G4INCLDeltaProductionChannel.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 "G4INCLDeltaProductionChannel.hh"
#include "G4INCLKinematicsUtils.hh"
#include "G4INCLBinaryCollisionAvatar.hh"
#include "G4INCLRandom.hh"
#include "G4INCLGlobals.hh"
#include "G4INCLLogger.hh"

namespace G4INCL {

  DeltaProductionChannel::DeltaProductionChannel(Particle *p1,
                         Particle *p2)
    : particle1(p1), particle2(p2)
  {}

  DeltaProductionChannel::~DeltaProductionChannel() {}

  G4double DeltaProductionChannel::sampleDeltaMass(G4double ecm) {
    const G4double ramass = 0.0;
    const G4int maxTries = 100000;
    G4int nTries = 0;
  deltaProd101: G4double rndm = Random::shoot();
    nTries++;
    G4double y = std::tan(Math::pi*(rndm-0.5));
    G4double x = 1232.+0.5*130.*y+ramass;
    if (x < ParticleTable::effectiveDeltaDecayThreshold && (nTries < maxTries))
      goto deltaProd101;
    if (ecm < x + ParticleTable::effectiveNucleonMass + 1.0 && (nTries < maxTries)) goto deltaProd101;

    // generation of the delta mass with the penetration factor
    // (see prc56(1997)2431)
    y=ecm*ecm;
    G4double q2=(y-1.157776E6)*(y-6.4E5)/y/4.0; // 1.157776E6 = 1076^2, 6.4E5 = 800^2
    G4double q3=std::pow(std::sqrt(q2), 3.);
    G4double f3max=q3/(q3+5.832E6); // 5.832E6 = 180^3
    y=x*x;
    q2=(y-1.157776E6)*(y-6.4E5)/y/4.0; // 1.157776E6 = 1076^2, 6.4E5 = 800^2
    q3=std::pow(std::sqrt(q2), 3.);
    G4double f3=q3/(q3+5.832E6); // 5.832E6 = 180^3
    rndm = Random::shoot();
    if (rndm > f3/f3max && (nTries < maxTries)) goto deltaProd101;
    if(nTries >= maxTries) {
      INCL_WARN("DeltaProductionChannel::sampleDeltaMass loop was stopped because maximum number of tries was reached. Delta mass " << x << " MeV with CM energy " << ecm << " MeV may be unphysical." << std::endl);
    }
    return x;
  }

  FinalState* DeltaProductionChannel::getFinalState() {
    /**
     * Delta production
     *
     * The production is not isotropic in this version it has the same
     * exp(b*t) structure as the nn elastic scattering (formula 2.3 of
     * j.cugnon et al, nucl phys a352(1981)505) parametrization of b
     * taken from ref. prc56(1997)2431
    */
    //    100 IF (K4.NE.1) GO TO 101 // ThA K4 = 2 by default
    //    ParticleType p1TypeOld = particle1->getType();
    //    ParticleType p2TypeOld = particle2->getType();
    G4double ecm = KinematicsUtils::totalEnergyInCM(particle1, particle2);

    const G4int isospin = ParticleTable::getIsospin(particle1->getType()) +
      ParticleTable::getIsospin(particle2->getType());

    // Calculate the outcome of the channel:
    G4double pin = particle1->getMomentum().mag();
    G4double rndm = 0.0, b = 0.0;

    G4double xmdel = sampleDeltaMass(ecm);
    //  deltaProduction103: // This label is not used
    G4double pnorm = KinematicsUtils::momentumInCM(ecm, ParticleTable::effectiveNucleonMass, xmdel);
    if (pnorm <= 0.0) pnorm=0.000001;
    G4int index=0;
    G4int index2=0;
    rndm = Random::shoot();
    if (rndm < 0.5) index=1;
    if (isospin == 0) { // pn case
      rndm = Random::shoot();
      if (rndm < 0.5) index2=1;
    }

    //    G4double x=0.001*0.5*ecm*std::sqrt(ecm*ecm-4.*ParticleTable::effectiveNucleonMass2)
    //      / ParticleTable::effectiveNucleonMass;
    G4double x = 0.001 * KinematicsUtils::momentumInLab(ecm*ecm, ParticleTable::effectiveNucleonMass, ParticleTable::effectiveNucleonMass);
    if(x < 1.4) {
      b=(5.287/(1.+std::exp((1.3-x)/0.05)))*1.e-6;
    } else {
      b=(4.65+0.706*(x-1.4))*1.e-6;
    }
    G4double xkh = 2.*b*pin*pnorm;
    rndm = Random::shoot();
    G4double ctet=1.0+std::log(1.-rndm*(1.-std::exp(-2.*xkh)))/xkh;
    if(std::abs(ctet) > 1.0) ctet = Math::sign(ctet);
    G4double stet = std::sqrt(1.-ctet*ctet);

    rndm = Random::shoot();
    G4double fi = Math::twoPi*rndm;
    G4double cfi = std::cos(fi);
    G4double sfi = std::sin(fi);
    // delta production: correction of the angular distribution 02/09/02

