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MEvv2vv.cc
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MEvv2vv.cc
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// -*- C++ -*-
//
// MEvv2vv.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 MEvv2vv class.
//
#include "MEvv2vv.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
#include "ThePEG/Handlers/StandardXComb.h"
#include "ThePEG/Helicity/WaveFunction/ScalarWaveFunction.h"
#include "ThePEG/Helicity/WaveFunction/TensorWaveFunction.h"
#include "ThePEG/Helicity/Vertex/Tensor/VVTVertex.h"
#include "ThePEG/Helicity/SpinInfo.h"
#include "ThePEG/StandardModel/StandardModelBase.h"
#include "Herwig++/MatrixElement/HardVertex.h"
#include <numeric>
using namespace Herwig;
using ThePEG::Helicity::ScalarWaveFunction;
using ThePEG::Helicity::TensorWaveFunction;
using ThePEG::Helicity::incoming;
using ThePEG::Helicity::outgoing;
using ThePEG::Helicity::SpinfoPtr;
void MEvv2vv::doinit() throw(InitException) {
GeneralHardME::doinit();
size_t ndiags = numberOfDiags();
theScaV.resize(ndiags);
theVecV.resize(ndiags);
theTenV.resize(ndiags);
for(size_t i = 0; i < ndiags; ++i) {
HPDiagram diag = getProcessInfo()[i];
tcPDPtr offshell = diag.intermediate;
if(!offshell)
theFPVertex = dynamic_ptr_cast<AbstractVVVVVertexPtr>
(diag.vertices.first);
else if(offshell->iSpin() == PDT::Spin0) {
AbstractVVSVertexPtr vert1 = dynamic_ptr_cast<AbstractVVSVertexPtr>
(diag.vertices.first);
AbstractVVSVertexPtr vert2 = dynamic_ptr_cast<AbstractVVSVertexPtr>
(diag.vertices.second);
theScaV[i] = make_pair(vert1, vert2);
}
else if(offshell->iSpin() == PDT::Spin1) {
AbstractVVVVertexPtr vert1 = dynamic_ptr_cast<AbstractVVVVertexPtr>
(diag.vertices.first);
AbstractVVVVertexPtr vert2 = dynamic_ptr_cast<AbstractVVVVertexPtr>
(diag.vertices.second);
theVecV[i] = make_pair(vert1, vert2);
}
else if(offshell->iSpin() == PDT::Spin2) {
AbstractVVTVertexPtr vert1 = dynamic_ptr_cast<AbstractVVTVertexPtr>
(diag.vertices.first);
AbstractVVTVertexPtr vert2 = dynamic_ptr_cast<AbstractVVTVertexPtr>
(diag.vertices.second);
theTenV[i] = make_pair(vert1, vert2);
}
}
}
double MEvv2vv::me2() const {
VBVector va(2), vb(2), vc(3), vd(3);
for(unsigned int i = 0; i < 2; ++i) {
va[i] = VectorWaveFunction(rescaledMomenta()[0], mePartonData()[0], 2*i,
incoming);
vb[i] = VectorWaveFunction(rescaledMomenta()[1], mePartonData()[1], 2*i,
incoming);
}
//always 0 and 2 polarisations
for(unsigned int i = 0; i < 2; ++i) {
vc[2*i] = VectorWaveFunction(rescaledMomenta()[2], mePartonData()[2], 2*i,
outgoing);
vd[2*i] = VectorWaveFunction(rescaledMomenta()[3], mePartonData()[3], 2*i,
outgoing);
}
bool mc = !(mePartonData()[2]->mass() > 0.*MeV);
//massive vector, also 1
if( !mc )
vc[1] = VectorWaveFunction(rescaledMomenta()[2], mePartonData()[2], 1,
outgoing);
bool md = !(mePartonData()[3]->mass() > 0.*MeV);
if( !md )
vd[1] = VectorWaveFunction(rescaledMomenta()[3], mePartonData()[3], 1,
outgoing);
double full_me(0.);
vv2vvHeME(va, vb, vc, mc, vd, md, full_me);
#ifndef NDEBUG
if( debugME() ) debug(full_me);
#endif
return full_me;
}
ProductionMatrixElement
MEvv2vv::vv2vvHeME(VBVector & vin1, VBVector & vin2,
VBVector & vout1, bool mc, VBVector & vout2, bool md,
