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63ba5337 | 1 | // SigmaGeneric.cc is a part of the PYTHIA event generator. |
2 | // Copyright (C) 2012 Johan Bijnens, 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 various generic | |
7 | // production processes, to be used as building blocks for some BSM processes. | |
8 | // Currently represented by QCD pair production of colour triplet objects, | |
9 | // with spin either 0, 1/2 or 1. | |
10 | ||
11 | // Cross sections are only provided for fixed m3 = m4, so do some gymnastics: | |
12 | // i) s34Avg picked so that beta34 same when s3, s4 -> s34Avg. | |
13 | // ii) tHQ = tH - mQ^2 = -0.5 sH (1 - beta34 cos(thetaH)) for m3 = m4 = mQ, | |
14 | // but tH - uH = sH beta34 cos(thetaH) also for m3 != m4, so use | |
15 | // tH, uH selected for m3 != m4 to derive tHQ, uHQ valid for m3 = m4. | |
16 | ||
17 | #include "SigmaGeneric.h" | |
18 | ||
19 | namespace Pythia8 { | |
20 | ||
21 | //========================================================================== | |
22 | ||
23 | // Sigma2gg2qGqGbar class. | |
24 | // Cross section for g g -> qG qGbar (generic quark of spin 0, 1/2 or 1). | |
25 | ||
26 | //-------------------------------------------------------------------------- | |
27 | ||
28 | // Initialize process. | |
29 | ||
30 | void Sigma2gg2qGqGbar::initProc() { | |
31 | ||
32 | // Number of colours. Anomalous coupling kappa - 1 used for vector state. | |
33 | nCHV = settingsPtr->mode("HiddenValley:Ngauge"); | |
34 | kappam1 = settingsPtr->parm("HiddenValley:kappa") - 1.; | |
35 | hasKappa = (abs(kappam1) > 1e-8); | |
36 | ||
37 | // Secondary open width fraction. | |
38 | openFracPair = particleDataPtr->resOpenFrac(idNew, -idNew); | |
39 | ||
40 | } | |
41 | ||
42 | //-------------------------------------------------------------------------- | |
43 | ||
44 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. | |
45 | ||
46 | void Sigma2gg2qGqGbar::sigmaKin() { | |
47 | ||
48 | // Modified Mandelstam variables for massive kinematics with m3 = m4. | |
49 | double delta = 0.25 * pow2(s3 - s4) / sH; | |
50 | double s34Avg = 0.5 * (s3 + s4) - delta; | |
51 | double tHavg = tH - delta; | |
52 | double uHavg = uH - delta; | |
53 | double tHQ = -0.5 * (sH - tH + uH); | |
54 | double uHQ = -0.5 * (sH + tH - uH); | |
55 | double tHQ2 = tHQ * tHQ; | |
56 | double uHQ2 = uHQ * uHQ; | |
57 | ||
58 | // Evaluate cross section for spin 0 colour triplet. | |
59 | if (spinSave == 0) { | |
60 | sigSum = 0.5 * ( 7. / 48. + 3. * pow2(uHavg - tHavg) / (16. * sH2) ) | |
61 | * ( 1. + 2. * s34Avg * tHavg / pow2(tHavg - s34Avg) | |
62 | + 2. * s34Avg * uHavg / pow2(uHavg - s34Avg) | |
63 | + 4. * pow2(s34Avg) / ((tHavg - s34Avg) * (uHavg - s34Avg)) ); | |
64 | ||
65 | // Equal probability for two possible colour flows. | |
66 | sigTS = 0.5 * sigSum; | |
67 | sigUS = sigTS; | |
68 | } | |
69 | ||
70 | // Evaluate cross section for spin 1/2 colour triplet. | |
71 | else if (spinSave == 1) { | |
72 | double tumHQ = tHQ * uHQ - s34Avg * sH; | |
73 | sigTS = ( uHQ / tHQ - 2.25 * uHQ2 / sH2 + 4.5 * s34Avg * tumHQ | |
74 | / ( sH * tHQ2) + 0.5 * s34Avg * (tHQ + s34Avg) / tHQ2 | |
75 | - s34Avg*s34Avg / (sH * tHQ) ) / 6.; | |
76 | sigUS = ( tHQ / uHQ - 2.25 * tHQ2 / sH2 + 4.5 * s34Avg * tumHQ | |
77 | / ( sH * uHQ2) + 0.5 * s34Avg * (uHQ + s34Avg) / uHQ2 | |
78 | - s34Avg*s34Avg / (sH * uHQ) ) / 6.; | |
