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"

G4SampleResonance::minMassMapType G4SampleResonance::minMassCache;

G4double G4SampleResonance::GetMinimumMass(const G4ParticleDefinition* p) const
{

        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 = const_cast<G4ParticleDefinition*>(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);
                        (self->minMassCache)[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
{
        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
{
        // Chooses a mass randomly between minMass and maxMass
        //     according to a Breit-Wigner function with constant
        //     width gamma and pole poleMass

        if ( minMass > maxMass )
        {
                throw G4HadronicException(__FILE__, __LINE__,
                                "SampleResonanceMass: mass range negative (minMass>maxMass)");
        }

        G4double returnMass;

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

        return returnMass;
}

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