G4LEPionPlusInelastic.cc

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// $Id$
//
// Hadronic Process: PionPlus Inelastic Process
// J.L. Chuma, TRIUMF, 19-Nov-1996
 
// Modified by J.L.Chuma 30-Apr-97: added originalTarget for CalculateMomenta
// fixing charge exchange - HPW Sep 2002.
 
#include <iostream>
 
#include "G4LEPionPlusInelastic.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "Randomize.hh"
 
G4LEPionPlusInelastic::G4LEPionPlusInelastic(const G4String& name)
 :G4InelasticInteraction(name)
{
  SetMinEnergy(0.0);
  SetMaxEnergy(55.*GeV);
  G4cout << "WARNING: model G4LEPionPlusInelastic is being deprecated and will\n"
         << "disappear in Geant4 version 10.0"  << G4endl;
}
 
 
void G4LEPionPlusInelastic::ModelDescription(std::ostream& outFile) const
{
  outFile << "G4LEPionPlusInelastic is one of the Low Energy Parameterized\n"
          << "(LEP) models used to implement inelastic pi+ scattering\n"
          << "from nuclei.  It is a re-engineered version of the GHEISHA\n"
          << "code of H. Fesefeldt.  It divides the initial collision\n"
          << "products into backward- and forward-going clusters which are\n"
          << "then decayed into final state hadrons.  The model does not\n"
          << "conserve energy on an event-by-event basis.  It may be\n"
          << "applied to pions with initial energies between 0 and 25\n"
          << "GeV.\n";
}
 
 
G4HadFinalState*
G4LEPionPlusInelastic::ApplyYourself(const G4HadProjectile& aTrack,
                                     G4Nucleus& targetNucleus)
{
  const G4HadProjectile *originalIncident = &aTrack;
  if (originalIncident->GetKineticEnergy()<= 0.1*MeV) {
    theParticleChange.SetStatusChange(isAlive);
    theParticleChange.SetEnergyChange(aTrack.GetKineticEnergy());
    theParticleChange.SetMomentumChange(aTrack.Get4Momentum().vect().unit()); 
    return &theParticleChange;      
  }
 
  // create the target particle
    
  G4DynamicParticle *originalTarget = targetNucleus.ReturnTargetParticle();
  G4ReactionProduct targetParticle( originalTarget->GetDefinition() );
    
  if (verboseLevel > 1) {
    const G4Material* targetMaterial = aTrack.GetMaterial();
    G4cout << "G4LEPionPlusInelastic::ApplyYourself called" << G4endl;
    G4cout << "kinetic energy = " << originalIncident->GetKineticEnergy() << "MeV, ";
    G4cout << "target material = " << targetMaterial->GetName() << ", ";
    G4cout << "target particle = " << originalTarget->GetDefinition()->GetParticleName()
           << G4endl;
  }
  G4ReactionProduct currentParticle( 
  const_cast<G4ParticleDefinition *>(originalIncident->GetDefinition() ) );
  currentParticle.SetMomentum( originalIncident->Get4Momentum().vect() );
  currentParticle.SetKineticEnergy( originalIncident->GetKineticEnergy() );
    
  // Fermi motion and evaporation
  // As of Geant3, the Fermi energy calculation had not been Done  
  G4double ek = originalIncident->GetKineticEnergy();
  G4double amas = originalIncident->GetDefinition()->GetPDGMass();
    
  G4double tkin = targetNucleus.Cinema(ek);
  ek += tkin;
  currentParticle.SetKineticEnergy(ek);
  G4double et = ek + amas;
  G4double p = std::sqrt( std::abs((et-amas)*(et+amas)) );
  G4double pp = currentParticle.GetMomentum().mag();
  if (pp > 0.0) {
    G4ThreeVector momentum = currentParticle.GetMomentum();
    currentParticle.SetMomentum( momentum * (p/pp) );
  }
    