79 | sigSum = sigTS + sigUS; | |
80 | } | |
81 | ||
82 | // Evaluate cross section for spin 1 colour triplet. | |
83 | else { | |
84 | double tmu = tHavg - uHavg; | |
85 | double s34Pos = s34Avg / sH; | |
86 | double s34Pos2 = s34Pos * s34Pos; | |
87 | double s34Neg = sH / s34Avg; | |
88 | double s34Neg2 = s34Neg * s34Neg; | |
89 | sigSum = pow2(tmu) * sH2 * (241./1536. - 1./32. * s34Pos | |
90 | + 9./16. * s34Pos2) | |
91 | + pow4(tmu) * (37./512. + 9./64. * s34Pos) | |
92 | + pow6(tmu) * (9./512. / sH2) | |
93 | + sH2 * sH2 * (133./1536. - 7./64. * s34Pos + 7./16. * s34Pos2); | |
94 | ||
95 | // Anomalous coupling. | |
96 | if (hasKappa) | |
97 | sigSum += pow2(tmu) * sH2 * (kappam1 * (143./384. - 7./3072 * s34Neg) | |
98 | + pow2(kappam1) * (- 1./768. * s34Neg + 185./768.) | |
99 | + pow3(kappam1) * (- 7./3072. * s34Neg2 | |
100 | - 25./3072. * s34Neg + 67./1536.) | |
101 | + pow4(kappam1) * (- 37./49152. * s34Neg2 | |
102 | - 25./6144. * s34Neg + 5./1536.) ) | |
103 | + pow4(tmu) * (kappam1 * 3./32. | |
104 | + pow2(kappam1) * (7./6144. * s34Neg2 - 7./768. * s34Neg + 3./128.) | |
105 | + pow3(kappam1) * (7./6144. * s34Neg2 - 7./1536. * s34Neg) | |
106 | + pow4(kappam1) * (- 1./49152. * s34Neg2 + 5./6144. * s34Neg) ) | |
107 | + pow6(tmu) * pow4(kappam1) * 13./49152. / pow2(s34Avg) | |
108 | + sH2 * sH2 * ( kappam1 * 77./384. | |
109 | + pow2(kappam1) * (7./6144. * s34Neg2 + 1./96.* s34Neg + 39./256.) | |
110 | + pow3(kappam1) * (7./6144. * s34Neg2 + 13./1024. * s34Neg + 61./1536.) | |
111 | + pow4(kappam1) * (25./49152. * s34Neg2 + 5./1536. * s34Neg + 1./512.) | |
112 | ); | |
113 | ||
114 | // Equal probability for two possible colour flows. | |
115 | sigSum /= pow2( (uHavg-s34Avg) * (tHavg-s34Avg) ); | |
116 | sigTS = 0.5 * sigSum; | |
117 | sigUS = sigTS; | |
118 | } | |
119 | ||
120 | // Final answer, with common factors. | |
121 | sigma = (M_PI / sH2) * pow2(alpS) * sigSum * nCHV * openFracPair; | |
122 | ||
123 | } | |
124 | ||
125 | //-------------------------------------------------------------------------- | |
126 | ||
127 | // Select identity, colour and anticolour. | |
128 | ||
129 | void Sigma2gg2qGqGbar::setIdColAcol() { | |
130 | ||
131 | // Flavours trivial. | |
132 | setId( 21, 21, idNew, -idNew); | |
133 | ||
134 | // Two colour flow topologies. | |
135 | double sigRand = sigSum * rndmPtr->flat(); | |
136 | if (sigRand < sigTS) setColAcol( 1, 2, 2, 3, 1, 0, 0, 3); | |
137 | else setColAcol( 1, 2, 3, 1, 3, 0, 0, 2); | |
138 | ||
139 | } | |
140 | ||
141 | //========================================================================== | |
142 | ||
143 | // Sigma2qqbar2qGqGbar class. | |
144 | // Cross section for q qbar -> qG qGbar (generic quark of spin 0, 1/2 or 1). | |
145 | ||
146 | //-------------------------------------------------------------------------- | |
147 | ||
148 | // Initialize process. | |
149 | ||
150 | void Sigma2qqbar2qGqGbar::initProc() { | |
151 | ||
152 | // Number of colours. Coupling kappa used for vector state. | |
153 | nCHV = settingsPtr->mode("HiddenValley:Ngauge"); | |
154 | kappa = settingsPtr->parm("HiddenValley:kappa"); | |
155 | ||
156 | // Secondary open width fraction. | |
157 | openFracPair = particleDataPtr->resOpenFrac(idNew, -idNew); | |
158 | ||
159 | } | |
160 | ||
161 | //-------------------------------------------------------------------------- | |
162 | ||
