1 | // HelicityMatrixElements.h is a part of the PYTHIA event generator. |
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2 | // Copyright (C) 2012 Philip Ilten, Torbjorn Sjostrand. |
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3 | // PYTHIA is licenced under the GNU GPL version 2, see COPYING for details. |
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4 | // Please respect the MCnet Guidelines, see GUIDELINES for details. |
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5 | |
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6 | // Header file for a number of physics classes used in tau decays. |
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7 | |
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8 | #ifndef Pythia8_HelicityMatrixElements_H |
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9 | #define Pythia8_HelicityMatrixElements_H |
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10 | |
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11 | #include "Basics.h" |
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12 | #include "Event.h" |
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13 | #include "HelicityBasics.h" |
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14 | #include "PythiaComplex.h" |
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15 | #include "PythiaStdlib.h" |
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16 | #include "StandardModel.h" |
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17 | |
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18 | namespace Pythia8 { |
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19 | |
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20 | //========================================================================== |
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21 | |
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22 | // The helicity matrix element class. |
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23 | |
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24 | class HelicityMatrixElement { |
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25 | |
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26 | public: |
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27 | |
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28 | // Constructor and destructor. |
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29 | HelicityMatrixElement() {}; |
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30 | virtual ~HelicityMatrixElement() {}; |
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31 | |
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32 | // Initialize the physics matrices and pointers. |
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33 | virtual void initPointers(ParticleData*, Couplings*); |
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34 | |
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35 | // Initialize the channel. |
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36 | virtual HelicityMatrixElement* initChannel(vector<HelicityParticle>&); |
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37 | |
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38 | // Calculate the matrix element weight for a decay. |
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39 | virtual double decayWeight(vector<HelicityParticle>&); |
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40 | |
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41 | // Calculate the maximum matrix element decay weight. |
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42 | virtual double decayWeightMax(vector<HelicityParticle>&) |
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43 | {return DECAYWEIGHTMAX;} |
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44 | |
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45 | // Calculate the helicity matrix element. |
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46 | virtual complex calculateME(vector<int>){return complex(0,0);} |
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47 | |
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48 | // Calculate the decay matrix for a particle. |
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49 | virtual void calculateD(vector<HelicityParticle>&); |
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50 | |
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51 | // Calculate the density matrix for a particle. |
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52 | virtual void calculateRho(unsigned int, vector<HelicityParticle>&); |
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53 | |
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54 | // Set a fermion line. |
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55 | void setFermionLine(int, HelicityParticle&, HelicityParticle&); |
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56 | |
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57 | // Calculate Breit-Wigner's with running widths and fixed. |
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58 | virtual complex breitWigner(double s, double M, double G); |
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59 | virtual complex sBreitWigner(double m0, double m1, double s, |
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60 | double M, double G); |
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61 | virtual complex pBreitWigner(double m0, double m1, double s, |
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62 | double M, double G); |
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63 | virtual complex dBreitWigner(double m0, double m1, double s, |
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64 | double M, double G); |
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65 | |
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66 | protected: |
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67 | |
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68 | // Maximum decay weight. WARNING: hardcoded constant. |
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69 | double DECAYWEIGHTMAX; |
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70 | |
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71 | // Physics matrices. |
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72 | vector< GammaMatrix > gamma; |
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73 | |
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74 | // Particle map vector. |
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75 | vector< int > pMap; |
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76 | |
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77 | // Particle ID vector. |
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78 | vector< int > pID; |
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79 | |
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80 | // Particle mass vector. |
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81 | vector< double > pM; |
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82 | |
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83 | // Wave functions. |
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84 | vector< vector< Wave4 > > u; |
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85 | |
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86 | // Initialize the constants for the matrix element (called by initChannel). |
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87 | virtual void initConstants() {}; |
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88 | |
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89 | // Initialize the wave functions (called by decayWeight and calculateRho/D). |
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90 | virtual void initWaves(vector<HelicityParticle>&) {}; |
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91 | |
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92 | // Pointer to particle data. |
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93 | ParticleData* particleDataPtr; |
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94 | |
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95 | // Pointer to Standard Model constants. |
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96 | Couplings* couplingsPtr; |
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97 | |
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98 | private: |
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99 | |
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100 | // Recursive sub-method to calculate the density matrix for a particle. |
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101 | void calculateRho(unsigned int, vector<HelicityParticle>&, |
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102 | vector<int>&, vector<int>&, unsigned int); |
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103 | |
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104 | // Recursive sub-method to calculate the decay matrix for a particle. |
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105 | void calculateD(vector<HelicityParticle>&, vector<int>&, vector<int>&, |
