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// $Id: G4eeToTwoPiModel.cc,v 1.7 2009/02/20 16:38:33 vnivanch Exp $
// GEANT4 tag $Name: geant4-09-03 $
//
// -------------------------------------------------------------------
//
// GEANT4 Class header file
//
//
// File name:     G4eeToTwoPiModel
//
// Author:        Vladimir Ivanchenko
//
// Creation date: 25.10.2003
//
// Modifications:
//
//
// -------------------------------------------------------------------
//


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#include "G4eeToTwoPiModel.hh"
#include "Randomize.hh"
#include "G4PionPlus.hh"
#include "G4PionMinus.hh"
#include "G4DynamicParticle.hh"
#include "G4PhysicsVector.hh"
#include "G4PhysicsLinearVector.hh"
#include "G4eeCrossSections.hh"

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using namespace std;

G4eeToTwoPiModel::G4eeToTwoPiModel(G4eeCrossSections* cr):
  cross(cr)
{
  massPi = G4PionPlus::PionPlus()->GetPDGMass();
  massRho = 775.5*MeV;
}

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G4eeToTwoPiModel::~G4eeToTwoPiModel()
{}

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G4double G4eeToTwoPiModel::ThresholdEnergy() const
{
  return 2.0*massPi;
}

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G4double G4eeToTwoPiModel::PeakEnergy() const
{
  return massRho;
}

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G4double G4eeToTwoPiModel::ComputeCrossSection(G4double e) const
{
  G4double ee = std::min(HighEnergy(),e);
  return cross->CrossSection2pi(ee);
}

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G4PhysicsVector* G4eeToTwoPiModel::PhysicsVector(G4double emin, 
                                                 G4double emax) const
{
  G4double tmin = std::max(emin, 2.0*massPi);
  G4double tmax = std::max(tmin, emax);
  G4int nbins = (G4int)((tmax - tmin)/(5.*MeV));
  G4PhysicsVector* v = new G4PhysicsLinearVector(emin,emax,nbins);
  v->SetSpline(true);
  return v;
}

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void G4eeToTwoPiModel::SampleSecondaries(std::vector<G4DynamicParticle*>* newp,
	    G4double e, const G4ThreeVector& direction)
{

  G4double tkin = 0.5*e - massPi;
  if(tkin < 0.0) tkin = 0.0;
  G4double cost;
  do {
    cost = 2.0*G4UniformRand() - 1.0;
  } while( G4UniformRand() > 1.0 - cost*cost );

  G4double sint = sqrt(1.0 - cost*cost);
  G4double phi  = twopi * G4UniformRand();

  G4ThreeVector dir(sint*cos(phi),sint*sin(phi), cost);
  dir.rotateUz(direction);

  // create G4DynamicParticle objects
  G4DynamicParticle* pip = 
     new G4DynamicParticle(G4PionPlus::PionPlus(),dir,tkin);
  G4DynamicParticle* pin = 
     new G4DynamicParticle(G4PionMinus::PionMinus(),-dir,tkin);
  newp->push_back(pip);
  newp->push_back(pin);
}

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