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SMTopDecayer.cc
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SMTopDecayer.cc
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// -*- C++ -*-
//
// SMTopDecayer.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 SMTopDecayer class.
//
#include "SMTopDecayer.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/Interface/ParVector.h"
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
#include "ThePEG/PDT/DecayMode.h"
#include "Herwig++/Decay/DecayVertex.h"
#include "ThePEG/Helicity/WaveFunction/VectorWaveFunction.h"
#include "Herwig++/PDT/ThreeBodyAllOn1IntegralCalculator.h"
using namespace Herwig;
using namespace ThePEG::Helicity;
SMTopDecayer::SMTopDecayer()
:_wquarkwgt(6,0.),_wleptonwgt(3,0.)
{
_wleptonwgt[0] = 0.302583;
_wleptonwgt[1] = 0.301024;
_wleptonwgt[2] = 0.299548;
_wquarkwgt[0] = 0.851719;
_wquarkwgt[1] = 0.0450162;
_wquarkwgt[2] = 0.0456962;
_wquarkwgt[3] = 0.859839;
_wquarkwgt[4] = 3.9704e-06;
_wquarkwgt[5] = 0.000489657;
generateIntermediates(true);
}
bool SMTopDecayer::accept(tcPDPtr parent, const PDVector & children) const {
if(abs(parent->id()) != ParticleID::t) return false;
int id0(0),id1(0),id2(0);
for(PDVector::const_iterator it = children.begin();
it != children.end();++it) {
int id=(**it).id(),absid(abs(id));
if(absid==ParticleID::b&&double(id)/double(parent->id())>0) {
id0=id;
}
else {
switch (absid) {
case ParticleID::nu_e:
case ParticleID::nu_mu:
case ParticleID::nu_tau:
id1 = id;
break;
case ParticleID::eminus:
case ParticleID::muminus:
case ParticleID::tauminus:
id2 = id;
break;
case ParticleID::b:
case ParticleID::d:
case ParticleID::s:
id1 = id;
break;
case ParticleID::u:
case ParticleID::c:
id2=id;
break;
default :
break;
}
}
}
if(id0==0||id1==0||id2==0) return false;
if(double(id1)/double(id2)>0) return false;
return true;
}
ParticleVector SMTopDecayer::decay(const Particle & parent,
const PDVector & children) const {
int id1(0),id2(0);
for(PDVector::const_iterator it = children.begin();
it != children.end();++it) {
int id=(**it).id(),absid=abs(id);
if(absid == ParticleID::b && double(id)/double(parent.id())>0) continue;
//leptons
if(absid > 10 && absid%2==0) id1=absid;
if(absid > 10 && absid%2==1) id2=absid;
//quarks
if(absid < 10 && absid%2==0) id2=absid;
if(absid < 10 && absid%2==1) id1=absid;
}
unsigned int imode(0);
if(id2 >=11 && id2<=16) imode = (id1-12)/2;
else imode = id1+1+id2/2;
bool cc = parent.id() == ParticleID::tbar;
ParticleVector out(generate(true,cc,imode,parent));
//arrange colour flow
PPtr pparent=const_ptr_cast<PPtr>(&parent);
out[1]->incomingColour(pparent,out[1]->id()<0);
ParticleVector products = out[0]->children();
if(products[0]->hasColour())
products[0]->colourNeighbour(products[1],true);
else if(products[0]->hasAntiColour())
products[0]->colourNeighbour(products[1],false);
return out;
}
void SMTopDecayer::persistentOutput(PersistentOStream & os) const {
os << _wvertex << _wquarkwgt << _wleptonwgt << _wplus;
}
void SMTopDecayer::persistentInput(PersistentIStream & is, int) {
is >> _wvertex >> _wquarkwgt >> _wleptonwgt >> _wplus;
}
ClassDescription<SMTopDecayer> SMTopDecayer::initSMTopDecayer;
// Definition of the static class description member.
