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5ad4eb21 | 1 | // HadronLevel.cc is a part of the PYTHIA event generator. |
2 | // Copyright (C) 2008 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 HadronLevel class. | |
7 | ||
8 | #include "HadronLevel.h" | |
9 | ||
10 | namespace Pythia8 { | |
11 | ||
12 | //************************************************************************** | |
13 | ||
14 | // The HadronLevel class. | |
15 | ||
16 | //********* | |
17 | ||
18 | // Constants: could be changed here if desired, but normally should not. | |
19 | // These are of technical nature, as described for each. | |
20 | ||
21 | // For breaking J-J string, pick a Gamma by taking a step with fictitious mass. | |
22 | const double HadronLevel::JJSTRINGM2MAX = 25.; | |
23 | const double HadronLevel::JJSTRINGM2FRAC = 0.1; | |
24 | ||
25 | // Iterate junction rest frame boost until convergence or too many tries. | |
26 | const double HadronLevel::CONVJNREST = 1e-5; | |
27 | const int HadronLevel::NTRYJNREST = 20; | |
28 | ||
29 | // Typical average transvere primary hadron mass <mThad>. | |
30 | const double HadronLevel::MTHAD = 0.9; | |
31 | ||
32 | //********* | |
33 | ||
34 | // Find settings. Initialize HadronLevel classes as required. | |
35 | ||
36 | bool HadronLevel::init(Info* infoPtrIn, TimeShower* timesDecPtr, | |
37 | DecayHandler* decayHandlePtr, vector<int> handledParticles) { | |
38 | ||
39 | // Save pointer. | |
40 | infoPtr = infoPtrIn; | |
41 | ||
42 | // Main flags. | |
43 | doHadronize = Settings::flag("HadronLevel:Hadronize"); | |
44 | doDecay = Settings::flag("HadronLevel:Decay"); | |
45 | doBoseEinstein = Settings::flag("HadronLevel:BoseEinstein"); | |
46 | ||
47 | // Boundary mass between string and ministring handling. | |
48 | mStringMin = Settings::parm("HadronLevel:mStringMin"); | |
49 | ||
50 | // For junction processing. | |
51 | eNormJunction = Settings::parm("StringFragmentation:eNormJunction"); | |
52 | ||
53 | // Particles that should decay or not before Bose-Einstein stage. | |
54 | widthSepBE = Settings::parm("BoseEinstein:widthSep"); | |
55 | ||
56 | // Initialize string and ministring fragmentation. | |
57 | stringFrag.init(infoPtr, &flavSel, &pTSel, &zSel); | |
58 | ministringFrag.init(infoPtr, &flavSel); | |
59 | ||
60 | // Initialize particle decays. | |
61 | decays.init(infoPtr, timesDecPtr, &flavSel, decayHandlePtr, | |
62 | handledParticles); | |
63 | ||
64 | // Initialize BoseEinstein. | |
65 | boseEinstein.init(infoPtr); | |
66 | ||
67 | // Initialize auxiliary administrative classes. | |
68 | colConfig.init( &flavSel); | |
69 | ||
70 | // Initialize auxiliary fragmentation classes. | |
71 | flavSel.init(); | |
72 | pTSel.init(); | |
73 | zSel.init(); | |
74 | ||
75 | // Done. | |
76 | return true; | |
77 | ||
78 | } | |
79 | ||
80 | //********* | |
81 | ||
82 | // Hadronize and decay the next parton-level. | |
83 | ||
84 | bool HadronLevel::next( Event& event) { | |
85 | ||
86 | // Colour-octet onia states must be decayed to singlet + gluon. | |
87 | if (!decayOctetOnia(event)) return false; | |
88 | ||
89 | // Possibility of hadronization inside decay, but then no BE second time. | |
90 | bool moreToDo; | |
91 | bool doBoseEinsteinNow = doBoseEinstein; | |
92 | do { | |
93 | moreToDo = false; | |
94 | ||
95 | // First part: string fragmentation. | |
96 | if (doHadronize) { | |
97 | ||
98 | // Find the complete colour singlet configuration of the event. | |
99 | if (!findSinglets( event)) return false; | |
100 | ||
101 | // Process all colour singlet (sub)system | |
102 | for (int iSub = 0; iSub < colConfig.size(); ++iSub) { | |
103 | ||
104 | // Collect sequentially all partons in a colour singlet subsystem. | |
105 | colConfig.collect(iSub, event); | |
106 | ||
107 | // String fragmentation of each colour singlet (sub)system. | |
108 | if ( colConfig[iSub].massExcess > mStringMin ) { | |
109 | if (!stringFrag.fragment( iSub, colConfig, event)) return false; | |
110 | ||
111 | // Low-mass string treated separately. Tell if diffractive system. | |
112 | } else { | |
113 | bool isDiff = infoPtr->isDiffractiveA() | |
114 | || infoPtr->isDiffractiveB(); | |
115 | if (!ministringFrag.fragment( iSub, colConfig, event, isDiff)) | |
116 | return false; | |
117 | } | |
118 | } | |
119 | } | |
120 | ||
121 | // Second part: sequential decays of short-lived particles (incl. K0). | |
122 | if (doDecay) { | |
123 | ||
124 | // Loop through all entries to find those that should decay. | |
