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// -*- C++ -*-
//
// MEPP2VV.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 MEPP2VV class.
//
#include "MEPP2VV.h"
#include "ThePEG/Interface/Switch.h"
#include "ThePEG/Interface/Parameter.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
#include "ThePEG/PDT/EnumParticles.h"
#include "ThePEG/MatrixElement/Tree2toNDiagram.h"
#include "ThePEG/Handlers/StandardXComb.h"
#include "Herwig++/Models/StandardModel/StandardModel.h"
#include "Herwig++/MatrixElement/HardVertex.h"
using namespace Herwig;
MEPP2VV::MEPP2VV() : _process(0), _maxflavour(5) , _mixingInWW(0),
scaleopt_(1), mu_F_(100.*GeV) , mu_UV_(100.*GeV) ,
scaleFact_(1.), spinCorrelations_(1), debugMCFM_(0) {
massOption(true ,1);
massOption(false,1);
}
unsigned int MEPP2VV::orderInAlphaS() const {
return 0;
}
unsigned int MEPP2VV::orderInAlphaEW() const {
return 2;
}
ClassDescription<MEPP2VV> MEPP2VV::initMEPP2VV;
// Definition of the static class description member.
void MEPP2VV::Init() {
static ClassDocumentation<MEPP2VV> documentation
("The MEPP2VV class simulates the production of W+W-, "
"W+/-Z0 and Z0Z0 in hadron-hadron collisions using the 2->2"
" matrix elements");
static Switch<MEPP2VV,unsigned int> interfaceProcess
("Process",
"Which processes to include",
&MEPP2VV::_process, 0, false, false);
static SwitchOption interfaceProcessAll
(interfaceProcess,
"All",
"Include all the processes",
0);
static SwitchOption interfaceProcessWW
(interfaceProcess,
"WW",
"Only include W+W-",
1);
static SwitchOption interfaceProcessWZ
(interfaceProcess,
"WZ",
"Only include W+/-Z",
2);
static SwitchOption interfaceProcessZZ
(interfaceProcess,
"ZZ",
"Only include ZZ",
3);
static SwitchOption interfaceProcessWpZ
(interfaceProcess,
"WpZ",
"Only include W+ Z",
4);
static SwitchOption interfaceProcessWmZ
(interfaceProcess,
"WmZ",
"Only include W- Z",
5);
static Parameter<MEPP2VV,int> interfaceMaximumFlavour
("MaximumFlavour",
"The maximum flavour allowed for the incoming quarks",
&MEPP2VV::_maxflavour, 5, 2, 5,
false, false, Interface::limited);
static Switch<MEPP2VV,bool> interfaceFlavourMixingInWWProduction
("FlavourMixingInWWProduction",
"Disable CKM mixing in WW production i.e. impose unitarity of the CKM matrix",
&MEPP2VV::_mixingInWW, 0, false, false);
static SwitchOption interfaceNoMixingInWW
(interfaceFlavourMixingInWWProduction,
"NoMixing",
"The CKM matrix is a unit matrix (equates to imposing unitarity of the CKM)",
0);
static SwitchOption interfaceMixingInWW
(interfaceFlavourMixingInWWProduction,
"Mixing",
"Allow the flvours of the intermediate and initial state quarks to differ",
1);
static Switch<MEPP2VV,unsigned int> interfaceFactorizationScaleOption
("FactorizationScaleOption",
"Option for the choice of factorization (and renormalization) scale",
&MEPP2VV::scaleopt_, 1, false, false);
static SwitchOption interfaceDynamic
(interfaceFactorizationScaleOption,
