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SigmaLeftRightSym.cc
1 // SigmaLeftRightSym.cc is a part of the PYTHIA event generator.
2 // Copyright (C) 2020 Torbjorn Sjostrand.
3 // PYTHIA is licenced under the GNU GPL v2 or later, 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 // left-right-symmetry simulation classes.
8 
9 #include "Pythia8/SigmaLeftRightSym.h"
10 
11 namespace Pythia8 {
12 
13 //==========================================================================
14 
15 // Sigma1ffbar2ZRight class.
16 // Cross section for f fbar -> Z_R^0 (righthanded gauge boson).
17 
18 //--------------------------------------------------------------------------
19 
20 // Initialize process.
21 
22 void Sigma1ffbar2ZRight::initProc() {
23 
24  // Store Z_R mass and width for propagator.
25  idZR = 9900023;
26  mRes = particleDataPtr->m0(idZR);
27  GammaRes = particleDataPtr->mWidth(idZR);
28  m2Res = mRes*mRes;
29  GamMRat = GammaRes / mRes;
30  sin2tW = coupSMPtr->sin2thetaW();
31 
32  // Set pointer to particle properties and decay table.
33  ZRPtr = particleDataPtr->particleDataEntryPtr(idZR);
34 
35 }
36 
37 //--------------------------------------------------------------------------
38 
39 // Evaluate sigmaHat(sHat), part independent of incoming flavour.
40 
41 void Sigma1ffbar2ZRight::sigmaKin() {
42 
43  // Set up Breit-Wigner. Width out only includes open channels.
44  double sigBW = 12. * M_PI/ ( pow2(sH - m2Res) + pow2(sH * GamMRat) );
45  double widthOut = ZRPtr->resWidthOpen(idZR, mH);
46 
47  // Prefactor for incoming widths. Combine. Done.
48  double preFac = alpEM * mH / ( 48. * sin2tW * (1. - sin2tW)
49  * (1. - 2. * sin2tW) );
50  sigma0 = preFac * sigBW * widthOut;
51 
52 }
53 
54 //--------------------------------------------------------------------------
55 
56 // Evaluate sigmaHat(sHat), including incoming flavour dependence.
57 
58 double Sigma1ffbar2ZRight::sigmaHat() {
59 
60  // Vector and axial couplings of incoming fermion pair.
61  int idAbs = abs(id1);
62  double af = 0.;
63  double vf = 0.;
64  if (idAbs < 9 && idAbs%2 == 1) {
65  af = -1. + 2. * sin2tW;
66  vf = -1. + 4. * sin2tW / 3.;
67  } else if (idAbs < 9) {
68  af = 1. - 2. * sin2tW;
69  vf = 1. - 8. * sin2tW / 3.;
70  } else if (idAbs < 19 && idAbs%2 == 1) {
71  af = -1. + 2. * sin2tW;
72  vf = -1. + 4. * sin2tW;
73  }
74 
75  // Colour factor. Answer.
76  double sigma = (vf*vf + af*af) * sigma0;
77  if (idAbs < 9) sigma /= 3.;
78  return sigma;
79 
80 }
81 
82 //--------------------------------------------------------------------------
83 
84 // Select identity, colour and anticolour.
85 
86 void Sigma1ffbar2ZRight::setIdColAcol() {
87 
88  // Flavours trivial.
89  setId( id1, id2, idZR);
90 
91  // Colour flow topologies. Swap when antiquarks.
92  if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0);
93  else setColAcol( 0, 0, 0, 0, 0, 0);
94  if (id1 < 0) swapColAcol();
95 
96 }
97 
98 //--------------------------------------------------------------------------
99 
100 // Evaluate weight for Z_R decay angle.
101 
102 double Sigma1ffbar2ZRight::weightDecay( Event& process, int iResBeg,
103  int iResEnd) {
104 
105  // Identity of mother of decaying reseonance(s).
106  int idMother = process[process[iResBeg].mother1()].idAbs();
107 
108  // For top decay hand over to standard routine.
109  if (idMother == 6)
110  return weightTopDecay( process, iResBeg, iResEnd);
111 
112  // Z_R should sit in entry 5.
113  if (iResBeg != 5 || iResEnd != 5) return 1.;
114 
115  // Couplings for in- and out-flavours.
