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MEvv2ss.cc
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MEvv2ss.cc
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// -*- C++ -*-
//
// MEvv2ss.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 MEvv2ss class.
//
#include "MEvv2ss.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 MEvv2ss::doinit() {
GeneralHardME::doinit();
scalar1_.resize(numberOfDiags());
scalar2_.resize(numberOfDiags());
vector_ .resize(numberOfDiags());
tensor_ .resize(numberOfDiags());
initializeMatrixElements(PDT::Spin1, PDT::Spin1,
PDT::Spin0, PDT::Spin0);
for(size_t i = 0; i < numberOfDiags(); ++i ) {
HPDiagram dg = getProcessInfo()[i];
if( !dg.intermediate ) {
contact_ = dynamic_ptr_cast<AbstractVVSSVertexPtr>(dg.vertices.first);
}
else if(dg.channelType == HPDiagram::tChannel) {
AbstractVSSVertexPtr vss1 =
dynamic_ptr_cast<AbstractVSSVertexPtr>(dg.vertices.first);
AbstractVSSVertexPtr vss2 =
dynamic_ptr_cast<AbstractVSSVertexPtr>(dg.vertices.second);
scalar2_[i] = make_pair(vss1, vss2);
}
else {
if( dg.intermediate->iSpin() == PDT::Spin0 ) {
AbstractVVSVertexPtr vvs =
dynamic_ptr_cast<AbstractVVSVertexPtr>(dg.vertices.first);
AbstractSSSVertexPtr sss =
dynamic_ptr_cast<AbstractSSSVertexPtr>(dg.vertices.second);
scalar1_[i] = make_pair(vvs, sss);
}
else if( dg.intermediate->iSpin() == PDT::Spin1 ) {
AbstractVVVVertexPtr vvv =
dynamic_ptr_cast<AbstractVVVVertexPtr>(dg.vertices.first);
AbstractVSSVertexPtr vss =
dynamic_ptr_cast<AbstractVSSVertexPtr>(dg.vertices.second);
vector_[i] = make_pair(vvv, vss);
}
else if( dg.intermediate->iSpin() == PDT::Spin2 ) {
AbstractVVTVertexPtr vvt =
dynamic_ptr_cast<AbstractVVTVertexPtr>(dg.vertices.first);
AbstractSSTVertexPtr sst =
dynamic_ptr_cast<AbstractSSTVertexPtr>(dg.vertices.second);
tensor_[i] = make_pair(vvt, sst);
}
}
}
}
double MEvv2ss::me2() const {
VBVector v1(2), v2(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);
}
ScalarWaveFunction sca1(rescaledMomenta()[2],mePartonData()[2],
Complex(1.,0.),outgoing);
ScalarWaveFunction sca2(rescaledMomenta()[3],mePartonData()[3],
Complex(1.,0.),outgoing);
double full_me(0.);
vv2ssME(v1, v2, sca1, sca2, full_me , true);
#ifndef NDEBUG
if( debugME() ) debug(full_me);
#endif
return full_me;
}
ProductionMatrixElement
MEvv2ss::vv2ssME(const VBVector & v1, const VBVector & v2,
const ScalarWaveFunction & sca1,
const ScalarWaveFunction & sca2,
double & me2, bool first) const {
const Energy2 m2(scale());
const Energy masst = sca1.mass(), massu = sca2.mass();
// 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.);
//loop over vector helicities
for(unsigned int iv1 = 0; iv1 < 2; ++iv1) {
for(unsigned int iv2 = 0; iv2 < 2; ++iv2) {
vector<Complex> flows(numberOfFlows(),0.);
// loop over diagrams
for(HPCount ix = 0; ix < numberOfDiags(); ++ix) {
Complex diag(0.);
const HPDiagram & current = getProcessInfo()[ix];
// do four-point diag first
if(current.channelType == HPDiagram::fourPoint) {
diag = contact_->evaluate(m2, v1[iv1], v2[iv2], sca1, sca2);
}
else {
tcPDPtr offshell = current.intermediate;
if(current.channelType == HPDiagram::tChannel) {
if(current.ordered.second) {
ScalarWaveFunction interS = scalar2_[ix].first->
evaluate(m2, 3, offshell, v1[iv1], sca1, masst);
diag = scalar2_[ix].second->evaluate(m2, v2[iv2], interS, sca2);
}
else {
ScalarWaveFunction interS = scalar2_[ix].first->
evaluate(m2, 3, offshell, v1[iv1], sca2, massu);
diag = scalar2_[ix].second->evaluate(m2, v2[iv2], interS, sca1);
}
}
else if(current.channelType == HPDiagram::sChannel) {
if(offshell->iSpin() == PDT::Spin0) {
ScalarWaveFunction interS = scalar1_[ix].first->
evaluate(m2, 1, offshell, v1[iv1], v2[iv2]);
diag = scalar1_[ix].second->evaluate(m2, interS, sca1, sca2);
}
else if(offshell->iSpin() == PDT::Spin1) {
VectorWaveFunction interV = vector_[ix].first->
evaluate(m2, 1, offshell, v1[iv1], v2[iv2]);
diag = vector_[ix].second->evaluate(m2, interV, sca1, sca2);
}
else if(offshell->iSpin() == PDT::Spin2) {
TensorWaveFunction interT = tensor_[ix].first->
evaluate(m2, 1, offshell, v1[iv1], v2[iv2]);
diag = tensor_[ix].second->evaluate(m2, sca1, sca2, interT);
}
}
else
diag = 0.;
}
me[ix] += norm(diag);
diagramME()[ix](2*iv1, 2*iv2, 0, 0) = 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, 0, 0) = 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 MEvv2ss::persistentOutput(PersistentOStream & os) const {
os << scalar1_ << scalar2_ << vector_ << tensor_ << contact_;
}
void MEvv2ss::persistentInput(PersistentIStream & is, int) {
is >> scalar1_ >> scalar2_ >> vector_ >> tensor_ >> contact_;
initializeMatrixElements(PDT::Spin1, PDT::Spin1,
PDT::Spin0, PDT::Spin0);
}
ClassDescription<MEvv2ss> MEvv2ss::initMEvv2ss;
// Definition of the static class description member.
