1 | // PhaseSpace.h 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 | // Header file for phase space generators in kinematics selection. |
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7 | // PhaseSpace: base class for phase space generators. |
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8 | // Base class for derived classes> 2 ->1 , 2 -> 2, 2 -> 2 elastic/diffractive, |
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9 | // 2 -> 2 minbias, 2 -> 3, Les Houches. |
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10 | |
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11 | #ifndef Pythia8_PhaseSpace_H |
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12 | #define Pythia8_PhaseSpace_H |
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13 | |
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14 | #include "Basics.h" |
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15 | #include "BeamParticle.h" |
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16 | #include "Info.h" |
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17 | #include "LesHouches.h" |
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18 | #include "MultipartonInteractions.h" |
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19 | #include "ParticleData.h" |
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20 | #include "PartonDistributions.h" |
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21 | #include "PythiaStdlib.h" |
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22 | #include "SigmaProcess.h" |
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23 | #include "SigmaTotal.h" |
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24 | #include "Settings.h" |
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25 | #include "StandardModel.h" |
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26 | #include "UserHooks.h" |
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27 | |
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28 | namespace Pythia8 { |
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29 | |
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30 | //========================================================================== |
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31 | |
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32 | // Forward reference to the UserHooks class. |
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33 | class UserHooks; |
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34 | |
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35 | //========================================================================== |
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36 | |
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37 | // PhaseSpace is a base class for phase space generators |
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38 | // used in the selection of hard-process kinematics. |
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39 | |
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40 | class PhaseSpace { |
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41 | |
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42 | public: |
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43 | |
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44 | // Destructor. |
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45 | virtual ~PhaseSpace() {} |
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46 | |
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47 | // Perform simple initialization and store pointers. |
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48 | void init(bool isFirst, SigmaProcess* sigmaProcessPtrIn, |
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49 | Info* infoPtrIn, Settings* settingsPtrIn, ParticleData* particleDataPtrIn, |
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50 | Rndm* rndmPtrIn, BeamParticle* beamAPtrIn, BeamParticle* beamBPtrIn, |
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51 | Couplings* couplingsPtrIn, SigmaTotal* sigmaTotPtrIn, |
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52 | UserHooks* userHooksPtrIn); |
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53 | |
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54 | // Update the CM energy of the event. |
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55 | void newECM(double eCMin) {eCM = eCMin; s = eCM * eCM;} |
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56 | |
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57 | // Store or replace Les Houches pointer. |
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58 | void setLHAPtr(LHAup* lhaUpPtrIn) {lhaUpPtr = lhaUpPtrIn;} |
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59 | |
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60 | // A pure virtual method, wherein an optimization procedure |
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61 | // is used to determine how phase space should be sampled. |
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62 | virtual bool setupSampling() = 0; |
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63 | |
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64 | // A pure virtual method, wherein a trial event kinematics |
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65 | // is to be selected in the derived class. |
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66 | virtual bool trialKin(bool inEvent = true, bool repeatSame = false) = 0; |
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67 | |
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68 | // A pure virtual method, wherein the accepted event kinematics |
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69 | // is to be constructed in the derived class. |
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70 | virtual bool finalKin() = 0; |
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71 | |
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72 | // Allow for nonisotropic decays when ME's available. |
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73 | void decayKinematics( Event& process); |
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74 | |
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75 | // Give back current or maximum cross section, or set latter. |
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76 | double sigmaNow() const {return sigmaNw;} |
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77 | double sigmaMax() const {return sigmaMx;} |
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78 | double biasSelectionWeight() const {return biasWt;} |
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79 | bool newSigmaMax() const {return newSigmaMx;} |
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80 | void setSigmaMax(double sigmaMaxIn) {sigmaMx = sigmaMaxIn;} |
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81 | |
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82 | // For Les Houches with negative event weight needs |
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83 | virtual double sigmaSumSigned() const {return sigmaMx;} |
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84 | |
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85 | // Give back constructed four-vectors and known masses. |
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86 | Vec4 p(int i) const {return pH[i];} |
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87 | double m(int i) const {return mH[i];} |
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88 | |
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89 | // Give back other event properties. |
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90 | double ecm() const {return eCM;} |
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91 | double x1() const {return x1H;} |
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92 | double x2() const {return x2H;} |
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93 | double sHat() const {return sH;} |
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94 | double tHat() const {return tH;} |
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95 | double uHat() const {return uH;} |
