1 // SigmaProcess.cc is a part of the PYTHIA event generator.
2 // Copyright (C) 2012 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.
6 // Function definitions (not found in the header) for the
7 // SigmaProcess class, and classes derived from it.
9 #include "SigmaProcess.h"
13 //==========================================================================
15 // The SigmaProcess class.
16 // Base class for cross sections.
18 //--------------------------------------------------------------------------
20 // Constants: could be changed here if desired, but normally should not.
21 // These are of technical nature, as described for each.
23 // Conversion of GeV^{-2} to mb for cross section.
24 const double SigmaProcess::CONVERT2MB = 0.389380;
26 // The sum of outgoing masses must not be too close to the cm energy.
27 const double SigmaProcess::MASSMARGIN = 0.1;
29 // Parameters of momentum rescaling procedure: maximally allowed
30 // relative energy error and number of iterations.
31 const double SigmaProcess::COMPRELERR = 1e-10;
32 const int SigmaProcess::NCOMPSTEP = 10;
34 //--------------------------------------------------------------------------
36 // Perform simple initialization and store pointers.
38 void SigmaProcess::init(Info* infoPtrIn, Settings* settingsPtrIn,
39 ParticleData* particleDataPtrIn, Rndm* rndmPtrIn, BeamParticle* beamAPtrIn,
40 BeamParticle* beamBPtrIn, Couplings* couplingsPtrIn,
41 SigmaTotal* sigmaTotPtrIn, SusyLesHouches* slhaPtrIn) {
45 settingsPtr = settingsPtrIn;
46 particleDataPtr = particleDataPtrIn;
48 beamAPtr = beamAPtrIn;
49 beamBPtr = beamBPtrIn;
50 couplingsPtr = couplingsPtrIn;
51 sigmaTotPtr = sigmaTotPtrIn;
54 // Read out some properties of beams to allow shorthand.
55 idA = (beamAPtr != 0) ? beamAPtr->id() : 0;
56 idB = (beamBPtr != 0) ? beamBPtr->id() : 0;
57 mA = (beamAPtr != 0) ? beamAPtr->m() : 0.;
58 mB = (beamBPtr != 0) ? beamBPtr->m() : 0.;
59 isLeptonA = (beamAPtr != 0) ? beamAPtr->isLepton() : false;
60 isLeptonB = (beamBPtr != 0) ? beamBPtr->isLepton() : false;
61 hasLeptonBeams = isLeptonA || isLeptonB;
63 // K factor, multiplying resolved processes. (But not here for MPI.)
64 Kfactor = settingsPtr->parm("SigmaProcess:Kfactor");
66 // Maximum incoming quark flavour.
67 nQuarkIn = settingsPtr->mode("PDFinProcess:nQuarkIn");
69 // Medium heavy fermion masses set massless or not in ME expressions.
70 mcME = (settingsPtr->flag("SigmaProcess:cMassiveME"))
71 ? particleDataPtr->m0(4) : 0.;
72 mbME = (settingsPtr->flag("SigmaProcess:bMassiveME"))
73 ? particleDataPtr->m0(5) : 0.;
74 mmuME = (settingsPtr->flag("SigmaProcess:muMassiveME"))
75 ? particleDataPtr->m0(13) : 0.;
76 mtauME = (settingsPtr->flag("SigmaProcess:tauMassiveME"))
77 ? particleDataPtr->m0(15) : 0.;
79 // Renormalization scale choice.
80 renormScale1 = settingsPtr->mode("SigmaProcess:renormScale1");
81 renormScale2 = settingsPtr->mode("SigmaProcess:renormScale2");
82 renormScale3 = settingsPtr->mode("SigmaProcess:renormScale3");
83 renormScale3VV = settingsPtr->mode("SigmaProcess:renormScale3VV");
84 renormMultFac = settingsPtr->parm("SigmaProcess:renormMultFac");
85 renormFixScale = settingsPtr->parm("SigmaProcess:renormFixScale");
87 // Factorization scale choice.
88 factorScale1 = settingsPtr->mode("SigmaProcess:factorScale1");
89 factorScale2 = settingsPtr->mode("SigmaProcess:factorScale2");
90 factorScale3 = settingsPtr->mode("SigmaProcess:factorScale3");
91 factorScale3VV = settingsPtr->mode("SigmaProcess:factorScale3VV");
92 factorMultFac = settingsPtr->parm("SigmaProcess:factorMultFac");
93 factorFixScale = settingsPtr->parm("SigmaProcess:factorFixScale");
95 // CP violation parameters for the BSM Higgs sector.
96 higgsH1parity = settingsPtr->mode("HiggsH1:parity");
97 higgsH1eta = settingsPtr->parm("HiggsH1:etaParity");
98 higgsH2parity = settingsPtr->mode("HiggsH2:parity");
99 higgsH2eta = settingsPtr->parm("HiggsH2:etaParity");
100 higgsA3parity = settingsPtr->mode("HiggsA3:parity");
101 higgsA3eta = settingsPtr->parm("HiggsA3:etaParity");
103 // If BSM not switched on then H1 should have SM properties.
104 if (!settingsPtr->flag("Higgs:useBSM")){
111 //--------------------------------------------------------------------------
113 // Set up allowed flux of incoming partons.
114 // addBeam: set up PDF's that need to be evaluated for the two beams.
115 // addPair: set up pairs of incoming partons from the two beams.
117 bool SigmaProcess::initFlux() {
119 // Reset arrays (in case of several init's in same run).
124 // Read in process-specific channel information.
125 string fluxType = inFlux();
127 // Case with g g incoming state.
128 if (fluxType == "gg") {
134 // Case with q g incoming state.
135 else if (fluxType == "qg") {
136 for (int i = -nQuarkIn; i <= nQuarkIn; ++i) {
137 int idNow = (i == 0) ? 21 : i;
141 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
148 // Case with q q', q qbar' or qbar qbar' incoming state.
149 else if (fluxType == "qq") {
150 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
155 for (int id1Now = -nQuarkIn; id1Now <= nQuarkIn; ++id1Now)
157 for (int id2Now = -nQuarkIn; id2Now <= nQuarkIn; ++id2Now)
159 addPair(id1Now, id2Now);
162 // Case with q qbar incoming state.
