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b584e2f5 | 1 | // SigmaLeptoquark.cc is a part of the PYTHIA event generator. |
2 | // Copyright (C) 2010 Torbjorn Sjostrand. | |
3 | // PYTHIA is licenced under the GNU GPL version 2, see COPYING for details. | |
4 | // Please respect the MCnet Guidelines, see GUIDELINES for details. | |
5 | ||
6 | // Function definitions (not found in the header) for the | |
7 | // leptoquark simulation classes. | |
8 | ||
9 | #include "SigmaLeptoquark.h" | |
10 | ||
11 | namespace Pythia8 { | |
12 | ||
13 | //========================================================================== | |
14 | ||
15 | // Sigma1ql2LeptoQuark class. | |
16 | // Cross section for q l -> LQ (leptoquark state). | |
17 | ||
18 | //-------------------------------------------------------------------------- | |
19 | ||
20 | // Initialize process. | |
21 | ||
22 | void Sigma1ql2LeptoQuark::initProc() { | |
23 | ||
24 | // Store LQ mass and width for propagator. | |
25 | mRes = particleDataPtr->m0(42); | |
26 | GammaRes = particleDataPtr->mWidth(42); | |
27 | m2Res = mRes*mRes; | |
28 | GamMRat = GammaRes / mRes; | |
29 | ||
30 | // Yukawa coupling strength. | |
31 | kCoup = settingsPtr->parm("LeptoQuark:kCoup"); | |
32 | ||
33 | // Set pointer to particle properties and decay table. | |
34 | LQPtr = particleDataPtr->particleDataEntryPtr(42); | |
35 | ||
36 | // Read out quark and lepton the LQ couples to. | |
37 | idQuark = LQPtr->channel(0).product(0); | |
38 | idLepton = LQPtr->channel(0).product(1); | |
39 | ||
40 | } | |
41 | ||
42 | //-------------------------------------------------------------------------- | |
43 | ||
44 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. | |
45 | ||
46 | void Sigma1ql2LeptoQuark::sigmaKin() { | |
47 | ||
48 | // Incoming width for correct quark-lepton pair. | |
49 | widthIn = 0.25 * alpEM * kCoup * mH; | |
50 | ||
51 | // Set up Breit-Wigner. | |
52 | sigBW = 4. * M_PI/ ( pow2(sH - m2Res) + pow2(sH * GamMRat) ); | |
53 | ||
54 | } | |
55 | ||
56 | //-------------------------------------------------------------------------- | |
57 | ||
58 | // Evaluate sigmaHat(sHat) for specific incoming flavours. | |
59 | ||
60 | double Sigma1ql2LeptoQuark::sigmaHat() { | |
61 | ||
62 | // Identify whether correct incoming flavours. | |
63 | int idLQ = 0; | |
64 | if (id1 == idQuark && id2 == idLepton) idLQ = 42; | |
65 | else if (id2 == idQuark && id1 == idLepton) idLQ = 42; | |
66 | else if (id1 == -idQuark && id2 == -idLepton) idLQ = -42; | |
67 | else if (id2 == -idQuark && id1 == -idLepton) idLQ = -42; | |
68 | if (idLQ == 0) return 0.; | |
69 | ||
70 | // Outgoing width and total sigma. Done. | |
71 | return widthIn * sigBW * LQPtr->resWidthOpen(idLQ, mH); | |
72 | ||
73 | } | |
74 | ||
75 | //-------------------------------------------------------------------------- | |
76 | ||
77 | // Select identity, colour and anticolour. | |
78 | ||
79 | void Sigma1ql2LeptoQuark::setIdColAcol() { | |
80 | ||
81 | // Flavours. | |
82 | int idq = (abs(id1) < 9) ? id1 : id2; | |
83 | int idLQ = (idq > 0) ? 42 : -42; | |
84 | setId( id1, id2, idLQ); | |
85 | ||
86 | // Colour flow topology. | |
87 | if (id1 == idq) setColAcol( 1, 0, 0, 0, 1, 0); | |
88 | else setColAcol( 0, 0, 1, 0, 1, 0); | |
89 | if (idq < 0) swapColAcol(); | |
90 | ||
91 | } | |
92 | ||
93 | //========================================================================== | |
94 | ||
95 | // Sigma2qg2LeptoQuarkl class. | |
96 | // Cross section for q g -> LQ l (leptoquark state). | |
97 | ||
98 | //-------------------------------------------------------------------------- | |
99 | ||
100 | // Initialize process. | |
101 | ||
102 | void Sigma2qg2LeptoQuarkl::initProc() { | |
103 | ||
104 | // Store LQ mass and width for propagator. | |
105 | mRes = particleDataPtr->m0(42); | |