125 | int iDec = 0; | |
126 | do { | |
127 | if ( event[iDec].isFinal() && event[iDec].canDecay() | |
128 | && event[iDec].mayDecay() && (event[iDec].idAbs() == 311 | |
129 | || event[iDec].mWidth() > widthSepBE) ) { | |
130 | decays.decay( iDec, event); | |
131 | if (decays.moreToDo()) moreToDo = true; | |
132 | } | |
133 | } while (++iDec < event.size()); | |
134 | } | |
135 | ||
136 | // Third part: include Bose-Einstein effects among current particles. | |
137 | if (doBoseEinsteinNow) { | |
138 | if (!boseEinstein.shiftEvent(event)) return false; | |
139 | doBoseEinsteinNow = false; | |
140 | } | |
141 | ||
142 | // Fourth part: sequential decays also of long-lived particles. | |
143 | if (doDecay) { | |
144 | ||
145 | // Loop through all entries to find those that should decay. | |
146 | int iDec = 0; | |
147 | do { | |
148 | if ( event[iDec].isFinal() && event[iDec].canDecay() | |
149 | && event[iDec].mayDecay() ) { | |
150 | decays.decay( iDec, event); | |
151 | if (decays.moreToDo()) moreToDo = true; | |
152 | } | |
153 | } while (++iDec < event.size()); | |
154 | } | |
155 | ||
156 | ||
157 | // Normally done first time around, but sometimes not (e.g. Upsilon). | |
158 | } while (moreToDo); | |
159 | ||
160 | // Done. | |
161 | return true; | |
162 | ||
163 | } | |
164 | ||
165 | //********* | |
166 | ||
167 | // Allow more decays if on/off switches changed. | |
168 | // Note: does not do sequential hadronization, e.g. for Upsilon. | |
169 | ||
170 | bool HadronLevel::moreDecays( Event& event) { | |
171 | ||
172 | // Colour-octet onia states must be decayed to singlet + gluon. | |
173 | if (!decayOctetOnia(event)) return false; | |
174 | ||
175 | // Loop through all entries to find those that should decay. | |
176 | int iDec = 0; | |
177 | do { | |
178 | if ( event[iDec].isFinal() && event[iDec].canDecay() | |
179 | && event[iDec].mayDecay() ) decays.decay( iDec, event); | |
180 | } while (++iDec < event.size()); | |
181 | ||
182 | // Done. | |
183 | return true; | |
184 | ||
185 | } | |
186 | ||
187 | //********* | |
188 | ||
189 | // Decay colour-octet onium states. | |
190 | ||
191 | bool HadronLevel::decayOctetOnia(Event& event) { | |
192 | ||
193 | // Onium states to be decayed. | |
194 | int idOnium[6] = { 9900443, 9900441, 9910441, | |
195 | 9900553, 9900551, 9910551 }; | |
196 | ||
197 | // Loop over particles and identify onia. | |
198 | for (int iDec = 0; iDec < event.size(); ++iDec) | |
199 | if (event[iDec].isFinal()) { | |
200 | int id = event[iDec].id(); | |
201 | bool isOnium = false; | |
202 | for (int j = 0; j < 6; ++j) if (id == idOnium[j]) isOnium = true; | |
203 | ||
204 | // Decay any onia encountered. | |
205 | if (isOnium) { | |
206 | if (!decays.decay( iDec, event)) return false; | |
207 | ||
208 | // Set colour flow by hand: gluon inherits octet-onium state. | |
209 | int iGlu = event.size() - 1; | |
210 | event[iGlu].cols( event[iDec].col(), event[iDec].acol() ); | |
211 | } | |
212 | } | |
213 | ||
214 | // Done. | |
215 | return true; | |
216 | ||
217 | } | |
218 | ||
219 | //********* | |
220 | ||
221 | // Trace colour flow in the event to form colour singlet subsystems. | |
222 | ||
223 | bool HadronLevel::findSinglets(Event& event) { | |
224 | ||
225 | // Find a list of final partons and of all colour ends and gluons. | |
226 | iColEnd.resize(0); | |
227 | iAcolEnd.resize(0); | |
228 | iColAndAcol.resize(0); | |
229 | for (int i = 0; i < event.size(); ++ i) if (event[i].isFinal()) { | |
230 | if (event[i].col() > 0 && event[i].acol() > 0) iColAndAcol.push_back(i); | |
231 | else if (event[i].col() > 0) iColEnd.push_back(i); | |
232 | else if (event[i].acol() > 0) iAcolEnd.push_back(i); | |
233 | } | |
234 | ||
235 | // Begin arrange the partons into separate colour singlets. | |
236 | colConfig.clear(); | |
237 | iPartonJun.resize(0); | |
238 | iPartonAntiJun.resize(0); | |
239 | ||
240 | // Junctions: loop over them, and identify kind. | |
241 | for (int iJun = 0; iJun < event.sizeJunction(); ++iJun) | |
242 | if (event.remainsJunction(iJun)) { | |
243 | event.remainsJunction(iJun, false); | |
244 | int kindJun = event.kindJunction(iJun); | |
245 | iParton.resize(0); | |
246 | ||
247 | // First kind: three (anti)colours out from junction. | |
248 | if (kindJun == 1 || kindJun == 2) { | |
249 | for (int iCol = 0; iCol < 3; ++iCol) { | |
250 | int indxCol = event.colJunction(iJun, iCol); | |
251 | iParton.push_back( -(10 + 10 * iJun + iCol) ); | |
