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d909f169 | 1 | |
2 | A new version of the Monte Carlo program HERWIG (version 6.1) is now | |
3 | available, and can be obtained from the following web site: | |
4 | ||
5 | http://hepwww.rl.ac.uk/theory/seymour/herwig/ | |
6 | ||
7 | This will temporarily be mirrored at CERN for the next few weeks: | |
8 | ||
9 | http://home.cern.ch/~seymour/herwig/ | |
10 | ||
11 | More complete information on HERWIG can be found in the publication | |
12 | G. Marchesini, B.R. Webber, G. Abbiendi, I.G. Knowles, M.H. Seymour | |
13 | and L. Stanco, Computer Phys. Commun. 67 (1992) 465 and also in the | |
14 | documentation for the previous version (5.9), which are available at | |
15 | the same site, together with other useful files and information. | |
16 | Here we merely give the new features relative to 5.9. | |
17 | ||
18 | If you use HERWIG, please refer to it something along the lines of: | |
19 | ||
20 | HERWIG 6.1, hep-ph/9912396; G. Marchesini, B.R. Webber, G. Abbiendi, | |
21 | I.G. Knowles, M.H. Seymour and L. Stanco, | |
22 | Computer Phys. Commun. 67 (1992) 465. | |
23 | ||
24 | ||
25 | *** NEW FEATURES OF THIS VERSION *** | |
26 | ||
27 | *---------------------------------------------------------------* | |
28 | | The main new features are: supersymmetric processes (both | | |
29 | | R-parity conserving & violating) in hadron-hadron collisions; | | |
30 | | new e+e- to four jets process; matrix element corrections to | | |
31 | | top decay and Drell-Yan processes; new soft underlying event | | |
32 | | options; updates to default particle data tables; new LaTeX & | | |
33 | | html printout options. | | |
34 | *---------------------------------------------------------------* | |
35 | ||
36 | * [N.B. Default values for input variables shown in square brackets.] | |
37 | ||
38 | * All R-parity conserving SUSY two-to-two processes in hadron-hadron | |
39 | collisions have been added. Their process numbers are: | |
40 | ||
41 | +-------+----------------------------------------------------------+ | |
42 | | IPROC | Process | | |
43 | +-------+----------------------------------------------------------+ | |
44 | | 3000 | 2 parton to 2 sparticles: the sum of 3010,3020 and 3030 | | |
45 | | 3010 | 2 parton to 2 spartons | | |
46 | | 3020 | 2 parton to 2 gauginos | | |
47 | | 3030 | 2 parton to 2 sleptons | | |
48 | +-------+----------------------------------------------------------+ | |
49 | ||
50 | Further details of the inclusion of superpartners and their decays | |
51 | are given below. | |
52 | ||
53 | Additional processes for the SUSY two Higgs doublet model are | |
54 | currently under test and will be released shortly. | |
55 | ||
56 | * All R-parity violating SUSY two-to-two processes via resonant | |
57 | sleptons and squarks in hadron collisions have been added. Their | |
58 | process numbers are: | |
59 | ||
60 | +-------+----------------------------------------------------------+ | |
61 | | IPROC | Processes derived from the LQD term in the superpotential| | |
62 | +-------+----------------------------------------------------------+ | |
63 | | 4000 | The sum of 4010,4020,4040 and 4050 | | |
64 | | 4010 | Neutralino lepton production (all neutralinos) | | |
65 | | 401i | As 4010 but only the ith neutralino | | |
66 | | 4020 | Chargino lepton production (all charginos) | | |
67 | | 402i | As 4020 but only the ith chargino | | |
68 | | 4040 | Slepton W/Z production | | |
69 | | 4050 | Slepton Higgs production | | |
70 | +-------+----------------------------------------------------------+ | |
71 | | 4060 | Sum of 4070 and 4080 | | |
72 | | 4070 | quark-antiquark production via LQD | | |
73 | | 4080 | lepton production via LLE and LQD | | |
74 | +=======+==========================================================+ | |
75 | | IPROC | Processes derived from the UDD term in the superpotential| | |
76 | +-------+----------------------------------------------------------+ | |