116  double ai, vi, af, vf;
117  int idInAbs = process[3].idAbs();
118  if (idInAbs < 9 && idInAbs%2 == 1) {
119  ai = -1. + 2. * sin2tW;
120  vi = -1. + 4. * sin2tW / 3.;
121  } else if (idInAbs < 9) {
122  ai = 1. - 2. * sin2tW;
123  vi = 1. - 8. * sin2tW / 3.;
124  } else {
125  ai = -1. + 2. * sin2tW;
126  vi = -1. + 4. * sin2tW;
127  }
128  int idOutAbs = process[6].idAbs();
129  if (idOutAbs < 9 && idOutAbs%2 == 1) {
130  af = -1. + 2. * sin2tW;
131  vf = -1. + 4. * sin2tW / 3.;
132  } else if (idOutAbs < 9) {
133  af = 1. - 2. * sin2tW;
134  vf = 1. - 8. * sin2tW / 3.;
135  } else {
136  af = -1. + 2. * sin2tW;
137  vf = -1. + 4. * sin2tW;
138  }
139 
140  // Phase space factors. Reconstruct decay angle.
141  double mr1 = pow2(process[6].m()) / sH;
142  double mr2 = pow2(process[7].m()) / sH;
143  double betaf = sqrtpos( pow2(1. - mr1 - mr2) - 4. * mr1 * mr2);
144  double cosThe = (process[3].p() - process[4].p())
145  * (process[7].p() - process[6].p()) / (sH * betaf);
146 
147  // Angular weight and its maximum.
148  double wt1 = (vi*vi + ai*ai) * (vf*vf + af*af * betaf*betaf);
149  double wt2 = (1. - betaf*betaf) * (vi*vi + ai*ai) * vf*vf;
150  double wt3 = betaf * 4. * vi * ai * vf * af;
151  if (process[3].id() * process[6].id() < 0) wt3 = -wt3;
152  double wt = wt1 * (1. + cosThe*cosThe) + wt2 * (1. - cosThe*cosThe)
153  + 2. * wt3 * cosThe;
154  double wtMax = 2. * (wt1 + abs(wt3));
155 
156  // Done.
157  return wt / wtMax;
158 
159 }
160 
161 //==========================================================================
162 
163 // Sigma1ffbar2WRight class.
164 // Cross section for f fbar' -> W_R^+- (righthanded gauge boson).
165 
166 //--------------------------------------------------------------------------
167 
168 // Initialize process.
169 
170 void Sigma1ffbar2WRight::initProc() {
171 
172  // Store W_R^+- mass and width for propagator.
173  idWR = 9900024;
174  mRes = particleDataPtr->m0(idWR);
175  GammaRes = particleDataPtr->mWidth(idWR);
176  m2Res = mRes*mRes;
177  GamMRat = GammaRes / mRes;
178  thetaWRat = 1. / (12. * coupSMPtr->sin2thetaW());
179 
180  // Set pointer to particle properties and decay table.
181  particlePtr = particleDataPtr->particleDataEntryPtr(idWR);
182 
183 }
184 
185 //--------------------------------------------------------------------------
186 
187 // Evaluate sigmaHat(sHat), part independent of incoming flavour.
188 
189 void Sigma1ffbar2WRight::sigmaKin() {
190 
191  // Common coupling factors.
192  double colQ = 3. * (1. + alpS / M_PI);
193 
194  // Reset quantities to sum. Declare variables inside loop.
195  double widOutPos = 0.;
196  double widOutNeg = 0.;
197  int id1Now, id2Now, id1Abs, id2Abs, id1Neg, id2Neg, onMode;
198  double widNow, widSecPos, widSecNeg, mf1, mf2, mr1, mr2, kinFac;
199 
200  // Loop over all W_R^+- decay channels.
201  for (int i = 0; i < particlePtr->sizeChannels(); ++i) {
202  id1Now = particlePtr->channel(i).product(0);
203  id2Now = particlePtr->channel(i).product(1);
204  id1Abs = abs(id1Now);
205  id2Abs = abs(id2Now);
206 
207  // Check that above threshold. Phase space.
208  mf1 = particleDataPtr->m0(id1Abs);
209  mf2 = particleDataPtr->m0(id2Abs);
210  if (mH > mf1 + mf2 + MASSMARGIN) {
211  mr1 = pow2(mf1 / mH);
212  mr2 = pow2(mf2 / mH);
213  kinFac = (1. - 0.5 * (mr1 + mr2) - 0.5 * pow2(mr1 - mr2))
214  * sqrtpos( pow2(1. - mr1 - mr2) - 4. * mr1 * mr2 );
215 
216  // Combine kinematics with colour factor and CKM couplings.
