EvtSVPHelAmp.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: EvtSVPHelAmp.cc
//
// Description: Routine to decay scalar -> vectors+photon
//              by specifying the helicity amplitudes
//
// Modification history:
//
//    RYD       July 26, 1997       Module created
//
//------------------------------------------------------------------------
//
#include "EvtSVPHelAmp.hh"
#include "../EvtGenBase/EvtComplex.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 <stdlib.h>
#include <string>
 
EvtSVPHelAmp::~EvtSVPHelAmp() {}
 
void EvtSVPHelAmp::getName( std::string& model_name ) { model_name = "SVP_HELAMP"; }
 
EvtDecayBase* EvtSVPHelAmp::clone() { return new EvtSVPHelAmp; }
 
void EvtSVPHelAmp::initProbMax() {
 
  setProbMax( getArg( 0 ) * getArg( 0 ) + getArg( 2 ) * getArg( 2 ) );
}
 
void EvtSVPHelAmp::init() {
 
  // check that there are 4 arguments
  checkNArg( 4 );
  checkNDaug( 2 );
 
  checkSpinParent( EvtSpinType::SCALAR );
 
  checkSpinDaughter( 0, EvtSpinType::VECTOR );
  checkSpinDaughter( 1, EvtSpinType::PHOTON );
}
 
void EvtSVPHelAmp::decay( EvtParticle* p ) {
 
  EvtComplex hp( getArg( 0 ) * cos( getArg( 1 ) ), getArg( 0 ) * sin( getArg( 1 ) ) );
  EvtComplex hm( getArg( 2 ) * cos( getArg( 3 ) ), getArg( 2 ) * sin( getArg( 3 ) ) );
 
  //  Routine to decay a vector into a vector and scalar.  Started
  //  by ryd on Oct 17, 1996.
 
  // This routine is adopted from EvtSVVHel and since there is
  // a photon that can not have helicity 0 this is put in by
  // setting the h0 amplitude to 0.
  EvtComplex h0 = EvtComplex( 0.0, 0.0 );
 
  EvtParticle *v1, *ph;
 
  p->initializePhaseSpace( getNDaug(), getDaugs() );
  v1                = p->getDaug( 0 );
  ph                = p->getDaug( 1 );
  EvtVector4R momv1 = v1->getP4();
  EvtVector4R momph = ph->getP4();
 
  EvtTensor4C d, g;
 
  g.setdiag( 1.0, -1.0, -1.0, -1.0 );
 
  EvtVector4R v, vp;
 
  v  = momv1 / momv1.d3mag();
  vp = ( momv1 + momph ) / ( momv1 + momph ).mass();
 
  d = ( ( 1.0 / sqrt( 3.0 ) ) * ( h0 - ( hp + hm ) ) * ( -1.0 / sqrt( 3.0 ) ) ) * g +
      ( ( 1.0 / sqrt( 2.0 ) ) * ( hp - hm ) * EvtComplex( 0.0, 1.0 ) *
        ( sqrt( 1.0 / 2.0 ) ) ) *
          dual( directProd( v, vp ) ) +
      ( sqrt( 2.0 / 3.0 ) * ( h0 + 0.5 * ( hp + hm ) ) * sqrt( 3.0 / 2.0 ) ) *
          ( directProd( v, v ) + ( 1.0 / 3.0 ) * g );
 
  EvtVector4C ep0, ep1, ep2;
 
  ep0 = d.cont1( v1->eps( 0 ).conj() );
  ep1 = d.cont1( v1->eps( 1 ).conj() );
  ep2 = d.cont1( v1->eps( 2 ).conj() );
 
  EvtVector4C ep20, ep21, ep22;
 
  ep20 = ph->epsParentPhoton( 0 ).conj();
  ep21 = ph->epsParentPhoton( 1 ).conj();
 
  vertex( 0, 0, ep0 * ep20 );
  vertex( 0, 1, ep0 * ep21 );
 
  vertex( 1, 0, ep1 * ep20 );
  vertex( 1, 1, ep1 * ep21 );
 
  vertex( 2, 0, ep2 * ep20 );
  vertex( 2, 1, ep2 * ep21 );
 
  return;
}