1 | // BeamRemnants.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 | // BeamRemnants class. |
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8 | |
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9 | #include "BeamRemnants.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 | // The BeamDipole class is purely internal to reconnectColours. |
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16 | |
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17 | class BeamDipole { |
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18 | |
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19 | public: |
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20 | |
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21 | // Constructor. |
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22 | BeamDipole( int colIn = 0, int iColIn = 0, int iAcolIn = 0) |
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23 | : col(colIn), iCol(iColIn), iAcol(iAcolIn) {} |
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24 | |
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25 | // Members. |
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26 | int col, iCol, iAcol; |
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27 | double p1p2; |
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28 | |
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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 | // The BeamRemnants class. |
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34 | |
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35 | //-------------------------------------------------------------------------- |
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36 | |
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37 | // Constants: could be changed here if desired, but normally should not. |
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38 | // These are of technical nature, as described for each. |
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39 | |
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40 | // If same (anti)colour appears twice in final state, repair or reject. |
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41 | const bool BeamRemnants::ALLOWCOLOURTWICE = true; |
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42 | |
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43 | // Maximum number of tries to match colours and kinematics in the event. |
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44 | const int BeamRemnants::NTRYCOLMATCH = 10; |
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45 | const int BeamRemnants::NTRYKINMATCH = 10; |
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46 | |
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47 | // Overall correction step for energy-momentum conservation; only |
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48 | // becomes relevant in rescattering scenarios when FSR dipole emissions |
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49 | // and primordial kT is added. Should hopefully not be needed. |
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50 | const bool BeamRemnants::CORRECTMISMATCH = false; |
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51 | |
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52 | //-------------------------------------------------------------------------- |
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53 | |
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54 | // Initialization. |
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55 | |
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56 | bool BeamRemnants::init( Info* infoPtrIn, Settings& settings, Rndm* rndmPtrIn, |
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57 | BeamParticle* beamAPtrIn, BeamParticle* beamBPtrIn, |
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58 | PartonSystems* partonSystemsPtrIn) { |
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59 | |
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60 | // Save pointers. |
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61 | infoPtr = infoPtrIn; |
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62 | rndmPtr = rndmPtrIn; |
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63 | beamAPtr = beamAPtrIn; |
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64 | beamBPtr = beamBPtrIn; |
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65 | partonSystemsPtr = partonSystemsPtrIn; |
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66 | |
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67 | // Width of primordial kT distribution. |
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68 | doPrimordialKT = settings.flag("BeamRemnants:primordialKT"); |
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69 | primordialKTsoft = settings.parm("BeamRemnants:primordialKTsoft"); |
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70 | primordialKThard = settings.parm("BeamRemnants:primordialKThard"); |
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71 | primordialKTremnant = settings.parm("BeamRemnants:primordialKTremnant"); |
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72 | halfScaleForKT = settings.parm("BeamRemnants:halfScaleForKT"); |
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73 | halfMassForKT = settings.parm("BeamRemnants:halfMassForKT"); |
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74 | |
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75 | // Handling of rescattering kinematics uncertainties from primodial kT. |
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76 | allowRescatter = settings.flag("MultipartonInteractions:allowRescatter"); |
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77 | doRescatterRestoreY = settings.flag("BeamRemnants:rescatterRestoreY"); |
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78 | |
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79 | // Parameters for colour reconnection scenario, partly borrowed from |
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80 | // multiparton interactions not to introduce too many new ones. |
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81 | doReconnect = settings.flag("BeamRemnants:reconnectColours"); |
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82 | reconnectRange = settings.parm("BeamRemnants:reconnectRange"); |
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83 | pT0Ref = settings.parm("MultipartonInteractions:pT0Ref"); |
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84 | ecmRef = settings.parm("MultipartonInteractions:ecmRef"); |
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85 | ecmPow = settings.parm("MultipartonInteractions:ecmPow"); |
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86 | |
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87 | // Total and squared CM energy at nominal energy. |
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88 | eCM = infoPtr->eCM(); |
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89 | sCM = eCM * eCM; |
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90 | |
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91 | // The MPI pT0 smoothening scale and its reconnection-strength combination. |
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92 | pT0 = pT0Ref * pow(eCM / ecmRef, ecmPow); |
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93 | pT20Rec = pow2(reconnectRange * pT0); |
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94 | |
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95 | // Done. |
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96 | return true; |
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97 | |
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98 | } |
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99 | |
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100 | //-------------------------------------------------------------------------- |
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101 | |
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102 | // Select the flavours/kinematics/colours of the two beam remnants. |
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103 | // Notation: iPar = all partons, iSys = matched systems of two beams, |
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104 | // iRem = additional partons in remnants. |
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105 | |
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106 | bool BeamRemnants::add( Event& event) { |
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107 | |
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108 | // Update to current CM energy. |
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109 | eCM = infoPtr->eCM(); |
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110 | sCM = eCM * eCM; |
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111 | |
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112 | // Check that flavour bookkept in event and in beam particles agree. |
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113 | for (int i = 0; i < beamAPtr->size(); ++i) { |