"Dynamic",
"Dynamic factorization scale equal to the current sqrt(sHat())",
1);
static SwitchOption interfaceFixed
(interfaceFactorizationScaleOption,
"Fixed",
"Use a fixed factorization scale set with FactorizationScaleValue",
2);
static Parameter<MEPP2VV,Energy> interfaceFactorizationScaleValue
("FactorizationScaleValue",
"Value to use in the event of a fixed factorization scale",
&MEPP2VV::mu_F_, GeV, 100.0*GeV, 50.0*GeV, 500.0*GeV,
true, false, Interface::limited);
static Parameter<MEPP2VV,Energy> interfaceRenormalizationScaleValue
("RenormalizationScaleValue",
"Value to use for the (UV) renormalization scale",
&MEPP2VV::mu_UV_, GeV, 100.0*GeV, 50.0*GeV, 500.0*GeV,
true, false, Interface::limited);
static Parameter<MEPP2VV,double> interfaceScaleFactor
("ScaleFactor",
"The factor used before sHat if using a running scale",
&MEPP2VV::scaleFact_, 1.0, 0.0, 10.0,
false, false, Interface::limited);
static Switch<MEPP2VV,unsigned int> interfaceSpinCorrelations
("SpinCorrelations",
"Option to remove spin correlation effects in boson decays "
" for testing purposes and for generating NLO spin correlations "
" by the method of Frixione, Laenen, Motylinski and Webber.",
&MEPP2VV::spinCorrelations_, 1, false, false);
static SwitchOption interfaceSpinCorrelationsOff
(interfaceSpinCorrelations,
"Off",
"Turning off the spin correlations in the vector boson decays",
0);
static SwitchOption interfaceSpinCorrelationsOn
(interfaceSpinCorrelations,
"On",
"Turning on the spin correlations in the vector boson decays",
1);
static Switch<MEPP2VV,unsigned int> interfaceDebugMCFM
("DebugMCFM",
"Option to make t-channel propagators massless for WW (as in MCFM)",
&MEPP2VV::debugMCFM_, 0, false, false);
static SwitchOption interfaceNoDebugging
(interfaceDebugMCFM,
"NoDebugging",
"Default massive t-channel propagators in WW production",
0);
static SwitchOption interfaceDebugging
(interfaceDebugMCFM,
"Debugging",
"Use massless t-channel propagators in WW production (as in MCFM)",
1);
}
void MEPP2VV::persistentOutput(PersistentOStream & os) const {
os << _vertexFFP << _vertexFFW << _vertexFFZ << _vertexWWW << _process
<< scaleopt_ << ounit(mu_F_,GeV) << ounit(mu_UV_,GeV)
<< scaleFact_ << spinCorrelations_ << debugMCFM_;
}
void MEPP2VV::persistentInput(PersistentIStream & is, int) {
is >> _vertexFFP >> _vertexFFW >> _vertexFFZ >> _vertexWWW >> _process
>> scaleopt_ >> iunit(mu_F_,GeV) >> iunit(mu_UV_,GeV)
>> scaleFact_ >> spinCorrelations_ >> debugMCFM_;
}
Energy2 MEPP2VV::scale() const {
return scaleopt_ == 1 ?
sqr(mePartonData()[2]->mass())+sqr(mePartonData()[3]->mass())
: sqr(mu_F_);
}
IBPtr MEPP2VV::clone() const {
return new_ptr(*this);
}
IBPtr MEPP2VV::fullclone() const {
return new_ptr(*this);
}
void MEPP2VV::doinit() throw(InitException) {
HwME2to2Base::doinit();
// get the vertices we need
// get a pointer to the standard model object in the run
static const tcHwSMPtr hwsm