252 | if (kindJun == 1 && !traceFromAcol(indxCol, event, iJun, iCol)) | |
253 | return false; | |
254 | if (kindJun == 2 && !traceFromCol(indxCol, event, iJun, iCol)) | |
255 | return false; | |
256 | } | |
257 | } | |
258 | ||
259 | // Keep in memory a junction hooked up with an antijunction, | |
260 | // else store found single-junction system. | |
261 | int nNeg = 0; | |
262 | for (int i = 0; i < int(iParton.size()); ++i) if (iParton[i] < 0) | |
263 | ++nNeg; | |
264 | if (nNeg > 3 && kindJun == 1) { | |
265 | for (int i = 0; i < int(iParton.size()); ++i) | |
266 | iPartonJun.push_back(iParton[i]); | |
267 | } else if (nNeg > 3 && kindJun == 2) { | |
268 | for (int i = 0; i < int(iParton.size()); ++i) | |
269 | iPartonAntiJun.push_back(iParton[i]); | |
270 | } else { | |
271 | // A junction may be eliminated by insert if two quarks are nearby. | |
272 | int nJunOld = event.sizeJunction(); | |
273 | colConfig.insert(iParton, event); | |
274 | if (event.sizeJunction() < nJunOld) --iJun; | |
275 | } | |
276 | } | |
277 | ||
278 | // Split junction-antijunction system into two, and store those. | |
279 | // (Only one system in extreme cases, and then second empty.) | |
280 | if (iPartonJun.size() > 0 && iPartonAntiJun.size() > 0) { | |
281 | if (!splitJunctionPair(event)) return false; | |
282 | colConfig.insert(iPartonJun, event); | |
283 | if (iPartonAntiJun.size() > 0) | |
284 | colConfig.insert(iPartonAntiJun, event); | |
285 | // Error if only one of junction and antijuction left here. | |
286 | } else if (iPartonJun.size() > 0 || iPartonAntiJun.size() > 0) { | |
287 | infoPtr->errorMsg("Error in HadronLevel::findSinglets: " | |
288 | "unmatched (anti)junction"); | |
289 | return false; | |
290 | } | |
291 | ||
292 | // Open strings: pick up each colour end and trace to its anticolor end. | |
293 | for (int iEnd = 0; iEnd < int(iColEnd.size()); ++iEnd) { | |
294 | iParton.resize(0); | |
295 | iParton.push_back( iColEnd[iEnd] ); | |
296 | int indxCol = event[ iColEnd[iEnd] ].col(); | |
297 | if (!traceFromCol(indxCol, event)) return false; | |
298 | ||
299 | // Store found open string system. Analyze its properties. | |
300 | colConfig.insert(iParton, event); | |
301 | } | |
302 | ||
303 | // Closed strings : begin at any gluon and trace until back at it. | |
304 | while (iColAndAcol.size() > 0) { | |
305 | iParton.resize(0); | |
306 | iParton.push_back( iColAndAcol[0] ); | |
307 | int indxCol = event[ iColAndAcol[0] ].col(); | |
308 | int indxAcol = event[ iColAndAcol[0] ].acol(); | |
309 | iColAndAcol[0] = iColAndAcol.back(); | |
310 | iColAndAcol.pop_back(); | |
311 | if (!traceInLoop(indxCol, indxAcol, event)) return false; | |
312 | ||
313 | // Store found closed string system. Analyze its properties. | |
314 | colConfig.insert(iParton, event); | |
315 | } | |
316 | ||
317 | // Done. | |
318 | return true; | |
319 | ||
320 | } | |
321 | ||
322 | //********* | |
323 | ||
324 | // Trace a colour line, from a colour to an anticolour. | |
325 | ||
326 | bool HadronLevel::traceFromCol(int indxCol, Event& event, int iJun, | |
327 | int iCol) { | |
328 | ||
329 | // Junction kind, if any. | |
330 | int kindJun = (iJun >= 0) ? event.kindJunction(iJun) : 0; | |
331 | ||
332 | // Begin to look for a matching anticolour. | |
333 | int loop = 0; | |
334 | int loopMax = iColAndAcol.size() + 2; | |
335 | bool hasFound = false; | |
336 | do { | |
337 | ++loop; | |
338 | hasFound= false; | |
339 | ||
340 | // First check list of matching anticolour ends. | |
341 | for (int i = 0; i < int(iAcolEnd.size()); ++i) | |
342 | if (event[ iAcolEnd[i] ].acol() == indxCol) { | |
343 | iParton.push_back( iAcolEnd[i] ); | |
344 | indxCol = 0; | |
345 | iAcolEnd[i] = iAcolEnd.back(); | |
346 | iAcolEnd.pop_back(); | |
347 | hasFound = true; | |
348 | break; | |
349 | } | |
350 | ||
351 | // Then check list of intermediate gluons. | |
352 | if (!hasFound) | |
353 | for (int i = 0; i < int(iColAndAcol.size()); ++i) | |
354 | if (event[ iColAndAcol[i] ].acol() == indxCol) { | |
355 | iParton.push_back( iColAndAcol[i] ); | |
356 | ||
357 | // Update to new colour. Remove gluon. | |
358 | indxCol = event[ iColAndAcol[i] ].col(); | |
359 | if (kindJun > 0) event.endColJunction(iJun, iCol, indxCol); | |
360 | iColAndAcol[i] = iColAndAcol.back(); | |
361 | iColAndAcol.pop_back(); | |
362 | hasFound = true; | |
363 | break; | |
364 | } | |
365 | ||
366 | // In a pinch, check list of end colours on other (anti)junction. | |
