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MEff2vv.cc
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MEff2vv.cc
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// -*- C++ -*-
//
// MEff2vv.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 MEff2vv class.
//
#include "MEff2vv.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
using namespace Herwig;
using ThePEG::Helicity::ScalarWaveFunction;
using ThePEG::Helicity::TensorWaveFunction;
using ThePEG::Helicity::incoming;
using ThePEG::Helicity::outgoing;
void MEff2vv::doinit() {
GeneralHardME::doinit();
fermion_.resize(numberOfDiags());
vector_.resize(numberOfDiags());
tensor_.resize(numberOfDiags());
scalar_.resize(numberOfDiags());
initializeMatrixElements(PDT::Spin1Half, PDT::Spin1Half,
PDT::Spin1, PDT::Spin1);
for(HPCount i = 0; i < numberOfDiags(); ++i) {
const HPDiagram & current = getProcessInfo()[i];
if(current.channelType == HPDiagram::tChannel) {
if(current.intermediate->iSpin() == PDT::Spin1Half)
fermion_[i] =
make_pair(dynamic_ptr_cast<AbstractFFVVertexPtr>(current.vertices.first),
dynamic_ptr_cast<AbstractFFVVertexPtr>(current.vertices.second));
}
else if(current.channelType == HPDiagram::sChannel) {
if(current.intermediate->iSpin() == PDT::Spin0)
scalar_[i] =
make_pair(dynamic_ptr_cast<AbstractFFSVertexPtr>(current.vertices.first ),
dynamic_ptr_cast<AbstractVVSVertexPtr>(current.vertices.second));
if(current.intermediate->iSpin() == PDT::Spin1)
vector_[i] =
make_pair(dynamic_ptr_cast<AbstractFFVVertexPtr>(current.vertices.first),
dynamic_ptr_cast<AbstractVVVVertexPtr>(current.vertices.second));
if(current.intermediate->iSpin() == PDT::Spin2)
tensor_[i] =
make_pair(dynamic_ptr_cast<AbstractFFTVertexPtr>(current.vertices.first),
dynamic_ptr_cast<AbstractVVTVertexPtr>(current.vertices.second));
}
}
}
double MEff2vv::me2() const {
SpinorVector sp(2);
SpinorBarVector sbar(2);
// vector
bool mc = !(mePartonData()[2]->mass() > ZERO);
bool md = !(mePartonData()[3]->mass() > ZERO);
VBVector v1(3), v2(3);
for( unsigned int i = 0; i < 2; ++i ) {
sp[i] = SpinorWaveFunction(rescaledMomenta()[0], mePartonData()[0], i, incoming);
sbar[i] = SpinorBarWaveFunction(rescaledMomenta()[1], mePartonData()[1], i,
incoming);
v1[2*i] = VectorWaveFunction(rescaledMomenta()[2], mePartonData()[2],2*i ,
outgoing);
v2[2*i] = VectorWaveFunction(rescaledMomenta()[3], mePartonData()[3], 2*i,
outgoing);
}
if( !mc ) v1[1] = VectorWaveFunction(rescaledMomenta()[2], mePartonData()[2], 1,
outgoing);
if( !md ) v2[1] = VectorWaveFunction(rescaledMomenta()[3], mePartonData()[3], 1,
outgoing);
double full_me(0.);
ff2vvME(sp, sbar, v1, mc, v2, md, full_me,true);
#ifndef NDEBUG
if( debugME() ) debug(full_me);
#endif
return full_me;
}
ProductionMatrixElement
MEff2vv::ff2vvME(const SpinorVector & sp, const SpinorBarVector sbar,
const VBVector & v1, bool m1, const VBVector & v2, bool m2,
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 and calculate diagrams
for(unsigned int if1 = 0; if1 < 2; ++if1) {
for(unsigned int if2 = 0; if2 < 2; ++if2) {
for(unsigned int vh1 = 0; vh1 < 3; ++vh1) {
if( vh1 == 1 && m1 ) ++vh1;
for(unsigned int vh2 = 0; vh2 < 3; ++vh2) {
if( vh2 == 1 && m2 ) ++vh2;
vector<Complex> flows(numberOfFlows(),0.);
//loop and calculate diagrams
for(HPCount ix = 0; ix < numberOfDiags(); ++ix) {
const HPDiagram & current = getProcessInfo()[ix];
tcPDPtr offshell = current.intermediate;
Complex diag(0.);
if(current.channelType == HPDiagram::tChannel) {
if(current.intermediate->iSpin() == PDT::Spin1Half) {
if(current.ordered.second) {
SpinorWaveFunction interF = fermion_[ix].first->
evaluate(q2, 3, offshell, sp[if1], v1[vh1]);
