Fragmentation.texi 22 KB
 Frank Siegert committed Mar 05, 2013 1 2 @node Hadronization @section Hadronization  Stefan Hoeche committed Jul 14, 2009 3 4  The hadronization setup is covered by the (fragmentation)' section of  Frank Siegert committed Mar 05, 2013 5 6 the steering file or the fragmentation data file Fragmentation.dat', respectively.  Stefan Hoeche committed Jul 14, 2009 7   Frank Siegert committed Mar 05, 2013 8 9 It covers the fragmentation of partons into primordial hadrons as well as the decays of unstable hadrons into stable final states.  archibald committed Aug 04, 2009 10   Stefan Hoeche committed Jul 23, 2009 11 @menu  Frank Siegert committed Mar 05, 2013 12 13 * Fragmentation:: The fragmentation module, and its parameters. * Hadron decays:: The hadron decay module, and its parameters.  Stefan Hoeche committed Jul 23, 2009 14 15 @end menu  Frank Siegert committed Mar 05, 2013 16 17 @node Fragmentation @subsection Fragmentation  Frank Krauss committed Oct 14, 2013 18 19 20  @subsubsection Fragmentation models  Stefan Hoeche committed Jul 23, 2009 21 @cindex FRAGMENTATION  Stefan Hoeche committed Oct 14, 2013 22 23 24 25 26 27 @cindex MSTJ @cindex MSTP @cindex MSTU @cindex PARP @cindex PARJ @cindex PARU  Frank Siegert committed Mar 05, 2013 28 29  The @code{FRAGMENTATION} parameter sets the fragmentation module to be employed  Frank Krauss committed Oct 14, 2013 30 31 32 33 34 35 36 37 38 39 40 41 during event generation. @itemize @bullet @item The default is @option{Ahadic}, enabling Sherpa's native hadronization model AHADIC++, based on the cluster fragmentation model introduced in @mycite{Field1982dg}, @mycite{Webber1983if}, @mycite{Gottschalk1986bv}, and @mycite{Marchesini1987cf} and implementing some modifications discussed in @mycite{Winter2003tt}. @item the hadronization can be disabled with the value @option{Off}. @item To evaluate uncertainties stemming from the hadronization, Sherpa also  Stefan Hoeche committed Oct 14, 2013 42 43 44 45 46 47 48  provides an interface to the Lund string fragmentation in Pythia 6.4 @mycite{Sjostrand2006za} by using the setting @option{Lund}. In this case, the standard Pythia switches @option{MSTJ}, @option{MSTP}, @option{MSTU}, @option{PARP}, @option{PARJ} and @option{PARU} can be used to steer the behaviour of the Lund string, see @mycite{Sjostrand2006za}. They are specified as @code{MSTJ()=}.  Frank Krauss committed Oct 14, 2013 49 50 @end itemize  Frank Siegert committed Jun 07, 2017 51 52 53 54 The following parameters steer the @option{Ahadic} fragmentation model and up-to-date default values of these parameters can be found in @code{AHADIC++/Tools/Hadronisation_Parameters.C}.  Frank Krauss committed Oct 14, 2013 55 @subsubsection Hadron constituents  Stefan Hoeche committed Oct 14, 2013 56 57 58 59 60 61 62 @cindex M_UP_DOWN @cindex M_STRANGE @cindex M_CHARM @cindex M_BOTTOM @cindex M_DIQUARK_OFFSET @cindex M_BIND_0 @cindex M_BIND_1  Frank Krauss committed Oct 14, 2013 63 64 65  The constituent masses of the quarks and diquarks are given by @itemize @bullet  Frank Siegert committed Jun 07, 2017 66 67 68 69 @item @code{M_UP_DOWN} @item @code{M_STRANGE} @item @code{M_CHARM} @item @code{M_BOTTOM}  Frank Krauss committed Oct 14, 2013 70 71 72 73 74 75 76 77 78 @end itemize The diquark masses are composed of the quark masses and some additional parameters, @iftex \bean m_{12} = (m_1+m_2+m_{\mathrm{offset}})\times(1+m_{\mathrm{bind}}) @end iftex with @itemize @bullet  Frank Siegert committed Jun 07, 2017 79 80 81 @item @code{M_DIQUARK_OFFSET} @item @code{M_BIND_0} @item @code{M_BIND_1}  Frank Krauss committed Oct 14, 2013 82 83 84 @end itemize @subsubsection Hadron multiplets  Stefan Hoeche committed Oct 14, 2013 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 @cindex MULTI_WEIGHT_L0R0_PSEUDOSCALARS @cindex MULTI_WEIGHT_L0R0_VECTORS @cindex MULTI_WEIGHT_L0R0_TENSORS2 @cindex MULTI_WEIGHT_L0R0_TENSORS3 @cindex MULTI_WEIGHT_L0R0_TENSORS4 @cindex MULTI_WEIGHT_L1R0_SCALARS @cindex MULTI_WEIGHT_L1R0_AXIALVECTORS @cindex MULTI_WEIGHT_L1R0_TENSORS2 @cindex MULTI_WEIGHT_L2R0_VECTORS @cindex MULTI_WEIGHT_L3R0_VECTORS @cindex MULTI_WEIGHT_L0R1_SCALARS @cindex MULTI_WEIGHT_L0R1_AXIALVECTORS @cindex MULTI_WEIGHT_L0R0_N_1/2 @cindex MULTI_WEIGHT_L0R0_N*_1/2 @cindex MULTI_WEIGHT_L1R0_N*_1/2 @cindex MULTI_WEIGHT_L1R0_N*_3/2 @cindex MULTI_WEIGHT_L0R0_DELTA_3/2 @cindex MULTI_WEIGHT_L1R0_DELTA*_3/2 @cindex HEAVY_BARYON_ENHANCEMEMT @cindex SINGLET_SUPPRESSION @cindex Mixing_0+ @cindex Mixing_1-  Frank Krauss committed Oct 14, 2013 107 108 109 110 111 112  For the selection of hadrons emerging in such cluster transitions and decays, an overlap between the cluster flavour content and the flavour part of the hadronic wave function is formed. This may be further modified by production probabilities, organised by multiplet and given by the parameters @itemize @bullet  Frank Siegert committed Jun 07, 2017 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 @item @code{MULTI_WEIGHT_L0R0_PSEUDOSCALARS} @item @code{MULTI_WEIGHT_L0R0_VECTORS} @item @code{MULTI_WEIGHT_L0R0_TENSORS2} @item @code{MULTI_WEIGHT_L0R0_TENSORS3} @item @code{MULTI_WEIGHT_L0R0_TENSORS4} @item @code{MULTI_WEIGHT_L1R0_SCALARS} @item @code{MULTI_WEIGHT_L1R0_AXIALVECTORS} @item @code{MULTI_WEIGHT_L1R0_TENSORS2} @item @code{MULTI_WEIGHT_L2R0_VECTORS} @item @code{MULTI_WEIGHT_L3R0_VECTORS} @item @code{MULTI_WEIGHT_L0R1_SCALARS} @item @code{MULTI_WEIGHT_L0R1_AXIALVECTORS} @item @code{MULTI_WEIGHT_L0R0_N_1/2} @item @code{MULTI_WEIGHT_L0R0_N*_1/2} @item @code{MULTI_WEIGHT_L1R0_N*_1/2} @item @code{MULTI_WEIGHT_L1R0_N*_3/2} @item @code{MULTI_WEIGHT_L0R0_DELTA_3/2} @item @code{MULTI_WEIGHT_L1R0_DELTA*_3/2}  Frank Krauss committed Oct 14, 2013 131 132 133 134 @end itemize In addition, there are some enhancement and suppression factors applied to heavy baryons and meson singlets, @itemize @bullet  Frank Siegert committed Jun 07, 2017 135 136 @item @code{HEAVY_BARYON_ENHANCEMEMT} @item @code{SINGLET_SUPPRESSION}  Frank Krauss committed Oct 14, 2013 137 138 139 140 @end itemize For the latter, Sherpa also allows to redfine the mixing angles through parameters such as @itemize @bullet  Frank Siegert committed Jun 07, 2017 141 142 @item @code{Mixing_0+} @item @code{Mixing_1-}  Frank Krauss committed Oct 14, 2013 143 144 145 @end itemize @subsubsection Cluster transition to hadrons - flavour part  Stefan Hoeche committed Oct 14, 2013 146 147 148 149 150 151 152 @cindex STRANGE_FRACTION @cindex BARYON_FRACTION @cindex P_@{QS@}/P_@{QQ@} @cindex P_@{SS@}/P_@{QQ@} @cindex P_@{QQ_1@}/P_@{QQ_0@} @cindex TRANSITION_OFFSET @cindex DECAY_OFFSET  Frank Krauss committed Oct 14, 2013 153 154 155 156 157 158 159  The phase space effects due to these masses govern to a large extent the flavour content of the non-perturbative gluon splittings at the end of the parton shower and in the decay of clusters. They are further modified by relative probabilities with respect to the production of up/down flavours through the parameters @itemize @bullet  Frank Siegert committed Jun 07, 2017 160 161 162 163 164 @item @code{STRANGE_FRACTION} @item @code{BARYON_FRACTION} @item @code{P_@{QS@}/P_@{QQ@}} @item @code{P_@{SS@}/P_@{QQ@}} @item @code{P_@{QQ_1@}/P_@{QQ_0@}}  Frank Krauss committed Oct 14, 2013 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 @end itemize The transition of clusters to hadrons is governed by the following considerations: @itemize @bullet @item Clusters can be interpreted as excited hadrons, with a continous mass spectrum. @item When a cluster becomes sufficiently light such that its mass is below the largest mass of any hadron with the same flavour content, it must be re-iterpreted as such a hadron. In this case it will be shifted on the corresponding hadron mass, and the recoil will be distributed to the neighbouring'' clusters or by emitting a soft photon. This comparison of masses clearly depends on the multiplets switched on in AHADIC++,  Frank Siegert committed Jun 07, 2017 180 181 182 183 184 185  see above. @c , and on an additional offset, which provides an important @c tuning parameter, namely @c @itemize @bullet @c @item @code{TRANSITION_OFFSET} (default 0 MeV). @c @end itemize  Frank Krauss committed Oct 14, 2013 186 187 188 189 @item In addition, clusters may becomes sufficiently light such that they should decay directly into two hadrons instead of two clusters. This decision is based on the heaviest hadrons accessible in  Frank Siegert committed Jun 07, 2017 190 191 192 193 194  a decay. @c , modulated by another offset parameter, @c @itemize @bullet @c @item @code{DECAY_OFFSET} (default 800 MeV). @c @end itemize  Frank Krauss committed Oct 14, 2013 195 196 197 198 199 200 @item If both options, transition and decay, are available, there is a competition between @end itemize @subsubsection Cluster transition and decay weights  Stefan Hoeche committed Oct 14, 2013 201 @cindex MassExponent_C->HH  Frank Krauss committed Oct 14, 2013 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220  The probability for a cluster C to be transformed into a hadron H is given by a combination of weights, obtained from the overlap with the flavour part of the hadronic wave function, the relative weight of the corresponding multiplet and a kinematic weight taking into account the mass difference of cluster and hadron and the width of the latter. @iftex \bean \mathcal{P}_{C\to H} = \left\langle f_1\bar f_2 | \psi_{H, 12}\right\rangle\,\times\, \mathcal{P}_{\mathrm{multiplet}}\,\times\, \left(\frac{m_H^2}{(m_C^2-m_H^2)+\Gamma_h^2/4.}\right) \eean @end iftex For the direct decay of a cluster into two hadrons the overlaps with the wave functions of all hadrons, their respective multiplet suppression weights, the flavour weight for the creation of the new flavour q and a kinematical factor are relevant. Here, yet another tuning paramter enters, @itemize @bullet  Frank Siegert committed Jun 07, 2017 221 @item @code{MassExponent_C->HH}  Frank Krauss committed Oct 14, 2013 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 @end itemize which partially compensates phase space effects favouring light hadrons, @iftex \bean \mathcal{P}_{C\to H_1H_2} = \mathcal{P}_q\,\times\, \left\langle f_1\bar f_2 | \psi_{H, 1q}\psi_{H, q2}\right\rangle \,\times\, \mathcal{P}_{\mathrm{multiplet}}\,\times\, \mathcal{P}_{\mathrm{multiplet}}\,\times\, \frac{\sqrt{[m_C^2-(m_{H_1}+m_{H_2})^2][m_C^2-(m_{H_1}-m_{H_2})^2]}} {16\pi m_C^3}\,\times\, \left(\frac{4m_{H_1}m_{H_2}}{m_C^2}\right)^\chi\,. \eean @end iftex @subsubsection Cluster decays - kinematics  Stefan Hoeche committed Oct 14, 2013 240 241 242 @cindex PT^2_0 @cindex PT_MAX @cindex Q_as^2  Frank Krauss committed Oct 14, 2013 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265  Cluster decays are generated by firstly emitting a non-perturbative gluon'' from one of the quarks, using a transverse momentum distribution as in the non-perturbative gluon decays, see below, and by then splitting this gluon into a quark--antiquark of anti-diquark--diquark pair, again with the same kinematics. In the first of these splittings, the emission of the gluon, though, the energy distribution of the gluon is given by the quark splitting function, if this quark has been produced in the perturbative phase of the event. If, in contrast, the quark stems from a cluster decay, the energy of the gluon is selected according to a flat distribution. In clusters decaying to hadrons, the transverse momentum is chosen according to a distribution given by an infrared-continued strong coupling and a term inversemly proportional to the infrared-modified transverse momentum, @iftex \bean \mathcal{P}(p_\perp^2) \propto \frac{\alpha_s^{(IR)}(p_\perp^2)}{p_\perp^2+p_{\perp,0}^2}\,, \eean @end iftex constrained to be below a maximal transverse momentum. The respective tuning parameters are @itemize @bullet  Frank Siegert committed Jun 07, 2017 266 267 268 @item @code{PT^2_0} @item @code{PT_MAX} @item @code{Q_as^2}  Frank Krauss committed Oct 14, 2013 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 @end itemize @iftex The strong coupling is given by \bean \alpha_s^{(IR)}(p_\perp^2) = \alpha_s(p_\perp^2+p_{\per,0}^2) \eean @end iftex @subsubsection Splitting kinematics In each splitting, the kinematics is given by the transverse momentum, the energy splitting parameter and the azimuthal angle. The latter, the azimuthal angle is always seleectred according to a flat distribution, while the energy splitting parameter will either be chosen according to the quark-to-gluon splitting function (if the quark is a leading quark, i.e. produced in the pertrubative phase), to the gluon-to-quark splitting function, or according to a flat distribution. The transverse momentum is given by the same distribution as in the cluster decays to hadrons.  Frank Siegert committed Mar 05, 2013 288 289 290 291  @node Hadron decays @subsection Hadron decays  Frank Siegert committed Aug 04, 2009 292 293 294 @cindex DECAYMODEL @cindex WIDTH[] @cindex MASS[]  Frank Siegert committed Mar 05, 2013 295 @cindex STABLE[]  archibald committed Jul 28, 2009 296 @cindex DECAYPATH  Frank Siegert committed Oct 26, 2012 297 @cindex SOFT_MASS_SMEARING  archibald committed Jul 28, 2009 298 299 @cindex MAX_PROPER_LIFETIME  Frank Siegert committed Mar 05, 2013 300 301 302 303 The treatment of hadron and tau decays is specified by @code{DECAYMODEL}. Its allowed values are either the default choice @option{Hadrons}, which renders the HADRONS++ module responsible for performing the decays, or the hadron decays can be disabled with the option @option{Off}.  archibald committed Jul 28, 2009 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321  HADRONS++ is the module within the Sherpa framework which is responsible for treating hadron and tau decays. It contains decay tables with branching ratios for approximately 2500 decay channels, of which many have their kinematics modelled according to a matrix element with corresponding form factors. Especially decays of the tau lepton and heavy mesons have form factor models similar to dedicated codes like Tauola @mycite{Jadach1993hs} and EvtGen @mycite{Lange2001uf}. Some general