367 | if (!hasFound && kindJun == 2 && event.sizeJunction() > 1) | |
368 | for (int iAntiJun = 0; iAntiJun < event.sizeJunction(); ++iAntiJun) | |
369 | if (iAntiJun != iJun && event.kindJunction(iAntiJun) == 1) | |
370 | for (int iColAnti = 0; iColAnti < 3; ++iColAnti) | |
371 | if (event.endColJunction(iAntiJun, iColAnti) == indxCol) { | |
372 | iParton.push_back( -(10 + 10 * iAntiJun + iColAnti) ); | |
373 | indxCol = 0; | |
374 | hasFound = true; | |
375 | break; | |
376 | } | |
377 | ||
378 | // Keep on tracing via gluons until reached end of leg. | |
379 | } while (hasFound && indxCol > 0 && loop < loopMax); | |
380 | ||
381 | // Something went wrong in colour tracing. | |
382 | if (!hasFound || loop == loopMax) { | |
383 | infoPtr->errorMsg("Error in HadronLevel::traceFromCol: " | |
384 | "colour tracing failed"); | |
385 | return false; | |
386 | } | |
387 | ||
388 | // Done. | |
389 | return true; | |
390 | ||
391 | } | |
392 | ||
393 | //********* | |
394 | ||
395 | // Trace a colour line, from an anticolour to a colour. | |
396 | ||
397 | bool HadronLevel::traceFromAcol(int indxCol, Event& event, int iJun, | |
398 | int iCol) { | |
399 | ||
400 | // Junction kind, if any. | |
401 | int kindJun = (iJun >= 0) ? event.kindJunction(iJun) : 0; | |
402 | ||
403 | // Begin to look for a matching colour. | |
404 | int loop = 0; | |
405 | int loopMax = iColAndAcol.size() + 2; | |
406 | bool hasFound = false; | |
407 | do { | |
408 | ++loop; | |
409 | hasFound= false; | |
410 | ||
411 | // First check list of matching colour ends. | |
412 | for (int i = 0; i < int(iColEnd.size()); ++i) | |
413 | if (event[ iColEnd[i] ].col() == indxCol) { | |
414 | iParton.push_back( iColEnd[i] ); | |
415 | indxCol = 0; | |
416 | iColEnd[i] = iColEnd.back(); | |
417 | iColEnd.pop_back(); | |
418 | hasFound = true; | |
419 | break; | |
420 | } | |
421 | ||
422 | // Then check list of intermediate gluons. | |
423 | if (!hasFound) | |
424 | for (int i = 0; i < int(iColAndAcol.size()); ++i) | |
425 | if (event[ iColAndAcol[i] ].col() == indxCol) { | |
426 | iParton.push_back( iColAndAcol[i] ); | |
427 | ||
428 | // Update to new colour. Remove gluon. | |
429 | indxCol = event[ iColAndAcol[i] ].acol(); | |
430 | if (kindJun > 0) event.endColJunction(iJun, iCol, indxCol); | |
431 | iColAndAcol[i] = iColAndAcol.back(); | |
432 | iColAndAcol.pop_back(); | |
433 | hasFound = true; | |
434 | break; | |
435 | } | |
436 | ||
437 | // In a pinch, check list of colours on other (anti)junction. | |
438 | if (!hasFound && kindJun == 1 && event.sizeJunction() > 1) | |
439 | for (int iAntiJun = 0; iAntiJun < event.sizeJunction(); ++iAntiJun) | |
440 | if (iAntiJun != iJun && event.kindJunction(iAntiJun) == 2) | |
441 | for (int iColAnti = 0; iColAnti < 3; ++iColAnti) | |
442 | if (event.endColJunction(iAntiJun, iColAnti) == indxCol) { | |
443 | iParton.push_back( -(10 + 10 * iAntiJun + iColAnti) ); | |
444 | indxCol = 0; | |
445 | hasFound = true; | |
446 | break; | |
447 | } | |
448 | ||
449 | // Keep on tracing via gluons until reached end of leg. | |
450 | } while (hasFound && indxCol > 0 && loop < loopMax); | |
451 | ||
452 | // Something went wrong in colour tracing. | |
453 | if (!hasFound || loop == loopMax) { | |
454 | infoPtr->errorMsg("Error in HadronLevel::traceFromAcol: " | |
455 | "colour tracing failed"); | |
456 | return false; | |
457 | } | |
458 | ||
459 | // Done. | |
460 | return true; | |
461 | ||
462 | } | |
463 | ||
464 | //********* | |
465 | ||
466 | // Trace a colour loop, from a colour back to the anticolour of the same. | |
467 | ||
468 | bool HadronLevel::traceInLoop(int indxCol, int indxAcol, Event& event) { | |
469 | ||
470 | // Move around until back where begun. | |
471 | int loop = 0; | |
472 | int loopMax = iColAndAcol.size() + 2; | |
473 | bool hasFound = false; | |
474 | do { | |
475 | ++loop; | |
476 | hasFound= false; | |
477 | ||
478 | // Check list of gluons. | |
479 | for (int i = 0; i < int(iColAndAcol.size()); ++i) | |
480 | if (event[ iColAndAcol[i] ].acol() == indxCol) { | |
481 | iParton.push_back( iColAndAcol[i] ); | |
482 | indxCol = event[ iColAndAcol[i] ].col(); | |
483 | iColAndAcol[i] = iColAndAcol.back(); | |
484 | iColAndAcol.pop_back(); | |
485 | hasFound = true; | |
486 | break; | |
487 | } | |
488 | } while (hasFound && indxCol != indxAcol && loop < loopMax); | |
489 | ||
490 | // Something went wrong in colour tracing. | |
491 | if (!hasFound || loop == loopMax) { | |
492 | infoPtr->errorMsg("Error in HadronLevel::traceInLoop: " | |