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114 | int j = (*beamAPtr)[i].iPos(); |
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115 | if ((*beamAPtr)[i].id() != event[j].id()) { |
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116 | infoPtr->errorMsg("Error in BeamRemnants::add: " |
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117 | "event and beam flavours do not match"); |
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118 | return false; |
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119 | } |
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120 | } |
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121 | for (int i = 0; i < beamBPtr->size(); ++i) { |
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122 | int j = (*beamBPtr)[i].iPos(); |
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123 | if ((*beamBPtr)[i].id() != event[j].id()) { |
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124 | infoPtr->errorMsg("Error in BeamRemnants::add: " |
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125 | "event and beam flavours do not match"); |
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126 | return false; |
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127 | } |
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128 | } |
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129 | |
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130 | // Number of scattering subsystems. Size of event record before treatment. |
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131 | nSys = partonSystemsPtr->sizeSys(); |
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132 | oldSize = event.size(); |
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133 | |
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134 | // Add required extra remnant flavour content. |
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135 | // Start all over if fails (in option where junctions not allowed). |
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136 | if ( !beamAPtr->remnantFlavours(event) |
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137 | || !beamBPtr->remnantFlavours(event) ) { |
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138 | infoPtr->errorMsg("Error in BeamRemnants::add:" |
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139 | " remnant flavour setup failed"); |
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140 | return false; |
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141 | } |
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142 | |
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143 | // Do the kinematics of the collision subsystems and two beam remnants. |
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144 | if (!setKinematics(event)) return false; |
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145 | |
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146 | // Allow colour reconnections. |
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147 | if (doReconnect) reconnectColours(event); |
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148 | |
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149 | // Save current modifiable colour configuration for fast restoration. |
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150 | vector<int> colSave; |
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151 | vector<int> acolSave; |
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152 | for (int i = oldSize; i < event.size(); ++i) { |
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153 | colSave.push_back( event[i].col() ); |
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154 | acolSave.push_back( event[i].acol() ); |
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155 | } |
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156 | event.saveJunctionSize(); |
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157 | |
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158 | // Allow several tries to match colours of initiators and remnants. |
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159 | // Frequent "failures" since shortcutting colours separately on |
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160 | // the two event sides may give "colour singlet gluons" etc. |
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161 | bool physical = true; |
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162 | for (int iTry = 0; iTry < NTRYCOLMATCH; ++iTry) { |
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163 | physical = true; |
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164 | |
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165 | // Reset list of colour "collapses" (transformations). |
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166 | colFrom.resize(0); |
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167 | colTo.resize(0); |
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168 | |
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169 | // First process each set of beam colours on its own. |
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170 | if (!beamAPtr->remnantColours(event, colFrom, colTo)) |
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171 | physical = false; |
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172 | if (!beamBPtr->remnantColours(event, colFrom, colTo)) |
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173 | physical = false; |
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174 | |
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175 | // Then check that colours and anticolours are matched in whole event. |
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176 | if ( physical && !checkColours(event) ) physical = false; |
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177 | |
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178 | // If no problems then done, else restore and loop. |
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179 | if (physical) break; |
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180 | for (int i = oldSize; i < event.size(); ++i) |
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181 | event[i].cols( colSave[i - oldSize], acolSave[i - oldSize] ); |
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182 | event.restoreJunctionSize(); |
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183 | infoPtr->errorMsg("Warning in BeamRemnants::add:" |
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184 | " colour tracing failed; will try again"); |
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185 | } |
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186 | |
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187 | // If no solution after several tries then failed. |
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188 | if (!physical) { |
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189 | infoPtr->errorMsg("Error in BeamRemnants::add:" |
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190 | " colour tracing failed after several attempts"); |
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191 | return false; |
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192 | } |
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193 | |
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194 | // Done. |
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195 | return true; |
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196 | |
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197 | } |
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198 | |
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199 | //-------------------------------------------------------------------------- |
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200 | |
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201 | // Set up trial transverse and longitudinal kinematics for each beam |
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202 | // separately. Final decisions involve comparing the two beams. |
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203 | |
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204 | bool BeamRemnants::setKinematics( Event& event) { |
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205 | |
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206 | // References to beams to simplify indexing. |
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207 | BeamParticle& beamA = *beamAPtr; |
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208 | BeamParticle& beamB = *beamBPtr; |
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209 | |
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210 | // Nothing to do for lepton-lepton scattering with all energy already used. |
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211 | if ( beamA.isUnresolvedLepton() && beamB.isUnresolvedLepton() ) |
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212 | return true; |
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213 | |
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214 | // Check that has not already used up beams. |
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215 | if ( (!beamA.isLepton() && beamA.xMax(-1) <= 0.) |
