1 | // SigmaEW.cc is a part of the PYTHIA event generator. |
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2 | // Copyright (C) 2012 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 | // Function definitions (not found in the header) for the |
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7 | // electroweak simulation classes (including photon processes). |
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8 | |
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9 | #include "SigmaEW.h" |
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10 | |
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11 | namespace Pythia8 { |
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12 | |
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13 | //========================================================================== |
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14 | |
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15 | // Sigma2qg2qgamma class. |
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16 | // Cross section for q g -> q gamma. |
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17 | |
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18 | //-------------------------------------------------------------------------- |
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19 | |
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20 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
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21 | |
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22 | void Sigma2qg2qgamma::sigmaKin() { |
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23 | |
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24 | // Calculate kinematics dependence. |
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25 | sigUS = (1./3.) * (sH2 + uH2) / (-sH * uH); |
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26 | |
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27 | // Answer. |
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28 | sigma0 = (M_PI/sH2) * alpS * alpEM * sigUS; |
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29 | |
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30 | } |
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31 | |
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32 | //-------------------------------------------------------------------------- |
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33 | |
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34 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
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35 | |
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36 | double Sigma2qg2qgamma::sigmaHat() { |
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37 | |
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38 | // Incoming flavour gives charge factor. |
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39 | int idNow = (id2 == 21) ? id1 : id2; |
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40 | double eNow = couplingsPtr->ef( abs(idNow) ); |
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41 | return sigma0 * pow2(eNow); |
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42 | |
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43 | } |
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44 | |
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45 | //-------------------------------------------------------------------------- |
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46 | |
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47 | // Select identity, colour and anticolour. |
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48 | |
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49 | void Sigma2qg2qgamma::setIdColAcol() { |
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50 | |
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51 | // Construct outgoing flavours. |
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52 | id3 = (id1 == 21) ? 22 : id1; |
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53 | id4 = (id2 == 21) ? 22 : id2; |
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54 | setId( id1, id2, id3, id4); |
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55 | |
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56 | // Colour flow topology. Swap if first is gluon, or when antiquark. |
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57 | setColAcol( 1, 0, 2, 1, 2, 0, 0, 0); |
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58 | if (id1 == 21) swapCol1234(); |
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59 | if (id1 < 0 || id2 < 0) swapColAcol(); |
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60 | |
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61 | } |
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62 | |
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63 | //========================================================================== |
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64 | |
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65 | // Sigma2qqbar2ggamma class. |
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66 | // Cross section for q qbar -> g gamma. |
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67 | |
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68 | //-------------------------------------------------------------------------- |
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69 | |
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70 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
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71 | |
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72 | void Sigma2qqbar2ggamma::sigmaKin() { |
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73 | |
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74 | // Calculate kinematics dependence. |
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75 | double sigTU = (8./9.) * (tH2 + uH2) / (tH * uH); |
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76 | |
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77 | // Answer. |
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78 | sigma0 = (M_PI/sH2) * alpS * alpEM * sigTU; |
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79 | |
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80 | } |
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81 | |
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82 | //-------------------------------------------------------------------------- |
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83 | |
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84 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
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85 | |
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86 | double Sigma2qqbar2ggamma::sigmaHat() { |
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87 | |
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88 | // Incoming flavour gives charge factor. |
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89 | double eNow = couplingsPtr->ef( abs(id1) ); |
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90 | return sigma0 * pow2(eNow); |
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91 | |
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92 | } |
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93 | |
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94 | //-------------------------------------------------------------------------- |
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95 | |
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96 | // Select identity, colour and anticolour. |
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97 | |
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98 | void Sigma2qqbar2ggamma::setIdColAcol() { |
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99 | |
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100 | // Outgoing flavours trivial. |
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101 | setId( id1, id2, 21, 22); |
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102 | |
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103 | // One colour flow topology. Swap if first is antiquark. |
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104 | setColAcol( 1, 0, 0, 2, 1, 2, 0, 0); |
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105 | if (id1 < 0) swapColAcol(); |
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106 | |
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107 | } |
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108 | |
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109 | //========================================================================== |
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110 | |
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111 | // Sigma2gg2ggamma class. |
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112 | // Cross section for g g -> g gamma. |
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113 | // Proceeds through a quark box, by default using 5 massless quarks. |
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114 | |
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115 | //-------------------------------------------------------------------------- |
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116 | |
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117 | // Initialize process, especially parton-flux object. |
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118 | |
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119 | void Sigma2gg2ggamma::initProc() { |
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120 | |
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121 | // Maximum quark flavour in loop. |
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122 | int nQuarkLoop = settingsPtr->mode("PromptPhoton:nQuarkLoop"); |
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123 | |
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124 | // Calculate charge factor from the allowed quarks in the box. |
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125 | chargeSum = - 1./3. + 2./3. - 1./3.; |
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126 | if (nQuarkLoop >= 4) chargeSum += 2./3.; |
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127 | if (nQuarkLoop >= 5) chargeSum -= 1./3.; |
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128 | if (nQuarkLoop >= 6) chargeSum += 2./3.; |
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129 | |
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130 | } |
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131 | |
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132 | //-------------------------------------------------------------------------- |
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133 | |
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134 | // Evaluate d(sigmaHat)/d(tHat). |
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135 | |
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136 | void Sigma2gg2ggamma::sigmaKin() { |
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137 | |
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138 | // Logarithms of Mandelstam variable ratios. |
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139 | double logST = log( -sH / tH ); |
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140 | double logSU = log( -sH / uH ); |
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141 | double logTU = log( tH / uH ); |
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142 | |
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143 | // Real and imaginary parts of separate amplitudes. |
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144 | double b0stuRe = 1. + (tH - uH) / sH * logTU |
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145 | + 0.5 * (tH2 + uH2) / sH2 * (pow2(logTU) + pow2(M_PI)); |
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146 | double b0stuIm = 0.; |
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147 | double b0tsuRe = 1. + (sH - uH) / tH * logSU |
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148 | + 0.5 * (sH2 + uH2) / tH2 * pow2(logSU); |
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149 | double b0tsuIm = -M_PI * ( (sH - uH) / tH + (sH2 + uH2) / tH2 * logSU); |
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150 | double b0utsRe = 1. + (sH - tH) / uH * logST |
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151 | + 0.5 * (sH2 + tH2) / uH2 * pow2(logST); |
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152 | double b0utsIm = -M_PI * ( (sH - tH) / uH + (sH2 + tH2) / uH2 * logST); |
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153 | double b1stuRe = -1.; |
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154 | double b1stuIm = 0.; |
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155 | double b2stuRe = -1.; |
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156 | double b2stuIm = 0.; |
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157 | |
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158 | // Calculate kinematics dependence. |
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159 | double sigBox = pow2(b0stuRe) + pow2(b0stuIm) + pow2(b0tsuRe) |
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160 | + pow2(b0tsuIm) + pow2(b0utsRe) + pow2(b0utsIm) + 4. * pow2(b1stuRe) |
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161 | + 4. * pow2(b1stuIm) + pow2(b2stuRe) + pow2(b2stuIm); |
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162 | |
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163 | // Answer. |
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164 | sigma = (5. / (192. * M_PI * sH2)) * pow2(chargeSum) |
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165 | * pow3(alpS) * alpEM * sigBox; |
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166 | |
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167 | } |
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168 | |
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169 | //-------------------------------------------------------------------------- |
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170 | |
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171 | // Select identity, colour and anticolour. |
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172 | |
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173 | void Sigma2gg2ggamma::setIdColAcol() { |
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174 | |
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175 | // Flavours and colours are trivial. |
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176 | setId( id1, id2, 21, 22); |
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177 | setColAcol( 1, 2, 2, 3, 1, 3, 0, 0); |
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178 | if (rndmPtr->flat() > 0.5) swapColAcol(); |
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179 | |
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180 | } |
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181 | |
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182 | //========================================================================== |
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183 | |
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184 | // Sigma2ffbar2gammagamma class. |
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185 | // Cross section for q qbar -> gamma gamma. |
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186 | |
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187 | //-------------------------------------------------------------------------- |
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188 | |
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189 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
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190 | |
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191 | void Sigma2ffbar2gammagamma::sigmaKin() { |
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192 | |
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193 | // Calculate kinematics dependence. |
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194 | sigTU = 2. * (tH2 + uH2) / (tH * uH); |
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195 | |
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196 | // Answer contains factor 1/2 from identical photons. |
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197 | sigma0 = (M_PI/sH2) * pow2(alpEM) * 0.5 * sigTU; |
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198 | |
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199 | } |
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200 | |
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201 | //-------------------------------------------------------------------------- |
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202 | |
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203 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
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204 | |
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205 | double Sigma2ffbar2gammagamma::sigmaHat() { |
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206 | |
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207 | // Incoming flavour gives charge and colour factors. |
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208 | double eNow = couplingsPtr->ef( abs(id1) ); |
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209 | double colFac = (abs(id1) < 9) ? 1. / 3. : 1.; |
