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MEvv2ff.cc
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// -*- C++ -*-
//
// MEvv2ff.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 MEvv2ff class.
//
#include "MEvv2ff.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
using namespace Herwig;
using ThePEG::Helicity::TensorWaveFunction;
using ThePEG::Helicity::incoming;
using ThePEG::Helicity::outgoing;
void MEvv2ff::doinit() {
GeneralHardME::doinit();
scalar_ .resize(numberOfDiags());
fermion_.resize(numberOfDiags());
vector_ .resize(numberOfDiags());
tensor_ .resize(numberOfDiags());
initializeMatrixElements(PDT::Spin1 , PDT::Spin1,
PDT::Spin1Half, PDT::Spin1Half);
for( size_t i = 0; i < numberOfDiags(); ++i ) {
HPDiagram dg = getProcessInfo()[i];
if( dg.channelType == HPDiagram::tChannel ) {
AbstractFFVVertexPtr ffv1 =
dynamic_ptr_cast<AbstractFFVVertexPtr>(dg.vertices.first);
AbstractFFVVertexPtr ffv2 =
dynamic_ptr_cast<AbstractFFVVertexPtr>(dg.vertices.second);
fermion_[i] = make_pair(ffv1, ffv2);
}
else if( dg.channelType == HPDiagram::sChannel ) {
if( dg.intermediate->iSpin() == PDT::Spin0 ) {
AbstractVVSVertexPtr vvs =
dynamic_ptr_cast<AbstractVVSVertexPtr>(dg.vertices.first );
AbstractFFSVertexPtr ffs =
dynamic_ptr_cast<AbstractFFSVertexPtr>(dg.vertices.second);
scalar_[i] = make_pair(vvs,ffs);
}
else if( dg.intermediate->iSpin() == PDT::Spin1) {
AbstractVVVVertexPtr vvv =
dynamic_ptr_cast<AbstractVVVVertexPtr>(dg.vertices.first);
AbstractFFVVertexPtr ffv =
dynamic_ptr_cast<AbstractFFVVertexPtr>(dg.vertices.second);
vector_[i] = make_pair(vvv,ffv);
}
else if(dg.intermediate->iSpin() == PDT::Spin2) {
AbstractVVTVertexPtr vvt =
dynamic_ptr_cast<AbstractVVTVertexPtr>(dg.vertices.first);
AbstractFFTVertexPtr fft =
dynamic_ptr_cast<AbstractFFTVertexPtr>(dg.vertices.second);
tensor_[i] = make_pair(vvt,fft);
}
}
}
}
double MEvv2ff::me2() const {
// Set up wavefuctions
VBVector v1(2), v2(2);
SpinorVector sp(2); SpinorBarVector sbar(2);
for( size_t i = 0; i < 2; ++i ) {
v1[i] = VectorWaveFunction(rescaledMomenta()[0],mePartonData()[0], 2*i,
incoming);
v2[i] = VectorWaveFunction(rescaledMomenta()[1],mePartonData()[1], 2*i,
incoming);
sbar[i] = SpinorBarWaveFunction(rescaledMomenta()[2], mePartonData()[2], i,
outgoing);
sp[i] = SpinorWaveFunction(rescaledMomenta()[3], mePartonData()[3], i,
outgoing);
}
double full_me(0.);
vv2ffME(v1, v2, sbar, sp, full_me,true);
#ifndef NDEBUG
if( debugME() ) debug(full_me);
#endif
return full_me;
}
ProductionMatrixElement
MEvv2ff::vv2ffME(const VBVector & v1, const VBVector & v2,
const SpinorBarVector & sbar,const SpinorVector & sp,
double & me2, bool first) const {
const Energy mass = sp[0].mass();
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.);
//sum over vector helicities
for(unsigned int iv1 = 0; iv1 < 2; ++iv1) {
for(unsigned int iv2 = 0; iv2 < 2; ++iv2) {
//sum over fermion helicities
for(unsigned int of1 = 0; of1 < 2; ++of1) {
for(unsigned int of2 = 0; of2 < 2; ++of2) {
vector<Complex> flows(numberOfFlows(),0.);
for(HPCount ix = 0; ix < numberOfDiags(); ++ix) {
Complex diag(0.);
const HPDiagram & current = getProcessInfo()[ix];
PDPtr offshell = current.intermediate;
if(current.channelType == HPDiagram::tChannel &&
offshell->iSpin() == PDT::Spin1Half) {
if(current.ordered.second) {
SpinorBarWaveFunction interF = fermion_[ix].first->
evaluate(q2, 3, offshell, sbar[of1], v1[iv1], mass);
diag = fermion_[ix].second->
evaluate(q2, sp[of2], interF, v2[iv2]);
}
else {
SpinorWaveFunction interF = fermion_[ix].second->
evaluate(q2, 3, offshell, sp[of2], v1[iv1], mass);
diag = fermion_[ix].first->
evaluate(q2, interF, sbar[of1], v2[iv2]);
}