void MEvv2ss::Init() {
static ClassDocumentation<MEvv2ss> documentation
("This class implements the ME for the vector-vector to scalar-scalar "
"hard-process");
}
void MEvv2ss::constructVertex(tSubProPtr sub) {
ParticleVector ext = hardParticles(sub);
VBVector v1, v2;
// set up the wavefunctions with real momenta
VectorWaveFunction(v1, ext[0], incoming, false, true);
VectorWaveFunction(v2, ext[1], incoming, false, true);
ScalarWaveFunction sca1(ext[2], outgoing, true);
ScalarWaveFunction sca2(ext[3], outgoing, true);
// calculate rescaled moment
setRescaledMomenta(ext);
// wavefunctions with rescaled momenta
VectorWaveFunction v1r (rescaledMomenta()[0],
ext[0]->dataPtr(), incoming);
VectorWaveFunction v2r (rescaledMomenta()[1],
ext[1]->dataPtr(), incoming);
sca1 = ScalarWaveFunction(rescaledMomenta()[2],
ext[2]->dataPtr(), outgoing);
sca2 = ScalarWaveFunction(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;
}
double dummy(0.);
ProductionMatrixElement pme = vv2ssME(v1, v2, sca1, sca2, dummy , false);
#ifndef NDEBUG
if( debugME() ) debug(dummy);
#endif
createVertex(pme,ext);
}
void MEvv2ss::debug(double me2) const {
if( !generator()->logfile().is_open() ) return;
if( mePartonData()[0]->id() != 21 || mePartonData()[1]->id() != 21) return;
long id3 = abs(mePartonData()[2]->id());
long id4 = abs(mePartonData()[3]->id());
int type = -1;
//SUSY gg>~q~q
if( ((id3 >= 1000001 && id3 <= 1000006 ) && (id4 >= 1000001 && id4 <= 1000006 ) ) ||
((id3 >= 2000001 && id3 <= 2000006 ) && (id4 >= 2000001 && id4 <= 2000006 ) ) ) {
type = 0;
}
// Sextet production
else if(mePartonData()[2]->iColour() == PDT::Colour6 &&
mePartonData()[3]->iColour() == PDT::Colour6bar ) {
type = 1;
}
else {
return;
}
double gs4 = sqr( 4.*Constants::pi*SM().alphaS(scale()));
int Nc = SM().Nc();
Energy4 s2 = sqr(sHat());
Energy2 m3s = meMomenta()[2].m2();
Energy2 m4s = meMomenta()[3].m2();
Energy4 spt2 = uHat()*tHat() - m3s*m4s;
Energy2 t3 = tHat()-m3s, u4 = uHat()-m4s;
Energy4 t3s = sqr(t3) , u4s = sqr(u4);
Energy8 pre = gs4*(sqr(spt2) + s2*m3s*m4s);
// matrix element
double analytic(0.);
// triplet scalars
if(type==0) {
analytic = pre*Nc*
( u4s + t3s - s2/sqr(Nc) )/2./(sqr(Nc) - 1.)/s2/t3s/u4s;
}
// sextet scalars
else if(type==1) {
analytic = pre*(Nc+2.)/(sqr(Nc)-1.)/Nc*
((Nc+2.)*(Nc-1.)/t3s/u4s - sqr(Nc)/t3/u4/s2);
}
double diff = abs(analytic - me2)/(analytic+me2);
if( diff > 1e-10 ) {
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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