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216 | || (!beamB.isLepton() && beamB.xMax(-1) <= 0.) ) { |
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217 | infoPtr->errorMsg("Error in BeamRemnants::setKinematics:" |
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218 | " no momentum left for beam remnants"); |
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219 | return false; |
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220 | } |
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221 | |
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222 | // Last beam-status particles. Offset relative to normal beam locations. |
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223 | int nBeams = 3; |
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224 | for (int i = 3; i < event.size(); ++i) |
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225 | if (event[i].statusAbs() < 20) nBeams = i + 1; |
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226 | int nOffset = nBeams - 3; |
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227 | |
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228 | // Reserve space for extra information on the systems and beams. |
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229 | int nMaxBeam = max( beamA.size(), beamB.size() ); |
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230 | vector<double> sHatSys(nMaxBeam); |
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231 | vector<double> kTwidth(nMaxBeam); |
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232 | vector<double> kTcomp(nMaxBeam); |
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233 | vector<RotBstMatrix> Msys(nSys); |
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234 | |
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235 | // Loop over all subsystems. Default values. Find invariant mass. |
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236 | double kTcompSumA = 0.; |
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237 | double kTcompSumB = 0.; |
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238 | for (int iSys = 0; iSys < nSys; ++iSys) { |
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239 | double kTwidthNow = 0.; |
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240 | double mHatDamp = 1.; |
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241 | int iInA = partonSystemsPtr->getInA(iSys); |
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242 | int iInB = partonSystemsPtr->getInB(iSys); |
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243 | double sHatNow = (event[iInA].p() + event[iInB].p()).m2Calc(); |
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244 | |
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245 | // Allow primordial kT reduction for small-mass and small-pT systems |
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246 | // (for hardest interaction pT -> renormalization scale so also 2 -> 1). |
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247 | if (doPrimordialKT) { |
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248 | double mHat = sqrt(sHatNow); |
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249 | mHatDamp = mHat / (mHat + halfMassForKT); |
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250 | double scale = (iSys == 0) ? infoPtr->QRen(iDS) |
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251 | : partonSystemsPtr->getPTHat(iSys); |
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252 | kTwidthNow = ( (halfScaleForKT * primordialKTsoft |
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253 | + scale * primordialKThard) / (halfScaleForKT + scale) ) * mHatDamp; |
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254 | } |
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255 | |
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256 | // Store properties of compensation systems and total compensation power. |
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257 | // Rescattered partons do not compensate, but may be massive. |
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258 | sHatSys[iSys] = sHatNow; |
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259 | kTwidth[iSys] = kTwidthNow ; |
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260 | kTcomp[iSys] = mHatDamp; |
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261 | if (beamA[iSys].isFromBeam()) kTcompSumA += mHatDamp; |
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262 | else beamA[iSys].m( event[iInA].m() ); |
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263 | if (beamB[iSys].isFromBeam()) kTcompSumB += mHatDamp; |
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264 | else beamB[iSys].m( event[iInB].m() ); |
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265 | } |
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266 | |
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267 | // Primordial kT and compensation power among remnants. |
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268 | double kTwidthNow = (doPrimordialKT) ? primordialKTremnant : 0.; |
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269 | for (int iRem = nSys; iRem < nMaxBeam; ++iRem) { |
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270 | sHatSys[iRem] = 0.; |
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271 | kTwidth[iRem] = kTwidthNow ; |
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272 | kTcomp[iRem] = 1.; |
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273 | } |
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274 | kTcompSumA += beamA.size() - nSys; |
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275 | kTcompSumB += beamB.size() - nSys; |
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276 | |
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277 | // Allow ten tries to construct kinematics (but normally works first). |
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278 | bool physical; |
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279 | double xSum[2], xInvM[2], w2Beam[2], wPosRem, wNegRem, w2Rem; |
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280 | for (int iTry = 0; iTry < NTRYKINMATCH; ++iTry) { |
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281 | physical = true; |
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282 | |
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283 | // Loop over the two beams. |
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284 | for (int iBeam = 0; iBeam < 2; ++iBeam) { |
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285 | BeamParticle& beam = (iBeam == 0) ? beamA : beamB; |
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286 | int nPar = beam.size(); |
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287 | |
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288 | // Generate Gaussian pT for initiator partons inside hadrons. |
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289 | // Store/restore rescattered parton momenta before primordial kT. |
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290 | if (beam.isHadron() && doPrimordialKT) { |
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291 | double pxSum = 0.; |
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292 | double pySum = 0.; |
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293 | for (int iPar = 0; iPar < nPar; ++iPar) { |
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294 | if ( beam[iPar].isFromBeam() ) { |
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295 | pair<double, double> gauss2 = rndmPtr->gauss2(); |
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296 | double px = kTwidth[iPar] * gauss2.first; |
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297 | double py = kTwidth[iPar] * gauss2.second; |
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298 | beam[iPar].px(px); |
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299 | beam[iPar].py(py); |
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300 | pxSum += px; |
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301 | pySum += py; |
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302 | } else { |
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303 | int iInAB = (iBeam == 0) ? partonSystemsPtr->getInA(iPar) |
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304 | : partonSystemsPtr->getInB(iPar); |
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305 | beam[iPar].p( event[iInAB].p() ); |
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306 | } |
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307 | } |
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308 | |
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309 | // Share recoil between all initiator partons, rescatterers excluded. |
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310 | double kTcompSum = (iBeam == 0) ? kTcompSumA : kTcompSumB; |
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311 | for (int iPar = 0; iPar < nPar; ++iPar) |
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312 | if (beam[iPar].isFromBeam() ) { |
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313 | beam[iPar].px( beam[iPar].px() - pxSum * kTcomp[iPar] / kTcompSum ); |
