EvtSemiLeptonicScalarAmp.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) 1998      Caltech, UCSB
//
// Module: EvtSemiLeptonicScalarAmp.cc
//
// Description: Routine to implement semileptonic decays to pseudo-scalar
//              mesons.
//
// Modification history:
//
//    DJL       April 17,1998       Module created
//
//------------------------------------------------------------------------
//
#include "EvtSemiLeptonicScalarAmp.hh"
#include "EvtAmp.hh"
#include "EvtDiracSpinor.hh"
#include "EvtGenKine.hh"
#include "EvtId.hh"
#include "EvtPDL.hh"
#include "EvtParticle.hh"
#include "EvtPatches.hh"
#include "EvtReport.hh"
#include "EvtSemiLeptonicFF.hh"
#include "EvtTensor4C.hh"
#include "EvtVector4C.hh"
 
void EvtSemiLeptonicScalarAmp::CalcAmp( EvtParticle* parent, EvtAmp& amp,
                                        EvtSemiLeptonicFF* FormFactors ) {
 
  static EvtId EM   = EvtPDL::getId( "e-" );
  static EvtId MUM  = EvtPDL::getId( "mu-" );
  static EvtId TAUM = EvtPDL::getId( "tau-" );
  static EvtId EP   = EvtPDL::getId( "e+" );
  static EvtId MUP  = EvtPDL::getId( "mu+" );
  static EvtId TAUP = EvtPDL::getId( "tau+" );
 
  // Add the lepton and neutrino 4 momenta to find q2
 
  EvtVector4R q  = parent->getDaug( 1 )->getP4() + parent->getDaug( 2 )->getP4();
  double      q2 = ( q.mass2() );
 
  double fpf, f0f;
  double mesonmass  = parent->getDaug( 0 )->mass();
  double parentmass = parent->mass();
 
  FormFactors->getscalarff( parent->getId(), parent->getDaug( 0 )->getId(), q2, mesonmass,
                            &fpf, &f0f );
 
  EvtVector4R p4b;
  p4b.set( parent->mass(), 0.0, 0.0, 0.0 );
  EvtVector4R p4meson = parent->getDaug( 0 )->getP4();
  double      mdiffoverq2;
  mdiffoverq2 = parentmass * parentmass - mesonmass * mesonmass;
  mdiffoverq2 = mdiffoverq2 / q2;
 
  EvtVector4C l1, l2;
 
  EvtId       l_num = parent->getDaug( 1 )->getId();
  EvtVector4C tds;
 
  if ( l_num == EM || l_num == MUM || l_num == TAUM )
  {
 
    tds = EvtVector4C( fpf * ( p4b + p4meson - ( mdiffoverq2 * ( p4b - p4meson ) ) ) +
                       +f0f * mdiffoverq2 * ( p4b - p4meson ) );
 
    l1 = EvtLeptonVACurrent( parent->getDaug( 1 )->spParent( 0 ),
                             parent->getDaug( 2 )->spParentNeutrino() );
    l2 = EvtLeptonVACurrent( parent->getDaug( 1 )->spParent( 1 ),
                             parent->getDaug( 2 )->spParentNeutrino() );
  }
  else
  {
    if ( l_num == EP || l_num == MUP || l_num == TAUP )
    {
 
      tds = EvtVector4C( fpf * ( p4b + p4meson - ( mdiffoverq2 * ( p4b - p4meson ) ) ) +
                         +f0f * mdiffoverq2 * ( p4b - p4meson ) );
 
      l1 = EvtLeptonVACurrent( parent->getDaug( 2 )->spParentNeutrino(),
                               parent->getDaug( 1 )->spParent( 0 ) );
      l2 = EvtLeptonVACurrent( parent->getDaug( 2 )->spParentNeutrino(),
                               parent->getDaug( 1 )->spParent( 1 ) );
    }
    else { report( ERROR, "EvtGen" ) << "dfnb89agngri wrong lepton number\n"; }
  }
 
  amp.vertex( 0, l1 * tds );
  amp.vertex( 1, l2 * tds );
}