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106 | unsigned int); |
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107 | |
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108 | // Recursive sub-method to calculate the matrix element weight for a decay. |
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109 | void decayWeight(vector<HelicityParticle>&, vector<int>&, vector<int>&, |
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110 | complex&, unsigned int); |
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111 | |
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112 | // Calculate the product of the decay matrices for a hard process. |
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113 | complex calculateProductD(unsigned int, unsigned int, |
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114 | vector<HelicityParticle>&, vector<int>&, vector<int>&); |
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115 | |
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116 | // Calculate the product of the decay matrices for a decay process. |
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117 | complex calculateProductD(vector<HelicityParticle>&, |
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118 | vector<int>&, vector<int>&); |
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119 | |
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120 | }; |
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121 | |
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122 | //========================================================================== |
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123 | |
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124 | // Helicity matrix element for the hard process of two fermions -> W -> |
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125 | // two fermions. |
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126 | |
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127 | class HMETwoFermions2W2TwoFermions : public HelicityMatrixElement { |
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128 | |
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129 | public: |
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130 | |
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131 | void initWaves(vector<HelicityParticle>&); |
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132 | |
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133 | complex calculateME(vector<int>); |
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134 | |
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135 | }; |
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136 | |
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137 | //========================================================================== |
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138 | |
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139 | // Helicity matrix element for the hard process of two fermions -> |
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140 | // photon -> two fermions. |
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141 | |
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142 | class HMETwoFermions2Gamma2TwoFermions : public HelicityMatrixElement { |
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143 | |
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144 | public: |
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145 | |
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146 | void initWaves(vector<HelicityParticle>&); |
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147 | |
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148 | complex calculateME(vector<int>); |
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149 | |
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150 | private: |
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151 | |
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152 | // Fermion line charge and interaction energy. |
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153 | double p0Q, p2Q, s; |
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154 | |
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155 | }; |
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156 | |
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157 | //========================================================================== |
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158 | |
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159 | // Helicity matrix element for the hard process of two fermions -> |
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160 | // Z -> two fermions. |
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161 | |
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162 | class HMETwoFermions2Z2TwoFermions : public HelicityMatrixElement { |
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163 | |
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164 | public: |
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165 | |
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166 | void initConstants(); |
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167 | |
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168 | void initWaves(vector<HelicityParticle>&); |
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169 | |
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170 | complex calculateME(vector<int>); |
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171 | |
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172 | private: |
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173 | |
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174 | // Vector and axial couplings. |
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175 | double p0CA, p2CA, p0CV, p2CV; |
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176 | |
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177 | // Weinberg angle, Z width (on-shell), Z mass (on-shell), and s. |
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178 | double cos2W, sin2W, zG, zM, s; |
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179 | |
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180 | // Bool whether the incoming fermions are oriented with the z-axis. |
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181 | bool zaxis; |
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182 | |
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183 | }; |
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184 | |
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185 | //========================================================================== |
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186 | |
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187 | // Helicity matrix element for the hard process of two fermions -> |
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188 | // photon/Z -> two fermions with full interference. |
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189 | |
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190 | // In general the initPointers and initChannel methods should not need to be |
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191 | // redeclared, but in this case each matrix element needs to be initialized. |
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192 | |
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193 | class HMETwoFermions2GammaZ2TwoFermions : public HelicityMatrixElement { |
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194 | |
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195 | public: |
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196 | |
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197 | HelicityMatrixElement* initChannel(vector<HelicityParticle>&); |
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198 | |
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199 | void initPointers(ParticleData*, Couplings*); |
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200 | |
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201 | void initWaves(vector<HelicityParticle>&); |
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202 | |
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203 | complex calculateME(vector<int>); |
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204 | |
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205 | private: |
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206 | |
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207 | HMETwoFermions2Z2TwoFermions zHME; |
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208 | HMETwoFermions2Gamma2TwoFermions gHME; |
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209 | |
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210 | }; |
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211 | |
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212 | //========================================================================== |
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213 | |