  // calculate black track energies  
  tkin = targetNucleus.EvaporationEffects(ek);
  ek -= tkin;
  currentParticle.SetKineticEnergy(ek);
  et = ek + amas;
  p = std::sqrt( std::abs((et-amas)*(et+amas)) );
  pp = currentParticle.GetMomentum().mag();
  if (pp > 0.0) {
    G4ThreeVector momentum = currentParticle.GetMomentum();
    currentParticle.SetMomentum( momentum * (p/pp) );
  }
 
  G4ReactionProduct modifiedOriginal = currentParticle;
 
  currentParticle.SetSide(1); // incident always goes in forward hemisphere
  targetParticle.SetSide(-1);  // target always goes in backward hemisphere
  G4bool incidentHasChanged = false;
  G4bool targetHasChanged = false;
  G4bool quasiElastic = false;
  G4FastVector<G4ReactionProduct,GHADLISTSIZE> vec;  // vec will contain the secondary particles
  G4int vecLen = 0;
  vec.Initialize(0);
    
  const G4double cutOff = 0.1*MeV;
  if (currentParticle.GetKineticEnergy() > cutOff)
    Cascade(vec, vecLen, originalIncident, currentParticle, targetParticle,
            incidentHasChanged, targetHasChanged, quasiElastic);
    
  CalculateMomenta(vec, vecLen,
                   originalIncident, originalTarget, modifiedOriginal,
                   targetNucleus, currentParticle, targetParticle,
                   incidentHasChanged, targetHasChanged, quasiElastic);
    
  SetUpChange(vec, vecLen, currentParticle, targetParticle, incidentHasChanged);
 
  if (isotopeProduction) DoIsotopeCounting(originalIncident, targetNucleus);
 
  delete originalTarget;
  return &theParticleChange;
}
 
 
void G4LEPionPlusInelastic::Cascade(
   G4FastVector<G4ReactionProduct,GHADLISTSIZE>& vec,
   G4int& vecLen,
   const G4HadProjectile* originalIncident,
   G4ReactionProduct& currentParticle,
   G4ReactionProduct& targetParticle,
   G4bool& incidentHasChanged,
   G4bool& targetHasChanged,
   G4bool& quasiElastic)
{
  // derived from original FORTRAN code CASPIP by H. Fesefeldt (18-Sep-1987)
  //
  // pi+  undergoes interaction with nucleon within nucleus.
  // Check if energetically possible to produce pions/kaons.
  // If not assume nuclear excitation occurs and input particle
  // is degraded in energy.  No other particles produced.
  // If reaction is possible find correct number of pions/protons/neutrons
  // produced using an interpolation to multiplicity data.
  // Replace some pions or protons/neutrons by kaons or strange baryons
  // according to average multiplicity per inelastic reactions.
 
  const G4double mOriginal = originalIncident->GetDefinition()->GetPDGMass();
  const G4double etOriginal = originalIncident->GetTotalEnergy();
  const G4double pOriginal = originalIncident->GetTotalMomentum();
  const G4double targetMass = targetParticle.GetMass();
  G4double centerofmassEnergy = std::sqrt(mOriginal*mOriginal +
                                          targetMass*targetMass +
                                          2.0*targetMass*etOriginal);
  G4double availableEnergy = centerofmassEnergy-(targetMass+mOriginal);
  static G4bool first = true;
  const G4int numMul = 1200;
  const G4int numSec = 60;
  static G4double protmul[numMul], protnorm[numSec]; // proton constants
  static G4double neutmul[numMul], neutnorm[numSec]; // neutron constants
 