77 | | 4100 | The sum of 4110, 4120, 4130, 4140 and 4150 | | |
78 | | 4110 | Neutralino quark production (all neutralinos) | | |
79 | | 411i | As 4110 but only the ith neutralino | | |
80 | | 4120 | Chargino quark production (all charginos) | | |
81 | | 412i | As 4120 but only the ith chargino | | |
82 | | 4130 | Gluino quark production | | |
83 | | 4140 | Squark W/Z production | | |
84 | | 4150 | Squark Higgs production | | |
85 | +-------+----------------------------------------------------------+ | |
86 | | 4160 | quark-quark production | | |
87 | +-------+----------------------------------------------------------+ | |
88 | ||
89 | In addition the R-parity violating decays of all superpartners is | |
90 | included. | |
91 | ||
92 | * A new process describing electron-positron annihilation to four jets | |
93 | has been added. This has IPROC=600+IQ, where a non-zero value for IQ | |
94 | guarantees production of quark flavour IQ whilst IQ=0 corresponds to | |
95 | the natural flavour mix. IPROC=650+IQ is as above but without those | |
96 | terms in the matrix element which orient the event w.r.t. the lepton | |
97 | beam direction. The matrix elements are based on those of Ellis Ross | |
98 | & Terrano with orientation terms from Catani & Seymour. The soft and | |
99 | collinear divergences are avoided by imposing a minimum y-cut, Y4JT | |
100 | [.01], on the initial 4 partons. The interjet distance is calculated | |
101 | using either the Durham or JADE metrics. This choice is governed by | |
102 | the logical variable DURHAM [.TRUE.]. Note that parameterizations of | |
103 | the volume of four-body phase space are used: these are accurate up | |
104 | to a few percent for y-cut values less than 0.14. Note, also that | |
105 | the phase space is for massless partons, as are the matrix elements, | |
106 | though a mass threshold cut is applied. Finally, the matrix elements | |
107 | for the q-qbar-g-g & q-qbar-q-qbar (same flavour quark) final states | |
108 | receive contributions from 2 colour flows each, the treatment of the | |
109 | interference terms being controlled by the array IOP4JT: | |
110 | ||
111 | q-qbar-g-g case: | |
112 | IOP4JT(1)=0 neglect, =1 extreme 2341; =2 extreme 3421 [0] | |
113 | ||
114 | q-qbar-q-qbar (identical quark flavour) case: | |
115 | IOP4JT(2)=0 neglect, =1 extreme 4123; =2 extreme 2143 [0] | |
116 | ||
117 | The scale EMSCA for the parton showers is set equal to SQRT(s*ymin) | |
118 | where ymin is the least distance, according to the selected metric, | |
119 | between any two partons. | |
120 | ||
121 | * Matrix element corrections to the simulation of top quark decays and | |
122 | Drell-Yan processes are now available using the same general method | |
123 | as already implemented for e+e- annihilation and DIS. If HARDME | |
124 | [.TRUE.] then fill the missing phase-space (`dead zone') using the | |
125 | exact 1st-order M.E. result (`hard corrections'). If SOFTME | |
126 | [.TRUE.] then correct emissions in the already-populated region of | |
127 | phase space using the exact amplitude for every emission that is | |
128 | capable of being the hardest so far (`soft corrections'). | |
129 | ||
130 | - For t -> bW decays the routine HWBTOP implements hard corrections. | |
131 | HWBRAN has been modified to implement the soft corrections to top | |
132 | decays. Since the dead zone includes part of the soft singularity | |
133 | a cutoff is required: only gluons with energy above GCUTME [2 GeV] | |
134 | (in the top rest frame) are corrected. Physical quantities are not | |
135 | strongly dependent on GCUTME in the range 1 to 5 GeV. For details | |
136 | see: | |
137 | ||
138 | G. Corcella and M.H. Seymour, Phys. Lett. B442 (1998) 417. | |
139 | ||
140 | - For the Drell-Yan process the routine HWBDYP implements the hard | |
141 | corrections whilst HWSBRN has been modified to implement the soft | |
142 | corrections to the initial state radiation. For details see: | |
143 | ||
144 | G. Corcella and M.H. Seymour, hep-ph/9908338. | |