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210 | return sigma0 * pow4(eNow) * colFac; |
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211 | |
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212 | } |
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213 | |
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214 | //-------------------------------------------------------------------------- |
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215 | |
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216 | // Select identity, colour and anticolour. |
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217 | |
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218 | void Sigma2ffbar2gammagamma::setIdColAcol() { |
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219 | |
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220 | // Outgoing flavours trivial. |
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221 | setId( id1, id2, 22, 22); |
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222 | |
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223 | // No colours at all or one flow topology. Swap if first is antiquark. |
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224 | if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0); |
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225 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
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226 | if (id1 < 0) swapColAcol(); |
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227 | |
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228 | } |
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229 | |
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230 | //========================================================================== |
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231 | |
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232 | // Sigma2gg2gammagamma class. |
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233 | // Cross section for g g -> gamma gamma. |
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234 | // Proceeds through a quark box, by default using 5 massless quarks. |
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235 | |
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236 | //-------------------------------------------------------------------------- |
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237 | |
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238 | // Initialize process. |
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239 | |
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240 | void Sigma2gg2gammagamma::initProc() { |
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241 | |
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242 | // Maximum quark flavour in loop. |
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243 | int nQuarkLoop = settingsPtr->mode("PromptPhoton:nQuarkLoop"); |
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244 | |
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245 | // Calculate charge factor from the allowed quarks in the box. |
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246 | charge2Sum = 1./9. + 4./9. + 1./9.; |
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247 | if (nQuarkLoop >= 4) charge2Sum += 4./9.; |
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248 | if (nQuarkLoop >= 5) charge2Sum += 1./9.; |
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249 | if (nQuarkLoop >= 6) charge2Sum += 4./9.; |
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250 | |
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251 | } |
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252 | |
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253 | //-------------------------------------------------------------------------- |
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254 | |
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255 | // Evaluate d(sigmaHat)/d(tHat). |
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256 | |
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257 | void Sigma2gg2gammagamma::sigmaKin() { |
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258 | |
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259 | // Logarithms of Mandelstam variable ratios. |
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260 | double logST = log( -sH / tH ); |
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261 | double logSU = log( -sH / uH ); |
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262 | double logTU = log( tH / uH ); |
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263 | |
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264 | // Real and imaginary parts of separate amplitudes. |
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265 | double b0stuRe = 1. + (tH - uH) / sH * logTU |
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266 | + 0.5 * (tH2 + uH2) / sH2 * (pow2(logTU) + pow2(M_PI)); |
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267 | double b0stuIm = 0.; |
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268 | double b0tsuRe = 1. + (sH - uH) / tH * logSU |
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269 | + 0.5 * (sH2 + uH2) / tH2 * pow2(logSU); |
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270 | double b0tsuIm = -M_PI * ( (sH - uH) / tH + (sH2 + uH2) / tH2 * logSU); |
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271 | double b0utsRe = 1. + (sH - tH) / uH * logST |
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272 | + 0.5 * (sH2 + tH2) / uH2 * pow2(logST); |
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273 | double b0utsIm = -M_PI * ( (sH - tH) / uH + (sH2 + tH2) / uH2 * logST); |
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274 | double b1stuRe = -1.; |
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275 | double b1stuIm = 0.; |
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276 | double b2stuRe = -1.; |
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277 | double b2stuIm = 0.; |
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278 | |
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279 | // Calculate kinematics dependence. |
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280 | double sigBox = pow2(b0stuRe) + pow2(b0stuIm) + pow2(b0tsuRe) |
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281 | + pow2(b0tsuIm) + pow2(b0utsRe) + pow2(b0utsIm) + 4. * pow2(b1stuRe) |
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282 | + 4. * pow2(b1stuIm) + pow2(b2stuRe) + pow2(b2stuIm); |
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283 | |
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284 | // Answer contains factor 1/2 from identical photons. |
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285 | sigma = (0.5 / (16. * M_PI * sH2)) * pow2(charge2Sum) |
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286 | * pow2(alpS) * pow2(alpEM) * sigBox; |
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287 | |
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288 | } |
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289 | |
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290 | //-------------------------------------------------------------------------- |
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291 | |
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292 | // Select identity, colour and anticolour. |
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293 | |
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294 | void Sigma2gg2gammagamma::setIdColAcol() { |
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295 | |
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296 | // Flavours and colours are trivial. |
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297 | setId( id1, id2, 22, 22); |
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298 | setColAcol( 1, 2, 2, 1, 0, 0, 0, 0); |
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299 | |
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300 | } |
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301 | |
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302 | //========================================================================== |
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303 | |
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304 | // Sigma2ff2fftgmZ class. |
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305 | // Cross section for f f' -> f f' via t-channel gamma*/Z0 exchange |
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306 | // (f is quark or lepton). |
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307 | |
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308 | //-------------------------------------------------------------------------- |
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309 | |
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310 | // Initialize process. |
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311 | |
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312 | void Sigma2ff2fftgmZ::initProc() { |
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313 | |
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314 | // Store Z0 mass for propagator. Common coupling factor. |
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315 | gmZmode = settingsPtr->mode("WeakZ0:gmZmode"); |
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316 | mZ = particleDataPtr->m0(23); |
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317 | mZS = mZ*mZ; |
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318 | thetaWRat = 1. / (16. * couplingsPtr->sin2thetaW() |
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319 | * couplingsPtr->cos2thetaW()); |
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320 | |
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321 | } |
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322 | |
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323 | //-------------------------------------------------------------------------- |
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324 | |
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325 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
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326 | |
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327 | void Sigma2ff2fftgmZ::sigmaKin() { |
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328 | |
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329 | // Cross section part common for all incoming flavours. |
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330 | double sigma0 = (M_PI / sH2) * pow2(alpEM); |
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331 | |
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332 | // Kinematical functions for gamma-gamma, gamma-Z and Z-Z parts. |
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333 | sigmagmgm = sigma0 * 2. * (sH2 + uH2) / tH2; |
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334 | sigmagmZ = sigma0 * 4. * thetaWRat * sH2 / (tH * (tH - mZS)); |
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335 | sigmaZZ = sigma0 * 2. * pow2(thetaWRat) * sH2 / pow2(tH - mZS); |
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336 | if (gmZmode == 1) {sigmagmZ = 0.; sigmaZZ = 0.;} |
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337 | if (gmZmode == 2) {sigmagmgm = 0.; sigmagmZ = 0.;} |
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338 | |
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339 | } |
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340 | |
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341 | //-------------------------------------------------------------------------- |
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342 | |
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343 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
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344 | |
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345 | double Sigma2ff2fftgmZ::sigmaHat() { |
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346 | |
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347 | // Couplings for current flavour combination. |
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348 | int id1Abs = abs(id1); |
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349 | double e1 = couplingsPtr->ef(id1Abs); |
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350 | double v1 = couplingsPtr->vf(id1Abs); |
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351 | double a1 = couplingsPtr->af(id1Abs); |
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352 | int id2Abs = abs(id2); |
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353 | double e2 = couplingsPtr->ef(id2Abs); |
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354 | double v2 = couplingsPtr->vf(id2Abs); |
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355 | double a2 = couplingsPtr->af(id2Abs); |
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356 | |
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357 | // Distinguish same-sign and opposite-sign fermions. |
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358 | double epsi = (id1 * id2 > 0) ? 1. : -1.; |
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359 | |
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360 | // Flavour-dependent cross section. |
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361 | double sigma = sigmagmgm * pow2(e1 * e2) |
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362 | + sigmagmZ * e1 * e2 * (v1 * v2 * (1. + uH2 / sH2) |
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363 | + a1 * a2 * epsi * (1. - uH2 / sH2)) |
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364 | + sigmaZZ * ((v1*v1 + a1*a1) * (v2*v2 + a2*a2) * (1. + uH2 / sH2) |
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365 | + 4. * v1 * a1 * v2 * a2 * epsi * (1. - uH2 / sH2)); |
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366 | |
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367 | // Spin-state extra factor 2 per incoming neutrino. |
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368 | if (id1Abs == 12 || id1Abs == 14 || id1Abs == 16) sigma *= 2.; |
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369 | if (id2Abs == 12 || id2Abs == 14 || id2Abs == 16) sigma *= 2.; |
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370 | |
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371 | // Answer. |
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372 | return sigma; |
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373 | |
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374 | } |
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375 | |
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376 | //-------------------------------------------------------------------------- |
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377 | |
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378 | // Select identity, colour and anticolour. |
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379 | |
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380 | void Sigma2ff2fftgmZ::setIdColAcol() { |
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381 | |
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382 | // Trivial flavours: out = in. |
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383 | setId( id1, id2, id1, id2); |
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384 | |
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385 | // Colour flow topologies. Swap when antiquarks. |
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386 | if (abs(id1) < 9 && abs(id2) < 9 && id1*id2 > 0) |
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387 | setColAcol( 1, 0, 2, 0, 1, 0, 2, 0); |
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388 | else if (abs(id1) < 9 && abs(id2) < 9) |
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389 | setColAcol( 1, 0, 0, 2, 1, 0, 0, 2); |
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390 | else if (abs(id1) < 9) setColAcol( 1, 0, 0, 0, 1, 0, 0, 0); |
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391 | else if (abs(id2) < 9) setColAcol( 0, 0, 1, 0, 0, 0, 1, 0); |
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392 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
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393 | if ( (abs(id1) < 9 && id1 < 0) || (abs(id1) > 10 && id2 < 0) ) |
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394 | swapColAcol(); |
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395 | |
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396 | } |
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397 | |
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398 | //========================================================================== |
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399 | |
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400 | // Sigma2ff2fftW class. |
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401 | // Cross section for f_1 f_2 -> f_3 f_4 via t-channel W+- exchange |
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402 | // (f is quark or lepton). |
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403 | |
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404 | //-------------------------------------------------------------------------- |
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405 | |
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406 | // Initialize process. |
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407 | |
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408 | void Sigma2ff2fftW::initProc() { |
