G4PolarizedPairProductionCrossSection.cc

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// $Id$
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// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:     G4PolarizedPairProductionCrossSection
//
// Author:        Andreas Schaelicke on the base of Karim Laihems code
//
// Creation date: 16.08.2006
//
 
#include "G4PolarizedPairProductionCrossSection.hh"
#include "G4PhysicalConstants.hh"
 
G4bool G4PolarizedPairProductionCrossSection::scrnInitialized=false;
G4double G4PolarizedPairProductionCrossSection::SCRN [3][20];  
// screening function lookup table;
 
void G4PolarizedPairProductionCrossSection::InitializeMe()
{
  if (!scrnInitialized) {
    SCRN [1][1]=  0.5   ; SCRN [2][1] = 0.0145;
    SCRN [1][2]=  1.0   ; SCRN [2][2] = 0.0490;
    SCRN [1][3]=  2.0   ; SCRN [2][3] = 0.1400;
    SCRN [1][4]=  4.0   ; SCRN [2][4] = 0.3312;
    SCRN [1][5]=  8.0   ; SCRN [2][5] = 0.6758;
    SCRN [1][6]=  15.0  ; SCRN [2][6] = 1.126;
    SCRN [1][7]=  20.0  ; SCRN [2][7] = 1.367;
    SCRN [1][8]=  25.0  ; SCRN [2][8] = 1.564;
    SCRN [1][9]=  30.0  ; SCRN [2][9] = 1.731;
    SCRN [1][10]= 35.0  ; SCRN [2][10]= 1.875;
    SCRN [1][11]= 40.0  ; SCRN [2][11]= 2.001;
    SCRN [1][12]= 45.0  ; SCRN [2][12]= 2.114;
    SCRN [1][13]= 50.0  ; SCRN [2][13]= 2.216;
    SCRN [1][14]= 60.0  ; SCRN [2][14]= 2.393;
    SCRN [1][15]= 70.0  ; SCRN [2][15]= 2.545;
    SCRN [1][16]= 80.0  ; SCRN [2][16]= 2.676;
    SCRN [1][17]= 90.0  ; SCRN [2][17]= 2.793;
    SCRN [1][18]= 100.0 ; SCRN [2][18]= 2.897;
    SCRN [1][19]= 120.0 ; SCRN [2][19]= 3.078;   
 
    scrnInitialized=true;
  }
}
 
G4PolarizedPairProductionCrossSection::G4PolarizedPairProductionCrossSection()
{
  InitializeMe();
}
 
 
void G4PolarizedPairProductionCrossSection::Initialize(G4double aGammaE, 
                               G4double aLept0E, 
                               G4double sintheta,
                               const G4StokesVector & beamPol,
                               const G4StokesVector & /*p1*/,
                               G4int /*flag*/)
{
  G4double aLept1E = aGammaE - aLept0E;
 
  G4double Stokes_P3  = beamPol.z()   ;   
  // **************************************************************************  
    
  G4double m0_c2  = electron_mass_c2; 
  G4double Lept0E = aLept0E/m0_c2+1.,   Lept0E2 = Lept0E * Lept0E ;
  G4double GammaE = aGammaE/m0_c2;
  G4double Lept1E = aLept1E/m0_c2-1.,   Lept1E2 = Lept1E * Lept1E ;
    
 
  //  const G4Element* theSelectedElement = theModel->SelectedAtom();
 
  // *******  Gamma Transvers Momentum
    
  G4double TMom = std::sqrt(Lept0E2 -1.)* sintheta, u    = TMom       , u2 =u * u ;
  G4double Xsi  = 1./(1.+u2)                      , Xsi2 = Xsi * Xsi  ; 
 
  //  G4double theZ  = theSelectedElement->GetZ();
    