145 | ||
146 | * The parameters of the model used for soft interactions are now | |
147 | available to the user for modification. The model is based on the | |
148 | minimum-bias event generator of the UA5 Collaboration, which starts | |
149 | from a parametrization of the pbar p inelastic charged multiplicity | |
150 | distribution as a negative binomial. The parameters are as follows | |
151 | (default parameter values are the UA5 ones used in previous | |
152 | versions): | |
153 | ||
154 | +-------+---------------------------+---------+ | |
155 | | Name | Description | Default | | |
156 | +-------+---------------------------+---------+ | |
157 | | PMBN1 | a in <n> = a*S^b+c | 9.11 | | |
158 | | PMBN2 | b in <n> = a*S^b+c | 0.115 | | |
159 | | PMBN3 | c in <n> = a*S^b+c | -9.50 | | |
160 | | | | | | |
161 | | PMBK1 | a in 1/k = a*log_e(S)+b | 0.029 | | |
162 | | PMBK2 | b in 1/k = a*log_e(S)+b | -0.104 | | |
163 | | | | | | |
164 | | PMBM1 | a in (M-m_1-m_2-a)e^{-bM} | 0.4 | | |
165 | | PMBM2 | b in (M-m_1-m_2-a)e^{-bM} | 2.0 | | |
166 | | | | | | |
167 | | PMBP1 | p_t slope for d,u | 5.2 | | |
168 | | PMBP2 | p_t slope for s,c | 3.0 | | |
169 | | PMBP3 | p_t slope for qq | 5.2 | | |
170 | +-------+---------------------------+---------+ | |
171 | ||
172 | The first three parametrize the mean charged multiplicity at | |
173 | c.m. energy \sqrt{s} as indicated. The next two specify the | |
174 | parameter k in the negative binomial charged multiplicity | |
175 | distribution. The parameters PMBM1 and PMBM2 describe the | |
176 | distribution of cluster masses M in the soft collision. These soft | |
177 | clusters are generated with a flat rapidity distribution with | |
178 | gaussian shoulders. The transverse momentum distribution of soft | |
179 | clusters has the form | |
180 | ||
181 | P(p_t)\propto p_t\exp(-b\sqrt{p_t^2+M^2}) | |
182 | ||
183 | where the slope parameter b depends as indicated on the flavour of | |
184 | the quark or diquark pair created when the cluster was produced. | |
185 | ||
186 | As an option, for underlying events the value of \sqrt{s} used to | |
187 | choose the multiplicity n may be enhanced by a parameter ENSOF to | |
188 | allow for an enhanced underlying activity in hard events. The actual | |
189 | charged multiplicity is then taken to be n plus the sum of the | |
190 | moduli of the charges of the colliding hadrons or clusters. | |
191 | ||
192 | * There have been a number of additions/changes to the default hadrons | |
193 | included via HWUDAT. Here the identification of hadrons follows the | |
194 | PDG ('98 edition) table 13.2 with numbering according to section 31. | |
195 | ||
196 | New isoscalars states have been added to try to complete the 1^3D_3, | |
197 | 1^1D_2 and 1^3D_1 multiplets: | |
198 | ||
199 | IDHW RNAME IDPDG IDHW RNAME IDPDG | |
200 | ---- ----- ----- ---- ----- ----- | |
201 | 395 OMEGA_3 227 396 PHI_3 337 | |
202 | 397 ETA_2(L) 10225 398 ETA_2(H) 10335 | |
203 | 399 OMEGA(H) 30223 | |
204 | ||
205 | Also the following states have been re-identified/replaced: | |
206 | ||
207 | IDHW RNAME IDPDG IDHW RNAME IDPDG | |
208 | ---- ----- ----- ---- ----- ----- | |
209 | 57 FH_1 20333 | |
210 | 293 F0P0 9010221 294 FH_00 10221 | |
211 | 62 A_0(H)0 10111 290 A_00 9000111 | |
212 | 63 A_0(H)+ 10211 291 A_0+ 9000211 | |
213 | 64 A_0(H)- -10211 292 A_0- -9000211 | |
214 | ||
215 | The f_1(1420) state completely replaces the f_1(1520) in the 1^3P_0 | |
216 | multiplet, taking over 57. The f_0(1370) (294) replaces the f_0(980) | |
217 | (293) in the 1^3P_0 multiplet; the latter is retained as it appears | |
218 | in the decays of several other states. The new a_0(1450) states (62 | |
219 | -64) replace the three old a_0(980) states (290 - 292) in the 1^3P_0 | |
220 | multiplet; the latter are kept, as they appear in f_1(1285) decays. | |
221 | ||
222 | By default production of the f_0(980) and a_0(980) states in cluster | |
223 | decays is vetoed. | |
224 | ||