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409 | |
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410 | // Store W+- mass for propagator. Common coupling factor. |
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411 | mW = particleDataPtr->m0(24); |
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412 | mWS = mW*mW; |
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413 | thetaWRat = 1. / (4. * couplingsPtr->sin2thetaW()); |
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414 | |
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415 | } |
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416 | |
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417 | //-------------------------------------------------------------------------- |
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418 | |
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419 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
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420 | |
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421 | void Sigma2ff2fftW::sigmaKin() { |
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422 | |
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423 | // Cross section part common for all incoming flavours. |
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424 | sigma0 = (M_PI / sH2) * pow2(alpEM * thetaWRat) |
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425 | * 4. * sH2 / pow2(tH - mWS); |
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426 | |
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427 | } |
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428 | |
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429 | //-------------------------------------------------------------------------- |
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430 | |
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431 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
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432 | |
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433 | double Sigma2ff2fftW::sigmaHat() { |
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434 | |
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435 | // Some flavour combinations not possible. |
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436 | int id1Abs = abs(id1); |
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437 | int id2Abs = abs(id2); |
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438 | if ( (id1Abs%2 == id2Abs%2 && id1 * id2 > 0) |
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439 | || (id1Abs%2 != id2Abs%2 && id1 * id2 < 0) ) return 0.; |
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440 | |
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441 | // Basic cross section. |
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442 | double sigma = sigma0; |
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443 | if (id1 * id2 < 0) sigma *= uH2 / sH2; |
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444 | |
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445 | // CKM factors for final states. |
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446 | sigma *= couplingsPtr->V2CKMsum(id1Abs) * couplingsPtr->V2CKMsum(id2Abs); |
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447 | |
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448 | // Spin-state extra factor 2 per incoming neutrino. |
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449 | if (id1Abs == 12 || id1Abs == 14 || id1Abs == 16) sigma *= 2.; |
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450 | if (id2Abs == 12 || id2Abs == 14 || id2Abs == 16) sigma *= 2.; |
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451 | |
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452 | // Answer. |
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453 | return sigma; |
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454 | |
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455 | } |
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456 | |
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457 | //-------------------------------------------------------------------------- |
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458 | |
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459 | // Select identity, colour and anticolour. |
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460 | |
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461 | void Sigma2ff2fftW::setIdColAcol() { |
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462 | |
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463 | // Pick out-flavours by relative CKM weights. |
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464 | id3 = couplingsPtr->V2CKMpick(id1); |
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465 | id4 = couplingsPtr->V2CKMpick(id2); |
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466 | setId( id1, id2, id3, id4); |
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467 | |
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468 | // Colour flow topologies. Swap when antiquarks. |
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469 | if (abs(id1) < 9 && abs(id2) < 9 && id1*id2 > 0) |
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470 | setColAcol( 1, 0, 2, 0, 1, 0, 2, 0); |
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471 | else if (abs(id1) < 9 && abs(id2) < 9) |
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472 | setColAcol( 1, 0, 0, 2, 1, 0, 0, 2); |
---|
473 | else if (abs(id1) < 9) setColAcol( 1, 0, 0, 0, 1, 0, 0, 0); |
---|
474 | else if (abs(id2) < 9) setColAcol( 0, 0, 1, 0, 0, 0, 1, 0); |
---|
475 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
476 | if ( (abs(id1) < 9 && id1 < 0) || (abs(id1) > 10 && id2 < 0) ) |
---|
477 | swapColAcol(); |
---|
478 | |
---|
479 | } |
---|
480 | |
---|
481 | |
---|
482 | //========================================================================== |
---|
483 | |
---|
484 | // Sigma2qq2QqtW class. |
---|
485 | // Cross section for q q' -> Q q" via t-channel W+- exchange. |
---|
486 | // Related to Sigma2ff2ffViaW class, but with massive matrix elements. |
---|
487 | |
---|
488 | //-------------------------------------------------------------------------- |
---|
489 | |
---|
490 | // Initialize process. |
---|
491 | |
---|
492 | void Sigma2qq2QqtW::initProc() { |
---|
493 | |
---|
494 | // Process name. |
---|
495 | nameSave = "q q -> Q q (t-channel W+-)"; |
---|
496 | if (idNew == 4) nameSave = "q q -> c q (t-channel W+-)"; |
---|
497 | if (idNew == 5) nameSave = "q q -> b q (t-channel W+-)"; |
---|
498 | if (idNew == 6) nameSave = "q q -> t q (t-channel W+-)"; |
---|
499 | if (idNew == 7) nameSave = "q q -> b' q (t-channel W+-)"; |
---|
500 | if (idNew == 8) nameSave = "q q -> t' q (t-channel W+-)"; |
---|
501 | |
---|
502 | // Store W+- mass for propagator. Common coupling factor. |
---|
503 | mW = particleDataPtr->m0(24); |
---|
504 | mWS = mW*mW; |
---|
505 | thetaWRat = 1. / (4. * couplingsPtr->sin2thetaW()); |
---|
506 | |
---|
507 | // Secondary open width fractions, relevant for top (or heavier). |
---|
508 | openFracPos = particleDataPtr->resOpenFrac(idNew); |
---|
509 | openFracNeg = particleDataPtr->resOpenFrac(-idNew); |
---|
510 | |
---|
511 | } |
---|
512 | |
---|
513 | //-------------------------------------------------------------------------- |
---|
514 | |
---|
515 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
516 | |
---|
517 | void Sigma2qq2QqtW::sigmaKin() { |
---|
518 | |
---|
519 | // Cross section part common for all incoming flavours. |
---|
520 | sigma0 = (M_PI / sH2) * pow2(alpEM * thetaWRat) * 4. / pow2(tH - mWS); |
---|
521 | |
---|
522 | } |
---|
523 | |
---|
524 | //-------------------------------------------------------------------------- |
---|
525 | |
---|
526 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
527 | |
---|
528 | double Sigma2qq2QqtW::sigmaHat() { |
---|
529 | |
---|
530 | // Some flavour combinations not possible. |
---|
531 | int id1Abs = abs(id1); |
---|
532 | int id2Abs = abs(id2); |
---|
533 | bool diff12 = (id1Abs%2 != id2Abs%2); |
---|
534 | if ( (!diff12 && id1 * id2 > 0) |
---|
535 | || ( diff12 && id1 * id2 < 0) ) return 0.; |
---|
536 | |
---|
537 | // Basic cross section. |
---|
538 | double sigma = sigma0; |
---|
539 | sigma *= (id1 * id2 > 0) ? sH * (sH - s3) : uH * (uH - s3); |
---|
540 | |
---|
541 | // Secondary width if t or tbar produced on either side. |
---|
542 | double openFrac1 = (id1 > 0) ? openFracPos : openFracNeg; |
---|
543 | double openFrac2 = (id2 > 0) ? openFracPos : openFracNeg; |
---|
544 | |
---|
545 | // CKM factors for final states; further impossible case. |
---|
546 | bool diff1N = (id1Abs%2 != idNew%2); |
---|
547 | bool diff2N = (id2Abs%2 != idNew%2); |
---|
548 | if (diff1N && diff2N) |
---|
549 | sigma *= ( couplingsPtr->V2CKMid(id1Abs, idNew) * openFrac1 |
---|
550 | * couplingsPtr->V2CKMsum(id2Abs) + couplingsPtr->V2CKMsum(id1Abs) |
---|
551 | * couplingsPtr->V2CKMid(id2Abs, idNew) * openFrac2 ); |
---|
552 | else if (diff1N) |
---|
553 | sigma *= couplingsPtr->V2CKMid(id1Abs, idNew) * openFrac1 |
---|
554 | * couplingsPtr->V2CKMsum(id2Abs); |
---|
555 | else if (diff2N) |
---|
556 | sigma *= couplingsPtr->V2CKMsum(id1Abs) |
---|
557 | * couplingsPtr->V2CKMid(id2Abs, idNew) * openFrac2; |
---|
558 | else sigma = 0.; |
---|
559 | |
---|
560 | // Spin-state extra factor 2 per incoming neutrino. |
---|
561 | if (id1Abs == 12 || id1Abs == 14 || id1Abs == 16) sigma *= 2.; |
---|
562 | if (id2Abs == 12 || id2Abs == 14 || id2Abs == 16) sigma *= 2.; |
---|
563 | |
---|
564 | // Answer. |
---|
565 | return sigma; |
---|
566 | |
---|
567 | } |
---|
568 | |
---|
569 | //-------------------------------------------------------------------------- |
---|
570 | |
---|
571 | // Select identity, colour and anticolour. |
---|
572 | |
---|
573 | void Sigma2qq2QqtW::setIdColAcol() { |
---|
574 | |
---|
575 | // For topologies like d dbar -> (t/c/u) (t/c/u)bar pick side. |
---|
576 | int id1Abs = abs(id1); |
---|
577 | int id2Abs = abs(id2); |
---|
578 | int side = 1; |
---|
579 | if ( (id1Abs + idNew)%2 == 1 && (id2Abs + idNew)%2 == 1 ) { |
---|
580 | double prob1 = couplingsPtr->V2CKMid(id1Abs, idNew) |
---|
581 | * couplingsPtr->V2CKMsum(id2Abs); |
---|
582 | prob1 *= (id1 > 0) ? openFracPos : openFracNeg; |
---|
583 | double prob2 = couplingsPtr->V2CKMid(id2Abs, idNew) |
---|
584 | * couplingsPtr->V2CKMsum(id1Abs); |
---|
585 | prob2 *= (id2 > 0) ? openFracPos : openFracNeg; |
---|
586 | if (prob2 > rndmPtr->flat() * (prob1 + prob2)) side = 2; |
---|
587 | } |
---|
588 | else if ((id2Abs + idNew)%2 == 1) side = 2; |
---|
589 | |
---|
590 | // Pick out-flavours by relative CKM weights. |
---|
591 | if (side == 1) { |
---|
592 | // q q' -> t q" : correct order from start. |
---|
593 | id3 = (id1 > 0) ? idNew : -idNew; |
---|
594 | id4 = couplingsPtr->V2CKMpick(id2); |
---|
595 | setId( id1, id2, id3, id4); |
---|
596 | } else { |
---|
597 | // q q' -> q" t : stored as t q" so swap tHat <-> uHat. |
---|
598 | swapTU = true; |
---|
599 | id3 = couplingsPtr->V2CKMpick(id1); |
---|
600 | id4 = (id2 > 0) ? idNew : -idNew; |
---|
601 | setId( id1, id2, id4, id3); |
---|
602 | } |
---|
603 | |
---|
604 | // Colour flow topologies. Swap when antiquarks on side 1. |
---|
605 | if (side == 1 && id1 * id2 > 0) setColAcol( 1, 0, 2, 0, 1, 0, 2, 0); |
---|
606 | else if (id1 * id2 > 0) setColAcol( 1, 0, 2, 0, 2, 0, 1, 0); |
---|
607 | else if (side == 1) setColAcol( 1, 0, 0, 2, 1, 0, 0, 2); |
---|
608 | else setColAcol( 1, 0, 0, 2, 0, 2, 1, 0); |
---|
609 | if (id1 < 0) swapColAcol(); |
---|
610 | |
---|
611 | } |
---|
612 | |
---|
613 | //-------------------------------------------------------------------------- |
---|
614 | |
---|
615 | // Evaluate weight for decay angles of W in top decay. |
---|
616 | |
---|
617 | double Sigma2qq2QqtW::weightDecay( Event& process, int iResBeg, |
---|
618 | int iResEnd) { |
---|
619 | |
---|
620 | // For top decay hand over to standard routine, else done. |
---|
621 | if (idNew == 6 && process[process[iResBeg].mother1()].idAbs() == 6) |
---|
622 | return weightTopDecay( process, iResBeg, iResEnd); |
---|
623 | else return 1.; |
---|
624 | |
---|
625 | } |
---|
626 | |
---|
627 | //========================================================================== |
---|
628 | |
---|
629 | // Sigma1ffbar2gmZ class. |
---|
630 | // Cross section for f fbar -> gamma*/Z0 (f is quark or lepton). |
---|
631 | |
---|
632 | //-------------------------------------------------------------------------- |
---|
633 | |
---|
634 | // Initialize process. |
---|
635 | |
---|
636 | void Sigma1ffbar2gmZ::initProc() { |
---|
637 | |
---|
638 | // Allow to pick only gamma* or Z0 part of full gamma*/Z0 expression. |
---|
639 | gmZmode = settingsPtr->mode("WeakZ0:gmZmode"); |
---|
640 | |
---|
641 | // Store Z0 mass and width for propagator. |
---|
642 | mRes = particleDataPtr->m0(23); |
---|
643 | GammaRes = particleDataPtr->mWidth(23); |
---|
644 | m2Res = mRes*mRes; |
---|
645 | GamMRat = GammaRes / mRes; |
---|
646 | thetaWRat = 1. / (16. * couplingsPtr->sin2thetaW() |
---|
647 | * couplingsPtr->cos2thetaW()); |
---|
648 | |
---|
649 | // Set pointer to particle properties and decay table. |
---|
650 | particlePtr = particleDataPtr->particleDataEntryPtr(23); |
---|
651 | |
---|
652 | } |
---|
653 | |
---|
654 | //-------------------------------------------------------------------------- |
---|
655 | |
---|
656 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. |
---|
657 | |
---|
658 | void Sigma1ffbar2gmZ::sigmaKin() { |
---|
659 | |
---|
660 | // Common coupling factors. |
---|
661 | double colQ = 3. * (1. + alpS / M_PI); |
---|
662 | |
---|
663 | // Reset quantities to sum. Declare variables in loop. |
---|
664 | gamSum = 0.; |
---|
665 | intSum = 0.; |
---|
666 | resSum = 0.; |
---|
667 | int idAbs, onMode; |
---|
668 | double mf, mr, psvec, psaxi, betaf, ef2, efvf, vf2af2, colf; |
---|
669 | |
---|
670 | // Loop over all Z0 decay channels. |
---|
671 | for (int i = 0; i < particlePtr->sizeChannels(); ++i) { |
---|
672 | idAbs = abs( particlePtr->channel(i).product(0) ); |
---|
673 | |
---|
674 | // Only contributions from three fermion generations, except top. |
---|
675 | if ( (idAbs > 0 && idAbs < 6) || ( idAbs > 10 && idAbs < 17)) { |
---|
676 | mf = particleDataPtr->m0(idAbs); |
---|
677 | |
---|
678 | // Check that above threshold. Phase space. |
---|
679 | if (mH > 2. * mf + MASSMARGIN) { |
---|
680 | mr = pow2(mf / mH); |
---|
681 | betaf = sqrtpos(1. - 4. * mr); |
---|
682 | psvec = betaf * (1. + 2. * mr); |
---|
683 | psaxi = pow3(betaf); |
---|
684 | |
---|
685 | // Combine phase space with couplings. |
---|
686 | ef2 = couplingsPtr->ef2(idAbs) * psvec; |
---|
687 | efvf = couplingsPtr->efvf(idAbs) * psvec; |
---|
688 | vf2af2 = couplingsPtr->vf2(idAbs) * psvec |
---|
689 | + couplingsPtr->af2(idAbs) * psaxi; |
---|
690 | colf = (idAbs < 6) ? colQ : 1.; |
---|
691 | |
---|
692 | // Store sum of combinations. For outstate only open channels. |
---|
693 | onMode = particlePtr->channel(i).onMode(); |
---|
694 | if (onMode == 1 || onMode == 2) { |
---|
695 | gamSum += colf * ef2; |
---|
696 | intSum += colf * efvf; |
---|
697 | resSum += colf * vf2af2; |
---|
698 | } |
---|
699 | |
---|
700 | // End loop over fermions. |
---|
701 | } |
---|
702 | } |
---|
703 | } |
---|
704 | |
---|
705 | // Calculate prefactors for gamma/interference/Z0 cross section terms. |
---|
706 | gamProp = 4. * M_PI * pow2(alpEM) / (3. * sH); |
---|
707 | intProp = gamProp * 2. * thetaWRat * sH * (sH - m2Res) |
---|
708 | / ( pow2(sH - m2Res) + pow2(sH * GamMRat) ); |
---|
709 | resProp = gamProp * pow2(thetaWRat * sH) |
---|
710 | / ( pow2(sH - m2Res) + pow2(sH * GamMRat) ); |
---|
711 | |
---|
712 | // Optionally only keep gamma* or Z0 term. |
---|
713 | if (gmZmode == 1) {intProp = 0.; resProp = 0.;} |
---|
714 | if (gmZmode == 2) {gamProp = 0.; intProp = 0.;} |
---|
715 | |
---|
716 | } |
---|
717 | |
---|
718 | //-------------------------------------------------------------------------- |
---|
719 | |
---|
720 | // Evaluate sigmaHat(sHat), including incoming flavour dependence. |
---|
721 | |
---|
722 | double Sigma1ffbar2gmZ::sigmaHat() { |
---|
723 | |
---|
724 | // Combine gamma, interference and Z0 parts. |
---|
725 | int idAbs = abs(id1); |
---|
726 | double sigma = couplingsPtr->ef2(idAbs) * gamProp * gamSum |
---|
727 | + couplingsPtr->efvf(idAbs) * intProp * intSum |
---|
728 | + couplingsPtr->vf2af2(idAbs) * resProp * resSum; |
---|
729 | |
---|
730 | // Colour factor. Answer. |
---|
731 | if (idAbs < 9) sigma /= 3.; |
---|
732 | return sigma; |
---|
733 | |
---|
734 | } |
---|
735 | |
---|
736 | //-------------------------------------------------------------------------- |
---|
737 | |
---|
738 | // Select identity, colour and anticolour. |
---|
739 | |
---|
740 | void Sigma1ffbar2gmZ::setIdColAcol() { |
---|
741 | |
---|
742 | // Flavours trivial. |
---|
743 | setId( id1, id2, 23); |
---|
744 | |
---|
745 | // Colour flow topologies. Swap when antiquarks. |
---|
746 | if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0); |
---|
747 | else setColAcol( 0, 0, 0, 0, 0, 0); |
---|
748 | if (id1 < 0) swapColAcol(); |
---|
749 | |
---|
750 | } |
---|
751 | |
---|
752 | //-------------------------------------------------------------------------- |
---|
753 | |
---|
754 | // Evaluate weight for gamma*/Z0 decay angle. |
---|
755 | |
---|
756 | double Sigma1ffbar2gmZ::weightDecay( Event& process, int iResBeg, |
---|
757 | int iResEnd) { |
---|
758 | |
---|
759 | // Z should sit in entry 5. |
---|
760 | if (iResBeg != 5 || iResEnd != 5) return 1.; |
---|
761 | |
---|
762 | // Couplings for in- and out-flavours. |
---|
763 | int idInAbs = process[3].idAbs(); |
