[819] | 1 | // |
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| 2 | // ******************************************************************** |
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| 3 | // * License and Disclaimer * |
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| 4 | // * * |
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| 5 | // * The Geant4 software is copyright of the Copyright Holders of * |
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| 6 | // * the Geant4 Collaboration. It is provided under the terms and * |
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| 7 | // * conditions of the Geant4 Software License, included in the file * |
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| 8 | // * LICENSE and available at http://cern.ch/geant4/license . These * |
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| 9 | // * include a list of copyright holders. * |
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| 10 | // * * |
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| 11 | // * Neither the authors of this software system, nor their employing * |
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| 12 | // * institutes,nor the agencies providing financial support for this * |
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| 13 | // * work make any representation or warranty, express or implied, * |
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| 14 | // * regarding this software system or assume any liability for its * |
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| 15 | // * use. Please see the license in the file LICENSE and URL above * |
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| 16 | // * for the full disclaimer and the limitation of liability. * |
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| 17 | // * * |
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| 18 | // * This code implementation is the result of the scientific and * |
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| 19 | // * technical work of the GEANT4 collaboration. * |
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| 20 | // * By using, copying, modifying or distributing the software (or * |
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| 21 | // * any work based on the software) you agree to acknowledge its * |
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| 22 | // * use in resulting scientific publications, and indicate your * |
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| 23 | // * acceptance of all terms of the Geant4 Software license. * |
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| 24 | // ******************************************************************** |
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| 25 | // |
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| 26 | // |
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[1196] | 27 | // $Id: G4AnnihiToMuPair.cc,v 1.6 2009/11/09 18:24:07 vnivanch Exp $ |
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[1337] | 28 | // GEANT4 tag $Name: geant4-09-04-beta-01 $ |
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[819] | 29 | // |
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| 30 | // ------------ G4AnnihiToMuPair physics process ------ |
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| 31 | // by H.Burkhardt, S. Kelner and R. Kokoulin, November 2002 |
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| 32 | // ----------------------------------------------------------------------------- |
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| 33 | // |
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| 34 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......// |
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| 35 | // |
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| 36 | // 27.01.03 : first implementation (hbu) |
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| 37 | // 04.02.03 : cosmetic simplifications (mma) |
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| 38 | // 25.10.04 : migrade to new interfaces of ParticleChange (vi) |
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| 39 | // |
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| 40 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 41 | |
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| 42 | #include "G4AnnihiToMuPair.hh" |
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| 43 | |
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| 44 | #include "G4ios.hh" |
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| 45 | #include "Randomize.hh" |
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| 46 | |
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| 47 | #include "G4Positron.hh" |
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| 48 | #include "G4MuonPlus.hh" |
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| 49 | #include "G4MuonMinus.hh" |
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| 50 | #include "G4Material.hh" |
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| 51 | #include "G4Step.hh" |
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| 52 | |
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| 53 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 54 | |
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| 55 | using namespace std; |
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| 56 | |
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| 57 | G4AnnihiToMuPair::G4AnnihiToMuPair(const G4String& processName, |
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| 58 | G4ProcessType type):G4VDiscreteProcess (processName, type) |
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| 59 | { |
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| 60 | //e+ Energy threshold |
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| 61 | const G4double Mu_massc2 = G4MuonPlus::MuonPlus()->GetPDGMass(); |
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| 62 | LowestEnergyLimit = 2*Mu_massc2*Mu_massc2/electron_mass_c2 - electron_mass_c2; |
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| 63 | |
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| 64 | //modele ok up to 1000 TeV due to neglected Z-interference |
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| 65 | HighestEnergyLimit = 1000*TeV; |
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| 66 | |
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[1196] | 67 | CurrentSigma = 0.0; |
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[819] | 68 | CrossSecFactor = 1.; |
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[961] | 69 | SetProcessSubType(6); |
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| 70 | |
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[819] | 71 | } |
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| 72 | |
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| 73 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 74 | |
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| 75 | G4AnnihiToMuPair::~G4AnnihiToMuPair() // (empty) destructor |
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| 76 | { } |
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| 77 | |
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| 78 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 79 | |
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| 80 | G4bool G4AnnihiToMuPair::IsApplicable(const G4ParticleDefinition& particle) |
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| 81 | { |
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| 82 | return ( &particle == G4Positron::Positron() ); |
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| 83 | } |
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| 84 | |
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| 85 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 86 | |
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| 87 | void G4AnnihiToMuPair::BuildPhysicsTable(const G4ParticleDefinition&) |
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| 88 | // Build cross section and mean free path tables |
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| 89 | //here no tables, just calling PrintInfoDefinition |
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| 90 | { |
