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MEee2VectorMeson.cc
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MEee2VectorMeson.cc
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// -*- C++ -*-
//
// MEee2VectorMeson.cc is a part of Herwig - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2019 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 MEee2VectorMeson class.
//
#include "MEee2VectorMeson.h"
#include "ThePEG/Utilities/DescribeClass.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/Interface/Switch.h"
#include "ThePEG/Interface/Parameter.h"
#include "ThePEG/Interface/Reference.h"
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
#include "ThePEG/PDT/EnumParticles.h"
#include "ThePEG/MatrixElement/Tree2toNDiagram.h"
#include "ThePEG/Cuts/Cuts.h"
#include "Herwig/PDT/GenericMassGenerator.h"
#include "ThePEG/Handlers/StandardXComb.h"
#include "Herwig/Models/StandardModel/StandardModel.h"
#include "Herwig/MatrixElement/HardVertex.h"
using namespace Herwig;
using namespace ThePEG;
using namespace ThePEG::Helicity;
void MEee2VectorMeson::getDiagrams() const {
tcPDPtr em = getParticleData(ParticleID::eminus);
tcPDPtr ep = getParticleData(ParticleID::eplus);
add(new_ptr((Tree2toNDiagram(2), em, ep, 1, vector_,-1)));
}
Energy2 MEee2VectorMeson::scale() const {
return sHat();
}
int MEee2VectorMeson::nDim() const {
return 0;
}
void MEee2VectorMeson::setKinematics() {
MEBase::setKinematics();
}
bool MEee2VectorMeson::generateKinematics(const double *) {
Lorentz5Momentum pout=meMomenta()[0]+meMomenta()[1];
pout.rescaleMass();
meMomenta()[2] = pout;
jacobian(1.0);
// check passes all the cuts
vector<LorentzMomentum> out(1,meMomenta()[2]);
tcPDVector tout(1,mePartonData()[2]);
return lastCuts().passCuts(tout, out, mePartonData()[0], mePartonData()[1]);
}
unsigned int MEee2VectorMeson::orderInAlphaS() const {
return 0;
}
unsigned int MEee2VectorMeson::orderInAlphaEW() const {
return 2;
}
Selector<const ColourLines *>
MEee2VectorMeson::colourGeometries(tcDiagPtr) const {
static ColourLines neutral ( " " );
Selector<const ColourLines *> sel;sel.insert(1.,&neutral);
return sel;
}
void MEee2VectorMeson::persistentOutput(PersistentOStream & os) const {
os << coupling_ << vector_ << massGen_ << lineShape_;
}
void MEee2VectorMeson::persistentInput(PersistentIStream & is, int) {
is >> coupling_ >> vector_ >> massGen_ >> lineShape_;
}
// The following static variable is needed for the type
// description system in ThePEG.
DescribeClass<MEee2VectorMeson,MEBase>
describeHerwigMEee2VectorMeson("Herwig::MEee2VectorMeson", "HwMELepton.so");
void MEee2VectorMeson::Init() {
static ClassDocumentation<MEee2VectorMeson> documentation
("The MEee2VectorMeson class implements the production of a vector meson"
" in e+e- collisions and is primilarly intended to test the hadron decay package");
static Switch<MEee2VectorMeson,bool> interfaceLineShape
("LineShape",
"Option for the vector meson lineshape",
&MEee2VectorMeson::lineShape_, false, false, false);
static SwitchOption interfaceLineShapeMassGenerator
(interfaceLineShape,
"MassGenerator",
"Use the mass generator if available",
true);
static SwitchOption interfaceLineShapeBreitWigner
(interfaceLineShape,
"BreitWigner",
"Use a Breit-Wigner with the naive running width",
false);
static Reference<MEee2VectorMeson,ParticleData> interfaceVectorMeson
("VectorMeson",
"The vector meson produced",
&MEee2VectorMeson::vector_, false, false, true, false, false);