= dynamic_ptr_cast<tcHwSMPtr>(standardModel());
if (!hwsm) throw InitException() << "hwsm pointer is null in"
<< " MEPP2VV::doinit()"
<< Exception::abortnow;
// get pointers to all required Vertex objects
_vertexFFZ = hwsm->vertexFFZ();
_vertexFFP = hwsm->vertexFFP();
_vertexWWW = hwsm->vertexWWW();
_vertexFFW = hwsm->vertexFFW();
}
double MEPP2VV::getCosTheta(double ctmin, double ctmax, const double * r) {
double rand = *r;
Energy2 m12 = sqr(meMomenta()[2].mass());
Energy2 m22 = sqr(meMomenta()[3].mass());
Energy2 D1 = sHat()-m12-m22;
Energy4 lambda = sqr(D1) - 4.*m12*m22;
if(meMomenta()[2].mass()==meMomenta()[3].mass())
lambda = sHat()*(sHat()-4.*m12);
double D = D1 / sqrt(lambda);
if(mePartonData()[2]->id()==ParticleID::Z0&&
mePartonData()[3]->id()==ParticleID::Z0) {
double prob = 0.5;
double costh;
double fraction1 = (D-ctmax)/(D-ctmin);
double fraction2 = (D+ctmin)/(D+ctmax);
if(rand<=prob) {
rand /=prob;
costh = D - (D - ctmin) * pow(fraction1, rand);
}
else {
rand = (rand-prob)/(1.-prob);
costh =-D + (D + ctmax) * pow(fraction2, rand);
}
jacobian(1./(prob /((costh - D) * log(fraction1))-
(1.-prob)/((costh + D) * log(fraction2))));
return costh;
}
else {
double fraction = (D-ctmax)/(D-ctmin);
double costh = D - (D - ctmin) * pow(fraction, rand);
jacobian((costh - D) * log(fraction));
return costh;
}
}
Selector<const ColourLines *>
MEPP2VV::colourGeometries(tcDiagPtr diag) const {
static ColourLines cs("1 -2");
static ColourLines ct("1 2 -3");
Selector<const ColourLines *> sel;
if(diag->id()>0) sel.insert(1.0, &cs);
else sel.insert(1.0, &ct);
return sel;
}
void MEPP2VV::getDiagrams() const {
typedef std::vector<pair<tcPDPtr,tcPDPtr> > Pairvector;
tcPDPtr wPlus = getParticleData(ParticleID::Wplus );
tcPDPtr wMinus = getParticleData(ParticleID::Wminus);
tcPDPtr z0 = getParticleData(ParticleID::Z0 );
tcPDPtr gamma = getParticleData(ParticleID::gamma);
// W+ W-
if(_process==0||_process==1) {
for(int ix=1;ix<=_maxflavour;++ix) {
tcPDPtr qk = getParticleData(ix);
tcPDPtr w1 = ix%2==0 ? wPlus : wMinus;
tcPDPtr w2 = ix%2!=0 ? wPlus : wMinus;
for(int iy=1;iy<=_maxflavour;++iy) {
if(!_mixingInWW&&(ix!=iy)) continue;
if(abs(ix-iy)%2!=0) continue;
tcPDPtr qb = getParticleData(-iy);
// s channel photon
add(new_ptr((Tree2toNDiagram(2),qk,qb,1,gamma,3,w1,3,w2,-4)));
// s-channel Z
add(new_ptr((Tree2toNDiagram(2),qk,qb,1, z0,3,w1,3,w2,-5)));
// t-channel
if(ix%2==0) {
int idiag=0;
for(int iz=1;iz<=5;iz+=2) {
--idiag;
tcPDPtr tc = getParticleData(iz);
add(new_ptr((Tree2toNDiagram(3), qk, tc, qb, 1, w1, 2, w2, idiag)));
}
}
else {
int idiag=0;
for(int iz=2;iz<=6;iz+=2) {
--idiag;
tcPDPtr tc = getParticleData(iz);
add(new_ptr((Tree2toNDiagram(3), qk, tc, qb, 1, w1, 2, w2, idiag)));
}
}
}
}
}
// W+/- Z
if(_process==0||_process==2||_process==4||_process==5) {
// possible parents
Pairvector parentpair;
parentpair.reserve(6);
// don't even think of putting 'break' in here!