225 | Also, the PDG numbers for the remnant particles have been changed to | |
226 | 98 for REMG and 99 for REMN. | |
227 | ||
228 | * Since version 6.1 contains a large number of supersymmetry processes | |
229 | several new particles have been added. | |
230 | ||
231 | Extra scalar bosons for the two Higgs Doublet (SUSY) scenario: | |
232 | ||
233 | IDHW RNAME IDPDG IDHW RNAME IDPDG | |
234 | ---- ----- ----- ---- ----- ----- | |
235 | 203 HIGGSL0 26 206 HIGGS+ 37 | |
236 | 204 HIGGSH0 35 207 HIGGS- -37 | |
237 | 205 HIGGSA0 36 | |
238 | ||
239 | Note that the lighter neutral scalar (203) is given the non-standard | |
240 | PDG number 26, in order to distinguish it from the minimal SM Higgs, | |
241 | PDG number 25. | |
242 | ||
243 | Extra sfermions and gauginos for SUSY scenarios: | |
244 | ||
245 | IDHW RNAME IDPDG IDHW RNAME IDPDG | |
246 | ---- ----- ----- ---- ----- ----- | |
247 | 401 SSDL 1000001 413 SSDR 2000001 | |
248 | | | | | | | | |
249 | 406 SST1 1000006 418 SST2 2000006 | |
250 | 407 SSDLBR -1000001 419 SSDRBR -2000001 | |
251 | | | | | | | | |
252 | 412 SST1BR -1000006 424 SST2BR -2000006 | |
253 | ||
254 | 425 SSEL- 1000011 437 SSER- 2000011 | |
255 | | | | | | | | |
256 | 430 SSNUTL 1000016 442 SSNUTR 2000016 | |
257 | 431 SSEL+ -1000011 443 SSER+ -2000011 | |
258 | | | | | | | | |
259 | 436 SSNUTLBR -1000016 448 SSNUTRBR -2000016 | |
260 | ||
261 | 449 GLUINO 1000021 454 CHGINO1+ 1000024 | |
262 | 450 NTLINO1 1000022 455 CHGINO2+ 1000037 | |
263 | 451 NTLINO2 1000023 456 CHGINO1 -1000024 | |
264 | 452 NTLINO3 1000025 457 CHGINO2 -1000037 | |
265 | 453 NTLINO4 1000035 458 GRAVTINO 1000039 | |
266 | ||
267 | The implementation of SUSY is discussed more fully below. Note that | |
268 | the default masses of the SUSY particles are zero and that they have | |
269 | no decay modes. Before a SUSY process can be simulated you must load | |
270 | the appropriate masses and decay modes generated using ISAWIG (see | |
271 | below) or an equivalent program. | |
272 | ||
273 | These new states don't interfere with the user's ability to add new | |
274 | particles as previously described. | |
275 | ||
276 | * It is now possible to create particle property and event listings in | |
277 | any combination of 3 formats - standard ASCII, LaTeX or html. These | |
278 | options are controlled by the new, logical variables PRNDEF [.TRUE.] | |
279 | PRNTEX [.FALSE.] and PRNWEB [.FALSE.]. The ASCII output is directed | |
280 | to stout (screen / log file) as in previous versions. When a listing | |
281 | of particle properties is requested (IPRINT.GE.2 or HWUDPR is called | |
282 | explicitly) then the following files are produced: | |
283 | ||
284 | If (PRNTEX): HW_decays.tex | |
285 | If (PRNWEB): HW_decays/index.html | |
286 | /PART0000001.html etc. | |
287 | ||
288 | The HW_decays.tex file is written to the working directory whilst | |
289 | the many **.html files appear in the sub-directory HW_decays/ which | |
290 | must have been created previously. Paper sizes and offsets for the | |
291 | LaTeX output are stored at the top of the block data file HWUDAT: | |
292 | they may need modifying to suit a particular printer. When event | |
293 | listings are requested (NEVHEP.LE.MAXPR.NE.0 or HWUEPR is called | |
294 | explicitly) the following files are created in the current working | |
295 | directory: | |
296 | ||
297 | If (PRNTEX): HWEV_*******.tex where *******=0000001 etc. | |
298 | If (PRNWEB): HWEV_*******.html is the event number | |
299 | ||
300 | Note the .html file automatically makes links to the index.html file | |
301 | of particle properties assumed to be in the HW_decays sub-directory. | |
302 | ||
303 | A new integer variable NPRFMT [1] has been introduced to control how | |
304 | many significant figures are shown in each of the 3 event outputs. | |
305 | Basically NPRFMT=1 gives short compact outputs whilst NPRFMT=2 gives | |
306 | long formats. | |
307 | ||
308 | Note that all the LaTeX files use the package longtable.sty to | |