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214 | // Helicity matrix element for the hard process of Z -> two fermions. |
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215 | |
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216 | class HMEZ2TwoFermions : public HelicityMatrixElement { |
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217 | |
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218 | public: |
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219 | |
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220 | void initConstants(); |
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221 | |
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222 | void initWaves(vector<HelicityParticle>&); |
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223 | |
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224 | complex calculateME(vector<int>); |
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225 | |
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226 | private: |
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227 | |
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228 | // Vector and axial couplings. |
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229 | double p2CA, p2CV; |
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230 | |
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231 | }; |
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232 | |
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233 | //========================================================================== |
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234 | |
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235 | // Helicity matrix element for the decay of a CP even Higgs -> two fermions. |
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236 | |
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237 | // Because the Higgs is spin zero the Higgs production mechanism is not |
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238 | // needed for calculating helicity density matrices. |
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239 | |
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240 | class HMEHiggsEven2TwoFermions : public HelicityMatrixElement { |
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241 | |
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242 | public: |
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243 | |
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244 | void initWaves(vector<HelicityParticle>&); |
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245 | |
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246 | complex calculateME(vector<int>); |
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247 | |
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248 | private: |
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249 | |
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250 | // Coupling constants of the fermions with the Higgs. |
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251 | double p2CA, p2CV; |
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252 | |
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253 | }; |
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254 | |
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255 | //========================================================================== |
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256 | |
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257 | // Helicity matrix element for the decay of a CP odd Higgs -> two fermions. |
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258 | |
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259 | class HMEHiggsOdd2TwoFermions : public HelicityMatrixElement { |
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260 | |
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261 | public: |
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262 | |
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263 | void initWaves(vector<HelicityParticle>&); |
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264 | |
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265 | complex calculateME(vector<int>); |
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266 | |
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267 | private: |
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268 | |
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269 | // Coupling constants of the fermions with the Higgs. |
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270 | double p2CA, p2CV; |
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271 | |
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272 | }; |
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273 | |
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274 | //========================================================================== |
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275 | |
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276 | // Helicity matrix element for the decay of a charged Higgs -> two fermions. |
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277 | |
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278 | class HMEHiggsCharged2TwoFermions : public HelicityMatrixElement { |
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279 | |
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280 | public: |
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281 | |
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282 | void initWaves(vector<HelicityParticle>&); |
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283 | |
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284 | complex calculateME(vector<int>); |
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285 | |
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286 | private: |
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287 | |
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288 | // Coupling constants of the fermions with the Higgs. |
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289 | double p2CA, p2CV; |
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290 | |
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291 | }; |
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292 | |
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293 | //========================================================================== |
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294 | |
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295 | // Helicity matrix element which provides an unpolarized on-diagonal helicity |
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296 | // density matrix. Used for unknown hard processes. |
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297 | |
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298 | class HMEUnpolarized : public HelicityMatrixElement { |
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299 | |
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300 | public: |
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301 | |
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302 | void calculateRho(unsigned int, vector<HelicityParticle>&); |
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303 | |
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304 | }; |
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305 | |
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306 | //========================================================================== |
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307 | |
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308 | // Base class for all tau decay helicity matrix elements. |
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309 | |
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310 | class HMETauDecay : public HelicityMatrixElement { |
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311 | |
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312 | public: |
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313 | |
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314 | virtual void initWaves(vector<HelicityParticle>&); |
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315 | |
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316 | virtual complex calculateME(vector<int>); |
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317 | |
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318 | virtual double decayWeightMax(vector<HelicityParticle>&); |
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319 | |
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320 | protected: |
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321 | |
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322 | virtual void initHadronicCurrent(vector<HelicityParticle>&) {}; |
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323 | |
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324 | virtual void calculateResonanceWeights(vector<double>&, vector<double>&, |
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325 | vector<complex>&); |
