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EvtLNuGamma.cpp
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EvtLNuGamma.cpp
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//--------------------------------------------------------------------------
//
// Environment:
// This software is part of the EvtGen package developed jointly
// for the BaBar and CLEO collaborations. If you use all or part
// of it, please give an appropriate acknowledgement.
//
// Copyright Information: See EvtGen/COPYRIGHT
// Copyright (C) 2001 Caltech
//
// Module: EvtLNuGamma.cc
//
// Description: B+ -> l+ nu gamma
//
//
// Modification history:
//
// Edward Chen April 24, 2001 Module created
//
//------------------------------------------------------------------------
//
#include "EvtGenBase/EvtPatches.hh"
#include <stdlib.h>
#include <iostream>
#include <string>
#include "EvtGenBase/EvtParticle.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtGenKine.hh"
#include "EvtGenModels/EvtLNuGamma.hh"
#include "EvtGenBase/EvtDiracSpinor.hh"
#include "EvtGenBase/EvtReport.hh"
#include "EvtGenBase/EvtComplex.hh"
#include "EvtGenBase/EvtVector4C.hh"
#include "EvtGenBase/EvtVector4R.hh"
#include "EvtGenBase/EvtTensor4C.hh"
EvtLNuGamma::EvtLNuGamma(){
_fafvzero = false;
}
EvtLNuGamma::~EvtLNuGamma() {}
std::string EvtLNuGamma::getName(){
return "LNUGAMMA";
}
EvtDecayBase* EvtLNuGamma::clone(){
return new EvtLNuGamma;
}
void EvtLNuGamma::init(){
// check that there are 3 or 4 arguments
checkNArg(3,4);
checkNDaug(3);
if (getNArg() == 4){
// Argv[3] is a flag set to 0 if abs(f_a/f_v) is 1
// and not set to 0 if f_a/f_v is set to 0.
if (getArg(3) > 0){
_fafvzero = true;
}
else{
_fafvzero = false;
}
}
else{
_fafvzero = false;
}
checkSpinParent(EvtSpinType::SCALAR);
checkSpinDaughter(0,EvtSpinType::DIRAC);
checkSpinDaughter(1,EvtSpinType::NEUTRINO);
checkSpinDaughter(2,EvtSpinType::PHOTON);
}
void EvtLNuGamma::initProbMax(){
setProbMax(7000.0);
}
void EvtLNuGamma::decay(EvtParticle *p){
static EvtId BM=EvtPDL::getId("B-");
static EvtId DM=EvtPDL::getId("D-");
p->initializePhaseSpace(getNDaug(),getDaugs());
EvtComplex myI(0,1);
EvtParticle *lept, *neut,*phot;
lept=p->getDaug(0);
neut=p->getDaug(1);
phot=p->getDaug(2);
EvtVector4C lept1,lept2,photon1,photon2;
if (p->getId()==BM||p->getId()==DM) {
lept1=EvtLeptonVACurrent(lept->spParent(0),neut->spParentNeutrino());
lept2=EvtLeptonVACurrent(lept->spParent(1),neut->spParentNeutrino());
}
else{
lept1=EvtLeptonVACurrent(neut->spParentNeutrino(),lept->spParent(0));
lept2=EvtLeptonVACurrent(neut->spParentNeutrino(),lept->spParent(1));
}
EvtVector4R photp = phot->getP4(); // Photon 4-momentum in parent rest frame
double photE = photp.get(0); // Photon energy in parent rest frame
EvtVector4C photone1 = phot->epsParentPhoton(0).conj();
EvtVector4C photone2 = phot->epsParentPhoton(1).conj();
EvtVector4R parVelocity(1,0,0,0); // Parent velocity in parent rest-frame
double fv,fa;
fv = getFormFactor(photE);
if (_fafvzero){
fa = 0.0;
}
else if (p->getId()==BM||p->getId()==DM) {
fa = - fv;
}
else{
fa = fv;
}
EvtVector4C temp1a = dual(EvtGenFunctions::directProd(parVelocity,photp)).cont2(photone1);
EvtVector4C temp2a = dual(EvtGenFunctions::directProd(parVelocity,photp)).cont2(photone2);
EvtVector4C temp1b = (photone1)*(parVelocity*photp);
EvtVector4C temp1c = (photp)*(photone1*parVelocity);
EvtVector4C temp2b = (photone2)*(parVelocity*photp);
EvtVector4C temp2c = (photp)*(photone2*parVelocity);
photon1 = (temp1a*fv) + (myI*fa*(temp1b - temp1c));
photon2 = (temp2a*fv) + (myI*fa*(temp2b - temp2c));
vertex(0,0,lept1.cont(photon1));
vertex(0,1,lept1.cont(photon2));
vertex(1,0,lept2.cont(photon1));
vertex(1,1,lept2.cont(photon2));
return;
}
double EvtLNuGamma::getFormFactor(double photonEnergy){
// Arg[0] = photon mass cutoff (GeV)
// Arg[1] = R (GeV^(-1))
// Arg[2] = m_b (GeV)
// Using Korchemsky et al. Phy Rev D 61 (2000) 114510
// Up to a constant
double formFactor = 0;
double qu = 2./3.;
double qb = -1./3.;
if (photonEnergy > getArg(0)){
formFactor = (1/photonEnergy) * ((qu*getArg(1)) - (qb/getArg(2)));
}
return formFactor;
}

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