    G4double xx = particle1->getMomentum().perp2();
    G4double zz = std::pow(particle1->getMomentum().getZ(), 2);
    G4double xp1, xp2, xp3;
    if (xx >= zz*1.e-8) {
      G4double yn = std::sqrt(xx);
      G4double zn = yn*pin;
      G4double ex[3], ey[3], ez[3];
      G4double p1 = particle1->getMomentum().getX();
      G4double p2 = particle1->getMomentum().getY();
      G4double p3 = particle1->getMomentum().getZ();
      ez[0] = p1/pin;
      ez[1] = p2/pin;
      ez[2] = p3/pin;
      ex[0] = p2/yn;
      ex[1] = -p1/yn;
      ex[2] = 0.0;
      ey[0] = p1*p3/zn;
      ey[1] = p2*p3/zn;
      ey[2] = -xx/zn;
      xp1 = (ex[0]*cfi*stet+ey[0]*sfi*stet+ez[0]*ctet)*pnorm;
      xp2 = (ex[1]*cfi*stet+ey[1]*sfi*stet+ez[1]*ctet)*pnorm;
      xp3 = (ex[2]*cfi*stet+ey[2]*sfi*stet+ez[2]*ctet)*pnorm;
    }else {
      xp1=pnorm*stet*cfi;
      xp2=pnorm*stet*sfi;
      xp3=pnorm*ctet;
    }
    // end of correction angular distribution of delta production
    G4double e3 = std::sqrt(xp1*xp1+xp2*xp2+xp3*xp3
              +ParticleTable::effectiveNucleonMass2);
    //      if(k4.ne.0) go to 161

    // long-lived delta
    if (index != 1) {
      ThreeVector mom(xp1, xp2, xp3);
      particle1->setMomentum(mom);
      //       e1=ecm-eout1
    } else {
      ThreeVector mom(-xp1, -xp2, -xp3);
      particle1->setMomentum(mom);
      //      e1=ecm-eout1
    }

    particle1->setEnergy(ecm - e3);
    particle2->setEnergy(e3);
    particle2->setMomentum(-particle1->getMomentum());

    // SYMMETRIZATION OF CHARGES IN pn -> N DELTA
    // THE TEST ON "INDEX" ABOVE SYMETRIZES THE EXCITATION OF ONE
    // OF THE NUCLEONS WITH RESPECT TO THE DELTA EXCITATION
    // (SEE NOTE 16/10/97)
    G4int is1 = ParticleTable::getIsospin(particle1->getType());
    G4int is2 = ParticleTable::getIsospin(particle2->getType());
    if (isospin == 0) {
      if(index2 == 1) {
        G4int isi=is1;
        is1=is2;
        is2=isi;
      }
      particle1->setHelicity(0.0);
    } else {
      rndm = Random::shoot();
      if (rndm >= 0.25) {
        is1=3*is1;
        is2=-is2;
      }
      particle1->setHelicity(ctet*ctet);
    }

    if(is1 == ParticleTable::getIsospin(DeltaMinus)) {
      particle1->setType(DeltaMinus);
    } else if(is1 == ParticleTable::getIsospin(DeltaZero)) {
      particle1->setType(DeltaZero);
    } else if(is1 == ParticleTable::getIsospin(DeltaPlus)) {
      particle1->setType(DeltaPlus);
    } else if(is1 == ParticleTable::getIsospin(DeltaPlusPlus)) {
      particle1->setType(DeltaPlusPlus);
    }

    if(is2 == ParticleTable::getIsospin(Proton)) {
      particle2->setType(Proton);
    } else if(is2 == ParticleTable::getIsospin(Neutron)) {
      particle2->setType(Neutron);
    }

    if(particle1->isDelta()) particle1->setMass(xmdel);
    if(particle2->isDelta()) particle2->setMass(xmdel);

    FinalState *fs = new FinalState;
    fs->addModifiedParticle(particle1);
    fs->addModifiedParticle(particle2);
    return fs;
  }
}