493 | "colour tracing failed"); | |
494 | return false; | |
495 | } | |
496 | ||
497 | // Done. | |
498 | return true; | |
499 | ||
500 | } | |
501 | ||
502 | //********* | |
503 | ||
504 | // Split junction-antijunction system into two, or simplify other way. | |
505 | ||
506 | bool HadronLevel::splitJunctionPair(Event& event) { | |
507 | ||
508 | // Construct separate index arrays for the three junction legs. | |
509 | int identJun = (-iPartonJun[0])/10; | |
510 | iJunLegA.resize(0); | |
511 | iJunLegB.resize(0); | |
512 | iJunLegC.resize(0); | |
513 | int leg = -1; | |
514 | for (int i = 0; i < int(iPartonJun.size()); ++ i) { | |
515 | if ( (-iPartonJun[i])/10 == identJun) ++leg; | |
516 | if (leg == 0) iJunLegA.push_back( iPartonJun[i] ); | |
517 | else if (leg == 1) iJunLegB.push_back( iPartonJun[i] ); | |
518 | else iJunLegC.push_back( iPartonJun[i] ); | |
519 | } | |
520 | ||
521 | // Construct separate index arrays for the three antijunction legs. | |
522 | int identAnti = (-iPartonAntiJun[0])/10; | |
523 | iAntiLegA.resize(0); | |
524 | iAntiLegB.resize(0); | |
525 | iAntiLegC.resize(0); | |
526 | leg = -1; | |
527 | for (int i = 0; i < int(iPartonAntiJun.size()); ++ i) { | |
528 | if ( (-iPartonAntiJun[i])/10 == identAnti) ++leg; | |
529 | if (leg == 0) iAntiLegA.push_back( iPartonAntiJun[i] ); | |
530 | else if (leg == 1) iAntiLegB.push_back( iPartonAntiJun[i] ); | |
531 | else iAntiLegC.push_back( iPartonAntiJun[i] ); | |
532 | } | |
533 | ||
534 | // Find interjunction legs, i.e. between junction and antijunction. | |
535 | int nMatch = 0; | |
536 | int legJun[3], legAnti[3], nGluLeg[3]; | |
537 | if (iJunLegA.back() < 0) { legJun[nMatch] = 0; | |
538 | legAnti[nMatch] = (-iJunLegA.back())%10; ++nMatch;} | |
539 | if (iJunLegB.back() < 0) { legJun[nMatch] = 1; | |
540 | legAnti[nMatch] = (-iJunLegB.back())%10; ++nMatch;} | |
541 | if (iJunLegC.back() < 0) { legJun[nMatch] = 2; | |
542 | legAnti[nMatch] = (-iJunLegC.back())%10; ++nMatch;} | |
543 | ||
544 | // Loop over interjunction legs. | |
545 | for (int iMatch = 0; iMatch < nMatch; ++iMatch) { | |
546 | vector<int>& iJunLeg = (legJun[iMatch] == 0) ? iJunLegA | |
547 | : ( (legJun[iMatch] == 1) ? iJunLegB : iJunLegC ); | |
548 | vector<int>& iAntiLeg = (legAnti[iMatch] == 0) ? iAntiLegA | |
549 | : ( (legAnti[iMatch] == 1) ? iAntiLegB : iAntiLegC ); | |
550 | ||
551 | // Find number of gluons on each. Do nothing for now if none. | |
552 | nGluLeg[iMatch] = iJunLeg.size() + iAntiLeg.size() - 4; | |
553 | if (nGluLeg[iMatch] == 0) continue; | |
554 | ||
555 | // Else pick up the gluons on the interjunction leg in order. | |
556 | iGluLeg.resize(0); | |
557 | for (int i = 1; i < int(iJunLeg.size()) - 1; ++i) | |
558 | iGluLeg.push_back( iJunLeg[i] ); | |
559 | for (int i = int(iAntiLeg.size()) - 2; i > 0; --i) | |
560 | iGluLeg.push_back( iAntiLeg[i] ); | |
561 | ||
562 | // Remove those gluons from the junction/antijunction leg lists. | |
563 | iJunLeg.resize(1); | |
564 | iAntiLeg.resize(1); | |
565 | ||
566 | // Pick a new quark at random; for simplicity no diquarks. | |
567 | int idQ = flavSel.pickLightQ(); | |
568 | int colQ, acolQ; | |
569 | ||
570 | // If one gluon on leg, split it into a collinear q-qbar pair. | |
571 | if (iGluLeg.size() == 1) { | |
572 | ||
573 | // Store the new q qbar pair, sharing gluon colour and momentum. | |
574 | colQ = event[ iGluLeg[0] ].col(); | |
575 | acolQ = event[ iGluLeg[0] ].acol(); | |
576 | Vec4 pQ = 0.5 * event[ iGluLeg[0] ].p(); | |
577 | double mQ = 0.5 * event[ iGluLeg[0] ].m(); | |
578 | int iQ = event.append( idQ, 75, iGluLeg[0], 0, 0, 0, colQ, 0, pQ, mQ ); | |
579 | int iQbar = event.append( -idQ, 75, iGluLeg[0], 0, 0, 0, 0, acolQ, | |
580 | pQ, mQ ); | |
581 | ||
582 | // Mark split gluon and update junction and antijunction legs. | |
583 | event[ iGluLeg[0] ].statusNeg(); | |
584 | event[ iGluLeg[0] ].daughters( iQ, iQbar); | |
585 | iJunLeg.push_back(iQ); | |
586 | iAntiLeg.push_back(iQbar); | |
587 | ||
588 | // If several gluons on the string, decide which g-g region to split up. | |
589 | } else { | |
590 | ||
591 | // Evaluate mass-squared for all adjacent gluon pairs. | |
592 | m2Pair.resize(0); | |
593 | double m2Sum = 0.; | |
594 | for (int i = 0; i < int(iGluLeg.size()) - 1; ++i) { | |
595 | double m2Now = 0.5 * event[ iGluLeg[i] ].p() | |
596 | * event[ iGluLeg[i + 1] ].p(); | |
597 | m2Pair.push_back(m2Now); | |
598 | m2Sum += m2Now; | |
599 | } | |
600 | ||