switch(_maxflavour) {
case 5:
parentpair.push_back(make_pair(getParticleData(ParticleID::b),
getParticleData(ParticleID::cbar)));
parentpair.push_back(make_pair(getParticleData(ParticleID::b),
getParticleData(ParticleID::ubar)));
case 4:
parentpair.push_back(make_pair(getParticleData(ParticleID::s),
getParticleData(ParticleID::cbar)));
parentpair.push_back(make_pair(getParticleData(ParticleID::d),
getParticleData(ParticleID::cbar)));
case 3:
parentpair.push_back(make_pair(getParticleData(ParticleID::s),
getParticleData(ParticleID::ubar)));
case 2:
parentpair.push_back(make_pair(getParticleData(ParticleID::d),
getParticleData(ParticleID::ubar)));
default:
;
}
// W+ Z
if(_process==0||_process==2||_process==4) {
for(unsigned int ix=0;ix<parentpair.size();++ix) {
add(new_ptr((Tree2toNDiagram(3), parentpair[ix].second->CC(),
parentpair[ix].first, parentpair[ix].first->CC(),
1, wPlus, 2, z0, -1)));
add(new_ptr((Tree2toNDiagram(3), parentpair[ix].second->CC(),
parentpair[ix].second->CC() , parentpair[ix].first->CC(),
2, wPlus, 1, z0, -2)));
add(new_ptr((Tree2toNDiagram(2), parentpair[ix].second->CC(),
parentpair[ix].first->CC(), 1, wPlus, 3, wPlus, 3, z0, -3)));
}
}
// W- Z
if(_process==0||_process==2||_process==5) {
for(unsigned int ix=0;ix<parentpair.size();++ix) {
add(new_ptr((Tree2toNDiagram(3), parentpair[ix].first,
parentpair[ix].second->CC(),
parentpair[ix].second, 1, wMinus, 2, z0, -1)));
add(new_ptr((Tree2toNDiagram(3), parentpair[ix].first,
parentpair[ix].first , parentpair[ix].second, 2, wMinus, 1, z0, -2)));
add(new_ptr((Tree2toNDiagram(2), parentpair[ix].first,
parentpair[ix].second, 1, wMinus, 3, wMinus, 3, z0, -3)));
}
}
}
// Z Z
if(_process==0||_process==3) {
for(int ix=1;ix<=_maxflavour;++ix) {
tcPDPtr qk = getParticleData(ix);
tcPDPtr qb = qk->CC();
add(new_ptr((Tree2toNDiagram(3), qk, qk, qb, 1, z0, 2, z0, -1)));
add(new_ptr((Tree2toNDiagram(3), qk, qk, qb, 2, z0, 1, z0, -2)));
}
}
}
Selector<MEBase::DiagramIndex>
MEPP2VV::diagrams(const DiagramVector & diags) const {
Selector<DiagramIndex> sel;
for ( DiagramIndex i = 0; i < diags.size(); ++i )
sel.insert(meInfo()[abs(diags[i]->id())], i);
return sel;
}
double MEPP2VV::me2() const {
// setup momenta and particle data for the external wavefunctions
// incoming
SpinorWaveFunction em_in( meMomenta()[0],mePartonData()[0],incoming);
SpinorBarWaveFunction ep_in( meMomenta()[1],mePartonData()[1],incoming);
// outgoing
VectorWaveFunction v1_out(meMomenta()[2],mePartonData()[2],outgoing);
VectorWaveFunction v2_out(meMomenta()[3],mePartonData()[3],outgoing);
vector<SpinorWaveFunction> f1;
vector<SpinorBarWaveFunction> a1;
vector<VectorWaveFunction> v1,v2;
// calculate the wavefunctions
for(unsigned int ix=0;ix<3;++ix) {
if(ix<2) {