106 | GammaRes = particleDataPtr->mWidth(42); | |
107 | m2Res = mRes*mRes; | |
108 | GamMRat = GammaRes / mRes; | |
109 | ||
110 | // Yukawa coupling strength. | |
111 | kCoup = settingsPtr->parm("LeptoQuark:kCoup"); | |
112 | ||
113 | // Read out quark and lepton the LQ couples to. | |
114 | ParticleDataEntry* LQPtr = particleDataPtr->particleDataEntryPtr(42); | |
115 | idQuark = LQPtr->channel(0).product(0); | |
116 | idLepton = LQPtr->channel(0).product(1); | |
117 | ||
118 | // Secondary open width fraction. | |
119 | openFracPos = LQPtr->resOpenFrac( 42); | |
120 | openFracNeg = LQPtr->resOpenFrac(-42); | |
121 | ||
122 | } | |
123 | ||
124 | //-------------------------------------------------------------------------- | |
125 | ||
126 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. | |
127 | ||
128 | void Sigma2qg2LeptoQuarkl::sigmaKin() { | |
129 | ||
130 | // Evaluate cross section. | |
131 | sigma0 = (M_PI / sH2) * kCoup * (alpS * alpEM / 6.) * (-tH / sH) | |
132 | * (uH2 + s3 * s3) / pow2(uH - s3); | |
133 | ||
134 | } | |
135 | ||
136 | //-------------------------------------------------------------------------- | |
137 | ||
138 | // Evaluate sigmaHat(sHat) for specific incoming flavours. | |
139 | ||
140 | double Sigma2qg2LeptoQuarkl::sigmaHat() { | |
141 | ||
142 | // Check that correct incoming flavour. | |
143 | if (abs(id1) != idQuark && abs(id2) != idQuark) return 0.; | |
144 | ||
145 | // Answer, with secondary width correction. | |
146 | double sigma = sigma0; | |
147 | sigma *= (id1 == idQuark || id2 == idQuark) ? openFracPos : openFracNeg; | |
148 | return sigma; | |
149 | ||
150 | } | |
151 | ||
152 | //-------------------------------------------------------------------------- | |
153 | ||
154 | // Select identity, colour and anticolour. | |
155 | ||
156 | void Sigma2qg2LeptoQuarkl::setIdColAcol() { | |
157 | ||
158 | // Flavour set up for q g -> H q. | |
159 | int idq = (id2 == 21) ? id1 : id2; | |
160 | int idLQ = (idq > 0) ? 42 : -42; | |
161 | int idlp = (idq > 0) ? idLepton : -idLepton; | |
162 | setId( id1, id2, idLQ, idlp); | |
163 | ||
164 | // tH defined between f and f': must swap tHat <-> uHat if q g in. | |
165 | swapTU = (id2 == 21); | |
166 | ||
167 | // Colour flow topologies. Swap when antiquarks. | |
168 | if (id2 == 21) setColAcol( 1, 0, 2, 1, 2, 0, 0, 0); | |
169 | else setColAcol( 2, 1, 1, 0, 2, 0, 0, 0); | |
170 | if (idq < 0) swapColAcol(); | |
171 | ||
172 | } | |
173 | ||
174 | //========================================================================== | |
175 | ||
176 | // Sigma2gg2LQLQbar class. | |
177 | // Cross section for g g -> LQ LQbar (leptoquark state). | |
178 | ||
179 | //-------------------------------------------------------------------------- | |
180 | ||
181 | // Initialize process. | |
182 | ||
183 | void Sigma2gg2LQLQbar::initProc() { | |
184 | ||
185 | // Store LQ mass and width for propagator. | |
186 | mRes = particleDataPtr->m0(42); | |
187 | GammaRes = particleDataPtr->mWidth(42); | |
188 | m2Res = mRes*mRes; | |
189 | GamMRat = GammaRes / mRes; | |
190 | ||
191 | // Secondary open width fraction. | |
192 | openFrac = particleDataPtr->resOpenFrac(42, -42); | |
193 | ||
194 | } | |
195 | ||
196 | //-------------------------------------------------------------------------- | |
197 | ||
198 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. | |
199 | ||
200 | void Sigma2gg2LQLQbar::sigmaKin() { | |
201 | ||
202 | // Average outgoing masses and adjust kinematics accordingly. | |
203 | double delta = 0.25 * pow2(s3 - s4) / sH; | |
204 | double m2avg = 0.5 * (s3 + s4) - delta; | |
205 | double tHavg = tH - delta; | |
206 | double uHavg = uH - delta; | |
207 | ||
208 | // Evaluate cross section. Secondary width for G*. | |
209 | sigma = (M_PI / sH2) * 0.5 * pow2(alpS) | |
