[1] | 1 | // SigmaLeptoquark.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 | // leptoquark simulation classes. |
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| 8 | |
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| 9 | #include "SigmaLeptoquark.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 | // Sigma1ql2LeptoQuark class. |
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| 16 | // Cross section for q l -> LQ (leptoquark state). |
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| 17 | |
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| 18 | //-------------------------------------------------------------------------- |
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| 19 | |
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| 20 | // Initialize process. |
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| 21 | |
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| 22 | void Sigma1ql2LeptoQuark::initProc() { |
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| 23 | |
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| 24 | // Store LQ mass and width for propagator. |
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| 25 | mRes = particleDataPtr->m0(42); |
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| 26 | GammaRes = particleDataPtr->mWidth(42); |
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| 27 | m2Res = mRes*mRes; |
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| 28 | GamMRat = GammaRes / mRes; |
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| 29 | |
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| 30 | // Yukawa coupling strength. |
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| 31 | kCoup = settingsPtr->parm("LeptoQuark:kCoup"); |
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| 32 | |
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| 33 | // Set pointer to particle properties and decay table. |
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| 34 | LQPtr = particleDataPtr->particleDataEntryPtr(42); |
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| 35 | |
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| 36 | // Read out quark and lepton the LQ couples to. |
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| 37 | idQuark = LQPtr->channel(0).product(0); |
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| 38 | idLepton = LQPtr->channel(0).product(1); |
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| 39 | |
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| 40 | } |
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| 41 | |
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| 42 | //-------------------------------------------------------------------------- |
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| 43 | |
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| 44 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. |
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| 45 | |
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| 46 | void Sigma1ql2LeptoQuark::sigmaKin() { |
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| 47 | |
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| 48 | // Incoming width for correct quark-lepton pair. |
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| 49 | widthIn = 0.25 * alpEM * kCoup * mH; |
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| 50 | |
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| 51 | // Set up Breit-Wigner. |
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| 52 | sigBW = 4. * M_PI/ ( pow2(sH - m2Res) + pow2(sH * GamMRat) ); |
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| 53 | |
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| 54 | } |
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| 55 | |
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| 56 | //-------------------------------------------------------------------------- |
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| 57 | |
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| 58 | // Evaluate sigmaHat(sHat) for specific incoming flavours. |
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| 59 | |
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| 60 | double Sigma1ql2LeptoQuark::sigmaHat() { |
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| 61 | |
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| 62 | // Identify whether correct incoming flavours. |
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| 63 | int idLQ = 0; |
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| 64 | if (id1 == idQuark && id2 == idLepton) idLQ = 42; |
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| 65 | else if (id2 == idQuark && id1 == idLepton) idLQ = 42; |
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| 66 | else if (id1 == -idQuark && id2 == -idLepton) idLQ = -42; |
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| 67 | else if (id2 == -idQuark && id1 == -idLepton) idLQ = -42; |
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| 68 | if (idLQ == 0) return 0.; |
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| 69 | |
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| 70 | // Outgoing width and total sigma. Done. |
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| 71 | return widthIn * sigBW * LQPtr->resWidthOpen(idLQ, mH); |
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| 72 | |
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| 73 | } |
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| 74 | |
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| 75 | //-------------------------------------------------------------------------- |
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| 76 | |
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| 77 | // Select identity, colour and anticolour. |
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| 78 | |
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| 79 | void Sigma1ql2LeptoQuark::setIdColAcol() { |
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| 80 | |
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| 81 | // Flavours. |
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| 82 | int idq = (abs(id1) < 9) ? id1 : id2; |
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| 83 | int idLQ = (idq > 0) ? 42 : -42; |
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| 84 | setId( id1, id2, idLQ); |
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| 85 | |
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| 86 | // Colour flow topology. |
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| 87 | if (id1 == idq) setColAcol( 1, 0, 0, 0, 1, 0); |
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| 88 | else setColAcol( 0, 0, 1, 0, 1, 0); |
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| 89 | if (idq < 0) swapColAcol(); |
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| 90 | |
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| 91 | } |
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| 92 | |
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| 93 | //========================================================================== |
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| 94 | |
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| 95 | // Sigma2qg2LeptoQuarkl class. |
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| 96 | // Cross section for q g -> LQ l (leptoquark state). |
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| 97 | |
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| 98 | //-------------------------------------------------------------------------- |
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| 99 | |
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| 100 | // Initialize process. |
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| 101 | |
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| 102 | void Sigma2qg2LeptoQuarkl::initProc() { |
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| 103 | |
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| 104 | // Store LQ mass and width for propagator. |
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| 105 | mRes = particleDataPtr->m0(42); |
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| 106 | GammaRes = particleDataPtr->mWidth(42); |
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| 107 | m2Res = mRes*mRes; |
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| 108 | GamMRat = GammaRes / mRes; |
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| 109 | |
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| 110 | // Yukawa coupling strength. |
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| 111 | kCoup = settingsPtr->parm("LeptoQuark:kCoup"); |
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| 112 | |
