Gabriele Cosmo
277 lines
10 KiB
C++
277 lines
10 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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//
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// ------------ G4AnnihiToMuPair physics process ------
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// by H.Burkhardt, S. Kelner and R. Kokoulin, November 2002
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// -----------------------------------------------------------------------------
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//
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......//
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//
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// 27.01.03 : first implementation (hbu)
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// 04.02.03 : cosmetic simplifications (mma)
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// 25.10.04 : migrade to new interfaces of ParticleChange (vi)
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// 28.02.18 : cross section now including SSS threshold factor
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//
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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#include "G4AnnihiToMuPair.hh"
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#include "G4Exp.hh"
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#include "G4LossTableManager.hh"
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#include "G4Material.hh"
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#include "G4MuonMinus.hh"
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#include "G4MuonPlus.hh"
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#include "G4PhysicalConstants.hh"
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#include "G4Positron.hh"
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#include "G4Step.hh"
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#include "G4SystemOfUnits.hh"
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#include "G4TauMinus.hh"
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#include "G4TauPlus.hh"
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#include "G4ios.hh"
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#include "Randomize.hh"
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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G4AnnihiToMuPair::G4AnnihiToMuPair(const G4String& processName,
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G4ProcessType type):G4VDiscreteProcess (processName, type)
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{
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//e+ Energy threshold
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if(processName == "AnnihiToTauPair") {
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SetProcessSubType(fAnnihilationToTauTau);
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part1 = G4TauPlus::TauPlus();
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part2 = G4TauMinus::TauMinus();
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fInfo = "e+e->tau+tau-";
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} else {
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SetProcessSubType(fAnnihilationToMuMu);
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part1 = G4MuonPlus::MuonPlus();
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part2 = G4MuonMinus::MuonMinus();
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}
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fMass = part1->GetPDGMass();
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fLowEnergyLimit = 2. * fMass * fMass / CLHEP::electron_mass_c2 - CLHEP::electron_mass_c2;
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// model is ok up to 1000 TeV due to neglected Z-interference
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fHighEnergyLimit = 1000. * TeV;
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fCurrentSigma = 0.0;
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fCrossSecFactor = 1.;
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fManager = G4LossTableManager::Instance();
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fManager->Register(this);
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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G4AnnihiToMuPair::~G4AnnihiToMuPair() // (empty) destructor
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{
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fManager->DeRegister(this);
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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G4bool G4AnnihiToMuPair::IsApplicable(const G4ParticleDefinition& particle)
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{
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return ( &particle == G4Positron::Positron() );
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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void G4AnnihiToMuPair::BuildPhysicsTable(const G4ParticleDefinition&)
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{
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PrintInfoDefinition();
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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void G4AnnihiToMuPair::SetCrossSecFactor(G4double fac)
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// Set the factor to artificially increase the cross section
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{
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fCrossSecFactor = fac;
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//G4cout << "The cross section for AnnihiToMuPair is artificially "
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// << "increased by the CrossSecFactor=" << fCrossSecFactor << G4endl;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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G4double G4AnnihiToMuPair::ComputeCrossSectionPerElectron(const G4double e)
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// Calculates the microscopic cross section in GEANT4 internal units.
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// It gives a good description from threshold to 1000 GeV
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{
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G4double rmuon = CLHEP::elm_coupling/fMass; //classical particle radius
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G4double sig0 = CLHEP::pi*rmuon*rmuon/3.; //constant in crossSection
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const G4double pial = CLHEP::pi*CLHEP::fine_structure_const; // pi * alphaQED
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if (e <= fLowEnergyLimit) return 0.0;
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const G4double xi = fLowEnergyLimit/e;
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const G4double piaxi = pial * std::sqrt(xi);
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G4double sigma = sig0 * xi * (1. + xi*0.5);
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//G4cout << "### xi= " << xi << " piaxi=" << piaxi << G4endl;
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// argument of the exponent below 0.1 or above 10
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// Sigma per electron * number of electrons per atom
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if(xi <= 1.0 - 100*piaxi*piaxi) {
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sigma *= std::sqrt(1.0 - xi);
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}
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else if (xi >= 1.0 - 0.01 * piaxi * piaxi) {
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sigma *= piaxi;
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}
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else {
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sigma *= piaxi / (1. - G4Exp(-piaxi / std::sqrt(1 - xi)));
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}
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// G4cout << "### sigma= " << sigma << G4endl;
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return sigma;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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G4double G4AnnihiToMuPair::ComputeCrossSectionPerAtom(const G4double energy,
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const G4double Z)
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{
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return ComputeCrossSectionPerElectron(energy)*Z;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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G4double G4AnnihiToMuPair::CrossSectionPerVolume(G4double energy,