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[1196] | 91 | CurrentSigma = 0.0; |
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| 92 | PrintInfoDefinition(); |
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[819] | 93 | } |
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| 94 | |
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| 95 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 96 | |
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| 97 | void G4AnnihiToMuPair::SetCrossSecFactor(G4double fac) |
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| 98 | // Set the factor to artificially increase the cross section |
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| 99 | { |
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| 100 | CrossSecFactor = fac; |
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| 101 | G4cout << "The cross section for AnnihiToMuPair is artificially " |
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| 102 | << "increased by the CrossSecFactor=" << CrossSecFactor << G4endl; |
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| 103 | } |
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| 104 | |
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| 105 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 106 | |
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| 107 | G4double G4AnnihiToMuPair::ComputeCrossSectionPerAtom(G4double Epos, G4double Z) |
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| 108 | // Calculates the microscopic cross section in GEANT4 internal units. |
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| 109 | // It gives a good description from threshold to 1000 GeV |
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| 110 | { |
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| 111 | static const G4double Mmuon = G4MuonPlus::MuonPlus()->GetPDGMass(); |
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| 112 | static const G4double Rmuon = elm_coupling/Mmuon; //classical particle radius |
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| 113 | static const G4double Sig0 = pi*Rmuon*Rmuon/3.; //constant in crossSection |
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| 114 | |
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| 115 | G4double CrossSection = 0.; |
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| 116 | if (Epos < LowestEnergyLimit) return CrossSection; |
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| 117 | |
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| 118 | G4double xi = LowestEnergyLimit/Epos; |
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| 119 | G4double SigmaEl = Sig0*xi*(1.+xi/2.)*sqrt(1.-xi); // per electron |
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| 120 | CrossSection = SigmaEl*Z; // number of electrons per atom |
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| 121 | return CrossSection; |
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| 122 | } |
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| 123 | |
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| 124 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 125 | |
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[1196] | 126 | G4double G4AnnihiToMuPair::CrossSectionPerVolume(G4double PositronEnergy, |
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| 127 | const G4Material* aMaterial) |
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| 128 | { |
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| 129 | const G4ElementVector* theElementVector = aMaterial->GetElementVector(); |
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| 130 | const G4double* NbOfAtomsPerVolume = aMaterial->GetVecNbOfAtomsPerVolume(); |
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| 131 | |
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| 132 | G4double SIGMA = 0.0; |
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| 133 | |
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| 134 | for ( size_t i=0 ; i < aMaterial->GetNumberOfElements() ; ++i ) |
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| 135 | { |
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| 136 | G4double AtomicZ = (*theElementVector)[i]->GetZ(); |
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| 137 | SIGMA += NbOfAtomsPerVolume[i] * |
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| 138 | ComputeCrossSectionPerAtom(PositronEnergy,AtomicZ); |
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| 139 | } |
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| 140 | return SIGMA; |
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| 141 | } |
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| 142 | |
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| 143 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 144 | |
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[819] | 145 | G4double G4AnnihiToMuPair::GetMeanFreePath(const G4Track& aTrack, |
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| 146 | G4double, G4ForceCondition*) |
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| 147 | |
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| 148 | // returns the positron mean free path in GEANT4 internal units |
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| 149 | |
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| 150 | { |
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| 151 | const G4DynamicParticle* aDynamicPositron = aTrack.GetDynamicParticle(); |
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| 152 | G4double PositronEnergy = aDynamicPositron->GetKineticEnergy() |
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| 153 | +electron_mass_c2; |
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| 154 | G4Material* aMaterial = aTrack.GetMaterial(); |
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[1196] | 155 | CurrentSigma = CrossSectionPerVolume(PositronEnergy, aMaterial); |
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[819] | 156 | |
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[1196] | 157 | // increase the CrossSection by CrossSecFactor (default 1) |
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| 158 | G4double mfp = DBL_MAX; |
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| 159 | if(CurrentSigma > DBL_MIN) mfp = 1.0/(CurrentSigma*CrossSecFactor); |
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[819] | 160 | |
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[1196] | 161 | return mfp; |
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[819] | 162 | } |
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| 163 | |
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| 164 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 165 | |
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| 166 | G4VParticleChange* G4AnnihiToMuPair::PostStepDoIt(const G4Track& aTrack, |
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| 167 | const G4Step& aStep) |
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| 168 | // |
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| 169 | // generation of e+e- -> mu+mu- |
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| 170 | // |
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| 171 | { |
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| 172 | |
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| 173 | aParticleChange.Initialize(aTrack); |
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| 174 | static const G4double Mele=electron_mass_c2; |
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| 175 | static const G4double Mmuon=G4MuonPlus::MuonPlus()->GetPDGMass(); |
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| 176 | |
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| 177 | // current Positron energy and direction, return if energy too low |
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| 178 | const G4DynamicParticle *aDynamicPositron = aTrack.GetDynamicParticle(); |
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[1196] | 179 | G4double Epos = aDynamicPositron->GetKineticEnergy() + Mele; |
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[819] | 180 | |
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[1196] | 181 | // test of cross section |
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| 182 | if(CurrentSigma*G4UniformRand() > |