163 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. | |
164 | ||
165 | void Sigma2qqbar2qGqGbar::sigmaKin() { | |
166 | ||
167 | // Modified Mandelstam variables for massive kinematics with m3 = m4. | |
168 | double delta = 0.25 * pow2(s3 - s4) / sH; | |
169 | double s34Avg = 0.5 * (s3 + s4) - delta; | |
170 | double tHavg = tH - delta; | |
171 | double uHavg = uH - delta; | |
172 | double tHQ = -0.5 * (sH - tH + uH); | |
173 | double uHQ = -0.5 * (sH + tH - uH); | |
174 | double tHQ2 = tHQ * tHQ; | |
175 | double uHQ2 = uHQ * uHQ; | |
176 | ||
177 | // Evaluate cross section for spin 0 colour triplet. | |
178 | if (spinSave == 0) { | |
179 | sigSum = (1./9.) * (sH * (sH - 4. * s34Avg) | |
180 | - pow2(uHavg - tHavg)) / sH2; | |
181 | } | |
182 | ||
183 | // Evaluate cross section for spin 1/2 colour triplet. | |
184 | else if (spinSave == 1) { | |
185 | sigSum = (4./9.) * ((tHQ2 + uHQ2) / sH2 + 2. * s34Avg / sH); | |
186 | } | |
187 | ||
188 | // Evaluate cross section for spin 1 colour triplet. | |
189 | else { | |
190 | double tuH34 = (tHavg + uHavg) / s34Avg; | |
191 | sigSum = (1./9.) * ( | |
192 | pow2(1. + kappa) * sH * s34Avg * (pow2(tuH34) - 4.) | |
193 | + (tHavg * uHavg - pow2(s34Avg)) * (8. + 2. * (1. - pow2(kappa)) * tuH34 | |
194 | + pow2(kappa) * pow2(tuH34)) ) / sH2; | |
195 | } | |
196 | ||
197 | // Final answer, with common factors. | |
198 | sigma = (M_PI / sH2) * pow2(alpS) * sigSum * nCHV * openFracPair; | |
199 | ||
200 | } | |
201 | ||
202 | //-------------------------------------------------------------------------- | |
203 | ||
204 | // Select identity, colour and anticolour. | |
205 | ||
206 | void Sigma2qqbar2qGqGbar::setIdColAcol() { | |
207 | ||
208 | // Flavours trivial. | |
209 | setId( id1, id2, idNew, -idNew); | |
210 | ||
211 | // tH defined between f and qG: must swap tHat <-> uHat if qbar q in. | |
212 | swapTU = (id1 < 0); | |
213 | ||
214 | // Colour flow topologies. | |
215 | if (id1 > 0) setColAcol( 1, 0, 0, 2, 1, 0, 0, 2); | |
216 | else setColAcol( 0, 2, 1, 0, 1, 0, 0, 2); | |
217 | ||
218 | } | |
219 | ||
220 | //========================================================================== | |
221 | ||
222 | // Sigma2ffbar2fGfGbar class. | |
223 | // Cross section for f fbar -> qG qGbar (generic quark of spin 0, 1/2 or 1) | |
224 | // via gamma^*/Z^* s-channel exchange. Still under development!! ?? | |
225 | ||
226 | //-------------------------------------------------------------------------- | |
227 | ||
228 | // Initialize process. | |
229 | ||
230 | void Sigma2ffbar2fGfGbar::initProc() { | |
231 | ||
232 | // Charge and number of colours. Coupling kappa used for vector state. | |
233 | if (settingsPtr->flag("HiddenValley:doKinMix")) | |
234 | eQHV2 = pow2(settingsPtr->parm("HiddenValley:kinMix")); | |
235 | else | |
236 | eQHV2 = pow2( particleDataPtr->charge(idNew) ); | |
237 | nCHV = settingsPtr->mode("HiddenValley:Ngauge"); | |
238 | kappa = settingsPtr->parm("HiddenValley:kappa"); | |
239 | ||
240 | // Coloured or uncoloured particle. | |
241 | hasColour = (particleDataPtr->colType(idNew) != 0); | |
242 | colFac = (hasColour) ? 3. : 1.; | |
243 | ||
244 | // Secondary open width fraction. | |
245 | openFracPair = particleDataPtr->resOpenFrac(idNew, -idNew); | |
246 | ||
247 | } | |
248 | ||
249 | //-------------------------------------------------------------------------- | |
250 | ||