double & mesq) const {
const HPCount ndiags = numberOfDiags();
const size_t ncf(numberOfFlows());
const vector<vector<double> > cfactors(getColourFactors());
const Energy2 q2(scale());
const Energy mass = vout1[0].mass();
vector<Complex> diag(ndiags, Complex(0.));
vector<double> me(ndiags, 0.);
ScalarWaveFunction interS; VectorWaveFunction interV;
TensorWaveFunction interT;
ProductionMatrixElement prodME(PDT::Spin1, PDT::Spin1, PDT::Spin1, PDT::Spin1);
for(unsigned int ihel1 = 0; ihel1 < 2; ++ihel1) {
for(unsigned int ihel2 = 0; ihel2 < 2; ++ihel2) {
for(unsigned int ohel1 = 0; ohel1 < 3; ++ohel1) {
if(mc && ohel1 == 1) ++ohel1;
for(unsigned int ohel2 = 0; ohel2 < 3; ++ohel2) {
if(md && ohel2 == 1) ++ohel2;
vector<Complex> cflows(ncf, Complex(0.0));
for(HPCount ix = 0; ix < ndiags; ++ix) {
HPDiagram current = getProcessInfo()[ix];
tcPDPtr offshell = current.intermediate;
if(!offshell) continue;
if(current.channelType == HPDiagram::sChannel) {
if(offshell->iSpin() == PDT::Spin1) {
interV = theVecV[ix].first->evaluate(q2, 1, offshell,
vin1[ihel1], vin2[ihel2]);
diag[ix] = theVecV[ix].second->evaluate(q2, vout1[ohel1],
vout2[ohel2], interV);
diag[ix] += theFPVertex->evaluate(q2, 0, vout1[ohel1], vin2[ihel2],
vout2[ohel2], vin1[ihel1]);
}
else if(offshell->iSpin() == PDT::Spin2) {
interT = theTenV[ix].first->evaluate(q2, 1, offshell,
vin1[ihel1], vin2[ihel2]);
diag[ix] = theTenV[ix].second->evaluate(q2, vout1[ohel1],
vout2[ohel2],interT);
}
}
else if(current.channelType == HPDiagram::tChannel) {
if(offshell->iSpin() == PDT::Spin1) {
if(current.ordered.second) {
interV = theVecV[ix].first->evaluate(q2, 3, offshell, vin1[ihel1],
vout1[ohel1], mass);
diag[ix] = theVecV[ix].second->evaluate(q2, vin2[ihel2], interV,
vout2[ohel2]);
diag[ix] += theFPVertex->evaluate(q2, 0, vin1[ihel1], vin2[ihel2],
vout1[ohel1], vout2[ohel2]);
}
else {
interV = theVecV[ix].first->evaluate(q2, 3, offshell, vin2[ihel2],
vout1[ohel1], mass);
diag[ix] = theVecV[ix].second->evaluate(q2, vin1[ihel1], interV,
vout2[ohel2]);
diag[ix] += theFPVertex->evaluate(q2, 0, vin2[ihel2], vin1[ihel1],
vout1[ohel1], vout2[ohel2]);
}
}
else if(offshell->iSpin() == PDT::Spin2) {
if(current.ordered.second) {
interT = theTenV[ix].first->evaluate(q2, 3, offshell, vin1[ihel1],
vout1[ohel1], mass);
diag[ix] = theTenV[ix].second->evaluate(q2, vin2[ihel2],
vout2[ohel2], interT);
}
else {
interT = theTenV[ix].first->evaluate(q2, 3, offshell, vin2[ihel2],
vout1[ohel1], mass);
diag[ix] = theTenV[ix].second->evaluate(q2, vin1[ihel1],
vout2[ohel2], interT);
}
}
}
else
diag[ix] = 0.0;
me[ix] += norm(diag[ix]);
//Compute flows
for(size_t iy = 0; iy < current.colourFlow.size(); ++iy)
cflows[current.colourFlow[iy].first - 1] +=
current.colourFlow[iy].second * diag[ix];
} //end of diagram loop
//set the appropriate element in ProductionMatrixElement
prodME(ihel1, ihel2, ohel1, ohel2) =
std::accumulate(cflows.begin(), cflows.end(), Complex(0.0, 0.0));
for(size_t ii = 0; ii < ncf; ++ii)
for(size_t ij = 0; ij < ncf; ++ij)
mesq += cfactors[ii][ij]*(cflows[ii]*conj(cflows[ij])).real();
}
}
}
}
const double identfact = mePartonData()[2]->id() == mePartonData()[3]->id()
? 0.5 : 1.;
const double colfact = mePartonData()[0]->iColour() == PDT::Colour8 ?