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96 | double pTHat() const {return pTH;} |
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97 | double thetaHat() const {return theta;} |
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98 | double phiHat() const {return phi;} |
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99 | double runBW3() const {return runBW3H;} |
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100 | double runBW4() const {return runBW4H;} |
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101 | double runBW5() const {return runBW5H;} |
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102 | |
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103 | // Inform whether beam particles are resolved in partons or scatter directly. |
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104 | virtual bool isResolved() const {return true;} |
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105 | |
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106 | protected: |
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107 | |
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108 | // Constructor. |
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109 | PhaseSpace() {} |
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110 | |
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111 | // Constants: could only be changed in the code itself. |
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112 | static const int NMAXTRY, NTRY3BODY; |
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113 | static const double SAFETYMARGIN, TINY, EVENFRAC, SAMESIGMA, WIDTHMARGIN, |
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114 | SAMEMASS, MASSMARGIN, EXTRABWWTMAX, THRESHOLDSIZE, |
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115 | THRESHOLDSTEP, YRANGEMARGIN, LEPTONXMIN, LEPTONXMAX, |
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116 | LEPTONXLOGMIN, LEPTONXLOGMAX, LEPTONTAUMIN, |
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117 | SHATMINZ, PT2RATMINZ, WTCORRECTION[11]; |
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118 | |
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119 | // MBR constants: form factor appoximation with two exponents. |
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120 | static const double FFA1, FFA2,FFB1, FFB2; |
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121 | |
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122 | // Pointer to cross section. |
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123 | SigmaProcess* sigmaProcessPtr; |
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124 | |
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125 | // Pointer to various information on the generation. |
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126 | Info* infoPtr; |
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127 | |
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128 | // Pointer to the settings database. |
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129 | Settings* settingsPtr; |
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130 | |
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131 | // Pointer to the particle data table. |
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132 | ParticleData* particleDataPtr; |
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133 | |
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134 | // Pointer to the random number generator. |
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135 | Rndm* rndmPtr; |
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136 | |
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137 | // Pointers to incoming beams. |
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138 | BeamParticle* beamAPtr; |
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139 | BeamParticle* beamBPtr; |
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140 | |
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141 | // Pointer to Standard Model couplings. |
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142 | Couplings* couplingsPtr; |
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143 | |
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144 | // Pointer to the total/elastic/diffractive cross section object. |
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145 | SigmaTotal* sigmaTotPtr; |
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146 | |
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147 | // Pointer to userHooks object for user interaction with program. |
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148 | UserHooks* userHooksPtr; |
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149 | |
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150 | // Pointer to LHAup for generating external events. |
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151 | LHAup* lhaUpPtr; |
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152 | |
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153 | // Initialization data, normally only set once. |
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154 | bool useBreitWigners, doEnergySpread, showSearch, showViolation, |
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155 | increaseMaximum; |
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156 | int gmZmodeGlobal; |
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157 | double mHatGlobalMin, mHatGlobalMax, pTHatGlobalMin, pTHatGlobalMax, |
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158 | pTHatMinDiverge, minWidthBreitWigners; |
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159 | |
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160 | // Information on incoming beams. |
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161 | int idA, idB; |
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162 | double mA, mB, eCM, s; |
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163 | bool hasLeptonBeams, hasPointLeptons; |
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164 | |
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165 | // Cross section information. |
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166 | bool newSigmaMx, canModifySigma, canBiasSelection, canBias2Sel; |
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167 | int gmZmode; |
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168 | double bias2SelPow, bias2SelRef, wtBW, sigmaNw, sigmaMx, sigmaPos, |
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169 | sigmaNeg, biasWt; |
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170 | |
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171 | // Process-specific kinematics properties, almost always available. |
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172 | double mHatMin, mHatMax, sHatMin, sHatMax, pTHatMin, pTHatMax, |
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173 | pT2HatMin, pT2HatMax; |
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174 | |
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175 | // Event-specific kinematics properties, almost always available. |
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176 | double x1H, x2H, m3, m4, m5, s3, s4, s5, mHat, sH, tH, uH, pAbs, p2Abs, |
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177 | pTH, theta, phi, betaZ; |
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178 | Vec4 pH[6]; |
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179 | double mH[6]; |
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180 | |
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181 | // Reselect decay products momenta isotropically in phase space. |
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182 | void decayKinematicsStep( Event& process, int iRes); |
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183 | |
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184 | // Much common code for normal 2 -> 1, 2 -> 2 and 2 -> 3 cases: |
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185 | |
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186 | // Determine how phase space should be sampled. |
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187 | void setup3Body(); |
