0]);
}
//opposite order
else if(outaColour == PDT::Colour3 && outbColour == PDT::Colour8) {
out[1]->incomingColour(const_ptr_cast<tPPtr>(&parent));
out[0]->antiColourNeighbour(out[1]);
}
else
throw Exception() << "Unknown outgoing colours for decaying "
<< "colour triplet in "
<< "GeneralTwoBodyDecayer::colourConnections() "
<< outaColour << " " << outbColour
<< Exception::runerror;
}
// incoming colour anti triplet
else if(incColour == PDT::Colour3bar) {
// colour antitriplet +singlet
if(outaColour == PDT::Colour3bar && outbColour == PDT::Colour0) {
out[0]->incomingAntiColour(const_ptr_cast<tPPtr>(&parent));
}
//opposite order
else if(outaColour == PDT::Colour0 && outbColour == PDT::Colour3bar) {
out[1]->incomingAntiColour(const_ptr_cast<tPPtr>(&parent));
}
//octet + antitriplet
else if(outaColour == PDT::Colour3bar && outbColour == PDT::Colour8) {
out[1]->incomingAntiColour(const_ptr_cast<tPPtr>(&parent));
out[0]->colourNeighbour(out[1]);
}
//opposite order
else if(outaColour == PDT::Colour8 && outbColour == PDT::Colour3bar) {
out[0]->incomingAntiColour(const_ptr_cast<tPPtr>(&parent));
out[1]->colourNeighbour(out[0]);
}
else
throw Exception() << "Unknown outgoing colours for decaying "
<< "colour antitriplet "
<< "in GeneralTwoBodyDecayer::colourConnections() "
<< outaColour << " " << outbColour
<< Exception::runerror;
}
//incoming colour octet
else if(incColour == PDT::Colour8) {
// triplet-antitriplet
if(outaColour == PDT::Colour3&&outbColour == PDT::Colour3bar) {
out[0]->incomingColour(const_ptr_cast<tPPtr>(&parent));
out[1]->incomingAntiColour(const_ptr_cast<tPPtr>(&parent));
}
// opposite order
else if(outbColour == PDT::Colour3&&outaColour == PDT::Colour3bar) {
out[0]->incomingAntiColour(const_ptr_cast<tPPtr>(&parent));
out[1]->incomingColour(const_ptr_cast<tPPtr>(&parent));
}
// neutral octet
else if(outaColour == PDT::Colour0&&outbColour == PDT::Colour8) {
out[1]->incomingColour(const_ptr_cast<tPPtr>(&parent));
out[1]->incomingAntiColour(const_ptr_cast<tPPtr>(&parent));
}
else if(outbColour == PDT::Colour0&&outaColour == PDT::Colour8) {
out[0]->incomingColour(const_ptr_cast<tPPtr>(&parent));
out[0]->incomingAntiColour(const_ptr_cast<tPPtr>(&parent));
}
else
throw Exception() << "Unknown outgoing colours for decaying "
<< "colour octet "
<< "in GeneralTwoBodyDecayer::colourConnections() "
<< outaColour << " " << outbColour
<< Exception::runerror;
}
else
throw Exception() << "Unknown incoming colour in "
<< "GeneralTwoBodyDecayer::colourConnections() "
<< incColour
<< Exception::runerror;
}
bool GeneralTwoBodyDecayer::twoBodyMEcode(const DecayMode & dm, int & mecode,
double & coupling) const {
long parent = dm.parent()->id();
ParticleMSet::const_iterator pit = dm.products().begin();
long id1 = (*pit)->id();
++pit;
long id2 = (*pit)->id();
bool order(false);
vector<int>::size_type ix(0);
do {
if( parent == _inpart[ix] ) {
long id1t(_outparta[ix]), id2t(_outpartb[ix]);
if( id1 == id1t && id2 == id2t ) {
order = true;
break;
}
if( id1 == id2t && id2 == id1t ) {
order = false;
break;
}
}
++ix;
}
while( ix < _inpart.size() );
mecode = -1;
coupling = 1.;
return order;
}
void GeneralTwoBodyDecayer::persistentOutput(PersistentOStream & os) const {
os << _thelist << _theVertex << _inpart << _outparta << _outpartb
<< _maxweight;
}
void GeneralTwoBodyDecayer::persistentInput(PersistentIStream & is, int) {
is >> _thelist >> _theVertex >>_inpart >>_outparta >>_outpartb
>> _maxweight;
}
AbstractClassDescription<GeneralTwoBodyDecayer>
GeneralTwoBodyDecayer::initGeneralTwoBodyDecayer;
// Definition of the static class description member.
