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diff --git a/Decay/Partonic/WeakPartonicDecayer.cc b/Decay/Partonic/WeakPartonicDecayer.cc
--- a/Decay/Partonic/WeakPartonicDecayer.cc
+++ b/Decay/Partonic/WeakPartonicDecayer.cc
@@ -1,637 +1,637 @@
// -*- C++ -*-
//
// WeakPartonicDecayer.cc 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.
//
//
// This is the implementation of the non-inlined, non-templated member
// functions of the WeakPartonicDecayer class.
//
#include "WeakPartonicDecayer.h"
#include "ThePEG/Utilities/DescribeClass.h"
#include "Herwig/Utilities/Kinematics.h"
#include "ThePEG/PDT/EnumParticles.h"
#include "ThePEG/PDT/DecayMode.h"
#include "ThePEG/Interface/Reference.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/PDT/ConstituentParticleData.h"
#include "ThePEG/Interface/Parameter.h"
#include "ThePEG/Interface/Switch.h"
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
#include "ThePEG/Repository/EventGenerator.h"
#include "ThePEG/Helicity/WaveFunction/SpinorWaveFunction.h"
#include "ThePEG/Helicity/WaveFunction/SpinorBarWaveFunction.h"
using namespace Herwig;
using namespace ThePEG::Helicity;
WeakPartonicDecayer::WeakPartonicDecayer() : MECode(0), _radprob(0.0), _maxtry(300),
_threemax(3.), _fourmax(3.)
{}
IBPtr WeakPartonicDecayer::clone() const {
return new_ptr(*this);
}
IBPtr WeakPartonicDecayer::fullclone() const {
return new_ptr(*this);
}
bool WeakPartonicDecayer::accept(tcPDPtr parent, const tPDVector & prod) const {
// check we can find the flavours of the quarks in the decaying meson
long id = parent->id();
int flav1, flav2;
if((id / 1000)%10) {
flav1 = (id/1000)%10;
flav2 = (id/10)%100;
}
else {
flav1 = id/100;
flav2 = (id/10)%10;
}
if(!flav1 || !flav2) return false;
// if two decay products one must be in triplet and one antitriplet
if(prod.size()==2) {
if((prod[0]->iColour()==PDT::Colour3&&prod[1]->iColour()==PDT::Colour3bar)||
(prod[0]->iColour()==PDT::Colour3bar&&prod[1]->iColour()==PDT::Colour3))
return true;
}
else if(prod.size()==3) {
if(((prod[0]->iColour()==PDT::Colour3 &&prod[2]->iColour()==PDT::Colour3bar)||
(prod[0]->iColour()==PDT::Colour3bar&&prod[2]->iColour()==PDT::Colour3))
&&prod[1]->iColour()==PDT::Colour8) return true;
}
else if(prod.size()==4) {
// first two particles should be leptons or q qbar
if((prod[0]->id()>=11&&prod[0]->id()<=16&&prod[1]->id()<=-11&&prod[1]->id()>=-16)||
(prod[1]->id()>=11&&prod[1]->id()<=16&&prod[0]->id()<=-11&&prod[0]->id()>=-16)||
(prod[0]->iColour()==PDT::Colour3 &&prod[1]->iColour()==PDT::Colour3bar )||
(prod[1]->iColour()==PDT::Colour3 &&prod[0]->iColour()==PDT::Colour3bar )) {
// third particle quark and fourth colour anti-triplet or
// thrid particle antiquark and fourth colour triplet
if((prod[2]->iColour()==PDT::Colour3bar&&prod[3]->iColour()==PDT::Colour3 )||
(prod[2]->iColour()==PDT::Colour3 &&prod[3]->iColour()==PDT::Colour3bar))
return true;
}
else return false;
}
return false;
}
ParticleVector WeakPartonicDecayer::decay(const Particle & parent,
const tPDVector & children) const {
static tcPDPtr gluon=getParticleData(ParticleID::g);
// make the particles
ParticleVector partons;
