G4MuonRadiativeDecayChannelWithSpin.hh

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//
// ------------------------------------------------------------
//      GEANT 4 class header file
//
//      History:
//               25 July 2007   P.Gumplinger - Triumf
//               10 August 2011 D. Mingming - Center for HEP, Tsinghua Univ.
//
//               Samples Radiative Muon Decay
//               References:
//                    TRIUMF/TWIST Technote TN-55:
//                    "Radiative muon decay" by P. Depommier and A. Vacheret
//                    ------------------------------------------------------
//                    Yoshitaka Kuno and Yasuhiro Okada
//                    "Muon Decays and Physics Beyond the Standard Model"
//                    Rev. Mod. Phys. 73, 151 (2001)
//
// ------------------------------------------------------------
//
//
//
//

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#ifndef G4MuonRadiativeDecayChannelWithSpin_h
#define G4MuonRadiativeDecayChannelWithSpin_h 1

#include <CLHEP/Units/PhysicalConstants.h>

#include "globals.hh"
#include "Randomize.hh"
#include "G4ThreeVector.hh"
#include "G4VDecayChannel.hh"

class G4MuonRadiativeDecayChannelWithSpin : public G4VDecayChannel
{
  // Class Decription
  // This class describes radiative muon decay kinemtics, but
  // gives incorrect energy spectrum for neutrinos

  public:  // With Description

    //Constructors
    G4MuonRadiativeDecayChannelWithSpin(const G4String& theParentName,
                                        G4double        theBR);
    //  Destructor
    virtual ~G4MuonRadiativeDecayChannelWithSpin();

  protected:
    // Copy constructor and assignment operator
    G4MuonRadiativeDecayChannelWithSpin(const G4MuonRadiativeDecayChannelWithSpin &);
    G4MuonRadiativeDecayChannelWithSpin & operator=(const G4MuonRadiativeDecayChannelWithSpin &);
  
  private:
    G4MuonRadiativeDecayChannelWithSpin();

  public:  // With Description

    virtual G4DecayProducts *DecayIt(G4double);

    void SetPolarization(G4ThreeVector);
    const G4ThreeVector& GetPolarization() const;

  private:

    G4ThreeVector parent_polarization;

    G4double fron(G4double Pmu, G4double x, G4double y,
                  G4double cthetaE, G4double cthetaG, G4double cthetaEG);

    // rn3dim generates random vectors, uniformly distributed over the surface 
    // of a sphere of given radius.
    // See http://wwwinfo.cern.ch/asdoc/shortwrupsdir/v131/top.html

    void rn3dim(G4double& x, G4double& y, G4double& z, G4double xlong);

    G4double atan4(G4double x, G4double y);

};

inline void G4MuonRadiativeDecayChannelWithSpin::
                                        SetPolarization(G4ThreeVector polar)
{
  parent_polarization = polar;
}

inline const G4ThreeVector& G4MuonRadiativeDecayChannelWithSpin::
                                        GetPolarization() const
{
  return parent_polarization;
}

inline void G4MuonRadiativeDecayChannelWithSpin::rn3dim(G4double& x,
                                                        G4double& y,
                                                        G4double& z,
                                                        G4double xlong)
{
      G4double a = 0.; G4double b = 0.; G4double c = 0.; G4double r = 0.;

      do {
         a = G4UniformRand() - 0.5;
         b = G4UniformRand() - 0.5;
         c = G4UniformRand() - 0.5;
         r = a*a + b*b + c*c;
      } while (r > 0.25);

      G4double rinv = xlong/(std::sqrt(r)); 
      x = a * rinv;
      y = b * rinv;
      z = c * rinv;

      return;
}

inline G4double G4MuonRadiativeDecayChannelWithSpin::atan4(G4double x,
                                                           G4double y)
{
      G4double phi = 0.;

      if        (x==0. && y>0.){
         phi = 0.5*CLHEP::pi;
      } else if (x==0. && y<0.){
         phi = 1.5*CLHEP::pi;
      } else if (y==0. && x>0.){
         phi = 0.;
      } else if (y==0. && x<0.){
         phi = CLHEP::pi;
      } else if (x>0.         ){
         phi = std::atan(y/x);
      } else if (x<0.         ){
         phi = std::atan(y/x) + CLHEP::pi;
      }

      return phi;
}

#endif