---|
764 | double ei = couplingsPtr->ef(idInAbs); |
---|
765 | double vi = couplingsPtr->vf(idInAbs); |
---|
766 | double ai = couplingsPtr->af(idInAbs); |
---|
767 | int idOutAbs = process[6].idAbs(); |
---|
768 | double ef = couplingsPtr->ef(idOutAbs); |
---|
769 | double vf = couplingsPtr->vf(idOutAbs); |
---|
770 | double af = couplingsPtr->af(idOutAbs); |
---|
771 | |
---|
772 | // Phase space factors. (One power of beta left out in formulae.) |
---|
773 | double mf = process[6].m(); |
---|
774 | double mr = mf*mf / sH; |
---|
775 | double betaf = sqrtpos(1. - 4. * mr); |
---|
776 | |
---|
777 | // Coefficients of angular expression. |
---|
778 | double coefTran = ei*ei * gamProp * ef*ef + ei * vi * intProp * ef * vf |
---|
779 | + (vi*vi + ai*ai) * resProp * (vf*vf + pow2(betaf) * af*af); |
---|
780 | double coefLong = 4. * mr * ( ei*ei * gamProp * ef*ef |
---|
781 | + ei * vi * intProp * ef * vf + (vi*vi + ai*ai) * resProp * vf*vf ); |
---|
782 | double coefAsym = betaf * ( ei * ai * intProp * ef * af |
---|
783 | + 4. * vi * ai * resProp * vf * af ); |
---|
784 | |
---|
785 | // Flip asymmetry for in-fermion + out-antifermion. |
---|
786 | if (process[3].id() * process[6].id() < 0) coefAsym = -coefAsym; |
---|
787 | |
---|
788 | // Reconstruct decay angle and weight for it. |
---|
789 | double cosThe = (process[3].p() - process[4].p()) |
---|
790 | * (process[7].p() - process[6].p()) / (sH * betaf); |
---|
791 | double wtMax = 2. * (coefTran + abs(coefAsym)); |
---|
792 | double wt = coefTran * (1. + pow2(cosThe)) |
---|
793 | + coefLong * (1. - pow2(cosThe)) + 2. * coefAsym * cosThe; |
---|
794 | |
---|
795 | // Done. |
---|
796 | return (wt / wtMax); |
---|
797 | |
---|
798 | } |
---|
799 | |
---|
800 | //========================================================================== |
---|
801 | |
---|
802 | // Sigma1ffbar2W class. |
---|
803 | // Cross section for f fbar' -> W+- (f is quark or lepton). |
---|
804 | |
---|
805 | //-------------------------------------------------------------------------- |
---|
806 | |
---|
807 | // Initialize process. |
---|
808 | |
---|
809 | void Sigma1ffbar2W::initProc() { |
---|
810 | |
---|
811 | // Store W+- mass and width for propagator. |
---|
812 | mRes = particleDataPtr->m0(24); |
---|
813 | GammaRes = particleDataPtr->mWidth(24); |
---|
814 | m2Res = mRes*mRes; |
---|
815 | GamMRat = GammaRes / mRes; |
---|
816 | thetaWRat = 1. / (12. * couplingsPtr->sin2thetaW()); |
---|
817 | |
---|
818 | // Set pointer to particle properties and decay table. |
---|
819 | particlePtr = particleDataPtr->particleDataEntryPtr(24); |
---|
820 | |
---|
821 | } |
---|
822 | |
---|
823 | //-------------------------------------------------------------------------- |
---|
824 | |
---|
825 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. |
---|
826 | |
---|
827 | void Sigma1ffbar2W::sigmaKin() { |
---|
828 | |
---|
829 | // Set up Breit-Wigner. Cross section for W+ and W- separately. |
---|
830 | double sigBW = 12. * M_PI / ( pow2(sH - m2Res) + pow2(sH * GamMRat) ); |
---|
831 | double preFac = alpEM * thetaWRat * mH; |
---|
832 | sigma0Pos = preFac * sigBW * particlePtr->resWidthOpen(24, mH); |
---|
833 | sigma0Neg = preFac * sigBW * particlePtr->resWidthOpen(-24, mH); |
---|
834 | |
---|
835 | } |
---|
836 | |
---|
837 | //-------------------------------------------------------------------------- |
---|
838 | |
---|
839 | // Evaluate sigmaHat(sHat), including incoming flavour dependence. |
---|
840 | |
---|
841 | double Sigma1ffbar2W::sigmaHat() { |
---|
842 | |
---|
843 | // Secondary width for W+ or W-. CKM and colour factors. |
---|
844 | int idUp = (abs(id1)%2 == 0) ? id1 : id2; |
---|
845 | double sigma = (idUp > 0) ? sigma0Pos : sigma0Neg; |
---|
846 | if (abs(id1) < 9) sigma *= couplingsPtr->V2CKMid(abs(id1), abs(id2)) / 3.; |
---|
847 | |
---|
848 | // Answer. |
---|
849 | return sigma; |
---|
850 | |
---|
851 | } |
---|
852 | |
---|
853 | //-------------------------------------------------------------------------- |
---|
854 | |
---|
855 | // Select identity, colour and anticolour. |
---|
856 | |
---|
857 | void Sigma1ffbar2W::setIdColAcol() { |
---|
858 | |
---|
859 | // Sign of outgoing W. |
---|
860 | int sign = 1 - 2 * (abs(id1)%2); |
---|
861 | if (id1 < 0) sign = -sign; |
---|
862 | setId( id1, id2, 24 * sign); |
---|
863 | |
---|
864 | // Colour flow topologies. Swap when antiquarks. |
---|
865 | if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0); |
---|
866 | else setColAcol( 0, 0, 0, 0, 0, 0); |
---|
867 | if (id1 < 0) swapColAcol(); |
---|
868 | |
---|
869 | } |
---|
870 | |
---|
871 | //-------------------------------------------------------------------------- |
---|
872 | |
---|
873 | // Evaluate weight for W decay angle. |
---|
874 | |
---|
875 | double Sigma1ffbar2W::weightDecay( Event& process, int iResBeg, |
---|
876 | int iResEnd) { |
---|
877 | |
---|
878 | // W should sit in entry 5. |
---|
879 | if (iResBeg != 5 || iResEnd != 5) return 1.; |
---|
880 | |
---|
881 | // Phase space factors. |
---|
882 | double mr1 = pow2(process[6].m()) / sH; |
---|
883 | double mr2 = pow2(process[7].m()) / sH; |
---|
884 | double betaf = sqrtpos( pow2(1. - mr1 - mr2) - 4. * mr1 * mr2); |
---|
885 | |
---|
886 | // Sign of asymmetry. |
---|
887 | double eps = (process[3].id() * process[6].id() > 0) ? 1. : -1.; |
---|
888 | |
---|
889 | // Reconstruct decay angle and weight for it. |
---|
890 | double cosThe = (process[3].p() - process[4].p()) |
---|
891 | * (process[7].p() - process[6].p()) / (sH * betaf); |
---|
892 | double wtMax = 4.; |
---|
893 | double wt = pow2(1. + betaf * eps * cosThe) - pow2(mr1 - mr2); |
---|
894 | |
---|
895 | // Done. |
---|
896 | return (wt / wtMax); |
---|
897 | |
---|
898 | } |
---|
899 | |
---|
900 | //========================================================================== |
---|
901 | |
---|
902 | // Sigma2ffbar2ffbarsgm class. |
---|
903 | // Cross section f fbar -> gamma* -> f' fbar', for multiparton interactions. |
---|
904 | |
---|
905 | |
---|
906 | //-------------------------------------------------------------------------- |
---|
907 | |
---|
908 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
909 | |
---|
910 | void Sigma2ffbar2ffbarsgm::sigmaKin() { |
---|
911 | |
---|
912 | // Pick new flavour. Allow three leptons and five quarks. |
---|
913 | double colQ = 1. + (alpS / M_PI); |
---|
914 | double flavWt = 3. + colQ * 11. / 3.; |
---|
915 | double flavRndm = rndmPtr->flat() * flavWt; |
---|
916 | if (flavRndm < 3.) { |
---|
917 | if (flavRndm < 1.) idNew = 11; |
---|
918 | else if (flavRndm < 2.) idNew = 13; |
---|
919 | else idNew = 15; |
---|
920 | } else { |
---|
921 | flavRndm = 3. * (flavRndm - 3.) / colQ; |
---|
922 | if (flavRndm < 4.) idNew = 2; |
---|
923 | else if (flavRndm < 8.) idNew = 4; |
---|
924 | else if (flavRndm < 9.) idNew = 1; |
---|
925 | else if (flavRndm < 10.) idNew = 3; |
---|
926 | else idNew = 5; |
---|
927 | } |
---|
928 | double mNew = particleDataPtr->m0(idNew); |
---|
929 | double m2New = mNew*mNew; |
---|
930 | |
---|
931 | // Calculate kinematics dependence. Give correct mass factors for |
---|
932 | // tHat, uHat defined as if massless kinematics, d(sigma)/d(Omega) |
---|
933 | // = beta (1 + cos^2(theta) + (1 - beta^2) sin^2(theta)). |
---|
934 | // Special case related to phase space form in multiparton interactions. |
---|
935 | double sigS = 0.; |
---|
936 | if (sH > 4. * m2New) { |
---|
937 | double beta = sqrt(1. - 4. * m2New / sH); |
---|
938 | sigS = beta * (2.* (tH2 + uH2) + 4. * (1. - beta * beta) * tH * uH) |
---|
939 | / sH2; |
---|
940 | } |
---|
941 | |
---|
942 | // Answer is proportional to number of outgoing flavours. |
---|
943 | sigma0 = (M_PI/sH2) * pow2(alpEM) * sigS * flavWt; |
---|
944 | |
---|
945 | } |
---|
946 | |
---|
947 | //-------------------------------------------------------------------------- |
---|
948 | |
---|
949 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
950 | |
---|
951 | double Sigma2ffbar2ffbarsgm::sigmaHat() { |
---|
952 | |
---|
953 | // Charge and colour factors. |
---|
954 | double eNow = couplingsPtr->ef( abs(id1) ); |
---|
955 | double sigma = sigma0 * pow2(eNow); |
---|
956 | if (abs(id1) < 9) sigma /= 3.; |
---|
957 | |
---|
958 | // Answer. |
---|
959 | return sigma; |
---|
960 | |
---|
961 | } |
---|
962 | |
---|
963 | //-------------------------------------------------------------------------- |
---|
964 | |
---|
965 | // Select identity, colour and anticolour. |
---|
966 | |
---|
967 | void Sigma2ffbar2ffbarsgm::setIdColAcol() { |
---|
968 | |
---|
969 | // Set outgoing flavours. |
---|
970 | id3 = (id1 > 0) ? idNew : -idNew; |
---|
971 | setId( id1, id2, id3, -id3); |
---|
972 | |
---|
973 | // Colour flow topologies. Swap when antiquarks. |
---|
974 | if (abs(id1) < 9 && idNew < 9) setColAcol( 1, 0, 0, 1, 2, 0, 0, 2); |
---|
975 | else if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0); |
---|
976 | else if (idNew < 9) setColAcol( 0, 0, 0, 0, 1, 0, 0, 1); |
---|
977 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
978 | if (id1 < 0) swapColAcol(); |
---|
979 | |
---|
980 | } |
---|
981 | |
---|
982 | //========================================================================== |
---|
983 | |
---|
984 | // Sigma2ffbar2FFbarsgmZ class. |
---|
985 | // Cross section f fbar -> gamma*/Z0 -> F Fbar. |
---|
986 | |
---|
987 | //-------------------------------------------------------------------------- |
---|
988 | |
---|
989 | // Initialize process. |
---|
990 | |
---|
991 | void Sigma2ffbar2FFbarsgmZ::initProc() { |
---|
992 | |
---|
993 | // Process name. |
---|
994 | nameSave = "f fbar -> F Fbar (s-channel gamma*/Z0)"; |
---|
995 | if (idNew == 4) nameSave = "f fbar -> c cbar (s-channel gamma*/Z0)"; |
---|
996 | if (idNew == 5) nameSave = "f fbar -> b bbar (s-channel gamma*/Z0)"; |
---|
997 | if (idNew == 6) nameSave = "f fbar -> t tbar (s-channel gamma*/Z0)"; |
---|
998 | if (idNew == 7) nameSave = "f fbar -> b' b'bar (s-channel gamma*/Z0)"; |
---|
999 | if (idNew == 8) nameSave = "f fbar -> t' t'bar (s-channel gamma*/Z0)"; |
---|
1000 | if (idNew == 15) nameSave = "f fbar -> tau+ tau- (s-channel gamma*/Z0)"; |
---|
1001 | if (idNew == 17) nameSave = "f fbar -> tau'+ tau'- (s-channel gamma*/Z0)"; |
---|
1002 | if (idNew == 18) |
---|
1003 | nameSave = "f fbar -> nu'_tau nu'bar_tau (s-channel gamma*/Z0)"; |
---|
1004 | |
---|
1005 | // Allow to pick only gamma* or Z0 part of full gamma*/Z0 expression. |
---|
1006 | gmZmode = settingsPtr->mode("WeakZ0:gmZmode"); |
---|
1007 | |
---|
1008 | // Store Z0 mass and width for propagator. |
---|
1009 | mRes = particleDataPtr->m0(23); |
---|
1010 | GammaRes = particleDataPtr->mWidth(23); |
---|
1011 | m2Res = mRes*mRes; |
---|
1012 | GamMRat = GammaRes / mRes; |
---|
1013 | thetaWRat = 1. / (16. * couplingsPtr->sin2thetaW() |
---|
1014 | * couplingsPtr->cos2thetaW()); |
---|
1015 | |
---|
1016 | // Store couplings of F. |
---|
1017 | ef = couplingsPtr->ef(idNew); |
---|
1018 | vf = couplingsPtr->vf(idNew); |
---|
1019 | af = couplingsPtr->af(idNew); |
---|
1020 | |
---|
1021 | // Secondary open width fraction, relevant for top (or heavier). |
---|
1022 | openFracPair = particleDataPtr->resOpenFrac(idNew, -idNew); |
---|
1023 | |
---|
1024 | } |
---|
1025 | |
---|
1026 | //-------------------------------------------------------------------------- |
---|
1027 | |
---|
1028 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
1029 | |
---|
1030 | void Sigma2ffbar2FFbarsgmZ::sigmaKin() { |
---|
1031 | |
---|
1032 | // Check that above threshold. |
---|
1033 | isPhysical = true; |
---|
1034 | if (mH < m3 + m4 + MASSMARGIN) { |
---|
1035 | isPhysical = false; |
---|
1036 | return; |
---|
1037 | } |
---|
1038 | |
---|
1039 | // Define average F, Fbar mass so same beta. Phase space. |
---|
1040 | double s34Avg = 0.5 * (s3 + s4) - 0.25 * pow2(s3 - s4) / sH; |
---|
1041 | mr = s34Avg / sH; |
---|
1042 | betaf = sqrtpos(1. - 4. * mr); |
---|
1043 | |
---|
1044 | // Final-state colour factor. |
---|
1045 | double colF = (idNew < 9) ? 3. * (1. + alpS / M_PI) : 1.; |
---|
1046 | |
---|
1047 | // Reconstruct decay angle so can reuse 2 -> 1 cross section. |
---|
1048 | cosThe = (tH - uH) / (betaf * sH); |
---|
1049 | |
---|
1050 | // Calculate prefactors for gamma/interference/Z0 cross section terms. |
---|
1051 | gamProp = colF * M_PI * pow2(alpEM) / sH2; |
---|
1052 | intProp = gamProp * 2. * thetaWRat * sH * (sH - m2Res) |
---|
1053 | / ( pow2(sH - m2Res) + pow2(sH * GamMRat) ); |
---|
1054 | resProp = gamProp * pow2(thetaWRat * sH) |
---|
1055 | / ( pow2(sH - m2Res) + pow2(sH * GamMRat) ); |
---|
1056 | |
---|
1057 | // Optionally only keep gamma* or Z0 term. |
---|
1058 | if (gmZmode == 1) {intProp = 0.; resProp = 0.;} |
---|
1059 | if (gmZmode == 2) {gamProp = 0.; intProp = 0.;} |
---|
1060 | |
---|
1061 | } |
---|
1062 | |
---|
1063 | //-------------------------------------------------------------------------- |
---|
1064 | |
---|
1065 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
1066 | |
---|
1067 | double Sigma2ffbar2FFbarsgmZ::sigmaHat() { |
---|
1068 | |
---|
1069 | // Fail if below threshold. |
---|
1070 | if (!isPhysical) return 0.; |
---|
1071 | |
---|
1072 | // Couplings for in-flavours. |
---|
1073 | int idAbs = abs(id1); |
---|
1074 | double ei = couplingsPtr->ef(idAbs); |
---|
1075 | double vi = couplingsPtr->vf(idAbs); |
---|
1076 | double ai = couplingsPtr->af(idAbs); |
---|
1077 | |
---|
1078 | // Coefficients of angular expression. |
---|
1079 | double coefTran = ei*ei * gamProp * ef*ef + ei * vi * intProp * ef * vf |
---|
1080 | + (vi*vi + ai*ai) * resProp * (vf*vf + pow2(betaf) * af*af); |
---|
1081 | double coefLong = 4. * mr * ( ei*ei * gamProp * ef*ef |
---|
1082 | + ei * vi * intProp * ef * vf + (vi*vi + ai*ai) * resProp * vf*vf ); |
---|
1083 | double coefAsym = betaf * ( ei * ai * intProp * ef * af |
---|
1084 | + 4. * vi * ai * resProp * vf * af ); |
---|
1085 | |
---|
1086 | // Combine gamma, interference and Z0 parts. |
---|
1087 | double sigma = coefTran * (1. + pow2(cosThe)) |
---|
1088 | + coefLong * (1. - pow2(cosThe)) + 2. * coefAsym * cosThe; |
---|
1089 | |
---|
1090 | // Top: corrections for closed decay channels. |
---|
1091 | sigma *= openFracPair; |
---|
1092 | |
---|
1093 | // Initial-state colour factor. Answer. |
---|
1094 | if (idAbs < 9) sigma /= 3.; |
---|
1095 | return sigma; |
---|
1096 | |
---|
1097 | } |
---|
1098 | |
---|
1099 | //-------------------------------------------------------------------------- |
---|
1100 | |
---|
1101 | // Select identity, colour and anticolour. |
---|
1102 | |
---|
1103 | void Sigma2ffbar2FFbarsgmZ::setIdColAcol() { |
---|
1104 | |
---|
1105 | // Set outgoing flavours. |
---|
1106 | id3 = (id1 > 0) ? idNew : -idNew; |
---|
1107 | setId( id1, id2, id3, -id3); |
---|
1108 | |
---|
1109 | // Colour flow topologies. Swap when antiquarks. |
---|
1110 | if (abs(id1) < 9 && idNew < 9) setColAcol( 1, 0, 0, 1, 2, 0, 0, 2); |
---|
1111 | else if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0); |
---|
1112 | else if (idNew < 9) setColAcol( 0, 0, 0, 0, 1, 0, 0, 1); |
---|
1113 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
1114 | if (id1 < 0) swapColAcol(); |
---|
1115 | |
---|
1116 | } |
---|
1117 | |
---|
1118 | //-------------------------------------------------------------------------- |
---|
1119 | |
---|
1120 | // Evaluate weight for decay angles of W in top decay. |
---|
1121 | |
---|
1122 | double Sigma2ffbar2FFbarsgmZ::weightDecay( Event& process, int iResBeg, |
---|
1123 | int iResEnd) { |
---|
1124 | |
---|
1125 | // For top decay hand over to standard routine, else done. |
---|
1126 | if (idNew == 6 && process[process[iResBeg].mother1()].idAbs() == 6) |
---|
1127 | return weightTopDecay( process, iResBeg, iResEnd); |
---|
1128 | else return 1.; |
---|
1129 | |
---|
1130 | } |
---|
1131 | |
---|
1132 | //========================================================================== |
---|
1133 | |
---|
1134 | // Sigma2ffbar2FfbarsW class. |
---|
1135 | // Cross section f fbar' -> W+- -> F fbar". |
---|
1136 | |
---|
1137 | //-------------------------------------------------------------------------- |
---|
1138 | |
---|
1139 | // Initialize process. |
---|
1140 | |
---|
1141 | void Sigma2ffbar2FfbarsW::initProc() { |
---|
1142 | |
---|
1143 | // Process name. |
---|
1144 | nameSave = "f fbar -> F fbar (s-channel W+-)"; |
---|
1145 | if (idNew == 4) nameSave = "f fbar -> c qbar (s-channel W+-)"; |
---|
1146 | if (idNew == 5) nameSave = "f fbar -> b qbar (s-channel W+-)"; |
---|
1147 | if (idNew == 6) nameSave = "f fbar -> t qbar (s-channel W+-)"; |
---|
1148 | if (idNew == 7) nameSave = "f fbar -> b' qbar (s-channel W+-)"; |
---|
1149 | if (idNew == 8) nameSave = "f fbar -> t' qbar (s-channel W+-)"; |
---|
1150 | if (idNew == 7 && idNew2 == 6) |
---|
1151 | nameSave = "f fbar -> b' tbar (s-channel W+-)"; |
---|
1152 | if (idNew == 8 && idNew2 == 7) |
---|
1153 | nameSave = "f fbar -> t' b'bar (s-channel W+-)"; |
---|
1154 | if (idNew == 15 || idNew == 16) |
---|
1155 | nameSave = "f fbar -> tau nu_taubar (s-channel W+-)"; |
---|
1156 | if (idNew == 17 || idNew == 18) |
---|
1157 | nameSave = "f fbar -> tau' nu'_taubar (s-channel W+-)"; |
---|
1158 | |
---|
1159 | // Store W+- mass and width for propagator. |
---|
1160 | mRes = particleDataPtr->m0(24); |
---|
1161 | GammaRes = particleDataPtr->mWidth(24); |
---|
1162 | m2Res = mRes*mRes; |
---|
1163 | GamMRat = GammaRes / mRes; |
---|
1164 | thetaWRat = 1. / (12. * couplingsPtr->sin2thetaW()); |
---|
1165 | |
---|
1166 | // For t/t' want to use at least b mass. |
---|
1167 | idPartner = idNew2; |
---|
1168 | if ( (idNew == 6 || idNew == 8) && idNew2 == 0 ) idPartner = 5; |
---|
1169 | |
---|
1170 | // Sum of CKM weights for quarks. |
---|
1171 | V2New = (idNew < 9) ? couplingsPtr->V2CKMsum(idNew) : 1.; |
---|
