G4ModifiedMephi.cc

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// -------------------------------------------------------------------
//
// GEANT4 Class file
//
//
// File name:     G4ModifiedMephi
//
// Author:        V. Ivanchenko
// 
// Creation date: 27 October 2020
//
// Modifications: 
//
//
// -------------------------------------------------------------------
//
 
#include "G4ModifiedMephi.hh"
#include "Randomize.hh"
#include "G4Log.hh"
#include <CLHEP/Units/PhysicalConstants.h>
 
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G4ModifiedMephi::G4ModifiedMephi(const G4String&)
  : G4VEmAngularDistribution("ModifiedMephi")
{}    
 
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G4ModifiedMephi::~G4ModifiedMephi() 
{}
 
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G4ThreeVector& 
G4ModifiedMephi::SampleDirection(const G4DynamicParticle* dp,
                                 G4double gEnergy, G4int, 
                                 const G4Material*)
{
  // Sample gamma angle (Z - axis along the parent particle).
  G4double cost = SampleCosTheta(dp->GetKineticEnergy(), gEnergy, 
                                 dp->GetDefinition()->GetPDGMass());
  G4double sint = std::sqrt((1.0 - cost)*(1.0 + cost));
  G4double phi  = CLHEP::twopi*G4UniformRand(); 
 
  fLocalDirection.set(sint*std::cos(phi), sint*std::sin(phi), cost);
  fLocalDirection.rotateUz(dp->GetMomentumDirection());
 
  return fLocalDirection;
}
 
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G4double G4ModifiedMephi::SampleCosTheta(G4double primKinEnergy, 
                                         G4double gEnergy,
                                         G4double mass)
{
  G4double gam  = 1.0 + primKinEnergy/mass;
  G4double rmax = gam*CLHEP::halfpi*std::min(1.0, gam*mass/gEnergy - 1.0);
  G4double rmax2= rmax*rmax;
  G4double x = G4UniformRand()*rmax2/(1.0 + rmax2);
 
  return std::cos(std::sqrt(x/(1.0 - x))/gam);
}
 
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void G4ModifiedMephi::SamplePairDirections(const G4DynamicParticle* dp,
                       G4double elecKinEnergy,
                       G4double posiKinEnergy,
                       G4ThreeVector& dirElectron,
                       G4ThreeVector& dirPositron,
                       G4int, const G4Material*)
{
  G4double phi  = CLHEP::twopi * G4UniformRand();
  G4double sinp = std::sin(phi);
  G4double cosp = std::cos(phi);
 
  G4double ekin = dp->GetKineticEnergy();
  G4double etwo = elecKinEnergy + posiKinEnergy;
  G4double mass = dp->GetDefinition()->GetPDGMass();
 
  G4double cost = SampleCosTheta(ekin, etwo, mass);
  G4double sint = std::sqrt((1.0 - cost)*(1.0 + cost));
 
  dirElectron.set(sint*cosp, sint*sinp, cost);
  dirElectron.rotateUz(dp->GetMomentumDirection());
 
  cost = SampleCosTheta(ekin, etwo, mass);
  sint = std::sqrt((1.0 - cost)*(1.0 + cost));
 
  dirPositron.set(-sint*cosp, -sint*sinp, cost);
  dirPositron.rotateUz(dp->GetMomentumDirection());
}
 
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void G4ModifiedMephi::PrintGeneratorInformation() const
{
  G4cout << "\n" << G4endl;
  G4cout << "Angular Generator is Modified Mephi" << G4endl;
} 
 
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