163 else if (fluxType == "qqbarSame") {
164 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
169 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
171 addPair(idNow, -idNow);
174 // Case with f f', f fbar', fbar fbar' incoming state.
175 else if (fluxType == "ff") {
176 // If beams are leptons then they are also the colliding partons.
177 if ( isLeptonA && isLeptonB ) {
181 // First beam is lepton and second is hadron.
182 } else if ( isLeptonA ) {
184 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
189 // First beam is hadron and second is lepton.
190 } else if ( isLeptonB ) {
192 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
197 // Hadron beams gives quarks.
199 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
204 for (int id1Now = -nQuarkIn; id1Now <= nQuarkIn; ++id1Now)
206 for (int id2Now = -nQuarkIn; id2Now <= nQuarkIn; ++id2Now)
208 addPair(id1Now, id2Now);
212 // Case with f fbar incoming state.
213 else if (fluxType == "ffbarSame") {
214 // If beams are antiparticle pair and leptons then also colliding partons.
215 if ( idA + idB == 0 && isLeptonA ) {
219 // Else assume both to be hadrons, for better or worse.
221 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
226 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
228 addPair(idNow, -idNow);
232 // Case with f fbar' charged(+-1) incoming state.
233 else if (fluxType == "ffbarChg") {
234 // If beams are leptons then also colliding partons.
235 if ( isLeptonA && isLeptonB && abs( particleDataPtr->chargeType(idA)
236 + particleDataPtr->chargeType(idB) ) == 3 ) {
240 // Hadron beams gives quarks.
242 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
247 for (int id1Now = -nQuarkIn; id1Now <= nQuarkIn; ++id1Now)
249 for (int id2Now = -nQuarkIn; id2Now <= nQuarkIn; ++id2Now)
250 if (id2Now != 0 && id1Now * id2Now < 0
251 && (abs(id1Now) + abs(id2Now))%2 == 1) addPair(id1Now, id2Now);
255 // Case with f fbar' generic incoming state.
256 else if (fluxType == "ffbar") {
257 // If beams are leptons then also colliding partons.
258 if (isLeptonA && isLeptonB && idA * idB < 0) {
262 // Hadron beams gives quarks.
264 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
269 for (int id1Now = -nQuarkIn; id1Now <= nQuarkIn; ++id1Now)
271 for (int id2Now = -nQuarkIn; id2Now <= nQuarkIn; ++id2Now)
272 if (id2Now != 0 && id1Now * id2Now < 0)
273 addPair(id1Now, id2Now);
277 // Case with f gamma incoming state.
278 else if (fluxType == "fgm") {
279 // Fermion from incoming side A.
284 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
290 // Fermion from incoming side B.
295 for (int idNow = -nQuarkIn; idNow <= nQuarkIn; ++idNow)
301 // Photons in the beams.
306 // Case with gamma gamma incoming state.
307 else if (fluxType == "ggm") {
316 // Case with gamma gamma incoming state.
317 else if (fluxType == "gmgm") {
323 // Unrecognized fluxType is bad sign. Else done.
325 infoPtr->errorMsg("Error in SigmaProcess::initFlux: "
326 "unrecognized inFlux type", fluxType);
333 //--------------------------------------------------------------------------
335 // Convolute matrix-element expression(s) with parton flux and K factor.
337 double SigmaProcess::sigmaPDF() {
339 // Evaluate and store the required parton densities.
340 for (int j = 0; j < sizeBeamA(); ++j)
341 inBeamA[j].pdf = beamAPtr->xfHard( inBeamA[j].id, x1Save, Q2FacSave);
342 for (int j = 0; j < sizeBeamB(); ++j)
343 inBeamB[j].pdf = beamBPtr->xfHard( inBeamB[j].id, x2Save, Q2FacSave);
345 // Loop over allowed incoming channels.
347 for (int i = 0; i < sizePair(); ++i) {
349 // Evaluate hard-scattering cross section. Include K factor.
350 inPair[i].pdfSigma = Kfactor
351 * sigmaHatWrap(inPair[i].idA, inPair[i].idB);
353 // Multiply by respective parton densities.
354 for (int j = 0; j < sizeBeamA(); ++j)
355 if (inPair[i].idA == inBeamA[j].id) {
356 inPair[i].pdfA = inBeamA[j].pdf;
357 inPair[i].pdfSigma *= inBeamA[j].pdf;
360 for (int j = 0; j < sizeBeamB(); ++j)
361 if (inPair[i].idB == inBeamB[j].id) {
362 inPair[i].pdfB = inBeamB[j].pdf;
363 inPair[i].pdfSigma *= inBeamB[j].pdf;
367 // Sum for all channels.
368 sigmaSumSave += inPair[i].pdfSigma;
376 //--------------------------------------------------------------------------
378 // Select incoming parton channel and extract parton densities (resolved).
380 void SigmaProcess::pickInState(int id1in, int id2in) {
382 // Multiparton interactions: partons already selected.
383 if (id1in != 0 && id2in != 0) {
388 // Pick channel. Extract channel flavours and pdf's.
389 double sigmaRand = sigmaSumSave * rndmPtr->flat();
390 for (int i = 0; i < sizePair(); ++i) {
391 sigmaRand -= inPair[i].pdfSigma;
392 if (sigmaRand <= 0.) {
395 pdf1Save = inPair[i].pdfA;
396 pdf2Save = inPair[i].pdfB;
403 //--------------------------------------------------------------------------
405 // Calculate incoming modified masses and four-vectors for matrix elements.
407 bool SigmaProcess::setupForMEin() {
409 // Initially assume it will work out to set up modified kinematics.
412 // Correct incoming c, b, mu and tau to be massive or not.
414 int id1Tmp = abs(id1);
415 if (id1Tmp == 4) mME[0] = mcME;
416 if (id1Tmp == 5) mME[0] = mbME;
417 if (id1Tmp == 13) mME[0] = mmuME;
418 if (id1Tmp == 15) mME[0] = mtauME;
420 int id2Tmp = abs(id2);
421 if (id2Tmp == 4) mME[1] = mcME;
422 if (id2Tmp == 5) mME[1] = mbME;
423 if (id2Tmp == 13) mME[1] = mmuME;
424 if (id2Tmp == 15) mME[1] = mtauME;
426 // If kinematically impossible return to massless case, but set error.
427 if (mME[0] + mME[1] >= mH) {
433 // Do incoming two-body kinematics for massless or massive cases.