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188 | bool setupSampling123(bool is2, bool is3, ostream& os = cout); |
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189 | |
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190 | // Select a trial kinematics phase space point. |
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191 | bool trialKin123(bool is2, bool is3, bool inEvent = true, |
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192 | ostream& os = cout); |
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193 | |
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194 | // Presence and properties of any s-channel resonances. |
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195 | int idResA, idResB; |
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196 | double mResA, mResB, GammaResA, GammaResB, tauResA, tauResB, widResA, |
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197 | widResB; |
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198 | bool sameResMass; |
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199 | |
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200 | // Kinematics properties specific to 2 -> 1/2/3. |
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201 | bool useMirrorWeight; |
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202 | double tau, y, z, tauMin, tauMax, yMax, zMin, zMax, ratio34, unity34, |
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203 | zNeg, zPos, wtTau, wtY, wtZ, wt3Body, runBW3H, runBW4H, runBW5H, |
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204 | intTau0, intTau1, intTau2, intTau3, intTau4, intTau5, intTau6, |
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205 | intY0, intY12, intY34, intY56, mTchan1, sTchan1, mTchan2, sTchan2, |
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206 | frac3Flat, frac3Pow1, frac3Pow2; |
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207 | Vec4 p3cm, p4cm, p5cm; |
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208 | |
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209 | // Coefficients for optimized selection in 2 -> 1/2/3. |
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210 | int nTau, nY, nZ; |
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211 | double tauCoef[8], yCoef[8], zCoef[8], tauCoefSum[8], yCoefSum[8], |
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212 | zCoefSum[8]; |
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213 | |
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214 | // Calculate kinematical limits for 2 -> 1/2/3. |
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215 | bool limitTau(bool is2, bool is3); |
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216 | bool limitY(); |
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217 | bool limitZ(); |
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218 | |
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219 | // Select kinematical variable between defined limits for 2 -> 1/2/3. |
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220 | void selectTau(int iTau, double tauVal, bool is2); |
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221 | void selectY(int iY, double yVal); |
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222 | void selectZ(int iZ, double zVal); |
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223 | bool select3Body(); |
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224 | |
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225 | // Solve equation system for better phase space coefficients in 2 -> 1/2/3. |
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226 | void solveSys( int n, int bin[8], double vec[8], double mat[8][8], |
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227 | double coef[8], ostream& os = cout); |
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228 | |
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229 | // Properties specific to resonance mass selection in 2 -> 2 and 2 -> 3. |
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230 | bool useBW[6]; |
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231 | int idMass[6]; |
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232 | double mPeak[6], sPeak[6], mWidth[6], mMin[6], mMax[6], mw[6], wmRat[6], |
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233 | mLower[6], mUpper[6], sLower[6], sUpper[6], fracFlat[6], fracInv[6], |
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234 | fracInv2[6], atanLower[6], atanUpper[6], intBW[6], intFlat[6], |
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235 | intInv[6], intInv2[6]; |
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236 | |
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237 | // Setup mass selection for one resonance at a time. Split in two parts. |
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238 | void setupMass1(int iM); |
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239 | void setupMass2(int iM, double distToThresh); |
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240 | |
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241 | // Do mass selection and find the associated weight. |
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242 | void trialMass(int iM); |
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243 | double weightMass(int iM); |
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244 | |
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245 | }; |
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246 | |
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247 | //========================================================================== |
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248 | |
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249 | // A derived class with 2 -> 1 kinematics set up in tau, y. |
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250 | |
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251 | class PhaseSpace2to1tauy : public PhaseSpace { |
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252 | |
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253 | public: |
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254 | |
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255 | // Constructor. |
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256 | PhaseSpace2to1tauy() {} |
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257 | |
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258 | // Optimize subsequent kinematics selection. |
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259 | virtual bool setupSampling() {if (!setupMass()) return false; |
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260 | return setupSampling123(false, false);} |
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261 | |
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262 | // Construct the trial kinematics. |
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263 | virtual bool trialKin(bool inEvent = true, bool = false) {wtBW = 1.; |
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264 | return trialKin123(false, false, inEvent);} |
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265 | |
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266 | // Construct the final event kinematics. |
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267 | virtual bool finalKin(); |
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268 | |
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269 | private: |
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270 | |
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271 | // Set up allowed mass range. |
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272 | bool setupMass(); |
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273 | |
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274 | }; |
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275 | |
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276 | //========================================================================== |
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277 | |
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278 | // A derived class with 2 -> 2 kinematics set up in tau, y, z = cos(theta). |