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314 | beam[iPar].py( beam[iPar].py() - pySum * kTcomp[iPar] / kTcompSum ); |
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315 | } |
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316 | |
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317 | // Without primordial kT: still need to store rescattered partons. |
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318 | } else if (beam.isHadron()) { |
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319 | for (int iPar = 0; iPar < nPar; ++iPar) |
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320 | if ( !beam[iPar].isFromBeam() ) { |
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321 | int iInAB = (iBeam == 0) ? partonSystemsPtr->getInA(iPar) |
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322 | : partonSystemsPtr->getInB(iPar); |
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323 | beam[iPar].p( event[iInAB].p() ); |
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324 | } |
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325 | } |
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326 | |
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327 | // Pick unrescaled x values for remnants. Sum up (unscaled) p+ and p-. |
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328 | xSum[iBeam] = 0.; |
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329 | xInvM[iBeam] = 0.; |
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330 | for (int iRem = nSys; iRem < nPar; ++iRem) { |
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331 | double xPrel = beam.xRemnant( iRem); |
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332 | beam[iRem].x(xPrel); |
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333 | xSum[iBeam] += xPrel; |
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334 | xInvM[iBeam] += beam[iRem].mT2()/xPrel; |
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335 | } |
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336 | |
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337 | // Squared transverse mass for each beam, using lightcone x. |
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338 | w2Beam[iBeam] = xSum[iBeam] * xInvM[iBeam]; |
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339 | |
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340 | // End separate treatment of the two beams. |
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341 | } |
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342 | |
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343 | // Recalculate kinematics of initiator systems with primordial kT. |
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344 | wPosRem = eCM; |
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345 | wNegRem = eCM; |
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346 | for (int iSys = 0; iSys < nSys; ++iSys) { |
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347 | int iA = beamA[iSys].iPos(); |
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348 | int iB = beamB[iSys].iPos(); |
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349 | double sHat = sHatSys[iSys]; |
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350 | |
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351 | // Classify system: rescattering on either or both sides? |
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352 | bool normalA = beamA[iSys].isFromBeam(); |
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353 | bool normalB = beamB[iSys].isFromBeam(); |
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354 | bool normalSys = normalA && normalB; |
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355 | bool doubleRes = !normalA && !normalB; |
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356 | |
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357 | // Check whether final-state system momentum matches initial-state one. |
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358 | if (allowRescatter && CORRECTMISMATCH) { |
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359 | Vec4 pInitial = event[iA].p() + event[iB].p(); |
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360 | Vec4 pFinal; |
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361 | for (int iMem = 0; iMem < partonSystemsPtr->sizeOut(iSys); ++iMem) { |
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362 | int iAB = partonSystemsPtr->getOut(iSys, iMem); |
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363 | if (event[iAB].isFinal()) pFinal += event[iAB].p(); |
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364 | } |
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365 | |
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366 | // Scale down primordial kT from side A if p+ increased. |
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367 | if (normalA && pFinal.pPos() > pInitial.pPos()) |
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368 | beamA[iSys].scalePT( pInitial.pPos() / pFinal.pPos() ); |
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369 | |
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370 | // Scale down primordial kT from side B if p- increased. |
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371 | if (normalB && pFinal.pNeg() > pInitial.pNeg()) |
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372 | beamB[iSys].scalePT( pInitial.pNeg() / pFinal.pNeg() ); |
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373 | } |
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374 | |
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375 | // Rescatter: possible change in sign of lightcone momentum of a |
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376 | // rescattered parton. If this happens, try to pick |
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377 | // new primordial kT values |
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378 | if (allowRescatter |
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379 | && (event[iA].pPos() / beamA[iSys].pPos() < 0 |
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380 | || event[iB].pNeg() / beamB[iSys].pNeg() < 0) ) { |
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381 | infoPtr->errorMsg("Warning in BeamRemnants::setKinematics:" |
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382 | " change in lightcone momentum sign; retrying kinematics"); |
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383 | physical = false; |
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384 | break; |
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385 | } |
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386 | |
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387 | // Begin kinematics of partons after primordial kT has been added. |
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388 | double sHatTAft = sHat + pow2( beamA[iSys].px() + beamB[iSys].px()) |
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389 | + pow2( beamA[iSys].py() + beamB[iSys].py()); |
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390 | double w2A = beamA[iSys].mT2(); |
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391 | double w2B = beamB[iSys].mT2(); |
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392 | double w2Diff = sHatTAft - w2A - w2B; |
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393 | double lambda = pow2(w2Diff) - 4. * w2A * w2B; |
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394 | |
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395 | // Too large transverse momenta means that kinematics will not work. |
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396 | if (lambda <= 0.) { |
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397 | physical = false; |
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398 | break; |
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399 | } |
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400 | double lamRoot = sqrtpos( lambda ); |
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401 | |
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402 | // Mirror solution if the two incoming have reverse rapidity ordering. |
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403 | if (allowRescatter && doubleRes && (event[iA].pPos() * event[iB].pNeg() |
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404 | < event[iA].pNeg() * event[iB].pPos()) ) lamRoot = -lamRoot; |
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405 | |
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406 | // Two procedures, which agree for normal scattering, separate here. |
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407 | // First option keeps rapidity (and mass) of system unchanged by |
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408 | // primordial kT, by modification of rescattered parton. |
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409 | if (normalSys || doRescatterRestoreY || doubleRes) { |
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410 | |
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411 | // Find kinematics of initial system: transverse mass, and |