switches which relate to hadron decays can be adjusted in the @code{(fragmentation)} section: @itemize @bullet @item @anchor{DECAYPATH} @code{DECAYPATH} The path to the parameter files for the hadron and tau decays (default: @code{Decaydata/}). It is important to note that the path has to be given relative to the current working directory. If it doesn't exist, the default Decaydata  Frank Siegert committed Mar 05, 2013 322  directory (@code{/share/SHERPA-MC/Decaydata}) will be used.  archibald committed Jul 28, 2009 323 @item Hadron properties like mass, width, stable/unstable and active can be set  Frank Siegert committed Mar 05, 2013 324  in full analogy to the settings for fundamental particles  Silvan Kuttimalai committed May 03, 2015 325  in the @code{(model)} section (cf. @ref{Models}).  Frank Krauss committed Oct 14, 2013 326 327 @item @anchor{SOFT_MASS_SMEARING} @code{SOFT_MASS_SMEARING = [0,1,2]} (default: 1)  archibald committed Jul 28, 2009 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378  Determines whether particles entering the hadron decay event phase should be put off-shell according to their mass distribution. It is taken care that no decay mode is suppressed by a potentially too low mass. While HADRONS++ determines this dynamically from the chosen decay channel, for @code{Pythia} as hadron decay handler its @code{w-cut} parameter is employed. Choosing option 2 instead of 1 will only set unstable (decayed) particles off-shell, but leave stable particles on-shell. @item @anchor{MAX_PROPER_LIFETIME} @code{MAX_PROPER_LIFETIME = [mm]} Parameter for maximum proper lifetime (in mm) up to which particles are considered unstable. If specified, this will make long-living particles stable, even if they are set unstable by default or by the user. @end itemize Many aspects of the above mentioned Decaydata'' can be adjusted. There exist three levels of data files, which are explained in the following sections. As with all other setup files, the user can either employ the default Decaydata'' in @code{/share/SHERPA-MC/Decaydata}, or overwrite it (also selectively) by creating the appropriate files in the directory specified by @code{DECAYPATH}. @subsubsection HadronDecays.dat @code{HadronDecays.dat} consists of a table of particles that are to be decayed by HADRONS++. Note: Even if decay tables exist for the other particles, only those particles decay that are set unstable, either by default, or in the model/fragmentation settings. It has the following structure, where each line adds one decaying particle: @iftex \begin{center} \begin{tabular}{|cccc|} \hline \verb!! &\verb!->! &\verb!/!&\verb!.dat! \\ \hline \hline $\downarrow$ & &$\downarrow$ &$\downarrow$ \\ decaying particle& & path to decay table & decay table file\\ \hline default names: && \verb!/!&\verb!Decays.dat!\\ \hline \end{tabular} \end{center} @end iftex @ifnottex @multitable @columnfractions .33 .33 .33 @item @ @ @ @ @ @ @ -> @tab /  Frank Siegert committed Dec 05, 2016 379 @tab .dat  archibald committed Jul 28, 2009 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 @item decaying particle @ @ @ @tab path to decay table @ @ @ @tab decay table file @item default names: @tab / @tab Decays.dat @end multitable @end ifnottex It is possible to specify different decay tables for the particle (positive kf-code) and anti-particle (negative kf-code). If only one is specified, it will be used for both particle and anti-particle. If more than one decay table is specified for the same kf-code, these tables will be used in the specified