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279 | |
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280 | class PhaseSpace2to2tauyz : public PhaseSpace { |
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281 | |
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282 | public: |
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283 | |
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284 | // Constructor. |
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285 | PhaseSpace2to2tauyz() {} |
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286 | |
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287 | // Optimize subsequent kinematics selection. |
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288 | virtual bool setupSampling() {if (!setupMasses()) return false; |
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289 | return setupSampling123(true, false);} |
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290 | |
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291 | // Construct the trial kinematics. |
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292 | virtual bool trialKin(bool inEvent = true, bool = false) { |
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293 | if (!trialMasses()) return false; |
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294 | return trialKin123(true, false, inEvent);} |
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295 | |
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296 | // Construct the final event kinematics. |
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297 | virtual bool finalKin(); |
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298 | |
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299 | private: |
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300 | |
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301 | // Set up for fixed or Breit-Wigner mass selection. |
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302 | bool setupMasses(); |
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303 | |
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304 | // Select fixed or Breit-Wigner-distributed masses. |
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305 | bool trialMasses(); |
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306 | |
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307 | // Pick off-shell initialization masses when on-shell not allowed. |
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308 | bool constrainedM3M4(); |
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309 | bool constrainedM3(); |
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310 | bool constrainedM4(); |
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311 | |
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312 | }; |
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313 | |
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314 | //========================================================================== |
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315 | |
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316 | // A derived class with 2 -> 2 kinematics set up for elastic scattering. |
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317 | |
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318 | class PhaseSpace2to2elastic : public PhaseSpace { |
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319 | |
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320 | public: |
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321 | |
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322 | // Constructor. |
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323 | PhaseSpace2to2elastic() {} |
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324 | |
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325 | // Construct the trial or final event kinematics. |
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326 | virtual bool setupSampling(); |
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327 | virtual bool trialKin(bool inEvent = true, bool = false); |
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328 | virtual bool finalKin(); |
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329 | |
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330 | // Are beam particles resolved in partons or scatter directly? |
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331 | virtual bool isResolved() const {return false;} |
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332 | |
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333 | private: |
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334 | |
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335 | // Constants: could only be changed in the code itself. |
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336 | static const double EXPMAX, CONVERTEL; |
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337 | |
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338 | // Kinematics properties specific to 2 -> 2 elastic. |
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339 | bool useCoulomb; |
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340 | double s1, s2, bSlope, lambda12S, tLow, tUpp, tAux, sigmaTot, rho, |
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341 | lambda, tAbsMin, phaseCst, alphaEM0, sigmaNuc, sigmaCou, signCou; |
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342 | |
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343 | // Calculation of alphaElectromagnetic. |
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344 | AlphaEM alphaEM; |
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345 | |
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346 | }; |
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347 | |
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348 | //========================================================================== |
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349 | |
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350 | // A derived class with 2 -> 2 kinematics set up for diffractive scattering. |
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351 | |
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352 | class PhaseSpace2to2diffractive : public PhaseSpace { |
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353 | |
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354 | public: |
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355 | |
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356 | // Constructor. |
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357 | PhaseSpace2to2diffractive(bool isDiffAin = false, bool isDiffBin = false) |
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358 | : isDiffA(isDiffAin), isDiffB(isDiffBin) {} |
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359 | |
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360 | // Construct the trial or final event kinematics. |
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361 | virtual bool setupSampling(); |
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362 | virtual bool trialKin(bool inEvent = true, bool = false); |
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363 | virtual bool finalKin(); |
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364 | |
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365 | // Are beam particles resolved in partons or scatter directly? |
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366 | virtual bool isResolved() const {return false;} |
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367 | |
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368 | private: |
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369 | |
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370 | // Constants: could only be changed in the code itself. |
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371 | static const int NTRY; |
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372 | static const double EXPMAX, DIFFMASSMARGIN; |
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373 | |
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374 | // Initialization data, in constructor or read from Settings. |
