1 | // |
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2 | // ******************************************************************** |
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3 | // * License and Disclaimer * |
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4 | // * * |
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6 | // * the Geant4 Collaboration. It is provided under the terms and * |
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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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27 | // $Id: G4TauLeptonicDecayChannel.cc,v 1.5 2006/06/29 19:26:18 gunter Exp $ |
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28 | // GEANT4 tag $Name: HEAD $ |
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29 | // |
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30 | // |
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31 | // ------------------------------------------------------------ |
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32 | // GEANT 4 class header file |
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33 | // |
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34 | // History: first implementation, based on object model of |
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35 | // 30 May 1997 H.Kurashige |
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36 | // |
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37 | // Fix bug in calcuration of electron energy in DecayIt 28 Feb. 01 H.Kurashige |
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38 | // ------------------------------------------------------------ |
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39 | |
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40 | #include "G4ParticleDefinition.hh" |
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41 | #include "G4DecayProducts.hh" |
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42 | #include "G4VDecayChannel.hh" |
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43 | #include "G4TauLeptonicDecayChannel.hh" |
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44 | #include "Randomize.hh" |
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45 | #include "G4LorentzVector.hh" |
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46 | #include "G4LorentzRotation.hh" |
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47 | |
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48 | |
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49 | G4TauLeptonicDecayChannel::G4TauLeptonicDecayChannel( |
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50 | const G4String& theParentName, |
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51 | G4double theBR, |
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52 | const G4String& theLeptonName) |
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53 | :G4VDecayChannel("Tau Leptonic Decay",1) |
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54 | { |
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55 | // set names for daughter particles |
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56 | if (theParentName == "tau+") { |
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57 | SetBR(theBR); |
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58 | SetParent("tau+"); |
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59 | SetNumberOfDaughters(3); |
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60 | if ((theLeptonName=="e-"||theLeptonName=="e+")){ |
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61 | SetDaughter(0, "e+"); |
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62 | SetDaughter(1, "nu_e"); |
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63 | SetDaughter(2, "anti_nu_tau"); |
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64 | } else { |
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65 | SetDaughter(0, "mu+"); |
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66 | SetDaughter(1, "nu_mu"); |
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67 | SetDaughter(2, "anti_nu_tau"); |
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68 | } |
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69 | } else if (theParentName == "tau-") { |
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70 | SetBR(theBR); |
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71 | SetParent("tau-"); |
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72 | SetNumberOfDaughters(3); |
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73 | if ((theLeptonName=="e-"||theLeptonName=="e+")){ |
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74 | SetDaughter(0, "e-"); |
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75 | SetDaughter(1, "anti_nu_e"); |
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76 | SetDaughter(2, "nu_tau"); |
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77 | } else { |
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78 | SetDaughter(0, "mu-"); |
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79 | SetDaughter(1, "anti_nu_mu"); |
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80 | SetDaughter(2, "nu_tau"); |
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81 | } |
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82 | } else { |
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83 | #ifdef G4VERBOSE |
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84 | if (GetVerboseLevel()>0) { |
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85 | G4cout << "G4TauLeptonicDecayChannel:: constructor :"; |
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86 | G4cout << " parent particle is not tau but "; |
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87 | G4cout << theParentName << G4endl; |
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88 | } |
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89 | #endif |
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90 | } |
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91 | } |
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92 | |
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93 | G4TauLeptonicDecayChannel::~G4TauLeptonicDecayChannel() |
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94 | { |
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95 | } |
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96 | |
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97 | G4DecayProducts *G4TauLeptonicDecayChannel::DecayIt(G4double) |
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98 | { |
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99 | // this version neglects muon polarization |
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100 | // assumes the pure V-A coupling |
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101 | // gives incorrect energy spectrum for neutrinos |
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102 | #ifdef G4VERBOSE |
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103 | if (GetVerboseLevel()>1) G4cout << "G4TauLeptonicDecayChannel::DecayIt "; |
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104 | #endif |
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105 | |
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106 | if (parent == 0) FillParent(); |
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107 | if (daughters == 0) FillDaughters(); |
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108 | |
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109 | // parent mass |
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110 | G4double parentmass = parent->GetPDGMass(); |
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111 | |
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112 | //daughters'mass |
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113 | G4double daughtermass[3]; |
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114 | for (G4int index=0; index<3; index++){ |
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115 | daughtermass[index] = daughters[index]->GetPDGMass(); |
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116 | } |
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117 | |
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118 | //create parent G4DynamicParticle at rest |
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119 | G4ThreeVector dummy; |