1172 | if (idNew2 != 0) V2New = couplingsPtr->V2CKMid(idNew, idNew2); |
---|
1173 | |
---|
1174 | // Secondary open width fractions, relevant for top or heavier. |
---|
1175 | openFracPos = particleDataPtr->resOpenFrac( idNew, -idNew2); |
---|
1176 | openFracNeg = particleDataPtr->resOpenFrac(-idNew, idNew2); |
---|
1177 | |
---|
1178 | } |
---|
1179 | |
---|
1180 | //-------------------------------------------------------------------------- |
---|
1181 | |
---|
1182 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
1183 | |
---|
1184 | void Sigma2ffbar2FfbarsW::sigmaKin() { |
---|
1185 | |
---|
1186 | // Check that above threshold. |
---|
1187 | isPhysical = true; |
---|
1188 | if (mH < m3 + m4 + MASSMARGIN) { |
---|
1189 | isPhysical = false; |
---|
1190 | return; |
---|
1191 | } |
---|
1192 | |
---|
1193 | // Phase space factors. |
---|
1194 | double mr1 = s3 / sH; |
---|
1195 | double mr2 = s4 / sH; |
---|
1196 | double betaf = sqrtpos( pow2(1. - mr1 - mr2) - 4. * mr1 * mr2); |
---|
1197 | |
---|
1198 | // Reconstruct decay angle so can reuse 2 -> 1 cross section. |
---|
1199 | double cosThe = (tH - uH) / (betaf * sH); |
---|
1200 | |
---|
1201 | // Set up Breit-Wigner and in- and out-widths. |
---|
1202 | double sigBW = 9. * M_PI * pow2(alpEM * thetaWRat) |
---|
1203 | / ( pow2(sH - m2Res) + pow2(sH * GamMRat) ); |
---|
1204 | |
---|
1205 | // Initial-state colour factor. |
---|
1206 | double colF = (idNew < 9) ? 3. * (1. + alpS / M_PI) * V2New : 1.; |
---|
1207 | |
---|
1208 | // Angular dependence. |
---|
1209 | double wt = pow2(1. + betaf * cosThe) - pow2(mr1 - mr2); |
---|
1210 | |
---|
1211 | // Temporary answer. |
---|
1212 | sigma0 = sigBW * colF * wt; |
---|
1213 | |
---|
1214 | } |
---|
1215 | |
---|
1216 | //-------------------------------------------------------------------------- |
---|
1217 | |
---|
1218 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
1219 | |
---|
1220 | double Sigma2ffbar2FfbarsW::sigmaHat() { |
---|
1221 | |
---|
1222 | // Fail if below threshold. |
---|
1223 | if (!isPhysical) return 0.; |
---|
1224 | |
---|
1225 | // CKM and colour factors. |
---|
1226 | double sigma = sigma0; |
---|
1227 | if (abs(id1) < 9) sigma *= couplingsPtr->V2CKMid(abs(id1), abs(id2)) / 3.; |
---|
1228 | |
---|
1229 | // Correction for secondary width in top (or heavier) decay. |
---|
1230 | int idSame = ((abs(id1) + idNew)%2 == 0) ? id1 : id2; |
---|
1231 | sigma *= (idSame > 0) ? openFracPos : openFracNeg; |
---|
1232 | |
---|
1233 | // Answer. |
---|
1234 | return sigma; |
---|
1235 | |
---|
1236 | } |
---|
1237 | |
---|
1238 | //-------------------------------------------------------------------------- |
---|
1239 | |
---|
1240 | // Select identity, colour and anticolour. |
---|
1241 | |
---|
1242 | void Sigma2ffbar2FfbarsW::setIdColAcol() { |
---|
1243 | |
---|
1244 | // Set outgoing flavours. |
---|
1245 | id3 = idNew; |
---|
1246 | id4 = (idNew2 != 0) ? idNew2 : couplingsPtr->V2CKMpick(idNew); |
---|
1247 | if (idNew%2 == 0) { |
---|
1248 | int idInUp = (abs(id1)%2 == 0) ? id1 : id2; |
---|
1249 | if (idInUp > 0) id4 = -id4; |
---|
1250 | else id3 = -id3; |
---|
1251 | } else { |
---|
1252 | int idInDn = (abs(id1)%2 == 1) ? id1 : id2; |
---|
1253 | if (idInDn > 0) id4 = -id4; |
---|
1254 | else id3 = -id3; |
---|
1255 | } |
---|
1256 | setId( id1, id2, id3, id4); |
---|
1257 | |
---|
1258 | // Swap tHat and uHat for fbar' f -> F f". |
---|
1259 | if (id1 * id3 < 0) swapTU = true; |
---|
1260 | |
---|
1261 | // Colour flow topologies. Swap when antiquarks. |
---|
1262 | if (abs(id1) < 9 && idNew < 9) setColAcol( 1, 0, 0, 1, 2, 0, 0, 2); |
---|
1263 | else if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0); |
---|
1264 | else if (idNew < 9) setColAcol( 0, 0, 0, 0, 1, 0, 0, 1); |
---|
1265 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
1266 | if (id1 < 0) swapCol12(); |
---|
1267 | if (id3 < 0) swapCol34(); |
---|
1268 | |
---|
1269 | } |
---|
1270 | |
---|
1271 | //-------------------------------------------------------------------------- |
---|
1272 | |
---|
1273 | // Evaluate weight for decay angles of W in top decay. |
---|
1274 | |
---|
1275 | double Sigma2ffbar2FfbarsW::weightDecay( Event& process, int iResBeg, |
---|
1276 | int iResEnd) { |
---|
1277 | |
---|
1278 | // For top decay hand over to standard routine, else done. |
---|
1279 | if (idNew == 6 && process[process[iResBeg].mother1()].idAbs() == 6) |
---|
1280 | return weightTopDecay( process, iResBeg, iResEnd); |
---|
1281 | else return 1.; |
---|
1282 | |
---|
1283 | } |
---|
1284 | |
---|
1285 | //========================================================================== |
---|
1286 | |
---|
1287 | // Sigma2ffbargmZWgmZW class. |
---|
1288 | // Collects common methods for f fbar -> gamma*/Z0/W+- gamma*/Z0/W-+. |
---|
1289 | |
---|
1290 | //-------------------------------------------------------------------------- |
---|
1291 | |
---|
1292 | // Calculate and store internal products. |
---|
1293 | |
---|
1294 | void Sigma2ffbargmZWgmZW::setupProd( Event& process, int i1, int i2, |
---|
1295 | int i3, int i4, int i5, int i6) { |
---|
1296 | |
---|
1297 | // Store incoming and outgoing momenta, |
---|
1298 | pRot[1] = process[i1].p(); |
---|
1299 | pRot[2] = process[i2].p(); |
---|
1300 | pRot[3] = process[i3].p(); |
---|
1301 | pRot[4] = process[i4].p(); |
---|
1302 | pRot[5] = process[i5].p(); |
---|
1303 | pRot[6] = process[i6].p(); |
---|
1304 | |
---|
1305 | // Do random rotation to avoid accidental zeroes in HA expressions. |
---|
1306 | bool smallPT = false; |
---|
1307 | do { |
---|
1308 | smallPT = false; |
---|
1309 | double thetaNow = acos(2. * rndmPtr->flat() - 1.); |
---|
1310 | double phiNow = 2. * M_PI * rndmPtr->flat(); |
---|
1311 | for (int i = 1; i <= 6; ++i) { |
---|
1312 | pRot[i].rot( thetaNow, phiNow); |
---|
1313 | if (pRot[i].pT2() < 1e-4 * pRot[i].pAbs2()) smallPT = true; |
---|
1314 | } |
---|
1315 | } while (smallPT); |
---|
1316 | |
---|
1317 | // Calculate internal products. |
---|
1318 | for (int i = 1; i < 6; ++i) { |
---|
1319 | for (int j = i + 1; j <= 6; ++j) { |
---|
1320 | hA[i][j] = |
---|
1321 | sqrt( (pRot[i].e() - pRot[i].pz()) * (pRot[j].e() + pRot[j].pz()) |
---|
1322 | / pRot[i].pT2() ) * complex( pRot[i].px(), pRot[i].py() ) |
---|
1323 | - sqrt( (pRot[i].e() + pRot[i].pz()) * (pRot[j].e() - pRot[j].pz()) |
---|
1324 | / pRot[j].pT2() ) * complex( pRot[j].px(), pRot[j].py() ); |
---|
1325 | hC[i][j] = conj( hA[i][j] ); |
---|
1326 | if (i <= 2) { |
---|
1327 | hA[i][j] *= complex( 0., 1.); |
---|
1328 | hC[i][j] *= complex( 0., 1.); |
---|
1329 | } |
---|
1330 | hA[j][i] = - hA[i][j]; |
---|
1331 | hC[j][i] = - hC[i][j]; |
---|
1332 | } |
---|
1333 | } |
---|
1334 | |
---|
1335 | } |
---|
1336 | |
---|
1337 | //-------------------------------------------------------------------------- |
---|
1338 | |
---|
1339 | // Evaluate the F function of Gunion and Kunszt. |
---|
1340 | |
---|
1341 | complex Sigma2ffbargmZWgmZW::fGK(int j1, int j2, int j3, int j4, int j5, |
---|
1342 | int j6) { |
---|
1343 | |
---|
1344 | return 4. * hA[j1][j3] * hC[j2][j6] |
---|
1345 | * ( hA[j1][j5] * hC[j1][j4] + hA[j3][j5] * hC[j3][j4] ); |
---|
1346 | |
---|
1347 | } |
---|
1348 | |
---|
1349 | //-------------------------------------------------------------------------- |
---|
1350 | |
---|
1351 | // Evaluate the Xi function of Gunion and Kunszt. |
---|
1352 | |
---|
1353 | double Sigma2ffbargmZWgmZW::xiGK( double tHnow, double uHnow) { |
---|
1354 | |
---|
1355 | return - 4. * s3 * s4 + tHnow * (3. * tHnow + 4. * uHnow) |
---|
1356 | + tHnow * tHnow * ( tHnow * uHnow / (s3 * s4) |
---|
1357 | - 2. * (1. / s3 + 1./s4) * (tHnow + uHnow) |
---|
1358 | + 2. * (s3 / s4 + s4 / s3) ); |
---|
1359 | |
---|
1360 | } |
---|
1361 | |
---|
1362 | //-------------------------------------------------------------------------- |
---|
1363 | |
---|
1364 | // Evaluate the Xj function of Gunion and Kunszt. |
---|
1365 | |
---|
1366 | double Sigma2ffbargmZWgmZW::xjGK( double tHnow, double uHnow) { |
---|
1367 | |
---|
1368 | return 8. * pow2(s3 + s4) - 8. * (s3 + s4) * (tHnow + uHnow) |
---|
1369 | - 6. * tHnow * uHnow - 2. * tHnow * uHnow * ( tHnow * uHnow |
---|
1370 | / (s3 * s4) - 2. * (1. / s3 + 1. / s4) * (tHnow + uHnow) |
---|
1371 | + 2. * (s3 / s4 + s4 / s3) ); |
---|
1372 | |
---|
1373 | } |
---|
1374 | |
---|
1375 | //========================================================================== |
---|
1376 | |
---|
1377 | // Sigma2ffbar2gmZgmZ class. |
---|
1378 | // Cross section for f fbar -> gamma*/Z0 gamma*/Z0 (f is quark or lepton). |
---|
1379 | |
---|
1380 | //-------------------------------------------------------------------------- |
---|
1381 | |
---|
1382 | // Initialize process. |
---|
1383 | |
---|
1384 | void Sigma2ffbar2gmZgmZ::initProc() { |
---|
1385 | |
---|
1386 | // Allow to pick only gamma* or Z0 part of full gamma*/Z0 expression. |
---|
1387 | gmZmode = settingsPtr->mode("WeakZ0:gmZmode"); |
---|
1388 | |
---|
1389 | // Store Z0 mass and width for propagator. |
---|
1390 | mRes = particleDataPtr->m0(23); |
---|
1391 | GammaRes = particleDataPtr->mWidth(23); |
---|
1392 | m2Res = mRes*mRes; |
---|
1393 | GamMRat = GammaRes / mRes; |
---|
1394 | thetaWRat = 1. / (16. * couplingsPtr->sin2thetaW() |
---|
1395 | * couplingsPtr->cos2thetaW()); |
---|
1396 | |
---|
1397 | // Set pointer to particle properties and decay table. |
---|
1398 | particlePtr = particleDataPtr->particleDataEntryPtr(23); |
---|
1399 | |
---|
1400 | } |
---|
1401 | |
---|
1402 | //-------------------------------------------------------------------------- |
---|
1403 | |
---|
1404 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
1405 | |
---|
1406 | void Sigma2ffbar2gmZgmZ::sigmaKin() { |
---|
1407 | |
---|
1408 | // Cross section part common for all incoming flavours. |
---|
1409 | sigma0 = (M_PI / sH2) * pow2(alpEM) * 0.5 |
---|
1410 | * ( (tH2 + uH2 + 2. * (s3 + s4) * sH) / (tH * uH) |
---|
1411 | - s3 * s4 * (1./tH2 + 1./uH2) ); |
---|
1412 | |
---|
1413 | // Common coupling factors at the resonance masses |
---|
1414 | double alpEM3 = couplingsPtr->alphaEM(s3); |
---|
1415 | double alpS3 = couplingsPtr->alphaS(s3); |
---|
1416 | double colQ3 = 3. * (1. + alpS3 / M_PI); |
---|
1417 | double alpEM4 = couplingsPtr->alphaEM(s4); |
---|
1418 | double alpS4 = couplingsPtr->alphaS(s4); |
---|
1419 | double colQ4 = 3. * (1. + alpS4 / M_PI); |
---|
1420 | |
---|
1421 | // Reset quantities to sum. Declare variables in loop. |
---|
1422 | gamSum3 = 0.; |
---|
1423 | intSum3 = 0.; |
---|
1424 | resSum3 = 0.; |
---|
1425 | gamSum4 = 0.; |
---|
1426 | intSum4 = 0.; |
---|
1427 | resSum4 = 0.; |
---|
1428 | int onMode; |
---|
1429 | double mf, mr, psvec, psaxi, betaf, ef2, efvf, vf2af2, colf; |
---|
1430 | |
---|
1431 | // Loop over all Z0 decay channels. |
---|
1432 | for (int i = 0; i < particlePtr->sizeChannels(); ++i) { |
---|
1433 | int idAbs = abs( particlePtr->channel(i).product(0) ); |
---|
1434 | |
---|
1435 | // Only contributions from three fermion generations, except top. |
---|
1436 | if ( (idAbs > 0 && idAbs < 6) || ( idAbs > 10 && idAbs < 17)) { |
---|
1437 | mf = particleDataPtr->m0(idAbs); |
---|
1438 | onMode = particlePtr->channel(i).onMode(); |
---|
1439 | |
---|
1440 | // First Z0: check that above threshold. Phase space. |
---|
1441 | if (m3 > 2. * mf + MASSMARGIN) { |
---|
1442 | mr = pow2(mf / m3); |
---|
1443 | betaf = sqrtpos(1. - 4. * mr); |
---|
1444 | psvec = betaf * (1. + 2. * mr); |
---|
1445 | psaxi = pow3(betaf); |
---|
1446 | |
---|
1447 | // First Z0: combine phase space with couplings. |
---|
1448 | ef2 = couplingsPtr->ef2(idAbs) * psvec; |
---|
1449 | efvf = couplingsPtr->efvf(idAbs) * psvec; |
---|
1450 | vf2af2 = couplingsPtr->vf2(idAbs) * psvec |
---|
1451 | + couplingsPtr->af2(idAbs) * psaxi; |
---|
1452 | colf = (idAbs < 6) ? colQ3 : 1.; |
---|
1453 | |
---|
1454 | // First Z0: store sum of combinations for open outstate channels. |
---|
1455 | if (onMode == 1 || onMode == 2) { |
---|
1456 | gamSum3 += colf * ef2; |
---|
1457 | intSum3 += colf * efvf; |
---|
1458 | resSum3 += colf * vf2af2; |
---|
1459 | } |
---|
1460 | } |
---|
1461 | |
---|
1462 | // Second Z0: check that above threshold. Phase space. |
---|
1463 | if (m4 > 2. * mf + MASSMARGIN) { |
---|
1464 | mr = pow2(mf / m4); |
---|
1465 | betaf = sqrtpos(1. - 4. * mr); |
---|
1466 | psvec = betaf * (1. + 2. * mr); |
---|
1467 | psaxi = pow3(betaf); |
---|
1468 | |
---|
1469 | // Second Z0: combine phase space with couplings. |
---|
1470 | ef2 = couplingsPtr->ef2(idAbs) * psvec; |
---|
1471 | efvf = couplingsPtr->efvf(idAbs) * psvec; |
---|
1472 | vf2af2 = couplingsPtr->vf2(idAbs) * psvec |
---|
1473 | + couplingsPtr->af2(idAbs) * psaxi; |
---|
1474 | colf = (idAbs < 6) ? colQ4 : 1.; |
---|
1475 | |
---|
1476 | // Second Z0: store sum of combinations for open outstate channels. |
---|
1477 | if (onMode == 1 || onMode == 2) { |
---|
1478 | gamSum4 += colf * ef2; |
---|
1479 | intSum4 += colf * efvf; |
---|
1480 | resSum4 += colf * vf2af2; |
---|
1481 | } |
---|
1482 | } |
---|
1483 | |
---|
1484 | // End loop over fermions. |
---|
1485 | } |
---|
1486 | } |
---|
1487 | |
---|
1488 | // First Z0: calculate prefactors for gamma/interference/Z0 terms. |
---|
1489 | gamProp3 = 4. * alpEM3 / (3. * M_PI * s3); |
---|
1490 | intProp3 = gamProp3 * 2. * thetaWRat * s3 * (s3 - m2Res) |
---|
1491 | / ( pow2(s3 - m2Res) + pow2(s3 * GamMRat) ); |
---|
1492 | resProp3 = gamProp3 * pow2(thetaWRat * s3) |
---|
1493 | / ( pow2(s3 - m2Res) + pow2(s3 * GamMRat) ); |
---|
1494 | |
---|
1495 | // First Z0: optionally only keep gamma* or Z0 term. |
---|
1496 | if (gmZmode == 1) {intProp3 = 0.; resProp3 = 0.;} |
---|
1497 | if (gmZmode == 2) {gamProp3 = 0.; intProp3 = 0.;} |
---|
1498 | |
---|
1499 | // Second Z0: calculate prefactors for gamma/interference/Z0 terms. |
---|
1500 | gamProp4 = 4. * alpEM4 / (3. * M_PI * s4); |
---|
1501 | intProp4 = gamProp4 * 2. * thetaWRat * s4 * (s4 - m2Res) |
---|
1502 | / ( pow2(s4 - m2Res) + pow2(s4 * GamMRat) ); |
---|
1503 | resProp4 = gamProp4 * pow2(thetaWRat * s4) |
---|
1504 | / ( pow2(s4 - m2Res) + pow2(s4 * GamMRat) ); |
---|
1505 | |
---|
1506 | // Second Z0: optionally only keep gamma* or Z0 term. |
---|
1507 | if (gmZmode == 1) {intProp4 = 0.; resProp4 = 0.;} |
---|
1508 | if (gmZmode == 2) {gamProp4 = 0.; intProp4 = 0.;} |
---|
1509 | |
---|
1510 | } |
---|
1511 | |
---|
1512 | //-------------------------------------------------------------------------- |
---|
1513 | |
---|
1514 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
1515 | |
---|
1516 | double Sigma2ffbar2gmZgmZ::sigmaHat() { |
---|
1517 | |
---|
1518 | // Charge/2, left- and righthanded couplings for in-fermion. |
---|
1519 | int idAbs = abs(id1); |
---|
1520 | double ei = 0.5 * couplingsPtr->ef(idAbs); |
---|
1521 | double li = couplingsPtr->lf(idAbs); |
---|
1522 | double ri = couplingsPtr->rf(idAbs); |
---|
1523 | |
---|
1524 | // Combine left/right gamma, interference and Z0 parts for each Z0. |
---|
1525 | double left3 = ei * ei * gamProp3 * gamSum3 |
---|
1526 | + ei * li * intProp3 * intSum3 |
---|
1527 | + li * li * resProp3 * resSum3; |
---|
1528 | double right3 = ei * ei * gamProp3 * gamSum3 |
---|
1529 | + ei * ri * intProp3 * intSum3 |
---|
1530 | + ri * ri * resProp3 * resSum3; |
---|
1531 | double left4 = ei * ei * gamProp4 * gamSum4 |
---|
1532 | + ei * li * intProp4 * intSum4 |
---|
1533 | + li * li * resProp4 * resSum4; |
---|
1534 | double right4 = ei * ei * gamProp4 * gamSum4 |
---|
1535 | + ei * ri * intProp4 * intSum4 |
---|
1536 | + ri * ri * resProp4 * resSum4; |
---|
1537 | |
---|
1538 | // Combine left- and right-handed couplings for the two Z0's. |
---|
1539 | double sigma = sigma0 * (left3 * left4 + right3 * right4); |
---|
1540 | |
---|
1541 | // Correct for the running-width Z0 propagators weight in PhaseSpace. |
---|
1542 | sigma /= (runBW3 * runBW4); |
---|
1543 | |
---|
1544 | // Initial-state colour factor. Answer. |
---|
1545 | if (idAbs < 9) sigma /= 3.; |
---|
1546 | return sigma; |
---|
1547 | |
---|
1548 | } |
---|
1549 | |
---|
1550 | //-------------------------------------------------------------------------- |
---|
1551 | |
---|
1552 | // Select identity, colour and anticolour. |
---|
1553 | |
---|
1554 | void Sigma2ffbar2gmZgmZ::setIdColAcol() { |
---|
1555 | |
---|
1556 | // Flavours trivial. |
---|
1557 | setId( id1, id2, 23, 23); |
---|
1558 | |
---|
1559 | // Colour flow topologies. Swap when antiquarks. |
---|
1560 | if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0); |
---|
1561 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
1562 | if (id1 < 0) swapColAcol(); |
---|
1563 | |
---|
1564 | } |
---|
1565 | |
---|
1566 | //-------------------------------------------------------------------------- |
---|
1567 | |
---|
1568 | // Evaluate correlated decay flavours of the two gamma*/Z0. |
---|
1569 | // Unique complication, caused by gamma*/Z0 mix different left/right. |
---|
1570 | |
---|
1571 | double Sigma2ffbar2gmZgmZ::weightDecayFlav( Event& process) { |
---|
1572 | |
---|
1573 | // Order so that fbar(1) f(2) -> f'(3) fbar'(4) f"(5) fbar"(6). |
---|
1574 | i1 = (process[3].id() < 0) ? 3 : 4; |
---|
1575 | i2 = 7 - i1; |
---|
1576 | i3 = (process[7].id() > 0) ? 7 : 8; |
---|
1577 | i4 = 15 - i3; |
---|
1578 | i5 = (process[9].id() > 0) ? 9 : 10; |
---|
1579 | i6 = 19 - i5; |
---|
1580 | |
---|
1581 | // Charge/2, left- and righthanded couplings for in- and out-fermions. |
---|
1582 | int idAbs = process[i1].idAbs(); |
---|
1583 | double ei = 0.5 * couplingsPtr->ef(idAbs); |
---|
1584 | double li = couplingsPtr->lf(idAbs); |
---|
1585 | double ri = couplingsPtr->rf(idAbs); |
---|
1586 | idAbs = process[i3].idAbs(); |
---|
1587 | double e3 = 0.5 * couplingsPtr->ef(idAbs); |
---|
1588 | double l3 = couplingsPtr->lf(idAbs); |
---|
1589 | double r3 = couplingsPtr->rf(idAbs); |
---|
1590 | idAbs = process[i5].idAbs(); |