void SMTopDecayer::Init() {
static ClassDocumentation<SMTopDecayer> documentation
("This is the implementation of the SMTopDecayer which "
"decays top quarks into bottom quarks and either leptons "
"or quark-antiquark pairs.");
static ParVector<SMTopDecayer,double> interfaceQuarkWeights
("QuarkWeights",
"Maximum weights for the hadronic decays",
&SMTopDecayer::_wquarkwgt, 6, 1.0, 0.0, 10.0,
false, false, Interface::limited);
static ParVector<SMTopDecayer,double> interfaceLeptonWeights
("LeptonWeights",
"Maximum weights for the semi-leptonic decays",
&SMTopDecayer::_wleptonwgt, 3, 1.0, 0.0, 10.0,
false, false, Interface::limited);
}
double SMTopDecayer::me2(bool vertex, const int,
const Particle & inpart,
const ParticleVector & decay) const {
RhoDMatrix rhot(PDT::Spin1Half);
rhot.average(); //diagonalise
DecayMatrixElement topMe(PDT::Spin1Half,PDT::Spin1Half,
PDT::Spin1Half,PDT::Spin1Half);
Energy2 scale(inpart.mass()*inpart.mass());
if(inpart.id() == ParticleID::t) {
//Vectors to hold all heliticies of spinors
vector<SpinorWaveFunction> twave,awave;
vector<SpinorBarWaveFunction> bwave,fwave;
//Set-up spinors for external particles
SpinorWaveFunction(twave,rhot,const_ptr_cast<tPPtr>(&inpart),
incoming,true,vertex);
SpinorBarWaveFunction(bwave,decay[0],outgoing,true,vertex);
SpinorWaveFunction(awave,decay[1],outgoing,true,vertex);
SpinorBarWaveFunction(fwave,decay[2],outgoing,true,vertex);
//Define intermediate vector wave-function for Wplus
tcPDPtr Wplus(getParticleData(ParticleID::Wplus));
VectorWaveFunction inter;
unsigned int thel,bhel,fhel,afhel;
for(thel = 0;thel<2;++thel){
for(bhel = 0;bhel<2;++bhel){
inter = _wvertex->evaluate(scale,1,Wplus,twave[thel],bwave[bhel]);
for(afhel=0;afhel<2;++afhel){
for(fhel=0;fhel<2;++fhel){
topMe(thel,bhel,afhel,fhel) =
_wvertex->evaluate(scale,awave[afhel],
fwave[fhel],inter);
}
}
}
}
}
if(inpart.id() == ParticleID::tbar) {
//Vectors to hold all heliticies of spinors
vector<SpinorWaveFunction> bbarWave,awave;
vector<SpinorBarWaveFunction> tbarWave,fwave;
//Set-up spinors for externl particles
SpinorBarWaveFunction(tbarWave,rhot,const_ptr_cast<tPPtr>(&inpart),
incoming,true,vertex);
SpinorWaveFunction(bbarWave,decay[0],outgoing,true,vertex);
SpinorBarWaveFunction(fwave,decay[1],outgoing,true,vertex);
SpinorWaveFunction(awave,decay[2],outgoing,true,vertex);
VectorWaveFunction inter;
tcPDPtr Wminus(getParticleData(ParticleID::Wminus));
unsigned int tbhel,bbhel,afhel,fhel;
for(tbhel = 0;tbhel<2;++tbhel){
for(bbhel = 0;bbhel<2;++bbhel){
inter = _wvertex->
evaluate(scale,1,Wminus,bbarWave[bbhel],tbarWave[tbhel]);
for(afhel=0;afhel<2;++afhel){
for(fhel=0;fhel<2;++fhel){
topMe(tbhel,bbhel,fhel,afhel) =
_wvertex->evaluate(scale,awave[afhel],
fwave[fhel],inter);
}
}
}
}
}
ME(topMe);
double output = (topMe.contract(rhot)).real();
if(abs(decay[1]->id())<=6) output *=3.;
return output;
}
void SMTopDecayer::doinit() throw(InitException) {
DecayIntegrator::doinit();
//get vertices from SM object
tcHwSMPtr hwsm = dynamic_ptr_cast<tcHwSMPtr>(standardModel());
if(!hwsm) throw InitException() << "Must have Herwig::StandardModel in "