434 if (mME[0] == 0. && mME[1] == 0.) {
435 pME[0] = 0.5 * mH * Vec4( 0., 0., 1., 1.);
436 pME[1] = 0.5 * mH * Vec4( 0., 0., -1., 1.);
438 double e0 = 0.5 * (mH * mH + mME[0] * mME[0] - mME[1] * mME[1]) / mH;
439 double pz0 = sqrtpos(e0 * e0 - mME[0] * mME[0]);
440 pME[0] = Vec4( 0., 0., pz0, e0);
441 pME[1] = Vec4( 0., 0., -pz0, mH - e0);
449 //--------------------------------------------------------------------------
451 // Evaluate weight for W decay distribution in t -> W b -> f fbar b.
453 double SigmaProcess::weightTopDecay( Event& process, int iResBeg,
456 // If not pair W d/s/b and mother t then return unit weight.
457 if (iResEnd - iResBeg != 1) return 1.;
459 int iB2 = iResBeg + 1;
460 int idW1 = process[iW1].idAbs();
461 int idB2 = process[iB2].idAbs();
466 if (idW1 != 24 || (idB2 != 1 && idB2 != 3 && idB2 != 5)) return 1.;
467 int iT = process[iW1].mother1();
468 if (iT <= 0 || process[iT].idAbs() != 6) return 1.;
470 // Find sign-matched order of W decay products.
471 int iF = process[iW1].daughter1();
472 int iFbar = process[iW1].daughter2();
473 if (iFbar - iF != 1) return 1.;
474 if (process[iT].id() * process[iF].id() < 0) swap(iF, iFbar);
476 // Weight and maximum weight.
477 double wt = (process[iT].p() * process[iFbar].p())
478 * (process[iF].p() * process[iB2].p());
479 double wtMax = ( pow4(process[iT].m()) - pow4(process[iW1].m()) ) / 8.;
486 //--------------------------------------------------------------------------
488 // Evaluate weight for Z0/W+- decay distributions in H -> Z0/W+ Z0/W- -> 4f
489 // and H -> gamma Z0 -> gamma f fbar.
491 double SigmaProcess::weightHiggsDecay( Event& process, int iResBeg,
494 // If not pair Z0 Z0, W+ W- or gamma Z0 then return unit weight.
495 if (iResEnd - iResBeg != 1) return 1.;
497 int iZW2 = iResBeg + 1;
498 int idZW1 = process[iZW1].id();
499 int idZW2 = process[iZW2].id();
500 if (idZW1 < 0 || idZW2 == 22) {
504 if ( (idZW1 != 23 || idZW2 != 23) && (idZW1 != 24 || idZW2 != -24)
505 && (idZW1 != 22 || idZW2 != 23) ) return 1.;
507 // If mother is not Higgs then return unit weight.
508 int iH = process[iZW1].mother1();
509 if (iH <= 0) return 1.;
510 int idH = process[iH].id();
511 if (idH != 25 && idH != 35 && idH !=36) return 1.;
513 // H -> gamma Z0 -> gamma f fbar is 1 + cos^2(theta) in Z rest frame.
515 int i5 = process[iZW2].daughter1();
516 int i6 = process[iZW2].daughter2();
517 double pgmZ = process[iZW1].p() * process[iZW2].p();
518 double pgm5 = process[iZW1].p() * process[i5].p();
519 double pgm6 = process[iZW1].p() * process[i6].p();
520 return (pow2(pgm5) + pow2(pgm6)) / pow2(pgmZ);
523 // Parameters depend on Higgs type: H0(H_1), H^0(H_2) or A^0(H_3).
524 int higgsParity = higgsH1parity;
525 double higgsEta = higgsH1eta;
527 higgsParity = higgsH2parity;
528 higgsEta = higgsH2eta;
529 } else if (idH == 36) {
530 higgsParity = higgsA3parity;
531 higgsEta = higgsA3eta;
534 // Option with isotropic decays.
535 if (higgsParity == 0) return 1.;
537 // Maximum and initial weight.
538 double wtMax = pow4(process[iH].m());
541 // Find sign-matched order of Z0/W+- decay products.
542 int i3 = process[iZW1].daughter1();
543 int i4 = process[iZW1].daughter2();
544 if (process[i3].id() < 0) swap( i3, i4);
545 int i5 = process[iZW2].daughter1();
546 int i6 = process[iZW2].daughter2();
547 if (process[i5].id() < 0) swap( i5, i6);
549 // Evaluate four-vector products and find masses..
550 double p35 = 2. * process[i3].p() * process[i5].p();
551 double p36 = 2. * process[i3].p() * process[i6].p();
552 double p45 = 2. * process[i4].p() * process[i5].p();
553 double p46 = 2. * process[i4].p() * process[i6].p();
554 double p34 = 2. * process[i3].p() * process[i4].p();
555 double p56 = 2. * process[i5].p() * process[i6].p();
556 double mZW1 = process[iZW1].m();
557 double mZW2 = process[iZW2].m();
559 // For mixed CP states need epsilon product and gauge boson masses.
560 double epsilonProd = 0.;
561 if (higgsParity == 3) {
563 for (int i = 0; i < 4; ++i) {
568 p[i][0] = process[ii].e();
569 p[i][1] = process[ii].px();
570 p[i][2] = process[ii].py();
571 p[i][3] = process[ii].pz();
574 = p[0][0]*p[1][1]*p[2][2]*p[3][3] - p[0][0]*p[1][1]*p[2][3]*p[3][2]
575 - p[0][0]*p[1][2]*p[2][1]*p[3][3] + p[0][0]*p[1][2]*p[2][3]*p[3][1]
576 + p[0][0]*p[1][3]*p[2][1]*p[3][2] - p[0][0]*p[1][3]*p[2][2]*p[3][1]
577 - p[0][1]*p[1][0]*p[2][2]*p[3][3] + p[0][1]*p[1][0]*p[2][3]*p[3][2]
578 + p[0][1]*p[1][2]*p[2][0]*p[3][3] - p[0][1]*p[1][2]*p[2][3]*p[3][0]
579 - p[0][1]*p[1][3]*p[2][0]*p[3][2] + p[0][1]*p[1][3]*p[2][2]*p[3][0]
580 + p[0][2]*p[1][0]*p[2][1]*p[3][3] - p[0][2]*p[1][0]*p[2][3]*p[3][1]
581 - p[0][2]*p[1][1]*p[2][0]*p[3][3] + p[0][2]*p[1][1]*p[2][3]*p[3][0]
582 + p[0][2]*p[1][3]*p[2][0]*p[3][1] - p[0][2]*p[1][3]*p[2][1]*p[3][0]
583 - p[0][3]*p[1][0]*p[2][1]*p[3][2] + p[0][3]*p[1][0]*p[2][2]*p[3][1]
584 + p[0][3]*p[1][1]*p[2][0]*p[3][2] - p[0][3]*p[1][1]*p[2][2]*p[3][0]
585 - p[0][3]*p[1][2]*p[2][0]*p[3][1] + p[0][3]*p[1][2]*p[2][1]*p[3][0];
588 // Z0 Z0 decay: vector and axial couplings of two fermion pairs.