309 | format the tables. Also if NPRFMT=2 or PRVTX=.TRUE. then the LaTeX | |
310 | files are designed to be printed in landscape mode. | |
311 | ||
312 | * There were previously some inconsistencies and ambiguities in our | |
313 | conventions for the mixing of flavour `octet' and `singlet' mesons. | |
314 | They are now: | |
315 | ||
316 | Multiplet Octet Singlet Mixing Angle | |
317 | --------- ----- ------- ------------ | |
318 | 1^1S_0 eta eta' ETAMIX=-23. | |
319 | 1^3S_1 phi omega PHIMIX=+36. | |
320 | 1^1P_1 h_1(1380) h_1(1170) H1MIX =ANGLE | |
321 | 1^3P_0 MISSING f_0(1370) F0MIX =ANGLE | |
322 | 1^3P_1 f_1(1420) f_1(1285) F1MIX =ANGLE | |
323 | 1^3P_2 f'_2 f_2 F2MIX =+26. | |
324 | 1^1D_2 eta_2(1645) eta_2(1870) ET2MIX=ANGLE | |
325 | 1^3D_1 MISSING omega(1600) OMHMIX=ANGLE | |
326 | 1^3D_3 phi_3 omega_3 PH3MIX=+28. | |
327 | ||
328 | After mixing the quark content of the physical states is given, in | |
329 | terms of the mixing angle, theta, by: | |
330 | ||
331 | (ddbar+uubar)/sqrt(2) ssbar | |
332 | --------------------- ----- | |
333 | Octet: cos(theta+theta_0) -sin(theta+theta_0) | |
334 | Singlet: sin(theta+theta_0) cos(theta+theta_0) | |
335 | ||
336 | where theta_0=ATAN(SQRT(2)). Hence, using the default value of | |
337 | ANGLE=ATAN(1/SQRT(2))*180/ACOS(-ONE) for theta gives ideal mixing, | |
338 | that is, the `octet' state = ssbar and the `singlet' = | |
339 | (ddbar+uubar)/sqrt(2). This choice is important to avoid large | |
340 | isospin violations in the 1^3P_0 and 1^3D_1 multiplets in which the | |
341 | octet member is unknown. | |
342 | ||
343 | * A new treatment of the colour interference terms in matrix elements | |
344 | has been introduced in this version. A non-planar, interference term | |
345 | is now shared between the planar terms corresponding to well defined | |
346 | colour flows in proportion to the size of the planar terms. Existing | |
347 | two-to-two QCD processes which have been affected are: | |
348 | ||
349 | Light Quarks Heavy Quarks | |
350 | ============ ============ | |
351 | Process IHPRO Process IHPRO | |
352 | ------- ----- ------- ----- | |
353 | q +q --> q +q 1,2 Q +g --> Q +g 10,11 | |
354 | q +qbar --> q +qbar 5,6 Qbar+g --> Qbar+g 21,22 | |
355 | qbar+q --> qbar+q 13,14 g +Q --> g +Q 23,24 | |
356 | qbar+qbar --> qbar+qbar 18,19 g +Qbar --> g +Qbar 25,26 | |
357 | g +g --> Q +Qbar 27,28 | |
358 | ||
359 | The present and previous treatments of the interference term are the | |
360 | same for the other two-to-two QCD processes which remain unaffected. | |
361 | ||
362 | This new procedure has been adopted for all the SUSY QCD processes. | |
363 | ||
364 | For details see: K. Odagiri, JHEP 10 (1998) 006 | |
365 | ||
366 | * A new process, direct gamma-gamma to charged particle pairs has been | |
367 | added. This has IPROC=16000+IQ: if IQ=1-6 then only quark flavour IQ | |
368 | is produced, if IQ=7,8 or 9 then only lepton flavour e, mu or tau is | |
369 | produced and if IQ=10 then only W pairs are produced: in these cases | |
370 | particle masses effects are included. Whilst if IQ=0 the natural mix | |
371 | of quark pairs are produced using massless MEs but including a mass | |
372 | threshold cut. The range of allowed transverse momenta is controlled | |
373 | by PTMIN & PTMAX as usual. | |
374 | ||
375 | * A new package ISAWIG has been created to work with ISAJET to produce | |
376 | a file of the SUSY particle masses, lifetimes and decay modes which | |
377 | can be read in by HERWIG. | |
378 | ||
379 | This package takes the outputs of the ISAJET SUGRA or general MSSM | |
380 | programs and produces a data file in a format that can be read in by | |
381 | the HWISSP subroutine described below. | |
382 | ||
383 | In addition to the decay modes included in the ISAJET package ISAWIG | |
384 | allows for the possibility of violating R-parity and includes the | |
385 | calculation of all 2-body squark and slepton, and 3-body gaugino and | |
386 | gluino R-parity violating decay modes. | |