<< "SMTopDecayer::doinit()";
_wvertex = hwsm->vertexFFW();
//initialise
_wvertex->init();
//set up decay modes
_wplus = getParticleData(ParticleID::Wplus);
DecayPhaseSpaceModePtr mode;
DecayPhaseSpaceChannelPtr Wchannel;
PDVector extpart(4);
vector<double> wgt(1,1.0);
extpart[0] = getParticleData(ParticleID::t);
extpart[1] = getParticleData(ParticleID::b);
//lepton modes
for(int i=11; i<17;i+=2) {
extpart[2] = getParticleData(-i);
extpart[3] = getParticleData(i+1);
mode = new_ptr(DecayPhaseSpaceMode(extpart,this));
Wchannel = new_ptr(DecayPhaseSpaceChannel(mode));
Wchannel->addIntermediate(extpart[0],0,0.0,-1,1);
Wchannel->addIntermediate(_wplus,0,0.0,2,3);
Wchannel->init();
mode->addChannel(Wchannel);
addMode(mode,_wleptonwgt[(i-11)/2],wgt);
}
//quark modes
unsigned int iz=0;
for(int ix=1;ix<6;ix+=2) {
for(int iy=2;iy<6;iy+=2) {
// check that the combination of particles is allowed
if(_wvertex->allowed(-ix,iy,ParticleID::Wminus)) {
extpart[2] = getParticleData(-ix);
extpart[3] = getParticleData( iy);
mode = new_ptr(DecayPhaseSpaceMode(extpart,this));
Wchannel = new_ptr(DecayPhaseSpaceChannel(mode));
Wchannel->addIntermediate(extpart[0],0,0.0,-1,1);
Wchannel->addIntermediate(_wplus,0,0.0,2,3);
Wchannel->init();
mode->addChannel(Wchannel);
addMode(mode,_wquarkwgt[iz],wgt);
++iz;
}
else {
throw InitException() << "SMTopDecayer::doinit() the W vertex"
<< "cannot handle all the quark modes"
<< Exception::abortnow;
}
}
}
}
void SMTopDecayer::dataBaseOutput(ofstream & os,bool header) const {
if(header) os << "update decayers set parameters=\"";
// parameters for the DecayIntegrator base class
for(unsigned int ix=0;ix<_wquarkwgt.size();++ix) {
os << "set " << fullName() << ":QuarkWeights " << ix << " "
<< _wquarkwgt[ix] << "\n";
}
for(unsigned int ix=0;ix<_wleptonwgt.size();++ix) {
os << "set " << fullName() << ":LeptonWeights " << ix << " "
<< _wleptonwgt[ix] << "\n";
}
DecayIntegrator::dataBaseOutput(os,false);
if(header) os << "\n\" where BINARY ThePEGName=\"" << fullName() << "\";" << endl;
}
void SMTopDecayer::doinitrun() {
DecayIntegrator::doinitrun();
if(initialize()) {
for(unsigned int ix=0;ix<numberModes();++ix) {
if(ix<3) _wleptonwgt[ix ] = mode(ix)->maxWeight();
else _wquarkwgt [ix-3] = mode(ix)->maxWeight();
}
}
}
WidthCalculatorBasePtr SMTopDecayer::threeBodyMEIntegrator(const DecayMode & dm) const {
// identify W decay products
int sign = dm.parent()->id() > 0 ? 1 : -1;
int iferm(0),ianti(0);
for(ParticleMSet::const_iterator pit=dm.products().begin();
pit!=dm.products().end();++pit) {
int id = (**pit).id();
if(id*sign != ParticleID::b) {
if (id*sign > 0 ) iferm = id*sign;
else ianti = id*sign;
}
}
assert(iferm!=0&&ianti!=0);
// work out which mode we are doing
int imode(-1);
for(unsigned int ix=0;ix<numberModes();++ix) {
if(mode(ix)->externalParticles(2)->id() == ianti &&
mode(ix)->externalParticles(3)->id() == iferm ) {
imode = ix;
break;
}
}
assert(imode>=0);
// get the masses we need
Energy m[3] = {mode(imode)->externalParticles(1)->mass(),
mode(imode)->externalParticles(3)->mass(),
mode(imode)->externalParticles(2)->mass()};
return
