G4SampleResonance.cc

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//
//
// ------------------------------------------------------------
//      GEANT 4 class header file
//
//      ---------------- G4SampleResonance ----------------
//             by Henning Weber, March 2001.
//      helper class for sampling resonance masses
// ------------------------------------------------------------


#include "globals.hh"
#include <iostream>
#include "G4SampleResonance.hh"
#include "G4DecayTable.hh"
#include "Randomize.hh"
#include "G4HadronicException.hh"

G4ThreadLocal G4SampleResonance::minMassMapType *G4SampleResonance::minMassCache_G4MT_TLS_ = 0;

G4double G4SampleResonance::GetMinimumMass(const G4ParticleDefinition* p) const
{  ;;;   if (!minMassCache_G4MT_TLS_) minMassCache_G4MT_TLS_ = new G4SampleResonance::minMassMapType  ; G4SampleResonance::minMassMapType &minMassCache = *minMassCache_G4MT_TLS_;  ;;;  

  G4double minResonanceMass = DBL_MAX;

  if ( p->IsShortLived() )
  {
    minMassMapIterator iter = minMassCache.find(p);
    if ( iter!=minMassCache.end() )
    {
      minResonanceMass = (*iter).second;
    }
    else
    {
      // G4cout << "--> request for " << p->GetParticleName() << G4endl;

      const G4DecayTable* theDecays = p->GetDecayTable();
      const G4int nDecays = theDecays->entries();

      for (G4int i=0; i<nDecays; i++)
      {
        const G4VDecayChannel* aDecay = theDecays->GetDecayChannel(i);
        const G4int nDaughters = aDecay->GetNumberOfDaughters();

        G4double minChannelMass = 0;

        for (G4int j=0; j<nDaughters; j++)
        {
          const G4ParticleDefinition* aDaughter = const_cast<G4VDecayChannel*>(aDecay)->GetDaughter(j);
          G4double minMass = GetMinimumMass(aDaughter);
          if (!minMass) minMass = DBL_MAX; // exclude gamma channel;
          minChannelMass+=minMass;
        }
        // G4cout << "channel mass for the above is " << minChannelMass/MeV << G4endl;
        if (minChannelMass < minResonanceMass) minResonanceMass = minChannelMass;

      }
      // replace this as soon as the compiler supports mutable!!
      G4SampleResonance* self = const_cast<G4SampleResonance*>(this);
      //Andrea Dotti (13Jan2013): Change needed for G4MT
      //(self->minMassCache)[p] = minResonanceMass;
      self->minMassCache_G4MT_TLS_->operator[](p) = minResonanceMass;

    }
  } 
  else
  {

    minResonanceMass = p->GetPDGMass();

  }
  // G4cout << "minimal mass for " << p->GetParticleName() << " is " << minResonanceMass/MeV << G4endl;

  return minResonanceMass;
} 



G4double G4SampleResonance::SampleMass(const G4ParticleDefinition* p, const G4double maxMass) const
{ if (!minMassCache_G4MT_TLS_) minMassCache_G4MT_TLS_ = new G4SampleResonance::minMassMapType  ;
  return SampleMass(p->GetPDGMass(), p->GetPDGWidth(), GetMinimumMass(p), maxMass);
}


G4double G4SampleResonance::SampleMass(const G4double poleMass, 
    const G4double gamma,
    const G4double minMass,
    const G4double maxMass) const
{ if (!minMassCache_G4MT_TLS_) minMassCache_G4MT_TLS_ = new G4SampleResonance::minMassMapType  ;
  // Chooses a mass randomly between minMass and maxMass
  //     according to a Breit-Wigner function with constant
  //     width gamma and pole poleMass


        //AR-14Nov2017 : protection for rare cases when a wide parent resonance, with a very small
        //               dynamic mass, decays into another wide (daughter) resonance: it can happen
        //               then that for the daugther resonance minMass > maxMass : in these cases,
        //               do not crash, but simply consider maxMass as the minimal mass for
        //               the sampling of the daughter resonance mass.
        G4double protectedMinMass = minMass;
  if ( minMass > maxMass )
  {
    //throw G4HadronicException(__FILE__, __LINE__,
    //        "SampleResonanceMass: mass range negative (minMass>maxMass)");
                protectedMinMass = maxMass;
  }

  G4double returnMass;

  if ( gamma < DBL_EPSILON )
  {
    returnMass = std::max(minMass, std::min(maxMass, poleMass));
  }
  else
  {
    //double fmin = BrWigInt0(minMass, gamma, poleMass);
    double fmin = BrWigInt0(protectedMinMass, gamma, poleMass);
    double fmax = BrWigInt0(maxMass, gamma, poleMass);
    double f = fmin + (fmax-fmin)*G4UniformRand();
    returnMass = BrWigInv(f, gamma, poleMass);
  }

  return returnMass;
}