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| 183 | CrossSectionPerVolume(Epos, aTrack.GetMaterial())) |
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| 184 | { |
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| 185 | return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep); |
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| 186 | } |
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[819] | 187 | |
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[1196] | 188 | if (Epos < LowestEnergyLimit) { |
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[819] | 189 | return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep); |
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[1196] | 190 | } |
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[819] | 191 | |
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| 192 | G4ParticleMomentum PositronDirection = |
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| 193 | aDynamicPositron->GetMomentumDirection(); |
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| 194 | G4double xi = LowestEnergyLimit/Epos; // xi is always less than 1, |
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| 195 | // goes to 0 at high Epos |
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| 196 | |
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| 197 | // generate cost |
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| 198 | // |
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| 199 | G4double cost; |
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| 200 | do cost = 2.*G4UniformRand()-1.; |
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| 201 | while (2.*G4UniformRand() > 1.+xi+cost*cost*(1.-xi) ); |
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| 202 | //1+cost**2 at high Epos |
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| 203 | G4double sint = sqrt(1.-cost*cost); |
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| 204 | |
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| 205 | // generate phi |
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| 206 | // |
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| 207 | G4double phi=2.*pi*G4UniformRand(); |
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| 208 | |
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| 209 | G4double Ecm = sqrt(0.5*Mele*(Epos+Mele)); |
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| 210 | G4double Pcm = sqrt(Ecm*Ecm-Mmuon*Mmuon); |
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| 211 | G4double beta = sqrt((Epos-Mele)/(Epos+Mele)); |
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| 212 | G4double gamma = Ecm/Mele; // =sqrt((Epos+Mele)/(2.*Mele)); |
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| 213 | G4double Pt = Pcm*sint; |
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| 214 | |
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| 215 | // energy and momentum of the muons in the Lab |
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| 216 | // |
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| 217 | G4double EmuPlus = gamma*( Ecm+cost*beta*Pcm); |
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| 218 | G4double EmuMinus = gamma*( Ecm-cost*beta*Pcm); |
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| 219 | G4double PmuPlusZ = gamma*(beta*Ecm+cost* Pcm); |
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| 220 | G4double PmuMinusZ = gamma*(beta*Ecm-cost* Pcm); |
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| 221 | G4double PmuPlusX = Pt*cos(phi); |
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| 222 | G4double PmuPlusY = Pt*sin(phi); |
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| 223 | G4double PmuMinusX =-Pt*cos(phi); |
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| 224 | G4double PmuMinusY =-Pt*sin(phi); |
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| 225 | // absolute momenta |
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| 226 | G4double PmuPlus = sqrt(Pt*Pt+PmuPlusZ *PmuPlusZ ); |
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| 227 | G4double PmuMinus = sqrt(Pt*Pt+PmuMinusZ*PmuMinusZ); |
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| 228 | |
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| 229 | // mu+ mu- directions for Positron in z-direction |
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| 230 | // |
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| 231 | G4ThreeVector |
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| 232 | MuPlusDirection ( PmuPlusX/PmuPlus, PmuPlusY/PmuPlus, PmuPlusZ/PmuPlus ); |
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| 233 | G4ThreeVector |
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| 234 | MuMinusDirection(PmuMinusX/PmuMinus,PmuMinusY/PmuMinus,PmuMinusZ/PmuMinus); |
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| 235 | |
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| 236 | // rotate to actual Positron direction |
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| 237 | // |
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| 238 | MuPlusDirection.rotateUz(PositronDirection); |
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| 239 | MuMinusDirection.rotateUz(PositronDirection); |
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| 240 | |
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| 241 | aParticleChange.SetNumberOfSecondaries(2); |
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| 242 | // create G4DynamicParticle object for the particle1 |
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| 243 | G4DynamicParticle* aParticle1= new G4DynamicParticle( |
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| 244 | G4MuonPlus::MuonPlus(),MuPlusDirection,EmuPlus-Mmuon); |
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| 245 | aParticleChange.AddSecondary(aParticle1); |
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| 246 | // create G4DynamicParticle object for the particle2 |
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| 247 | G4DynamicParticle* aParticle2= new G4DynamicParticle( |
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| 248 | G4MuonMinus::MuonMinus(),MuMinusDirection,EmuMinus-Mmuon); |
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| 249 | aParticleChange.AddSecondary(aParticle2); |
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| 250 | |
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| 251 | // Kill the incident positron |
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| 252 | // |
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| 253 | aParticleChange.ProposeEnergy(0.); |
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| 254 | aParticleChange.ProposeTrackStatus(fStopAndKill); |
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| 255 | |
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| 256 | return &aParticleChange; |
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| 257 | } |
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| 258 | |
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| 259 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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| 260 | |
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| 261 | void G4AnnihiToMuPair::PrintInfoDefinition() |
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| 262 | { |
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[961] | 263 | G4String comments ="e+e->mu+mu- annihilation, atomic e- at rest, SubType=."; |
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| 264 | G4cout << G4endl << GetProcessName() << ": " << comments |
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| 265 | << GetProcessSubType() << G4endl; |
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| 266 | G4cout << " threshold at " << LowestEnergyLimit/GeV << " GeV" |
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[819] | 267 | << " good description up to " |
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| 268 | << HighestEnergyLimit/TeV << " TeV for all Z." << G4endl; |
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| 269 | } |
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| 270 | |
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| 271 | //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo...... |
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