void GeneralTwoBodyDecayer::Init() {
static ClassDocumentation<GeneralTwoBodyDecayer> documentation
("This class is designed to be a base class for all 2 body decays"
"in a general model");
static Reference<GeneralTwoBodyDecayer,Helicity::VertexBase> interfaceDecayVertex
("DecayVertex",
"Pointer to decayer vertex",
&GeneralTwoBodyDecayer::_theVertex, false, false, true, false);
static ParVector<GeneralTwoBodyDecayer,double> interfaceMaxWeight
("MaxWeight",
"Maximum weight for integration",
&GeneralTwoBodyDecayer::_maxweight, 1.0, -1, 0, 0,
false, false, false,&GeneralTwoBodyDecayer::setWeight, 0 ,0, 0, 0);
static ParVector<GeneralTwoBodyDecayer,int> interfaceIncomingPart
("Incoming",
"PDG Codes for incoming particles",
&GeneralTwoBodyDecayer::_inpart, 0, -1, 0, 0,
false, false, false);
static ParVector<GeneralTwoBodyDecayer,int> interfaceOutgoingPartA
("OutgoingA",
"PDG Codes for first set of outgoing particles",
&GeneralTwoBodyDecayer::_outparta, 0, -1, 0, 0,
false, false, false);
static ParVector<GeneralTwoBodyDecayer,int> interfaceOutgoingPartB
("OutgoingB",
"PDG Codes for second set of outgoing particles",
&GeneralTwoBodyDecayer::_outpartb, 0, -1, 0, 0,
false, false, false);
}
double GeneralTwoBodyDecayer::brat(const DecayMode &, const Particle & p,
double oldbrat) const {
ParticleVector children = p.children();
if( children.size() != 2 || !p.data().widthGenerator() )
return oldbrat;
// partial width for this mode
Energy scale = p.mass();
Energy pwidth =
partialWidth( make_pair(p.dataPtr(), scale),
make_pair(children[0]->dataPtr(), children[0]->mass()),
make_pair(children[1]->dataPtr(), children[1]->mass()) );
Energy width = p.data().widthGenerator()->width(p.data(), scale);
return pwidth/width;
}
void GeneralTwoBodyDecayer::doinitrun() {
DecayIntegrator::doinitrun();
for(unsigned int ix=0;ix<numberModes();++ix) {
double fact = pow(1.5,int(mode(ix)->externalParticles(0)->iSpin())-1);
mode(ix)->setMaxWeight(fact*mode(ix)->maxWeight());
}
}
double GeneralTwoBodyDecayer::colourFactor(tcPDPtr in, tcPDPtr out1,
tcPDPtr out2) const {
// identical particle symmetry factor
double output = out1->id()==out2->id() ? 0.5 : 1.;
// colour neutral incoming particle
if(in->iColour()==PDT::Colour0) {
// both colour neutral
if(out1->iColour()==PDT::Colour0 && out2->iColour()==PDT::Colour0)
output *= 1.;
// colour triplet/ antitriplet
else if((out1->iColour()==PDT::Colour3 && out2->iColour()==PDT::Colour3bar) ||
(out1->iColour()==PDT::Colour3bar && out2->iColour()==PDT::Colour3 ) ) {
output *= 3.;
}
// colour octet colour octet
else if(out1->iColour()==PDT::Colour8 && out2->iColour()==PDT::Colour8 ) {
output *= 8.;
}
else
throw Exception() << "Unknown colour for the outgoing particles"
<< " for decay colour neutral particle in "
<< "GeneralTwoBodyDecayer::colourFactor() for "
<< in->PDGName() << " -> "
<< out1->PDGName() << " " << out2->PDGName()
<< Exception::runerror;
}
// triplet
else if(in->iColour()==PDT::Colour3) {
// colour triplet + neutral
if((out1->iColour()==PDT::Colour0 && out2->iColour()==PDT::Colour3) ||
(out1->iColour()==PDT::Colour3 && out2->iColour()==PDT::Colour0) ) {
output *= 1.;
}
// colour triplet + octet
else if((out1->iColour()==PDT::Colour8 && out2->iColour()==PDT::Colour3) ||