251 | // Evaluate d(sigmaHat)/d(tHat), part independent of incoming flavour. | |
252 | ||
253 | void Sigma2ffbar2fGfGbar::sigmaKin() { | |
254 | ||
255 | // Modified Mandelstam variables for massive kinematics with m3 = m4. | |
256 | double delta = 0.25 * pow2(s3 - s4) / sH; | |
257 | double s34Avg = 0.5 * (s3 + s4) - delta; | |
258 | double tHavg = tH - delta; | |
259 | double uHavg = uH - delta; | |
260 | double tHQ = -0.5 * (sH - tH + uH); | |
261 | double uHQ = -0.5 * (sH + tH - uH); | |
262 | double tHQ2 = tHQ * tHQ; | |
263 | double uHQ2 = uHQ * uHQ; | |
264 | ||
265 | // Evaluate cross section for spin 0 colour triplet. | |
266 | if (spinSave == 0) { | |
267 | sigSum = 0.5 * (sH * (sH - 4. * s34Avg) - pow2(uHavg - tHavg)) / sH2; | |
268 | } | |
269 | ||
270 | // Evaluate cross section for spin 1/2 colour triplet. | |
271 | else if (spinSave == 1) { | |
272 | sigSum = 2. * ((tHQ2 + uHQ2) / sH2 + 2. * s34Avg / sH); | |
273 | } | |
274 | ||
275 | // Evaluate cross section for spin 1 colour triplet. | |
276 | else { | |
277 | double tuH34 = (tHavg + uHavg) / s34Avg; | |
278 | sigSum = 0.5 * ( pow2(1. + kappa) * sH * s34Avg * (pow2(tuH34) - 4.) | |
279 | + (tHavg * uHavg - pow2(s34Avg)) * (8. + 2. * (1. - pow2(kappa)) * tuH34 | |
280 | + pow2(kappa) * pow2(tuH34)) ) / sH2; | |
281 | } | |
282 | ||
283 | // Final-state charge factors. | |
284 | sigSum *= colFac * eQHV2 * (1. + alpS / M_PI); | |
285 | ||
286 | // Final answer, except for initial-state weight | |
287 | sigma0 = (M_PI / sH2) * pow2(alpEM) * sigSum * nCHV * openFracPair; | |
288 | ||
289 | } | |
290 | ||
291 | //-------------------------------------------------------------------------- | |
292 | ||
293 | // Evaluate d(sigmaHat)/d(tHat), including incoming flavour dependence. | |
294 | ||
295 | double Sigma2ffbar2fGfGbar::sigmaHat() { | |
296 | ||
297 | // Charge and colour factors. | |
298 | double eNow = couplingsPtr->ef( abs(id1) ); | |
299 | double sigma = sigma0 * pow2(eNow); | |
300 | if (abs(id1) < 9) sigma /= 3.; | |
301 | ||
302 | // Answer. | |
303 | return sigma; | |
304 | ||
305 | } | |
306 | ||
307 | //-------------------------------------------------------------------------- | |
308 | ||
309 | // Select identity, colour and anticolour. | |
310 | ||
311 | void Sigma2ffbar2fGfGbar::setIdColAcol() { | |
312 | ||
313 | // Flavours trivial. | |
314 | setId( id1, id2, idNew, -idNew); | |
315 | ||
316 | // tH defined between f and qG: must swap tHat <-> uHat if fbar f in. | |
317 | swapTU = (id1 < 0); | |
318 | ||
319 | // Colour flow topologies. | |
320 | if (hasColour) { | |
321 | if (id1 > 0 && id1 < 7) setColAcol( 1, 0, 0, 1, 2, 0, 0, 2); | |
322 | else if (id1 > -7 && id1 < 0) setColAcol( 0, 1, 1, 0, 2, 0, 0, 2); | |
323 | else setColAcol( 0, 0, 0, 0, 1, 0, 0, 1); | |
324 | } else { | |
325 | if (id1 > 0 && id1 < 7) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0); | |
326 | else if (id1 > -7 && id1 < 0) setColAcol( 0, 1, 1, 0, 0, 0, 0, 0); | |
327 | else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0); | |
328 | } | |
329 | ||
330 | } | |
331 | ||
332 | //========================================================================== | |
333 | ||
334 | // Sigma1ffbar2Zv class. | |
335 | // Cross section for f fbar -> Zv, where Zv couples both to the SM and | |
336 | // to a hidden sector. Primitive coupling structure. | |
337 | ||
338 | //-------------------------------------------------------------------------- | |