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326 | |
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327 | }; |
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328 | |
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329 | //========================================================================== |
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330 | |
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331 | // Helicity matrix element for a tau decaying into a single scalar meson. |
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332 | |
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333 | class HMETau2Meson : public HMETauDecay { |
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334 | |
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335 | public: |
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336 | |
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337 | void initConstants(); |
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338 | |
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339 | void initHadronicCurrent(vector<HelicityParticle>&); |
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340 | |
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341 | }; |
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342 | |
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343 | //========================================================================== |
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344 | |
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345 | // Helicity matrix element for a tau decaying into two leptons. |
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346 | |
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347 | class HMETau2TwoLeptons : public HMETauDecay { |
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348 | |
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349 | public: |
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350 | |
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351 | void initConstants(); |
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352 | |
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353 | void initWaves(vector<HelicityParticle>&); |
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354 | |
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355 | complex calculateME(vector<int>); |
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356 | |
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357 | }; |
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358 | |
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359 | //========================================================================== |
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360 | |
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361 | // Helicity matrix element for a tau decaying into two mesons through a |
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362 | // vector meson resonance. |
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363 | |
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364 | class HMETau2TwoMesonsViaVector : public HMETauDecay { |
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365 | |
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366 | public: |
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367 | |
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368 | void initConstants(); |
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369 | |
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370 | void initHadronicCurrent(vector<HelicityParticle>&); |
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371 | |
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372 | private: |
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373 | |
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374 | // Resonance masses, widths, and weights. |
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375 | vector<double> vecM, vecG, vecP, vecA; |
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376 | vector<complex> vecW; |
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377 | |
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378 | }; |
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379 | |
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380 | //========================================================================== |
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381 | |
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382 | // Helicity matrix element for a tau decay into two mesons through a vector |
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383 | // or scalar meson resonance. |
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384 | |
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385 | class HMETau2TwoMesonsViaVectorScalar : public HMETauDecay { |
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386 | |
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387 | public: |
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388 | |
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389 | void initConstants(); |
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390 | |
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391 | void initHadronicCurrent(vector<HelicityParticle>&); |
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392 | |
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393 | private: |
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394 | |
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395 | // Coupling to vector and scalar resonances. |
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396 | double scaC, vecC; |
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397 | |
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398 | // Resonance masses, widths, and weights. |
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399 | vector<double> scaM, scaG, scaP, scaA, vecM, vecG, vecP, vecA; |
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400 | vector<complex> scaW, vecW; |
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401 | |
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402 | }; |
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403 | |
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404 | //========================================================================== |
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405 | |
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406 | // Helicity matrix element for a tau decay into three mesons (base class). |
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407 | |
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408 | class HMETau2ThreeMesons : public HMETauDecay { |
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409 | |
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410 | public: |
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411 | |
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412 | void initConstants(); |
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413 | |
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414 | void initHadronicCurrent(vector<HelicityParticle>&); |
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415 | |
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416 | protected: |
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417 | |
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418 | // Decay mode of the tau. |
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419 | enum Mode{Pi0Pi0Pim, PimPimPip, Pi0PimK0b, PimPipKm, Pi0PimEta, PimKmKp, |
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420 | Pi0K0Km, KlPimKs, Pi0Pi0Km, KlKlPim, PimKsKs, PimK0bK0, Uknown}; |
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421 | Mode mode; |
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422 | |
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423 | // Initialize decay mode and resonance constants (called by initConstants). |
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424 | virtual void initMode(); |
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425 | virtual void initResonances() {;} |
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426 | |
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427 | // Initialize the momenta. |
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428 | virtual void initMomenta(vector<HelicityParticle>&); |
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429 | |
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430 | // Center of mass energies and momenta. |
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431 | double s1, s2, s3, s4; |
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432 | Wave4 q, q2, q3, q4; |
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433 | |
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434 | // Stored a1 Breit-Wigner (for speed). |
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435 | complex a1BW; |
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436 | |
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437 | // Form factors. |