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375 | bool isDiffA, isDiffB; |
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376 | int PomFlux; |
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377 | double epsilonPF, alphaPrimePF; |
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378 | |
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379 | // Initialization: kinematics properties specific to 2 -> 2 diffractive. |
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380 | double m3ElDiff, m4ElDiff, s1, s2, lambda12, lambda34, tLow, tUpp, |
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381 | cRes, sResXB, sResAX, sProton, bMin, bSlope, bSlope1, bSlope2, |
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382 | probSlope1, xIntPF, xtCorPF, mp24DL, coefDL, tAux, tAux1, tAux2; |
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383 | |
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384 | // Parameters for MBR model. |
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385 | double sdpmax, ddpmax, dymin0, dymax, amx, am1, am2, t; |
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386 | double eps, alph, alph2, m2min, dyminSD, dyminDD, dyminSigSD, dyminSigDD; |
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387 | |
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388 | }; |
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389 | |
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390 | //========================================================================== |
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391 | |
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392 | // A derived class with 2 -> 3 kinematics set up for central diffractive |
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393 | // scattering. |
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394 | |
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395 | class PhaseSpace2to3diffractive : public PhaseSpace { |
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396 | |
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397 | public: |
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398 | |
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399 | // Constructor. |
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400 | PhaseSpace2to3diffractive() {} |
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401 | |
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402 | // Construct the trial or final event kinematics. |
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403 | virtual bool setupSampling(); |
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404 | virtual bool trialKin(bool inEvent = true, bool = false); |
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405 | virtual bool finalKin(); |
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406 | |
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407 | // Are beam particles resolved in partons or scatter directly? |
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408 | virtual bool isResolved() const {return false;} |
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409 | |
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410 | private: |
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411 | |
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412 | // Constants: could only be changed in the code itself. |
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413 | static const int NTRY, NINTEG2; |
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414 | static const double EXPMAX, DIFFMASSMIN, DIFFMASSMARGIN; |
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415 | |
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416 | // Local variables to calculate DPE kinematics. |
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417 | int PomFlux; |
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418 | double epsilonPF, alphaPrimePF, s1, s2, m5min, s5min, tLow[2], tUpp[2], |
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419 | bMin[2], tAux[2], bSlope1, bSlope2, probSlope1[2], tAux1[2], |
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420 | tAux2[2], bSlope, xIntPF, xIntInvPF, xtCorPF, mp24DL, coefDL, |
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421 | epsMBR, alphMBR, m2minMBR, dyminMBR, dyminSigMBR, dyminInvMBR, |
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422 | dpepmax, t1, t2; |
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423 | Vec4 p1, p2, p3, p4, p5; |
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424 | |
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425 | }; |
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426 | |
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427 | //========================================================================== |
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428 | |
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429 | // A derived class for minumum bias events. Hardly does anything, since |
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430 | // the real action is taken care of by the MultipartonInteractions class. |
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431 | |
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432 | class PhaseSpace2to2minbias : public PhaseSpace { |
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433 | |
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434 | public: |
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435 | |
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436 | // Constructor. |
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437 | PhaseSpace2to2minbias() {} |
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438 | |
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439 | // Construct the trial or final event kinematics. |
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440 | virtual bool setupSampling() {sigmaNw = sigmaProcessPtr->sigmaHat(); |
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441 | sigmaMx = sigmaNw; return true;} |
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442 | virtual bool trialKin( bool , bool = false) {return true;} |
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443 | virtual bool finalKin() {return true;} |
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444 | |
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445 | private: |
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446 | |
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447 | }; |
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448 | |
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449 | //========================================================================== |
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450 | |
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451 | // A derived class with 2 -> 3 kinematics 1 + 2 -> 3 + 4 + 5 set up in |
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452 | // tau, y, pT2_4, pT2_5, phi_4, phi_5 and y_3 (partial cylindrical symmetry). |
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453 | |
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454 | class PhaseSpace2to3tauycyl : public PhaseSpace { |
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455 | |
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456 | public: |
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457 | |
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458 | // Constructor. |
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459 | PhaseSpace2to3tauycyl() {} |
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460 | |
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461 | // Optimize subsequent kinematics selection. |
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462 | virtual bool setupSampling() {if (!setupMasses()) return false; |
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463 | setup3Body(); return setupSampling123(false, true);} |
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464 | |
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465 | // Construct the trial kinematics. |