em_in.reset(ix);
f1.push_back(em_in);
ep_in.reset(ix);
a1.push_back(ep_in);
}
v1_out.reset(ix);
v1.push_back(v1_out);
v2_out.reset(ix);
v2.push_back(v2_out);
}
return helicityME(f1,a1,v1,v2,false);
}
double MEPP2VV::helicityME(vector<SpinorWaveFunction> & f1,
vector<SpinorBarWaveFunction> & a1,
vector<VectorWaveFunction> & v1,
vector<VectorWaveFunction> & v2,
bool calc) const {
// cerr << "testing process"
// << mePartonData()[0]->PDGName() << " "
// << mePartonData()[1]->PDGName() << " -> "
// << mePartonData()[2]->PDGName() << " "
// << mePartonData()[3]->PDGName() << "\n";
double output(0.);
vector<double> me(5,0.0);
ProductionMatrixElement newme(PDT::Spin1Half,PDT::Spin1Half,
PDT::Spin1,PDT::Spin1);
// q qbar -> Z Z
if(mePartonData()[2]->id()==ParticleID::Z0&&
mePartonData()[3]->id()==ParticleID::Z0) {
vector<Complex> diag(2,0.0);
SpinorWaveFunction inter;
for(unsigned int ihel1=0;ihel1<2;++ihel1) {
for(unsigned int ihel2=0;ihel2<2;++ihel2) {
for(unsigned int ohel1=0;ohel1<3;++ohel1) {
for(unsigned int ohel2=0;ohel2<3;++ohel2) {
inter = _vertexFFZ->evaluate(scale(),1,f1[ihel1].getParticle(),
f1[ihel1],v1[ohel1]);
diag[0] = _vertexFFZ->evaluate(scale(),inter,a1[ihel2],v2[ohel2]);
inter = _vertexFFZ->evaluate(scale(),1,f1[ihel1].getParticle(),
f1[ihel1] ,v2[ohel2]);
diag[1] = _vertexFFZ->evaluate(scale(),inter,a1[ihel2],v1[ohel1]);
// individual diagrams
for (size_t ii=0; ii<2; ++ii) me[ii] += std::norm(diag[ii]);
// full matrix element
diag[0] += diag[1];
output += std::norm(diag[0]);
// storage of the matrix element for spin correlations
if(calc) newme(ihel1,ihel2,ohel1,ohel2) = diag[0];
}
}
}
}
// identical particle factor
output /= 2.;
}
// q qbar -> W W
else if(abs(mePartonData()[2]->id())==ParticleID::Wplus&&
abs(mePartonData()[3]->id())==ParticleID::Wplus) {
// particle data for the t-channel intermediate
tcPDPtr tc[3];
if(f1[0].getParticle()->id()%2==0) {
for(unsigned int ix=0;ix<3;++ix) tc[ix] = getParticleData(1+2*ix);
}
else {
for(unsigned int ix=0;ix<3;++ix) tc[ix] = getParticleData(2+2*ix);
}
tcPDPtr gamma = getParticleData(ParticleID::gamma);
tcPDPtr z0 = getParticleData(ParticleID::Z0);
vector<Complex> diag(5,0.0);
VectorWaveFunction interP,interZ;
bool sChannel =
f1[0].getParticle()->id() == -a1[0].getParticle()->id();
for(unsigned int ihel1=0;ihel1<2;++ihel1) {
for(unsigned int ihel2=0;ihel2<2;++ihel2) {
if(sChannel) {
interP = _vertexFFP->evaluate(scale(),1,gamma,f1[ihel1],a1[ihel2]);
interZ = _vertexFFZ->evaluate(scale(),1,z0 ,f1[ihel1],a1[ihel2]);
}
for(unsigned int ohel1=0;ohel1<3;++ohel1) {
for(unsigned int ohel2=0;ohel2<3;++ohel2) {
// s-channel photon
diag[3] = sChannel ?
_vertexWWW->evaluate(scale(),interP,v2[ohel2],v1[ohel1]) : 0.;
// s-channel Z0
diag[4] = sChannel ?