---|
1591 | double e4 = 0.5 * couplingsPtr->ef(idAbs); |
---|
1592 | double l4 = couplingsPtr->lf(idAbs); |
---|
1593 | double r4 = couplingsPtr->rf(idAbs); |
---|
1594 | |
---|
1595 | // Left- and righthanded couplings combined with propagators. |
---|
1596 | c3LL = ei * ei * gamProp3 * e3 * e3 |
---|
1597 | + ei * li * intProp3 * e3 * l3 |
---|
1598 | + li * li * resProp3 * l3 * l3; |
---|
1599 | c3LR = ei * ei * gamProp3 * e3 * e3 |
---|
1600 | + ei * li * intProp3 * e3 * r3 |
---|
1601 | + li * li * resProp3 * r3 * r3; |
---|
1602 | c3RL = ei * ei * gamProp3 * e3 * e3 |
---|
1603 | + ei * ri * intProp3 * e3 * l3 |
---|
1604 | + ri * ri * resProp3 * l3 * l3; |
---|
1605 | c3RR = ei * ei * gamProp3 * e3 * e3 |
---|
1606 | + ei * ri * intProp3 * e3 * r3 |
---|
1607 | + ri * ri * resProp3 * r3 * r3; |
---|
1608 | c4LL = ei * ei * gamProp4 * e4 * e4 |
---|
1609 | + ei * li * intProp4 * e4 * l4 |
---|
1610 | + li * li * resProp4 * l4 * l4; |
---|
1611 | c4LR = ei * ei * gamProp4 * e4 * e4 |
---|
1612 | + ei * li * intProp4 * e4 * r4 |
---|
1613 | + li * li * resProp4 * r4 * r4; |
---|
1614 | c4RL = ei * ei * gamProp4 * e4 * e4 |
---|
1615 | + ei * ri * intProp4 * e4 * l4 |
---|
1616 | + ri * ri * resProp4 * l4 * l4; |
---|
1617 | c4RR = ei * ei * gamProp4 * e4 * e4 |
---|
1618 | + ei * ri * intProp4 * e4 * r4 |
---|
1619 | + ri * ri * resProp4 * r4 * r4; |
---|
1620 | |
---|
1621 | // Flavour weight and maximum. |
---|
1622 | flavWt = (c3LL + c3LR) * (c4LL + c4LR) + (c3RL + c3RR) * (c4RL + c4RR); |
---|
1623 | double flavWtMax = (c3LL + c3LR + c3RL + c3RR) * (c4LL + c4LR + c4RL + c4RR); |
---|
1624 | |
---|
1625 | // Done. |
---|
1626 | return flavWt / flavWtMax; |
---|
1627 | |
---|
1628 | } |
---|
1629 | |
---|
1630 | //-------------------------------------------------------------------------- |
---|
1631 | |
---|
1632 | // Evaluate weight for decay angles of the two gamma*/Z0. |
---|
1633 | |
---|
1634 | double Sigma2ffbar2gmZgmZ::weightDecay( Event& process, int iResBeg, |
---|
1635 | int iResEnd) { |
---|
1636 | |
---|
1637 | // Two resonance decays, but with common weight. |
---|
1638 | if (iResBeg != 5 || iResEnd != 6) return 1.; |
---|
1639 | |
---|
1640 | // Set up four-products and internal products. |
---|
1641 | setupProd( process, i1, i2, i3, i4, i5, i6); |
---|
1642 | |
---|
1643 | // Flip tHat and uHat if first incoming is fermion. |
---|
1644 | double tHres = tH; |
---|
1645 | double uHres = uH; |
---|
1646 | if (process[3].id() > 0) swap( tHres, uHres); |
---|
1647 | |
---|
1648 | // Kinematics factors (norm(x) = |x|^2). |
---|
1649 | double fGK135 = norm( fGK( 1, 2, 3, 4, 5, 6) / tHres |
---|
1650 | + fGK( 1, 2, 5, 6, 3, 4) / uHres ); |
---|
1651 | double fGK145 = norm( fGK( 1, 2, 4, 3, 5, 6) / tHres |
---|
1652 | + fGK( 1, 2, 5, 6, 4, 3) / uHres ); |
---|
1653 | double fGK136 = norm( fGK( 1, 2, 3, 4, 6, 5) / tHres |
---|
1654 | + fGK( 1, 2, 6, 5, 3, 4) / uHres ); |
---|
1655 | double fGK146 = norm( fGK( 1, 2, 4, 3, 6, 5) / tHres |
---|
1656 | + fGK( 1, 2, 6, 5, 4, 3) / uHres ); |
---|
1657 | double fGK253 = norm( fGK( 2, 1, 5, 6, 3, 4) / tHres |
---|
1658 | + fGK( 2, 1, 3, 4, 5, 6) / uHres ); |
---|
1659 | double fGK263 = norm( fGK( 2, 1, 6, 5, 3, 4) / tHres |
---|
1660 | + fGK( 2, 1, 3, 4, 6, 5) / uHres ); |
---|
1661 | double fGK254 = norm( fGK( 2, 1, 5, 6, 4, 3) / tHres |
---|
1662 | + fGK( 2, 1, 4, 3, 5, 6) / uHres ); |
---|
1663 | double fGK264 = norm( fGK( 2, 1, 6, 5, 4, 3) / tHres |
---|
1664 | + fGK( 2, 1, 4, 3, 6, 5) / uHres ); |
---|
1665 | |
---|
1666 | // Weight and maximum. |
---|
1667 | double wt = c3LL * c4LL * fGK135 + c3LR * c4LL * fGK145 |
---|
1668 | + c3LL * c4LR * fGK136 + c3LR * c4LR * fGK146 |
---|
1669 | + c3RL * c4RL * fGK253 + c3RR * c4RL * fGK263 |
---|
1670 | + c3RL * c4RR * fGK254 + c3RR * c4RR * fGK264; |
---|
1671 | double wtMax = 16. * s3 * s4 * flavWt |
---|
1672 | * ( (tHres*tHres + uHres*uHres + 2. * sH * (s3 + s4)) / (tHres * uHres) |
---|
1673 | - s3 * s4 * (1. / (tHres*tHres) + 1. / (uHres*uHres)) ); |
---|
1674 | |
---|
1675 | // Done. |
---|
1676 | return wt / wtMax; |
---|
1677 | |
---|
1678 | } |
---|
1679 | |
---|
1680 | //========================================================================== |
---|
1681 | |
---|
1682 | // Sigma2ffbar2ZW class. |
---|
1683 | // Cross section for f fbar' -> Z0 W+- (f is quark or lepton). |
---|
1684 | |
---|
1685 | //-------------------------------------------------------------------------- |
---|
1686 | |
---|
1687 | // Initialize process. |
---|
1688 | |
---|
1689 | void Sigma2ffbar2ZW::initProc() { |
---|
1690 | |
---|
1691 | // Store W+- mass and width for propagator. |
---|
1692 | mW = particleDataPtr->m0(24); |
---|
1693 | widW = particleDataPtr->mWidth(24); |
---|
1694 | mWS = mW*mW; |
---|
1695 | mwWS = pow2(mW * widW); |
---|
1696 | |
---|
1697 | // Left-handed couplings for up/nu- and down/e-type quarks. |
---|
1698 | lun = (hasLeptonBeams) ? couplingsPtr->lf(12) : couplingsPtr->lf(2); |
---|
1699 | lde = (hasLeptonBeams) ? couplingsPtr->lf(11) : couplingsPtr->lf(1); |
---|
1700 | |
---|
1701 | // Common weak coupling factor. |
---|
1702 | sin2thetaW = couplingsPtr->sin2thetaW(); |
---|
1703 | cos2thetaW = couplingsPtr->cos2thetaW(); |
---|
1704 | thetaWRat = 1. / (4. * cos2thetaW); |
---|
1705 | cotT = sqrt(cos2thetaW / sin2thetaW); |
---|
1706 | thetaWpt = (9. - 8. * sin2thetaW) / 4.; |
---|
1707 | thetaWmm = (8. * sin2thetaW - 6.) / 4.; |
---|
1708 | |
---|
1709 | // Secondary open width fractions. |
---|
1710 | openFracPos = particleDataPtr->resOpenFrac(23, 24); |
---|
1711 | openFracNeg = particleDataPtr->resOpenFrac(23, -24); |
---|
1712 | |
---|
1713 | } |
---|
1714 | |
---|
1715 | //-------------------------------------------------------------------------- |
---|
1716 | |
---|
1717 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. |
---|
1718 | |
---|
1719 | void Sigma2ffbar2ZW::sigmaKin() { |
---|
1720 | |
---|
1721 | // Evaluate cross section, as programmed by Merlin Kole (after tidying), |
---|
1722 | // based on Brown, Sahdev, Mikaelian, Phys Rev. D20 (1979) 1069. |
---|
1723 | /* |
---|
1724 | double resBW = 1. / (pow2(sH - mWS) + mwWS); |
---|
1725 | double prefac = 12.0 * M_PI * pow2(alpEM) / (sH2 * 8. * sin2thetaW); |
---|
1726 | double temp1 = tH * uH - s3 * s4; |
---|
1727 | double temp2 = temp1 / (s3 * s4); |
---|
1728 | double temp3 = (s3 + s4) / sH; |
---|
1729 | double temp4 = s3 * s4 / sH; |
---|
1730 | double partA = temp2 * (0.25 - 0.5 * temp3 |
---|
1731 | + (pow2(s3 + s4) + 8. * s3 * s4)/(4. * sH2) ) |
---|
1732 | + (s3 + s4)/(s3 * s4) * (sH/2. - s3 - s4 + pow2(s3 - s4)/(2. * sH)); |
---|
1733 | double partB1 = lun * (0.25 * temp2 * (1. - temp3 - 4. * temp4 / tH) |
---|
1734 | + ((s3 + s4)/(2. * s3 * s4)) * (sH - s3 - s4 + 2. * s3 * s4 / tH) ); |
---|
1735 | double partB2 = lde * ( 0.25 * temp2 * (1.- temp3 - 4. * temp4 / uH) |
---|
1736 | + ((s3 + s4)/(2. * s3 * s4)) * (sH - s3 - s4 + 2. * s3 * s4 / uH) ); |
---|
1737 | double partE = 0.25 * temp2 + 0.5 *(s3 + s4) / temp4; |
---|
1738 | sigma0 = prefac * (pow2(cotT) * sH2 * resBW * partA |
---|
1739 | + 2.* sH * cotT * resBW * (sH - mWS) * (partB2 - partB1) |
---|
1740 | + pow2(lun - lde) * partE + pow2(lde) * temp1/uH2 |
---|
1741 | + pow2(lun) * temp1/tH2 + 2. * lun * lde * sH * (s3 + s4) / (uH * tH)); |
---|
1742 | */ |
---|
1743 | |
---|
1744 | // Evaluate cross section. Expression from EHLQ, with bug fix, |
---|
1745 | // but can still give negative cross section so suspect. |
---|
1746 | double resBW = 1. / (pow2(sH - mWS) + mwWS); |
---|
1747 | sigma0 = (M_PI / sH2) * 0.5 * pow2(alpEM / sin2thetaW); |
---|
1748 | sigma0 *= sH * resBW * (thetaWpt * pT2 + thetaWmm * (s3 + s4)) |
---|
1749 | + (sH - mWS) * resBW * sH * (pT2 - s3 - s4) * (lun / tH - lde / uH) |
---|
1750 | + thetaWRat * sH * pT2 * ( lun*lun / tH2 + lde*lde / uH2 ) |
---|
1751 | + 2. * thetaWRat * sH * (s3 + s4) * lun * lde / (tH * uH); |
---|
1752 | // Need to protect against negative cross sections at times. |
---|
1753 | sigma0 = max(0., sigma0); |
---|
1754 | |
---|
1755 | } |
---|
1756 | |
---|
1757 | //-------------------------------------------------------------------------- |
---|
1758 | |
---|
1759 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
1760 | |
---|
1761 | double Sigma2ffbar2ZW::sigmaHat() { |
---|
1762 | |
---|
1763 | // CKM and colour factors. |
---|
1764 | double sigma = sigma0; |
---|
1765 | if (abs(id1) < 9) sigma *= couplingsPtr->V2CKMid(abs(id1), abs(id2)) / 3.; |
---|
1766 | |
---|
1767 | // Corrections for secondary widths in Z0 and W+- decays. |
---|
1768 | int idUp = (abs(id1)%2 == 0) ? id1 : id2; |
---|
1769 | sigma *= (idUp > 0) ? openFracPos : openFracNeg; |
---|
1770 | |
---|
1771 | // Answer. |
---|
1772 | return sigma; |
---|
1773 | |
---|
1774 | } |
---|
1775 | |
---|
1776 | //-------------------------------------------------------------------------- |
---|
1777 | |
---|
1778 | // Select identity, colour and anticolour. |
---|
1779 | |
---|
1780 | void Sigma2ffbar2ZW::setIdColAcol() { |
---|
1781 | |
---|
1782 | // Sign of outgoing W. |
---|
1783 | int sign = 1 - 2 * (abs(id1)%2); |
---|
1784 | if (id1 < 0) sign = -sign; |
---|
1785 | setId( id1, id2, 23, 24 * sign); |
---|
1786 | |
---|
1787 | // tHat is defined between (f, W-) or (fbar, W+), |
---|
1788 | // so OK for u/ubar on side 1, but must swap tHat <-> uHat if d/dbar. |
---|
1789 | if (abs(id1)%2 == 1) swapTU = true; |
---|
1790 | |
---|
1791 | // Colour flow topologies. Swap when antiquarks. |
---|
1792 | if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0); |
---|
1793 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
1794 | if (id1 < 0) swapColAcol(); |
---|
1795 | |
---|
1796 | } |
---|
1797 | |
---|
1798 | //-------------------------------------------------------------------------- |
---|
1799 | |
---|
1800 | // Evaluate weight for Z0 and W+- decay angles. |
---|
1801 | |
---|
1802 | double Sigma2ffbar2ZW::weightDecay( Event& process, int iResBeg, int iResEnd) { |
---|
1803 | |
---|
1804 | // Two resonance decays, but with common weight. |
---|
1805 | if (iResBeg != 5 || iResEnd != 6) return 1.; |
---|
1806 | |
---|
1807 | // Order so that fbar(1) f(2) -> f'(3) fbar'(4) f"(5) fbar"(6) |
---|
1808 | // with f' fbar' from W+- and f" fbar" from Z0 (note flip Z0 <-> W+-). |
---|
1809 | int i1 = (process[3].id() < 0) ? 3 : 4; |
---|
1810 | int i2 = 7 - i1; |
---|
1811 | int i3 = (process[9].id() > 0) ? 9 : 10; |
---|
1812 | int i4 = 19 - i3; |
---|
1813 | int i5 = (process[7].id() > 0) ? 7 : 8; |
---|
1814 | int i6 = 15 - i5; |
---|
1815 | |
---|
1816 | // Set up four-products and internal products. |
---|
1817 | setupProd( process, i1, i2, i3, i4, i5, i6); |
---|
1818 | |
---|
1819 | // Swap tHat and uHat if incoming fermion is downtype. |
---|
1820 | double tHres = tH; |
---|
1821 | double uHres = uH; |
---|
1822 | if (process[i2].id()%2 == 1) swap( tHres, uHres); |
---|
1823 | |
---|
1824 | // Couplings of incoming (anti)fermions and outgoing from Z0. |
---|
1825 | int idAbs = process[i1].idAbs(); |
---|
1826 | double ai = couplingsPtr->af(idAbs); |
---|
1827 | double li1 = couplingsPtr->lf(idAbs); |
---|
1828 | idAbs = process[i2].idAbs(); |
---|
1829 | double li2 = couplingsPtr->lf(idAbs); |
---|
1830 | idAbs = process[i5].idAbs(); |
---|
1831 | double l4 = couplingsPtr->lf(idAbs); |
---|
1832 | double r4 = couplingsPtr->rf(idAbs); |
---|
1833 | |
---|
1834 | // W propagator/interference factor. |
---|
1835 | double Wint = cos2thetaW * (sH - mWS) / (pow2(sH - mWS) + mwWS); |
---|
1836 | |
---|
1837 | // Combinations of couplings and kinematics (norm(x) = |x|^2). |
---|
1838 | double aWZ = li2 / tHres - 2. * Wint * ai; |
---|
1839 | double bWZ = li1 / uHres + 2. * Wint * ai; |
---|
1840 | double fGK135 = norm( aWZ * fGK( 1, 2, 3, 4, 5, 6) |
---|
1841 | + bWZ * fGK( 1, 2, 5, 6, 3, 4) ); |
---|
1842 | double fGK136 = norm( aWZ * fGK( 1, 2, 3, 4, 6, 5) |
---|
1843 | + bWZ * fGK( 1, 2, 6, 5, 3, 4) ); |
---|
1844 | double xiT = xiGK( tHres, uHres); |
---|
1845 | double xiU = xiGK( uHres, tHres); |
---|
1846 | double xjTU = xjGK( tHres, uHres); |
---|
1847 | |
---|
1848 | // Weight and maximum weight. |
---|
1849 | double wt = l4*l4 * fGK135 + r4*r4 * fGK136; |
---|
1850 | double wtMax = 4. * s3 * s4 * (l4*l4 + r4*r4) |
---|
1851 | * (aWZ * aWZ * xiT + bWZ * bWZ * xiU + aWZ * bWZ * xjTU); |
---|
1852 | |
---|
1853 | // Done. |
---|
1854 | return wt / wtMax; |
---|
1855 | |
---|
1856 | } |
---|
1857 | |
---|
1858 | //========================================================================== |
---|
1859 | |
---|
1860 | // Sigma2ffbar2WW class. |
---|
1861 | // Cross section for f fbar -> W- W+ (f is quark or lepton). |
---|
1862 | |
---|
1863 | //-------------------------------------------------------------------------- |
---|
1864 | |
---|
1865 | // Initialize process. |
---|
1866 | |
---|
1867 | void Sigma2ffbar2WW::initProc() { |
---|
1868 | |
---|
1869 | // Store Z0 mass and width for propagator. Common coupling factor. |
---|
1870 | mZ = particleDataPtr->m0(23); |
---|
1871 | widZ = particleDataPtr->mWidth(23); |
---|
1872 | mZS = mZ*mZ; |
---|
1873 | mwZS = pow2(mZ * widZ); |
---|
1874 | thetaWRat = 1. / (4. * couplingsPtr->sin2thetaW()); |
---|
1875 | |
---|
1876 | // Secondary open width fraction. |
---|
1877 | openFracPair = particleDataPtr->resOpenFrac(24, -24); |
---|
1878 | |
---|
1879 | } |
---|
1880 | |
---|
1881 | //-------------------------------------------------------------------------- |
---|
1882 | |
---|
1883 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. |
---|
1884 | |
---|
1885 | void Sigma2ffbar2WW::sigmaKin() { |
---|
1886 | |
---|
1887 | // Cross section part common for all incoming flavours. |
---|
1888 | sigma0 = (M_PI / sH2) * pow2(alpEM); |
---|
1889 | |
---|
1890 | // Z0 propagator and gamma*/Z0 interference. |
---|
1891 | double Zprop = sH2 / (pow2(sH - mZS) + mwZS); |
---|
1892 | double Zint = Zprop * (1. - mZS / sH); |
---|
1893 | |
---|
1894 | // Common coupling factors (g = gamma*, Z = Z0, f = t-channel fermion). |
---|
1895 | cgg = 0.5; |
---|
1896 | cgZ = thetaWRat * Zint; |
---|
1897 | cZZ = 0.5 * pow2(thetaWRat) * Zprop; |
---|
1898 | cfg = thetaWRat; |
---|
1899 | cfZ = pow2(thetaWRat) * Zint; |
---|
1900 | cff = pow2(thetaWRat); |
---|
1901 | |
---|
1902 | // Kinematical functions. |
---|
1903 | double rat34 = sH * (2. * (s3 + s4) + pT2) / (s3 * s4); |
---|
1904 | double lambdaS = pow2(sH - s3 - s4) - 4. * s3 * s4; |
---|
1905 | double intA = (sH - s3 - s4) * rat34 / sH; |
---|
1906 | double intB = 4. * (s3 + s4 - pT2); |
---|
1907 | gSS = (lambdaS * rat34 + 12. * sH * pT2) / sH2; |
---|
1908 | gTT = rat34 + 4. * sH * pT2 / tH2; |
---|
1909 | gST = intA + intB / tH; |
---|
1910 | gUU = rat34 + 4. * sH * pT2 / uH2; |
---|
1911 | gSU = intA + intB / uH; |
---|
1912 | |
---|
1913 | } |
---|
1914 | |
---|
1915 | //-------------------------------------------------------------------------- |
---|
1916 | |
---|
1917 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
1918 | |
---|
1919 | double Sigma2ffbar2WW::sigmaHat() { |
---|
1920 | |
---|
1921 | // Flavour-specific couplings. |
---|
1922 | int idAbs = abs(id1); |
---|
1923 | double ei = couplingsPtr->ef(idAbs); |
---|
1924 | double vi = couplingsPtr->vf(idAbs); |
---|
1925 | double ai = couplingsPtr->af(idAbs); |
---|
1926 | |
---|
1927 | // Combine, with different cases for up- and down-type in-flavours. |
---|
1928 | double sigma = sigma0; |
---|
1929 | sigma *= (idAbs%2 == 1) |
---|
1930 | ? (cgg * ei*ei + cgZ * ei * vi + cZZ * (vi*vi + ai*ai)) * gSS |
---|
1931 | + (cfg * ei + cfZ * (vi + ai)) * gST + cff * gTT |
---|
1932 | : (cgg * ei*ei + cgZ * ei * vi + cZZ * (vi*vi + ai*ai)) * gSS |
---|
1933 | - (cfg * ei + cfZ * (vi + ai)) * gSU + cff * gUU; |
---|
1934 | |
---|
1935 | // Initial-state colour factor. Correction for secondary widths. Answer. |
---|
1936 | if (idAbs < 9) sigma /= 3.; |
---|
1937 | sigma *= openFracPair; |
---|
1938 | return sigma; |
---|
1939 | |
---|
1940 | } |
---|
1941 | |
---|
1942 | //-------------------------------------------------------------------------- |
---|
1943 | |
---|
1944 | // Select identity, colour and anticolour. |
---|
1945 | |
---|
1946 | void Sigma2ffbar2WW::setIdColAcol() { |
---|
1947 | |
---|
1948 | // Always order W- W+, i.e. W- first. |
---|
1949 | setId( id1, id2, -24, 24); |
---|
1950 | |
---|
1951 | // tHat is defined between (f, W-) or (fbar, W+), |
---|
1952 | if (id1 < 0) swapTU = true; |
---|
1953 | |
---|
1954 | // Colour flow topologies. Swap when antiquarks. |
---|
1955 | if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0); |
---|
1956 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
1957 | if (id1 < 0) swapColAcol(); |
---|
1958 | |
---|
1959 | } |
---|
1960 | |
---|
1961 | //-------------------------------------------------------------------------- |
---|
1962 | |
---|
1963 | // Evaluate weight for W+ and W- decay angles. |
---|
1964 | |
---|
1965 | double Sigma2ffbar2WW::weightDecay( Event& process, int iResBeg, int iResEnd) { |
---|
1966 | |
---|
1967 | // Two resonance decays, but with common weight. |
---|
1968 | if (iResBeg != 5 || iResEnd != 6) return 1.; |
---|
1969 | |
---|
1970 | // Order so that fbar(1) f(2) -> f'(3) fbar'(4) f"(5) fbar"(6). |
---|
1971 | // with f' fbar' from W- and f" fbar" from W+. |
---|
1972 | int i1 = (process[3].id() < 0) ? 3 : 4; |
---|
1973 | int i2 = 7 - i1; |
---|
1974 | int i3 = (process[7].id() > 0) ? 7 : 8; |
---|
1975 | int i4 = 15 - i3; |
---|
1976 | int i5 = (process[9].id() > 0) ? 9 : 10; |
---|
1977 | int i6 = 19 - i5; |
---|
1978 | |
---|
1979 | // Set up four-products and internal products. |
---|
1980 | setupProd( process, i1, i2, i3, i4, i5, i6); |
---|
1981 | |
---|
1982 | // tHat and uHat of fbar f -> W- W+ opposite to previous convention. |
---|
1983 | double tHres = uH; |
---|
1984 | double uHres = tH; |
---|
1985 | |
---|
