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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. |