G4PionRadiativeDecayChannel.cc

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// G4PionRadiativeDecayChannel class implementation
//      GEANT 4 class header file
//
// Author: P.Gumplinger, 30 July 2007
// Reference: M. Blecher, TRIUMF/PIENU Technote
//            "Inclusion of pi->enug in the Monte Carlo"
// --------------------------------------------------------------------
 
#include "G4PionRadiativeDecayChannel.hh"
 
#include "G4DecayProducts.hh"
#include "G4LorentzVector.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "Randomize.hh"
 
namespace
{
const G4double beta = 3.6612e-03;
const G4double cib = 1.16141e-03;
const G4double csdp = 3.45055e-02;
const G4double csdm = 5.14122e-03;
const G4double cif = 4.63543e-05;
const G4double cig = 1.78928e-05;
const G4double xl = 2. * 0.1 * MeV / 139.57 * MeV;
const G4double yl = ((1. - xl) + std::sqrt((1 - xl) * (1 - xl) + 4 * beta * beta)) / 2.;
 
const G4double xu = 1. - (yl - std::sqrt(yl * yl - 4. * beta * beta)) / 2.;
const G4double yu = 1. + beta * beta;
 
inline G4double D2W(const G4double x, const G4double y)
{
  return cib * (1. - y) * (1. + ((1. - x) * (1. - x))) / ((x * x) * (x + y - 1.))
         + csdp * (1. - x) * ((x + y - 1.) * (x + y - 1.)) + csdm * (1. - x) * ((1. - y) * (1. - y))
         + cif * (x - 1.) * (1. - y) / x + cig * (1. - y) * (1. - x + (x * x) / (x + y - 1.)) / x;
}
 
const G4double d2wmax = D2W(xl, yl);
}  // namespace
 
G4PionRadiativeDecayChannel::G4PionRadiativeDecayChannel(const G4String& theParentName,
                                                         G4double theBR)
  : G4VDecayChannel("Radiative Pion Decay", 1)
{
  // set names for daughter particles
  if (theParentName == "pi+") {
    SetBR(theBR);
    SetParent("pi+");
    SetNumberOfDaughters(3);
    SetDaughter(0, "e+");
    SetDaughter(1, "gamma");
    SetDaughter(2, "nu_e");
  }
  else if (theParentName == "pi-") {
    SetBR(theBR);
    SetParent("pi-");
    SetNumberOfDaughters(3);
    SetDaughter(0, "e-");
    SetDaughter(1, "gamma");
    SetDaughter(2, "anti_nu_e");
  }
  else {
#ifdef G4VERBOSE
    if (GetVerboseLevel() > 0) {
      G4cout << "G4RadiativePionDecayChannel::G4PionRadiativeDecayChannel()" << G4endl;
      G4cout << "Parent particle is not charged pion: ";
      G4cout << theParentName << G4endl;
    }
#endif
  }
}
 
G4PionRadiativeDecayChannel&
G4PionRadiativeDecayChannel::operator=(const G4PionRadiativeDecayChannel& 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 != nullptr) 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* G4PionRadiativeDecayChannel::DecayIt(G4double)
{
#ifdef G4VERBOSE
  if (GetVerboseLevel() > 1) G4cout << "G4PionRadiativeDecayChannel::DecayIt ";
#endif
 
  CheckAndFillParent();
  CheckAndFillDaughters();
 
  // parent mass
  G4double parentmass = G4MT_parent->GetPDGMass();
 
  G4double EMPI = parentmass;
 
  // daughters'mass
  const G4int N_DAUGHTER = 3;
  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];
  }
 
  G4double EMASS = daughtermass[0];
 
  // create parent G4DynamicParticle at rest
  G4ThreeVector dummy;
  auto parentparticle = new G4DynamicParticle(G4MT_parent, dummy, 0.0);
  // create G4Decayproducts
  auto products = new G4DecayProducts(*parentparticle);
  delete parentparticle;
 
  G4double x, y;
 
  const std::size_t MAX_LOOP = 1000;
 
  for (std::size_t loop_counter1 = 0; loop_counter1 < MAX_LOOP; ++loop_counter1) {
    for (std::size_t loop_counter2 = 0; loop_counter2 < MAX_LOOP; ++loop_counter2) {
      x = xl + G4UniformRand() * (xu - xl);
      y = yl + G4UniformRand() * (yu - yl);
      if (x + y > 1.) break;
    }
    G4double d2w = D2W(x, y);
    if (d2w > G4UniformRand() * d2wmax) break;
  }
 
  // Calculate the angle between positron and photon (cosine)
  //
  G4double cthetaGE =
    (y * (x - 2.) + 2. * (1. - x + beta * beta)) / (x * std::sqrt(y * y - 4. * beta * beta));
 
  G4double G = x * EMPI / 2.;
  G4double E = y * EMPI / 2.;
 
  if (E < EMASS) E = EMASS;
 
  // calculate daughter momentum
  G4double daughtermomentum[2];
 
  daughtermomentum[0] = std::sqrt(E * E - EMASS * EMASS);
 
  G4double cthetaE = 2. * G4UniformRand() - 1.;
  G4double sthetaE = std::sqrt(1. - cthetaE * cthetaE);
 
  G4double phiE = twopi * G4UniformRand() * rad;
  G4double cphiE = std::cos(phiE);
  G4double sphiE = std::sin(phiE);
 
  // Coordinates of the decay positron
  //
  G4double px = sthetaE * cphiE;
  G4double py = sthetaE * sphiE;
  G4double pz = cthetaE;
 
  G4ThreeVector direction0(px, py, pz);
 
  auto daughterparticle0 =
    new G4DynamicParticle(G4MT_daughters[0], daughtermomentum[0] * direction0);
 
  products->PushProducts(daughterparticle0);
 
  daughtermomentum[1] = G;
 
  G4double sthetaGE = std::sqrt(1. - cthetaGE * cthetaGE);
 
  G4double phiGE = twopi * G4UniformRand() * rad;
  G4double cphiGE = std::cos(phiGE);
  G4double sphiGE = std::sin(phiGE);
 
  // Coordinates of the decay gamma with respect to the decay positron
  //
  px = sthetaGE * cphiGE;
  py = sthetaGE * sphiGE;
  pz = cthetaGE;
 
  G4ThreeVector direction1(px, py, pz);
 
  direction1.rotateUz(direction0);
 
  auto daughterparticle1 =
    new G4DynamicParticle(G4MT_daughters[1], daughtermomentum[1] * direction1);
 
  products->PushProducts(daughterparticle1);
 
  // output message
#ifdef G4VERBOSE
  if (GetVerboseLevel() > 1) {
    G4cout << "G4PionRadiativeDecayChannel::DecayIt() -";
    G4cout << " create decay products in rest frame " << G4endl;
    products->DumpInfo();
  }
#endif
 
  return products;
}