G4DalitzDecayChannel.cc

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// G4DalitzDecayChannel class implementation
//
// Author: H.Kurashige, 30 May 1997
// --------------------------------------------------------------------
 
#include "G4DalitzDecayChannel.hh"
 
#include "G4DecayProducts.hh"
#include "G4LorentzRotation.hh"
#include "G4LorentzVector.hh"
#include "G4ParticleDefinition.hh"
#include "G4PhaseSpaceDecayChannel.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4VDecayChannel.hh"
#include "Randomize.hh"
 
G4DalitzDecayChannel::G4DalitzDecayChannel(const G4String& theParentName, G4double theBR,
                                           const G4String& theLeptonName,
                                           const G4String& theAntiLeptonName)
  : G4VDecayChannel("Dalitz Decay", 1)
{
  // set names for daughter particles
  SetParent(theParentName);
  SetBR(theBR);
  SetNumberOfDaughters(3);
  G4String gammaName = "gamma";
  SetDaughter(idGamma, gammaName);
  SetDaughter(idLepton, theLeptonName);
  SetDaughter(idAntiLepton, theAntiLeptonName);
}
 
G4DalitzDecayChannel& G4DalitzDecayChannel::operator=(const G4DalitzDecayChannel& 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* G4DalitzDecayChannel::DecayIt(G4double)
{
#ifdef G4VERBOSE
  if (GetVerboseLevel() > 1) G4cout << "G4DalitzDecayChannel::DecayIt ";
#endif
  CheckAndFillParent();
  CheckAndFillDaughters();
 
  // parent mass
  G4double parentmass = G4MT_parent->GetPDGMass();
 
  // create parent G4DynamicParticle at rest
  G4ThreeVector dummy;
  auto parentparticle = new G4DynamicParticle(G4MT_parent, dummy, 0.0);
 
  // daughters' mass
  G4double leptonmass = G4MT_daughters[idLepton]->GetPDGMass();
 
  // Generate t ( = std::exp(x):mass Square of (l+ l-) system)
  G4double xmin = 2.0 * std::log(2.0 * leptonmass);
  G4double xmax = 2.0 * std::log(parentmass);
  G4double wmax = 1.5;
  G4double x, w, ww, w1, w2, w3, t;
  const std::size_t MAX_LOOP = 10000;
  for (std::size_t loop_counter = 0; loop_counter < MAX_LOOP; ++loop_counter) {
    x = G4UniformRand() * (xmax - xmin) + xmin;
    w = G4UniformRand() * wmax;
    t = std::exp(x);
    w1 = (1.0 - 4.0 * leptonmass * leptonmass / t);
    if (w1 > 0.0) {
      w2 = (1.0 + 2.0 * leptonmass * leptonmass / t);
      w3 = (1.0 - t / parentmass / parentmass);
      w3 = w3 * w3 * w3;
      ww = w3 * w2 * std::sqrt(w1);
    }
    else {
      ww = 0.0;
    }
    if (w <= ww) break;
  }
 
  // calculate gamma momentum
  G4double Pgamma = G4PhaseSpaceDecayChannel::Pmx(parentmass, 0.0, std::sqrt(t));
  G4double costheta = 2. * G4UniformRand() - 1.0;
  G4double sintheta = std::sqrt((1.0 - costheta) * (1.0 + costheta));
  G4double phi = twopi * G4UniformRand() * rad;
  G4ThreeVector gdirection(sintheta * std::cos(phi), sintheta * std::sin(phi), costheta);
 
  // create G4DynamicParticle for gamma
  auto gammaparticle = new G4DynamicParticle(G4MT_daughters[idGamma], gdirection, Pgamma);
 
  // calculate beta of (l+ l-)system
  G4double beta = Pgamma / (parentmass - Pgamma);
 
  // calculate lepton momentum in the rest frame of (l+ l-)system
  G4double Plepton = G4PhaseSpaceDecayChannel::Pmx(std::sqrt(t), leptonmass, leptonmass);
  G4double Elepton = std::sqrt(Plepton * Plepton + leptonmass * leptonmass);
  costheta = 2. * G4UniformRand() - 1.0;
  sintheta = std::sqrt((1.0 - costheta) * (1.0 + costheta));
  phi = twopi * G4UniformRand() * rad;
  G4ThreeVector ldirection(sintheta * std::cos(phi), sintheta * std::sin(phi), costheta);
  // create G4DynamicParticle for leptons  in the rest frame of (l+ l-)system
  auto leptonparticle =
    new G4DynamicParticle(G4MT_daughters[idLepton], ldirection, Elepton - leptonmass);
  auto antileptonparticle =
    new G4DynamicParticle(G4MT_daughters[idAntiLepton], -1.0 * ldirection, Elepton - leptonmass);
  // boost leptons in the rest frame of the parent
  G4LorentzVector p4 = leptonparticle->Get4Momentum();
  p4.boost(-1.0 * gdirection.x() * beta, -1.0 * gdirection.y() * beta,
           -1.0 * gdirection.z() * beta);
  leptonparticle->Set4Momentum(p4);
  p4 = antileptonparticle->Get4Momentum();
  p4.boost(-1.0 * gdirection.x() * beta, -1.0 * gdirection.y() * beta,
           -1.0 * gdirection.z() * beta);
  antileptonparticle->Set4Momentum(p4);
 
  // create G4Decayproducts
  auto products = new G4DecayProducts(*parentparticle);
  delete parentparticle;
  products->PushProducts(gammaparticle);
  products->PushProducts(leptonparticle);
  products->PushProducts(antileptonparticle);
 
#ifdef G4VERBOSE
  if (GetVerboseLevel() > 1) {
    G4cout << "G4DalitzDecayChannel::DecayIt ";
    G4cout << "  create decay products in rest frame " << G4endl;
    products->DumpInfo();
  }
#endif
  return products;
}