G4MuMinusCapturePrecompound.cc

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// $Id$
//
//-----------------------------------------------------------------------------
//
// GEANT4 Class file 
//
// File name:  G4MuMinusCapturePrecompound
//
// Author:        V.Ivanchenko (Vladimir.Ivantchenko@cern.ch)
// 
// Creation date: 22 April 2012 on base of G4MuMinusCaptureCascade
//
//
//-----------------------------------------------------------------------------
//
// Modifications: 
//
//-----------------------------------------------------------------------------

#include "G4MuMinusCapturePrecompound.hh"
#include "Randomize.hh" 
#include "G4RandomDirection.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4MuonMinus.hh"
#include "G4NeutrinoMu.hh"
#include "G4Neutron.hh"
#include "G4Proton.hh"
#include "G4Triton.hh"
#include "G4LorentzVector.hh"
#include "G4ParticleDefinition.hh"
#include "G4NucleiProperties.hh"
#include "G4VPreCompoundModel.hh"
#include "G4PreCompoundModel.hh"
#include "G4HadronicInteractionRegistry.hh"

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G4MuMinusCapturePrecompound::G4MuMinusCapturePrecompound(
    G4VPreCompoundModel* ptr)
  : G4HadronicInteraction("muMinusNuclearCapture")
{ 
  fMuMass = G4MuonMinus::MuonMinus()->GetPDGMass(); 
  fProton = G4Proton::Proton();
  fNeutron = G4Neutron::Neutron();
  fThreshold = 10*MeV;
  fPreCompound = ptr;
  if(!ptr) { 
    G4HadronicInteraction* p =
      G4HadronicInteractionRegistry::Instance()->FindModel("PRECO");
    ptr = static_cast<G4VPreCompoundModel*>(p); 
    fPreCompound = ptr;
    if(!ptr) { fPreCompound = new G4PreCompoundModel(); }
  }
}

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G4MuMinusCapturePrecompound::~G4MuMinusCapturePrecompound()
{
  result.Clear();
}

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G4HadFinalState* 
G4MuMinusCapturePrecompound::ApplyYourself(const G4HadProjectile& projectile, 
                                           G4Nucleus& targetNucleus)
{
  result.Clear();
  result.SetStatusChange(stopAndKill);
  fTime = projectile.GetGlobalTime();
  G4double time0 = fTime;

  G4double muBindingEnergy = projectile.GetBoundEnergy();

  G4int Z = targetNucleus.GetZ_asInt(); 
  G4int A = targetNucleus.GetA_asInt();
  G4double massA = G4NucleiProperties::GetNuclearMass(A, Z);

  /*
  G4cout << "G4MuMinusCapturePrecompound::ApplyYourself: Emu= "
         << muBindingEnergy << G4endl;
  */
  // Energy on K-shell
  G4double muEnergy = fMuMass + muBindingEnergy;
  G4double muMom = std::sqrt(muBindingEnergy*(muBindingEnergy + 2.0*fMuMass));
  G4double availableEnergy = massA + fMuMass - muBindingEnergy;
  G4double residualMass = G4NucleiProperties::GetNuclearMass(A, Z - 1);

  G4ThreeVector vmu = muMom*G4RandomDirection();
  G4LorentzVector aMuMom(vmu, muEnergy);

  // p or 3He as a target 
  // two body reaction mu- + A(Z,A) -> nuMu + A(Z-1,A)
  if((1 == Z && 1 == A) || (2 == Z && 3 == A)) {

    G4ParticleDefinition* pd = 0;
    if(1 == Z) { pd = fNeutron; }
    else { pd = G4Triton::Triton(); }

    //
    //  Computation in assumption of CM reaction
    //  
    G4double e = 0.5*(availableEnergy - 
                      residualMass*residualMass/availableEnergy);

    G4ThreeVector nudir = G4RandomDirection();
    AddNewParticle(G4NeutrinoMu::NeutrinoMu(), nudir, e);
    nudir *= -1.0;
    AddNewParticle(pd, nudir, availableEnergy - e - residualMass);


  } else {
    // sample mu- + p -> nuMu + n reaction in CM of muonic atom

    // muon
//    
// NOTE by K.Genser and J.Yarba:
// The code below isn't working because emu always turns smaller than fMuMass
// For this reason the sqrt is producing a NaN    
//
//    G4double emu = (availableEnergy*availableEnergy - massA*massA
//                  + fMuMass*fMuMass)/(2*availableEnergy);
//    G4ThreeVector mudir = G4RandomDirection();
//    G4LorentzVector momMuon(std::sqrt(emu*emu - fMuMass*fMuMass)*mudir, emu);