217  widNow = kinFac;
218  if (id1Abs < 9) widNow *= colQ * coupSMPtr->V2CKMid(id1Abs, id2Abs);
219 
220  // Secondary width from top and righthanded neutrino decay.
221  id1Neg = (id1Abs < 19) ? -id1Now : id1Abs;
222  id2Neg = (id2Abs < 19) ? -id2Now : id2Abs;
223  widSecPos = particleDataPtr->resOpenFrac(id1Now, id2Now);
224  widSecNeg = particleDataPtr->resOpenFrac(id1Neg, id2Neg);
225 
226  // Add weight for channels on for all, W_R^+ and W_R^-, respectively.
227  onMode = particlePtr->channel(i).onMode();
228  if (onMode == 1 || onMode == 2) widOutPos += widNow * widSecPos;
229  if (onMode == 1 || onMode == 3) widOutNeg += widNow * widSecNeg;
230 
231  // End loop over fermions.
232  }
233  }
234 
235  // Set up Breit-Wigner. Cross section for W_R^+ and W_R^- separately.
236  double sigBW = 12. * M_PI * pow2(alpEM * thetaWRat) * sH
237  / ( pow2(sH - m2Res) + pow2(sH * GamMRat) );
238  sigma0Pos = sigBW * widOutPos;
239  sigma0Neg = sigBW * widOutNeg;
240 
241 }
242 
243 //--------------------------------------------------------------------------
244 
245 // Evaluate sigmaHat(sHat), including incoming flavour dependence.
246 
247 double Sigma1ffbar2WRight::sigmaHat() {
248 
249  // Secondary width for W_R^+ or W_R^-. CKM and colour factors.
250  int idUp = (abs(id1)%2 == 0) ? id1 : id2;
251  double sigma = (idUp > 0) ? sigma0Pos : sigma0Neg;
252  if (abs(id1) < 9) sigma *= coupSMPtr->V2CKMid(abs(id1), abs(id2)) / 3.;
253 
254  // Answer.
255  return sigma;
256 
257 }
258 
259 //--------------------------------------------------------------------------
260 
261 // Select identity, colour and anticolour.
262 
263 void Sigma1ffbar2WRight::setIdColAcol() {
264 
265  // Sign of outgoing W_R.
266  int sign = (abs(id1)%2 == 0) ? 1 : -1;
267  if (id1 < 0) sign = -sign;
268  setId( id1, id2, idWR * sign);
269 
270  // Colour flow topologies. Swap when antiquarks.
271  if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0);
272  else setColAcol( 0, 0, 0, 0, 0, 0);
273  if (id1 < 0) swapColAcol();
274 
275 }
276 
277 //--------------------------------------------------------------------------
278 
279 // Evaluate weight for W_R decay angle.
280 
281 double Sigma1ffbar2WRight::weightDecay( Event& process, int iResBeg,
282  int iResEnd) {
283 
284  // Identity of mother of decaying reseonance(s).
285  int idMother = process[process[iResBeg].mother1()].idAbs();
286 
287  // For top decay hand over to standard routine.
288  if (idMother == 6)
289  return weightTopDecay( process, iResBeg, iResEnd);
290 
291  // W_R should sit in entry 5.
292  if (iResBeg != 5 || iResEnd != 5) return 1.;
293 
294  // Phase space factors.
295  double mr1 = pow2(process[6].m()) / sH;
296  double mr2 = pow2(process[7].m()) / sH;
297  double betaf = sqrtpos( pow2(1. - mr1 - mr2) - 4. * mr1 * mr2);
298 
299  // Sign of asymmetry.
300  double eps = (process[3].id() * process[6].id() > 0) ? 1. : -1.;
301 
302  // Reconstruct decay angle and weight for it.
303  double cosThe = (process[3].p() - process[4].p())
304  * (process[7].p() - process[6].p()) / (sH * betaf);
305  double wtMax = 4.;
306  double wt = pow2(1. + betaf * eps * cosThe) - pow2(mr1 - mr2);
307 
308  // Done.
309  return (wt / wtMax);
310 
311 }
312 
313 //==========================================================================
314 
315 // Sigma1ll2Hchgchg class.
316 // Cross section for l l -> H_L^++-- or H_R^++-- (doubly charged Higgs).
317 
318 //--------------------------------------------------------------------------
319 
320 // Initialize process.
321 
322 void Sigma1ll2Hchgchg::initProc() {
323 
324  // Set process properties: H_L^++-- or H_R^++--.
