G4INCLPionResonanceDecayChannel.cc

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//
// INCL++ intra-nuclear cascade model
// Alain Boudard, CEA-Saclay, France
// Joseph Cugnon, University of Liege, Belgium
// Jean-Christophe David, CEA-Saclay, France
// Pekka Kaitaniemi, CEA-Saclay, France, and Helsinki Institute of Physics, Finland
// Sylvie Leray, CEA-Saclay, France
// Davide Mancusi, CEA-Saclay, France
//
#define INCLXX_IN_GEANT4_MODE 1
 
#include "globals.hh"
 
#include "G4INCLPionResonanceDecayChannel.hh"
#include "G4INCLKinematicsUtils.hh"
#include "G4INCLBinaryCollisionAvatar.hh"
#include "G4INCLRandom.hh"
#include "G4INCLGlobals.hh"
#include "G4INCLPhaseSpaceGenerator.hh"
// #include <cassert>
 
 
namespace G4INCL {
    
    const G4double PionResonanceDecayChannel::angularSlope = 0.; // Slope to be defined, if needed.
    
    PionResonanceDecayChannel::PionResonanceDecayChannel(Particle *p, ThreeVector const &dir)
    :theParticle(p), incidentDirection(dir)
    { }
    
    PionResonanceDecayChannel::~PionResonanceDecayChannel() {}
    
//  Decay during the intranuclear cascade for Omega only
  G4double PionResonanceDecayChannel::computeDecayTime(Particle *p) {
  const G4double m = p->getMass();
  const G4double geff = p->getEnergy()/m;
//      const G4double geta = 1.31e-3;
        const G4double gomega = 8.49;
        G4double gg=0.;
        switch (p->getType()) {
/*          case Eta:
                gg=geta;
                break;*/
            case Omega:
                gg=gomega;
                break;
            default:
                INCL_FATAL("Unrecognized pion resonance type; type=" << p->getType() << '\n');
                break;
        }
        const G4double tpires = -G4INCL::PhysicalConstants::hc/gg*std::log(Random::shoot())*geff;
        return tpires;
    }
    
    void PionResonanceDecayChannel::sampleAngles(G4double *ctet_par, G4double *stet_par, G4double *phi_par) {
 
        (*ctet_par) = -1.0 + 2.0*Random::shoot();
        if(std::abs(*ctet_par) > 1.0) (*ctet_par) = Math::sign(*ctet_par);
        (*stet_par) = std::sqrt(1.-(*ctet_par)*(*ctet_par));
        (*phi_par) = Math::twoPi * Random::shoot();
    }
    
    void PionResonanceDecayChannel::fillFinalState(FinalState *fs) {
        
        ParticleType createdType;
        ParticleType pionType1=Neutron; // to avoid forgetting pionType definition when 3 particles are emitted
        ParticleType pionType2=Neutron; 
 
        const G4double sqrtS = theParticle->getMass();
        G4int nbpart = 3; // number of emitted particles
        G4double drnd=Random::shoot();
        switch (theParticle->getType()) {
            case Eta:
                if (drnd < 0.3972) { // renormalized to the only four decays taken into account here
//      2 photons
                    nbpart=2;
                    theParticle->setType(Photon);
                    createdType = Photon;
                }
                else if (drnd < 0.7265) {
//      3 pi0
                    theParticle->setType(PiZero);
                    pionType1 = PiZero;
                    pionType2 = PiZero;
                }
                else if (drnd < 0.9575) {
//      pi+ pi- pi0
                theParticle->setType(PiZero);
                pionType1 = PiPlus;
                pionType2 = PiMinus;
            }
                else {
//      pi+ pi- photon
                    theParticle->setType(Photon);
                    pionType1 = PiPlus;
                    pionType2 = PiMinus;
                }
            break;
            case Omega:
                if (drnd < 0.9009) { // renormalized to the only three decays taken into account here
//      pi+ pi- pi0
                    theParticle->setType(PiZero);
                    pionType1 = PiPlus;
                    pionType2 = PiMinus;
                }
                else if (drnd < 0.9845) {
//      pi0 photon
                    nbpart=2;
                    theParticle->setType(PiZero);
                    createdType = Photon;
                }
                else {
//      pi+ pi-
                    nbpart=2;
                    theParticle->setType(PiPlus);
                    createdType = PiMinus;
                }
                break;
            default:
                INCL_FATAL("Unrecognized pion resonance type; type=" << theParticle->getType() << '\n');
                break;
        }
 
        if (nbpart == 2) {          
            G4double fi, ctet, stet;
            sampleAngles(&ctet, &stet, &fi);
            
            G4double cfi = std::cos(fi);
            G4double sfi = std::sin(fi);
            G4double beta = incidentDirection.mag();
            
            G4double q1, q2, q3;
            G4double sal=0.0;
            if (beta >= 1.0e-10)
                sal = incidentDirection.perp()/beta;
            if (sal >= 1.0e-6) {
                G4double b1 = incidentDirection.getX();
                G4double b2 = incidentDirection.getY();
                G4double b3 = incidentDirection.getZ();
                G4double cal = b3/beta;
                G4double t1 = ctet+cal*stet*sfi/sal;
                G4double t2 = stet/sal;
                q1=(b1*t1+b2*t2*cfi)/beta;
                q2=(b2*t1-b1*t2*cfi)/beta;
                q3=(b3*t1/beta-t2*sfi);
            } else {
                q1 = stet*cfi;
                q2 = stet*sfi;
                q3 = ctet;
            }
                        
            G4double xq = KinematicsUtils::momentumInCM(sqrtS,
                                                      theParticle->getMass(),
                                                      ParticleTable::getINCLMass(createdType));
            q1 *= xq;
            q2 *= xq;
            q3 *= xq;
            
            ThreeVector createdMomentum(q1, q2, q3);
            ThreeVector createdPosition(theParticle->getPosition());
            Particle *createdParticle = new Particle(createdType, createdMomentum, createdPosition);
            theParticle->setMomentum(-createdMomentum);
            theParticle->adjustEnergyFromMomentum();
            
            fs->addModifiedParticle(theParticle);
            fs->addCreatedParticle(createdParticle);
            
        }
        else if (nbpart == 3) {
// assert(pionType1!=Neutron && pionType2!=Neutron);
            ParticleList list;
            list.push_back(theParticle);
            const ThreeVector &rposdecay = theParticle->getPosition();
            const ThreeVector zero;
            Particle *Pion1 = new Particle(pionType1,zero,rposdecay);
            Particle *Pion2 = new Particle(pionType2,zero,rposdecay);
            list.push_back(Pion1);
            list.push_back(Pion2);
            
            fs->addModifiedParticle(theParticle);
            fs->addCreatedParticle(Pion1);
            fs->addCreatedParticle(Pion2);
 
            //          PhaseSpaceGenerator::generateBiased(sqrtS, list, 0, angularSlope); Biasing?
            PhaseSpaceGenerator::generate(sqrtS, list);
        }
 
    }
}