1./64. : 1;
DVector save(ndiags);
for(DVector::size_type ix = 0; ix < ndiags; ++ix)
save[ix] = 0.25*identfact*colfact*me[ix];
meInfo(save);
mesq *= 0.25*identfact*colfact;
return prodME;
}
Selector<const ColourLines *>
MEvv2vv::colourGeometries(tcDiagPtr diag) const {
static vector<ColourLines> colourflows(16);
//88->8->88
colourflows[0] = ColourLines("1 -2, -1 -3 -4, 4 -5, 2 3 5");
colourflows[1] = ColourLines("-1 2, 1 3 4, -4 5, -2 -3 -5");
colourflows[2] = ColourLines("1 -2, -1 -3 -5, 5 -4, 2 3 4");
colourflows[3] = ColourLines("-1 2, 1 3 5, -5 4, -2 -3 -4");
colourflows[4] = ColourLines("1 4, -1 -2 3, -3 -5, -4 2 5");
colourflows[5] = ColourLines("-1 -4, 1 2 -3, 3 5, 4 -2 -5");
colourflows[6] = ColourLines("1 4, -1 -2 -5, 3 5, -3 2 -4");
colourflows[7] = ColourLines("-1 -4, 1 2 5, -3 -5, 3 -2 4");
colourflows[8] = ColourLines("1 5, -1 -2 3, -3 -4, -5 2 4");
colourflows[9] = ColourLines("-1 -5, 1 2 -3, 3 4, 5 -2 -4");
colourflows[10] = ColourLines("1 5, -1 -2 -4, 3 4, -3 2 -5");
colourflows[11] = ColourLines("-1 -5, 1 2 4, -3 -4, 3 -2 5");
//88->0->88
colourflows[12] = ColourLines("1 -2, 2 -1, 4 -5, 5 -4");
colourflows[13] = ColourLines("1 4, -1 -4, 3 5, -5 -3");
colourflows[14] = ColourLines("1 5, -1 -5, 3 4, -3 -4");
//88->0->00
colourflows[15] = ColourLines("1 -2,2 -1");
HPDiagram current = getProcessInfo()[abs(diag->id()) - 1];
Selector<const ColourLines *> select;
if(current.channelType == HPDiagram::sChannel) {
if(current.intermediate->iColour() == PDT::Colour8) {
select.insert(0.25, &colourflows[0]);
select.insert(0.25, &colourflows[1]);
select.insert(0.25, &colourflows[2]);
select.insert(0.25, &colourflows[3]);
}
else {
if(getParticleData(current.outgoing.first)->iColour() == PDT::Colour0)
select.insert(1., &colourflows[15]);
else
select.insert(1., &colourflows[12]);
}
}
else if(current.channelType == HPDiagram::tChannel) {
if(current.ordered.second) {
if(current.intermediate->iColour() == PDT::Colour8) {
select.insert(0.25, &colourflows[4]);
select.insert(0.25, &colourflows[5]);
select.insert(0.25, &colourflows[6]);
select.insert(0.25, &colourflows[7]);
}
else
select.insert(1., &colourflows[13]);
}
else {
if(current.intermediate->iColour() == PDT::Colour8) {
select.insert(0.25, &colourflows[8]);
select.insert(0.25, &colourflows[9]);
select.insert(0.25, &colourflows[10]);
select.insert(0.25, &colourflows[11]);
}
else
select.insert(1., &colourflows[14]);
}
}
else
throw MEException() << "MEvv2vv::colourGeometries - Trying to set ColourLines "
<< "for an unknown diagram type. "
<< Exception::warning;
return select;
}
void MEvv2vv::persistentOutput(PersistentOStream & os) const {
os << theScaV << theVecV << theTenV << theFPVertex;
}
void MEvv2vv::persistentInput(PersistentIStream & is, int) {
is >> theScaV >> theVecV >> theTenV >> theFPVertex;
}
ClassDescription<MEvv2vv> MEvv2vv::initMEvv2vv;
// Definition of the static class description member.
