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// $Id: G4PolarizedGammaConversionModel.cc,v 1.6 2007/11/01 17:32:34 schaelic Exp $
// GEANT4 tag $Name: geant4-09-02 $
//
// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:     G4PolarizedGammaConversionModel
//
// Author:        Karim Laihem
//
// Creation date: 19.04.2005
//
// Modifications:
// 21-08-06 Modified to fit in g4.8.1 framework (A.Schaelicke)
// 19-03-07 Add initialisation of crossSectionCalculator (VI)
//
// Class Description:
//
// Implementation of gamma convertion to e+e- in the field of a nucleus 
// including polarization transfer

// -------------------------------------------------------------------
//

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#include "G4PolarizedGammaConversionModel.hh"
#include "G4Electron.hh"
#include "G4Positron.hh"
#include "G4Gamma.hh"
#include "Randomize.hh"
#include "G4DataVector.hh"
#include "G4PhysicsLogVector.hh"
#include "G4ParticleChangeForGamma.hh"
#include "G4PolarizedPairProductionCrossSection.hh"
#include "G4PolarizationHelper.hh"

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G4PolarizedGammaConversionModel::G4PolarizedGammaConversionModel(const G4ParticleDefinition* pd,
					 const G4String& nam)
  : G4BetheHeitlerModel(pd,nam), crossSectionCalculator(0)
{
}

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G4PolarizedGammaConversionModel::~G4PolarizedGammaConversionModel()
{
  if (crossSectionCalculator) delete crossSectionCalculator;
}

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void G4PolarizedGammaConversionModel::Initialise(const G4ParticleDefinition* pd,
				     const G4DataVector& dv)
{
  G4BetheHeitlerModel::Initialise(pd,dv);
  if (!crossSectionCalculator)
    crossSectionCalculator = new G4PolarizedPairProductionCrossSection();
}

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void G4PolarizedGammaConversionModel::SampleSecondaries(std::vector<G4DynamicParticle*>* vdp,
							const G4MaterialCutsCouple* couple,
							const G4DynamicParticle* dp,
							G4double tmin,
							G4double maxEnergy)
{
  G4BetheHeitlerModel::SampleSecondaries(vdp, couple, dp, tmin, maxEnergy);
 
  if(vdp && vdp->size()>0) {
    G4double gamEnergy0 = dp->GetKineticEnergy();
    G4double lepEnergy1 = (*vdp)[0]->GetKineticEnergy();
    G4double sintheta   = dp->GetMomentumDirection().cross((*vdp)[0]->GetMomentumDirection()).mag();
    if (sintheta>1.) sintheta=1.;

    G4StokesVector beamPol = dp->GetPolarization();
    beamPol.SetPhoton();

    // determine interaction plane
    G4ThreeVector  nInteractionFrame = 
      G4PolarizationHelper::GetFrame(dp->GetMomentumDirection(), 
				     (*vdp)[0]->GetMomentumDirection());

    // transform polarization into interaction frame
    beamPol.InvRotateAz(nInteractionFrame,dp->GetMomentumDirection());

    // calulcate polarization transfer
    crossSectionCalculator->SetMaterial(GetCurrentElement()->GetN(), // number of nucleons
					GetCurrentElement()->GetZ(), 
					GetCurrentElement()->GetfCoulomb());
    crossSectionCalculator->Initialize(gamEnergy0, lepEnergy1, sintheta,
				       beamPol, G4StokesVector::ZERO);

    // deterimine final state polarization
    G4StokesVector lep1Pol = crossSectionCalculator->GetPol2();
    lep1Pol.RotateAz(nInteractionFrame,(*vdp)[0]->GetMomentumDirection());
    (*vdp)[0]->SetPolarization(lep1Pol.p1(),
			       lep1Pol.p2(),
			       lep1Pol.p3());

    size_t num = vdp->size();
    if (num!=2) G4cout<<" WARNING "<<num<<" secondaries in polarized pairproduction not supported!\n"; 
    for (size_t i =1; i<num; ++i) {
      G4StokesVector lep2Pol = crossSectionCalculator->GetPol3();
      lep2Pol.RotateAz(nInteractionFrame,(*vdp)[i]->GetMomentumDirection());
      (*vdp)[i]->SetPolarization(lep2Pol.p1(),
				 lep2Pol.p2(),
				 lep2Pol.p3());

    }
  }
}

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