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 "EvtGenBase/EvtPatches.hh"
#include <stdlib.h>
#include <iostream>
#include <math.h>
#include "EvtGenBase/EvtComplex.hh"
#include "EvtGenBase/EvtDiracParticle.hh"
#include "EvtGenBase/EvtVector4R.hh"
#include "EvtGenBase/EvtPDL.hh"
#include "EvtGenBase/EvtReport.hh"
#include "EvtGenBase/EvtSpinDensity.hh"
#include "EvtGenBase/EvtGammaMatrix.hh"
 
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;
 
}