325  if (leftRight == 1) {
326  idHLR = 9900041;
327  codeSave = 3121;
328  nameSave = "l l -> H_L^++--";
329  } else {
330  idHLR = 9900042;
331  codeSave = 3141;
332  nameSave = "l l -> H_R^++--";
333  }
334 
335  // Read in Yukawa matrix for couplings to a lepton pair.
336  yukawa[1][1] = parm("LeftRightSymmmetry:coupHee");
337  yukawa[2][1] = parm("LeftRightSymmmetry:coupHmue");
338  yukawa[2][2] = parm("LeftRightSymmmetry:coupHmumu");
339  yukawa[3][1] = parm("LeftRightSymmmetry:coupHtaue");
340  yukawa[3][2] = parm("LeftRightSymmmetry:coupHtaumu");
341  yukawa[3][3] = parm("LeftRightSymmmetry:coupHtautau");
342 
343  // Store H_L/R mass and width for propagator.
344  mRes = particleDataPtr->m0(idHLR);
345  GammaRes = particleDataPtr->mWidth(idHLR);
346  m2Res = mRes*mRes;
347  GamMRat = GammaRes / mRes;
348 
349  // Set pointer to particle properties and decay table.
350  particlePtr = particleDataPtr->particleDataEntryPtr(idHLR);
351 
352 }
353 
354 //--------------------------------------------------------------------------
355 
356 // Evaluate sigmaHat(sHat), including incoming flavour dependence.
357 
358 double Sigma1ll2Hchgchg::sigmaHat() {
359 
360  // Initial state must consist of two identical-sign leptons.
361  if (id1 * id2 < 0) return 0.;
362  int id1Abs = abs(id1);
363  int id2Abs = abs(id2);
364  if (id1Abs != 11 && id1Abs != 13 && id1Abs != 15) return 0.;
365  if (id2Abs != 11 && id2Abs != 13 && id2Abs != 15) return 0.;
366 
367  // Set up Breit-Wigner, inwidth and outwidth.
368  double sigBW = 8. * M_PI / ( pow2(sH - m2Res) + pow2(sH * GamMRat) );
369  double widIn = pow2(yukawa[(id1Abs-9)/2][(id2Abs-9)/2])
370  * mH / (8. * M_PI);
371  int idSgn = (id1 < 0) ? idHLR : -idHLR;
372  double widOut = particlePtr->resWidthOpen( idSgn, mH);
373 
374  // Answer.
375  return widIn * sigBW * widOut;
376 
377 }
378 
379 //--------------------------------------------------------------------------
380 
381 // Select identity, colour and anticolour.
382 
383 void Sigma1ll2Hchgchg::setIdColAcol() {
384 
385  // Sign of outgoing H_L/R.
386  int idSgn = (id1 < 0) ? idHLR : -idHLR;
387  setId( id1, id2, idSgn);
388 
389  // No colours whatsoever.
390  setColAcol( 0, 0, 0, 0, 0, 0);
391 
392 }
393 
394 //--------------------------------------------------------------------------
395 
396 // Evaluate weight for H_L/R sequential decay angles.
397 
398 double Sigma1ll2Hchgchg::weightDecay( Event& process, int iResBeg,
399  int iResEnd) {
400 
401  // Identity of mother of decaying reseonance(s).
402  int idMother = process[process[iResBeg].mother1()].idAbs();
403 
404  // For top decay hand over to standard routine.
405  if (idMother == 6)
406  return weightTopDecay( process, iResBeg, iResEnd);
407 
408  // Else isotropic decay.
409  return 1.;
410 
411 }
412 
413 //==========================================================================
414 
415 // Sigma2lgm2Hchgchgl class.
416 // Cross section for l gamma -> H_L^++-- l or H_R^++-- l
417 // (doubly charged Higgs).
418 
419 //--------------------------------------------------------------------------
420 
421 // Initialize process.
422 
423 void Sigma2lgm2Hchgchgl::initProc() {
424 
425  // Set process properties: H_L^++-- or H_R^++-- and e/mu/tau.