_vertexWWW->evaluate(scale(),interZ,v2[ohel2],v1[ohel1]) : 0.;
// t-channel
for(unsigned int ix=0;ix<3;++ix) {
// cerr << "testing in loop " << f1[ihel1].getParticle()->PDGName()
// << " " << tc[ix]->PDGName() << " "
// << a1[ihel2].getParticle()->PDGName()
// << "\n";
SpinorWaveFunction inter =
_vertexFFW->evaluate(scale(),1,tc[ix],f1[ihel1],v1[ohel1]);
diag[ix] =
_vertexFFW->evaluate(scale(),inter,a1[ihel2],v2[ohel2]);
if(debugMCFM_) {
Energy2 the_that;
the_that =(meMomenta()[0]-meMomenta()[2]).m2();
Energy2 the_m2(sqr(tc[ix]->mass()));
diag[ix]*=(the_that - the_m2) / the_that;
}
}
// individual diagrams
for (size_t ii=0; ii<5; ++ii) me[ii] += std::norm(diag[ii]);
// full matrix element
// cerr << "testing diagrams "
// << diag[0] << " " << diag[1] << " "
// << diag[2] << " " << diag[3] << " "
// << diag[4] << "\n";
diag[0] += diag[1]+diag[2]+diag[3]+diag[4];
output += std::norm(diag[0]);
// storage of the matrix element for spin correlations
if(calc) newme(ihel1,ihel2,ohel1,ohel2) = diag[0];
}
}
}
}
}
// q qbar -> W Z
else {
vector<Complex> diag(3,0.0);
SpinorWaveFunction inter;
for(unsigned int ihel1=0;ihel1<2;++ihel1) {
for(unsigned int ihel2=0;ihel2<2;++ihel2) {
VectorWaveFunction interW =
_vertexFFW->evaluate(scale(),1,v1[0].getParticle()->CC(),
f1[ihel1],a1[ihel2]);
for(unsigned int ohel1=0;ohel1<3;++ohel1) {
for(unsigned int ohel2=0;ohel2<3;++ohel2) {
// t-channel diagrams
inter = _vertexFFW->evaluate(scale(),1,a1[ihel1].getParticle(),
f1[ihel1],v1[ohel1]);
diag[0] = _vertexFFZ->evaluate(scale(),inter,a1[ihel2],v2[ohel2]);
inter = _vertexFFZ->evaluate(scale(),1,f1[ihel1].getParticle(),
f1[ihel1] ,v2[ohel2]);
diag[1] = _vertexFFW->evaluate(scale(),inter,a1[ihel2],v1[ohel1]);
// s-channel diagram
diag[2] = _vertexWWW->evaluate(scale(),interW,v1[ohel1],v2[ohel2]);
// individual diagrams
for (size_t ii=0; ii<3; ++ii) me[ii] += std::norm(diag[ii]);
// full matrix element
diag[0] += diag[1]+diag[2];
output += std::norm(diag[0]);
// storage of the matrix element for spin correlations
if(calc) newme(ihel1,ihel2,ohel1,ohel2) = diag[0];
}
}
}
}
}
DVector save(5);
for (size_t i = 0; i < 5; ++i) {
save[i] = 0.25 * me[i];
}
meInfo(save);
if(calc) _me.reset(newme);
return 0.25*output/3.;
}
void MEPP2VV::constructVertex(tSubProPtr sub) {
if(!spinCorrelations_) return;
SpinfoPtr spin[4];
// Extract the 4 particles in the hard process.
ParticleVector hard;
hard.push_back(sub->incoming().first);
hard.push_back(sub->incoming().second);
hard.push_back(sub->outgoing()[0]);
hard.push_back(sub->outgoing()[1]);
// Make sure the particles are ordered correctly in hard.
unsigned int order[4]={0,1,2,3};
if(hard[0]->id()<0) swap(order[0],order[1]);
if(hard[2]->id()!=mePartonData()[2]->id()) swap(order[2],order[3]);
// Declare and calculate the external wavefunctions.
vector<SpinorWaveFunction> fin;
vector<SpinorBarWaveFunction> ain;
vector<VectorWaveFunction> v2,v1;
SpinorWaveFunction( fin,hard[order[0]],incoming,false,true);
SpinorBarWaveFunction(ain,hard[order[1]],incoming,false,true);
VectorWaveFunction( v1 ,hard[order[2]],outgoing,true,false,true);
VectorWaveFunction( v2 ,hard[order[3]],outgoing,true,false,true);
// VectorWaveFunction(v2,hard[order[3]],outgoing,true,true,true);
// v2[1]=v2[2];
// Calculate the matrix element.
helicityME(fin,ain,v1,v2,true);
// get the spin info objects
for(unsigned int ix=0;ix<4;++ix)
spin[ix]=dynamic_ptr_cast<SpinfoPtr>(hard[order[ix]]->spinInfo());
// construct the vertex
HardVertexPtr hardvertex=new_ptr(HardVertex());
// set the matrix element for the vertex
hardvertex->ME(_me);
// set the pointers and to and from the vertex
for(unsigned int ix=0;ix<4;++ix) spin[ix]->setProductionVertex(hardvertex);
}

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