601 | // Pick breakup region with probability proportional to mass-squared. | |
602 | double m2Reg = m2Sum * Rndm::flat(); | |
603 | int iReg = -1; | |
604 | do m2Reg -= m2Pair[++iReg]; | |
605 | while (m2Reg > 0. && iReg < int(iGluLeg.size()) - 1); | |
606 | m2Reg = m2Pair[iReg]; | |
607 | ||
608 | // Pick breaking point of string in chosen region (symmetrically). | |
609 | double m2Temp = min( JJSTRINGM2MAX, JJSTRINGM2FRAC * m2Reg); | |
610 | double xPos = 0.5; | |
611 | double xNeg = 0.5; | |
612 | do { | |
613 | double zTemp = zSel.zFrag( idQ, 0, m2Temp); | |
614 | xPos = 1. - zTemp; | |
615 | xNeg = m2Temp / (zTemp * m2Reg); | |
616 | } while (xNeg > 1.); | |
617 | if (Rndm::flat() > 0.5) swap(xPos, xNeg); | |
618 | ||
619 | // Pick up two "mother" gluons of breakup. Mark them decayed. | |
620 | Particle& gJun = event[ iGluLeg[iReg] ]; | |
621 | Particle& gAnti = event[ iGluLeg[iReg + 1] ]; | |
622 | gJun.statusNeg(); | |
623 | gAnti.statusNeg(); | |
624 | int dau1 = event.size(); | |
625 | gJun.daughters(dau1, dau1 + 3); | |
626 | gAnti.daughters(dau1, dau1 + 3); | |
627 | int mother1 = min( iGluLeg[iReg], iGluLeg[iReg + 1]); | |
628 | int mother2 = max( iGluLeg[iReg], iGluLeg[iReg + 1]); | |
629 | ||
630 | // Can keep one of old colours but need one new so unambiguous. | |
631 | colQ = gJun.acol(); | |
632 | acolQ = event.nextColTag(); | |
633 | ||
634 | // Store copied gluons with reduced momenta. | |
635 | int iGjun = event.append( 21, 75, mother1, mother2, 0, 0, | |
636 | gJun.col(), gJun.acol(), (1. - 0.5 * xPos) * gJun.p(), | |
637 | (1. - 0.5 * xPos) * gJun.m()); | |
638 | int iGanti = event.append( 21, 75, mother1, mother2, 0, 0, | |
639 | acolQ, gAnti.acol(), (1. - 0.5 * xNeg) * gAnti.p(), | |
640 | (1. - 0.5 * xNeg) * gAnti.m()); | |
641 | ||
642 | // Store the new q qbar pair with remaining momenta. | |
643 | int iQ = event.append( idQ, 75, mother1, mother2, 0, 0, | |
644 | colQ, 0, 0.5 * xNeg * gAnti.p(), 0.5 * xNeg * gAnti.m() ); | |
645 | int iQbar = event.append( -idQ, 75, mother1, mother2, 0, 0, | |
646 | 0, acolQ, 0.5 * xPos * gJun.p(), 0.5 * xPos * gJun.m() ); | |
647 | ||
648 | // Update junction and antijunction legs with gluons and quarks. | |
649 | for (int i = 0; i < iReg; ++i) | |
650 | iJunLeg.push_back( iGluLeg[i] ); | |
651 | iJunLeg.push_back(iGjun); | |
652 | iJunLeg.push_back(iQ); | |
653 | for (int i = int(iGluLeg.size()) - 1; i > iReg + 1; --i) | |
654 | iAntiLeg.push_back( iGluLeg[i] ); | |
655 | iAntiLeg.push_back(iGanti); | |
656 | iAntiLeg.push_back(iQbar); | |
657 | } | |
658 | ||
659 | // Update end colours for both g -> q qbar and g g -> g g q qbar. | |
660 | event.endColJunction(identJun - 1, legJun[iMatch], colQ); | |
661 | event.endColJunction(identAnti - 1, legAnti[iMatch], acolQ); | |
662 | } | |
663 | ||
664 | // Update list of interjunction legs after splittings above. | |
665 | int iMatchUp = 0; | |
666 | while (iMatchUp < nMatch) { | |
667 | if (nGluLeg[iMatchUp] > 0) { | |
668 | for (int i = iMatchUp; i < nMatch - 1; ++i) { | |
669 | legJun[i] = legJun[i + 1]; | |
670 | legAnti[i] = legAnti[i + 1]; | |
671 | nGluLeg[i] = nGluLeg[i + 1]; | |
672 | } --nMatch; | |
673 | } else ++iMatchUp; | |
674 | } | |
675 | ||
676 | // Should not ever have three empty interjunction legs. | |
677 | if (nMatch == 3) { | |
678 | infoPtr->errorMsg("Error in HadronLevel::splitJunctionPair: " | |
679 | "three empty junction-junction legs"); | |
680 | return false; | |
681 | } | |
682 | ||
683 | // If two legs are empty, then collapse system to a single string. | |
684 | if (nMatch == 2) { | |
685 | int legJunLeft = 3 - legJun[0] - legJun[1]; | |
686 | int legAntiLeft = 3 - legAnti[0] - legAnti[1]; | |
687 | vector<int>& iJunLeg = (legJunLeft == 0) ? iJunLegA | |
688 | : ( (legJunLeft == 1) ? iJunLegB : iJunLegC ); | |
689 | vector<int>& iAntiLeg = (legAntiLeft == 0) ? iAntiLegA | |
690 | : ( (legAntiLeft == 1) ? iAntiLegB : iAntiLegC ); | |
691 | iPartonJun.resize(0); | |
692 | for (int i = int(iJunLeg.size()) - 1; i > 0; --i) | |
693 | iPartonJun.push_back( iJunLeg[i] ); | |
694 | for (int i = 1; i < int(iAntiLeg.size()); ++i) | |
695 | iPartonJun.push_back( iAntiLeg[i] ); | |
696 | ||
697 | // Other string system empty. Remove junctions from their list. Done. | |
698 | iPartonAntiJun.resize(0); | |
699 | event.eraseJunction( max(identJun, identAnti) - 1); | |
700 | event.eraseJunction( min(identJun, identAnti) - 1); | |
701 | return true; | |
702 | } | |
703 | ||