static Parameter<MEee2VectorMeson,double> interfaceCoupling
("Coupling",
"The leptonic coupling of the vector meson",
&MEee2VectorMeson::coupling_, 0., 0.0, 100.0,
false, false, Interface::limited);
}
Selector<MEBase::DiagramIndex>
MEee2VectorMeson::diagrams(const DiagramVector &) const {
Selector<DiagramIndex> sel;sel.insert(1.0, 0);
return sel;
}
CrossSection MEee2VectorMeson::dSigHatDR() const {
InvEnergy2 wgt;
Energy M(vector_->mass()),G(vector_->width());
Energy2 M2(sqr(M));
if(massGen_&&lineShape_)
wgt = Constants::pi*massGen_->BreitWignerWeight(sqrt(sHat()));
else
wgt = sHat()*G/M/(sqr(sHat()-M2)+sqr(sHat()*G/M));
return sqr(4.*Constants::pi*SM().alphaEM(sHat()))*me2()*jacobian()*wgt*sqr(hbarc)*sqr(M2/sHat());
}
void MEee2VectorMeson::doinit() {
MEBase::doinit();
// mass generator
tMassGenPtr mass=vector_->massGenerator();
if(mass) {
massGen_=dynamic_ptr_cast<GenericMassGeneratorPtr>(mass);
}
}
double MEee2VectorMeson::me2() const {
double aver=0.;
// get the order right
int ielectron(0),ipositron(1);
if(mePartonData()[0]->id()!=11) swap(ielectron,ipositron);
// the vectors for the wavefunction to be passed to the matrix element
vector<SpinorWaveFunction> fin;
vector<SpinorBarWaveFunction> ain;
vector<VectorWaveFunction> vout;
for(unsigned int ihel=0;ihel<2;++ihel) {
fin.push_back(SpinorWaveFunction(meMomenta()[ielectron],
mePartonData()[ielectron],ihel,incoming));
ain.push_back(SpinorBarWaveFunction(meMomenta()[ipositron],
mePartonData()[ipositron],ihel,incoming));
}
for(unsigned int ihel=0;ihel<3;++ihel) {
vout.push_back(VectorWaveFunction(meMomenta()[2],mePartonData()[2],ihel,outgoing));
}
ProductionMatrixElement temp=HelicityME(fin,ain,vout,aver);
return aver;
}
// the helicity amplitude matrix element
ProductionMatrixElement MEee2VectorMeson::HelicityME(vector<SpinorWaveFunction> fin,
vector<SpinorBarWaveFunction> ain,
vector<VectorWaveFunction> vout,
double & aver) const {
ProductionMatrixElement output(PDT::Spin1Half,PDT::Spin1Half,PDT::Spin1);
Complex product;
// sum over helicities to get the matrix element
unsigned int inhel1,inhel2,outhel1;
aver = 0.;
LorentzPolarizationVectorE vec;
Energy ecms = sqrt(sHat());
for(inhel1=0;inhel1<2;++inhel1) {
for(inhel2=0;inhel2<2;++inhel2) {
vec = fin[inhel1].dimensionedWave().vectorCurrent(ain[inhel2].dimensionedWave());
vec /= coupling_;
for(outhel1=0;outhel1<3;++outhel1) {
product = vec.dot(vout[outhel1].wave())/ecms;
output(inhel1,inhel2,outhel1)=product;
aver += norm(product);
}
}
}
aver *= 0.25;
return output;
}
void MEee2VectorMeson::constructVertex(tSubProPtr sub) {
// extract the particles in the hard process
ParticleVector hard;
hard.push_back(sub->incoming().first);hard.push_back(sub->incoming().second);
hard.push_back(sub->outgoing()[0]);
if(hard[0]->id()<hard[1]->id()) swap(hard[0],hard[1]);
vector<SpinorWaveFunction> fin;
vector<SpinorBarWaveFunction> ain;
vector<VectorWaveFunction> vout;
SpinorWaveFunction( fin ,hard[0],incoming,false,true);
SpinorBarWaveFunction(ain ,hard[1],incoming,false,true);
VectorWaveFunction(vout ,hard[2],outgoing,true,false,true);
double dummy;
ProductionMatrixElement prodme=HelicityME(fin,ain,vout,dummy);
// construct the vertex
HardVertexPtr hardvertex=new_ptr(HardVertex());
// set the matrix element for the vertex
hardvertex->ME(prodme);
// set the pointers and to and from the vertex
for(unsigned int ix=0;ix<3;++ix) {
(hard[ix]->spinInfo())->productionVertex(hardvertex);
}
}

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