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412 | // longitudinal momentum carried by all or rescattered partons. |
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413 | double sHatTBef = sHat; |
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414 | double wPosBef, wNegBef, wPosBefRes, wNegBefRes; |
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415 | // Normal scattering. |
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416 | if (normalSys) { |
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417 | wPosBef = beamA[iSys].x() * eCM; |
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418 | wNegBef = beamB[iSys].x() * eCM; |
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419 | wPosBefRes = 0.; |
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420 | wNegBefRes = 0.; |
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421 | // Rescattering on side A. |
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422 | } else if (normalB) { |
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423 | sHatTBef += event[iA].pT2(); |
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424 | wPosBef = event[iA].pPos(); |
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425 | wNegBef = event[iA].pNeg() + beamB[iSys].x() * eCM; |
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426 | wPosBefRes = beamA[iSys].pPos(); |
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427 | wNegBefRes = beamA[iSys].pNeg(); |
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428 | // Rescattering on side B. |
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429 | } else if (normalA) { |
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430 | sHatTBef += event[iB].pT2(); |
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431 | wPosBef = beamA[iSys].x() * eCM + event[iB].pPos(); |
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432 | wNegBef = event[iB].pNeg(); |
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433 | wPosBefRes = beamB[iSys].pPos(); |
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434 | wNegBefRes = beamB[iSys].pNeg(); |
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435 | // Rescattering on both sides. |
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436 | } else { |
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437 | sHatTBef += pow2( event[iA].px() + event[iB].px()) |
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438 | + pow2( event[iA].py() + event[iB].py()); |
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439 | wPosBef = event[iA].pPos() + event[iB].pPos(); |
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440 | wNegBef = event[iA].pNeg() + event[iB].pNeg(); |
---|
441 | wPosBefRes = beamA[iSys].pPos() + beamB[iSys].pPos(); |
---|
442 | wNegBefRes = beamA[iSys].pNeg() + beamB[iSys].pNeg(); |
---|
443 | } |
---|
444 | |
---|
445 | // Rescale outgoing momenta to keep same mass and rapidity of system |
---|
446 | // as originally, and solve for kinematics. |
---|
447 | double rescale = sqrt(sHatTAft / sHatTBef); |
---|
448 | double wPosAft = rescale * wPosBef; |
---|
449 | double wNegAft = rescale * wNegBef; |
---|
450 | wPosRem -= wPosAft - wPosBefRes; |
---|
451 | wNegRem -= wNegAft - wNegBefRes; |
---|
452 | double wPosA = 0.5 * (sHatTAft + w2A - w2B + lamRoot) / wNegAft; |
---|
453 | double wNegB = 0.5 * (sHatTAft + w2B - w2A + lamRoot) / wPosAft; |
---|
454 | |
---|
455 | // Store modified beam parton momenta. |
---|
456 | beamA[iSys].e( 0.5 * (wPosA + w2A / wPosA) ); |
---|
457 | beamA[iSys].pz( 0.5 * (wPosA - w2A / wPosA) ); |
---|
458 | beamB[iSys].e( 0.5 * (w2B / wNegB + wNegB) ); |
---|
459 | beamB[iSys].pz( 0.5 * (w2B / wNegB - wNegB) ); |
---|
460 | |
---|
461 | // Second option keeps rescattered parton (and system mass) unchanged |
---|
462 | // by primordial kT, by modification of system rapidity. |
---|
463 | } else { |
---|
464 | |
---|
465 | // Rescattering on side A: preserve already scattered parton. |
---|
466 | if (normalB) { |
---|
467 | double wPosA = beamA[iSys].pPos(); |
---|
468 | double wNegB = 0.5 * (w2Diff + lamRoot) / wPosA; |
---|
469 | beamB[iSys].e( 0.5 * (w2B / wNegB + wNegB) ); |
---|
470 | beamB[iSys].pz( 0.5 * (w2B / wNegB - wNegB) ); |
---|
471 | wPosRem -= w2B / wNegB; |
---|
472 | wNegRem -= wNegB; |
---|
473 | |
---|
474 | |
---|
475 | // Rescattering on side B: preserve already scattered parton. |
---|
476 | } else if (normalA) { |
---|
477 | double wNegB = beamB[iSys].pNeg(); |
---|
478 | double wPosA = 0.5 * (w2Diff + lamRoot) / wNegB; |
---|
479 | beamA[iSys].e( 0.5 * (wPosA + w2A / wPosA) ); |
---|
480 | beamA[iSys].pz( 0.5 * (wPosA - w2A / wPosA) ); |
---|
481 | wPosRem -= wPosA; |
---|
482 | wNegRem -= w2A / wPosA; |
---|
483 | |
---|
484 | // Primordial kT in double rescattering does change the mass of |
---|
485 | // the system without any possible fix in this framework, which |
---|
486 | // leads to incorrect boosts. Current choice is therefore always |
---|
487 | // to handle it with the first procedure, where mass is retained. |
---|
488 | } else { |
---|
489 | } |
---|
490 | } |
---|
491 | |
---|
492 | // Construct system rotation and boost caused by primordial kT. |
---|
493 | Msys[iSys].reset(); |
---|
494 | Msys[iSys].toCMframe( event[iA].p(), event[iB].p() ); |
---|
495 | Msys[iSys].fromCMframe( beamA[iSys].p(), beamB[iSys].p() ); |
---|
496 | |
---|
497 | // Boost rescattered partons in subsequent beam A list. |
---|
498 | for (int iSys2 = iSys + 1; iSys2 < nSys; ++iSys2) { |
---|
499 | if (!beamA[iSys2].isFromBeam()) { |
---|
500 | int iBefResc = event[ beamA[iSys2].iPos() ].mother1(); |
---|
501 | for (int iMem = 0; iMem < partonSystemsPtr->sizeOut(iSys); ++iMem) |
---|
502 | if (partonSystemsPtr->getOut(iSys, iMem) == iBefResc) { |
---|
503 | Vec4 pTemp = event[iBefResc].p(); |
---|
504 | pTemp.rotbst( Msys[iSys] ); |
---|
505 | beamA[iSys2].p( pTemp ); |
---|
506 | } |
---|
507 | } |
---|
508 | |
---|
509 | // Boost rescattered partons in subsequent beam B list. |
---|
510 | if (!beamB[iSys2].isFromBeam()) { |
---|
511 | int iBefResc = event[ beamB[iSys2].iPos() ].mother1(); |
---|
512 | for (int iMem = 0; iMem < partonSystemsPtr->sizeOut(iSys); ++iMem) |
---|
513 | if (partonSystemsPtr->getOut(iSys, iMem) == iBefResc) { |
---|
514 | Vec4 pTemp = event[iBefResc].p(); |
---|
515 | pTemp.rotbst( Msys[iSys] ); |
---|
516 | beamB[iSys2].p( pTemp ); |
---|
517 | } |
---|
518 | } |
---|
519 | } |
---|
520 | } |
---|
521 | |
---|
522 | // Check that remaining momentum is enough for remnants. |
---|
523 | if (wPosRem < 0. || wNegRem < 0.) physical = false; |
---|
524 | w2Rem = wPosRem * wNegRem; |
---|
525 | if (sqrtpos(w2Rem) < sqrt(w2Beam[0]) + sqrt(w2Beam[1])) |
---|
526 | physical = false; |
---|
527 | |
---|
528 | // End of loop over ten tries. Do not loop when solution found. |
---|
529 | if (physical) break; |
---|
530 | } |
---|
531 | |
---|
532 | // If no solution after ten tries then failed. |
---|
533 | if (!physical) { |
---|
534 | infoPtr->errorMsg("Error in BeamRemnants::setKinematics:" |
---|
535 | " kinematics construction failed"); |
---|
536 | return false; |
---|
537 | } |
---|
538 | |
---|
539 | // For successful initiator kinematics process whole systems. |
---|
540 | Vec4 pSumOut; |
---|
541 | for (int iSys = 0; iSys < nSys; ++iSys) { |
---|
542 | |
---|
543 | // Copy initiators and their systems and boost them accordingly. |
---|
544 | // Update subsystem and beams info on new positions of partons. |
---|
545 | // Update daughter info of mothers, i.e. of beams, for hardest interaction. |
---|
546 | if (beamA[iSys].isFromBeam()) { |
---|
547 | int iA = beamA[iSys].iPos(); |
---|
548 | int iAcopy = event.copy(iA, -61); |
---|
549 | event[iAcopy].rotbst(Msys[iSys]); |
---|
550 | partonSystemsPtr->setInA(iSys, iAcopy); |
---|
551 | beamA[iSys].iPos( iAcopy); |
---|
552 | if (iSys == 0) { |
---|
553 | int mother = event[iAcopy].mother1(); |
---|
554 | event[mother].daughter1(iAcopy); |
---|
555 | } |
---|
556 | } |
---|
557 | if (beamB[iSys].isFromBeam()) { |
---|
558 | int iB = beamB[iSys].iPos(); |
---|
559 | int iBcopy = event.copy(iB, -61); |
---|
560 | event[iBcopy].rotbst(Msys[iSys]); |
---|
561 | partonSystemsPtr->setInB(iSys, iBcopy); |
---|
562 | beamB[iSys].iPos( iBcopy); |
---|
563 | if (iSys == 0) { |
---|
564 | int mother = event[iBcopy].mother1(); |
---|
565 | event[mother].daughter1(iBcopy); |
---|
566 | } |
---|
567 | } |
---|
568 | |
---|
569 | for (int iMem = 0; iMem < partonSystemsPtr->sizeOut(iSys); ++iMem) { |
---|
570 | int iAB = partonSystemsPtr->getOut(iSys, iMem); |
---|
571 | if (event[iAB].isFinal()) { |
---|
572 | int iABcopy = event.copy(iAB, 62); |
---|
573 | event[iABcopy].rotbst(Msys[iSys]); |
---|
574 | partonSystemsPtr->setOut(iSys, iMem, iABcopy); |
---|
575 | pSumOut += event[iABcopy].p(); |
---|
576 | } |
---|
577 | } |
---|
578 | |
---|
579 | } |
---|
580 | |
---|
581 | // Colour dipoles spanning systems gives mismatch between FSR recoils |
---|
582 | // and primordial kT boosts. |
---|
583 | if (allowRescatter && CORRECTMISMATCH) { |
---|
584 | |
---|
585 | // Find summed pT of beam remnants = - wanted pT of systems. |
---|
586 | double pxBeams = 0.; |
---|
587 | double pyBeams = 0.; |