426  idHLR = (leftRight == 1) ? 9900041 : 9900042;
427  codeSave = (leftRight == 1) ? 3122 : 3142;
428  if (idLep == 13) codeSave += 1;
429  if (idLep == 15) codeSave += 2;
430  if (codeSave == 3122) nameSave = "l^+- gamma -> H_L^++-- e^-+";
431  else if (codeSave == 3123) nameSave = "l^+- gamma -> H_L^++-- mu^-+";
432  else if (codeSave == 3124) nameSave = "l^+- gamma -> H_L^++-- tau^-+";
433  else if (codeSave == 3142) nameSave = "l^+- gamma -> H_R^++-- e^-+";
434  else if (codeSave == 3143) nameSave = "l^+- gamma -> H_R^++-- mu^-+";
435  else nameSave = "l^+- gamma -> H_R^++-- tau^-+";
436 
437  // Read in relevantYukawa matrix for couplings to a lepton pair.
438  if (idLep == 11) {
439  yukawa[1] = parm("LeftRightSymmmetry:coupHee");
440  yukawa[2] = parm("LeftRightSymmmetry:coupHmue");
441  yukawa[3] = parm("LeftRightSymmmetry:coupHtaue");
442  } else if (idLep == 13) {
443  yukawa[1] = parm("LeftRightSymmmetry:coupHmue");
444  yukawa[2] = parm("LeftRightSymmmetry:coupHmumu");
445  yukawa[3] = parm("LeftRightSymmmetry:coupHtaumu");
446  } else {
447  yukawa[1] = parm("LeftRightSymmmetry:coupHtaue");
448  yukawa[2] = parm("LeftRightSymmmetry:coupHtaumu");
449  yukawa[3] = parm("LeftRightSymmmetry:coupHtautau");
450  }
451 
452  // Secondary open width fractions.
453  openFracPos = particleDataPtr->resOpenFrac( idHLR);
454  openFracNeg = particleDataPtr->resOpenFrac(-idHLR);
455 
456 }
457 
458 //--------------------------------------------------------------------------
459 
460 // Evaluate sigmaHat(sHat), including incoming flavour dependence.
461 
462 double Sigma2lgm2Hchgchgl::sigmaHat() {
463 
464  // Initial state must consist of a lepton and a photon.
465  int idIn = (id2 == 22) ? id1 : id2;
466  int idInAbs = abs(idIn);
467  if (idInAbs != 11 && idInAbs != 13 && idInAbs != 15) return 0.;
468 
469  // Incoming squared lepton mass.
470  double s1 = pow2( particleDataPtr->m0(idInAbs) );
471 
472  // Kinematical expressions.
473  double smm1 = 8. * (sH + tH - s3) * (sH + tH - 2. * s3 - s1 - s4)
474  / pow2(uH - s3);
475  double smm2 = 2. * ( (2. * s3 - 3. * s1) * s4 + (s1 - 2. * s4) * tH
476  - (tH - s4) * sH ) / pow2(tH - s4);
477  double smm3 = 2. * ( (2. * s3 - 3. * s4 + tH) * s1
478  - (2. * s1 - s4 + tH) * sH ) / pow2(sH - s1);
479  double smm12 = 4. * ( (2. * s1 - s4 - 2. * s3 + tH) * sH
480  + (tH - 3. * s3 - 3. * s4) * tH + (2. * s3 - 2. * s1
481  + 3. * s4) * s3 ) / ( (uH - s3) * (tH - s4) );
482  double smm13 = -4. * ( (tH + s1 - 2. * s4) * tH - (s3 + 3. * s1 - 2. * s4)
483  * s3 + (s3 + 3. * s1 + tH) * sH - pow2(tH - s3 + sH) )
484  / ( (uH - s3) * (sH - s1) );
485  double smm23 = -4. * ( (s1 - s4 + s3) * tH - s3*s3 + s3 * (s1 + s4)
486  - 3. * s1 * s4 - (s1 - s4 - s3 + tH) * sH)
487  / ( (sH - s1) * (tH - s4) );
488  double sigma = alpEM * pow2(sH / (sH - s1) ) * (smm1 + smm2 + smm3
489  + smm12 + smm13 + smm23) / (4. * sH2);
490 
491  // Lepton Yukawa and secondary widths.
492  sigma *= pow2(yukawa[(idInAbs-9)/2]);
493  sigma *= (idIn < 0) ? openFracPos : openFracNeg;
494 
495  // Answer.
496  return sigma;
497 
498 }
499 
500 //--------------------------------------------------------------------------
501 
502 // Select identity, colour and anticolour.
503 
504 void Sigma2lgm2Hchgchgl::setIdColAcol() {
505 
506  // Sign of outgoing H_L/R.