(out1->iColour()==PDT::Colour3 && out2->iColour()==PDT::Colour8) ) {
output *= 4./3.;
}
else
throw Exception() << "Unknown colour for the outgoing particles"
<< " for decay colour triplet particle in "
<< "GeneralTwoBodyDecayer::colourFactor() for "
<< in->PDGName() << " -> "
<< out1->PDGName() << " " << out2->PDGName()
<< Exception::runerror;
}
// anti triplet
else if(in->iColour()==PDT::Colour3bar) {
// colour anti triplet + neutral
if((out1->iColour()==PDT::Colour0 && out2->iColour()==PDT::Colour3bar ) ||
(out1->iColour()==PDT::Colour3bar && out2->iColour()==PDT::Colour0 ) ) {
output *= 1.;
}
// colour anti triplet + octet
else if((out1->iColour()==PDT::Colour8 && out2->iColour()==PDT::Colour3bar ) ||
(out1->iColour()==PDT::Colour3bar && out2->iColour()==PDT::Colour8 ) ) {
output *= 4./3.;
}
else
throw Exception() << "Unknown colour for the outgoing particles"
<< " for decay colour anti triplet particle in "
<< "GeneralTwoBodyDecayer::colourFactor() for "
<< in->PDGName() << " -> "
<< out1->PDGName() << " " << out2->PDGName()
<< Exception::runerror;
}
else if(in->iColour()==PDT::Colour8) {
// colour octet + neutral
if((out1->iColour()==PDT::Colour0 && out2->iColour()==PDT::Colour8 ) ||
(out1->iColour()==PDT::Colour8 && out2->iColour()==PDT::Colour0 ) ) {
output *= 1.;
}
// colour triplet/antitriplet
else if((out1->iColour()==PDT::Colour3 && out2->iColour()==PDT::Colour3bar) ||
(out1->iColour()==PDT::Colour3bar && out2->iColour()==PDT::Colour3 ) ) {
output *= 0.5;
}
else
throw Exception() << "Unknown colour for the outgoing particles"
<< " for decay colour octet particle in "
<< "GeneralTwoBodyDecayer::colourFactor() for "
<< in->PDGName() << " -> "
<< out1->PDGName() << " " << out2->PDGName()
<< Exception::runerror;
}
else
throw Exception() << "Unknown colour for the decaying particle in "
<< "GeneralTwoBodyDecayer::colourFactor() for "
<< in->PDGName() << " -> "
<< out1->PDGName() << " " << out2->PDGName()
<< Exception::runerror;
return output;
}
Energy GeneralTwoBodyDecayer::partialWidth(PMPair inpart, PMPair outa,
PMPair outb) const {
// select the number of the mode
tPDVector children;
children.push_back(const_ptr_cast<PDPtr>(outa.first));
children.push_back(const_ptr_cast<PDPtr>(outb.first));
bool cc;
int nmode=modeNumber(cc,inpart.first,children);
tcPDPtr newchild[2] = {mode(nmode)->externalParticles(1),
mode(nmode)->externalParticles(2)};
// make the particles
Lorentz5Momentum pparent = Lorentz5Momentum(inpart.second);
PPtr parent = inpart.first->produceParticle(pparent);
Lorentz5Momentum pout[2];
double ctheta,phi;
Kinematics::generateAngles(ctheta,phi);
Kinematics::twoBodyDecay(pparent, outa.second, outb.second,
ctheta, phi,pout[0],pout[1]);
if( ( !cc && outa.first!=newchild[0]) ||
( cc && !(( outa.first->CC() && outa.first->CC() == newchild[0])||
( !outa.first->CC() && outa.first == newchild[0]) )))
swap(pout[0],pout[1]);
ParticleVector decay;
decay.push_back(newchild[0]->produceParticle(pout[0]));
decay.push_back(newchild[1]->produceParticle(pout[1]));
double me = me2(-1,*parent,decay,Initialize);
Energy pcm = Kinematics::pstarTwoBodyDecay(inpart.second,
outa.second, outb.second);
return me/(8.*Constants::pi)*pcm;
}

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