387 | ||
388 | * A new subroutine HWISSP has been added to read the file of particle | |
389 | properties produced by the ISAWIG program. In principle the user can | |
390 | produce a similar file provided that the correct format is used. The | |
391 | format should be as follows. | |
392 | ||
393 | First the SUSY particle and top quark masses and lifetimes are given | |
394 | as, for example: | |
395 | ||
396 | 65 | |
397 | 401 927.3980 0.74510E-13 | |
398 | 402 925.3307 0.74009E-13 | |
399 | ....etc. | |
400 | ||
401 | That is, | |
402 | ||
403 | NSUSY=Number of SUSY+top particles | |
404 | IDHW, RMASS(IDHW) & RLTIM(IDHW) | |
405 | repeated NSUSY times. | |
406 | ||
407 | Next each particle's decay modes together with their branching | |
408 | ratios and matrix element codes are given as, for example: | |
409 | ||
410 | 6 | |
411 | 401 0.18842796E-01 0 450 1 0 0 0 | |
412 | | | | | | | | | | |
413 | 401 0.32755006E-02 0 457 2 0 0 0 | |
414 | 6 | |
415 | 402 0.94147678E-02 0 450 2 0 0 0 | |
416 | ....etc. | |
417 | ||
418 | That is, | |
419 | ||
420 | Number of decay modes for a given particle (IDK) | |
421 | IDK(*), BRFRAC(*), NME(*) & IDKPRD(1-5,*) | |
422 | repeated for each mode. | |
423 | ||
424 | Repeated for each particle (NSUSY times). | |
425 | ||
426 | The order in which the decay products appear is significant: this is | |
427 | important inorder to obtain appropriate showering and hadronization. | |
428 | The correct ordering for each decay mode is indicated below. | |
429 | ||
430 | +----------+------------------------+------------------------------+ | |
431 | | Decaying | Type of Mode | Order of Decay Products: | | |
432 | | Particle | | 1st | 2nd | 3rd | | |
433 | +----------+------------------------+---------+---------+----------+ | |
434 | | Top | 2 body to Higgs | Higgs | Bottom | | | |
435 | | +------------------------+---------+---------+----------+ | |
436 | | | 3 body via Higgs/W | quarks or leptons | Bottom | | |
437 | | | | from W/Higgs | | | |
438 | +----------+------------------------+---------+---------+----------+ | |
439 | | Gluino | 2 body modes: | | | | | |
440 | | | without gluon | any order | | | |
441 | | | with gluon | gluon | colour | | | |
442 | | | | | neutral | | | |
443 | | +------------------------+---------+---------+----------+ | |
444 | | | 3 body modes: | colour | q or qbar | | |
445 | | | R-parity conserved | neutral | | | |
446 | +----------+------------------------+---------+---------+----------+ | |
447 | | Squark/ | 2 body modes: | | | | | |
448 | | Slepton | Gaugino/Gluino | Gaugino | quark | | | |
449 | | | Quark/Lepton | Gluino | lepton | | | |
450 | | +------------------------+---------+---------+----------+ | |
451 | | | 3 body modes: |sparticle| particles from | | |
452 | | | Weak | | W decay | | |
453 | +----------+------------------------+---------+---------+----------+ | |
454 | | Squark | 2 body modes: | | | | | |
455 | | | Lepton Number Violated | quark | lepton | | | |
456 | | | Baryon Number Violated | quark | quark | | | |
457 | +----------+------------------------+---------+---------+----------+ | |
458 | | Slepton | 2 body modes: | q or qbar | | | |
459 | | | Lepton Number Violated | | | | | |
460 | +----------+------------------------+---------+---------+----------+ | |
461 | | Higgs | 2 body modes: | | | | | |
462 | | | (s)quark-(s)qbar | (s)q or (s)qbar | | | |
463 | | | (s)lepton-(s)lepton | (s)l or (s)lbar | | | |
464 | | +------------------------+---------+---------+----------+ | |
465 | | | 3 body modes: | colour | q or qbar | | |
466 | | | | neutral | l or lbar | | |
467 | +----------+------------------------+---------+---------+----------+ | |
468 | | Gaugino | 2 body modes: | | | | | |
469 | | | squark-quark | q or sq | | | |
470 | | | slepton-lepton | l or sl | | | |
471 | | +------------------------+---------+---------+----------+ | |
472 | | | 3 body modes: | colour | q or qbar | | |
473 | | | R-parity conserved | neutral | l or lbar | | |