  // npos = number of pi+, nneg = number of pi-, nzero = number of pi0
  G4int counter, nt=0, npos=0, nneg=0, nzero=0;
  const G4double c = 1.25;
  const G4double b[] = { 0.70, 0.70 };
    if( first ) {      // compute normalization constants, this will only be Done once
      first = false;
      G4int i;
      for( i=0; i<numMul; ++i )protmul[i] = 0.0;
      for( i=0; i<numSec; ++i )protnorm[i] = 0.0;
      counter = -1;
      for( npos=0; npos<(numSec/3); ++npos ) {
        for( nneg=std::max(0,npos-2); nneg<=npos; ++nneg ) {
          for( nzero=0; nzero<numSec/3; ++nzero ) {
            if( ++counter < numMul ) {
              nt = npos+nneg+nzero;
              if( nt > 0 ) {
                protmul[counter] = Pmltpc(npos,nneg,nzero,nt,b[0],c);
                protnorm[nt-1] += protmul[counter];
              }
            }
          }
        }
      }
      for( i=0; i<numMul; ++i )neutmul[i] = 0.0;
      for( i=0; i<numSec; ++i )neutnorm[i] = 0.0;
      counter = -1;
      for( npos=0; npos<numSec/3; ++npos ) {
        for( nneg=std::max(0,npos-1); nneg<=(npos+1); ++nneg ) {
          for( nzero=0; nzero<numSec/3; ++nzero ) {
            if( ++counter < numMul ) {
              nt = npos+nneg+nzero;
              if( (nt>0) && (nt<=numSec) ) {
                neutmul[counter] = Pmltpc(npos,nneg,nzero,nt,b[1],c);
                neutnorm[nt-1] += neutmul[counter];
              }
            }
          }
        }
      }
      for( i=0; i<numSec; ++i ) {
        if( protnorm[i] > 0.0 )protnorm[i] = 1.0/protnorm[i];
        if( neutnorm[i] > 0.0 )neutnorm[i] = 1.0/neutnorm[i];
      }
    }   // end of initialization
    
    const G4double expxu = 82.;           // upper bound for arg. of exp
    const G4double expxl = -expxu;        // lower bound for arg. of exp
    G4ParticleDefinition *aNeutron = G4Neutron::Neutron();
    G4ParticleDefinition *aProton = G4Proton::Proton();
    G4ParticleDefinition *aPiZero = G4PionZero::PionZero();
    G4int ieab = static_cast<G4int>(availableEnergy*5.0/GeV);
    const G4double supp[] = {0.,0.2,0.45,0.55,0.65,0.75,0.85,0.90,0.94,0.98};
    G4double test, w0, wp, wt, wm;
    if( (availableEnergy < 2.0*GeV) && (G4UniformRand() >= supp[ieab]) )
    {
      // suppress high multiplicity events at low momentum
      // only one pion will be produced
      // charge exchange reaction is included in inelastic cross section
      
      const G4double cech[] = {1.,0.95,0.79,0.32,0.19,0.16,0.14,0.12,0.10,0.08};
      G4int iplab = G4int(std::min( 9.0, pOriginal/GeV*5.0 ));
      if( G4UniformRand() <= cech[iplab] )
      {
        if( targetParticle.GetDefinition() == aNeutron )
        {
          currentParticle.SetDefinitionAndUpdateE( aPiZero );  // charge exchange
          targetParticle.SetDefinitionAndUpdateE( aProton );
          incidentHasChanged = true;
          targetHasChanged = true;
        }
      }
      
      if( availableEnergy <= G4PionMinus::PionMinus()->GetPDGMass() )
      {
        quasiElastic = true;
        return;
      }
      
