TEvtGen/EvtGenBase/EvtDiracParticle.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: EvtDiracParticle.cc
  12 //
  13 // Description: Class to describe spin 1/2 particles.
  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/EvtDiracParticle.hh"
  27 #include "EvtGenBase/EvtVector4R.hh"
  28 #include "EvtGenBase/EvtPDL.hh"
  29 #include "EvtGenBase/EvtReport.hh"
  30 #include "EvtGenBase/EvtSpinDensity.hh"
  31 #include "EvtGenBase/EvtGammaMatrix.hh"
  32 using std::endl;
  33
  34 EvtDiracParticle::~EvtDiracParticle(){}
  35
  36
  37 EvtDiracParticle::EvtDiracParticle(){
  38
  39   return;
  40
  41 }
  42
  43 void EvtDiracParticle::init(EvtId part_n,const EvtVector4R& p4){
  44
  45   _validP4=true;
  46   setp(p4);
  47   setpart_num(part_n);
  48
  49   if (EvtPDL::getStdHep(part_n)==0){
  50     report(ERROR,"EvtGen") << "Error in EvtDiracParticle::init, part_n="
  51                            << part_n.getId()<<endl;
  52     ::abort();
  53   }
  54
  55   if (EvtPDL::getStdHep(part_n)>0){
  56
  57     _spinorRest[0].set(EvtComplex(sqrt(2.0*mass()),0.0),EvtComplex(0.0,0.0),
  58                        EvtComplex(0.0,0.0),EvtComplex(0.0,0.0));
  59     _spinorRest[1].set(EvtComplex(0.0,0.0),EvtComplex(sqrt(2.0*mass()),0.0),
  60                        EvtComplex(0.0,0.0),EvtComplex(0.0,0.0));
  61
  62     _spinorParent[0]=boostTo(_spinorRest[0],p4);
  63     _spinorParent[1]=boostTo(_spinorRest[1],p4);
  64
  65
  66   }
  67   else{
  68
  69     _spinorRest[0].set(EvtComplex(0.0,0.0),EvtComplex(0.0,0.0),
  70                      EvtComplex(sqrt(2.0*mass()),0.0),EvtComplex(0.0,0.0));
  71     _spinorRest[1].set(EvtComplex(0.0,0.0),EvtComplex(0.0,0.0),
  72                      EvtComplex(0.0,0.0),EvtComplex(sqrt(2.0*mass()),0.0));
  73
  74     _spinorParent[0]=boostTo(_spinorRest[0],p4);
  75     _spinorParent[1]=boostTo(_spinorRest[1],p4);
  76
  77
  78
  79   }
  80
  81   setLifetime();
  82 }
  83
  84
  85 void EvtDiracParticle::init(EvtId part_n,const EvtVector4R& p4,
  86                             const EvtDiracSpinor & prod1,
  87                             const EvtDiracSpinor & prod2,
  88                             const EvtDiracSpinor & rest1,
  89                             const EvtDiracSpinor & rest2){
  90
  91   _validP4=true;
  92   setp(p4);
  93   setpart_num(part_n);
  94
  95   if (EvtPDL::getStdHep(part_n)==0){
  96     report(ERROR,"EvtGen") << "Error in EvtDiracParticle::init, part_n="
  97                            << part_n.getId()<<std::endl;
  98     ::abort();
  99   }
 100   _spinorRest[0]=rest1;
 101   _spinorRest[1]=rest2;
 102   _spinorParent[0]=prod1;
 103   _spinorParent[1]=prod2;
 104
 105   setLifetime();
 106 }
 107
 108
 109
 110 EvtSpinDensity EvtDiracParticle::rotateToHelicityBasis() const{
 111
 112   EvtDiracSpinor spplus;
 113   EvtDiracSpinor spminus;
 114
 115   double sqmt2=sqrt(2.*(getP4().mass()));
 116
 117   if (EvtPDL::getStdHep(getId())>0){
 118     spplus.set(1.0,0.0,0.0,0.0);
 119     spminus.set(0.0,1.0,0.0,0.0);
 120   } else {
 121     spplus.set(0.0,0.0,0.0,1.0);
 122     spminus.set(0.0,0.0,1.0,0.0);
 123   }
 124
 125
 126   EvtSpinDensity R;
 127   R.setDim(2);
 128
 129   for (int i=0; i<2; i++) {
 130     if (EvtPDL::getStdHep(getId())>0){
 131       R.set(0,i,(spplus*_spinorRest[i])/sqmt2);
 132       R.set(1,i,(spminus*_spinorRest[i])/sqmt2);
 133     } else {
 134       R.set(0,i,(_spinorRest[i]*spplus)/sqmt2);
 135       R.set(1,i,(_spinorRest[i]*spminus)/sqmt2);
 136     }
 137   }
 138
 139   return R;
 140
 141 }
 142
 143
 144 EvtSpinDensity EvtDiracParticle::rotateToHelicityBasis(double alpha,
 145                                                        double beta,
 146                                                        double gamma) const{
 147
 148
 149   EvtDiracSpinor spplus;
 150   EvtDiracSpinor spminus;
 151
 152   double sqmt2=sqrt(2.*(getP4().mass()));
 153
 154   if (EvtPDL::getStdHep(getId())>0){
 155     spplus.set(1.0,0.0,0.0,0.0);
 156     spminus.set(0.0,1.0,0.0,0.0);
 157   } else {
 158     spplus.set(0.0,0.0,0.0,1.0);
 159     spminus.set(0.0,0.0,1.0,0.0);
 160   }
 161
 162   spplus.applyRotateEuler(alpha,beta,gamma);
 163   spminus.applyRotateEuler(alpha,beta,gamma);
 164
 165   EvtSpinDensity R;
 166   R.setDim(2);
 167
 168   for (int i=0; i<2; i++) {
 169     if (EvtPDL::getStdHep(getId())>0){
 170       R.set(0,i,(spplus*_spinorRest[i])/sqmt2);
 171       R.set(1,i,(spminus*_spinorRest[i])/sqmt2);
 172     } else {
 173       R.set(0,i,(_spinorRest[i]*spplus)/sqmt2);
 174       R.set(1,i,(_spinorRest[i]*spminus)/sqmt2);
 175     }
 176   }
 177
 178   return R;
 179
 180 }
 181
 182
 183