507  int idIn = (id2 == 22) ? id1 : id2;
508  int idSgn = (idIn < 0) ? idHLR : -idHLR;
509  int idOut = (idIn < 0) ? idLep : -idLep;
510  setId( id1, id2, idSgn, idOut);
511 
512  // tHat is defined between incoming lepton and outgoing Higgs.
513  if (id1 == 22) swapTU = true;
514 
515  // No colours whatsoever.
516  setColAcol( 0, 0, 0, 0, 0, 0, 0, 0);
517 
518 }
519 
520 //--------------------------------------------------------------------------
521 
522 // Evaluate weight for H_L/R sequential decay angles.
523 
524 double Sigma2lgm2Hchgchgl::weightDecay( Event& process, int iResBeg,
525  int iResEnd) {
526 
527  // Identity of mother of decaying reseonance(s).
528  int idMother = process[process[iResBeg].mother1()].idAbs();
529 
530  // For top decay hand over to standard routine.
531  if (idMother == 6)
532  return weightTopDecay( process, iResBeg, iResEnd);
533 
534  // Else isotropic decay.
535  return 1.;
536 
537 }
538 
539 //==========================================================================
540 
541 // Sigma3ff2HchgchgfftWW class.
542 // Cross section for f_1 f_2 -> H_(L/R)^++-- f_3 f_4 (W+- W+- fusion).
543 
544 //--------------------------------------------------------------------------
545 
546 // Initialize process.
547 
548 void Sigma3ff2HchgchgfftWW::initProc() {
549 
550  // Set process properties: H_L^++-- or H_R^++--.
551  if (leftRight == 1) {
552  idHLR = 9900041;
553  codeSave = 3125;
554  nameSave = "f_1 f_2 -> H_L^++-- f_3 f_4 (W+- W+- fusion)";
555  } else {
556  idHLR = 9900042;
557  codeSave = 3145;
558  nameSave = "f_1 f_2 -> H_R^++-- f_3 f_4 (W+- W+- fusion)";
559  }
560 
561  // Common fixed mass and coupling factor.
562  double mW = particleDataPtr->m0(24);
563  double mWR = particleDataPtr->m0(9900024);
564  mWS = (leftRight == 1) ? pow2(mW) : pow2(mWR);
565  double gL = parm("LeftRightSymmmetry:gL");
566  double gR = parm("LeftRightSymmmetry:gR");
567  double vL = parm("LeftRightSymmmetry:vL");
568  prefac = (leftRight == 1) ? pow2(pow4(gL) * vL)
569  : 2. * pow2(pow3(gR) * mWR);
570  // Secondary open width fractions.
571  openFracPos = particleDataPtr->resOpenFrac( idHLR);
572  openFracNeg = particleDataPtr->resOpenFrac(-idHLR);
573 
574 }
575 
576 //--------------------------------------------------------------------------
577 
578 // Evaluate sigmaHat(sHat), part independent of incoming flavour.
579 
580 void Sigma3ff2HchgchgfftWW::sigmaKin() {
581 
582  // Required four-vector products.
583  double pp12 = 0.5 * sH;
584  double pp14 = 0.5 * mH * p4cm.pNeg();
585  double pp15 = 0.5 * mH * p5cm.pNeg();
586  double pp24 = 0.5 * mH * p4cm.pPos();
587  double pp25 = 0.5 * mH * p5cm.pPos();
588  double pp45 = p4cm * p5cm;
589 
590  // Cross section: kinematics part. Combine with couplings.
591  double propT = 1. / ( (2. * pp14 + mWS) * (2. * pp25 + mWS) );
592  double propU = 1. / ( (2. * pp24 + mWS) * (2. * pp15 + mWS) );
593  sigma0TU = prefac * pp12 * pp45 * pow2(propT + propU);
594  sigma0T = prefac * pp12 * pp45 * 2. * pow2(propT);
595 
596 }
597 
598 //--------------------------------------------------------------------------
599 
600 // Evaluate sigmaHat(sHat), including incoming flavour dependence.
601 
602 double Sigma3ff2HchgchgfftWW::sigmaHat() {
603 
604  // Do not allow creation of righthanded neutrinos for H_R.
605  int id1Abs = abs(id1);
606  int id2Abs = abs(id2);
607  if ( leftRight == 2 && (id1Abs > 10 || id2Abs > 10) ) return 0.;
608 
609  // Many flavour combinations not possible because of charge.