      nneg = npos = nzero = 0;
      if( targetParticle.GetDefinition() == aProton ) {
        test = std::exp( std::min( expxu, std::max( expxl, -sqr(1.0+b[0])/(2.0*c*c) ) ) );
        w0 = test;
        wp = test;        
        if( G4UniformRand() < w0/(w0+wp) )
          nzero =1;
        else
          npos = 1;
      } else { // target is a neutron
        test = std::exp( std::min( expxu, std::max( expxl, -sqr(1.0+b[1])/(2.0*c*c) ) ) );
        w0 = test;
        wp = test;        
        test = std::exp( std::min( expxu, std::max( expxl, -sqr(-1.0+b[1])/(2.0*c*c) ) ) );
        wm = test;
        wt = w0+wp+wm;
        wp = w0+wp;
        G4double ran = G4UniformRand();
        if( ran < w0/wt )
          nzero = 1;
        else if( ran < wp/wt )
          npos = 1;
        else
          nneg = 1;
      }
    } else {
      if( availableEnergy <= G4PionMinus::PionMinus()->GetPDGMass() )
      {
        quasiElastic = true;
        return;
      }
      G4double n, anpn;
      GetNormalizationConstant( availableEnergy, n, anpn );
      G4double ran = G4UniformRand();
      G4double dum, excs = 0.0;
      if( targetParticle.GetDefinition() == aProton ) {
        counter = -1;
        for( npos=0; (npos<numSec/3) && (ran>=excs); ++npos ) {
          for( nneg=std::max(0,npos-2); (nneg<=npos) && (ran>=excs); ++nneg ) {
            for( nzero=0; (nzero<numSec/3) && (ran>=excs); ++nzero ) {
              if( ++counter < numMul ) {
                nt = npos+nneg+nzero;
                if( nt > 0 ) {
                  test = std::exp( std::min( expxu, std::max( expxl, -(pi/4.0)*(nt*nt)/(n*n) ) ) );
                  dum = (pi/anpn)*nt*protmul[counter]*protnorm[nt-1]/(2.0*n*n);
                  if( std::fabs(dum) < 1.0 ) {
                    if( test >= 1.0e-10 )excs += dum*test;
                  } else {
                    excs += dum*test;
                  }
                }
              }
            }
          }
        }
        if( ran >= excs )
        {
          quasiElastic = true;
          return;  // 3 previous loops continued to the end
        }
        npos--; nneg--; nzero--;
      } else { // target must be a neutron
        counter = -1;
        for( npos=0; (npos<numSec/3) && (ran>=excs); ++npos ) {
          for( nneg=std::max(0,npos-1); (nneg<=(npos+1)) && (ran>=excs); ++nneg ) {
            for( nzero=0; (nzero<numSec/3) && (ran>=excs); ++nzero ) {
              if( ++counter < numMul ) {
                nt = npos+nneg+nzero;
                if( (nt>=1) && (nt<=numSec) ) {
                  test = std::exp( std::min( expxu, std::max( expxl, -(pi/4.0)*(nt*nt)/(n*n) ) ) );
                  dum = (pi/anpn)*nt*neutmul[counter]*neutnorm[nt-1]/(2.0*n*n);
                  if( std::fabs(dum) < 1.0 ) {
                    if( test >= 1.0e-10 )excs += dum*test;
                  } else {
                    excs += dum*test;
                  }
                }
              }
            }
          }
        }
        if( ran >= excs )  // 3 previous loops continued to the end
        {
          quasiElastic = true;
          return;  // 3 previous loops continued to the end
        }
        npos--; nneg--; nzero--;
      }
    }
    if( targetParticle.GetDefinition() == aProton ) {
      switch( npos-nneg ) {
       case 1:
         if( G4UniformRand() < 0.5 ) {
           currentParticle.SetDefinitionAndUpdateE( aPiZero );
           incidentHasChanged = true;
         } else {
           targetParticle.SetDefinitionAndUpdateE( aNeutron );
           targetHasChanged = true;
         }
         break;
       case 2:
         currentParticle.SetDefinitionAndUpdateE( aPiZero );
         targetParticle.SetDefinitionAndUpdateE( aNeutron );
         incidentHasChanged = true;
         targetHasChanged = true;
         break;
       default:
         break;
      }
    } else {
      switch( npos-nneg ) {
       case 0:
         if( G4UniformRand() < 0.25 ) {
           currentParticle.SetDefinitionAndUpdateE( aPiZero );
           targetParticle.SetDefinitionAndUpdateE( aProton );
           incidentHasChanged = true;
           targetHasChanged = true;
         }
         break;
       case 1:
         currentParticle.SetDefinitionAndUpdateE( aPiZero );
         incidentHasChanged = true;
         break;
       default:
         targetParticle.SetDefinitionAndUpdateE( aProton );
         targetHasChanged = true;
         break;
      }
    }
  SetUpPions( npos, nneg, nzero, vec, vecLen );
  return;
}