---|
588 | for (int iRem = nSys; iRem < beamA.size(); ++iRem) { |
---|
589 | pxBeams += beamA[iRem].px(); |
---|
590 | pyBeams += beamA[iRem].py(); |
---|
591 | } |
---|
592 | for (int iRem = nSys; iRem < beamB.size(); ++iRem) { |
---|
593 | pxBeams += beamB[iRem].px(); |
---|
594 | pyBeams += beamB[iRem].py(); |
---|
595 | } |
---|
596 | |
---|
597 | // Boost all final partons in systems transversely, and also their sum. |
---|
598 | Vec4 pSumTo( -pxBeams, -pyBeams, pSumOut.pz(), sqrt( pow2(pxBeams) |
---|
599 | + pow2(pyBeams) + pow2(pSumOut.pz()) + pSumOut.m2Calc() ) ); |
---|
600 | RotBstMatrix Mmismatch; |
---|
601 | Mmismatch.bst( pSumOut, pSumTo); |
---|
602 | for (int iSys = 0; iSys < nSys; ++iSys) |
---|
603 | for (int iMem = 0; iMem < partonSystemsPtr->sizeOut(iSys); ++iMem) { |
---|
604 | int iAB = partonSystemsPtr->getOut(iSys, iMem); |
---|
605 | if (event[iAB].isFinal()) event[iAB].rotbst(Mmismatch); |
---|
606 | } |
---|
607 | pSumOut.rotbst(Mmismatch); |
---|
608 | |
---|
609 | // Reset energy and momentum sum, to be compensated by beam remnants. |
---|
610 | wPosRem = eCM - (pSumOut.e() + pSumOut.pz()); |
---|
611 | wNegRem = eCM - (pSumOut.e() - pSumOut.pz()); |
---|
612 | w2Rem = wPosRem * wNegRem; |
---|
613 | if ( wPosRem < 0. || wNegRem < 0. |
---|
614 | || sqrtpos(w2Rem) < sqrt(w2Beam[0]) + sqrt(w2Beam[1])) { |
---|
615 | infoPtr->errorMsg("Error in BeamRemnants::setKinematics:" |
---|
616 | " kinematics construction failed owing to recoil mismatch"); |
---|
617 | return false; |
---|
618 | } |
---|
619 | } |
---|
620 | |
---|
621 | // Construct x rescaling factors for the two remants. |
---|
622 | double lambdaRoot = sqrtpos( pow2(w2Rem - w2Beam[0] - w2Beam[1]) |
---|
623 | - 4. * w2Beam[0] * w2Beam[1] ); |
---|
624 | double rescaleA = (w2Rem + w2Beam[0] - w2Beam[1] + lambdaRoot) |
---|
625 | / (2. * w2Rem * xSum[0]) ; |
---|
626 | double rescaleB = (w2Rem + w2Beam[1] - w2Beam[0] + lambdaRoot) |
---|
627 | / (2. * w2Rem * xSum[1]) ; |
---|
628 | |
---|
629 | // Construct energy and pz for remnants in first beam. |
---|
630 | for (int iRem = nSys; iRem < beamA.size(); ++iRem) { |
---|
631 | double pPos = rescaleA * beamA[iRem].x() * wPosRem; |
---|
632 | double pNeg = beamA[iRem].mT2() / pPos; |
---|
633 | beamA[iRem].e( 0.5 * (pPos + pNeg) ); |
---|
634 | beamA[iRem].pz( 0.5 * (pPos - pNeg) ); |
---|
635 | |
---|
636 | // Add these partons to the normal event record. |
---|
637 | int iNew = event.append( beamA[iRem].id(), 63, 1 + nOffset, 0, 0, 0, |
---|
638 | beamA[iRem].col(), beamA[iRem].acol(), beamA[iRem].p(), |
---|
639 | beamA[iRem].m() ); |
---|
640 | beamA[iRem].iPos( iNew); |
---|
641 | } |
---|
642 | |
---|
643 | // Construct energy and pz for remnants in second beam. |
---|
644 | for (int iRem = nSys; iRem < beamB.size(); ++iRem) { |
---|
645 | double pNeg = rescaleB * beamB[iRem].x() * wNegRem; |
---|
646 | double pPos = beamB[iRem].mT2() / pNeg; |
---|
647 | beamB[iRem].e( 0.5 * (pPos + pNeg) ); |
---|
648 | beamB[iRem].pz( 0.5 * (pPos - pNeg) ); |
---|
649 | |
---|
650 | // Add these partons to the normal event record. |
---|
651 | int iNew = event.append( beamB[iRem].id(), 63, 2 + nOffset, 0, 0, 0, |
---|
652 | beamB[iRem].col(), beamB[iRem].acol(), beamB[iRem].p(), |
---|
653 | beamB[iRem].m() ); |
---|
654 | beamB[iRem].iPos( iNew); |
---|
655 | } |
---|
656 | |
---|
657 | // Done. |
---|
658 | return true; |
---|
659 | |
---|
660 | } |
---|
661 | |
---|
662 | //-------------------------------------------------------------------------- |
---|
663 | |
---|
664 | // Allow colour reconnections by mergings of collision subsystems. |
---|
665 | // iRec is system that may be reconnected, by moving its gluons to iSys, |
---|
666 | // where minimal pT (or equivalently Lambda) is used to pick location. |
---|
667 | // Therefore all dipoles in iSys have to be found, and all gluons in iRec. |
---|
668 | // Matching q-qbar pairs are treated by analogy with gluons. |
---|
669 | // Note: owing to rescatterings some outgoing partons must be skipped. |
---|
670 | |
---|
671 | bool BeamRemnants::reconnectColours( Event& event) { |
---|
672 | |
---|
673 | // References to beams to simplify indexing. |
---|
674 | BeamParticle& beamA = *beamAPtr; |
---|
675 | BeamParticle& beamB = *beamBPtr; |
---|
676 | |
---|
677 | // Prepare record of which systems should be merged onto another. |
---|
678 | // The iSys system must have colour in final state to attach to it. |
---|
679 | vector<int> iMerge(nSys); |
---|
680 | vector<bool> hasColour(nSys); |
---|
681 | for (int iSys = 0; iSys < nSys; ++iSys) { |
---|
682 | iMerge[iSys] = iSys; |
---|
683 | bool hasCol = false; |
---|
684 | for (int iMem = 0; iMem < partonSystemsPtr->sizeOut(iSys); ++iMem) { |
---|
685 | int iNow = partonSystemsPtr->getOut( iSys, iMem); |
---|
686 | if (event[iNow].isFinal() && (event[iNow].col() > 0 |
---|
687 | || event[iNow].acol() > 0) ) { |
---|
688 | hasCol = true; |
---|
689 | break; |
---|
690 | } |
---|
691 | } |
---|
692 | hasColour[iSys] = hasCol; |
---|
693 | } |
---|
694 | |
---|
695 | // Loop over systems to decide which should be reconnected. |
---|
696 | for (int iRec = nSys - 1; iRec > 0; --iRec) { |
---|
697 | |
---|
698 | // Determine reconnection strength from pT scale of system. |
---|
699 | double pT2Rec = pow2( partonSystemsPtr->getPTHat(iRec) ); |
---|
700 | double probRec = pT20Rec / (pT20Rec + pT2Rec); |
---|
701 | |
---|
702 | // Loop over other systems iSys at higher pT scale and |
---|
703 | // decide whether to reconnect the iRec gluons onto one of them. |
---|
704 | for (int iSys = iRec - 1; iSys >= 0; --iSys) |
---|
705 | if (hasColour[iSys] && probRec > rndmPtr->flat()) { |
---|
706 | |
---|
707 | // The iRec system and all merged with it to be merged with iSys. |
---|
708 | iMerge[iRec] = iSys; |
---|
709 | for (int iRec2 = iRec + 1; iRec2 < nSys; ++iRec2) |
---|
710 | if (iMerge[iRec2] == iRec) iMerge[iRec2] = iSys; |
---|
711 | |
---|
712 | // Once a system has been merged do not test it anymore. |
---|
713 | break; |
---|
714 | } |
---|
715 | } |
---|
716 | |
---|
717 | // Loop over systems. Check whether other systems to be merged with it. |
---|
718 | for (int iSys = 0; iSys < nSys; ++iSys) { |
---|
719 | int nMerge = 0; |
---|
720 | for (int iRec = iSys + 1; iRec < nSys; ++iRec) |
---|
721 | if (iMerge[iRec] == iSys) ++nMerge; |
---|
722 | if (nMerge == 0) continue; |
---|
723 | |
---|
724 | // Incoming partons not counted if rescattered. |
---|
725 | int iInASys = partonSystemsPtr->getInA(iSys); |
---|
726 | bool hasInA = (beamA[iSys].isFromBeam()); |
---|
727 | int iInBSys = partonSystemsPtr->getInB(iSys); |
---|
728 | bool hasInB = (beamB[iSys].isFromBeam()); |
---|
729 | |
---|
730 | // Begin find dipoles in iSys system. |
---|
731 | vector<BeamDipole> dipoles; |
---|
732 | int sizeOut = partonSystemsPtr->sizeOut(iSys); |
---|
733 | for (int iMem = 0; iMem < sizeOut; ++iMem) { |
---|
734 | |
---|
735 | // Find colour dipoles to beam remnant. |
---|
736 | int iNow = partonSystemsPtr->getOut( iSys, iMem); |
---|
737 | if (!event[iNow].isFinal()) continue; |
---|
738 | int col = event[iNow].col(); |
---|
739 | if (col > 0) { |
---|
740 | if (hasInA && event[iInASys].col() == col) |
---|
741 | dipoles.push_back( BeamDipole( col, iNow, iInASys ) ); |
---|
742 | else if (hasInB && event[iInBSys].col() == col) |
---|
743 | dipoles.push_back( BeamDipole( col, iNow, iInBSys ) ); |
---|
744 | |
---|
745 | // Find colour dipole between final-state partons. |
---|
746 | else for (int iMem2 = 0; iMem2 < sizeOut; ++iMem2) |
---|
747 | if (iMem2 != iMem) { |
---|
748 | int iNow2 = partonSystemsPtr->getOut( iSys, iMem2); |
---|
749 | if (!event[iNow2].isFinal()) continue; |
---|
750 | if (event[iNow2].acol() == col) { |
---|
751 | dipoles.push_back( BeamDipole( col, iNow, iNow2) ); |
---|
752 | break; |
---|
753 | } |
---|
754 | } |
---|
755 | } |
---|
756 | |
---|
757 | // Find anticolour dipoles to beam remnant. |
---|
758 | int acol = event[iNow].acol(); |
---|
759 | if (acol > 0) { |
---|
760 | if (hasInA && event[iInASys].acol() == acol) |
---|
761 | dipoles.push_back( BeamDipole( acol, iInASys, iNow ) ); |
---|
762 | else if (hasInB && event[iInBSys].acol() == acol) |
---|
763 | dipoles.push_back( BeamDipole( acol, iInBSys, iNow ) ); |
---|
764 | } |
---|
765 | } |
---|
766 | |
---|
767 | // Skip mergings if no dipoles found. |
---|
768 | if (dipoles.size() == 0) continue; |
---|
769 | |
---|
770 | // Find dipole sizes. |
---|
771 | for (int iDip = 0; iDip < int(dipoles.size()); ++iDip) |
---|
772 | dipoles[iDip].p1p2 = event[dipoles[iDip].iCol].p() |
---|
773 | * event[dipoles[iDip].iAcol].p(); |
---|
774 | |
---|
775 | // Loop over systems iRec to be merged with iSys. |
---|
776 | for (int iRec = iSys + 1; iRec < nSys; ++iRec) { |
---|
777 | if (iMerge[iRec] != iSys) continue; |
---|
778 | |
---|
779 | // Information on iRec. Vectors for gluons and anything else. |
---|
780 | int sizeRec = partonSystemsPtr->sizeOut(iRec); |
---|
781 | int iInARec = partonSystemsPtr->getInA(iRec); |
---|
782 | int iInBRec = partonSystemsPtr->getInB(iRec); |
---|
783 | int nGluRec = 0; |
---|
784 | vector<int> iGluRec; |
---|
785 | vector<double> pT2GluRec; |
---|
786 | int nAnyRec = 0; |
---|