for(unsigned int ix=0;ix<children.size();++ix) {
partons.push_back(children[ix]->produceParticle());
// these products have the mass but should have constituent mass
partons[ix]->set5Momentum(Lorentz5Momentum(children[ix]->constituentMass()));
}
// 2-body decays
if(partons.size()==2) {
// no gluon if not select based on probability or if three body not allowed
if(UseRandom::rnd()>_radprob||
parent.mass()<gluon->constituentMass()+partons[0]->mass()+partons[1]->mass()) {
double ctheta,phi;
Lorentz5Momentum pout[2];
for(unsigned int ix=0;ix<2;++ix) pout[ix].setMass(partons[ix]->mass());
Kinematics::generateAngles(ctheta,phi);
Kinematics::twoBodyDecay(parent.momentum(),pout[0].mass(),pout[1].mass(),
ctheta,phi,pout[0],pout[1]);
for(unsigned int ix=0; ix<2;++ix) partons[ix]->setMomentum(pout[ix]);
if(partons[0]->dataPtr()->iColour()==PDT::Colour3) {
partons[0]->antiColourNeighbour(partons[1]);
}
else {
partons[0]-> colourNeighbour(partons[1]);
}
}
else {
Lorentz5Momentum pout[3];
for(unsigned int ix=0;ix<2;++ix) pout[ix].setMass(partons[ix]->mass());
// add gluon
partons.push_back(gluon->produceParticle());
partons.back()->set5Momentum(gluon->constituentMass());
// momentum of gluon
pout[2] = Lorentz5Momentum(gluon->constituentMass());
Kinematics::threeBodyDecay(parent.momentum(),pout[1],pout[0],pout[2]);
for(unsigned int ix=0; ix<3;++ix) partons[ix]->setMomentum(pout[ix]);
if(partons[0]->dataPtr()->iColour()==PDT::Colour3) {
partons[0]->antiColourNeighbour(partons[2]);
partons[1]-> colourNeighbour(partons[2]);
}
else {
partons[0]-> colourNeighbour(partons[2]);
partons[1]->antiColourNeighbour(partons[2]);
}
}
}
// 3-body decays
else if(partons.size()==3) {
// set masses of products
Lorentz5Momentum pout[3],pin(parent.momentum());
for(unsigned int ix=0;ix<3;++ix) pout[ix].setMass(partons[ix]->mass());
double xs(partons[2]->mass()/pin.e()),xb(1.-xs);
pout[2]=xs*pin;
// Get the particle quark that is decaying
long idQ, idSpec;
idSpec = partons[2]->id();
idQ = (parent.id()/1000)%10;
if(!idQ) idQ = (parent.id()/100)%10;
// Now the odd case of a B_c where the c decays, not the b
if(idSpec == idQ) idQ = (parent.id()/10)%10;
// momentum of the decaying quark
PPtr inter = getParticleData(idQ)->produceParticle(parent.momentum()*xb);
// two body decay of heavy quark
double ctheta,phi;
Kinematics::generateAngles(ctheta,phi);
Kinematics::twoBodyDecay(inter->momentum(),pout[0].mass(),pout[1].mass(),
ctheta,phi,pout[0],pout[1]);
// set the momenta of the decay products
for(unsigned int ix=0; ix<3;++ix) partons[ix]->setMomentum(pout[ix]);
// make the colour connections
// quark first
if(partons[0]->data().iColour()==PDT::Colour3) {
partons[0]->antiColourNeighbour(partons[1]);
partons[1]->colourNeighbour(partons[0]);
partons[1]->antiColourNeighbour(partons[2]);
partons[2]->colourNeighbour(partons[1]);
}
// antiquark first
else {
partons[0]->colourNeighbour(partons[1]);
partons[1]->antiColourNeighbour(partons[0]);
partons[1]->colourNeighbour(partons[2]);
partons[2]->antiColourNeighbour(partons[1]);
}
}
// 4-body decays
- else if(partons.size()==4) {
+ else if(partons.size()==4) {