590 double vf1 = couplingsPtr->vf(process[i3].idAbs());
591 double af1 = couplingsPtr->af(process[i3].idAbs());
592 double vf2 = couplingsPtr->vf(process[i5].idAbs());
593 double af2 = couplingsPtr->af(process[i5].idAbs());
594 double va12asym = 4. * vf1 * af1 * vf2 * af2
595 / ( (vf1*vf1 + af1*af1) * (vf2*vf2 + af2*af2) );
596 double etaMod = higgsEta / pow2( particleDataPtr->m0(23) );
598 // Normal CP-even decay.
599 if (higgsParity == 1) wt = 8. * (1. + va12asym) * p35 * p46
600 + 8. * (1. - va12asym) * p36 * p45;
602 // CP-odd decay (normal for A0(H_3)).
603 else if (higgsParity == 2) wt = ( pow2(p35 + p46)
604 + pow2(p36 + p45) - 2. * p34 * p56
605 - 2. * pow2(p35 * p46 - p36 * p45) / (p34 * p56)
606 + va12asym * (p35 + p36 - p45 - p46) * (p35 + p45 - p36 - p46) )
610 else wt = 32. * ( 0.25 * ( (1. + va12asym) * p35 * p46
611 + (1. - va12asym) * p36 * p45 ) - 0.5 * etaMod * epsilonProd
612 * ( (1. + va12asym) * (p35 + p46) - (1. - va12asym) * (p36 + p45) )
613 + 0.0625 * etaMod * etaMod * (-2. * pow2(p34 * p56)
614 - 2. * pow2(p35 * p46 - p36 * p45)
615 + p34 * p56 * (pow2(p35 + p46) + pow2(p36 + p45))
616 + va12asym * p34 * p56 * (p35 + p36 - p45 - p46)
617 * (p35 + p45 - p36 - p46) ) ) / ( 1. + 2. * etaMod * mZW1 * mZW2
618 + 2. * pow2(etaMod * mZW1 * mZW2) * (1. + va12asym) );
621 } else if (idZW1 == 24) {
622 double etaMod = higgsEta / pow2( particleDataPtr->m0(24) );
624 // Normal CP-even decay.
625 if (higgsParity == 1) wt = 16. * p35 * p46;
627 // CP-odd decay (normal for A0(H_3)).
628 else if (higgsParity == 2) wt = 0.5 * ( pow2(p35 + p46)
629 + pow2(p36 + p45) - 2. * p34 * p56
630 - 2. * pow2(p35 * p46 - p36 * p45) / (p34 * p56)
631 + (p35 + p36 - p45 - p46) * (p35 + p45 - p36 - p46) );
634 else wt = 32. * ( 0.25 * 2. * p35 * p46
635 - 0.5 * etaMod * epsilonProd * 2. * (p35 + p46)
636 + 0.0625 * etaMod * etaMod * (-2. * pow2(p34 * p56)
637 - 2. * pow2(p35 * p46 - p36 * p45)
638 + p34 * p56 * (pow2(p35 + p46) + pow2(p36 + p45))
639 + p34 * p56 * (p35 + p36 - p45 - p46) * (p35 + p45 - p36 - p46) ) )
640 / ( 1. * 2. * etaMod * mZW1 * mZW2 + 2. * pow2(etaMod * mZW1 * mZW2) );
648 //==========================================================================
650 // The Sigma1Process class.
651 // Base class for resolved 2 -> 1 cross sections; derived from SigmaProcess.
653 //--------------------------------------------------------------------------
655 // Wrapper to sigmaHat, to (a) store current incoming flavours,
656 // (b) convert from GeV^-2 to mb where required, and
657 // (c) convert from |M|^2 to d(sigmaHat)/d(tHat) where required.
659 double Sigma1Process::sigmaHatWrap(int id1in, int id2in) {
663 double sigmaTmp = sigmaHat();
666 // Convert 2 * pi * delta(p^2 - m^2) to Breit-Wigner with same area.
667 int idTmp = resonanceA();
668 double mTmp = particleDataPtr->m0(idTmp);
669 double GamTmp = particleDataPtr->mWidth(idTmp);
670 sigmaTmp *= 2. * mTmp * GamTmp / ( pow2(sH - mTmp * mTmp)
671 + pow2(mTmp * GamTmp) );
673 if (convert2mb()) sigmaTmp *= CONVERT2MB;
678 //--------------------------------------------------------------------------
680 // Input and complement kinematics for resolved 2 -> 1 process.
682 void Sigma1Process::store1Kin( double x1in, double x2in, double sHin) {
684 // Default value only sensible for these processes.
687 // Incoming parton momentum fractions and sHat.
694 // Different options for renormalization scale, but normally sHat.
695 Q2RenSave = renormMultFac * sH;
696 if (renormScale1 == 2) Q2RenSave = renormFixScale;
698 // Different options for factorization scale, but normally sHat.
699 Q2FacSave = factorMultFac * sH;
700 if (factorScale1 == 2) Q2FacSave = factorFixScale;
702 // Evaluate alpha_strong and alpha_EM.
703 alpS = couplingsPtr->alphaS(Q2RenSave);
704 alpEM = couplingsPtr->alphaEM(Q2RenSave);
708 //--------------------------------------------------------------------------
710 // Calculate modified masses and four-vectors for matrix elements.
712 bool Sigma1Process::setupForME() {
714 // Common initial-state handling.
715 bool allowME = setupForMEin();
717 // Final state trivial here.
