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EvtLNuGamma.cpp
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EvtLNuGamma.cpp
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/***********************************************************************
* Copyright 1998-2020 CERN for the benefit of the EvtGen authors *
* *
* This file is part of EvtGen. *
* *
* EvtGen is free software: you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation, either version 3 of the License, or *
* (at your option) any later version. *
* *
* EvtGen is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU General Public License for more details. *
* *
* You should have received a copy of the GNU General Public License *
* along with EvtGen. If not, see <https://www.gnu.org/licenses/>. *
***********************************************************************/
#include "EvtGenModels/EvtLNuGamma.hh"
#include "EvtGenBase/EvtComplex.hh"
#include "EvtGenBase/EvtDiracSpinor.hh"
#include "EvtGenBase/EvtGenKine.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtParticle.hh"
#include "EvtGenBase/EvtPatches.hh"
#include "EvtGenBase/EvtReport.hh"
#include "EvtGenBase/EvtTensor4C.hh"
#include "EvtGenBase/EvtVector4C.hh"
#include "EvtGenBase/EvtVector4R.hh"
#include <iostream>
#include <stdlib.h>
#include <string>
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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