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120 | G4DynamicParticle * parentparticle = new G4DynamicParticle( parent, dummy, 0.0); |
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121 | //create G4Decayproducts |
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122 | G4DecayProducts *products = new G4DecayProducts(*parentparticle); |
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123 | delete parentparticle; |
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124 | |
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125 | // calculate daughter momentum |
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126 | G4double daughtermomentum[3]; |
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127 | G4double energy; |
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128 | |
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129 | // calcurate lepton momentum |
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130 | G4double pmax = (parentmass*parentmass-daughtermass[0]*daughtermass[0])/2./parentmass; |
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131 | G4double p, e; |
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132 | G4double r; |
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133 | do { |
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134 | // determine momentum/energy |
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135 | r = G4UniformRand(); |
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136 | p = pmax*G4UniformRand(); |
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137 | e = std::sqrt(p*p + daughtermass[0]*daughtermass[0]); |
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138 | } while (r > spectrum(p,e,parentmass,daughtermass[0]) ); |
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139 | energy = e- daughtermass[0]; |
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140 | |
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141 | //create daughter G4DynamicParticle |
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142 | // daughter 0 (lepton) |
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143 | daughtermomentum[0] = p; |
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144 | G4double costheta, sintheta, phi, sinphi, cosphi; |
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145 | costheta = 2.*G4UniformRand()-1.0; |
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146 | sintheta = std::sqrt((1.0-costheta)*(1.0+costheta)); |
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147 | phi = twopi*G4UniformRand()*rad; |
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148 | sinphi = std::sin(phi); |
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149 | cosphi = std::cos(phi); |
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150 | G4ThreeVector direction0(sintheta*cosphi,sintheta*sinphi,costheta); |
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151 | G4DynamicParticle * daughterparticle |
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152 | = new G4DynamicParticle( daughters[0], direction0*daughtermomentum[0]); |
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153 | products->PushProducts(daughterparticle); |
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154 | |
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155 | // daughter 1 ,2 (nutrinos) |
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156 | // create neutrinos in the C.M frame of two neutrinos |
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157 | G4double energy2 = parentmass-e; |
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158 | G4double vmass = std::sqrt((energy2-daughtermomentum[0])*(energy2+daughtermomentum[0])); |
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159 | G4double beta = -1.0*daughtermomentum[0]/energy2; |
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160 | G4double costhetan = 2.*G4UniformRand()-1.0; |
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161 | G4double sinthetan = std::sqrt((1.0-costhetan)*(1.0+costhetan)); |
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162 | G4double phin = twopi*G4UniformRand()*rad; |
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163 | G4double sinphin = std::sin(phin); |
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164 | G4double cosphin = std::cos(phin); |
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165 | |
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166 | G4ThreeVector direction1(sinthetan*cosphin,sinthetan*sinphin,costhetan); |
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167 | G4DynamicParticle * daughterparticle1 |
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168 | = new G4DynamicParticle( daughters[1], direction1*(vmass/2.)); |
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169 | G4DynamicParticle * daughterparticle2 |
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170 | = new G4DynamicParticle( daughters[2], direction1*(-1.0*vmass/2.)); |
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171 | |
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172 | // boost to the muon rest frame |
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173 | G4LorentzVector p4; |
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174 | p4 = daughterparticle1->Get4Momentum(); |
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175 | p4.boost( direction0.x()*beta, direction0.y()*beta, direction0.z()*beta); |
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176 | daughterparticle1->Set4Momentum(p4); |
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177 | p4 = daughterparticle2->Get4Momentum(); |
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178 | p4.boost( direction0.x()*beta, direction0.y()*beta, direction0.z()*beta); |
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179 | daughterparticle2->Set4Momentum(p4); |
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180 | products->PushProducts(daughterparticle1); |
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181 | products->PushProducts(daughterparticle2); |
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182 | daughtermomentum[1] = daughterparticle1->GetTotalMomentum(); |
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183 | daughtermomentum[2] = daughterparticle2->GetTotalMomentum(); |
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184 | |
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185 | |
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186 | // output message |
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187 | #ifdef G4VERBOSE |
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188 | if (GetVerboseLevel()>1) { |
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189 | G4cout << "G4TauLeptonicDecayChannel::DecayIt "; |
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190 | G4cout << " create decay products in rest frame " <<G4endl; |
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191 | products->DumpInfo(); |
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192 | } |
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193 | #endif |
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194 | return products; |
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195 | } |
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196 | |
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197 | |
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198 | |
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199 | |
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200 | G4double G4TauLeptonicDecayChannel::spectrum(G4double p, |
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201 | G4double e, |
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202 | G4double mtau, |
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203 | G4double ml) |
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204 | { |
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205 | G4double f1; |
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206 | f1 = 3.0*e*(mtau*mtau+ml*ml)-4.0*mtau*e*e-2.0*mtau*ml*ml; |
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207 | return p*(f1)/(mtau*mtau*mtau*mtau)/(0.6); |
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208 | } |
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209 | |
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210 | |
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211 | |
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