704 | // If one leg is empty then, depending on string length, either | |
705 | // (a) annihilate junction and antijunction into two simple strings, or | |
706 | // (b) split the empty leg by borrowing energy from nearby legs. | |
707 | if (nMatch == 1) { | |
708 | ||
709 | // Identify the two external legs of either junction. | |
710 | vector<int>& iJunLeg0 = (legJun[0] == 0) ? iJunLegB : iJunLegA; | |
711 | vector<int>& iJunLeg1 = (legJun[0] == 2) ? iJunLegB : iJunLegC; | |
712 | vector<int>& iAntiLeg0 = (legAnti[0] == 0) ? iAntiLegB : iAntiLegA; | |
713 | vector<int>& iAntiLeg1 = (legAnti[0] == 2) ? iAntiLegB : iAntiLegC; | |
714 | ||
715 | // Simplified procedure: mainly study first parton on each leg. | |
716 | Vec4 pJunLeg0 = event[ iJunLeg0[1] ].p(); | |
717 | Vec4 pJunLeg1 = event[ iJunLeg1[1] ].p(); | |
718 | Vec4 pAntiLeg0 = event[ iAntiLeg0[1] ].p(); | |
719 | Vec4 pAntiLeg1 = event[ iAntiLeg1[1] ].p(); | |
720 | ||
721 | // Starting frame hopefully intermediate to two junction directions. | |
722 | Vec4 pStart = pJunLeg0 / pJunLeg0.e() + pJunLeg1 / pJunLeg1.e() | |
723 | + pAntiLeg0 / pAntiLeg0.e() + pAntiLeg1 / pAntiLeg1.e(); | |
724 | ||
725 | // Loop over iteration to junction/antijunction rest frames (JRF/ARF). | |
726 | RotBstMatrix MtoJRF, MtoARF; | |
727 | Vec4 pInJRF[3], pInARF[3]; | |
728 | for (int iJun = 0; iJun < 2; ++iJun) { | |
729 | int offset = (iJun == 0) ? 0 : 2; | |
730 | ||
731 | // Iterate from system rest frame towards the junction rest frame. | |
732 | RotBstMatrix MtoRF, Mstep; | |
733 | MtoRF.bstback(pStart); | |
734 | Vec4 pInRF[4]; | |
735 | int iter = 0; | |
736 | do { | |
737 | ++iter; | |
738 | ||
739 | // Find rest-frame momenta on the three sides of the junction. | |
740 | // Only consider first parton on each leg, for simplicity. | |
741 | pInRF[0 + offset] = pJunLeg0; | |
742 | pInRF[1 + offset] = pJunLeg1; | |
743 | pInRF[2 - offset] = pAntiLeg0; | |
744 | pInRF[3 - offset] = pAntiLeg1; | |
745 | for (int i = 0; i < 4; ++i) pInRF[i].rotbst(MtoRF); | |
746 | ||
747 | // For third side add both legs beyond other junction, weighted. | |
748 | double wt2 = 1. - exp( -pInRF[2].e() / eNormJunction); | |
749 | double wt3 = 1. - exp( -pInRF[3].e() / eNormJunction); | |
750 | pInRF[2] = wt2 * pInRF[2] + wt3 * pInRF[3]; | |
751 | ||
752 | // Find new junction rest frame from the set of momenta. | |
753 | Mstep = stringFrag.junctionRestFrame( pInRF[0], pInRF[1], pInRF[2]); | |
754 | MtoRF.rotbst( Mstep ); | |
755 | } while (iter < 3 || (Mstep.deviation() > CONVJNREST | |
756 | && iter < NTRYJNREST) ); | |
757 | ||
758 | // Store final boost and rest-frame (weighted) momenta. | |
759 | if (iJun == 0) { | |
760 | MtoJRF = MtoRF; | |
761 | for (int i = 0; i < 3; ++i) pInJRF[i] = pInRF[i]; | |
762 | } else { | |
763 | MtoARF = MtoRF; | |
764 | for (int i = 0; i < 3; ++i) pInARF[i] = pInRF[i]; | |
765 | } | |
766 | } | |
767 | ||
768 | // Opposite operations: boost from JRF/ARF to original system. | |
769 | RotBstMatrix MfromJRF = MtoJRF; | |
770 | MfromJRF.invert(); | |
771 | RotBstMatrix MfromARF = MtoARF; | |
772 | MfromARF.invert(); | |
773 | ||
774 | // Velocity vectors of junctions and momentum of legs in lab frame. | |
775 | Vec4 vJun(0., 0., 0., 1.); | |
776 | vJun.rotbst(MfromJRF); | |
777 | Vec4 vAnti(0., 0., 0., 1.); | |
778 | vAnti.rotbst(MfromARF); | |
779 | Vec4 pLabJ[3], pLabA[3]; | |
780 | for (int i = 0; i < 3; ++i) { | |
781 | pLabJ[i] = pInJRF[i]; | |
782 | pLabJ[i].rotbst(MfromJRF); | |
783 | pLabA[i] = pInARF[i]; | |
784 | pLabA[i].rotbst(MfromARF); | |
785 | } | |
786 | ||
787 | // Calculate Lambda-measure length of three possible topologies. | |
788 | double vJvA = vJun * vAnti; | |
789 | double vJvAe2y = vJvA + sqrt(vJvA*vJvA - 1.); | |
790 | double LambdaJA = (2. * pInJRF[0].e()) * (2. * pInJRF[1].e()) | |
791 | * (2. * pInARF[0].e()) * (2. * pInARF[1].e()) * vJvAe2y; | |
792 | double Lambda00 = (2. * pLabJ[0] * pLabA[0]) | |
793 | * (2. * pLabJ[1] * pLabA[1]); | |
794 | double Lambda01 = (2. * pLabJ[0] * pLabA[1]) | |
795 | * (2. * pLabJ[1] * pLabA[0]); | |
796 | ||
797 | // Case when either topology without junctions is the shorter one. | |
798 | if (LambdaJA > min( Lambda00, Lambda01)) { | |
799 | vector<int>& iAntiMatch0 = (Lambda00 < Lambda01) | |
800 | ? iAntiLeg0 : iAntiLeg1; | |
801 | vector<int>& iAntiMatch1 = (Lambda00 < Lambda01) | |
802 | ? iAntiLeg1 : iAntiLeg0; | |
803 | ||
804 | // Define two quark-antiquark strings. | |
805 | iPartonJun.resize(0); | |