new_ptr(ThreeBodyAllOn1IntegralCalculator<SMTopDecayer>
(3,_wplus->mass(),_wplus->width(),0.0,*this,imode,m[0],m[1],m[2]));
}
InvEnergy SMTopDecayer::threeBodydGammads(const int imode, const Energy2 mt2,
const Energy2 mffb2, const Energy mb,
const Energy mf, const Energy mfb) const {
Energy mffb(sqrt(mffb2));
Energy mw(_wplus->mass());
Energy2 mw2(sqr(mw)),gw2(sqr(_wplus->width()));
Energy mt(sqrt(mt2));
Energy Eb = 0.5*(mt2-mffb2-sqr(mb))/mffb;
Energy Ef = 0.5*(mffb2-sqr(mfb)+sqr(mf))/mffb;
Energy Ebm = sqrt(sqr(Eb)-sqr(mb));
Energy Efm = sqrt(sqr(Ef)-sqr(mf));
Energy2 upp = sqr(Eb+Ef)-sqr(Ebm-Efm);
Energy2 low = sqr(Eb+Ef)-sqr(Ebm+Efm);
InvEnergy width=(dGammaIntegrand(mffb2,upp,mt,mb,mf,mfb,mw)-
dGammaIntegrand(mffb2,low,mt,mb,mf,mfb,mw))
/32./mt2/mt/8/pow(Constants::pi,3)/(sqr(mffb2-mw2)+mw2*gw2);
// couplings
width *= 0.25*sqr(4.*Constants::pi*generator()->standardModel()->alphaEM(mt2)/
generator()->standardModel()->sin2ThetaW());
width *= generator()->standardModel()->CKM(*mode(imode)->externalParticles(0),
*mode(imode)->externalParticles(1));
if(abs(mode(imode)->externalParticles(2)->id())<=6) {
width *=3.;
if(abs(mode(imode)->externalParticles(2)->id())%2==0)
width *=generator()->standardModel()->CKM(*mode(imode)->externalParticles(2),
*mode(imode)->externalParticles(3));
else
width *=generator()->standardModel()->CKM(*mode(imode)->externalParticles(3),
*mode(imode)->externalParticles(2));
}
// final spin average
assert(!isnan(width*GeV));
return 0.5*width;
}
Energy6 SMTopDecayer::dGammaIntegrand(Energy2 mffb2, Energy2 mbf2, Energy mt,
Energy mb, Energy mf, Energy mfb, Energy mw) const {
Energy2 mt2(sqr(mt)) ,mb2(sqr(mb)) ,mf2(sqr(mf )),mfb2(sqr(mfb )),mw2(sqr(mw ));
Energy4 mt4(sqr(mt2)),mb4(sqr(mb2)),mf4(sqr(mf2)),mfb4(sqr(mfb2)),mw4(sqr(mw2));
return -mbf2 * ( + 6 * mb2 * mf2 * mfb2 * mffb2 + 6 * mb2 * mt2 * mfb2 * mffb2
+ 6 * mb2 * mt2 * mf2 * mffb2 + 12 * mb2 * mt2 * mf2 * mfb2
- 3 * mb2 * mfb4 * mffb2 + 3 * mb2 * mf2 * mffb2 * mffb2
- 3 * mb2 * mf4 * mffb2 - 6 * mb2 * mt2 * mfb4
- 6 * mb2 * mt2 * mf4 - 3 * mb4 * mfb2 * mffb2
- 3 * mb4 * mf2 * mffb2 - 6 * mb4 * mf2 * mfb2
+ 3 * mt4 * mf4 + 3 * mb4 * mfb4
+ 3 * mb4 * mf4 + 3 * mt4 * mfb4
+ 3 * mb2 * mfb2 * mffb2 * mffb2 + 3 * mt2 * mfb2 * mffb2 * mffb2
- 3 * mt2 * mfb4 * mffb2 + 3 * mt2 * mf2 * mffb2 * mffb2
- 3 * mt2 * mf4 * mffb2 - 3 * mt4 * mfb2 * mffb2
- 3 * mt4 * mf2 * mffb2 - 6 * mt4 * mf2 * mfb2
+ 6 * mt2 * mf2 * mfb2 * mffb2 + 12 * mt2 * mf2 * mw4
+ 12 * mb2 * mfb2 * mw4 + 12 * mb2 * mt2 * mw4
+ 6 * mw2 * mt2 * mfb2 * mbf2 - 12 * mw2 * mt2 * mf2 * mffb2
- 6 * mw2 * mt2 * mf2 * mbf2 - 12 * mw2 * mt2 * mf2 * mfb2
- 12 * mw2 * mb2 * mfb2 * mffb2 - 6 * mw2 * mb2 * mfb2 * mbf2
+ 6 * mw2 * mb2 * mf2 * mbf2 - 12 * mw2 * mb2 * mf2 * mfb2
- 12 * mw2 * mb2 * mt2 * mfb2 - 12 * mw2 * mb2 * mt2 * mf2
+ 12 * mf2 * mfb2 * mw4 + 4 * mbf2 * mbf2 * mw4
- 6 * mfb2 * mbf2 * mw4 - 6 * mf2 * mbf2 * mw4
- 6 * mt2 * mbf2 * mw4 - 6 * mb2 * mbf2 * mw4
+ 12 * mw2 * mt2 * mf4 + 12 * mw2 * mt4 * mf2
+ 12 * mw2 * mb2 * mfb4 + 12 * mw2 * mb4 * mfb2) /mw4 / 3.;
}

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