// swap 0 and 1 if needed
if(partons[1]->dataPtr()->iColour()!=PDT::Colour0&&
partons[1]->dataPtr()->iColour()!=partons[2]->dataPtr()->iColour())
swap(partons[0],partons[1]);
// get the momenta of the decaying quark and the spectator
Lorentz5Momentum pin(parent.momentum());
double xs(partons[3]->mass()/pin.e()),xb(1.-xs);
Lorentz5Momentum pspect(xs*pin),pdec(xb*pin);
pspect.setMass(partons[3]->mass());
pdec.rescaleMass();
// Get the particle quark that is decaying
long idQ, idSpec;
idSpec = partons[3]->id();
idQ = (abs(parent.id())/1000)%10;
if(!idQ) idQ = (abs(parent.id())/100)%10;
// Now the odd case of a B_c where the c decays, not the b
if(abs(idSpec) == idQ) idQ = (abs(parent.id())/10)%10;
// change sign if spectator quark or antidiquark
if((idSpec>0&&idSpec<6)||idSpec<-6) idQ = -idQ;
// check if W products coloured
bool Wcol = partons[0]->coloured();
// particle data object
tcPDPtr dec = getParticleData(idQ);
// spin density matrix for the decaying quark
RhoDMatrix rhoin(PDT::Spin1Half,true);
if(parent.dataPtr()->iSpin()!=PDT::Spin0 && parent.spinInfo()) {
parent.spinInfo()->decay();
RhoDMatrix rhoHadron = parent.spinInfo()->rhoMatrix();
// particles with spin 0 diquark
if(abs(parent.id())==5122 || abs(parent.id())==4122 ||
abs(parent.id())==5122 || abs(parent.id())==4122 ||
abs(parent.id())==5132 || abs(parent.id())==4132 ||
abs(parent.id())==5232 || abs(parent.id())==4232) {
for(unsigned int ix=0;ix<2;++ix) rhoin(ix,ix) = rhoHadron(ix,ix);
}
// particles with spin 1 diquark
else if(abs(parent.id())==5332 || abs(parent.id())==4332) {
rhoin(0,0) = 2./3.*rhoHadron(1,1)+1./3.*rhoHadron(0,0);
rhoin(1,1) = 2./3.*rhoHadron(0,0)+1./3.*rhoHadron(1,1);
}
}
// momenta of the decay products
vector<Lorentz5Momentum> pout(3,Lorentz5Momentum());
for(unsigned int ix=0;ix<3;++ix) pout[ix].setMass(partons[ix]->mass());
// charges of the exchanged boson and check if colour rearranged
int c1 = dec ->iCharge()-partons[2]->dataPtr()->iCharge();
int c2 = partons[0]->dataPtr()->iCharge()+partons[1]->dataPtr()->iCharge();
bool rearranged = !(c1==c2&&abs(c1)==3);
if(MECode==0) rearranged=false;
if(rearranged) {
int c3 = dec ->iCharge()-partons[1]->dataPtr()->iCharge();
int c4 = partons[0]->dataPtr()->iCharge()+partons[2]->dataPtr()->iCharge();
if(!(c3==c4&&abs(c3)==3)) {
generator()->log() << "Unknown order for colour rearranged decay"
<< " in WeakPartonicDecayer::decay()\n";
generator()->log() << c1 << " " << c2 << " " << c3 << " " << c4 << "\n";
generator()->log() << parent << "\n" << dec->PDGName() << "\n";
for(unsigned int ix=0;ix<4;++ix) generator()->log() << *partons[ix] << "\n";
throw Exception() << "Unknown order for colour rearranged decay"
<< " in WeakPartonicDecayer::decay() "
<< Exception::runerror;
}
swap(pout[1] ,pout[2] );
swap(partons[1],partons[2]);
}
// decide if three or four body using prob
bool threeBody = UseRandom::rnd() > _radprob;
// if four body not kinematically possible must be three body
if(pdec.mass()<gluon->constituentMass()+pout[0].mass()+
pout[1].mass()+pout[2].mass()) threeBody=true;
// if code ==0 always three body
if(MECode==0) threeBody=true;
// three body decay