610  int chg1 = (( id1Abs%2 == 0 && id1 > 0)
611  || (id1Abs%2 == 1 && id1 < 0) ) ? 1 : -1;
612  int chg2 = (( id2Abs%2 == 0 && id2 > 0)
613  || (id2Abs%2 == 1 && id2 < 0) ) ? 1 : -1;
614  if (abs(chg1 + chg2) != 2) return 0.;
615 
616  // Basic cross section. CKM factors for final states.
617  double sigma = (id2 == id1 && id1Abs > 10) ? sigma0TU : sigma0T;
618  sigma *= coupSMPtr->V2CKMsum(id1Abs)
619  * coupSMPtr->V2CKMsum(id2Abs);
620 
621  // Secondary width for H0.
622  sigma *= (chg1 + chg2 == 2) ? openFracPos : openFracNeg;
623 
624  // Spin-state extra factor 2 per incoming neutrino.
625  if (id1Abs == 12 || id1Abs == 14 || id1Abs == 16) sigma *= 2.;
626  if (id2Abs == 12 || id2Abs == 14 || id2Abs == 16) sigma *= 2.;
627 
628  // Answer.
629  return sigma;
630 
631 }
632 
633 //--------------------------------------------------------------------------
634 
635 // Select identity, colour and anticolour.
636 
637 void Sigma3ff2HchgchgfftWW::setIdColAcol() {
638 
639  // Pick out-flavours by relative CKM weights.
640  int id1Abs = abs(id1);
641  int id2Abs = abs(id2);
642  id4 = coupSMPtr->V2CKMpick(id1);
643  id5 = coupSMPtr->V2CKMpick(id2);
644 
645  // Find charge of Higgs .
646  id3 = (( id1Abs%2 == 0 && id1 > 0) || (id1Abs%2 == 1 && id1 < 0) )
647  ? idHLR : -idHLR;
648  setId( id1, id2, id3, id4, id5);
649 
650  // Colour flow topologies. Swap when antiquarks.
651  if (id1Abs < 9 && id2Abs < 9 && id1*id2 > 0)
652  setColAcol( 1, 0, 2, 0, 0, 0, 1, 0, 2, 0);
653  else if (id1Abs < 9 && id2Abs < 9)
654  setColAcol( 1, 0, 0, 2, 0, 0, 1, 0, 0, 2);
655  else if (id1Abs < 9) setColAcol( 1, 0, 0, 0, 0, 0, 1, 0, 0, 0);
656  else if (id2Abs < 9) setColAcol( 0, 0, 1, 0, 0, 0, 0, 0, 1, 0);
657  else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
658  if ( (id1Abs < 9 && id1 < 0) || (id1Abs > 10 && id2 < 0) )
659  swapColAcol();
660 
661 }
662 
663 //--------------------------------------------------------------------------
664 
665 // Evaluate weight for decay angles.
666 
667 double Sigma3ff2HchgchgfftWW::weightDecay( Event& process, int iResBeg,
668  int iResEnd) {
669 
670  // Identity of mother of decaying reseonance(s).
671  int idMother = process[process[iResBeg].mother1()].idAbs();
672 
673  // For top decay hand over to standard routine.
674  if (idMother == 6)
675  return weightTopDecay( process, iResBeg, iResEnd);
676 
677  // Else done.
678  return 1.;
679 
680 }
681 
682 //==========================================================================
683 
684 // Sigma2ffbar2HchgchgHchgchg class.
685 // Cross section for f fbar -> H_(L/R)^++ H_(L/R)^-- (doubly charged Higgs).
686 
687 //--------------------------------------------------------------------------
688 
689 // Initialize process.
690 
691 void Sigma2ffbar2HchgchgHchgchg::initProc() {
692 
693  // Set process properties: H_L^++ H_L^-- or H_R^++ H_R^--.
694  if (leftRight == 1) {
695  idHLR = 9900041;
696  codeSave = 3126;
697  nameSave = "f fbar -> H_L^++ H_L^--";
698  } else {
699  idHLR = 9900042;
700  codeSave = 3146;
701  nameSave = "f fbar -> H_R^++ H_R^--";
702  }
703 
704  // Read in Yukawa matrix for couplings to a lepton pair.
705  yukawa[1][1] = parm("LeftRightSymmmetry:coupHee");
706  yukawa[2][1] = parm("LeftRightSymmmetry:coupHmue");
707  yukawa[2][2] = parm("LeftRightSymmmetry:coupHmumu");
708  yukawa[3][1] = parm("LeftRightSymmmetry:coupHtaue");
709  yukawa[3][2] = parm("LeftRightSymmmetry:coupHtaumu");
710  yukawa[3][3] = parm("LeftRightSymmmetry:coupHtautau");
711 
712  // Electroweak parameters.