719 pME[2] = Vec4( 0., 0., 0., mH);
726 //==========================================================================
728 // The Sigma2Process class.
729 // Base class for resolved 2 -> 2 cross sections; derived from SigmaProcess.
731 //--------------------------------------------------------------------------
733 // Input and complement kinematics for resolved 2 -> 2 process.
735 void Sigma2Process::store2Kin( double x1in, double x2in, double sHin,
736 double tHin, double m3in, double m4in, double runBW3in, double runBW4in) {
738 // Default ordering of particles 3 and 4.
741 // Incoming parton momentum fractions.
745 // Incoming masses and their squares.
746 bool masslessKin = (id3Mass() == 0) && (id4Mass() == 0);
759 // Standard Mandelstam variables and their squares.
762 uH = (masslessKin) ? -(sH + tH) : s3 + s4 - (sH + tH);
768 // The nominal Breit-Wigner factors with running width.
772 // Calculate squared transverse momentum.
773 pT2 = (masslessKin) ? tH * uH / sH : (tH * uH - s3 * s4) / sH;
775 // Special case: pick scale as if 2 -> 1 process in disguise.
778 // Different options for renormalization scale, but normally sHat.
779 Q2RenSave = renormMultFac * sH;
780 if (renormScale1 == 2) Q2RenSave = renormFixScale;
782 // Different options for factorization scale, but normally sHat.
783 Q2FacSave = factorMultFac * sH;
784 if (factorScale1 == 2) Q2FacSave = factorFixScale;
786 // Normal case with "true" 2 -> 2.
789 // Different options for renormalization scale.
790 if (masslessKin) Q2RenSave = (renormScale2 < 4) ? pT2 : sH;
791 else if (renormScale2 == 1) Q2RenSave = pT2 + min(s3, s4);
792 else if (renormScale2 == 2) Q2RenSave = sqrt((pT2 + s3) * (pT2 + s4));
793 else if (renormScale2 == 3) Q2RenSave = pT2 + 0.5 * (s3 + s4);
795 Q2RenSave *= renormMultFac;
796 if (renormScale2 == 5) Q2RenSave = renormFixScale;
798 // Different options for factorization scale.
799 if (masslessKin) Q2FacSave = (factorScale2 < 4) ? pT2 : sH;
800 else if (factorScale2 == 1) Q2FacSave = pT2 + min(s3, s4);
801 else if (factorScale2 == 2) Q2FacSave = sqrt((pT2 + s3) * (pT2 + s4));
802 else if (factorScale2 == 3) Q2FacSave = pT2 + 0.5 * (s3 + s4);
804 Q2FacSave *= factorMultFac;
805 if (factorScale2 == 5) Q2FacSave = factorFixScale;
808 // Evaluate alpha_strong and alpha_EM.
809 alpS = couplingsPtr->alphaS(Q2RenSave);
810 alpEM = couplingsPtr->alphaEM(Q2RenSave);
814 //--------------------------------------------------------------------------
816 // As above, special kinematics for multiparton interactions.
818 void Sigma2Process::store2KinMPI( double x1in, double x2in,
819 double sHin, double tHin, double uHin, double alpSin, double alpEMin,
820 bool needMasses, double m3in, double m4in) {
822 // Default ordering of particles 3 and 4.
825 // Incoming x values.
829 // Standard Mandelstam variables and their squares.
838 // Strong and electroweak couplings.
842 // Assume vanishing masses. (Will be modified in final kinematics.)
850 cosTheta = (tH - uH) / sH;
851 sinTheta = 2. * sqrtpos( tH * uH ) / sH;
853 // In some cases must use masses and redefine meaning of tHat and uHat.
859 sHMass = sH - s3 - s4;
860 sHBeta = sqrtpos(sHMass*sHMass - 4. * s3 * s4);
861 tH = -0.5 * (sHMass - sHBeta * cosTheta);
862 uH = -0.5 * (sHMass + sHBeta * cosTheta);
867 // pT2 with masses (at this stage) included.
868 pT2Mass = 0.25 * sHBeta * pow2(sinTheta);
872 //--------------------------------------------------------------------------
874 // Perform kinematics for a multiparton interaction, including a rescattering.
876 bool Sigma2Process::final2KinMPI( int i1Res, int i2Res, Vec4 p1Res, Vec4 p2Res,
877 double m1Res, double m2Res) {
879 // Have to set flavours and colours.
882 // Check that masses of outgoing particles not too big.
883 m3 = particleDataPtr->m0(idSave[3]);
884 m4 = particleDataPtr->m0(idSave[4]);
886 if (m3 + m4 + MASSMARGIN > mH) return false;
890 // Do kinematics of the production; without or with masses.
891 double e1In = 0.5 * mH;
894 if (i1Res > 0 || i2Res > 0) {
895 double s1 = m1Res * m1Res;
896 double s2 = m2Res * m2Res;
897 e1In = 0.5 * (sH + s1 - s2) / mH;
898 e2In = 0.5 * (sH + s2 - s1) / mH;
899 pzIn = sqrtpos( e1In*e1In - s1 );
902 // Do kinematics of the decay.
903 double e3 = 0.5 * (sH + s3 - s4) / mH;
904 double e4 = 0.5 * (sH + s4 - s3) / mH;
905 double pAbs = sqrtpos( e3*e3 - s3 );
906 phi = 2. * M_PI * rndmPtr->flat();
907 double pZ = pAbs * cosTheta;
908 pTFin = pAbs * sinTheta;
909 double pX = pTFin * sin(phi);
910 double pY = pTFin * cos(phi);
911 double scale = 0.5 * mH * sinTheta;
913 // Fill particle info.
914 int status1 = (i1Res == 0) ? -31 : -34;
915 int status2 = (i2Res == 0) ? -31 : -34;
916 parton[1] = Particle( idSave[1], status1, 0, 0, 3, 4,
917 colSave[1], acolSave[1], 0., 0., pzIn, e1In, m1Res, scale);
918 parton[2] = Particle( idSave[2], status2, 0, 0, 3, 4,
919 colSave[2], acolSave[2], 0., 0., -pzIn, e2In, m2Res, scale);
920 parton[3] = Particle( idSave[3], 33, 1, 2, 0, 0,
921 colSave[3], acolSave[3], pX, pY, pZ, e3, m3, scale);
922 parton[4] = Particle( idSave[4], 33, 1, 2, 0, 0,
923 colSave[4], acolSave[4], -pX, -pY, -pZ, e4, m4, scale);
925 // Boost particles from subprocess rest frame to event rest frame.