if( threeBody ) {
if(MECode==0) {
Kinematics::threeBodyDecay(pdec,pout[1],pout[0],pout[2]);
}
else {
// generate the kinematics
double wgt(0.);
Energy2 mb2max = sqr(pdec.mass() - pout[2].mass());
Energy2 mb2min = sqr(pout[0].mass() + pout[1].mass());
unsigned int ntry = 0;
do {
++ntry;
Energy2 mb2 = (mb2max-mb2min)*UseRandom::rnd()+mb2min;
double CosAngle, AzmAngle;
// perform first decay
Lorentz5Momentum p01;
p01.setMass(sqrt(mb2));
Kinematics::generateAngles(CosAngle,AzmAngle);
Kinematics::twoBodyDecay(pdec,pout[2].mass(),p01.mass(),
CosAngle,AzmAngle,pout[2],p01);
// perform second decay
Kinematics::generateAngles(CosAngle,AzmAngle);
Kinematics::twoBodyDecay(p01,pout[0].mass(),pout[1].mass(),
CosAngle,AzmAngle,pout[0],pout[1]);
// kinematic piece of the weight
wgt =
Kinematics::pstarTwoBodyDecay(pdec.mass(),p01 .mass(),pout[2].mass())/pdec.mass()*
Kinematics::pstarTwoBodyDecay(p01 .mass(),pout[0].mass(),pout[1].mass())/p01.mass();
// piece to improve weight variation (not kinematics dependent)
- wgt *= pdec.mass()/Kinematics::pstarTwoBodyDecay(pdec.mass(),sqrt(mb2min),pout[2].mass());
- // integration over m23^2
- wgt *= (mb2max-mb2min)/sqr(pdec.mass());
+ // and integration over m23^2 (N.B. m23^2 fac on bottom for efficiency)
+ wgt *= pdec.mass()/Kinematics::pstarTwoBodyDecay(pdec.mass(),sqrt(mb2min),pout[2].mass())
+ /(mb2max-mb2min)*sqr(pdec.mass());
// set momenta of particles
for(unsigned int ix=0;ix<pout.size();++ix) partons[ix]->setMomentum(pout[ix]);
// matrix element piece
wgt *= threeBodyMatrixElement(dec,rhoin,pdec,partons);
// check doesn't violate max
if(wgt>_threemax) {
ostringstream message;
message << "Maximum weight for three-body decay "
<< "violated in WeakPartonicDecayer::decay()"
<< "Maximum = " << _threemax << " weight = " << wgt;
generator()->logWarning( Exception(message.str(),Exception::warning) );
}
}
while( wgt < _threemax*UseRandom::rnd() && ntry < _maxtry );
if(ntry==_maxtry) throw Exception()
<< "Too many attempts to generate three body kinematics in "
<< "WeakPartonicDecayer::decay()" << Exception::eventerror;
}
partons[3]->setMomentum(pspect);
// set up the colour connections
if(rearranged) swap(partons[1],partons[2]);
if(Wcol) {
if(partons[0]->data().iColour()==PDT::Colour3)
partons[0]->antiColourNeighbour(partons[1]);
else
partons[0]-> colourNeighbour(partons[1]);
}
if(partons[2]->data().iColour()==PDT::Colour3) {
partons[2]->antiColourNeighbour(partons[3]);
}
else {
partons[2]-> colourNeighbour(partons[3]);
}
}
// four body decay
else {
// generate the extra gluon
partons.push_back(gluon->produceParticle());
partons.back()->set5Momentum(gluon->constituentMass());
// momentum of gluon
pout.push_back(Lorentz5Momentum(gluon->constituentMass()));
// generate the kinematics
Energy2 ms2min(sqr(pout[0].mass()+pout[1].mass()+pout[2].mass()));
Energy2 ms2max(sqr(pdec.mass()-pout[3].mass()));
double wgt(0.);
unsigned int ntry=0;
bool initial = true;
do {
++ntry;
Energy2 ms2 = ms2min+UseRandom::rnd()*(ms2max-ms2min);
Energy ms = sqrt(ms2);
// and the W
Energy2 mb2max = sqr(ms -pout[2].mass());
Energy2 mb2min = sqr(pout[0].mass()+pout[1].mass());