474 | +----------+------------------------+---------+---------+----------+ | |
475 | | Gaugino/ | 3 body modes: | particles in the order i,j,k | | |
476 | | Gluino | R-parity violating | | | |
477 | +----------+------------------------+---------+---------+----------+ | |
478 | ||
479 | A new matrix element code has been added for these decays: | |
480 | ||
481 | NME = 300 3 body R-parity violating gaugino and gluino decays | |
482 | ||
483 | in addition, an extra matrix element code has been reserved for use | |
484 | in a forthcoming version: | |
485 | ||
486 | NME = 200 3 body top quark via charged Higgs | |
487 | ||
488 | The indices i,j,k in R-parity violating gaugino/gluino decays refer | |
489 | to the ordering of the indices in the R-parity violating couplings | |
490 | in the superpotential. The convention is as in: | |
491 | ||
492 | H.Dreiner, P.Richardson and M.H.Seymour, hep-ph/9912407. | |
493 | ||
494 | Next a number of parameters derived from the SUSY Lagrangian must be | |
495 | given. These are: the ratio of Higgs VEVs, tan(beta), and the scalar | |
496 | Higgs mixing angle, alpha; the mixing parameters for the Higgses, | |
497 | gauginos and the sleptons; the trilinear couplings; and the Higgsino | |
498 | mass parameter mu. | |
499 | ||
500 | Finally the logical variable RPARTY should be set: if FALSE then | |
501 | R-parity is violated, and the R-parity violating couplings must also | |
502 | be supplied, otherwise not. | |
503 | ||
504 | Details of the FORMAT statements employed can be found by examining | |
505 | the subroutine HWISSP. | |
506 | ||
507 | The integer argument in the call to HWISSP(N) gives the unit number | |
508 | to be read from. If the data is stored in a `fort.N' file no further | |
509 | action is required but if the data is to be read from a file named | |
510 | `fname.dat' then appropriate OPEN and CLOSE statements must be added | |
511 | by hand: | |
512 | ||
513 | OPEN(UNIT=N,FORM='FORMATTED',STATUS='UNKNOWN',FILE='fname.dat') | |
514 | CALL HWISSP(N) | |
515 | CLOSE(UNIT=N) | |
516 | ||
517 | A number of sets of SUSY parameter files, produced using ISAWIG, for | |
518 | the standard LHC SUGRA and GMSB points are available from the HERWIG | |
519 | home page: http://hepwww.rl.ac.uk/theory/seymour/herwig/ | |
520 | ||
521 | * A large number of changes have been made to enable SUSY processes to | |
522 | be included in hadron-hadron collisions. The main changes are: | |
523 | ||
524 | - The subroutine HWDHQK has been replaced by HWDHOB which does both | |
525 | heavy quark and SUSY particle decays. | |
526 | ||
527 | - The subroutines HWBCON HWCGSP & HWCFOR have been adapted to handle | |
528 | the colour connections found in normal SUSY decays. | |
529 | ||
530 | - The subroutine HWBRCN has been included to deal with the inter-jet | |
531 | colour connections arising in R-parity violating SUSY. Also HWCBVI | |
532 | HWCBVT and HWCBCT have been added to handle the hadronization of | |
533 | baryon number violating SUSY decays and processes. If the variable | |
534 | RPARTY=.TRUE. [default] then the old HWBCON colour connection code | |
535 | is used else the new HWBRCN | |
536 | ||
537 | * The option of separate treatments for `light' and b-quark containing | |
538 | clusters are now available. The 3 variables, PSPLT (which controls | |
539 | the mass spectrum of the fragments in heavy cluster splitting) CLDIR | |
540 | (which controls whether perturbatively produced (anti-)quarks retain | |
541 | some knowledge of their direction in cluster decays to hadrons) and | |
542 | CLSMR (which defines to what extent the hadron and constituent quark | |
543 | directions are aligned), have been made two dimensional. | |
544 | ||
545 | ARRAY(1) controls clusters that do NOT contain a b quark | |
546 | ARRAY(2) controls clusters that do contain a b quark | |
547 | ||
548 | [ Default ARRAY(1)=ARRAY(2) equivalent to earlier versions. ] | |
549 | ||
550 | * A new variable EFFMIN [1E-3] has been introduced, it allows the user | |
