EvtNeutrinoParticle.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: EvtNeutrinoParticle.cc
//
// Description: Class to describe neutrinos
//
// Modification history:
//
//    DJL/RYD     September 25, 1996         Module created
//
//------------------------------------------------------------------------
//
#include "EvtNeutrinoParticle.hh"
#include "EvtComplex.hh"
#include "EvtPDL.hh"
#include "EvtPatches.hh"
#include "EvtReport.hh"
#include "EvtVector4R.hh"
#include <iostream>
#include <math.h>
#include <stdlib.h>
 
using std::endl;
 
EvtNeutrinoParticle::~EvtNeutrinoParticle() {}
 
EvtNeutrinoParticle::EvtNeutrinoParticle() { return; }
 
void EvtNeutrinoParticle::init( EvtId part_n, const EvtVector4R& p4 ) {
 
  _validP4 = true;
  setp( p4 );
  setpart_num( part_n );
 
  double e, px, py, pz;
  e  = p4.get( 0 );
  px = p4.get( 1 );
  py = p4.get( 2 );
  pz = p4.get( 3 );
 
  if ( EvtPDL::getStdHep( part_n ) == 0 )
  {
    report( ERROR, "EvtGen" ) << "Error in EvtNeutrinoParticle::init, part_n="
                              << part_n.getId() << endl;
  }
 
  if ( EvtPDL::getStdHep( part_n ) > 0 )
  {
 
    double beta, alpha, p2, norm;
 
    // See Sakurai p. 167-169
    // and Renton p. 126
 
    p2 = px * px + py * py + pz * pz;
 
    beta  = acos( pz / sqrt( p2 ) );
    alpha = atan2( py, px );
 
    norm = sqrt( 2 * e );
 
    double cosb, sinb, cosa, sina;
 
    cosb = cos( 0.5 * beta );
    sinb = sin( 0.5 * beta );
 
    cosa = cos( 0.5 * alpha );
    sina = sin( 0.5 * alpha );
 
    spinor_parent.set(
        -norm * sinb * EvtComplex( cosa, -sina ), norm * cosb * EvtComplex( cosa, sina ),
        norm * sinb * EvtComplex( cosa, -sina ), -norm * cosb * EvtComplex( cosa, sina ) );
  }
  else
  {
 
    px = -p4.get( 1 );
    py = -p4.get( 2 );
    pz = -p4.get( 3 );
 
    double pn, sqrpn;
 
    pn    = e;
    sqrpn = sqrt( pn - pz );
 
    spinor_parent.set( ( 1.0 / sqrpn ) * EvtComplex( px, -py ), EvtComplex( sqrpn, 0.0 ),
                       ( -1.0 / sqrpn ) * EvtComplex( px, -py ), -EvtComplex( sqrpn, 0.0 ) );
  }
 
  setLifetime();
}
 
EvtDiracSpinor EvtNeutrinoParticle::spParentNeutrino() const { return spinor_parent; }
 
EvtDiracSpinor EvtNeutrinoParticle::spNeutrino() const {
 
  report( ERROR, "EvtGen" ) << "Tried to get neutrino spinor in restframe";
  report( ERROR, "EvtGen" ) << "Will terminate execution.";
 
  ::abort();
 
  return spinor_rest;
}
 
EvtSpinDensity EvtNeutrinoParticle::rotateToHelicityBasis() const {
 
  report( ERROR, "EvtGen" ) << "rotateToHelicityBasis not implemented for neutrino.";
  report( ERROR, "EvtGen" ) << "Will terminate execution.";
 
  ::abort();
 
  EvtSpinDensity rho;
  return rho;
}
 
EvtSpinDensity EvtNeutrinoParticle::rotateToHelicityBasis( double alpha, double beta,
                                                           double gamma ) const {
 
  report( ERROR, "EvtGen" )
      << "rotateToHelicityBasis(alpha,beta,gamma) not implemented for neutrino.";
  report( ERROR, "EvtGen" ) << "Will terminate execution.";
 
  ::abort();
 
  EvtSpinDensity rho;
  return rho;
}