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MEfv2vf.cc
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MEfv2vf.cc
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// -*- C++ -*-
//
// MEfv2vf.cc is a part of Herwig++ - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2011 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 MEfv2vf class.
//
#include "MEfv2vf.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
using namespace Herwig;
using ThePEG::Helicity::incoming;
using ThePEG::Helicity::outgoing;
using ThePEG::Helicity::SpinorWaveFunction;
using ThePEG::Helicity::SpinorBarWaveFunction;
using ThePEG::Helicity::VectorWaveFunction;
void MEfv2vf::doinit() {
GeneralHardME::doinit();
fermion_.resize(numberOfDiags());
vector_.resize(numberOfDiags());
flowME().resize(numberOfFlows(),
ProductionMatrixElement(PDT::Spin1Half, PDT::Spin1,
PDT::Spin1, PDT::Spin1Half));
diagramME().resize(numberOfDiags(),
ProductionMatrixElement(PDT::Spin1Half, PDT::Spin1,
PDT::Spin1, PDT::Spin1Half));
for(HPCount ix = 0; ix < numberOfDiags(); ++ix) {
HPDiagram diagram = getProcessInfo()[ix];
PDT::Spin offspin = diagram.intermediate->iSpin();
if(diagram.channelType == HPDiagram::sChannel ||
( diagram.channelType == HPDiagram::tChannel
&& offspin == PDT::Spin1Half)) {
AbstractFFVVertexPtr vert1 = dynamic_ptr_cast<AbstractFFVVertexPtr>
(diagram.vertices.first);
AbstractFFVVertexPtr vert2 = dynamic_ptr_cast<AbstractFFVVertexPtr>
(diagram.vertices.second);
fermion_[ix] = make_pair(vert1, vert2);
}
else {
if(offspin == PDT::Spin1) {
AbstractFFVVertexPtr vert1 = dynamic_ptr_cast<AbstractFFVVertexPtr>
(diagram.vertices.first);
AbstractVVVVertexPtr vert2 = dynamic_ptr_cast<AbstractVVVVertexPtr>
(diagram.vertices.second);
vector_[ix] = make_pair(vert1, vert2);
}
}
}
}
void MEfv2vf::doinitrun() {
GeneralHardME::doinitrun();
flowME().resize(numberOfFlows(),
ProductionMatrixElement(PDT::Spin1Half, PDT::Spin1,
PDT::Spin1, PDT::Spin1Half));
diagramME().resize(numberOfDiags(),
ProductionMatrixElement(PDT::Spin1Half, PDT::Spin1,
PDT::Spin1, PDT::Spin1Half));
}
double MEfv2vf::me2() const {
//wavefunctions
SpinorVector sp(2);
VBVector vecIn(2), vecOut(3);
SpinorBarVector spb(2);
double fullme(0.);
bool mc = !(mePartonData()[2]->mass() > ZERO);
if(mePartonData()[0]->id() > 0) {
for(unsigned int i = 0; i < 2; ++i) {
sp[i] = SpinorWaveFunction(rescaledMomenta()[0], mePartonData()[0], i,
incoming);
vecIn[i] = VectorWaveFunction(rescaledMomenta()[1], mePartonData()[1], 2*i,
incoming);
vecOut[2*i] = VectorWaveFunction(rescaledMomenta()[2], mePartonData()[2], 2*i,
outgoing);
spb[i] = SpinorBarWaveFunction(rescaledMomenta()[3], mePartonData()[3], i,
outgoing);
}
if( !mc )
vecOut[1] = VectorWaveFunction(rescaledMomenta()[2], mePartonData()[2], 1,
outgoing);
fv2vfHeME(sp, vecIn, vecOut, mc, spb, fullme,true);
}
else {
for(unsigned int i = 0; i < 2; ++i) {
spb[i] = SpinorBarWaveFunction(rescaledMomenta()[0], mePartonData()[0], i,
incoming);