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| 113 | // Read out quark and lepton the LQ couples to. |
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| 114 | ParticleDataEntry* LQPtr = particleDataPtr->particleDataEntryPtr(42); |
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| 115 | idQuark = LQPtr->channel(0).product(0); |
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| 116 | idLepton = LQPtr->channel(0).product(1); |
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| 117 | |
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| 118 | // Secondary open width fraction. |
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| 119 | openFracPos = LQPtr->resOpenFrac( 42); |
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| 120 | openFracNeg = LQPtr->resOpenFrac(-42); |
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| 121 | |
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| 122 | } |
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| 123 | |
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| 124 | //-------------------------------------------------------------------------- |
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| 125 | |
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| 126 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. |
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| 127 | |
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| 128 | void Sigma2qg2LeptoQuarkl::sigmaKin() { |
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| 129 | |
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| 130 | // Evaluate cross section. |
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| 131 | sigma0 = (M_PI / sH2) * kCoup * (alpS * alpEM / 6.) * (-tH / sH) |
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| 132 | * (uH2 + s3 * s3) / pow2(uH - s3); |
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| 133 | |
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| 134 | } |
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| 135 | |
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| 136 | //-------------------------------------------------------------------------- |
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| 137 | |
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| 138 | // Evaluate sigmaHat(sHat) for specific incoming flavours. |
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| 139 | |
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| 140 | double Sigma2qg2LeptoQuarkl::sigmaHat() { |
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| 141 | |
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| 142 | // Check that correct incoming flavour. |
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| 143 | if (abs(id1) != idQuark && abs(id2) != idQuark) return 0.; |
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| 144 | |
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| 145 | // Answer, with secondary width correction. |
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| 146 | double sigma = sigma0; |
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| 147 | sigma *= (id1 == idQuark || id2 == idQuark) ? openFracPos : openFracNeg; |
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| 148 | return sigma; |
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| 149 | |
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| 150 | } |
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| 151 | |
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| 152 | //-------------------------------------------------------------------------- |
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| 153 | |
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| 154 | // Select identity, colour and anticolour. |
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| 155 | |
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| 156 | void Sigma2qg2LeptoQuarkl::setIdColAcol() { |
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| 157 | |
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| 158 | // Flavour set up for q g -> H q. |
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| 159 | int idq = (id2 == 21) ? id1 : id2; |
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| 160 | int idLQ = (idq > 0) ? 42 : -42; |
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| 161 | int idlp = (idq > 0) ? -idLepton : idLepton; |
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| 162 | setId( id1, id2, idLQ, idlp); |
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| 163 | |
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| 164 | // tH defined between f and f': must swap tHat <-> uHat if q g in. |
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| 165 | swapTU = (id2 == 21); |
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| 166 | |
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| 167 | // Colour flow topologies. Swap when antiquarks. |
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| 168 | if (id2 == 21) setColAcol( 1, 0, 2, 1, 2, 0, 0, 0); |
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| 169 | else setColAcol( 2, 1, 1, 0, 2, 0, 0, 0); |
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| 170 | if (idq < 0) swapColAcol(); |
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| 171 | |
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| 172 | } |
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| 173 | |
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| 174 | //========================================================================== |
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| 175 | |
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| 176 | // Sigma2gg2LQLQbar class. |
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| 177 | // Cross section for g g -> LQ LQbar (leptoquark state). |
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| 178 | |
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| 179 | //-------------------------------------------------------------------------- |
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| 180 | |
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| 181 | // Initialize process. |
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| 182 | |
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| 183 | void Sigma2gg2LQLQbar::initProc() { |
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| 184 | |
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| 185 | // Store LQ mass and width for propagator. |
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| 186 | mRes = particleDataPtr->m0(42); |
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| 187 | GammaRes = particleDataPtr->mWidth(42); |
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| 188 | m2Res = mRes*mRes; |
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| 189 | GamMRat = GammaRes / mRes; |
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| 190 | |
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| 191 | // Secondary open width fraction. |
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| 192 | openFrac = particleDataPtr->resOpenFrac(42, -42); |
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| 193 | |
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| 194 | } |
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| 195 | |
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| 196 | //-------------------------------------------------------------------------- |
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| 197 | |
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| 198 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. |
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| 199 | |
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| 200 | void Sigma2gg2LQLQbar::sigmaKin() { |
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| 201 | |
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| 202 | // Average outgoing masses and adjust kinematics accordingly. |
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| 203 | double delta = 0.25 * pow2(s3 - s4) / sH; |
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| 204 | double m2avg = 0.5 * (s3 + s4) - delta; |
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| 205 | double tHavg = tH - delta; |
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| 206 | double uHavg = uH - delta; |
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| 207 | |
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| 208 | // Evaluate cross section. Secondary width for G*. |
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| 209 | sigma = (M_PI / sH2) * 0.5 * pow2(alpS) |
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| 210 | * ( 7. / 48. + 3. * pow2(uHavg - tHavg) / (16. * sH2) ) |
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| 211 | * ( 1. + 2. * m2avg * tHavg / pow2(tHavg - m2avg) |
