TEvtGen/EvtGenBase/EvtPhotonParticle.cpp

   1 //--------------------------------------------------------------------------
   2 //
   3 // Environment:
   4 //      This software is part of the EvtGen package developed jointly
   5 //      for the BaBar and CLEO collaborations.  If you use all or part
   6 //      of it, please give an appropriate acknowledgement.
   7 //
   8 // Copyright Information: See EvtGen/COPYRIGHT
   9 //      Copyright (C) 1998      Caltech, UCSB
  10 //
  11 // Module: EvtPhotonParticle.cc
  12 //
  13 // Description: Class to describe massless vectors
  14 //
  15 // Modification history:
  16 //
  17 //    DJL/RYD   September 25, 1996           Module created
  18 //
  19 //------------------------------------------------------------------------
  20 //
  21 #include "EvtGenBase/EvtPatches.hh"
  22 #include <stdlib.h>
  23 #include <iostream>
  24 #include <math.h>
  25 #include "EvtGenBase/EvtComplex.hh"
  26 #include "EvtGenBase/EvtPhotonParticle.hh"
  27 #include "EvtGenBase/EvtVector4C.hh"
  28 #include "EvtGenBase/EvtReport.hh"
  29 using std::endl;
  30
  31 EvtPhotonParticle::EvtPhotonParticle() {
  32 }
  33
  34 EvtPhotonParticle::~EvtPhotonParticle(){}
  35
  36 void EvtPhotonParticle::init(EvtId part_n,const EvtVector4R& p4){
  37
  38   init(part_n,p4.get(0),p4.get(1),
  39        p4.get(2),p4.get(3));
  40 }
  41
  42 void EvtPhotonParticle::init(EvtId part_n,double e,double px,double py,double pz){
  43
  44   _validP4=true;
  45   setp(e,px,py,pz);
  46   setpart_num(part_n);
  47
  48   setLifetime();
  49
  50   //defere calculation of basis vectors untill they are needed!
  51   _evalBasis=0;
  52
  53 }
  54
  55
  56 EvtVector4C EvtPhotonParticle::epsParentPhoton(int i){
  57
  58   if (!_evalBasis){
  59
  60     _evalBasis=1;
  61     eps1.set(EvtComplex(0.0,0.0), EvtComplex(-1.0/sqrt(2.0),0.0),
  62              EvtComplex(0.0,-1.0/sqrt(2.0)), EvtComplex(0.0,0.0));
  63     eps2.set(EvtComplex(0.0,0.0), EvtComplex(1.0/sqrt(2.0),0.0),
  64              EvtComplex(0.0,-1.0/sqrt(2.0)), EvtComplex(0.0,0.0));
  65
  66     // These are for photon along z axis.  Rotate to get
  67     // correct direction...
  68
  69     double phi,theta;
  70
  71     EvtVector4R p=this->getP4();
  72
  73     double px=p.get(1);
  74     double py=p.get(2);
  75     double pz=p.get(3);
  76
  77     phi = atan2(py,px);
  78     theta = acos(pz/sqrt(px*px+py*py+pz*pz));
  79     eps1.applyRotateEuler(phi,theta,-phi);
  80     eps2.applyRotateEuler(phi,theta,-phi);
  81
  82   }
  83
  84
  85   EvtVector4C temp;
  86
  87   switch(i) {
  88
  89   case 0:
  90     temp=eps1;
  91     break;
  92   case 1:
  93     temp=eps2;
  94     break;
  95   default:
  96     report(ERROR,"EvtGen") << "EvtPhotonParticle.cc: Asked "
  97                            << "for state:"<<i<<endl;
  98     ::abort();
  99     break;
 100   }
 101
 102   return temp;
 103 }
 104
 105 EvtVector4C EvtPhotonParticle::epsPhoton(int ){
 106
 107   report(ERROR,"EvtGen") << "EvtPhotonParticle.cc: Can not get "
 108                          << "state in photons restframe."<<endl;;
 109   ::abort();
 110   return EvtVector4C();
 111
 112 }
 113
 114
 115 EvtSpinDensity EvtPhotonParticle::rotateToHelicityBasis() const {
 116
 117   EvtVector4C eplus(0.0,-1.0/sqrt(2.0),
 118                     EvtComplex(0.0,-1.0/sqrt(2.0)),0.0);
 119   EvtVector4C eminus(0.0,1.0/sqrt(2.0),
 120                      EvtComplex(0.0,-1.0/sqrt(2.0)),0.0);
 121
 122   //Really uggly have to cast away constness because the
 123   //function epsParentPhoton caches the state vectors...
 124   EvtVector4C e1=((EvtParticle*)this)->epsParentPhoton(0);
 125   EvtVector4C e2=((EvtParticle*)this)->epsParentPhoton(1);
 126
 127
 128   EvtSpinDensity R;
 129   R.setDim(2);
 130
 131   R.set(0,0,(eplus.conj())*e1);
 132   R.set(0,1,(eplus.conj())*e2);
 133
 134   R.set(1,0,(eminus.conj())*e1);
 135   R.set(1,1,(eminus.conj())*e2);
 136
 137   return R;
 138
 139 }
 140
 141
 142 EvtSpinDensity EvtPhotonParticle::rotateToHelicityBasis(double alpha,
 143                                                         double beta,
 144                                                         double gamma) const{
 145
 146   EvtVector4C eplus(0.0,-1.0/sqrt(2.0),
 147                     EvtComplex(0.0,-1.0/sqrt(2.0)),0.0);
 148   EvtVector4C eminus(0.0,1.0/sqrt(2.0),
 149                      EvtComplex(0.0,-1.0/sqrt(2.0)),0.0);
 150
 151   eplus.applyRotateEuler(alpha,beta,gamma);
 152   eminus.applyRotateEuler(alpha,beta,gamma);
 153
 154
 155   //Really uggly have to cast away constness because the
 156   //function epsParentPhoton caches the state vectors...
 157   EvtVector4C e1=((EvtParticle*)this)->epsParentPhoton(0);
 158   EvtVector4C e2=((EvtParticle*)this)->epsParentPhoton(1);
 159
 160   EvtSpinDensity R;
 161   R.setDim(2);
 162
 163   R.set(0,0,(eplus.conj())*e1);
 164   R.set(0,1,(eplus.conj())*e2);
 165
 166   R.set(1,0,(eminus.conj())*e1);
 167   R.set(1,1,(eminus.conj())*e2);
 168
 169   return R;
 170
 171 }
 172
 173