G4VXResonance.cc

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//
// -------------------------------------------------------------------
//      GEANT4 Class file
//
//      For information related to this code contact:
//
//      File name:     G4VXResonance
//
//      Author:        
// 
//      Creation date: 15 April 1999
//
//      Modifications: 
//      
// -------------------------------------------------------------------

#include "globals.hh"
#include "G4ios.hh"
#include "G4KineticTrack.hh"
#include "G4VXResonance.hh"
#include "Randomize.hh"
#include "G4Proton.hh"
#include "G4HadTmpUtil.hh"

G4VXResonance::G4VXResonance()
{ }


G4VXResonance::~G4VXResonance() 
{  }


G4bool G4VXResonance::operator==(const G4VXResonance &right) const
{
  return (this == (G4VXResonance *) &right);
}


G4bool G4VXResonance::operator!=(const G4VXResonance &right) const
{
  return (this != (G4VXResonance *) &right);
}


G4double G4VXResonance::IsospinCorrection(const G4KineticTrack& trk1, 
                                          const G4KineticTrack& trk2,
                                          G4int isoOut1, G4int isoOut2,
                                          G4double /*iSpinOut1*/, G4double /*iSpinOut2*/) const
{
  G4double result = 0.;
 
  const G4ParticleDefinition* in1 = trk1.GetDefinition();
  const G4ParticleDefinition* in2 = trk2.GetDefinition();

  G4int isoIn1  = in1->GetPDGiIsospin();
  G4int iso3In1 = in1->GetPDGiIsospin3();
  G4int isoIn2  = in2->GetPDGiIsospin();
  G4int iso3In2 = in2->GetPDGiIsospin3();

  G4int isoProton = G4Proton::ProtonDefinition()->GetPDGiIsospin();
  G4int iso3Proton = G4Proton::ProtonDefinition()->GetPDGiIsospin3();
  
  G4double pWeight = clebsch.Weight(isoProton,iso3Proton, isoProton,iso3Proton, isoOut1,isoOut2);
  if (pWeight == 0.) throw G4HadronicException(__FILE__, __LINE__, "G4VXResonance::IsospinCorrection, no resonances - pWeight is zero");

  if (in1->IsShortLived() || in2->IsShortLived())
  {
    // Resonances in the initial state
    G4int iSpinProton = G4Proton::ProtonDefinition()->GetPDGiSpin();
    G4double degeneracyFactor = DegeneracyFactor(trk1,trk2,iSpinProton,iSpinProton);

    G4double factor = degeneracyFactor * pWeight;
    if (factor > DBL_MIN)
    {
      // Randomly select the Isospin3 of the initial state resonances
      std::vector<G4double> iso = clebsch.GenerateIso3(isoIn1,iso3In1, 
                                                  isoIn2,iso3In2, 
                                                  isoProton,isoProton);
      G4int isoA = G4lrint(iso[0]);
      G4int isoB = G4lrint(iso[1]);
      G4double rWeight =  clebsch.Weight(isoProton,isoA,
                                         isoProton,isoB,
                                         isoOut1,isoOut2);
      result = rWeight / pWeight;
    }
  }
  else
  {
    G4double weight = clebsch.Weight(isoIn1,iso3In1, isoIn2,iso3In2, isoOut1,isoOut2);
    result = weight / pWeight;
  }
  
  return result;
}


#include "G4DetailedBalancePhaseSpaceIntegral.hh"

G4double G4VXResonance::DetailedBalance(const G4KineticTrack& trk1, 
                                        const G4KineticTrack& trk2,
                                        G4int isoOut1, G4int isoOut2,
                                        G4double iSpinOut1, G4double iSpinOut2,
                                        G4double mOut1, G4double mOut2) const
{
  // To handle the cases when resonances are involved the modified
  // detailed balance of P. Danielewicz and G.F. Bertsch, Nucl. Phys. A533(1991) 712
  // is used; in other words, the width of the resonances are folded to get the
  // mean square of the final state momentum.

  const G4ParticleDefinition* in1 = trk1.GetDefinition();
  const G4ParticleDefinition* in2 = trk2.GetDefinition();
  if(in1->IsShortLived() && in2->IsShortLived())
  {
    throw G4HadronicException(__FILE__, __LINE__, "Detailed balance for resonance scattering still on the schedule.");
  }

  G4double result = 0.;

  G4int isoIn1 = in1->GetPDGiIsospin();
  G4int iso3In1 = in1->GetPDGiIsospin3();
  G4int isoIn2 = in2->GetPDGiIsospin();
  G4int iso3In2 = in2->GetPDGiIsospin3();  
  G4double weight = clebsch.Weight(isoIn1, iso3In1, isoIn2, iso3In2, isoOut1, isoOut2);
  
  if (weight > 00001)
  {
    // adding spin counting here ...... does not look quite consistent, but is correct anyway. 
    // revisit in the next design iteration @@
    G4double degeneracy = DegeneracyFactor(trk1,trk2,iSpinOut1,iSpinOut2);
    G4double factor = degeneracy * weight;

    // now the phase-space
    G4double S = (trk1.Get4Momentum() + trk2.Get4Momentum()).mag2();
    G4double m_1 = in1->GetPDGMass();
    G4double m_2 = in2->GetPDGMass();
    
    // on-shell
    G4double pinitial2 = (S - (m_1+m_2) * (m_1+m_2)) * (S - (m_1-m_2) * (m_1-m_2)) / (4.0*S);
    G4double pfinal2 = (S - (mOut1+mOut2) * (mOut1+mOut2)) * (S - ( mOut1-mOut2) * (mOut1-mOut2)) / (4.0*S);
    G4double relativeMomsquared = pfinal2/pinitial2;

    // resonance-nucleon scattering - inverse channel
    if(in1->IsShortLived())
    {
      G4DetailedBalancePhaseSpaceIntegral theI(in1);
      relativeMomsquared = 1./theI.GetPhaseSpaceIntegral(std::sqrt(S));
    }
    else if(in2->IsShortLived())
    {
      G4DetailedBalancePhaseSpaceIntegral theI(in2);
      relativeMomsquared = 1./theI.GetPhaseSpaceIntegral(std::sqrt(S));
    }

    result = factor * relativeMomsquared;
  }

  return result;
}
  

G4double G4VXResonance::DegeneracyFactor(const G4KineticTrack& trk1, 
                                         const G4KineticTrack& trk2,
                                         G4double iSpinOut1, G4double iSpinOut2) const 
{
  G4double value = 0.;

  const G4ParticleDefinition* in1 = trk1.GetDefinition();
  const G4ParticleDefinition* in2 = trk2.GetDefinition();

  G4double sIn1 =  in1->GetPDGiSpin()  + 1.;
  G4double sIn2 =  in2->GetPDGiSpin()  + 1.;
  
  G4double denom = sIn1 * sIn2;
  if (denom > 0.)
  {
    value = (iSpinOut1+1) * (iSpinOut2+1) / denom;
  }
  return value;
}