  //  G4double fCoul = theSelectedElement->GetfCoulomb();
  G4double delta = 12. * std::pow(theZ, 1./3.) * Lept0E * Lept1E * Xsi / (121. * GammaE); 
  G4double GG=0.;
 
  if(delta < 0.5) {
    GG = std::log(2.* Lept0E * Lept1E / GammaE) - 2. - fCoul; 
  }
  else if ( delta < 120) {
    for (G4int j=2; j<=19; j++)  {
      if(SCRN[1][j] >= delta)    {
    GG =std::log(2 * Lept0E * Lept1E / GammaE) - 2 - fCoul
      -(SCRN[2][j-1]+(delta-SCRN[1][j-1])*(SCRN[2][j]-SCRN[2][j-1])/(SCRN[1][j]-SCRN[1][j-1]));
    break;
      }
    }
  }
  else  {
    G4double alpha_sc  = (111 * std::pow(theZ, -1./3.)) / Xsi;
    GG = std::log(alpha_sc)- 2 - fCoul;
  }
 
  if(GG<-1) GG=-1;     // *KL* do we need this ?!
 
 
  G4double I_Lepton = (Lept0E2 + Lept1E2)*(3+2*GG) + 2 * Lept0E * Lept1E * (1 + 4 * u2 * Xsi2 * GG);
 
    //    G4double D_Lepton1 = -8 * Lept0E * Lept1E * u2 * Xsi2 * GG / I_Lepton;
 
  G4double L_Lepton1 = GammaE * ((Lept0E - Lept1E) * (3. + 2. * GG)+2 * Lept1E * (1 + 4 * u2 * Xsi2 * GG))/I_Lepton;   
 
  G4double T_Lepton1 = 4 * GammaE * Lept1E * Xsi * u * (1. - 2. * Xsi) * GG / I_Lepton ;
 
 
  G4double Stokes_S1 = (Stokes_P3 * T_Lepton1) ;
  G4double Stokes_S2 = 0;
  G4double Stokes_S3 = (Stokes_P3 * L_Lepton1) ; 
    
 
  theFinalElectronPolarization.setX(Stokes_S1);
  theFinalElectronPolarization.setY(Stokes_S2);
  theFinalElectronPolarization.setZ(Stokes_S3);
 
  if(theFinalElectronPolarization.mag2()>1) { 
    G4cout<<" WARNING in pol-conv theFinalElectronPolarization \n";
    G4cout
      <<"\t"<<theFinalElectronPolarization
      <<"\t GG\t"<<GG
      <<"\t delta\t"<<delta
      <<G4endl;
    theFinalElectronPolarization.setX(0);
    theFinalElectronPolarization.setY(0);
    theFinalElectronPolarization.setZ(Stokes_S3);
    if(Stokes_S3>1) theFinalElectronPolarization.setZ(1);
  }
 
 
  G4double L_Lepton2 = GammaE * ((Lept1E - Lept0E) * (3. + 2. * GG)+2 * Lept0E * (1 + 4 * u2 * Xsi2 * GG))/I_Lepton;   
 
  G4double T_Lepton2 = 4 * GammaE * Lept0E * Xsi * u * (1. - 2. * Xsi) * GG / I_Lepton ;
 
  G4double Stokes_SS1 = (Stokes_P3 * T_Lepton2) ;
  G4double Stokes_SS2 = 0;
  G4double Stokes_SS3 = (Stokes_P3 * L_Lepton2) ; 
 
  theFinalPositronPolarization.SetPhoton();
 
  theFinalPositronPolarization.setX(Stokes_SS1);
  theFinalPositronPolarization.setY(Stokes_SS2);
  theFinalPositronPolarization.setZ(Stokes_SS3);
    
  if(theFinalPositronPolarization.mag2()>1) {
    G4cout<<" WARNING in pol-conv theFinalPositronPolarization \n";
    G4cout
      <<"\t"<<theFinalPositronPolarization
      <<"\t GG\t"<<GG
      <<"\t delta\t"<<delta
      <<G4endl;
  }
}
 
G4double G4PolarizedPairProductionCrossSection::XSection(const G4StokesVector & /*pol2*/,
                             const G4StokesVector & /*pol3*/)
{
  G4cout<<"ERROR dummy routine G4PolarizedPairProductionCrossSection::XSection called \n";
  return 0;
}
 
  // return expected mean polarisation
G4StokesVector G4PolarizedPairProductionCrossSection::GetPol2()
{
  // electron/positron
  return theFinalElectronPolarization;
}
G4StokesVector G4PolarizedPairProductionCrossSection::GetPol3()
{
  // photon
  return theFinalPositronPolarization;;
}