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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27 | // Hadronic Process: Nuclear De-excitations |
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28 | // by V. Lara |
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29 | |
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30 | |
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31 | #include "G4FermiPhaseSpaceDecay.hh" |
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32 | #include "G4HadronicException.hh" |
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33 | #include "Randomize.hh" |
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34 | |
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35 | #include <algorithm> |
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36 | #include <numeric> |
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37 | #include <functional> |
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38 | |
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39 | |
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40 | std::vector<G4LorentzVector*> * |
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41 | G4FermiPhaseSpaceDecay::KopylovNBodyDecay(const G4double M, const std::vector<G4double>& m) const |
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42 | // Calculates momentum for N fragments (Kopylov's method of sampling is used) |
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43 | { |
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44 | G4int N = m.size(); |
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45 | |
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46 | std::vector<G4LorentzVector*>* P = new std::vector<G4LorentzVector*>; |
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47 | P->insert(P->begin(), N, static_cast<G4LorentzVector*>(0)); |
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48 | |
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49 | G4double mtot = std::accumulate( m.begin(), m.end(), 0.0); |
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50 | G4double mu = mtot; |
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51 | G4double PFragMagCM = 0.0; |
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52 | G4double Mass = M; |
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53 | G4double T = M-mtot; |
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54 | G4LorentzVector PFragCM(0.0,0.0,0.0,0.0); |
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55 | G4LorentzVector PFragLab(0.0,0.0,0.0,0.0); |
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56 | G4LorentzVector PRestCM(0.0,0.0,0.0,0.0); |
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57 | G4LorentzVector PRestLab(0.0,0.0,0.0,Mass); |
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58 | |
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59 | for (G4int k = N-1; k > 0; k--) |
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60 | { |
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61 | mu -= m[k]; |
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62 | if (k>1) T *= BetaKopylov(k); |
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63 | else T = 0.0; |
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64 | |
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65 | G4double RestMass = mu + T; |
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66 | |
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67 | PFragMagCM = PtwoBody(Mass,m[k],RestMass); |
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68 | if (PFragMagCM < 0) |
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69 | { |
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70 | throw G4HadronicException(__FILE__, __LINE__, "G4FermiPhaseSpaceDecay::KopylovNBodyDecay: Error sampling fragments momenta!!"); |
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71 | } |
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72 | |
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73 | |
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74 | // Create a unit vector with a random direction isotropically distributed |
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75 | G4ParticleMomentum RandVector(IsotropicVector(PFragMagCM)); |
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76 | |
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77 | PFragCM.setVect(RandVector); |
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78 | PFragCM.setE(std::sqrt(RandVector.mag2()+m[k]*m[k])); |
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79 | |
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80 | PRestCM.setVect(-RandVector); |
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81 | PRestCM.setE(std::sqrt(RandVector.mag2()+RestMass*RestMass)); |
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82 | |
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83 | |
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84 | G4ThreeVector BoostV = PRestLab.boostVector(); |
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85 | |
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86 | PFragLab = PFragCM; |
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87 | PFragLab.boost(BoostV); |
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88 | PRestLab = PRestCM; |
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89 | PRestLab.boost(BoostV); |
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90 | |
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91 | P->operator[](k) = new G4LorentzVector(PFragLab); |
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92 | |
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93 | Mass = RestMass; |
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94 | } |
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95 | |
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96 | P->operator[](0) = new G4LorentzVector(PRestLab); |
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97 | |
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98 | return P; |
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99 | |
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100 | } |
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101 | |
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102 | |
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103 | |
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104 | std::vector<G4LorentzVector*> * |
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105 | G4FermiPhaseSpaceDecay::NBodyDecay(const G4double M, const std::vector<G4double>& m) const |
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106 | { |
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107 | // Number of fragments |
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108 | G4int N = m.size(); |
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109 | G4int i, j; |
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110 | // Total Daughters Mass |
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111 | G4double mtot = std::accumulate( m.begin(), m.end(), 0.0); |
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112 | G4double Emax = M - mtot + m[0]; |
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113 | G4double Emin = 0.0; |
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114 | G4double Wmax = 1.0; |
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115 | for (i = 1; i < N; i++) |
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116 | { |
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117 | Emax += m[i]; |
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118 | Emin += m[i-1]; |
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119 | Wmax *= this->PtwoBody(Emax, Emin, m[i]); |
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120 | } |
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121 | |
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122 | G4int ntries = 0; |
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123 | G4double weight = 1.0; |
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124 | std::vector<G4double> p(N); |
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125 | do |
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126 | { |
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127 | // Sample uniform random numbers in increasing order |
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128 | std::vector<G4double> r; |
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129 | r.reserve(N); |
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130 | r.push_back(0.0); |
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131 | for (i = 1; i < N-1; i++) r.push_back(G4UniformRand()); |