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438 | virtual complex F1() {return complex(0, 0);} |
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439 | virtual complex F2() {return complex(0, 0);} |
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440 | virtual complex F3() {return complex(0, 0);} |
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441 | virtual complex F4() {return complex(0, 0);} |
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442 | |
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443 | // Phase space and Breit-Wigner for the a1. |
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444 | virtual double a1PhaseSpace(double); |
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445 | virtual complex a1BreitWigner(double); |
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446 | |
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447 | // Sum running p and fixed width Breit-Wigner resonances. |
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448 | complex T(double m0, double m1, double s, |
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449 | vector<double>& M, vector<double>& G, vector<double>& W); |
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450 | complex T(double s, vector<double>& M, vector<double>& G, vector<double>& W); |
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451 | |
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452 | }; |
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453 | |
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454 | //========================================================================== |
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455 | |
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456 | // Helicity matrix element for a tau decay into three pions. |
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457 | |
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458 | class HMETau2ThreePions : public HMETau2ThreeMesons { |
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459 | |
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460 | private: |
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461 | |
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462 | void initResonances(); |
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463 | |
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464 | // Resonance masses, widths, and weights. |
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465 | vector<double> rhoM, rhoG, rhoPp, rhoAp, rhoPd, rhoAd; |
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466 | double f0M, f0G, f0P, f0A, f2M, f2G, f2P, f2A; |
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467 | double sigM, sigG, sigP, sigA; |
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468 | vector<complex> rhoWp, rhoWd; |
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469 | complex f0W, f2W, sigW; |
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470 | |
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471 | // Form factors. |
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472 | complex F1(); |
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473 | complex F2(); |
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474 | complex F3(); |
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475 | |
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476 | // Running width and Breit-Wigner for the a1. |
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477 | double a1PhaseSpace(double); |
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478 | complex a1BreitWigner(double); |
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479 | |
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480 | }; |
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481 | |
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482 | //========================================================================== |
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483 | |
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484 | // Helicity matrix element for a tau decay into three mesons with kaons. |
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485 | |
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486 | class HMETau2ThreeMesonsWithKaons : public HMETau2ThreeMesons { |
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487 | |
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488 | private: |
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489 | |
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490 | void initResonances(); |
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491 | |
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492 | // Resonance masses, widths, and weights. |
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493 | vector<double> rhoMa, rhoGa, rhoWa, rhoMv, rhoGv, rhoWv; |
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494 | vector<double> kstarMa, kstarGa, kstarWa, kstarMv, kstarGv, kstarWv; |
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495 | vector<double> k1Ma, k1Ga, k1Wa, k1Mb, k1Gb, k1Wb; |
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496 | vector<double> omegaM, omegaG, omegaW; |
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497 | double kM, piM, piW; |
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498 | |
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499 | // Form factors. |
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500 | complex F1(); |
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501 | complex F2(); |
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502 | complex F4(); |
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503 | |
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504 | }; |
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505 | |
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506 | //========================================================================== |
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507 | |
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508 | // Helicity matrix element for a tau decay into generic three mesons. |
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509 | |
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510 | class HMETau2ThreeMesonsGeneric : public HMETau2ThreeMesons { |
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511 | |
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512 | private: |
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513 | |
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514 | void initResonances(); |
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515 | |
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516 | // Resonance masses, widths, and weights. |
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517 | vector<double> rhoMa, rhoGa, rhoWa, rhoMv, rhoGv, rhoWv; |
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518 | vector<double> kstarM, kstarG, kstarW, k1M, k1G, k1W; |
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519 | double kM, piM, piW; |
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520 | |
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521 | // Form factors. |
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522 | complex F1(); |
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523 | complex F2(); |
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524 | complex F4(); |
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525 | |
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526 | }; |
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527 | |
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528 | //========================================================================== |
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529 | |
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530 | // Helicity matrix element for a tau decay into two pions and a photon. |
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531 | |
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532 | class HMETau2TwoPionsGamma : public HMETauDecay { |
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533 | |
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534 | public: |
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535 | |
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536 | void initConstants(); |
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537 | |
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538 | void initWaves(vector<HelicityParticle>&); |
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539 | |
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540 | complex calculateME(vector<int>); |
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541 | |
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542 | protected: |
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543 | |
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544 | // Resonance masses, widths, and weights. |
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545 | vector<double> rhoM, rhoG, rhoW, omegaM, omegaG, omegaW; |
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546 | double piM; |