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| 212 | + 2. * m2avg * uHavg / pow2(uHavg - m2avg) |
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| 213 | + 4. * m2avg * m2avg / ((tHavg - m2avg) * (uHavg - m2avg)) ); |
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| 214 | sigma *= openFrac; |
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| 215 | |
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| 216 | } |
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| 217 | |
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| 218 | //-------------------------------------------------------------------------- |
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| 219 | |
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| 220 | // Select identity, colour and anticolour. |
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| 221 | |
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| 222 | void Sigma2gg2LQLQbar::setIdColAcol() { |
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| 223 | |
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| 224 | // Flavours trivial. |
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| 225 | setId( 21, 21, 42, -42); |
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| 226 | |
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| 227 | // Colour flow topologies: random choice between two mirrors. |
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| 228 | if (rndmPtr->flat() < 0.5) setColAcol( 1, 2, 2, 3, 1, 0, 0, 3); |
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| 229 | else setColAcol( 1, 2, 3, 1, 3, 0, 0, 2); |
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| 230 | |
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| 231 | } |
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| 232 | |
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| 233 | //========================================================================== |
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| 234 | |
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| 235 | // Sigma2qqbar2LQLQbar class. |
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| 236 | // Cross section for q qbar -> LQ LQbar (leptoquark state). |
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| 237 | |
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| 238 | //-------------------------------------------------------------------------- |
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| 239 | |
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| 240 | // Initialize process. |
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| 241 | |
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| 242 | void Sigma2qqbar2LQLQbar::initProc() { |
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| 243 | |
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| 244 | // Store LQ mass and width for propagator. |
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| 245 | mRes = particleDataPtr->m0(42); |
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| 246 | GammaRes = particleDataPtr->mWidth(42); |
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| 247 | m2Res = mRes*mRes; |
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| 248 | GamMRat = GammaRes / mRes; |
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| 249 | |
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| 250 | // Yukawa coupling strength. |
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| 251 | kCoup = settingsPtr->parm("LeptoQuark:kCoup"); |
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| 252 | |
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| 253 | // Read out quark and lepton the LQ couples to. |
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| 254 | ParticleDataEntry* LQPtr = particleDataPtr->particleDataEntryPtr(42); |
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| 255 | idQuark = LQPtr->channel(0).product(0); |
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| 256 | |
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| 257 | // Secondary open width fraction. |
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| 258 | openFrac = particleDataPtr->resOpenFrac(42, -42); |
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| 259 | |
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| 260 | } |
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| 261 | |
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| 262 | //-------------------------------------------------------------------------- |
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| 263 | |
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| 264 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. |
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| 265 | |
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| 266 | void Sigma2qqbar2LQLQbar::sigmaKin() { |
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| 267 | |
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| 268 | // Average outgoing masses and adjust kinematics accordingly. |
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| 269 | double delta = 0.25 * pow2(s3 - s4) / sH; |
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| 270 | double m2avg = 0.5 * (s3 + s4) - delta; |
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| 271 | double tHavg = tH - delta; |
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| 272 | double uHavg = uH - delta; |
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| 273 | |
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| 274 | // Evaluate cross section for quark of different flavour than LQ. |
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| 275 | sigmaDiff = (M_PI / sH2) * (pow2(alpS) / 9.) |
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| 276 | * ( sH * (sH - 4. * m2avg) - pow2(uHavg - tHavg) ) / sH2; |
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| 277 | |
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| 278 | // Evaluate cross section for quark of same flavour as LQ. |
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| 279 | sigmaSame = sigmaDiff + (M_PI / sH2) * (pow2(kCoup * alpEM) / 8.) |
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| 280 | * (-sH * tHavg - pow2(m2avg-tHavg)) / pow2(tHavg) |
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| 281 | + (M_PI / sH2) * (kCoup * alpEM * alpS / 18.) * ( (m2avg - tHavg) |
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| 282 | * (uHavg - tHavg) + sH * (m2avg + tHavg) ) / (sH * tHavg); |
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| 283 | |
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| 284 | // Open fraction. |
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| 285 | sigmaDiff *= openFrac; |
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| 286 | sigmaSame *= openFrac; |
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| 287 | |
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| 288 | } |
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| 289 | |
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| 290 | //-------------------------------------------------------------------------- |
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| 291 | |
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| 292 | // Select identity, colour and anticolour. |
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| 293 | |
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| 294 | void Sigma2qqbar2LQLQbar::setIdColAcol() { |
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| 295 | |
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| 296 | // Flavours trivial. |
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| 297 | setId( id1, id2, 42, -42); |
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| 298 | |
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| 299 | // tH defined between f and LQ: must swap tHat <-> uHat if qbar q in. |
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| 300 | swapTU = (id1 < 0); |
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| 301 | |
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| 302 | // Colour flow topologies. |
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| 303 | if (id1 > 0) setColAcol( 1, 0, 0, 2, 1, 0, 0, 2); |
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| 304 | else setColAcol( 0, 2, 1, 0, 1, 0, 0, 2); |
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| 305 | |
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| 306 | } |
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| 307 | |
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| 308 | //========================================================================== |
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| 309 | |
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| 310 | } // end namespace Pythia8 |
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