vecIn[i] = VectorWaveFunction(rescaledMomenta()[1], mePartonData()[1], 2*i,
incoming);
vecOut[2*i] = VectorWaveFunction(rescaledMomenta()[2], mePartonData()[2], 2*i,
outgoing);
sp[i] = SpinorWaveFunction(rescaledMomenta()[3], mePartonData()[3], i,
outgoing);
}
if( !mc )
vecOut[1] = VectorWaveFunction(rescaledMomenta()[2], mePartonData()[2], 1,
outgoing);
fbv2vfbHeME(spb, vecIn, vecOut, mc, sp, fullme,true);
}
#ifndef NDEBUG
if( debugME() ) debug(fullme);
#endif
return fullme;
}
ProductionMatrixElement
MEfv2vf::fv2vfHeME(const SpinorVector & spIn, const VBVector & vecIn,
const VBVector & vecOut, bool mc,
const SpinorBarVector & spbOut,
double & me2, bool first) const {
const Energy2 q2(scale());
// weights for the selection of the diagram
vector<double> me(numberOfDiags(), 0.);
// weights for the selection of the colour flow
vector<double> flow(numberOfFlows(),0.);
me2 = 0.;
//loop over helicities
for(unsigned int ifh = 0; ifh < 2; ++ifh) {
for(unsigned int ivh = 0; ivh < 2; ++ivh) {
for(unsigned int ovh = 0; ovh < 3; ++ovh) {
if(mc && ovh == 1) ++ovh;
for(unsigned int ofh = 0; ofh < 2; ++ofh) {
vector<Complex> flows(numberOfFlows(),0.);
for(HPCount ix = 0; ix < numberOfDiags(); ++ix) {
Complex diag(0.);
const HPDiagram & current = getProcessInfo()[ix];
tcPDPtr offshell = current.intermediate;
if(current.channelType == HPDiagram::tChannel) {
//t-chan spin-1/2
if(offshell->iSpin() == PDT::Spin1Half) {
SpinorBarWaveFunction interFB = fermion_[ix].second->
evaluate(q2, 3, offshell, spbOut[ofh], vecIn[ivh]);
diag = fermion_[ix].first->
evaluate(q2, spIn[ifh], interFB, vecOut[ovh]);
}
else if(offshell->iSpin() == PDT::Spin1) {
VectorWaveFunction interV = vector_[ix].second->
evaluate(q2, 3, offshell, vecIn[ivh], vecOut[ovh]);
diag = vector_[ix].first->
evaluate(q2, spIn[ifh], spbOut[ofh], interV);
}
else
diag = 0.0;
}
else if(current.channelType == HPDiagram::sChannel) {
SpinorBarWaveFunction interFB = fermion_[ix].second->
evaluate(q2, 1, offshell, spbOut[ofh], vecOut[ovh]);
diag = fermion_[ix].first->
evaluate(q2, spIn[ifh], interFB, vecIn[ivh]);
}
me[ix] += norm(diag);
diagramME()[ix](ifh, 2*ivh, ovh, ofh) = diag;
//Compute flows
for(size_t iy = 0; iy < current.colourFlow.size(); ++iy) {
assert(current.colourFlow[iy].first<flows.size());
flows[current.colourFlow[iy].first] +=
current.colourFlow[iy].second * diag;
}
}
// MEs for the different colour flows
for(unsigned int iy = 0; iy < numberOfFlows(); ++iy)
flowME()[iy](ifh, 2*ivh, ovh, ofh) = flows[iy];
//Now add flows to me2 with appropriate colour factors
for(size_t ii = 0; ii < numberOfFlows(); ++ii)
for(size_t ij = 0; ij < numberOfFlows(); ++ij)
me2 += getColourFactors()[ii][ij]*(flows[ii]*conj(flows[ij])).real();
// contribution to the colour flow
for(unsigned int ii = 0; ii < numberOfFlows(); ++ii) {
flow[ii] += getColourFactors()[ii][ii]*norm(flows[ii]);
}
}
}
}
}
// if not computing the cross section return the selected colour flow
if(!first) return flowME()[colourFlow()];