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const G4Material* aMaterial)
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{
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return ComputeCrossSectionPerElectron(energy)*aMaterial->GetTotNbOfElectPerVolume();
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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G4double G4AnnihiToMuPair::GetMeanFreePath(const G4Track& aTrack,
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G4double, G4ForceCondition*)
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// returns the positron mean free path in GEANT4 internal units
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{
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const G4DynamicParticle* aDynamicPositron = aTrack.GetDynamicParticle();
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G4double energy = aDynamicPositron->GetTotalEnergy();
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const G4Material* aMaterial = aTrack.GetMaterial();
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// cross section before step
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fCurrentSigma = CrossSectionPerVolume(energy, aMaterial);
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// increase the CrossSection by CrossSecFactor (default 1)
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return (fCurrentSigma > 0.0) ? 1.0/(fCurrentSigma*fCrossSecFactor) : DBL_MAX;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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G4VParticleChange* G4AnnihiToMuPair::PostStepDoIt(const G4Track& aTrack,
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const G4Step& aStep)
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//
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// generation of e+e- -> mu+mu-
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//
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{
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aParticleChange.Initialize(aTrack);
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// current Positron energy and direction, return if energy too low
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const G4DynamicParticle *aDynamicPositron = aTrack.GetDynamicParticle();
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const G4double Mele = CLHEP::electron_mass_c2;
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G4double Epos = aDynamicPositron->GetTotalEnergy();
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G4double xs = CrossSectionPerVolume(Epos, aTrack.GetMaterial());
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// test of cross section
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if(xs > 0.0 && fCurrentSigma*G4UniformRand() > xs) {
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return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
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}
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const G4ThreeVector PosiDirection = aDynamicPositron->GetMomentumDirection();
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G4double xi = fLowEnergyLimit/Epos; // xi is always less than 1,
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// goes to 0 at high Epos
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// generate cost; probability function 1+cost**2 at high Epos
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//
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G4double cost;
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do { cost = 2.*G4UniformRand()-1.; }
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// Loop checking, 07-Aug-2015, Vladimir Ivanchenko
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while (2.*G4UniformRand() > 1.+xi+cost*cost*(1.-xi) );
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G4double sint = std::sqrt(1.-cost*cost);
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// generate phi
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//
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G4double phi = 2.*CLHEP::pi*G4UniformRand();
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G4double Ecm = std::sqrt(0.5*Mele*(Epos+Mele));
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G4double Pcm = std::sqrt(Ecm*Ecm - fMass*fMass);
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G4double beta = std::sqrt((Epos-Mele)/(Epos+Mele));
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G4double gamma = Ecm/Mele;
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G4double Pt = Pcm*sint;
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// energy and momentum of the muons in the Lab
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//
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G4double EmuPlus = gamma*(Ecm + cost*beta*Pcm);
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G4double EmuMinus = gamma*(Ecm - cost*beta*Pcm);
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G4double PmuPlusZ = gamma*(beta*Ecm + cost*Pcm);
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G4double PmuMinusZ = gamma*(beta*Ecm - cost*Pcm);
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G4double PmuPlusX = Pt*std::cos(phi);
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G4double PmuPlusY = Pt*std::sin(phi);
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G4double PmuMinusX =-PmuPlusX;
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G4double PmuMinusY =-PmuPlusY;
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// absolute momenta
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G4double PmuPlus = std::sqrt(Pt*Pt+PmuPlusZ *PmuPlusZ );
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G4double PmuMinus = std::sqrt(Pt*Pt+PmuMinusZ*PmuMinusZ);
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// mu+ mu- directions for Positron in z-direction
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//
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G4ThreeVector MuPlusDirection(PmuPlusX / PmuPlus, PmuPlusY / PmuPlus, PmuPlusZ / PmuPlus);
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G4ThreeVector MuMinusDirection(PmuMinusX / PmuMinus, PmuMinusY / PmuMinus, PmuMinusZ / PmuMinus);
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// rotate to actual Positron direction
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//
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MuPlusDirection.rotateUz(PosiDirection);
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MuMinusDirection.rotateUz(PosiDirection);
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aParticleChange.SetNumberOfSecondaries(2);
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// create G4DynamicParticle object for the particle1
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auto aParticle1 = new G4DynamicParticle(part1, MuPlusDirection, EmuPlus - fMass);
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aParticleChange.AddSecondary(aParticle1);
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// create G4DynamicParticle object for the particle2
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auto aParticle2 = new G4DynamicParticle(part2, MuMinusDirection, EmuMinus - fMass);
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aParticleChange.AddSecondary(aParticle2);
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// Kill the incident positron
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//
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aParticleChange.ProposeEnergy(0.);
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aParticleChange.ProposeTrackStatus(fStopAndKill);
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return &aParticleChange;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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void G4AnnihiToMuPair::PrintInfoDefinition()
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{
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G4String comments = fInfo + " annihilation, atomic e- at rest, SubType=";
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G4cout << G4endl << GetProcessName() << ": " << comments << GetProcessSubType() << G4endl;
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G4cout << " threshold at " << fLowEnergyLimit / CLHEP::GeV << " GeV"
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<< " good description up to " << fHighEnergyLimit / CLHEP::TeV << " TeV for all Z."
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<< G4endl;
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}
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//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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