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547 | |
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548 | // Form factor. |
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549 | complex F(double s, vector<double> M, vector<double> G, vector<double> W); |
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550 | |
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551 | }; |
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552 | |
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553 | //========================================================================== |
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554 | |
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555 | // Helicity matrix element for a tau decay into four pions. |
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556 | |
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557 | class HMETau2FourPions : public HMETauDecay { |
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558 | |
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559 | public: |
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560 | |
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561 | void initConstants(); |
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562 | |
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563 | void initHadronicCurrent(vector<HelicityParticle>& p); |
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564 | |
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565 | private: |
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566 | |
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567 | // G-function form factors (fits). |
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568 | double G(int i, double s); |
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569 | |
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570 | // T-vector functions. |
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571 | Wave4 t1(Wave4&, Wave4&, Wave4&, Wave4&, Wave4&); |
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572 | Wave4 t2(Wave4&, Wave4&, Wave4&, Wave4&, Wave4&); |
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573 | Wave4 t3(Wave4&, Wave4&, Wave4&, Wave4&, Wave4&); |
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574 | |
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575 | // Breit-Wigner denominators for the intermediate mesons. |
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576 | complex a1D(double s); |
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577 | complex rhoD(double s); |
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578 | complex sigD(double s); |
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579 | complex omeD(double s); |
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580 | |
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581 | // Form factors needed for the a1, rho, and omega. |
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582 | double a1FormFactor(double s); |
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583 | double rhoFormFactor1(double s); |
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584 | double rhoFormFactor2(double s); |
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585 | double omeFormFactor(double s); |
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586 | |
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587 | // Masses and widths of the intermediate mesons. |
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588 | double a1M, a1G, rhoM, rhoG, sigM, sigG, omeM, omeG; |
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589 | |
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590 | // Masses for the pions (charged and neutral). |
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591 | double picM, pinM; |
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592 | |
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593 | // Amplitude, phases, and weights for mixing. |
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594 | double sigA, sigP, omeA, omeP; |
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595 | complex sigW, omeW; |
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596 | |
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597 | // Cut-off for a1 form factor. |
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598 | double lambda2; |
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599 | |
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600 | }; |
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601 | |
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602 | //========================================================================== |
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603 | |
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604 | // Helicity matrix element for a tau decaying into five pions. |
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605 | |
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606 | class HMETau2FivePions : public HMETauDecay { |
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607 | |
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608 | public: |
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609 | |
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610 | void initConstants(); |
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611 | |
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612 | void initHadronicCurrent(vector<HelicityParticle>&); |
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613 | |
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614 | private: |
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615 | |
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616 | // Hadronic currents. |
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617 | Wave4 Ja(Wave4 &q, Wave4 &q1, Wave4 &q2, Wave4 &q3, Wave4 &q4, Wave4 &q5); |
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618 | Wave4 Jb(Wave4 &q, Wave4 &q1, Wave4 &q2, Wave4 &q3, Wave4 &q4, Wave4 &q5); |
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619 | |
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620 | // Simplified s-wave Breit-Wigner assuming massless products. |
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621 | complex breitWigner(double s, double M, double G); |
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622 | |
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623 | // Masses and widths of intermediates. |
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624 | double a1M, a1G, rhoM, rhoG, omegaM, omegaG, omegaW, sigmaM, sigmaG, sigmaW; |
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625 | |
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626 | }; |
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627 | |
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628 | //========================================================================== |
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629 | |
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630 | // Helicity matrix element for a tau decay into flat phase space. |
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631 | |
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632 | class HMETau2PhaseSpace : public HMETauDecay { |
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633 | |
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634 | public: |
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635 | |
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636 | void initWaves(vector<HelicityParticle>&) {}; |
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637 | |
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638 | complex calculateME(vector<int>) {return 1;} |
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639 | |
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640 | void calculateD(vector<HelicityParticle>&) {}; |
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641 | |
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642 | void calculateRho(unsigned int, vector<HelicityParticle>&) {}; |
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643 | |
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644 | double decayWeight(vector<HelicityParticle>&) {return 1.0;} |
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645 | |
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646 | double decayWeightMax(vector<HelicityParticle>&) {return 1.0;} |
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647 | |
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648 | }; |
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649 | |
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650 | //========================================================================== |
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651 | |
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652 | } // end namespace Pythia8 |
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653 | |
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654 | #endif // end Pythia8_HelicityMatrixElements_H |
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