926 // Normal multiparton interaction: only longitudinal boost.
927 if (i1Res == 0 && i2Res == 0) {
928 double betaZ = (x1Save - x2Save) / (x1Save + x2Save);
929 for (int i = 1; i <= 4; ++i) parton[i].bst(0., 0., betaZ);
930 // Rescattering: generic rotation and boost required.
933 M.fromCMframe( p1Res, p2Res);
934 for (int i = 1; i <= 4; ++i) parton[i].rotbst(M);
942 //--------------------------------------------------------------------------
944 // Calculate modified masses and four-vectors for matrix elements.
946 bool Sigma2Process::setupForME() {
948 // Common initial-state handling.
949 bool allowME = setupForMEin();
951 // Correct outgoing c, b, mu and tau to be massive or not.
953 int id3Tmp = abs(id3Mass());
954 if (id3Tmp == 4) mME[2] = mcME;
955 if (id3Tmp == 5) mME[2] = mbME;
956 if (id3Tmp == 13) mME[2] = mmuME;
957 if (id3Tmp == 15) mME[2] = mtauME;
959 int id4Tmp = abs(id4Mass());
960 if (id4Tmp == 4) mME[3] = mcME;
961 if (id4Tmp == 5) mME[3] = mbME;
962 if (id4Tmp == 13) mME[3] = mmuME;
963 if (id4Tmp == 15) mME[3] = mtauME;
965 // If kinematically impossible turn to massless case, but set error.
966 if (mME[2] + mME[3] >= mH) {
972 // Calculate scattering angle in subsystem rest frame.
973 double sH34 = sqrtpos( pow2(sH - s3 - s4) - 4. * s3 * s4);
974 double cThe = (tH - uH) / sH34;
975 double sThe = sqrtpos(1. - cThe * cThe);
977 // Setup massive kinematics with preserved scattering angle.
978 double s3ME = pow2(mME[2]);
979 double s4ME = pow2(mME[3]);
980 double sH34ME = sqrtpos( pow2(sH - s3ME - s4ME) - 4. * s3ME * s4ME);
981 double pAbsME = 0.5 * sH34ME / mH;
983 // Normally allowed with unequal (or vanishing) masses.
984 if (id3Tmp == 0 || id3Tmp != id4Tmp) {
985 pME[2] = Vec4( pAbsME * sThe, 0., pAbsME * cThe,
986 0.5 * (sH + s3ME - s4ME) / mH);
987 pME[3] = Vec4( -pAbsME * sThe, 0., -pAbsME * cThe,
988 0.5 * (sH + s4ME - s3ME) / mH);
990 // For equal (anti)particles (e.g. W+ W-) use averaged mass.
992 mME[2] = sqrtpos(0.5 * (s3ME + s4ME) - 0.25 * pow2(s3ME - s4ME) / sH);
994 pME[2] = Vec4( pAbsME * sThe, 0., pAbsME * cThe, 0.5 * mH);
995 pME[3] = Vec4( -pAbsME * sThe, 0., -pAbsME * cThe, 0.5 * mH);
1003 //==========================================================================
1005 // The Sigma3Process class.
1006 // Base class for resolved 2 -> 3 cross sections; derived from SigmaProcess.
1008 //--------------------------------------------------------------------------
1010 // Input and complement kinematics for resolved 2 -> 3 process.
1012 void Sigma3Process::store3Kin( double x1in, double x2in, double sHin,
1013 Vec4 p3cmIn, Vec4 p4cmIn, Vec4 p5cmIn, double m3in, double m4in,
1014 double m5in, double runBW3in, double runBW4in, double runBW5in) {
1016 // Default ordering of particles 3 and 4 - not relevant here.
1019 // Incoming parton momentum fractions.
1023 // Incoming masses and their squares.
1024 if (id3Mass() == 0 && id4Mass() == 0 && id5Mass() == 0) {
1040 // Standard Mandelstam variables and four-momenta in rest frame.
1048 // The nominal Breit-Wigner factors with running width.
1053 // Special case: pick scale as if 2 -> 1 process in disguise.
1056 // Different options for renormalization scale, but normally sHat.
1057 Q2RenSave = renormMultFac * sH;
1058 if (renormScale1 == 2) Q2RenSave = renormFixScale;
1060 // Different options for factorization scale, but normally sHat.
1061 Q2FacSave = factorMultFac * sH;
1062 if (factorScale1 == 2) Q2RenSave = factorFixScale;
1064 // "Normal" 2 -> 3 processes, i.e. not vector boson fusion.
1065 } else if ( idTchan1() != 23 && idTchan1() != 24 && idTchan2() != 23
1066 && idTchan2() != 24 ) {
1067 double mT3S = s3 + p3cm.pT2();
1068 double mT4S = s4 + p4cm.pT2();
1069 double mT5S = s5 + p5cm.pT2();
1071 // Different options for renormalization scale.
1072 if (renormScale3 == 1) Q2RenSave = min( mT3S, min(mT4S, mT5S) );
1073 else if (renormScale3 == 2) Q2RenSave = sqrt( mT3S * mT4S * mT5S
1074 / max( mT3S, max(mT4S, mT5S) ) );
1075 else if (renormScale3 == 3) Q2RenSave = pow( mT3S * mT4S * mT5S,
1077 else if (renormScale3 == 4) Q2RenSave = (mT3S + mT4S + mT5S) / 3.;
1078 else Q2RenSave = sH;
1079 Q2RenSave *= renormMultFac;
1080 if (renormScale3 == 6) Q2RenSave = renormFixScale;
1082 // Different options for factorization scale.
1083 if (factorScale3 == 1) Q2FacSave = min( mT3S, min(mT4S, mT5S) );
1084 else if (factorScale3 == 2) Q2FacSave = sqrt( mT3S * mT4S * mT5S
1085 / max( mT3S, max(mT4S, mT5S) ) );
1086 else if (factorScale3 == 3) Q2FacSave = pow( mT3S * mT4S * mT5S,
1088 else if (factorScale3 == 4) Q2FacSave = (mT3S + mT4S + mT5S) / 3.;
1089 else Q2FacSave = sH;
1090 Q2FacSave *= factorMultFac;
1091 if (factorScale3 == 6) Q2FacSave = factorFixScale;
1093 // Vector boson fusion 2 -> 3 processes; recoils in positions 4 and 5.