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132 | r.push_back(1.0); |
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133 | std::sort(r.begin(),r.end(), std::less<G4double>()); |
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134 | |
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135 | // Calculate virtual masses |
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136 | std::vector<G4double> vm(N); |
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137 | vm[0] = 0.0; |
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138 | std::partial_sum(m.begin(), m.end(), vm.begin()); |
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139 | std::transform(r.begin(), r.end(), r.begin(), std::bind2nd(std::multiplies<G4double>(), M-mtot)); |
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140 | std::transform(r.begin(), r.end(), vm.begin(), vm.begin(), std::plus<G4double>()); |
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141 | r.clear(); |
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142 | |
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143 | // Calcualte daughter momenta |
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144 | weight = 1.0; |
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145 | for (j = 0; j < N-1; j++) |
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146 | { |
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147 | p[j] = PtwoBody(vm[j+1],vm[j],m[j+1]); |
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148 | if (p[j] < 0.0) |
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149 | { |
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150 | G4cerr << "G4FermiPhaseSpaceDecay::Decay: Daughter momentum less than zero\n"; |
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151 | weight = 0.0; |
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152 | break; |
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153 | } |
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154 | else |
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155 | { |
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156 | weight *= p[j]; |
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157 | } |
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158 | } |
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159 | p[N-1] = PtwoBody(vm[N-2], m[N-2], m[N-1]); |
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160 | |
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161 | |
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162 | if (ntries++ > 1000000) |
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163 | { |
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164 | throw G4HadronicException(__FILE__, __LINE__, "G4FermiPhaseSpaceDecay::Decay: Cannot determine decay kinematics"); |
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165 | } |
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166 | } |
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167 | while ( weight < G4UniformRand()*Wmax ); |
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168 | |
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169 | std::vector<G4LorentzVector*> * P = new std::vector<G4LorentzVector*>; |
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170 | P->insert(P->begin(),N, static_cast<G4LorentzVector*>(0)); |
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171 | |
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172 | G4ParticleMomentum a3P = this->IsotropicVector(p[0]); |
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173 | |
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174 | P->operator[](0) = new G4LorentzVector( a3P, std::sqrt(a3P.mag2()+m[0]*m[0]) ); |
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175 | P->operator[](1) = new G4LorentzVector(-a3P, std::sqrt(a3P.mag2()+m[1]*m[1]) ); |
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176 | for (i = 2; i < N; i++) |
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177 | { |
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178 | a3P = this->IsotropicVector(p[i-1]); |
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179 | P->operator[](i) = new G4LorentzVector(a3P, std::sqrt(a3P.mag2() + m[i]*m[i])); |
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180 | G4ThreeVector Beta = (-1.0)*P->operator[](i)->boostVector(); |
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181 | // boost already created particles |
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182 | for (j = 0; j < i; j++) |
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183 | { |
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184 | P->operator[](j)->boost(Beta); |
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185 | } |
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186 | } |
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187 | |
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188 | return P; |
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189 | } |
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190 | |
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191 | |
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192 | |
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193 | |
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194 | std::vector<G4LorentzVector*> * |
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195 | G4FermiPhaseSpaceDecay:: |
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196 | TwoBodyDecay(const G4double M, const std::vector<G4double>& m) const |
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197 | { |
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198 | G4double m0 = m.front(); |
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199 | G4double m1 = m.back(); |
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200 | G4double psqr = this->PtwoBody(M,m0,m1); |
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201 | G4ParticleMomentum p = this->IsotropicVector(std::sqrt(psqr)); |
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202 | |
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203 | G4LorentzVector * P41 = new G4LorentzVector; |
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204 | P41->setVect(p); |
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205 | P41->setE(std::sqrt(psqr+m0*m0)); |
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206 | |
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207 | G4LorentzVector * P42 = new G4LorentzVector; |
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208 | P42->setVect(-p); |
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209 | P42->setE(std::sqrt(psqr+m1*m1)); |
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210 | |
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211 | std::vector<G4LorentzVector*> * result = new std::vector<G4LorentzVector*>; |
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212 | result->push_back(P41); |
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213 | result->push_back(P42); |
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214 | return result; |
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215 | } |
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216 | |
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217 | |
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218 | |
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219 | |
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220 | G4ParticleMomentum G4FermiPhaseSpaceDecay::IsotropicVector(const G4double Magnitude) const |
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221 | // Samples a isotropic random vectorwith a magnitud given by Magnitude. |
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222 | // By default Magnitude = 1.0 |
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223 | { |
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224 | G4double CosTheta = 1.0 - 2.0*G4UniformRand(); |
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225 | G4double SinTheta = std::sqrt(1.0 - CosTheta*CosTheta); |
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226 | G4double Phi = twopi*G4UniformRand(); |
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227 | G4ParticleMomentum Vector(Magnitude*std::cos(Phi)*SinTheta, |
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228 | Magnitude*std::sin(Phi)*SinTheta, |
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229 | Magnitude*CosTheta); |
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230 | return Vector; |
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231 | } |
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232 | |
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233 | |
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