551 | to set the minimum acceptable efficiency for event generation. | |
552 | ||
553 | * All hadron & lepton masses are now given to five significant figures | |
554 | whenever possible. | |
555 | ||
556 | * The treatment of the perturbative g --> qqbar vertex in the partonic | |
557 | showers has been improved. The total rate is unchanged, but the | |
558 | angular distribution now covers the full range, rather than being | |
559 | confined to the angular-ordered region as before. | |
560 | ||
561 | * The treatment of the intrinsic transverse momentum of partons in an | |
562 | incoming hadron has been improved. It is now chosen before the | |
563 | initial state cascade is performed, and is held fixed even if the | |
564 | generated cascade is rejected. This removes a correlation between | |
565 | the amount of perturbative and non-perturbative transverse momentum | |
566 | generated that existed before. | |
567 | ||
568 | * Space-time positioning of clusters is now smeared according to a | |
569 | Gaussian distribution of width 1/(cluster mass). | |
570 | ||
571 | * For e+e- processes with ISR a check was added requiring TMNISR to be | |
572 | greater than the light quark threshold. | |
573 | ||
574 | * The treatment of the W resonance in top decays has been improved. | |
575 | ||
576 | * The common block file HERWIG61.INC has had many new variables added, | |
577 | these are listed at the top of the file. | |
578 | ||
579 | * Corrections for bugs have been made affecting the following: | |
580 | ||
581 | - eta-eta' mixing: the parameterization was nonstandard (see above). | |
582 | ||
583 | - 4/5 body phase space generation: was not flat - affected resonance | |
584 | decays only. | |
585 | ||
586 | - Drell-Yan: the overall normalization was too small by a factor 2/3 | |
587 | also the t-channel contribution to q-qbar-> q-qbar was incorrectly | |
588 | normalized. | |
589 | ||
590 | - HWHV1J: the normalization of Z+jet production rate was a factor 4 | |
591 | too small; there was an incorrect correlation between the (signed) | |
592 | W and jet rapidities; the treatment of the W/Z Breit-Wigner lead a | |
593 | normalization error by a factor 3/pi. | |
594 | ||
595 | - HWHWPR: there was an overall normalization error of (M_ff'/M_w)^2, | |
596 | this only affected the line shape and normalization for the t-bbar | |
597 | final state for which M_ff' is large. | |
598 | ||
599 | - B_d/_s mixing: an incorrect formula was used. | |
600 | ||
601 | - VMIN2: the effective cut-off on the space-time distances travelled | |
602 | by light partons in a shower was incorrectly implemented. Also its | |
603 | default value has been increased to [0.1], which affects the | |
604 | colour reconnection probability. | |
605 | ||
606 | - A number of fixes to improve safety against overflowing the HEPEVT | |
607 | common block. | |
608 | ||
609 | - Fix to the underlying event to prevent errors with heavy quarks. | |
610 | ||
611 | - HWMODK/HWIODK: a number of corrections were made and the code made | |
612 | more robust. | |
613 | ||
614 | - HWURES: the minimum threshold for the decay of diquark-antidiquark | |
615 | clusters was incorrectly set. | |
616 | ||
617 | - The calculation of the top lifetime has been corrected and the QCD | |
618 | corrections included - this only affects the treatment of colour | |
619 | reconnection. | |
620 | ||
621 | - The space-time positioning of clusters sometimes led to them being | |
622 | produced outside the forward lightcone. This has been rectified. | |
623 | ||
624 | As usual, if you wish to be removed from the HERWIG mailing list, or | |
625 | if you know someone who wants to be added, please let one of us | |
626 | know. | |
627 | ||
628 | Mike Seymour, Bryan Webber, Ian Knowles, Peter Richardson, Kosuke | |
629 | Odagiri, Stefano Moretti, Gennaro Corcella, Pino Marchesini | |
630 | ||
631 | CERN, Edinburgh, Oxford, RAL, Rochester, Milano, etc, | |
632 | 16th December 1999. |