Energy2 mb2 = (mb2max-mb2min)*UseRandom::rnd()+mb2min;
wgt = (mb2max-mb2min)/(ms2max-mb2min);
// perform first decay
Lorentz5Momentum ps;
double CosAngle,AzmAngle;
Kinematics::generateAngles(CosAngle,AzmAngle);
Kinematics::twoBodyDecay(pdec,pout[3].mass(),ms,CosAngle,AzmAngle,pout[3],ps);
// generate the kinematics
// perform second decay
Kinematics::generateAngles(CosAngle,AzmAngle);
Lorentz5Momentum p01;
p01.setMass(sqrt(mb2));
Kinematics::twoBodyDecay(ps,pout[2].mass(),p01.mass(),
CosAngle,AzmAngle,pout[2],p01);
// perform third decay
Kinematics::generateAngles(CosAngle,AzmAngle);
Kinematics::twoBodyDecay(p01,pout[0].mass(),pout[1].mass(),
CosAngle,AzmAngle,pout[0],pout[1]);
// kinematic piece of the weight
wgt *= 16.*
Kinematics::pstarTwoBodyDecay(pdec.mass(),pout[3].mass(),ms )/pdec.mass()*
Kinematics::pstarTwoBodyDecay(ms ,p01 .mass(),pout[2].mass())/ms*
Kinematics::pstarTwoBodyDecay(p01 .mass(),pout[0].mass(),pout[1].mass())/p01.mass();
wgt *= fourBodyMatrixElement(pdec,pout[2],pout[0],pout[1],pout[3],Wcol,initial);
// check doesn't violate max
if(wgt>_threemax) {
ostringstream message;
message << "Maximum weight for four-body decay "
<< "violated in WeakPartonicDecayer::decay()"
<< "Maximum = " << _fourmax << " weight = " << wgt;
generator()->logWarning( Exception(message.str(),Exception::warning) );
}
}
while ( wgt < _fourmax*UseRandom::rnd() && ntry < _maxtry );
if(ntry==_maxtry) throw Exception()
<< "Too many attempts to generate four body kinematics in "
<< "WeakPartonicDecayer::decay()" << Exception::eventerror;
// set momenta of particles
for(unsigned int ix=0;ix<3;++ix) partons[ix]->setMomentum(pout[ix]);
partons[3]->setMomentum(pspect);
partons[4]->setMomentum(pout[3]);
// special for tau leptons to get correlations
threeBodyMatrixElement(dec,rhoin,pdec,partons);
// set up the colour connections
if(rearranged) swap(partons[1],partons[2]);
// radiation from initial-state
if(initial) {
if(Wcol) {
if(partons[0]->data().iColour()==PDT::Colour3)
partons[0]->antiColourNeighbour(partons[1]);
else
partons[0]-> colourNeighbour(partons[1]);
}
if(partons[2]->data().iColour()==PDT::Colour3) {
partons[2]->antiColourNeighbour(partons[4]);
partons[3]-> colourNeighbour(partons[4]);
}
else {
partons[2]-> colourNeighbour(partons[4]);
partons[3]->antiColourNeighbour(partons[4]);
}
}
// radiation from final-state
else {
if(partons[0]->data().iColour()==PDT::Colour3) {
partons[0]->antiColourNeighbour(partons[4]);
partons[1]-> colourNeighbour(partons[4]);
}
else {
partons[0]-> colourNeighbour(partons[4]);
partons[1]->antiColourNeighbour(partons[4]);
}
if(partons[2]->data().iColour()==PDT::Colour3) {
partons[2]->antiColourNeighbour(partons[3]);
}
else {
partons[2]-> colourNeighbour(partons[3]);
}
}
}
}
return partons;
}
void WeakPartonicDecayer::persistentOutput(PersistentOStream & os) const {
os << MECode << _radprob << _maxtry << _threemax << _fourmax;
}
void WeakPartonicDecayer::persistentInput(PersistentIStream & is, int) {
is >> MECode >> _radprob >> _maxtry >> _threemax >> _fourmax;
}
// The following static variable is needed for the type
// description system in ThePEG.