1095 double sV4 = pow2( particleDataPtr->m0(idTchan1()) );
1096 double sV5 = pow2( particleDataPtr->m0(idTchan2()) );
1097 double mT3S = s3 + p3cm.pT2();
1098 double mTV4S = sV4 + p4cm.pT2();
1099 double mTV5S = sV5 + p5cm.pT2();
1101 // Different options for renormalization scale.
1102 if (renormScale3VV == 1) Q2RenSave = max( sV4, sV5);
1103 else if (renormScale3VV == 2) Q2RenSave = sqrt( mTV4S * mTV5S );
1104 else if (renormScale3VV == 3) Q2RenSave = pow( mT3S * mTV4S * mTV5S,
1106 else if (renormScale3VV == 4) Q2RenSave = (mT3S * mTV4S * mTV5S) / 3.;
1107 else Q2RenSave = sH;
1108 Q2RenSave *= renormMultFac;
1109 if (renormScale3VV == 6) Q2RenSave = renormFixScale;
1111 // Different options for factorization scale.
1112 if (factorScale3VV == 1) Q2FacSave = max( sV4, sV5);
1113 else if (factorScale3VV == 2) Q2FacSave = sqrt( mTV4S * mTV5S );
1114 else if (factorScale3VV == 3) Q2FacSave = pow( mT3S * mTV4S * mTV5S,
1116 else if (factorScale3VV == 4) Q2FacSave = (mT3S * mTV4S * mTV5S) / 3.;
1117 else Q2FacSave = sH;
1118 Q2FacSave *= factorMultFac;
1119 if (factorScale3VV == 6) Q2FacSave = factorFixScale;
1122 // Evaluate alpha_strong and alpha_EM.
1123 alpS = couplingsPtr->alphaS(Q2RenSave);
1124 alpEM = couplingsPtr->alphaEM(Q2RenSave);
1128 //--------------------------------------------------------------------------
1130 // Calculate modified masses and four-vectors for matrix elements.
1132 bool Sigma3Process::setupForME() {
1134 // Common initial-state handling.
1135 bool allowME = setupForMEin();
1137 // Correct outgoing c, b, mu and tau to be massive or not.
1139 int id3Tmp = abs(id3Mass());
1140 if (id3Tmp == 4) mME[2] = mcME;
1141 if (id3Tmp == 5) mME[2] = mbME;
1142 if (id3Tmp == 13) mME[2] = mmuME;
1143 if (id3Tmp == 15) mME[2] = mtauME;
1145 int id4Tmp = abs(id4Mass());
1146 if (id4Tmp == 4) mME[3] = mcME;
1147 if (id4Tmp == 5) mME[3] = mbME;
1148 if (id4Tmp == 13) mME[3] = mmuME;
1149 if (id4Tmp == 15) mME[3] = mtauME;
1151 int id5Tmp = abs(id5Mass());
1152 if (id5Tmp == 4) mME[4] = mcME;
1153 if (id5Tmp == 5) mME[4] = mbME;
1154 if (id5Tmp == 13) mME[4] = mmuME;
1155 if (id5Tmp == 15) mME[4] = mtauME;
1157 // If kinematically impossible turn to massless case, but set error.
1158 if (mME[2] + mME[3] + mME[4] >= mH) {
1165 // Form new average masses if identical particles.
1166 if (id3Tmp != 0 && id4Tmp == id3Tmp && id5Tmp == id3Tmp) {
1167 double mAvg = (mME[2] + mME[3] + mME[4]) / 3.;
1171 } else if (id3Tmp != 0 && id4Tmp == id3Tmp) {
1172 mME[2] = sqrtpos(0.5 * (pow2(mME[2]) + pow2(mME[3]))
1173 - 0.25 * pow2(pow2(mME[2]) - pow2(mME[3])) / sH);
1175 } else if (id3Tmp != 0 && id5Tmp == id3Tmp) {
1176 mME[2] = sqrtpos(0.5 * (pow2(mME[2]) + pow2(mME[4]))
1177 - 0.25 * pow2(pow2(mME[2]) - pow2(mME[4])) / sH);
1179 } else if (id4Tmp != 0 && id5Tmp == id4Tmp) {
1180 mME[3] = sqrtpos(0.5 * (pow2(mME[3]) + pow2(mME[4]))
1181 - 0.25 * pow2(pow2(mME[3]) - pow2(mME[4])) / sH);
1185 // Iterate rescaled three-momenta until convergence.
1186 double m2ME3 = pow2(mME[2]);
1187 double m2ME4 = pow2(mME[3]);
1188 double m2ME5 = pow2(mME[4]);
1189 double p2ME3 = p3cm.pAbs2();
1190 double p2ME4 = p4cm.pAbs2();
1191 double p2ME5 = p5cm.pAbs2();
1192 double p2sum = p2ME3 + p2ME4 + p2ME5;
1193 double eME3 = sqrt(m2ME3 + p2ME3);
1194 double eME4 = sqrt(m2ME4 + p2ME4);
1195 double eME5 = sqrt(m2ME5 + p2ME5);
1196 double esum = eME3 + eME4 + eME5;
1197 double p2rat = p2ME3 / eME3 + p2ME4 / eME4 + p2ME5 / eME5;
1199 while ( abs(esum - mH) > COMPRELERR * mH && iStep < NCOMPSTEP ) {
1201 double compFac = 1. + 2. * (mH - esum) / p2rat;
1205 eME3 = sqrt(m2ME3 + p2ME3);
1206 eME4 = sqrt(m2ME4 + p2ME4);
1207 eME5 = sqrt(m2ME5 + p2ME5);
1208 esum = eME3 + eME4 + eME5;
1209 p2rat = p2ME3 / eME3 + p2ME4 / eME4 + p2ME5 / eME5;
1212 // If failed convergence set error flag.
1213 if (abs(esum - mH) > COMPRELERR * mH) allowME = false;
1215 // Set up accepted kinematics.
1216 double totFac = sqrt( (p2ME3 + p2ME4 + p2ME5) / p2sum);
1217 pME[2] = totFac * p3cm;
1219 pME[3] = totFac * p4cm;
1221 pME[4] = totFac * p5cm;
1229 //==========================================================================
1231 // The SigmaLHAProcess class.