787 | vector<int> iAnyRec; |
---|
788 | vector<bool> freeAnyRec; |
---|
789 | |
---|
790 | // Copy of gluon positions in descending order. |
---|
791 | for (int iMem = 0; iMem < sizeRec; ++iMem) { |
---|
792 | int iNow = partonSystemsPtr->getOut( iRec, iMem); |
---|
793 | if (!event[iNow].isFinal()) continue; |
---|
794 | if (event[iNow].isGluon()) { |
---|
795 | ++nGluRec; |
---|
796 | iGluRec.push_back( iNow ); |
---|
797 | pT2GluRec.push_back( event[iNow].pT2() ); |
---|
798 | for (int i = nGluRec - 1; i > 1; --i) { |
---|
799 | if (pT2GluRec[i - 1] > pT2GluRec[i]) break; |
---|
800 | swap( iGluRec[i - 1], iGluRec[i] ); |
---|
801 | swap( pT2GluRec[i - 1], pT2GluRec[i] ); |
---|
802 | } |
---|
803 | // Copy of anything else, mainly quarks, in no particular order. |
---|
804 | } else { |
---|
805 | ++nAnyRec; |
---|
806 | iAnyRec.push_back( iNow ); |
---|
807 | freeAnyRec.push_back( true ); |
---|
808 | } |
---|
809 | } |
---|
810 | |
---|
811 | // For each gluon in iRec now find the dipole that gives the smallest |
---|
812 | // (pGlu * pI) (pGlu * pJ) / (pI * pJ), i.e. minimal pT (and Lambda). |
---|
813 | for (int iGRec = 0; iGRec < nGluRec; ++iGRec) { |
---|
814 | int iGlu = iGluRec[iGRec]; |
---|
815 | Vec4 pGlu = event[iGlu].p(); |
---|
816 | int iDipMin = 0; |
---|
817 | double pT2DipMin = sCM; |
---|
818 | for (int iDip = 0; iDip < int(dipoles.size()); ++iDip) { |
---|
819 | double pT2Dip = (pGlu * event[dipoles[iDip].iCol].p()) |
---|
820 | * (pGlu * event[dipoles[iDip].iAcol].p()) / dipoles[iDip].p1p2; |
---|
821 | if (pT2Dip < pT2DipMin) { |
---|
822 | iDipMin = iDip; |
---|
823 | pT2DipMin = pT2Dip; |
---|
824 | } |
---|
825 | } |
---|
826 | |
---|
827 | // Attach the gluon to the dipole, i.e. split the dipole in two. |
---|
828 | int colGlu = event[iGlu].col(); |
---|
829 | int acolGlu = event[iGlu].acol(); |
---|
830 | int colDip = dipoles[iDipMin].col; |
---|
831 | int iColDip = dipoles[iDipMin].iCol; |
---|
832 | int iAcolDip = dipoles[iDipMin].iAcol; |
---|
833 | event[iGlu].acol( colDip ); |
---|
834 | if (event[iAcolDip].acol() == colDip) |
---|
835 | event[iAcolDip].acol( colGlu ); |
---|
836 | else event[iAcolDip].col( colGlu ); |
---|
837 | dipoles[iDipMin].iAcol = iGlu; |
---|
838 | dipoles[iDipMin].p1p2 = event[iColDip].p() * pGlu; |
---|
839 | dipoles.push_back( BeamDipole( colGlu, iGlu, iAcolDip ) ); |
---|
840 | dipoles.back().p1p2 = pGlu * event[iAcolDip].p(); |
---|
841 | |
---|
842 | // Remove gluon from old system: reconnect colours. |
---|
843 | for (int i = oldSize; i < event.size(); ++i) |
---|
844 | if (i != iGlu && i != iAcolDip) { |
---|
845 | if (event[i].isFinal()) { |
---|
846 | if (event[i].acol() == colGlu) event[i].acol( acolGlu ); |
---|
847 | } else { |
---|
848 | if (event[i].col() == colGlu) event[i].col( acolGlu ); |
---|
849 | } |
---|
850 | } |
---|
851 | |
---|
852 | // Update any junction legs that match reconnected dipole. |
---|
853 | for (int iJun = 0; iJun < event.sizeJunction(); ++iJun) { |
---|
854 | |
---|
855 | // Only junctions need to be updated, not antijunctions. |
---|
856 | if (event.kindJunction(iJun) % 2 == 0) continue; |
---|
857 | for (int leg = 0; leg < 3; ++leg) { |
---|
858 | int col = event.colJunction(iJun, leg); |
---|
859 | if (col == colDip) |
---|
860 | event.colJunction(iJun, leg, colGlu); |
---|
861 | } |
---|
862 | } |
---|
863 | |
---|
864 | } |
---|
865 | |
---|
866 | // See if any matching quark-antiquark pairs among the rest. |
---|
867 | for (int iQRec = 0; iQRec < nAnyRec; ++iQRec) { |
---|
868 | int iQ = iAnyRec[iQRec]; |
---|
869 | int idQ = event[iQ].id(); |
---|
870 | if (freeAnyRec[iQRec] && idQ > 0 && idQ < 6) |
---|
871 | for (int iQbarRec = 0; iQbarRec < nAnyRec; ++iQbarRec) { |
---|
872 | int iQbar = iAnyRec[iQbarRec]; |
---|
873 | if (freeAnyRec[iQbarRec] && event[iQbar].id() == -idQ) { |
---|
874 | |
---|
875 | // Check that these can be traced back to same gluon splitting. |
---|
876 | // For now also avoid qqbar pairs produced in rescatterings.?? |
---|
877 | int iTopQ = event.iTopCopyId(iQ); |
---|
878 | int iTopQbar = event.iTopCopyId(iQbar); |
---|
879 | int iMother = event[iTopQ].mother1(); |
---|
880 | if (event[iTopQbar].mother1() == iMother |
---|
881 | && event[iMother].isGluon() && event[iMother].status() != -34 |
---|
882 | && event[iMother + 1].status() != -34 ) { |
---|
883 | |
---|
884 | // Now find the dipole that gives the smallest |
---|
885 | // ((pQ + pQbar) * pI) ((pQ + pQbar) * pJ) / (pI * pJ). |
---|
886 | Vec4 pGlu = event[iQ].p() + event[iQbar].p(); |
---|
887 | int iDipMin = 0; |
---|
888 | double pT2DipMin = sCM; |
---|
889 | for (int iDip = 0; iDip < int(dipoles.size()); ++iDip) { |
---|
890 | double pT2Dip = (pGlu * event[dipoles[iDip].iCol].p()) |
---|
891 | * (pGlu * event[dipoles[iDip].iAcol].p()) |
---|
892 | / dipoles[iDip].p1p2; |
---|
893 | if (pT2Dip < pT2DipMin) { |
---|
894 | iDipMin = iDip; |
---|
895 | pT2DipMin = pT2Dip; |
---|
896 | } |
---|
897 | } |
---|
898 | |
---|
899 | // Attach the q-qbar pair to the dipole, i.e. split the dipole. |
---|
900 | int colGlu = event[iQ].col(); |
---|
901 | int acolGlu = event[iQbar].acol(); |
---|
902 | int colDip = dipoles[iDipMin].col; |
---|
903 | int iColDip = dipoles[iDipMin].iCol; |
---|
904 | int iAcolDip = dipoles[iDipMin].iAcol; |
---|
905 | event[iQbar].acol( colDip ); |
---|
906 | if (event[iAcolDip].acol() == colDip) |
---|
907 | event[iAcolDip].acol( colGlu ); |
---|
908 | else event[iAcolDip].col( colGlu ); |
---|
909 | dipoles[iDipMin].iAcol = iQbar; |
---|
910 | dipoles[iDipMin].p1p2 = event[iColDip].p() * event[iQbar].p(); |
---|
911 | dipoles.push_back( BeamDipole( colGlu, iQ, iAcolDip ) ); |
---|
912 | dipoles.back().p1p2 = event[iQ].p() * event[iAcolDip].p(); |
---|
913 | |
---|
914 | // Remove q-qbar pair from old system: reconnect colours. |
---|
915 | freeAnyRec[iQRec] = false; |
---|
916 | freeAnyRec[iQbarRec] = false; |
---|
917 | for (int i = oldSize; i < event.size(); ++i) |
---|
918 | if (i != iQRec && i != iQbarRec && i != iColDip |
---|
919 | && i != iAcolDip) { |
---|
920 | if (event[i].isFinal()) { |
---|
921 | if (event[i].acol() == colGlu) event[i].acol( acolGlu ); |
---|
922 | } else { |
---|
923 | if (event[i].col() == colGlu) event[i].col( acolGlu ); |
---|
924 | } |
---|
925 | } |
---|
926 | |
---|
927 | // Update any junction legs that match reconnected dipole. |
---|
928 | for (int iJun = 0; iJun < event.sizeJunction(); ++iJun) { |
---|
929 | |
---|
930 | // Only junctions need to be updated, not antijunctions. |
---|
931 | if (event.kindJunction(iJun) % 2 == 0) continue; |
---|
932 | for (int leg = 0; leg < 3; ++leg) { |
---|
933 | int col = event.colJunction(iJun, leg); |
---|
934 | if (col == colDip) |
---|
935 | event.colJunction(iJun, leg, colGlu); |
---|
936 | } |
---|
937 | } |
---|
938 | |
---|
939 | // Done with processing of q-qbar pairs. |
---|
940 | } |
---|
941 | } |
---|
942 | } |
---|
943 | } |
---|
944 | |
---|
945 | // If only two beam gluons left of system, set their colour = anticolour. |
---|
946 | // Used by BeamParticle::remnantColours to skip irrelevant gluons. |
---|
947 | if ( event[iInARec].isGluon() && !event[iInARec].isRescatteredIncoming() |
---|
948 | && event[iInBRec].isGluon() && !event[iInBRec].isRescatteredIncoming() |
---|
949 | && event[iInARec].col() == event[iInBRec].acol() |
---|
950 | && event[iInARec].acol() == event[iInBRec].col() ) { |
---|
951 | event[iInARec].acol( event[iInARec].col() ); |
---|
952 | event[iInBRec].acol( event[iInBRec].col() ); |
---|
953 | } |
---|
954 | |
---|
955 | // End of loops over iRec and iSys systems. |
---|
956 | } |
---|
957 | } |
---|
958 | |
---|
959 | // Done. |
---|
960 | return true; |
---|
961 | |
---|
962 | } |
---|
963 | |
---|
964 | //-------------------------------------------------------------------------- |
---|
965 | |
---|
966 | // Collapse colours and check that they are consistent. |
---|
967 | |
---|
968 | bool BeamRemnants::checkColours( Event& event) { |
---|
969 | |
---|
970 | // No colours in lepton beams so no need to do anything. |
---|
971 | if (beamAPtr->isLepton() && beamBPtr->isLepton()) return true; |
---|
972 | |
---|
973 | // Remove ambiguities when one colour collapses two ways. |
---|
974 | // Resolve chains where one colour is mapped to another. |
---|
975 | for (int iCol = 1; iCol < int(colFrom.size()); ++iCol) |
---|
976 | for (int iColRef = 0; iColRef < iCol; ++iColRef) { |
---|
977 | if (colFrom[iCol] == colFrom[iColRef]) { |
---|
978 | colFrom[iCol] = colTo[iCol]; |
---|
979 | colTo[iCol] = colTo[iColRef]; |
---|
980 | } |
---|
981 | if (colTo[iCol] == colFrom[iColRef]) colTo[iCol] = colTo[iColRef]; |
---|
982 | } |
---|
983 | |
---|
984 | // Transform event record colours from beam remnant colour collapses. |
---|
985 | for (int i = oldSize; i < event.size(); ++i) { |
---|
986 | int col = event[i].col(); |
---|
987 | int acol = event[i].acol(); |
---|
988 | for (int iCol = 0; iCol < int(colFrom.size()); ++iCol) { |
---|
989 | if (col == colFrom[iCol]) {col = colTo[iCol]; event[i].col(col);} |
---|
990 | if (acol == colFrom[iCol]) {acol = colTo[iCol]; event[i].acol(acol);} |
---|
991 | } |
---|
992 | } |
---|
993 | |
---|
994 | // Transform junction colours from beam remnant colour collapses. |
---|