806 | for (int i = int(iJunLeg0.size()) - 1; i > 0; --i) | |
807 | iPartonJun.push_back( iJunLeg0[i] ); | |
808 | for (int i = 1; i < int(iAntiMatch0.size()); ++i) | |
809 | iPartonJun.push_back( iAntiMatch0[i] ); | |
810 | iPartonAntiJun.resize(0); | |
811 | for (int i = int(iJunLeg1.size()) - 1; i > 0; --i) | |
812 | iPartonAntiJun.push_back( iJunLeg1[i] ); | |
813 | for (int i = 1; i < int(iAntiMatch1.size()); ++i) | |
814 | iPartonAntiJun.push_back( iAntiMatch1[i] ); | |
815 | ||
816 | // Remove junctions from their list. Done. | |
817 | event.eraseJunction( max(identJun, identAnti) - 1); | |
818 | event.eraseJunction( min(identJun, identAnti) - 1); | |
819 | return true; | |
820 | } | |
821 | ||
822 | // Case where junction and antijunction to be separated. | |
823 | // Shuffle (p+/p-) momentum of order <mThad> between systems, | |
824 | // times 2/3 for 120 degree in JRF, times 1/2 for two legs, | |
825 | // but not more than half of what nearest parton carries. | |
826 | double eShift = MTHAD / (3. * sqrt(vJvAe2y)); | |
827 | double fracJ0 = min(0.5, eShift / pInJRF[0].e()); | |
828 | double fracJ1 = min(0.5, eShift / pInJRF[0].e()); | |
829 | Vec4 pFromJun = fracJ0 * pJunLeg0 + fracJ1 * pJunLeg1; | |
830 | double fracA0 = min(0.5, eShift / pInARF[0].e()); | |
831 | double fracA1 = min(0.5, eShift / pInARF[0].e()); | |
832 | Vec4 pFromAnti = fracA0 * pAntiLeg0 + fracA1 * pAntiLeg1; | |
833 | ||
834 | // Copy partons with scaled-down momenta and update legs. | |
835 | int iNew = event.copy(iJunLeg0[1], 76); | |
836 | event[iNew].rescale5(1. - fracJ0); | |
837 | iJunLeg0[1] = iNew; | |
838 | iNew = event.copy(iJunLeg1[1], 76); | |
839 | event[iNew].rescale5(1. - fracJ1); | |
840 | iJunLeg1[1] = iNew; | |
841 | iNew = event.copy(iAntiLeg0[1], 76); | |
842 | event[iNew].rescale5(1. - fracA0); | |
843 | iAntiLeg0[1] = iNew; | |
844 | iNew = event.copy(iAntiLeg1[1], 76); | |
845 | event[iNew].rescale5(1. - fracA1); | |
846 | iAntiLeg1[1] = iNew; | |
847 | ||
848 | // Pick a new quark at random; for simplicity no diquarks. | |
849 | int idQ = flavSel.pickLightQ(); | |
850 | ||
851 | // Update junction colours for new quark and antiquark. | |
852 | int colQ = event.nextColTag(); | |
853 | int acolQ = event.nextColTag(); | |
854 | event.endColJunction(identJun - 1, legJun[0], colQ); | |
855 | event.endColJunction(identAnti - 1, legAnti[0], acolQ); | |
856 | ||
857 | // Store new quark and antiquark with momentum from other junction. | |
858 | int mother1 = min(iJunLeg0[1], iJunLeg1[1]); | |
859 | int mother2 = max(iJunLeg0[1], iJunLeg1[1]); | |
860 | int iNewJ = event.append( idQ, 76, mother1, mother2, 0, 0, | |
861 | colQ, 0, pFromAnti, pFromAnti.mCalc() ); | |
862 | mother1 = min(iAntiLeg0[1], iAntiLeg1[1]); | |
863 | mother2 = max(iAntiLeg0[1], iAntiLeg1[1]); | |
864 | int iNewA = event.append( -idQ, 76, mother1, mother2, 0, 0, | |
865 | 0, acolQ, pFromJun, pFromJun.mCalc() ); | |
866 | ||
867 | // Bookkeep new quark and antiquark on third legs. | |
868 | if (legJun[0] == 0) iJunLegA[1] = iNewJ; | |
869 | else if (legJun[0] == 1) iJunLegB[1] = iNewJ; | |
870 | else iJunLegC[1] = iNewJ; | |
871 | if (legAnti[0] == 0) iAntiLegA[1] = iNewA; | |
872 | else if (legAnti[0] == 1) iAntiLegB[1] = iNewA; | |
873 | else iAntiLegC[1] = iNewA; | |
874 | ||
875 | // Done with splitting junction from antijunction. | |
876 | } | |
877 | ||
878 | // Put together new junction parton list. | |
879 | iPartonJun.resize(0); | |
880 | for (int i = 0; i < int(iJunLegA.size()); ++i) | |
881 | iPartonJun.push_back( iJunLegA[i] ); | |
882 | for (int i = 0; i < int(iJunLegB.size()); ++i) | |
883 | iPartonJun.push_back( iJunLegB[i] ); | |
884 | for (int i = 0; i < int(iJunLegC.size()); ++i) | |
885 | iPartonJun.push_back( iJunLegC[i] ); | |
886 | ||
887 | // Put together new antijunction parton list. | |
888 | iPartonAntiJun.resize(0); | |
889 | for (int i = 0; i < int(iAntiLegA.size()); ++i) | |
890 | iPartonAntiJun.push_back( iAntiLegA[i] ); | |
891 | for (int i = 0; i < int(iAntiLegB.size()); ++i) | |
892 | iPartonAntiJun.push_back( iAntiLegB[i] ); | |
893 | for (int i = 0; i < int(iAntiLegC.size()); ++i) | |
894 | iPartonAntiJun.push_back( iAntiLegC[i] ); | |
895 | ||
896 | // Now the two junction systems are separated and can be stored. | |
897 | return true; | |
898 | ||
899 | } | |
900 | ||
901 | //************************************************************************** | |
902 | ||
903 | } // end namespace Pythia8 | |
904 |