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466 | virtual bool trialKin(bool inEvent = true, bool = false) { |
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467 | if (!trialMasses()) return false; |
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468 | return trialKin123(false, true, inEvent);} |
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469 | |
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470 | // Construct the final event kinematics. |
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471 | virtual bool finalKin(); |
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472 | |
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473 | private: |
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474 | |
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475 | // Constants: could only be changed in the code itself. |
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476 | static const int NITERNR; |
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477 | |
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478 | // Set up for fixed or Breit-Wigner mass selection. |
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479 | bool setupMasses(); |
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480 | |
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481 | // Select fixed or Breit-Wigner-distributed masses. |
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482 | bool trialMasses(); |
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483 | |
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484 | }; |
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485 | |
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486 | //========================================================================== |
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487 | |
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488 | // A derived class with 2 -> 3 kinematics 1 + 2 -> 3 + 4 + 5 set up in |
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489 | // y3, y4, y5, pT2_3, pT2_5, phi_3 and phi_5, and with R separation cut. |
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490 | // Intended specifically for (essentially massless) 2 -> 3 QCD processes. |
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491 | |
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492 | class PhaseSpace2to3yyycyl : public PhaseSpace { |
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493 | |
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494 | public: |
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495 | |
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496 | // Constructor. |
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497 | PhaseSpace2to3yyycyl() {} |
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498 | |
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499 | // Optimize subsequent kinematics selection. |
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500 | virtual bool setupSampling(); |
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501 | |
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502 | // Construct the trial kinematics. |
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503 | virtual bool trialKin(bool inEvent = true, bool = false); |
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504 | |
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505 | // Construct the final event kinematics. |
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506 | virtual bool finalKin(); |
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507 | |
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508 | private: |
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509 | |
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510 | // Phase space cuts specifically for 2 -> 3 QCD processes. |
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511 | double pTHat3Min, pTHat3Max, pTHat5Min, pTHat5Max, RsepMin, R2sepMin; |
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512 | bool hasBaryonBeams; |
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513 | |
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514 | // Event kinematics choices. |
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515 | double pT3Min, pT3Max, pT5Min, pT5Max, y3Max, y4Max, y5Max, |
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516 | pT3, pT4, pT5, phi3, phi4, phi5, y3, y4, y5, dphi; |
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517 | Vec4 pInSum; |
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518 | |
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519 | }; |
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520 | |
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521 | //========================================================================== |
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522 | |
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523 | // A derived class for Les Houches events. |
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524 | |
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525 | class PhaseSpaceLHA : public PhaseSpace { |
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526 | |
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527 | public: |
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528 | |
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529 | // Constructor. |
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530 | PhaseSpaceLHA() {idProcSave = 0;} |
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531 | |
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532 | // Find maximal cross section for comparison with internal processes. |
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533 | virtual bool setupSampling(); |
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534 | |
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535 | // Construct the next process, by interface to Les Houches class. |
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536 | virtual bool trialKin( bool , bool repeatSame = false); |
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537 | |
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538 | // Set scale, alpha_s and alpha_em if not done. |
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539 | virtual bool finalKin() {sigmaProcessPtr->setScale(); return true;} |
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540 | |
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541 | // For Les Houches with negative event weight needs |
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542 | virtual double sigmaSumSigned() const {return sigmaSgn;} |
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543 | |
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544 | private: |
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545 | |
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546 | // Constants. |
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547 | static const double CONVERTPB2MB; |
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548 | |
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549 | // Local properties. |
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550 | int strategy, stratAbs, nProc, idProcSave; |
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551 | double xMaxAbsSum, xSecSgnSum, sigmaSgn; |
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552 | vector<int> idProc; |
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553 | vector<double> xMaxAbsProc; |
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554 | |
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555 | }; |
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556 | |
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557 | //========================================================================== |
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558 | |
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559 | } // end namespace Pythia8 |
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560 | |
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561 | #endif // Pythia8_PhaseSpace_H |
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562 | |
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