G4MuonDecayChannel.cc

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// 
// ------------------------------------------------------------
//      GEANT 4 class header file
//
//      History: first implementation, based on object model of
//      30 May  1997 H.Kurashige
//
// - Fix bug in calculation of electron energy in DecayIt()
//   28 Feb 01 H.Kurashige 
// - Adding V-A fluxes for neutrinos using a new algorithm, 2005
//   M. Melissas ( melissas AT cppm.in2p3.fr)
//   J. Brunner ( brunner AT cppm.in2p3.fr) 
// ------------------------------------------------------------

#include "G4ParticleDefinition.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4DecayProducts.hh"
#include "G4VDecayChannel.hh"
#include "G4MuonDecayChannel.hh"
#include "Randomize.hh"
#include "G4LorentzVector.hh"
#include "G4LorentzRotation.hh"
#include "G4RotationMatrix.hh"

G4MuonDecayChannel::G4MuonDecayChannel()
                   :G4VDecayChannel()
{
}

G4MuonDecayChannel::G4MuonDecayChannel(const G4String& theParentName, 
               G4double        theBR)
                   :G4VDecayChannel("Muon Decay",1)
{
  // set names for daughter particles
  if (theParentName == "mu+") {
    SetBR(theBR);
    SetParent("mu+");
    SetNumberOfDaughters(3);
    SetDaughter(0, "e+");
    SetDaughter(1, "nu_e");
    SetDaughter(2, "anti_nu_mu");
  } else if (theParentName == "mu-") {
    SetBR(theBR);
    SetParent("mu-");
    SetNumberOfDaughters(3);
    SetDaughter(0, "e-");
    SetDaughter(1, "anti_nu_e");
    SetDaughter(2, "nu_mu");
  } else {
#ifdef G4VERBOSE
    if (GetVerboseLevel()>0) {
      G4cout << "G4MuonDecayChannel:: constructor :";
      G4cout << " parent particle is not muon but ";
      G4cout << theParentName << G4endl;
    }
#endif
  }
}

G4MuonDecayChannel::G4MuonDecayChannel(const G4MuonDecayChannel &right):
  G4VDecayChannel(right)
{
}

G4MuonDecayChannel::~G4MuonDecayChannel()
{
}

G4MuonDecayChannel & G4MuonDecayChannel::operator=(const G4MuonDecayChannel & right)
{
  if (this != &right) { 
    kinematics_name = right.kinematics_name;
    verboseLevel = right.verboseLevel;
    rbranch = right.rbranch;

    // copy parent name
    parent_name = new G4String(*right.parent_name);

    // clear daughters_name array
    ClearDaughtersName();

    // recreate array
    numberOfDaughters = right.numberOfDaughters;
    if ( numberOfDaughters >0 ) {
      if (daughters_name !=0) ClearDaughtersName();
      daughters_name = new G4String*[numberOfDaughters];
      //copy daughters name
      for (G4int index=0; index < numberOfDaughters; index++) {
          daughters_name[index] = new G4String(*right.daughters_name[index]);
      }
    }
  }
  return *this;
}

G4DecayProducts *G4MuonDecayChannel::DecayIt(G4double) 
{
  // this version neglects muon polarization,and electron mass  
  //              assumes the pure V-A coupling
  //              the Neutrinos are correctly V-A. 
#ifdef G4VERBOSE
  if (GetVerboseLevel()>1) G4cout << "G4MuonDecayChannel::DecayIt ";
#endif

  CheckAndFillParent();
  CheckAndFillDaughters();
 
  // parent mass
  G4double parentmass = G4MT_parent->GetPDGMass();
  const int N_DAUGHTER=3;

  //daughters'mass
  G4double daughtermass[N_DAUGHTER]; 
  G4double sumofdaughtermass = 0.0;
  for (G4int index=0; index<N_DAUGHTER; index++){
    daughtermass[index] = G4MT_daughters[index]->GetPDGMass();
    sumofdaughtermass += daughtermass[index];
  }

   //create parent G4DynamicParticle at rest
  G4ThreeVector dummy;
  G4DynamicParticle * parentparticle = new G4DynamicParticle( G4MT_parent, dummy, 0.0);
  //create G4Decayproducts
  G4DecayProducts *products = new G4DecayProducts(*parentparticle);
  delete parentparticle;

  // calculate daughter momentum
  G4double daughtermomentum[N_DAUGHTER];
    // calcurate electron energy
  G4double xmax = (1.0+daughtermass[0]*daughtermass[0]/parentmass/parentmass);
  G4double x;
  
  G4double Ee,Ene;
  
  G4double gam;
  G4double EMax=parentmass/2-daughtermass[0];
  
  const size_t MAX_LOOP=1000;
   //Generating Random Energy
  for (size_t loop1=0; loop1 <MAX_LOOP; ++loop1){
    Ee=G4UniformRand();
    for (size_t loop2 =0; loop2<MAX_LOOP; ++loop2){
      x=xmax*G4UniformRand();
      gam=G4UniformRand();
      if (gam <= x*(1.-x)) break;
      x = xmax;
    }
    Ene=x;
    if ( Ene >= (1.-Ee)) break;
    Ene = 1.-Ee;
  }
  G4double Enm=(2.-Ee-Ene);


 //initialisation of rotation parameters

  G4double costheta,sintheta,rphi,rtheta,rpsi;
  costheta= 1.-2./Ee-2./Ene+2./Ene/Ee;
  sintheta=std::sqrt(1.-costheta*costheta);
  

  rphi=twopi*G4UniformRand()*rad;
  rtheta=(std::acos(2.*G4UniformRand()-1.));
  rpsi=twopi*G4UniformRand()*rad;

  G4RotationMatrix rot;
  rot.set(rphi,rtheta,rpsi);

  //electron 0
  daughtermomentum[0]=std::sqrt(Ee*Ee*EMax*EMax+2.0*Ee*EMax * daughtermass[0]);
  G4ThreeVector direction0(0.0,0.0,1.0);

  direction0 *= rot;

  G4DynamicParticle * daughterparticle = new G4DynamicParticle ( G4MT_daughters[0],  direction0 * daughtermomentum[0]);

  products->PushProducts(daughterparticle);
  
  //electronic neutrino  1

  daughtermomentum[1]=std::sqrt(Ene*Ene*EMax*EMax+2.0*Ene*EMax * daughtermass[1]);
  G4ThreeVector direction1(sintheta,0.0,costheta);

  direction1 *= rot;

  G4DynamicParticle * daughterparticle1 = new G4DynamicParticle ( G4MT_daughters[1],   direction1 * daughtermomentum[1]);
  products->PushProducts(daughterparticle1);

  //muonnic neutrino 2
  
     daughtermomentum[2]=std::sqrt(Enm*Enm*EMax*EMax +2.0*Enm*EMax*daughtermass[2]);
  G4ThreeVector direction2(-Ene/Enm*sintheta,0,-Ee/Enm-Ene/Enm*costheta);

  direction2 *= rot;

  G4DynamicParticle * daughterparticle2 = new G4DynamicParticle ( G4MT_daughters[2],
   direction2 * daughtermomentum[2]);
  products->PushProducts(daughterparticle2);

 // output message
#ifdef G4VERBOSE
  if (GetVerboseLevel()>1) {
    G4cout << "G4MuonDecayChannel::DecayIt ";
    G4cout << "  create decay products in rest frame " <<G4endl;
    products->DumpInfo();
  }
#endif
  return products;
}