diag = fermion_[ix].second->
evaluate(q2, interF, sbar[if2],v2[vh2]);
}
else {
SpinorWaveFunction interF = fermion_[ix].first->
evaluate(q2, 3 , offshell, sp[if1], v2[vh2]);
diag = fermion_[ix].second->
evaluate(q2, interF, sbar[if2],v1[vh1]);
}
}
}
else if(current.channelType == HPDiagram::sChannel) {
if(current.intermediate->iSpin() == PDT::Spin0) {
ScalarWaveFunction interS = scalar_[ix].first->
evaluate(q2, 1, offshell, sp[if1], sbar[if2]);
diag = scalar_[ix].second->
evaluate(q2, v1[vh1], v2[vh2],interS);
}
else if(current.intermediate->iSpin() == PDT::Spin1) {
VectorWaveFunction interV = vector_[ix].first->
evaluate(q2, 1, offshell, sp[if1], sbar[if2]);
diag = vector_[ix].second->
evaluate(q2, v1[vh1],v2[vh2], interV);
}
else if(current.intermediate->iSpin() == PDT::Spin2) {
TensorWaveFunction interT = tensor_[ix].first->
evaluate(q2, 1, offshell, sp[if1], sbar[if2]);
diag = tensor_[ix].second->
evaluate(q2, v1[vh1], v2[vh2],interT);
}
}
me[ix] += norm(diag);
diagramME()[ix](if1, if2, vh1, vh2) = 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](if1, if2, vh1, vh2) = 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 MEff2vv::persistentOutput(PersistentOStream & os) const {
os << fermion_ << vector_ << tensor_ << scalar_;
}
void MEff2vv::persistentInput(PersistentIStream & is, int) {
is >> fermion_ >> vector_ >> tensor_ >> scalar_;
initializeMatrixElements(PDT::Spin1Half, PDT::Spin1Half,
PDT::Spin1, PDT::Spin1);
}
ClassDescription<MEff2vv> MEff2vv::initMEff2vv;
// Definition of the static class description member.
void MEff2vv::Init() {
static ClassDocumentation<MEff2vv> documentation
("This class implements the matrix element calculation of the 2->2 "
"process, fermion-antifermion -> vector vector");
}
void MEff2vv::constructVertex(tSubProPtr sub) {
//get particles
ParticleVector ext = hardParticles(sub);
vector<SpinorWaveFunction> sp;
SpinorWaveFunction(sp, ext[0], incoming, false);
vector<SpinorBarWaveFunction> sbar;
SpinorBarWaveFunction(sbar, ext[1], incoming, false);
vector<VectorWaveFunction> v1, v2;
bool mc = !(ext[2]->data().mass() > ZERO);
bool md = !(ext[3]->data().mass() > ZERO);
VectorWaveFunction(v1, ext[2], outgoing, true, mc);
VectorWaveFunction(v2, ext[3], outgoing, true, md);
//Need to use rescale momenta to calculate matrix element
setRescaledMomenta(ext);
// wavefunctions with rescaled momenta
SpinorWaveFunction spr (rescaledMomenta()[0],
ext[0]->dataPtr(), incoming);
SpinorBarWaveFunction sbr(rescaledMomenta()[1],
ext[1]->dataPtr(), incoming);
VectorWaveFunction vr1 (rescaledMomenta()[2],
ext[2]->dataPtr(), outgoing);
VectorWaveFunction vr2 (rescaledMomenta()[3],
ext[3]->dataPtr(), outgoing);
for( unsigned int ihel = 0; ihel < 2; ++ihel ) {
spr.reset(ihel);
sp[ihel] = spr;
sbr.reset(ihel);
sbar[ihel] = sbr;
vr1.reset(2*ihel);
v1[2*ihel] = vr1;
vr2.reset(2*ihel);
v2[2*ihel] = vr2;
}
if( !mc ) {
vr1.reset(1);
v1[1] = vr1;
}
if( !md ) {
vr2.reset(1);
v2[1] = vr2;
}
double dummy(0.);
ProductionMatrixElement pme = ff2vvME(sp, sbar, v1, mc, v2, md, dummy,false);
#ifndef NDEBUG
if( debugME() ) debug(dummy);
#endif
createVertex(pme,ext);
}
void MEff2vv::debug(double me2) const {
if( !generator()->logfile().is_open() ) return;
if( (mePartonData()[0]->id() != 1 && mePartonData()[0]->id() != 2) ||
(mePartonData()[1]->id() != -1 && mePartonData()[1]->id() != -2) ||
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);
double analytic = gs4*( mf2*( (57.*s/t3/u4) - (4.*s*s*s/t3/t3/u4/u4)
- (108./s) )
+ (20.*s*s/t3/u4) - 93. + (108.*t3*u4/s/s) )/27.;
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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