DescribeClass<WeakPartonicDecayer,PartonicDecayerBase>
describeHerwigWeakPartonicDecayer("Herwig::WeakPartonicDecayer", "HwPartonicDecay.so");
void WeakPartonicDecayer::Init() {
static ClassDocumentation<WeakPartonicDecayer> documentation
("The WeakPartonicDecayer class performs partonic decays of hadrons containing a "
"heavy quark.");
static Switch<WeakPartonicDecayer,int> interfaceMECode
("MECode",
"The code for the type of matrix element to be used.",
&WeakPartonicDecayer::MECode, 0, false, false);
static SwitchOption interfaceMECodePhaseSpace
(interfaceMECode,
"PhaseSpace",
"Phase space decays",
0);
static SwitchOption interfaceMECodeWeak
(interfaceMECode,
"Weak",
"Weak matrix element",
100);
static Parameter<WeakPartonicDecayer,double> interfaceRadiationProbability
("RadiationProbability",
"The probability that QCD radiation produces an extra q qbar pair",
&WeakPartonicDecayer::_radprob, 0., 0.0, 1.,
false, false, Interface::limited);
static Parameter<WeakPartonicDecayer,unsigned int> interfaceMaxTry
("MaxTry",
"The maximum number of attempts to generate the kinematics",
&WeakPartonicDecayer::_maxtry, 300, 10, 1000,
false, false, Interface::limited);
static Parameter<WeakPartonicDecayer,double> interfaceThreeMax
("ThreeMax",
"Maximum weight for sampling of three-body decays",
&WeakPartonicDecayer::_threemax, 3.0, 1.0, 1000.0,
false, false, Interface::limited);
static Parameter<WeakPartonicDecayer,double> interfaceFourMax
("FourMax",
"Maximum weight for sampling of four-body decays",
&WeakPartonicDecayer::_fourmax, 3.0, 1.0, 1000.0,
false, false, Interface::limited);
}
double WeakPartonicDecayer::VAWt(Energy2 t0, Energy2 t1, Energy2 t2, InvEnergy4 t3) {
return (t1-t0)*(t0-t2)*t3;
}
void WeakPartonicDecayer::dataBaseOutput(ofstream & output,
bool header) const {
if(header) output << "update decayers set parameters=\"";
// parameters for the PartonicDecayerBase base class
PartonicDecayerBase::dataBaseOutput(output,false);
output << "newdef " << name() << ":MECode " << MECode << " \n";
if(header) output << "\n\" where BINARY ThePEGName=\""
<< fullName() << "\";" << endl;
}
double WeakPartonicDecayer::
threeBodyMatrixElement(tcPDPtr dec, const RhoDMatrix & rhoin,
Lorentz5Momentum & pdec,
ParticleVector & partons) const {
// spinors
LorentzSpinor <SqrtEnergy> w0[2],w2[2];
LorentzSpinorBar<SqrtEnergy> w1[2],w3[2];
// spinors for the decaying particle and first product
if(dec->id()>0) {
SpinorWaveFunction win(pdec,dec,0,incoming);
w0[0] = win.dimensionedWave();
win.reset(1);
w0[1] = win.dimensionedWave();
SpinorBarWaveFunction wout(partons[2]->momentum(),
partons[2]->dataPtr(),0,outgoing);
w1[0] = wout.dimensionedWave();
wout.reset(1);
w1[1] = wout.dimensionedWave();
}
else {
SpinorBarWaveFunction win(pdec,dec,0,incoming);
w1[0] = win.dimensionedWave();
win.reset(1);
w1[1] = win.dimensionedWave();
SpinorWaveFunction wout(partons[2]->momentum(),
partons[2]->dataPtr(),0,outgoing);
w0[0] = wout.dimensionedWave();
wout.reset(1);
w0[1] = wout.dimensionedWave();
}
// spinors for the W decay products
bool lorder = true;
if(partons[0]->id()<0) {
SpinorWaveFunction wout2(partons[0]->momentum(),
partons[0]->dataPtr(),0,outgoing);
SpinorBarWaveFunction wout3(partons[1]->momentum(),
partons[1]->dataPtr(),0,outgoing);