713  mRes = particleDataPtr->m0(23);
714  GammaRes = particleDataPtr->mWidth(23);
715  m2Res = mRes*mRes;
716  GamMRat = GammaRes / mRes;
717  sin2tW = coupSMPtr->sin2thetaW();
718  preFac = (1. - 2. * sin2tW) / ( 8. * sin2tW * (1. - sin2tW) );
719 
720  // Open fraction from secondary widths.
721  openFrac = particleDataPtr->resOpenFrac( idHLR, -idHLR);
722 
723 }
724 
725 //--------------------------------------------------------------------------
726 
727 // Evaluate sigmaHat(sHat), including incoming flavour dependence.
728 
729 double Sigma2ffbar2HchgchgHchgchg::sigmaHat() {
730 
731  // Electroweak couplings to gamma^*/Z^0.
732  int idAbs = abs(id1);
733  double ei = coupSMPtr->ef(idAbs);
734  double vi = coupSMPtr->vf(idAbs);
735  double ai = coupSMPtr->af(idAbs);
736 
737  // Part via gamma^*/Z^0 propagator. No Z^0 coupling to H_R.
738  double resProp = 1. / ( pow2(sH - m2Res) + pow2(sH * GamMRat) );
739  double sigma = 8. * pow2(alpEM) * ei*ei / sH2;
740  if (leftRight == 1) sigma += 8. * pow2(alpEM)
741  * (2. * ei * vi * preFac * (sH - m2Res) * resProp / sH
742  + (vi * vi + ai * ai) * pow2(preFac) * resProp);
743 
744  // Part via t-channel lepton + interference; sum over possibilities.
745  if (idAbs == 11 || idAbs == 13 || idAbs == 15) {
746  double yuk2Sum;
747  if (idAbs == 11) yuk2Sum
748  = pow2(yukawa[1][1]) + pow2(yukawa[2][1]) + pow2(yukawa[3][1]);
749  else if (idAbs == 13) yuk2Sum
750  = pow2(yukawa[2][1]) + pow2(yukawa[2][2]) + pow2(yukawa[3][2]);
751  else yuk2Sum
752  = pow2(yukawa[3][1]) + pow2(yukawa[3][2]) + pow2(yukawa[3][3]);
753  yuk2Sum /= 4. * M_PI;
754  sigma += 8. * alpEM * ei * yuk2Sum / (sH * tH)
755  + 4. * pow2(yuk2Sum) / tH2;
756  if (leftRight == 1) sigma += 8. * alpEM * (vi + ai) * yuk2Sum
757  * preFac * (sH - m2Res) * resProp / tH;
758  }
759 
760  // Common kinematical factor. Colour factor.
761  sigma *= M_PI * (tH * uH - s3 * s4) / sH2;
762  if (idAbs < 9) sigma /= 3.;
763 
764  // Answer.
765  return sigma;
766 
767 }
768 
769 //--------------------------------------------------------------------------
770 
771 // Select identity, colour and anticolour.
772 
773 void Sigma2ffbar2HchgchgHchgchg::setIdColAcol() {
774 
775  // Outgoing flavours trivial.
776  setId( id1, id2, idHLR, -idHLR);
777 
778  // tHat is defined between incoming fermion and outgoing H--.
779  if (id1 > 0) swapTU = true;
780 
781  // No colours at all or one flow topology. Swap if first is antiquark.
782  if (abs(id1) < 9) setColAcol( 1, 0, 0, 1, 0, 0, 0, 0);
783  else setColAcol( 0, 0, 0, 0, 0, 0, 0, 0);
784  if (id1 < 0) swapColAcol();
785 
786 }
787 
788 //--------------------------------------------------------------------------
789 
790 // Evaluate weight for H_L/R sequential decay angles.
791 
792 double Sigma2ffbar2HchgchgHchgchg::weightDecay( Event& process,
793  int iResBeg, int iResEnd) {
794 
795  // Identity of mother of decaying reseonance(s).
796  int idMother = process[process[iResBeg].mother1()].idAbs();
797 
798  // For top decay hand over to standard routine.
799  if (idMother == 6)
800  return weightTopDecay( process, iResBeg, iResEnd);
801 
802  // Else isotropic decay.
803  return 1.;
804 
805 }
806 
807 //==========================================================================
808 
809 } // end namespace Pythia8
Event
Definition: AgUStep.h:26
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