1 | // |
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2 | // ******************************************************************** |
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3 | // * License and Disclaimer * |
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15 | // * use. Please see the license in the file LICENSE and URL above * |
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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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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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27 | // $Id: G4AnnihiToMuPair.cc,v 1.6 2009/11/09 18:24:07 vnivanch Exp $ |
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28 | // GEANT4 tag $Name: geant4-09-04-beta-01 $ |
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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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67 | CurrentSigma = 0.0; |
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68 | CrossSecFactor = 1.; |
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69 | SetProcessSubType(6); |
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70 | |
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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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91 | CurrentSigma = 0.0; |
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92 | PrintInfoDefinition(); |
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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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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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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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155 | CurrentSigma = CrossSectionPerVolume(PositronEnergy, aMaterial); |
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156 | |
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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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160 | |
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161 | return mfp; |
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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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179 | G4double Epos = aDynamicPositron->GetKineticEnergy() + Mele; |
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180 | |
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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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187 | |
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188 | if (Epos < LowestEnergyLimit) { |
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189 | return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep); |
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190 | } |
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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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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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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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