1986 | // Couplings of incoming (anti)fermion. |
---|
1987 | int idAbs = process[i1].idAbs(); |
---|
1988 | double ai = couplingsPtr->af(idAbs); |
---|
1989 | double li = couplingsPtr->lf(idAbs); |
---|
1990 | double ri = couplingsPtr->rf(idAbs); |
---|
1991 | |
---|
1992 | // gamma*/Z0 propagator/interference factor. |
---|
1993 | double Zint = mZS * (sH - mZS) / (pow2(sH - mZS) + mwZS); |
---|
1994 | |
---|
1995 | // Combinations of couplings and kinematics (norm(x) = |x|^2). |
---|
1996 | double dWW = (li * Zint + ai) / sH; |
---|
1997 | double aWW = dWW + 0.5 * (ai + 1.) / tHres; |
---|
1998 | double bWW = dWW + 0.5 * (ai - 1.) / uHres; |
---|
1999 | double cWW = ri * Zint / sH; |
---|
2000 | double fGK135 = norm( aWW * fGK( 1, 2, 3, 4, 5, 6) |
---|
2001 | - bWW * fGK( 1, 2, 5, 6, 3, 4) ); |
---|
2002 | double fGK253 = norm( cWW * ( fGK( 2, 1, 5, 6, 3, 4) |
---|
2003 | - fGK( 2, 1, 3, 4, 5, 6) ) ); |
---|
2004 | double xiT = xiGK( tHres, uHres); |
---|
2005 | double xiU = xiGK( uHres, tHres); |
---|
2006 | double xjTU = xjGK( tHres, uHres); |
---|
2007 | |
---|
2008 | // Weight and maximum weight. |
---|
2009 | double wt = fGK135 + fGK253; |
---|
2010 | double wtMax = 4. * s3 * s4 |
---|
2011 | * ( aWW * aWW * xiT + bWW * bWW * xiU - aWW * bWW * xjTU |
---|
2012 | + cWW * cWW * (xiT + xiU - xjTU) ); |
---|
2013 | |
---|
2014 | // Done. |
---|
2015 | return wt / wtMax; |
---|
2016 | } |
---|
2017 | |
---|
2018 | //========================================================================== |
---|
2019 | |
---|
2020 | // Sigma2ffbargmZggm class. |
---|
2021 | // Collects common methods for f fbar -> gamma*/Z0 g/gamma and permutations. |
---|
2022 | |
---|
2023 | //-------------------------------------------------------------------------- |
---|
2024 | |
---|
2025 | // Initialize process. |
---|
2026 | |
---|
2027 | void Sigma2ffbargmZggm::initProc() { |
---|
2028 | |
---|
2029 | // Allow to pick only gamma* or Z0 part of full gamma*/Z0 expression. |
---|
2030 | gmZmode = settingsPtr->mode("WeakZ0:gmZmode"); |
---|
2031 | |
---|
2032 | // Store Z0 mass and width for propagator. |
---|
2033 | mRes = particleDataPtr->m0(23); |
---|
2034 | GammaRes = particleDataPtr->mWidth(23); |
---|
2035 | m2Res = mRes*mRes; |
---|
2036 | GamMRat = GammaRes / mRes; |
---|
2037 | thetaWRat = 1. / (16. * couplingsPtr->sin2thetaW() |
---|
2038 | * couplingsPtr->cos2thetaW()); |
---|
2039 | |
---|
2040 | // Set pointer to particle properties and decay table. |
---|
2041 | particlePtr = particleDataPtr->particleDataEntryPtr(23); |
---|
2042 | |
---|
2043 | } |
---|
2044 | |
---|
2045 | //-------------------------------------------------------------------------- |
---|
2046 | |
---|
2047 | // Evaluate sum of flavour couplings times phase space. |
---|
2048 | |
---|
2049 | void Sigma2ffbargmZggm::flavSum() { |
---|
2050 | |
---|
2051 | // Coupling factors for Z0 subsystem. |
---|
2052 | double alpSZ = couplingsPtr->alphaS(s3); |
---|
2053 | double colQZ = 3. * (1. + alpSZ / M_PI); |
---|
2054 | |
---|
2055 | // Reset quantities to sum. Declare variables in loop. |
---|
2056 | gamSum = 0.; |
---|
2057 | intSum = 0.; |
---|
2058 | resSum = 0.; |
---|
2059 | int onMode; |
---|
2060 | double mf, mr, psvec, psaxi, betaf, ef2, efvf, vf2af2, colf; |
---|
2061 | |
---|
2062 | // Loop over all Z0 decay channels. |
---|
2063 | for (int i = 0; i < particlePtr->sizeChannels(); ++i) { |
---|
2064 | int idAbs = abs( particlePtr->channel(i).product(0) ); |
---|
2065 | |
---|
2066 | // Only contributions from three fermion generations, except top. |
---|
2067 | if ( (idAbs > 0 && idAbs < 6) || ( idAbs > 10 && idAbs < 17)) { |
---|
2068 | mf = particleDataPtr->m0(idAbs); |
---|
2069 | |
---|
2070 | // Check that above threshold. Phase space. |
---|
2071 | if (m3 > 2. * mf + MASSMARGIN) { |
---|
2072 | mr = pow2(mf / m3); |
---|
2073 | betaf = sqrtpos(1. - 4. * mr); |
---|
2074 | psvec = betaf * (1. + 2. * mr); |
---|
2075 | psaxi = pow3(betaf); |
---|
2076 | |
---|
2077 | // Combine phase space with couplings. |
---|
2078 | ef2 = couplingsPtr->ef2(idAbs) * psvec; |
---|
2079 | efvf = couplingsPtr->efvf(idAbs) * psvec; |
---|
2080 | vf2af2 = couplingsPtr->vf2(idAbs) * psvec |
---|
2081 | + couplingsPtr->af2(idAbs) * psaxi; |
---|
2082 | colf = (idAbs < 6) ? colQZ : 1.; |
---|
2083 | |
---|
2084 | // Store sum of combinations. For outstate only open channels. |
---|
2085 | onMode = particlePtr->channel(i).onMode(); |
---|
2086 | if (onMode == 1 || onMode == 2) { |
---|
2087 | gamSum += colf * ef2; |
---|
2088 | intSum += colf * efvf; |
---|
2089 | resSum += colf * vf2af2; |
---|
2090 | } |
---|
2091 | |
---|
2092 | // End loop over fermions. |
---|
2093 | } |
---|
2094 | } |
---|
2095 | } |
---|
2096 | |
---|
2097 | // Done. Return values in gamSum, intSum and resSum. |
---|
2098 | |
---|
2099 | } |
---|
2100 | |
---|
2101 | //-------------------------------------------------------------------------- |
---|
2102 | |
---|
2103 | // Calculate common parts of gamma/interference/Z0 propagator terms. |
---|
2104 | |
---|
2105 | void Sigma2ffbargmZggm::propTerm() { |
---|
2106 | |
---|
2107 | // Calculate prefactors for gamma/interference/Z0 cross section terms. |
---|
2108 | gamProp = 4. * alpEM / (3. * M_PI * s3); |
---|
2109 | intProp = gamProp * 2. * thetaWRat * s3 * (s3 - m2Res) |
---|
2110 | / ( pow2(s3 - m2Res) + pow2(s3 * GamMRat) ); |
---|
2111 | resProp = gamProp * pow2(thetaWRat * s3) |
---|
2112 | / ( pow2(s3 - m2Res) + pow2(s3 * GamMRat) ); |
---|
2113 | |
---|
2114 | // Optionally only keep gamma* or Z0 term. |
---|
2115 | if (gmZmode == 1) {intProp = 0.; resProp = 0.;} |
---|
2116 | if (gmZmode == 2) {gamProp = 0.; intProp = 0.;} |
---|
2117 | |
---|
2118 | } |
---|
2119 | |
---|
2120 | //-------------------------------------------------------------------------- |
---|
2121 | |
---|
2122 | // Evaluate weight for gamma*/Z0 decay angle. |
---|
2123 | |
---|
2124 | double Sigma2ffbargmZggm::weightDecay( Event& process, int iResBeg, |
---|
2125 | int iResEnd) { |
---|
2126 | |
---|
2127 | // Z should sit in entry 5 and one more parton in entry 6. |
---|
2128 | if (iResBeg != 5 || iResEnd != 6) return 1.; |
---|
2129 | |
---|
2130 | // In an outgoing sense fermions are labelled f(1) fbar(2) f'(3) fbar'(4) |
---|
2131 | // where f' fbar' come from gamma*/Z0 decay. |
---|
2132 | int i1, i2; |
---|
2133 | int i3 = (process[7].id() > 0) ? 7 : 8; |
---|
2134 | int i4 = 15 - i3; |
---|
2135 | |
---|
2136 | // Order so that fbar(1) f(2) -> gamma*/Z0 g/gamma. |
---|
2137 | if (process[3].idAbs() < 20 && process[4].idAbs() < 20) { |
---|
2138 | i1 = (process[3].id() < 0) ? 3 : 4; |
---|
2139 | i2 = 7 - i1; |
---|
2140 | |
---|
2141 | // Order so that f(2)/fbar(1) g/gamma -> f(1)/fbar(2) f'(3) gamma*/Z0. |
---|
2142 | } else if (process[3].idAbs() < 20) { |
---|
2143 | i1 = (process[3].id() < 0) ? 3 : 6; |
---|
2144 | i2 = 9 - i1; |
---|
2145 | } else { |
---|
2146 | i1 = (process[4].id() < 0) ? 4 : 6; |
---|
2147 | i2 = 10 - i1; |
---|
2148 | } |
---|
2149 | |
---|
2150 | // Charge/2, left- and righthanded couplings for in- and out-fermion. |
---|
2151 | int id1Abs = process[i1].idAbs(); |
---|
2152 | double ei = 0.5 * couplingsPtr->ef(id1Abs); |
---|
2153 | double li = couplingsPtr->lf(id1Abs); |
---|
2154 | double ri = couplingsPtr->rf(id1Abs); |
---|
2155 | int id3Abs = process[i3].idAbs(); |
---|
2156 | double ef = 0.5 * couplingsPtr->ef(id3Abs); |
---|
2157 | double lf = couplingsPtr->lf(id3Abs); |
---|
2158 | double rf = couplingsPtr->rf(id3Abs); |
---|
2159 | |
---|
2160 | // Combinations of left/right for in/out, gamma*/interference/Z0. |
---|
2161 | double clilf = ei*ei * gamProp * ef*ef + ei*li * intProp * ef*lf |
---|
2162 | + li*li * resProp * lf*lf; |
---|
2163 | double clirf = ei*ei * gamProp * ef*ef + ei*li * intProp * ef*rf |
---|
2164 | + li*li * resProp * rf*rf; |
---|
2165 | double crilf = ei*ei * gamProp * ef*ef + ei*ri * intProp * ef*lf |
---|
2166 | + ri*ri * resProp * lf*lf; |
---|
2167 | double crirf = ei*ei * gamProp * ef*ef + ei*ri * intProp * ef*rf |
---|
2168 | + ri*ri * resProp * rf*rf; |
---|
2169 | |
---|
2170 | // Evaluate four-vector products. |
---|
2171 | double p13 = process[i1].p() * process[i3].p(); |
---|
2172 | double p14 = process[i1].p() * process[i4].p(); |
---|
2173 | double p23 = process[i2].p() * process[i3].p(); |
---|
2174 | double p24 = process[i2].p() * process[i4].p(); |
---|
2175 | |
---|
2176 | // Calculate weight and its maximum. |
---|
2177 | double wt = (clilf + crirf) * (p13*p13 + p24*p24) |
---|
2178 | + (clirf + crilf) * (p14*p14 + p23*p23) ; |
---|
2179 | double wtMax = (clilf + clirf + crilf + crirf) |
---|
2180 | * (pow2(p13 + p14) + pow2(p23 + p24)); |
---|
2181 | |
---|
2182 | // Done. |
---|
2183 | return (wt / wtMax); |
---|
2184 | |
---|
2185 | } |
---|
2186 | |
---|
2187 | //========================================================================== |
---|
2188 | |
---|
2189 | // Sigma2qqbar2gmZg class. |
---|
2190 | // Cross section for q qbar -> gamma*/Z0 g. |
---|
2191 | |
---|
2192 | //-------------------------------------------------------------------------- |
---|
2193 | |
---|
2194 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
2195 | |
---|
2196 | void Sigma2qqbar2gmZg::sigmaKin() { |
---|
2197 | |
---|
2198 | // Cross section part common for all incoming flavours. |
---|
2199 | sigma0 = (M_PI / sH2) * (alpEM * alpS) |
---|
2200 | * (2./9.) * (tH2 + uH2 + 2. * sH * s3) / (tH * uH); |
---|
2201 | |
---|
2202 | // Calculate flavour sums for final state. |
---|
2203 | flavSum(); |
---|
2204 | |
---|
2205 | // Calculate prefactors for gamma/interference/Z0 cross section terms. |
---|
2206 | propTerm(); |
---|
2207 | |
---|
2208 | } |
---|
2209 | |
---|
2210 | //-------------------------------------------------------------------------- |
---|
2211 | |
---|
2212 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
2213 | |
---|
2214 | double Sigma2qqbar2gmZg::sigmaHat() { |
---|
2215 | |
---|
2216 | // Combine gamma, interference and Z0 parts. |
---|
2217 | int idAbs = abs(id1); |
---|
2218 | double sigma = sigma0 |
---|
2219 | * ( couplingsPtr->ef2(idAbs) * gamProp * gamSum |
---|
2220 | + couplingsPtr->efvf(idAbs) * intProp * intSum |
---|
2221 | + couplingsPtr->vf2af2(idAbs) * resProp * resSum); |
---|
2222 | |
---|
2223 | // Correct for the running-width Z0 propagater weight in PhaseSpace. |
---|
2224 | sigma /= runBW3; |
---|
2225 | |
---|
2226 | // Answer. |
---|
2227 | return sigma; |
---|
2228 | |
---|
2229 | } |
---|
2230 | |
---|
2231 | //-------------------------------------------------------------------------- |
---|
2232 | |
---|
2233 | // Select identity, colour and anticolour. |
---|
2234 | |
---|
2235 | void Sigma2qqbar2gmZg::setIdColAcol() { |
---|
2236 | |
---|
2237 | // Flavours trivial. |
---|
2238 | setId( id1, id2, 23, 21); |
---|
2239 | |
---|
2240 | // Colour flow topologies. Swap when antiquarks. |
---|
2241 | setColAcol( 1, 0, 0, 2, 0, 0, 1, 2); |
---|
2242 | if (id1 < 0) swapColAcol(); |
---|
2243 | |
---|
2244 | } |
---|
2245 | |
---|
2246 | //========================================================================== |
---|
2247 | |
---|
2248 | // Sigma2qg2gmZq class. |
---|
2249 | // Cross section for q g -> gamma*/Z0 q. |
---|
2250 | |
---|
2251 | //-------------------------------------------------------------------------- |
---|
2252 | |
---|
2253 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
2254 | |
---|
2255 | void Sigma2qg2gmZq::sigmaKin() { |
---|
2256 | |
---|
2257 | // Cross section part common for all incoming flavours. |
---|
2258 | sigma0 = (M_PI / sH2) * (alpEM * alpS) |
---|
2259 | * (1./12.) * (sH2 + uH2 + 2. * tH * s3) / (-sH * uH); |
---|
2260 | |
---|
2261 | // Calculate flavour sums for final state. |
---|
2262 | flavSum(); |
---|
2263 | |
---|
2264 | // Calculate prefactors for gamma/interference/Z0 cross section terms. |
---|
2265 | propTerm(); |
---|
2266 | |
---|
2267 | } |
---|
2268 | |
---|
2269 | //-------------------------------------------------------------------------- |
---|
2270 | |
---|
2271 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
2272 | |
---|
2273 | double Sigma2qg2gmZq::sigmaHat() { |
---|
2274 | |
---|
2275 | // Combine gamma, interference and Z0 parts. |
---|
2276 | int idAbs = (id2 == 21) ? abs(id1) : abs(id2); |
---|
2277 | double sigma = sigma0 |
---|
2278 | * ( couplingsPtr->ef2(idAbs) * gamProp * gamSum |
---|
2279 | + couplingsPtr->efvf(idAbs) * intProp * intSum |
---|
2280 | + couplingsPtr->vf2af2(idAbs) * resProp * resSum); |
---|
2281 | |
---|
2282 | // Correct for the running-width Z0 propagater weight in PhaseSpace. |
---|
2283 | sigma /= runBW3; |
---|
2284 | |
---|
2285 | // Answer. |
---|
2286 | return sigma; |
---|
2287 | |
---|
2288 | } |
---|
2289 | |
---|
2290 | //-------------------------------------------------------------------------- |
---|
2291 | |
---|
2292 | // Select identity, colour and anticolour. |
---|
2293 | |
---|
2294 | void Sigma2qg2gmZq::setIdColAcol() { |
---|
2295 | |
---|
2296 | // Flavour set up for q g -> gamma*/Z0 q. |
---|
2297 | int idq = (id2 == 21) ? id1 : id2; |
---|
2298 | setId( id1, id2, 23, idq); |
---|
2299 | |
---|
2300 | // tH defined between f and f': must swap tHat <-> uHat if q g in. |
---|
2301 | swapTU = (id2 == 21); |
---|
2302 | |
---|
2303 | // Colour flow topologies. Swap when antiquarks. |
---|
2304 | if (id2 == 21) setColAcol( 1, 0, 2, 1, 0, 0, 2, 0); |
---|
2305 | else setColAcol( 2, 1, 1, 0, 0, 0, 2, 0); |
---|
2306 | if (idq < 0) swapColAcol(); |
---|
2307 | |
---|
2308 | } |
---|
2309 | |
---|
2310 | //========================================================================== |
---|
2311 | |
---|
2312 | // Sigma2ffbar2gmZgm class. |
---|
2313 | // Cross section for f fbar -> gamma*/Z0 gamma. |
---|
2314 | |
---|
2315 | //-------------------------------------------------------------------------- |
---|
2316 | |
---|
2317 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
2318 | |
---|
2319 | void Sigma2ffbar2gmZgm::sigmaKin() { |
---|
2320 | |
---|
2321 | // Cross section part common for all incoming flavours. |
---|
2322 | sigma0 = (M_PI / sH2) * (alpEM*alpEM) |
---|
2323 | * 0.5 * (tH2 + uH2 + 2. * sH * s3) / (tH * uH); |
---|
2324 | |
---|
2325 | // Calculate flavour sums for final state. |
---|
2326 | flavSum(); |
---|
2327 | |
---|
2328 | // Calculate prefactors for gamma/interference/Z0 cross section terms. |
---|
2329 | propTerm(); |
---|
2330 | |
---|
2331 | |
---|
2332 | } |
---|
2333 | |
---|
2334 | //-------------------------------------------------------------------------- |
---|
2335 | |
---|
2336 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
2337 | |
---|
2338 | double Sigma2ffbar2gmZgm::sigmaHat() { |
---|
2339 | |
---|
2340 | // Combine gamma, interference and Z0 parts. |
---|
2341 | int idAbs = abs(id1); |
---|
2342 | double sigma = sigma0 * couplingsPtr->ef2(idAbs) |
---|
2343 | * ( couplingsPtr->ef2(idAbs) * gamProp * gamSum |
---|
2344 | + couplingsPtr->efvf(idAbs) * intProp * intSum |
---|
2345 | + couplingsPtr->vf2af2(idAbs) * resProp * resSum); |
---|
2346 | |
---|
2347 | // Correct for the running-width Z0 propagater weight in PhaseSpace. |
---|
2348 | sigma /= runBW3; |
---|
2349 | |
---|
2350 | // Colour factor. Answer. |
---|
2351 | if (idAbs < 9) sigma /= 3.; |
---|
2352 | return sigma; |
---|
2353 | |
---|
2354 | } |
---|
2355 | |
---|
2356 | //-------------------------------------------------------------------------- |
---|
2357 | |
---|
2358 | // Select identity, colour and anticolour. |
---|
2359 | |
---|
2360 | void Sigma2ffbar2gmZgm::setIdColAcol() { |
---|
2361 | |
---|
2362 | // Flavours trivial. |
---|
2363 | setId( id1, id2, 23, 22); |
---|
2364 | |
---|
2365 | // Colour flow topologies. Swap when antiquarks. |
---|
2366 | if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0); |
---|
2367 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
2368 | if (id1 < 0) swapColAcol(); |
---|
2369 | |
---|
2370 | } |
---|
2371 | |
---|
2372 | //========================================================================== |
---|
2373 | |
---|
2374 | // Sigma2fgm2gmZf class. |
---|
2375 | // Cross section for f gamma -> gamma*/Z0 f'. |
---|
2376 | |
---|
2377 | //-------------------------------------------------------------------------- |
---|
2378 | |
---|
2379 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
2380 | |
---|
2381 | void Sigma2fgm2gmZf::sigmaKin() { |
---|
2382 | |
---|
2383 | // Cross section part common for all incoming flavours. |
---|
2384 | sigma0 = (M_PI / sH2) * (alpEM*alpEM) |
---|
2385 | * 0.5 * (sH2 + uH2 + 2. * tH * s3) / (- sH * uH); |
---|
2386 | |
---|
2387 | // Calculate flavour sums for final state. |
---|
2388 | flavSum(); |
---|
2389 | |
---|
2390 | // Calculate prefactors for gamma/interference/Z0 cross section terms. |
---|
2391 | propTerm(); |
---|
2392 | |
---|
2393 | } |
---|
2394 | |
---|
2395 | //-------------------------------------------------------------------------- |
---|
2396 | |
---|
2397 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
2398 | |
---|
2399 | double Sigma2fgm2gmZf::sigmaHat() { |
---|
2400 | |
---|
2401 | // Combine gamma, interference and Z0 parts. |
---|
2402 | int idAbs = (id2 == 22) ? abs(id1) : abs(id2); |
---|
2403 | double sigma = sigma0 * couplingsPtr->ef2(idAbs) |
---|
2404 | * ( couplingsPtr->ef2(idAbs) * gamProp * gamSum |
---|
2405 | + couplingsPtr->efvf(idAbs) * intProp * intSum |
---|
2406 | + couplingsPtr->vf2af2(idAbs) * resProp * resSum); |
---|
2407 | |
---|
2408 | // Correct for the running-width Z0 propagater weight in PhaseSpace. |
---|
2409 | sigma /= runBW3; |
---|
2410 | |
---|
2411 | // Answer. |
---|
2412 | return sigma; |
---|
2413 | |
---|
2414 | } |
---|
2415 | |
---|
2416 | //-------------------------------------------------------------------------- |
---|
2417 | |
---|
2418 | // Select identity, colour and anticolour. |
---|
2419 | |