lorder = partons[0]->dataPtr()->charged();
w2[0] = wout2.dimensionedWave();
w3[0] = wout3.dimensionedWave();
wout2.reset(1);
wout3.reset(1);
w2[1] = wout2.dimensionedWave();
w3[1] = wout3.dimensionedWave();
}
else {
SpinorWaveFunction wout2(partons[1]->momentum(),
partons[1]->dataPtr(),0,outgoing);
SpinorBarWaveFunction wout3(partons[0]->momentum(),
partons[0]->dataPtr(),0,outgoing);
lorder = partons[1]->dataPtr()->charged();
w2[0] = wout2.dimensionedWave();
w3[0] = wout3.dimensionedWave();
wout2.reset(1);
wout3.reset(1);
w2[1] = wout2.dimensionedWave();
w3[1] = wout3.dimensionedWave();
}
bool tau = abs(partons[0]->id())==ParticleID::tauminus || abs(partons[1]->id())==ParticleID::tauminus;
// calculate the currents
LorentzPolarizationVectorE Jbc[2][2],Jdec[2][2];
for(unsigned int ix=0;ix<2;++ix) {
for(unsigned int iy=0;iy<2;++iy) {
if(dec->id()>0)
Jbc [ix][iy] = w0[ix].leftCurrent(w1[iy]);
else
Jbc [ix][iy] = w0[iy].leftCurrent(w1[ix]);
if(lorder)
Jdec[ix][iy] = w2[ix].leftCurrent(w3[iy]);
else
Jdec[ix][iy] = w2[iy].leftCurrent(w3[ix]);
}
}
// compute the matrix element
Complex me[2][2][2][2];
double total=0.;
for(unsigned int i0=0;i0<2;++i0) {
for(unsigned int i1=0;i1<2;++i1) {
for(unsigned int i2=0;i2<2;++i2) {
for(unsigned int i3=0;i3<2;++i3) {
me[i0][i1][i2][i3] = Jbc[i0][i1].dot(Jdec[i2][i3])/sqr(pdec.mass());
total += rhoin(i0,i0).real()*norm(me[i0][i1][i2][i3]);
}
}
}
}
total *=2.;
if(tau) {
RhoDMatrix rho(PDT::Spin1Half);
for(unsigned int it1=0;it1<2;++it1) {
for(unsigned int it2=0;it2<2;++it2) {
for(unsigned int i0=0;i0<2;++i0) {
for(unsigned int i1=0;i1<2;++i1) {
for(unsigned int i2=0;i2<2;++i2) {
rho(it1,it2) += me[i0][i1][it1][i2 ]*conj(me[i0][i1][it2][i2 ]);
}
}
}
}
}
// normalize matrix to unit trace
rho.normalize();
for(unsigned int ix=0;ix<2;++ix) {
if(abs(partons[ix]->id())!=ParticleID::tauminus) continue;
bool loc = partons[ix]->id() < 0;
// create the spin info object
FermionSpinPtr spin = new_ptr(FermionSpinInfo(partons[ix]->momentum(),true));
// assign spinors
for(unsigned int iy=0;iy<2;++iy) {
spin->setBasisState(iy, loc ? w2[iy] : w3[iy].bar());
}
// assign rho
spin->rhoMatrix() = rho;
// assign spin info
partons[ix]->spinInfo(spin);
}
}
return total;
}
double WeakPartonicDecayer::
fourBodyMatrixElement(Lorentz5Momentum & p0,Lorentz5Momentum & p1,
Lorentz5Momentum & p2,Lorentz5Momentum & p3,
Lorentz5Momentum & pg, bool Wcol, bool & initial) const {
Energy2 d01(p0*p1),d02(p0*p2),d03(p0*p3),d0g(p0*pg);
Energy2 d12(p1*p2),d13(p1*p3),d1g(p1*pg);
Energy2 d23(p2*p3),d2g(p2*pg),d3g(p3*pg);
Energy2 m02(sqr(p0.mass())),m12(sqr(p1.mass())),m22(sqr(p2.mass())),
m32(sqr(p3.mass()));
Energy2 mei =
+1./d0g/d1g *( -d01*d12*d3g+d01*d03*d2g+2*d01*d03*d12 )
+1./d0g *( d12*d3g-d03*d12-d02*d03 )
+1./d1g *( d12*d13+d03*d2g+d03*d12 )
+m12/sqr(d1g)*( -d03*d2g-d03*d12 )
+m02/sqr(d0g)*( d12*d3g-d03*d12 );
Energy2 mef = !Wcol ? ZERO :
+1./d2g/d3g *( d0g*d12*d23+d03*d1g*d23+2*d03*d12*d23 )
+1./d2g *( d03*d1g+d03*d12-d02*d12 )
+1./d3g *( d0g*d12-d03*d13+d03*d12 )
+m32/sqr(d3g)*( -d0g*d12-d03*d12 )
+m22/sqr(d2g)*( -d03*d1g-d03*d12 );
initial = mef/(mei+mef)<UseRandom::rnd();
return 0.5*(mei+mef)/sqr(p0.mass()-p1.mass()-p2.mass()-p3.mass()-pg.mass());
}

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