}
else if(current.channelType == HPDiagram::sChannel) {
if(offshell->iSpin() == PDT::Spin0) {
ScalarWaveFunction interS = scalar_[ix].first->
evaluate(q2, 1, offshell, v1[iv1], v2[iv2]);
diag = scalar_[ix].second->
evaluate(q2, sp[of2], sbar[of1], interS);
}
else if(offshell->iSpin() == PDT::Spin1) {
VectorWaveFunction interV = vector_[ix].first->
evaluate(q2, 1, offshell, v1[iv1], v2[iv2]);
diag = vector_[ix].second->
evaluate(q2, sp[of2], sbar[of1], interV);
}
else if(offshell->iSpin() == PDT::Spin2) {
TensorWaveFunction interT = tensor_[ix].first->
evaluate(q2, 1, offshell, v1[iv1], v2[iv2]);
diag = tensor_[ix].second->
evaluate(q2, sp[of2], sbar[of1], interT);
}
}
else diag = 0.;
me[ix] += norm(diag);
diagramME()[ix](2*iv1, 2*iv2, of1, of2) = 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](2*iv1, 2*iv2, of1, of2) = 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 MEvv2ff::persistentOutput(PersistentOStream & os) const {
os << scalar_ << fermion_ << vector_ << tensor_;
}
void MEvv2ff::persistentInput(PersistentIStream & is, int) {
is >> scalar_ >> fermion_ >> vector_ >> tensor_;
initializeMatrixElements(PDT::Spin1 , PDT::Spin1,
PDT::Spin1Half, PDT::Spin1Half);
}
ClassDescription<MEvv2ff> MEvv2ff::initMEvv2ff;
// Definition of the static class description member.
void MEvv2ff::Init() {
static ClassDocumentation<MEvv2ff> documentation
("The MEvv2ff class handles the ME calculation for the general "
"spin configuration vector-vector to fermion-antifermion\n.");
}
void MEvv2ff::constructVertex(tSubProPtr sub) {
ParticleVector ext = hardParticles(sub);
// wavefunction with real momenta
VBVector v1, v2;
VectorWaveFunction(v1, ext[0], incoming, false, true);
VectorWaveFunction(v2, ext[1], incoming, false, true);
SpinorBarVector sbar;
SpinorBarWaveFunction(sbar, ext[2], outgoing, true);
SpinorVector sp;
SpinorWaveFunction(sp, ext[3], outgoing, true);
// rescale momenta
setRescaledMomenta(ext);
// wavefuncions with rescaled momenta
VectorWaveFunction v1r(rescaledMomenta()[0],
ext[0]->dataPtr(), incoming);
VectorWaveFunction v2r(rescaledMomenta()[1],
ext[1]->dataPtr(), incoming);
SpinorBarWaveFunction sbr(rescaledMomenta()[2],
ext[2]->dataPtr(), outgoing);
SpinorWaveFunction spr(rescaledMomenta()[3],
ext[3]->dataPtr(), outgoing);
for( unsigned int ihel = 0; ihel < 2; ++ihel ) {
v1r.reset(2*ihel);
v1[ihel] = v1r;
v2r.reset(2*ihel);
v2[ihel] = v2r;
sbr.reset(ihel);
sbar[ihel] = sbr;
spr.reset(ihel);
sp[ihel] = spr;
}
double dummy(0.);
ProductionMatrixElement pme = vv2ffME(v1, v2, sbar, sp, dummy,false);
#ifndef NDEBUG
if( debugME() ) debug(dummy);
#endif
createVertex(pme,ext);
}
void MEvv2ff::debug(double me2) const {
if( !generator()->logfile().is_open() ) return;
long id3(abs(mePartonData()[2]->id())), id4(abs(mePartonData()[3]->id()));
if( mePartonData()[0]->id() != 21 || mePartonData()[1]->id() != 21 ||
id3 != id4 || (id3 != 1000021 && id3 != 5100002 && id3 != 5100001 &&
id3 != 6100002 && id3 != 6100001) )
return;
tcSMPtr sm = generator()->standardModel();
double gs4 = sqr( 4.*Constants::pi*sm->alphaS(scale()) );
int Nc = sm->Nc();
Energy2 s(sHat());
Energy2 mf2 = meMomenta()[2].m2();
Energy4 spt2 = uHat()*tHat() - sqr(mf2);
Energy2 t3(tHat() - mf2), u4(uHat() - mf2);
double analytic(0.);
if( id3 == 1000021 ) {
analytic = gs4*sqr(Nc)*u4*t3*
( sqr(u4) + sqr(t3) + 4.*mf2*s*spt2/u4/t3 ) *
( 1./sqr(s*t3) + 1./sqr(s*u4) + 1./sqr(u4*t3) )/2./(Nc*Nc - 1.);
}
else {
double brac = sqr(s)/6./t3/u4 - 3./8.;
analytic = gs4*( -4.*sqr(mf2)*brac/t3/u4 + 4.*mf2*brac/s + brac
- 1./3. + 3.*t3*u4/4/s/s);
}
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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