EvtDiracParticle.cc

Go to the documentation of this file.

//--------------------------------------------------------------------------
//
// 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: EvtDiracParticle.cc
//
// Description: Class to describe spin 1/2 particles.
//
// Modification history:
//
//    DJL/RYD     September 25, 1996         Module created
//
//------------------------------------------------------------------------
//
#include "EvtDiracParticle.hh"
#include "EvtComplex.hh"
#include "EvtGammaMatrix.hh"
#include "EvtPDL.hh"
#include "EvtPatches.hh"
#include "EvtReport.hh"
#include "EvtSpinDensity.hh"
#include "EvtVector4R.hh"
#include <iostream>
#include <math.h>
#include <stdlib.h>
 
using std::endl;
 
EvtDiracParticle::~EvtDiracParticle() {}
 
EvtDiracParticle::EvtDiracParticle() { return; }
 
void EvtDiracParticle::init( EvtId part_n, const EvtVector4R& p4 ) {
 
  _validP4 = true;
  setp( p4 );
  setpart_num( part_n );
 
  if ( EvtPDL::getStdHep( part_n ) == 0 )
  {
    report( ERROR, "EvtGen" ) << "Error in EvtDiracParticle::init, part_n=" << part_n.getId()
                              << endl;
    ::abort();
  }
 
  if ( EvtPDL::getStdHep( part_n ) > 0 )
  {
 
    _spinorRest[0].set( EvtComplex( sqrt( 2.0 * mass() ), 0.0 ), EvtComplex( 0.0, 0.0 ),
                        EvtComplex( 0.0, 0.0 ), EvtComplex( 0.0, 0.0 ) );
    _spinorRest[1].set( EvtComplex( 0.0, 0.0 ), EvtComplex( sqrt( 2.0 * mass() ), 0.0 ),
                        EvtComplex( 0.0, 0.0 ), EvtComplex( 0.0, 0.0 ) );
 
    _spinorParent[0] = boostTo( _spinorRest[0], p4 );
    _spinorParent[1] = boostTo( _spinorRest[1], p4 );
  }
  else
  {
 
    _spinorRest[0].set( EvtComplex( 0.0, 0.0 ), EvtComplex( 0.0, 0.0 ),
                        EvtComplex( sqrt( 2.0 * mass() ), 0.0 ), EvtComplex( 0.0, 0.0 ) );
    _spinorRest[1].set( EvtComplex( 0.0, 0.0 ), EvtComplex( 0.0, 0.0 ), EvtComplex( 0.0, 0.0 ),
                        EvtComplex( sqrt( 2.0 * mass() ), 0.0 ) );
 
    _spinorParent[0] = boostTo( _spinorRest[0], p4 );
    _spinorParent[1] = boostTo( _spinorRest[1], p4 );
  }
 
  setLifetime();
}
 
EvtSpinDensity EvtDiracParticle::rotateToHelicityBasis() const {
 
  EvtDiracSpinor spplus;
  EvtDiracSpinor spminus;
 
  double sqmt2 = sqrt( 2. * ( getP4().mass() ) );
 
  if ( EvtPDL::getStdHep( getId() ) > 0 )
  {
    spplus.set( 1.0, 0.0, 0.0, 0.0 );
    spminus.set( 0.0, 1.0, 0.0, 0.0 );
  }
  else
  {
    spplus.set( 0.0, 0.0, 1.0, 0.0 );
    spminus.set( 0.0, 0.0, 0.0, 1.0 );
  }
 
  EvtSpinDensity R;
  R.SetDim( 2 );
 
  for ( int i = 0; i < 2; i++ )
  {
    R.Set( 0, i, ( spplus * _spinorRest[i] ) / sqmt2 );
    R.Set( 1, i, ( spminus * _spinorRest[i] ) / sqmt2 );
  }
 
  return R;
}
 
EvtSpinDensity EvtDiracParticle::rotateToHelicityBasis( double alpha, double beta,
                                                        double gamma ) const {
 
  EvtDiracSpinor spplus;
  EvtDiracSpinor spminus;
 
  double sqmt2 = sqrt( 2. * ( getP4().mass() ) );
 
  if ( EvtPDL::getStdHep( getId() ) > 0 )
  {
    spplus.set( 1.0, 0.0, 0.0, 0.0 );
    spminus.set( 0.0, 1.0, 0.0, 0.0 );
  }
  else
  {
    spplus.set( 0.0, 0.0, 1.0, 0.0 );
    spminus.set( 0.0, 0.0, 0.0, 1.0 );
  }
 
  spplus.applyRotateEuler( alpha, beta, gamma );
  spminus.applyRotateEuler( alpha, beta, gamma );
 
  EvtSpinDensity R;
  R.SetDim( 2 );
 
  for ( int i = 0; i < 2; i++ )
  {
    R.Set( 0, i, ( spplus * _spinorRest[i] ) / sqmt2 );
    R.Set( 1, i, ( spminus * _spinorRest[i] ) / sqmt2 );
  }
 
  return R;
}