210 | * ( 7. / 48. + 3. * pow2(uHavg - tHavg) / (16. * sH2) ) | |
211 | * ( 1. + 2. * m2avg * tHavg / pow2(tHavg - m2avg) | |
212 | + 2. * m2avg * uHavg / pow2(uHavg - m2avg) | |
213 | + 4. * m2avg * m2avg / ((tHavg - m2avg) * (uHavg - m2avg)) ); | |
214 | sigma *= openFrac; | |
215 | ||
216 | } | |
217 | ||
218 | //-------------------------------------------------------------------------- | |
219 | ||
220 | // Select identity, colour and anticolour. | |
221 | ||
222 | void Sigma2gg2LQLQbar::setIdColAcol() { | |
223 | ||
224 | // Flavours trivial. | |
225 | setId( 21, 21, 42, -42); | |
226 | ||
227 | // Colour flow topologies: random choice between two mirrors. | |
228 | if (rndmPtr->flat() < 0.5) setColAcol( 1, 2, 2, 3, 1, 0, 0, 3); | |
229 | else setColAcol( 1, 2, 3, 1, 3, 0, 0, 2); | |
230 | ||
231 | } | |
232 | ||
233 | //========================================================================== | |
234 | ||
235 | // Sigma2qqbar2LQLQbar class. | |
236 | // Cross section for q qbar -> LQ LQbar (leptoquark state). | |
237 | ||
238 | //-------------------------------------------------------------------------- | |
239 | ||
240 | // Initialize process. | |
241 | ||
242 | void Sigma2qqbar2LQLQbar::initProc() { | |
243 | ||
244 | // Store LQ mass and width for propagator. | |
245 | mRes = particleDataPtr->m0(42); | |
246 | GammaRes = particleDataPtr->mWidth(42); | |
247 | m2Res = mRes*mRes; | |
248 | GamMRat = GammaRes / mRes; | |
249 | ||
250 | // Yukawa coupling strength. | |
251 | kCoup = settingsPtr->parm("LeptoQuark:kCoup"); | |
252 | ||
253 | // Read out quark and lepton the LQ couples to. | |
254 | ParticleDataEntry* LQPtr = particleDataPtr->particleDataEntryPtr(42); | |
255 | idQuark = LQPtr->channel(0).product(0); | |
256 | ||
257 | // Secondary open width fraction. | |
258 | openFrac = particleDataPtr->resOpenFrac(42, -42); | |
259 | ||
260 | } | |
261 | ||
262 | //-------------------------------------------------------------------------- | |
263 | ||
264 | // Evaluate sigmaHat(sHat), part independent of incoming flavour. | |
265 | ||
266 | void Sigma2qqbar2LQLQbar::sigmaKin() { | |
267 | ||
268 | // Average outgoing masses and adjust kinematics accordingly. | |
269 | double delta = 0.25 * pow2(s3 - s4) / sH; | |
270 | double m2avg = 0.5 * (s3 + s4) - delta; | |
271 | double tHavg = tH - delta; | |
272 | double uHavg = uH - delta; | |
273 | ||
274 | // Evaluate cross section for quark of different flavour than LQ. | |
275 | sigmaDiff = (M_PI / sH2) * (pow2(alpS) / 9.) | |
276 | * ( sH * (sH - 4. * m2avg) - pow2(uHavg - tHavg) ) / sH2; | |
277 | ||
278 | // Evaluate cross section for quark of same flavour as LQ. | |
279 | sigmaSame = sigmaDiff + (M_PI / sH2) * (pow2(kCoup * alpEM) / 8.) | |
280 | * (-sH * tHavg - pow2(m2avg-tHavg)) / pow2(tHavg) | |
281 | + (M_PI / sH2) * (kCoup * alpEM * alpS / 18.) * ( (m2avg - tHavg) | |
282 | * (uHavg - tHavg) + sH * (m2avg + tHavg) ) / (sH * tHavg); | |
283 | ||
284 | // Open fraction. | |
285 | sigmaDiff *= openFrac; | |
286 | sigmaSame *= openFrac; | |
287 | ||
288 | } | |
289 | ||
290 | //-------------------------------------------------------------------------- | |
291 | ||
292 | // Select identity, colour and anticolour. | |
293 | ||
294 | void Sigma2qqbar2LQLQbar::setIdColAcol() { | |
295 | ||
296 | // Flavours trivial. | |
297 | setId( id1, id2, 42, -42); | |
298 | ||
299 | // tH defined between f and LQ: must swap tHat <-> uHat if qbar q in. | |
300 | swapTU = (id1 < 0); | |
301 | ||
302 | // Colour flow topologies. | |
303 | if (id1 > 0) setColAcol( 1, 0, 0, 2, 1, 0, 0, 2); | |
304 | else setColAcol( 0, 2, 1, 0, 1, 0, 0, 2); | |
305 | ||
306 | } | |
307 | ||
308 | //========================================================================== | |
309 | ||
310 | } // end namespace Pythia8 |