me2 = selectColourFlow(flow,me,me2);
return flowME()[colourFlow()];
}
ProductionMatrixElement
MEfv2vf::fbv2vfbHeME(const SpinorBarVector & spbIn, const VBVector & vecIn,
const VBVector & vecOut, bool mc,
const SpinorVector & spOut,
double & me2, bool first) const {
const Energy2 q2(scale());
// weights for the selection of the diagram
vector<double> me(numberOfDiags(), 0.);
// weights for the selection of the colour flow
vector<double> flow(numberOfFlows(),0.);
me2 = 0.;
//loop over helicities
for(unsigned int ifh = 0; ifh < 2; ++ifh) {
for(unsigned int ivh = 0; ivh < 2; ++ivh) {
for(unsigned int ovh = 0; ovh < 3; ++ovh) {
if(mc && ovh == 1) ++ovh;
for(unsigned int ofh = 0; ofh < 2; ++ofh) {
vector<Complex> flows(numberOfFlows(),0.);
for(HPCount ix = 0; ix < numberOfDiags(); ++ix) {
Complex diag(0.);
const HPDiagram & current = getProcessInfo()[ix];
tcPDPtr offshell = current.intermediate;
if(current.channelType == HPDiagram::tChannel) {
if(offshell->iSpin() == PDT::Spin1Half) {
SpinorBarWaveFunction interFB = fermion_[ix].first->
evaluate(q2, 3, offshell, spbIn[ifh], vecOut[ovh]);
diag = fermion_[ix].second->
evaluate(q2, spOut[ofh], interFB, vecIn[ivh]);
}
else if(offshell->iSpin() == PDT::Spin1) {
VectorWaveFunction interV = vector_[ix].first->
evaluate(q2, 3, offshell, spOut[ofh], spbIn[ifh]);
diag = vector_[ix].second->
evaluate(q2, vecIn[ivh], interV, vecOut[ovh]);
}
else diag = 0.0;
}
else if(current.channelType == HPDiagram::sChannel) {
if(offshell->iSpin() == PDT::Spin1Half) {
SpinorBarWaveFunction interFB = fermion_[ix].first->
evaluate(q2, 1, offshell, spbIn[ifh], vecIn[ivh]);
diag = fermion_[ix].second->
evaluate(q2, spOut[ofh], interFB, vecOut[ovh]);
}
}
me[ix] += norm(diag);
diagramME()[ix](ifh, ivh, ovh, ofh) = diag;
//Compute flows
for(size_t iy = 0; iy < current.colourFlow.size(); ++iy) {
assert(current.colourFlow[iy].first<flows.size());
flows[current.colourFlow[iy].first] +=
current.colourFlow[iy].second * diag;
}
}
// MEs for the different colour flows
for(unsigned int iy = 0; iy < numberOfFlows(); ++iy)
flowME()[iy](ifh, ivh, ovh, ofh) = flows[iy];
//Now add flows to me2 with appropriate colour factors
for(size_t ii = 0; ii < numberOfFlows(); ++ii)
for(size_t ij = 0; ij < numberOfFlows(); ++ij)
me2 += getColourFactors()[ii][ij]*(flows[ii]*conj(flows[ij])).real();
// contribution to the colour flow
for(unsigned int ii = 0; ii < numberOfFlows(); ++ii) {
flow[ii] += getColourFactors()[ii][ii]*norm(flows[ii]);
}
}
}
}
}
// if not computing the cross section return the selected colour flow
if(!first) return flowME()[colourFlow()];
me2 = selectColourFlow(flow,me,me2);
return flowME()[colourFlow()];
}
void MEfv2vf::persistentOutput(PersistentOStream & os) const {
os << fermion_ << vector_;
}
void MEfv2vf::persistentInput(PersistentIStream & is, int) {
is >> fermion_ >> vector_;
}
ClassDescription<MEfv2vf> MEfv2vf::initMEfv2vf;
// Definition of the static class description member.
