EvtLNuGamma.cc

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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 "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>
 
EvtLNuGamma::EvtLNuGamma() { _fafvzero = false; }
 
EvtLNuGamma::~EvtLNuGamma() {}
 
void EvtLNuGamma::getName( std::string& model_name ) { model_name = "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-" );
  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 )
  {
    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 ) { fa = -fv; }
  else { fa = fv; }
 
  EvtVector4C temp1a = dual( directProd( parVelocity, photp ) ).cont2( photone1 );
  EvtVector4C temp2a = dual( 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;
}