995 | for (int iJun = 0; iJun < event.sizeJunction(); ++iJun) |
---|
996 | for (int leg = 0; leg < 3; ++leg) { |
---|
997 | int col = event.colJunction(iJun, leg); |
---|
998 | for (int iCol = 0; iCol < int(colFrom.size()); ++iCol) { |
---|
999 | if (col == colFrom[iCol]) { |
---|
1000 | col = colTo[iCol]; |
---|
1001 | event.colJunction(iJun, leg, col); |
---|
1002 | } |
---|
1003 | } |
---|
1004 | } |
---|
1005 | |
---|
1006 | // Arrays for current colours and anticolours, and for singlet gluons. |
---|
1007 | vector<int> colList; |
---|
1008 | vector<int> acolList; |
---|
1009 | vector<int> iSingletGluon; |
---|
1010 | |
---|
1011 | // Find current colours and anticolours in the event record. |
---|
1012 | for (int i = oldSize; i < event.size(); ++i) |
---|
1013 | if (event[i].isFinal()) { |
---|
1014 | int id = event[i].id(); |
---|
1015 | int col = event[i].col(); |
---|
1016 | int acol = event[i].acol(); |
---|
1017 | int colType = event[i].colType(); |
---|
1018 | |
---|
1019 | // Quarks must have colour set, antiquarks anticolour, gluons both. |
---|
1020 | if ( (id > 0 && id < 9 && (col <= 0 || acol != 0) ) |
---|
1021 | || (id < 0 && id > -9 && (col != 0 || acol <= 0) ) |
---|
1022 | || (id == 21 && (col <= 0 || acol <= 0) ) ) { |
---|
1023 | infoPtr->errorMsg("Error in BeamRemnants::checkColours: " |
---|
1024 | "q/qbar/g has wrong colour slots set"); |
---|
1025 | return false; |
---|
1026 | } |
---|
1027 | |
---|
1028 | // Sextets must have one positive and one negative tag |
---|
1029 | if ( (colType == 3 && (col <= 0 || acol >= 0)) |
---|
1030 | || (colType == -3 && (col >= 0 || acol <= 0)) ) { |
---|
1031 | infoPtr->errorMsg("Error in BeamRemnants::checkColours: " |
---|
1032 | "sextet has wrong colours"); |
---|
1033 | } |
---|
1034 | |
---|
1035 | // Save colours/anticolours, and position of colour singlet gluons. |
---|
1036 | if ( col > 0) colList.push_back( col ); |
---|
1037 | if (acol > 0) acolList.push_back( acol ); |
---|
1038 | if (col > 0 && acol == col) iSingletGluon.push_back(i); |
---|
1039 | // Colour sextets |
---|
1040 | if ( col < 0) acolList.push_back( -col ); |
---|
1041 | if (acol < 0) colList.push_back( -acol ); |
---|
1042 | } |
---|
1043 | |
---|
1044 | // Run though list of singlet gluons and put them on final-state dipole |
---|
1045 | // (i,j) that offers smallest (p_g p_i) * (p_g p_j) / (p_i p_j). |
---|
1046 | for (int iS = 0; iS < int(iSingletGluon.size()); ++iS) { |
---|
1047 | int iGlu = iSingletGluon[iS]; |
---|
1048 | int iAcolDip = -1; |
---|
1049 | double pT2DipMin = sCM; |
---|
1050 | for (int iC = oldSize; iC < event.size(); ++iC) |
---|
1051 | if (iC != iGlu && event[iC].isFinal()) { |
---|
1052 | int colDip = event[iC].col(); |
---|
1053 | if (colDip > 0 && event[iC].acol() !=colDip) |
---|
1054 | for (int iA = oldSize; iA < event.size(); ++iA) |
---|
1055 | if (iA != iGlu && iA != iC && event[iA].isFinal() |
---|
1056 | && event[iA].acol() == colDip && event[iA].col() !=colDip) { |
---|
1057 | double pT2Dip = (event[iGlu].p() * event[iC].p()) |
---|
1058 | * (event[iGlu].p() * event[iA].p()) |
---|
1059 | / (event[iC].p() * event[iA].p()); |
---|
1060 | if (pT2Dip < pT2DipMin) { |
---|
1061 | iAcolDip = iA; |
---|
1062 | pT2DipMin = pT2Dip; |
---|
1063 | } |
---|
1064 | } |
---|
1065 | } |
---|
1066 | |
---|
1067 | // Fail if no dipole. Else insert singlet gluon onto relevant dipole. |
---|
1068 | if (iAcolDip == -1) return false; |
---|
1069 | event[iGlu].acol( event[iAcolDip].acol() ); |
---|
1070 | event[iAcolDip].acol( event[iGlu].col() ); |
---|
1071 | |
---|
1072 | // Update any junction legs that match reconnected dipole. |
---|
1073 | for (int iJun = 0; iJun < event.sizeJunction(); ++iJun) { |
---|
1074 | |
---|
1075 | // Only junctions need to be updated, not antijunctions. |
---|
1076 | if (event.kindJunction(iJun) % 2 == 0) continue; |
---|
1077 | for (int leg = 0; leg < 3; ++leg) { |
---|
1078 | int col = event.colJunction(iJun, leg); |
---|
1079 | if (col == event[iGlu].acol()) |
---|
1080 | event.colJunction(iJun, leg, event[iGlu].col()); |
---|
1081 | } |
---|
1082 | } |
---|
1083 | |
---|
1084 | } |
---|
1085 | |
---|
1086 | // Check that not the same colour or anticolour appears twice. |
---|
1087 | for (int iCol = 0; iCol < int(colList.size()) - 1; ++iCol) { |
---|
1088 | int col = colList[iCol]; |
---|
1089 | for (int iCol2 = iCol + 1; iCol2 < int(colList.size()); ++iCol2) |
---|
1090 | if (colList[iCol2] == col) { |
---|
1091 | infoPtr->errorMsg("Warning in BeamRemnants::checkColours:" |
---|
1092 | " colour appears twice"); |
---|
1093 | if (!ALLOWCOLOURTWICE) return false; |
---|
1094 | } |
---|
1095 | } |
---|
1096 | for (int iAcol = 0; iAcol < int(acolList.size()) - 1; ++iAcol) { |
---|
1097 | int acol = acolList[iAcol]; |
---|
1098 | for (int iAcol2 = iAcol + 1; iAcol2 < int(acolList.size()); ++iAcol2) |
---|
1099 | if (acolList[iAcol2] == acol) { |
---|
1100 | infoPtr->errorMsg("Warning in BeamRemnants::checkColours:" |
---|
1101 | " anticolour appears twice"); |
---|
1102 | if (!ALLOWCOLOURTWICE) return false; |
---|
1103 | } |
---|
1104 | } |
---|
1105 | |
---|
1106 | // Remove all matching colour-anticolour pairs. |
---|
1107 | bool foundPair = true; |
---|
1108 | while (foundPair && colList.size() > 0 && acolList.size() > 0) { |
---|
1109 | foundPair = false; |
---|
1110 | for (int iCol = 0; iCol < int(colList.size()); ++iCol) { |
---|
1111 | for (int iAcol = 0; iAcol < int(acolList.size()); ++iAcol) { |
---|
1112 | if (acolList[iAcol] == colList[iCol]) { |
---|
1113 | colList[iCol] = colList.back(); colList.pop_back(); |
---|
1114 | acolList[iAcol] = acolList.back(); acolList.pop_back(); |
---|
1115 | foundPair = true; |
---|
1116 | break; |
---|
1117 | } |
---|
1118 | } |
---|
1119 | if (foundPair) break; |
---|
1120 | } |
---|
1121 | } |
---|
1122 | |
---|
1123 | // Check that remaining (anti)colours are accounted for by junctions. |
---|
1124 | for (int iJun = 0; iJun < event.sizeJunction(); ++iJun) { |
---|
1125 | int kindJun = event.kindJunction(iJun); |
---|
1126 | for (int leg = 0; leg < 3; ++leg) { |
---|
1127 | int colEnd = event.colJunction(iJun, leg); |
---|
1128 | |
---|
1129 | // Junction connected to three colours. |
---|
1130 | if (kindJun == 1) { |
---|
1131 | for (int iCol = 0; iCol < int(colList.size()); ++iCol) |
---|
1132 | if (colList[iCol] == colEnd) { |
---|
1133 | // Found colour match: remove and exit. |
---|
1134 | colList[iCol] = colList.back(); |
---|
1135 | colList.pop_back(); |
---|
1136 | break; |
---|
1137 | } |
---|
1138 | } |
---|
1139 | |
---|
1140 | // Junction connected to three anticolours. |
---|
1141 | else if (kindJun == 2) { |
---|
1142 | for (int iAcol = 0; iAcol < int(acolList.size()); ++iAcol) |
---|
1143 | if (acolList[iAcol] == colEnd) { |
---|
1144 | // Found colour match: remove and exit. |
---|
1145 | acolList[iAcol] = acolList.back(); |
---|
1146 | acolList.pop_back(); |
---|
1147 | break; |
---|
1148 | } |
---|
1149 | } |
---|
1150 | |
---|
1151 | // Other junction types |
---|
1152 | else if ( kindJun == 3 || kindJun == 5) { |
---|
1153 | for (int iCol = 0; iCol < int(colList.size()); ++iCol) |
---|
1154 | if (colList[iCol] == colEnd) { |
---|
1155 | // Found colour match: remove and exit. |
---|
1156 | colList[iCol] = colList.back(); |
---|
1157 | colList.pop_back(); |
---|
1158 | break; |
---|
1159 | } |
---|
1160 | } |
---|
1161 | |
---|
1162 | // Other antijunction types |
---|
1163 | else if ( kindJun == 4 || kindJun == 6) { |
---|
1164 | for (int iAcol = 0; iAcol < int(acolList.size()); ++iAcol) |
---|
1165 | if (acolList[iAcol] == colEnd) { |
---|
1166 | // Found colour match: remove and exit. |
---|
1167 | acolList[iAcol] = acolList.back(); |
---|
1168 | acolList.pop_back(); |
---|
1169 | break; |
---|
1170 | } |
---|
1171 | } |
---|
1172 | |
---|
1173 | // End junction check. |
---|
1174 | } |
---|
1175 | } |
---|
1176 | |
---|
1177 | |
---|
1178 | // Repair step - sometimes needed when rescattering allowed. |
---|
1179 | if (colList.size() > 0 || acolList.size() > 0) { |
---|
1180 | infoPtr->errorMsg("Warning in BeamRemnants::checkColours:" |
---|
1181 | " need to repair unmatched colours"); |
---|
1182 | } |
---|
1183 | while (colList.size() > 0 && acolList.size() > 0) { |
---|
1184 | |
---|
1185 | // Replace one colour and one anticolour index by a new common one. |
---|
1186 | int colMatch = colList.back(); |
---|
1187 | int acolMatch = acolList.back(); |
---|
1188 | int colNew = event.nextColTag(); |
---|
1189 | colList.pop_back(); |
---|
1190 | acolList.pop_back(); |
---|
1191 | for (int i = oldSize; i < event.size(); ++i) |
---|
1192 | if (event[i].isFinal() && event[i].col() == colMatch) { |
---|
1193 | event[i].col( colNew); |
---|
1194 | break; |
---|
1195 | } |
---|
1196 | for (int i = oldSize; i < event.size(); ++i) |
---|
1197 | if (event[i].isFinal() && event[i].acol() == acolMatch) { |
---|
1198 | event[i].acol( colNew); |
---|
1199 | break; |
---|
1200 | } |
---|
1201 | } |
---|
1202 | |
---|
1203 | // Done. |
---|
1204 | return (colList.size() == 0 && acolList.size() == 0); |
---|
1205 | |
---|
1206 | } |
---|
1207 | |
---|
1208 | //========================================================================== |
---|
1209 | |
---|
1210 | } // end namespace Pythia8 |
---|