void MEfv2vf::Init() {
static ClassDocumentation<MEfv2vf> documentation
("This is the implementation of the matrix element for a fermion-vector boson"
"to a vector-fermion.");
}
void MEfv2vf::constructVertex(tSubProPtr sub) {
ParticleVector ext = hardParticles(sub);
VBVector v1, v3;
bool mc = !(ext[2]->data().mass() > ZERO);
SpinorVector sp;
SpinorBarVector sbar;
VectorWaveFunction(v1, ext[1], incoming, false, true);
VectorWaveFunction(v3, ext[2], outgoing, true, mc);
double dummy(0.);
//Need to use rescale momenta to calculate matrix element
setRescaledMomenta(ext);
// wavefunctions with rescaled momenta
VectorWaveFunction vir(rescaledMomenta()[1],
ext[1]->dataPtr(), incoming);
VectorWaveFunction vor(rescaledMomenta()[2],
ext[2]->dataPtr(), outgoing);
if( ext[0]->id() > 0 ) {
SpinorWaveFunction (sp , ext[0], incoming, false);
SpinorBarWaveFunction(sbar, ext[3], outgoing, true);
SpinorWaveFunction spr (rescaledMomenta()[0],
ext[0]->dataPtr(), incoming);
SpinorBarWaveFunction sbr(rescaledMomenta()[3],
ext[3]->dataPtr(), outgoing);
for( unsigned int ihel = 0; ihel < 2; ++ihel ) {
spr.reset(ihel);
sp[ihel] = spr;
vir.reset(2*ihel);
v1[ihel] = vir;
vor.reset(2*ihel);
v3[2*ihel] = vor;
sbr.reset(ihel);
sbar[ihel] = sbr;
}
if( !mc ) {
vor.reset(1);
v3[1] = vor;
}
ProductionMatrixElement pme = fv2vfHeME(sp, v1, v3, mc, sbar, dummy,false);
createVertex(pme,ext);
}
else {
SpinorBarWaveFunction(sbar, ext[0], incoming, false);
SpinorWaveFunction(sp, ext[3], outgoing, true);
SpinorBarWaveFunction sbr(rescaledMomenta()[0],
ext[0]->dataPtr(), incoming);
SpinorWaveFunction spr (rescaledMomenta()[3],
ext[3]->dataPtr(), outgoing);
for( unsigned int ihel = 0; ihel < 2; ++ihel ) {
sbr.reset(ihel);
sbar[ihel] = sbr;
vir.reset(2*ihel);
v1[ihel] = vir;
vor.reset(2*ihel);
v3[2*ihel] = vor;
spr.reset(ihel);
sp[ihel] = spr;
}
if( !mc ) {
vor.reset(1);
v3[1] = vor;
}
ProductionMatrixElement pme = fbv2vfbHeME(sbar, v1, v3, mc, sp, dummy,false);
createVertex(pme,ext);
}
#ifndef NDEBUG
if( debugME() ) debug(dummy);
#endif
}
void MEfv2vf::debug(double me2) const {
if( !generator()->logfile().is_open() ) return;
long id1 = abs(mePartonData()[0]->id());
long id4 = abs(mePartonData()[3]->id());
if( (id1 != 1 && id1 != 2) || mePartonData()[1]->id() != 21 ||
mePartonData()[2]->id() != 5100021 ||
(id4 != 5100001 && id4 != 5100002 &&
id4 != 6100001 && id4 != 6100002) ) return;
tcSMPtr sm = generator()->standardModel();
double gs4 = sqr( 4.*Constants::pi*sm->alphaS(scale()) );
Energy2 s(sHat());
Energy2 mf2 = meMomenta()[2].m2();
// Energy4 spt2 = uHat()*tHat() - sqr(mf2);
//swap t and u as formula defines process vf->vf
Energy2 t3(uHat() - mf2), u4(tHat() - mf2);
Energy4 s2(sqr(s)), t3s(sqr(t3)), u4s(sqr(u4));
double analytic = -gs4*( 5.*s2/12./t3s + s2*s/t3s/u4 + 11.*s*u4/6./t3s
+ 5.*u4s/12./t3s + u4s*u4/s/t3s)/3.;
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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