G4INCLPhaseSpaceDecay.cc

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//
// INCL++ intra-nuclear cascade model
// Pekka Kaitaniemi, CEA and Helsinki Institute of Physics
// Davide Mancusi, CEA
// Alain Boudard, CEA
// Sylvie Leray, CEA
// Joseph Cugnon, University of Liege
//
#define INCLXX_IN_GEANT4_MODE 1

#include "globals.hh"

#include "G4INCLPhaseSpaceDecay.hh"
#include "G4INCLRandom.hh"
#include "G4INCLKinematicsUtils.hh"
#include <algorithm>
#include <numeric>
#include <functional>

namespace G4INCL {
  namespace PhaseSpaceDecay {
    namespace {
      // Generate scale factor for final state particle
      G4double betaKopylov(G4int K) {
        G4int N = 3*K - 5;
        G4double xN = G4double(N);
        G4double Fmax = std::sqrt(std::pow(xN/(xN+1.),N)/(xN+1.));

        G4double F, chi;
        do {
          chi = Random::shoot();
          F = std::sqrt(std::pow(chi,N)*(1.-chi));
        } while ( Fmax*Random::shoot() > F);
        return chi;
      }
    }

    void decay(const G4double initialMass, ThreeVector const &theBoostVector, ParticleList &particles) {

      size_t N = particles.size();
      std::vector<G4double> masses(N);
      std::vector<G4double> sumMasses(N);
      std::transform(particles.begin(), particles.end(), masses.begin(), std::mem_fun(&Particle::getMass));
      std::partial_sum(masses.begin(), masses.end(), sumMasses.begin());

      G4double PFragMagCM = 0.0;
      G4double T = initialMass-sumMasses.back();
// assert(T>-1.e-5);
      if(T<0.)
        T=0.;

      ThreeVector PFragCM, PRestCM, PRestLab;

      // The first particle in the list will pick up all the recoil
      Particle *restParticle = particles.front();
      restParticle->setMass(initialMass);
      restParticle->adjustEnergyFromMomentum();

      ThreeVector boostV;

      G4int k=N-1;
      for (ParticleList::reverse_iterator p=particles.rbegin(); k>0; ++p, --k) {
        const G4double mu = sumMasses[k-1];
        T *= (k>1) ? betaKopylov(k) : 0.;

        const G4double restMass = mu + T;

        PFragMagCM = KinematicsUtils::momentumInCM(restParticle->getMass(), masses[k], restMass);
        PFragCM = Random::normVector(PFragMagCM);
        (*p)->setMomentum(PFragCM);
        (*p)->adjustEnergyFromMomentum();
        restParticle->setMass(restMass);
        restParticle->setMomentum(-PFragCM);
        restParticle->adjustEnergyFromMomentum();

        (*p)->boost(boostV);
        (*p)->boost(theBoostVector);
        restParticle->boost(boostV);

        boostV = -restParticle->boostVector();
      }
      restParticle->setMass(masses[0]);
      restParticle->adjustEnergyFromMomentum();
      restParticle->boost(theBoostVector);
    }
  }
}