1232 // Wrapper for Les Houches Accord external input; derived from SigmaProcess.
1233 // Note: arbitrary subdivision into PhaseSpaceLHA and SigmaLHAProcess tasks.
1235 //--------------------------------------------------------------------------
1237 // Evaluate weight for decay angles.
1239 double SigmaLHAProcess::weightDecay( Event& process, int iResBeg,
1242 // Do nothing if decays present already at input.
1243 if (iResBeg < process.savedSizeValue()) return 1.;
1245 // Identity of mother of decaying reseonance(s).
1246 int idMother = process[process[iResBeg].mother1()].idAbs();
1248 // For Higgs decay hand over to standard routine.
1249 if (idMother == 25 || idMother == 35 || idMother == 36)
1250 return weightHiggsDecay( process, iResBeg, iResEnd);
1252 // For top decay hand over to standard routine.
1254 return weightTopDecay( process, iResBeg, iResEnd);
1261 //--------------------------------------------------------------------------
1263 // Set scale, alpha_strong and alpha_EM when not set.
1265 void SigmaLHAProcess::setScale() {
1267 // If scale has not been set, then to set.
1268 double scaleLHA = lhaUpPtr->scale();
1269 if (scaleLHA < 0.) {
1271 // Final-state partons and their invariant mass.
1274 for (int i = 3; i < lhaUpPtr->sizePart(); ++i)
1275 if (lhaUpPtr->mother1(i) == 1) {
1277 pFinSum += Vec4( lhaUpPtr->px(i), lhaUpPtr->py(i),
1278 lhaUpPtr->pz(i), lhaUpPtr->e(i) );
1280 int nFin = iFin.size();
1281 sH = pFinSum * pFinSum;
1285 // If 1 final-state particle then use Sigma1Process logic.
1287 Q2RenSave = renormMultFac * sH;
1288 if (renormScale1 == 2) Q2RenSave = renormFixScale;
1289 Q2FacSave = factorMultFac * sH;
1290 if (factorScale1 == 2) Q2FacSave = factorFixScale;
1292 // If 2 final-state particles then use Sigma2Process logic.
1293 } else if (nFin == 2) {
1294 double s3 = pow2(lhaUpPtr->m(iFin[0]));
1295 double s4 = pow2(lhaUpPtr->m(iFin[1]));
1296 double pT2 = pow2(lhaUpPtr->px(iFin[0])) + pow2(lhaUpPtr->py(iFin[0]));
1297 if (renormScale2 == 1) Q2RenSave = pT2 + min(s3, s4);
1298 else if (renormScale2 == 2) Q2RenSave = sqrt((pT2 + s3) * (pT2 + s4));
1299 else if (renormScale2 == 3) Q2RenSave = pT2 + 0.5 * (s3 + s4);
1300 else Q2RenSave = sH;
1301 Q2RenSave *= renormMultFac;
1302 if (renormScale2 == 5) Q2RenSave = renormFixScale;
1303 if (factorScale2 == 1) Q2FacSave = pT2 + min(s3, s4);
1304 else if (factorScale2 == 2) Q2FacSave = sqrt((pT2 + s3) * (pT2 + s4));
1305 else if (factorScale2 == 3) Q2FacSave = pT2 + 0.5 * (s3 + s4);
1306 else Q2FacSave = sH;
1307 Q2FacSave *= factorMultFac;
1308 if (factorScale2 == 5) Q2FacSave = factorFixScale;
1310 // If 3 or more final-state particles then use Sigma3Process logic.
1314 double mTSprod = 1.;
1316 for (int i = 0; i < nFin; ++i) {
1317 double mTSnow = pow2(lhaUpPtr->m(iFin[i]))
1318 + pow2(lhaUpPtr->px(iFin[i])) + pow2(lhaUpPtr->py(iFin[i]));
1319 if (mTSnow < mTSlow) {mTSmed = mTSlow; mTSlow = mTSnow;}
1320 else if (mTSnow < mTSmed) mTSmed = mTSnow;
1324 if (renormScale3 == 1) Q2RenSave = mTSlow;
1325 else if (renormScale3 == 2) Q2RenSave = sqrt(mTSlow * mTSmed);
1326 else if (renormScale3 == 3) Q2RenSave = pow(mTSprod, 1. / nFin);
1327 else if (renormScale3 == 4) Q2RenSave = mTSsum / nFin;
1328 else Q2RenSave = sH;
1329 Q2RenSave *= renormMultFac;
1330 if (renormScale3 == 6) Q2RenSave = renormFixScale;
1331 if (factorScale3 == 1) Q2FacSave = mTSlow;
1332 else if (factorScale3 == 2) Q2FacSave = sqrt(mTSlow * mTSmed);
1333 else if (factorScale3 == 3) Q2FacSave = pow(mTSprod, 1. / nFin);
1334 else if (factorScale3 == 4) Q2FacSave = mTSsum / nFin;
1335 else Q2FacSave = sH;
1336 Q2FacSave *= factorMultFac;
1337 if (factorScale3 == 6) Q2FacSave = factorFixScale;
1341 // If alpha_strong and alpha_EM have not been set, then set them.
1342 if (lhaUpPtr->alphaQCD() < 0.001) {
1343 double Q2RenNow = (scaleLHA < 0.) ? Q2RenSave : pow2(scaleLHA);
1344 alpS = couplingsPtr->alphaS(Q2RenNow);
1346 if (lhaUpPtr->alphaQED() < 0.001) {
1347 double Q2RenNow = (scaleLHA < 0.) ? Q2RenSave : pow2(scaleLHA);
1348 alpEM = couplingsPtr->alphaEM(Q2RenNow);
1353 //--------------------------------------------------------------------------
1355 // Obtain number of final-state partons from LHA object.
1357 int SigmaLHAProcess::nFinal() const {
1359 // At initialization size unknown, so return 0.
1360 if (lhaUpPtr->sizePart() <= 0) return 0;
1362 // Sum up all particles that has first mother = 1.
1364 for (int i = 3; i < lhaUpPtr->sizePart(); ++i)
1365 if (lhaUpPtr->mother1(i) == 1) ++nFin;
1370 //==========================================================================
1372 } // end namespace Pythia8