339 | ||
340 | // Initialize process. | |
341 | ||
342 | void Sigma1ffbar2Zv::initProc() { | |
343 | ||
344 | // Store Zv mass and width for propagator. | |
345 | idZv = 4900023; | |
346 | mRes = particleDataPtr->m0(idZv); | |
347 | GammaRes = particleDataPtr->mWidth(idZv); | |
348 | m2Res = mRes*mRes; | |
349 | GamMRat = GammaRes / mRes; | |
350 | ||
351 | // Set pointer to particle properties and decay table. | |
352 | particlePtr = particleDataPtr->particleDataEntryPtr(idZv); | |
353 | ||
354 | } | |
355 | ||
356 | //-------------------------------------------------------------------------- | |
357 | ||
358 | // Evaluate sigmaHat(sHat); first step when inflavours unknown. | |
359 | ||
360 | void Sigma1ffbar2Zv::sigmaKin() { | |
361 | ||
362 | // Breit-Wigner, including some (guessed) spin factors. | |
363 | double sigBW = 12. * M_PI / ( pow2(sH - m2Res) + pow2(sH * GamMRat) ); | |
364 | ||
365 | // Outgoing width: only includes channels left open. | |
366 | double widthOut = particlePtr->resWidthOpen(663, mH); | |
367 | ||
368 | // Temporary answer. | |
369 | sigOut = sigBW * widthOut; | |
370 | ||
371 | } | |
372 | ||
373 | //-------------------------------------------------------------------------- | |
374 | ||
375 | // Evaluate sigmaHat(sHat); second step when inflavours known. | |
376 | ||
377 | double Sigma1ffbar2Zv::sigmaHat() { | |
378 | ||
379 | // Incoming quark or lepton; for former need two 1/3 colour factors. | |
380 | int id1Abs = abs(id1); | |
381 | double widthIn = particlePtr->resWidthChan( mH, id1Abs, -id1Abs); | |
382 | if (id1Abs < 6) widthIn /= 9.; | |
383 | return widthIn * sigOut; | |
384 | ||
385 | } | |
386 | ||
387 | //-------------------------------------------------------------------------- | |
388 | ||
389 | // Select identity, colour and anticolour. | |
390 | ||
391 | void Sigma1ffbar2Zv::setIdColAcol() { | |
392 | ||
393 | // Flavours trivial. | |
394 | setId( id1, id2, idZv); | |
395 | ||
396 | // Colour flow topologies. Swap when antiquarks. | |
397 | if (abs(id1) < 6) setColAcol( 1, 0, 0, 1, 0, 0); | |
398 | else setColAcol( 0, 0, 0, 0, 0, 0); | |
399 | if (id1 < 0) swapColAcol(); | |
400 | ||
401 | } | |
402 | ||
403 | //-------------------------------------------------------------------------- | |
404 | ||
405 | // Evaluate weight for decay angles. | |
406 | ||
407 | double Sigma1ffbar2Zv::weightDecay( Event& process, int iResBeg, | |
408 | int iResEnd) { | |
409 | ||
410 | // Identity of mother of decaying resonance(s). | |
411 | int idMother = process[process[iResBeg].mother1()].idAbs(); | |
412 | ||
413 | // For Z' itself angular distribution as if gamma*. | |
414 | if (iResBeg == 5 && iResEnd == 5) { | |
415 | double mr = 4. * pow2(process[6].m()) / sH; | |
416 | double cosThe = (process[3].p() - process[4].p()) | |
417 | * (process[7].p() - process[6].p()) / (sH * sqrtpos(1. - mr)); | |
418 | double wt = 1. + pow2(cosThe) + mr * (1. - pow2(cosThe)); | |
419 | return 0.5 * wt; | |
420 | } | |
421 | ||
422 | // For top decay hand over to standard routine. | |
423 | if (idMother == 6) | |
424 | return weightTopDecay( process, iResBeg, iResEnd); | |
425 | ||
426 | // Else done. | |
427 | return 1.; | |
428 | ||
429 | } | |
430 | ||
431 | //========================================================================== | |
432 | ||
433 | } // end namespace Pythia8 |