void MEvv2vv::Init() {
static ClassDocumentation<MEvv2vv> documentation
("This is the implementation of the 2 to 2 ME for a pair"
"of massless vector-bosons to a pair of vector bosons");
}
void MEvv2vv::constructVertex(tSubProPtr sub) {
ParticleVector ext(4);
ext[0] = sub->incoming().first;
ext[1] = sub->incoming().second;
ext[2] = sub->outgoing()[0];
ext[3] = sub->outgoing()[1];
//Ensure particles are in the same order as specified in the diagrams
if( ext[0]->id() != getIncoming().first ) swap(ext[0], ext[1]);
if( ext[2]->id() != getOutgoing().first ) swap(ext[2], ext[3]);
VBVector v1, v2, v3, v4;
VectorWaveFunction(v1, ext[0], incoming, false, true);
VectorWaveFunction(v2, ext[1], incoming, false, true);
//function to calculate me2 expects massless incoming vectors
// and this constructor sets the '1' polarisation at element [2]
//in the vector
bool mc = !(ext[2]->data().mass() > 0.*MeV);
bool md = !(ext[3]->data().mass() > 0.*MeV);
VectorWaveFunction(v3, ext[2], outgoing, true, mc);
VectorWaveFunction(v4, ext[3], outgoing, true, md);
double dummy(0.);
//Need to use rescale momenta to calculate matrix element
cPDVector data(4);
vector<Lorentz5Momentum> momenta(4);
for( size_t i = 0; i < 4; ++i ) {
data[i] = ext[i]->dataPtr();
momenta[i] = ext[i]->momentum();
}
rescaleMomenta(momenta, data);
VectorWaveFunction vr1(rescaledMomenta()[0], data[0], incoming);
VectorWaveFunction vr2(rescaledMomenta()[1], data[1], incoming);
VectorWaveFunction vr3(rescaledMomenta()[2], data[2], outgoing);
VectorWaveFunction vr4(rescaledMomenta()[3], data[3], outgoing);
for( unsigned int ihel = 0; ihel < 2; ++ihel ) {
vr1.reset(2*ihel);
v1[ihel] = vr1;
vr2.reset(2*ihel);
v2[ihel] = vr2;
vr3.reset(2*ihel);
v3[2*ihel] = vr3;
vr4.reset(2*ihel);
v4[2*ihel] = vr4;
}
if( !mc ) {
vr3.reset(1);
v3[1] = vr3;
}
if( !md ) {
vr4.reset(1);
v4[1] = vr4;
}
ProductionMatrixElement pme = vv2vvHeME(v1, v2, v3, mc, v4, md, dummy);
#ifndef NDEBUG
if( debugME() ) debug(dummy);
#endif
HardVertexPtr hv = new_ptr(HardVertex());
hv->ME(pme);
for(unsigned int i = 0; i < 4; ++i)
dynamic_ptr_cast<SpinfoPtr>(ext[i]->spinInfo())->setProductionVertex(hv);
}
void MEvv2vv::debug(double me2) const {
if( !generator()->logfile().is_open() ) return;
if( mePartonData()[0]->id() != 21 || mePartonData()[1]->id() != 21 ||
mePartonData()[2]->id() != 5100021 ||
mePartonData()[3]->id() != 5100021 ) return;
tcSMPtr sm = generator()->standardModel();
double gs4 = sqr( 4.*Constants::pi*sm->alphaS(scale()) );
Energy2 s(sHat());
Energy2 mf2 = meMomenta()[2].m2();
Energy2 t3(tHat() - mf2), u4(uHat() - mf2);
Energy4 s2(sqr(s)), t3s(sqr(t3)), u4s(sqr(u4));
Energy4 num = s2 + t3s + u4s;
double analytic = 3.*mf2*( mf2*num/t3s/u4s - num/s/t3/u4 ) + 1.
+ sqr(num)*num/4./s2/t3s/u4s - t3*u4/s2;
analytic *= 9.*gs4/8.;
double diff = abs( analytic - me2 );
if( diff > 1e-4 ) {
generator()->log()
<< mePartonData()[0]->PDGName() << ","
<< mePartonData()[1]->PDGName() << "->"
<< mePartonData()[2]->PDGName() << ","
<< mePartonData()[3]->PDGName() << " difference: "
<< setprecision(10) << diff << " ratio: " << analytic/me2 << '\n';
}
}

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