---|
2420 | void Sigma2fgm2gmZf::setIdColAcol() { |
---|
2421 | |
---|
2422 | // Flavour set up for q gamma -> gamma*/Z0 q. |
---|
2423 | int idq = (id2 == 22) ? id1 : id2; |
---|
2424 | setId( id1, id2, 23, idq); |
---|
2425 | |
---|
2426 | // tH defined between f and f': must swap tHat <-> uHat if q gamma in. |
---|
2427 | swapTU = (id2 == 22); |
---|
2428 | |
---|
2429 | // Colour flow topologies. Swap when antiquarks. |
---|
2430 | if (abs(id1) < 9) setColAcol( 1, 0, 0, 0, 0, 0, 1, 0); |
---|
2431 | else if (abs(id2) < 9) setColAcol( 0, 0, 1, 0, 0, 0, 1, 0); |
---|
2432 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
2433 | if (idq < 0) swapColAcol(); |
---|
2434 | |
---|
2435 | } |
---|
2436 | |
---|
2437 | //========================================================================== |
---|
2438 | |
---|
2439 | // Sigma2ffbarWggm class. |
---|
2440 | // Collects common methods for f fbar -> W+- g/gamma and permutations. |
---|
2441 | |
---|
2442 | //-------------------------------------------------------------------------- |
---|
2443 | |
---|
2444 | // Evaluate weight for W+- decay angle. |
---|
2445 | |
---|
2446 | double Sigma2ffbarWggm::weightDecay( Event& process, int iResBeg, |
---|
2447 | int iResEnd) { |
---|
2448 | |
---|
2449 | // W should sit in entry 5 and one more parton in entry 6. |
---|
2450 | if (iResBeg != 5 || iResEnd != 6) return 1.; |
---|
2451 | |
---|
2452 | // In an outgoing sense fermions are labelled f(1) fbar(2) f'(3) fbar'(4) |
---|
2453 | // where f' fbar' come from W+- decay. |
---|
2454 | int i1, i2; |
---|
2455 | int i3 = (process[7].id() > 0) ? 7 : 8; |
---|
2456 | int i4 = 15 - i3; |
---|
2457 | |
---|
2458 | // Order so that fbar(1) f(2) -> W+- g/gamma. |
---|
2459 | if (process[3].idAbs() < 20 && process[4].idAbs() < 20) { |
---|
2460 | i1 = (process[3].id() < 0) ? 3 : 4; |
---|
2461 | i2 = 7 - i1; |
---|
2462 | |
---|
2463 | // Order so that f(2)/fbar(1) g/gamma -> f(1)/fbar(2) f'(3) W+-. |
---|
2464 | } else if (process[3].idAbs() < 20) { |
---|
2465 | i1 = (process[3].id() < 0) ? 3 : 6; |
---|
2466 | i2 = 9 - i1; |
---|
2467 | } else { |
---|
2468 | i1 = (process[4].id() < 0) ? 4 : 6; |
---|
2469 | i2 = 10 - i1; |
---|
2470 | } |
---|
2471 | |
---|
2472 | // Evaluate four-vector products. |
---|
2473 | double p13 = process[i1].p() * process[i3].p(); |
---|
2474 | double p14 = process[i1].p() * process[i4].p(); |
---|
2475 | double p23 = process[i2].p() * process[i3].p(); |
---|
2476 | double p24 = process[i2].p() * process[i4].p(); |
---|
2477 | |
---|
2478 | // Calculate weight and its maximum. |
---|
2479 | double wt = pow2(p13) + pow2(p24); |
---|
2480 | double wtMax = pow2(p13 + p14) + pow2(p23 + p24); |
---|
2481 | |
---|
2482 | // Done. |
---|
2483 | return (wt / wtMax); |
---|
2484 | |
---|
2485 | } |
---|
2486 | |
---|
2487 | //========================================================================== |
---|
2488 | |
---|
2489 | // Sigma2qqbar2Wg class. |
---|
2490 | // Cross section for q qbar' -> W+- g. |
---|
2491 | |
---|
2492 | //-------------------------------------------------------------------------- |
---|
2493 | |
---|
2494 | // Initialize process. |
---|
2495 | |
---|
2496 | void Sigma2qqbar2Wg::initProc() { |
---|
2497 | |
---|
2498 | // Secondary open width fractions, relevant for top (or heavier). |
---|
2499 | openFracPos = particleDataPtr->resOpenFrac(24); |
---|
2500 | openFracNeg = particleDataPtr->resOpenFrac(-24); |
---|
2501 | |
---|
2502 | } |
---|
2503 | |
---|
2504 | //-------------------------------------------------------------------------- |
---|
2505 | |
---|
2506 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
2507 | |
---|
2508 | void Sigma2qqbar2Wg::sigmaKin() { |
---|
2509 | |
---|
2510 | // Cross section part common for all incoming flavours. |
---|
2511 | sigma0 = (M_PI / sH2) * (alpEM * alpS / couplingsPtr->sin2thetaW()) |
---|
2512 | * (2./9.) * (tH2 + uH2 + 2. * sH * s3) / (tH * uH); |
---|
2513 | |
---|
2514 | } |
---|
2515 | |
---|
2516 | //-------------------------------------------------------------------------- |
---|
2517 | |
---|
2518 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
2519 | |
---|
2520 | double Sigma2qqbar2Wg::sigmaHat() { |
---|
2521 | |
---|
2522 | // CKM factor. Secondary width for W+ or W-. |
---|
2523 | double sigma = sigma0 * couplingsPtr->V2CKMid(abs(id1), abs(id2)); |
---|
2524 | int idUp = (abs(id1)%2 == 0) ? id1 : id2; |
---|
2525 | sigma *= (idUp > 0) ? openFracPos : openFracNeg; |
---|
2526 | |
---|
2527 | // Answer. |
---|
2528 | return sigma; |
---|
2529 | |
---|
2530 | } |
---|
2531 | |
---|
2532 | //-------------------------------------------------------------------------- |
---|
2533 | |
---|
2534 | // Select identity, colour and anticolour. |
---|
2535 | |
---|
2536 | void Sigma2qqbar2Wg::setIdColAcol() { |
---|
2537 | |
---|
2538 | // Sign of outgoing W. |
---|
2539 | int sign = 1 - 2 * (abs(id1)%2); |
---|
2540 | if (id1 < 0) sign = -sign; |
---|
2541 | setId( id1, id2, 24 * sign, 21); |
---|
2542 | |
---|
2543 | // Colour flow topologies. Swap when antiquarks. |
---|
2544 | setColAcol( 1, 0, 0, 2, 0, 0, 1, 2); |
---|
2545 | if (id1 < 0) swapColAcol(); |
---|
2546 | |
---|
2547 | } |
---|
2548 | |
---|
2549 | //========================================================================== |
---|
2550 | |
---|
2551 | // Sigma2qg2Wq class. |
---|
2552 | // Cross section for q g -> W+- q'. |
---|
2553 | |
---|
2554 | //-------------------------------------------------------------------------- |
---|
2555 | |
---|
2556 | // Initialize process. |
---|
2557 | |
---|
2558 | void Sigma2qg2Wq::initProc() { |
---|
2559 | |
---|
2560 | // Secondary open width fractions, relevant for top (or heavier). |
---|
2561 | openFracPos = particleDataPtr->resOpenFrac(24); |
---|
2562 | openFracNeg = particleDataPtr->resOpenFrac(-24); |
---|
2563 | |
---|
2564 | } |
---|
2565 | |
---|
2566 | //-------------------------------------------------------------------------- |
---|
2567 | |
---|
2568 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
2569 | |
---|
2570 | void Sigma2qg2Wq::sigmaKin() { |
---|
2571 | |
---|
2572 | // Cross section part common for all incoming flavours. |
---|
2573 | sigma0 = (M_PI / sH2) * (alpEM * alpS / couplingsPtr->sin2thetaW()) |
---|
2574 | * (1./12.) * (sH2 + uH2 + 2. * tH * s3) / (-sH * uH); |
---|
2575 | |
---|
2576 | } |
---|
2577 | |
---|
2578 | //-------------------------------------------------------------------------- |
---|
2579 | |
---|
2580 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
2581 | |
---|
2582 | double Sigma2qg2Wq::sigmaHat() { |
---|
2583 | |
---|
2584 | // CKM factor. Secondary width for W+ or W-. |
---|
2585 | int idAbs = (id2 == 21) ? abs(id1) : abs(id2); |
---|
2586 | double sigma = sigma0 * couplingsPtr->V2CKMsum(idAbs); |
---|
2587 | int idUp = (id2 == 21) ? id1 : id2; |
---|
2588 | if (idAbs%2 == 1) idUp = -idUp; |
---|
2589 | sigma *= (idUp > 0) ? openFracPos : openFracNeg; |
---|
2590 | |
---|
2591 | // Answer. |
---|
2592 | return sigma; |
---|
2593 | |
---|
2594 | } |
---|
2595 | |
---|
2596 | //-------------------------------------------------------------------------- |
---|
2597 | |
---|
2598 | // Select identity, colour and anticolour. |
---|
2599 | |
---|
2600 | void Sigma2qg2Wq::setIdColAcol() { |
---|
2601 | |
---|
2602 | // Sign of outgoing W. Flavour of outgoing quark. |
---|
2603 | int idq = (id2 == 21) ? id1 : id2; |
---|
2604 | int sign = 1 - 2 * (abs(idq)%2); |
---|
2605 | if (idq < 0) sign = -sign; |
---|
2606 | id4 = couplingsPtr->V2CKMpick(idq); |
---|
2607 | |
---|
2608 | // Flavour set up for q g -> W q. |
---|
2609 | setId( id1, id2, 24 * sign, id4); |
---|
2610 | |
---|
2611 | // tH defined between f and f': must swap tHat <-> uHat if q g in. |
---|
2612 | swapTU = (id2 == 21); |
---|
2613 | |
---|
2614 | // Colour flow topologies. Swap when antiquarks. |
---|
2615 | if (id2 == 21) setColAcol( 1, 0, 2, 1, 0, 0, 2, 0); |
---|
2616 | else setColAcol( 2, 1, 1, 0, 0, 0, 2, 0); |
---|
2617 | if (idq < 0) swapColAcol(); |
---|
2618 | |
---|
2619 | } |
---|
2620 | |
---|
2621 | //========================================================================== |
---|
2622 | |
---|
2623 | // Sigma2ffbar2Wgm class. |
---|
2624 | // Cross section for f fbar' -> W+- gamma. |
---|
2625 | |
---|
2626 | //-------------------------------------------------------------------------- |
---|
2627 | |
---|
2628 | // Initialize process. |
---|
2629 | |
---|
2630 | void Sigma2ffbar2Wgm::initProc() { |
---|
2631 | |
---|
2632 | // Secondary open width fractions, relevant for top (or heavier). |
---|
2633 | openFracPos = particleDataPtr->resOpenFrac(24); |
---|
2634 | openFracNeg = particleDataPtr->resOpenFrac(-24); |
---|
2635 | |
---|
2636 | } |
---|
2637 | |
---|
2638 | //-------------------------------------------------------------------------- |
---|
2639 | |
---|
2640 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
2641 | |
---|
2642 | void Sigma2ffbar2Wgm::sigmaKin() { |
---|
2643 | |
---|
2644 | // Cross section part common for all incoming flavours. |
---|
2645 | sigma0 = (M_PI / sH2) * (alpEM*alpEM / couplingsPtr->sin2thetaW()) |
---|
2646 | * 0.5 * (tH2 + uH2 + 2. * sH * s3) / (tH * uH); |
---|
2647 | } |
---|
2648 | |
---|
2649 | //-------------------------------------------------------------------------- |
---|
2650 | |
---|
2651 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
2652 | |
---|
2653 | double Sigma2ffbar2Wgm::sigmaHat() { |
---|
2654 | |
---|
2655 | // Extrafactor different for e nu and q qbar' instate. |
---|
2656 | int id1Abs = abs(id1); |
---|
2657 | int id2Abs = abs(id2); |
---|
2658 | double chgUp = (id1Abs > 10) ? 0. : 2./3.; |
---|
2659 | double sigma = sigma0 * pow2( chgUp - tH / (tH + uH) ); |
---|
2660 | |
---|
2661 | // CKM and colour factors. Secondary width for W+ or W-. |
---|
2662 | if (id1Abs < 9) sigma *= couplingsPtr->V2CKMid(id1Abs, id2Abs) / 3.; |
---|
2663 | int idUp = (abs(id1)%2 == 0) ? id1 : id2; |
---|
2664 | sigma *= (idUp > 0) ? openFracPos : openFracNeg; |
---|
2665 | |
---|
2666 | // Answer. |
---|
2667 | return sigma; |
---|
2668 | |
---|
2669 | } |
---|
2670 | |
---|
2671 | //-------------------------------------------------------------------------- |
---|
2672 | |
---|
2673 | // Select identity, colour and anticolour. |
---|
2674 | |
---|
2675 | void Sigma2ffbar2Wgm::setIdColAcol() { |
---|
2676 | |
---|
2677 | // Sign of outgoing W. |
---|
2678 | int sign = 1 - 2 * (abs(id1)%2); |
---|
2679 | if (id1 < 0) sign = -sign; |
---|
2680 | setId( id1, id2, 24 * sign, 22); |
---|
2681 | |
---|
2682 | // tH defined between (f,W-) or (fbar',W+). |
---|
2683 | swapTU = (sign * id1 > 0); |
---|
2684 | |
---|
2685 | // Colour flow topologies. Swap when antiquarks. |
---|
2686 | if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0); |
---|
2687 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
2688 | if (id1 < 0) swapColAcol(); |
---|
2689 | |
---|
2690 | } |
---|
2691 | |
---|
2692 | //========================================================================== |
---|
2693 | |
---|
2694 | // Sigma2fgm2Wf class. |
---|
2695 | // Cross section for f gamma -> W+- f'. |
---|
2696 | |
---|
2697 | //-------------------------------------------------------------------------- |
---|
2698 | |
---|
2699 | // Initialize process. |
---|
2700 | |
---|
2701 | void Sigma2fgm2Wf::initProc() { |
---|
2702 | |
---|
2703 | // Secondary open width fractions, relevant for top (or heavier). |
---|
2704 | openFracPos = particleDataPtr->resOpenFrac(24); |
---|
2705 | openFracNeg = particleDataPtr->resOpenFrac(-24); |
---|
2706 | |
---|
2707 | } |
---|
2708 | |
---|
2709 | //-------------------------------------------------------------------------- |
---|
2710 | |
---|
2711 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. |
---|
2712 | |
---|
2713 | void Sigma2fgm2Wf::sigmaKin() { |
---|
2714 | |
---|
2715 | // Cross section part common for all incoming flavours. |
---|
2716 | sigma0 = (M_PI / sH2) * (alpEM*alpEM / couplingsPtr->sin2thetaW()) |
---|
2717 | * 0.5 * (sH2 + uH2 + 2. * tH * s3) / (pT2 * s3 - sH * uH); |
---|
2718 | |
---|
2719 | } |
---|
2720 | |
---|
2721 | //-------------------------------------------------------------------------- |
---|
2722 | |
---|
2723 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. |
---|
2724 | |
---|
2725 | double Sigma2fgm2Wf::sigmaHat() { |
---|
2726 | |
---|
2727 | // Extrafactor dependent on charge of incoming fermion. |
---|
2728 | int idAbs = (id2 == 22) ? abs(id1) : abs(id2); |
---|
2729 | double charge = (idAbs > 10) ? 1. : ( (idAbs%2 == 1) ? 1./3. : 2./3. ); |
---|
2730 | double sigma = sigma0 * pow2( charge - sH / (sH + uH) ); |
---|
2731 | |
---|
2732 | // CKM factor. Secondary width for W+ or W-. |
---|
2733 | sigma *= couplingsPtr->V2CKMsum(idAbs); |
---|
2734 | int idUp = (id2 == 22) ? id1 : id2; |
---|
2735 | if (idAbs%2 == 1) idUp = -idUp; |
---|
2736 | sigma *= (idUp > 0) ? openFracPos : openFracNeg; |
---|
2737 | |
---|
2738 | // Answer. |
---|
2739 | return sigma; |
---|
2740 | |
---|
2741 | } |
---|
2742 | |
---|
2743 | //-------------------------------------------------------------------------- |
---|
2744 | |
---|
2745 | // Select identity, colour and anticolour. |
---|
2746 | |
---|
2747 | void Sigma2fgm2Wf::setIdColAcol() { |
---|
2748 | |
---|
2749 | // Sign of outgoing W. Flavour of outgoing fermion. |
---|
2750 | int idq = (id2 == 22) ? id1 : id2; |
---|
2751 | int sign = 1 - 2 * (abs(idq)%2); |
---|
2752 | if (idq < 0) sign = -sign; |
---|
2753 | id4 = couplingsPtr->V2CKMpick(idq); |
---|
2754 | |
---|
2755 | // Flavour set up for q gamma -> W q. |
---|
2756 | setId( id1, id2, 24 * sign, id4); |
---|
2757 | |
---|
2758 | // tH defined between f and f': must swap tHat <-> uHat if q gamma in. |
---|
2759 | swapTU = (id2 == 22); |
---|
2760 | |
---|
2761 | // Colour flow topologies. Swap when antiquarks. |
---|
2762 | if (abs(id1) < 9) setColAcol( 1, 0, 0, 0, 0, 0, 1, 0); |
---|
2763 | else if (abs(id2) < 9) setColAcol( 0, 0, 1, 0, 0, 0, 1, 0); |
---|
2764 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
2765 | if (idq < 0) swapColAcol(); |
---|
2766 | |
---|
2767 | } |
---|
2768 | |
---|
2769 | //========================================================================== |
---|
2770 | |
---|
2771 | // Sigma2gmgm2ffbar class. |
---|
2772 | // Cross section for gamma gamma -> l lbar. |
---|
2773 | |
---|
2774 | //-------------------------------------------------------------------------- |
---|
2775 | |
---|
2776 | // Initialize process wrt flavour. |
---|
2777 | |
---|
2778 | void Sigma2gmgm2ffbar::initProc() { |
---|
2779 | |
---|
2780 | // Process name. |
---|
2781 | nameSave = "gamma gamma -> f fbar"; |
---|
2782 | if (idNew == 1) nameSave = "gamma gamma -> q qbar (uds)"; |
---|
2783 | if (idNew == 4) nameSave = "gamma gamma -> c cbar"; |
---|
2784 | if (idNew == 5) nameSave = "gamma gamma -> b bbar"; |
---|
2785 | if (idNew == 6) nameSave = "gamma gamma -> t tbar"; |
---|
2786 | if (idNew == 11) nameSave = "gamma gamma -> e+ e-"; |
---|
2787 | if (idNew == 13) nameSave = "gamma gamma -> mu+ mu-"; |
---|
2788 | if (idNew == 15) nameSave = "gamma gamma -> tau+ tau-"; |
---|
2789 | |
---|
2790 | // Generate massive phase space, except for u+d+s. |
---|
2791 | idMass = 0; |
---|
2792 | if (idNew > 3) idMass = idNew; |
---|
2793 | |
---|
2794 | // Charge and colour factor. |
---|
2795 | ef4 = 1.; |
---|
2796 | if (idNew == 1) ef4 = 3. * (pow4(2./3.) + 2. * pow4(1./3.)); |
---|
2797 | if (idNew == 4 || idNew == 6) ef4 = 3. * pow4(2./3.); |
---|
2798 | if (idNew == 5) ef4 = 3. * pow4(1./3.); |
---|
2799 | |
---|
2800 | // Secondary open width fraction. |
---|
2801 | openFracPair = particleDataPtr->resOpenFrac(idNew, -idNew); |
---|
2802 | |
---|
2803 | } |
---|
2804 | |
---|
2805 | //-------------------------------------------------------------------------- |
---|
2806 | |
---|
2807 | // Evaluate d(sigmaHat)/d(tHat) - no incoming flavour dependence. |
---|
2808 | |
---|
2809 | void Sigma2gmgm2ffbar::sigmaKin() { |
---|
2810 | |
---|
2811 | // Pick current flavour for u+d+s mix by e_q^4 weights. |
---|
2812 | if (idNew == 1) { |
---|
2813 | double rId = 18. * rndmPtr->flat(); |
---|
2814 | idNow = 1; |
---|
2815 | if (rId > 1.) idNow = 2; |
---|
2816 | if (rId > 17.) idNow = 3; |
---|
2817 | s34Avg = pow2(particleDataPtr->m0(idNow)); |
---|
2818 | } else { |
---|
2819 | idNow = idNew; |
---|
2820 | s34Avg = 0.5 * (s3 + s4) - 0.25 * pow2(s3 - s4) / sH; |
---|
2821 | } |
---|
2822 | |
---|
2823 | // Modified Mandelstam variables for massive kinematics with m3 = m4. |
---|
2824 | double tHQ = -0.5 * (sH - tH + uH); |
---|
2825 | double uHQ = -0.5 * (sH + tH - uH); |
---|
2826 | double tHQ2 = tHQ * tHQ; |
---|
2827 | double uHQ2 = uHQ * uHQ; |
---|
2828 | |
---|
2829 | // Calculate kinematics dependence. |
---|
2830 | if (sH < 4. * s34Avg) sigTU = 0.; |
---|
2831 | else sigTU = 2. * (tHQ * uHQ - s34Avg * sH) |
---|
2832 | * (tHQ2 + uHQ2 + 2. * s34Avg * sH) / (tHQ2 * uHQ2); |
---|
2833 | |
---|
2834 | // Answer. |
---|
2835 | sigma = (M_PI / sH2) * pow2(alpEM) * ef4 * sigTU * openFracPair; |
---|
2836 | |
---|
2837 | } |
---|
2838 | |
---|
2839 | //-------------------------------------------------------------------------- |
---|
2840 | |
---|
2841 | // Select identity, colour and anticolour. |
---|
2842 | |
---|
2843 | void Sigma2gmgm2ffbar::setIdColAcol() { |
---|
2844 | |
---|
2845 | // Flavours are trivial. |
---|
2846 | setId( id1, id2, idNow, -idNow); |
---|
2847 | |
---|
2848 | // Colour flow in singlet state. |
---|
2849 | if (idNow < 10) setColAcol( 0, 0, 0, 0, 1, 0, 0, 1); |
---|
2850 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); |
---|
2851 | |
---|
2852 | } |
---|
2853 | |
---|
2854 | //========================================================================== |
---|
2855 | |
---|
2856 | } // end namespace Pythia8 |
---|