    // nucleus
    G4LorentzVector momInitial(0.0,0.0,0.0,availableEnergy);
    G4LorentzVector momResidual, momNu;

    // pick random proton inside nucleus 
    G4double eEx;
    fNucleus.Init(A, Z);
    const std::vector<G4Nucleon>& nucleons= fNucleus.GetNucleons();
    G4ParticleDefinition* pDef;

    G4int nneutrons = 1;
    G4int reentryCount = 0;
  
    do {
      ++reentryCount;
      G4int index = 0;
      do {
        index=G4int(A*G4UniformRand());
        pDef = nucleons[index].GetDefinition();
      } while(pDef != fProton);
      G4LorentzVector momP = nucleons[index].Get4Momentum();

      // Get CMS kinematics
      G4LorentzVector theCMS = momP + aMuMom;
      G4ThreeVector bst = theCMS.boostVector();

      G4double Ecms = theCMS.mag();
      G4double Enu  = 0.5*(Ecms - neutron_mass_c2*neutron_mass_c2/Ecms);
      eEx = 0.0;

      if(Enu > 0.0) {
        // make the nu, and transform to lab;
        momNu.set(Enu*G4RandomDirection(), Enu);

        // nu in lab.
        momNu.boost(bst);
        momResidual = momInitial - momNu;
        eEx = momResidual.mag() - residualMass;

        // release neutron
        
        if(eEx > 0.0) {
          G4double eth = residualMass - massA + fThreshold + 2*neutron_mass_c2;
          if(Ecms - Enu > eth) {
            theCMS -= momNu;
            G4double ekin =  theCMS.e() - eth;
            G4ThreeVector dir = theCMS.vect().unit();
            AddNewParticle(fNeutron, dir, ekin);
            momResidual -= 
              result.GetSecondary(0)->GetParticle()->Get4Momentum();
            --Z;
            --A; 
            residualMass = G4NucleiProperties::GetNuclearMass(A, Z);
            nneutrons = 0;  
          }
        }
      }
      if(Enu <= 0.0 && eEx <= 0.0 && reentryCount > 100) {
        G4ExceptionDescription ed;
        ed << "Call for " << GetModelName() << G4endl;
        ed << "Target  Z= " << Z  
           << "  A= " << A << G4endl;
        ed << " ApplyYourself does not completed after 100 attempts" << G4endl;
        G4Exception("G4MuMinusCapturePrecompound::AtRestDoIt", "had006", 
                    FatalException, ed);        
      }
    } while(eEx <= 0.0);

    G4ThreeVector dir = momNu.vect().unit();
    AddNewParticle(G4NeutrinoMu::NeutrinoMu(), dir, momNu.e());

    G4Fragment initialState(A, Z, momResidual);
    initialState.SetNumberOfExcitedParticle(nneutrons,0);
    initialState.SetNumberOfHoles(1,1);

    // decay time for pre-compound/de-excitation starts from zero
    G4ReactionProductVector* rpv = fPreCompound->DeExcite(initialState);
    size_t n = rpv->size();
    for(size_t i=0; i<n; ++i) {
      G4ReactionProduct* rp = (*rpv)[i];

      // reaction time
      fTime = time0 + rp->GetTOF();
      G4ThreeVector direction = rp->GetMomentum().unit();
      AddNewParticle(rp->GetDefinition(), direction, rp->GetKineticEnergy());
      delete rp;
    }
    delete rpv;
  } 
  if(verboseLevel > 1)
    G4cout << "G4MuMinusCapturePrecompound::ApplyYourself:  Nsec= " 
           << result.GetNumberOfSecondaries() 
           <<" E0(MeV)= " <<availableEnergy/MeV
           <<" Mres(GeV)= " <<residualMass/GeV
           <<G4endl;

  return &result;
}

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void G4MuMinusCapturePrecompound::ModelDescription(std::ostream& outFile) const
{
  outFile << "Sampling of mu- capture by atomic nucleus from K-shell"
          << " mesoatom orbit.\n"
          << "Primary reaction mu- + p -> n + neutrino, neutron providing\n"
          << "  initial excitation of the target nucleus and PreCompound"
          << " model samples final state\n";
}

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