sequence during one event. The first matching particle appearing in the event is decayed according to the first table, and so on until the last table is reached, which will be used for the remaining particles of this kf-code. Additionally, this file may contain the keyword @code{CREATE_BOOKLET} on a separate line, which will cause HADRONS++ to write a LaTeX document containing all decay tables. @subsubsection Decay table files The decay table contains information about outgoing particles for each channel, its branching ratio and eventually the name of the file that stores parameters for a specific channel. If the latter is not specified HADRONS++ will produce it and modify the decay table file accordingly. Additionally to the branching ratio, one may specify the error associated with it, and its source. Every hadron is supposed to have its own decay table in its own subdirectory. The structure of a decay table is @iftex \begin{center} \begin{tabular}{|ccccc|} \hline \verb!{kf1,kf2,kf3,...}! &\verb!|! &\verb!BR(!$\Delta$\verb!BR)[Origin]! &\verb!|! &\verb!.dat! \\ \hline $\downarrow$ &&$\downarrow$ &&$\downarrow$ \\ outgoing particles&&branching ratio && decay channel file\\ \hline \end{tabular} \end{center} @end iftex @ifnottex @multitable @columnfractions .33 .33 .33 @item @{kf1,kf2,kf3,...@} @tab BR(delta BR)[Origin] @ @ @ @ @ @ @tab .dat @item outgoing particles @ @ @ @ @ @ @tab branching ratio @ @ @ @ @ @ @tab decay channel file @end multitable @end ifnottex It should be stressed here that the branching ratio which is explicitly given for any individual channel in this file is @strong{always used} regardless of any matrix-element value. @anchor{Decay channel files} @subsubsection Decay channel files A decay channel file contains various information about that specific decay channel. There are different sections, some of which are optional: @itemize @bullet @item @verbatim AlwaysIntegrate = 0 CPAsymmetryC = 0.0 CPAsymmetryS = 0.0 @end verbatim @itemize @bullet @item @code{AlwaysIntegrate = [0,1]} For each decay channel, one needs an integration result for unweighting the kinematics (see below). This result is stored in the decay channel file, such that the integration is not needed for each run. The AlwaysIntegrate option allows to bypass the stored integration result, and do the integration nonetheless (same effect as deleting the integration result). @item @code{CPAsymmetryC/CPAsymmetryS} If one wants to include time dependent CP asymmetries through interference between mixing and decay one can set the coefficients of the cos and sin terms respectively. HADRONS++ will then respect these asymmetries between particle and anti-particle in the choice of decay channels. @end itemize @item @verbatim 1.0 MyIntegrator1 0.5 MyIntegrator2 @end verbatim Specifies the phase-space mappings and their weight. @item @verbatim 1.0 0.0 my_matrix_element[X,X,X,X,X,...] 1.0 0.0 my_current1[X,X,...] my_current2[X,X,X,...] @end verbatim Specifies the matrix elements or currents used for the kinematics, their respective weights, and the order in which the particles (momenta) enter them. For more details, the  Stefan Hoeche committed Aug 03, 2009 489  reader is referred to @mycite{Krauss2010xx}.  archibald committed Jul 28, 2009 490 491 492 493 494 495 496 497 498 499 500 501  @item @verbatim parameter1 = value1 parameter2 = value2 ... @end verbatim Each matrix element or current may have an additional section where one can specify needed parameters, e.g. which form factor model to choose. Each parameter has to be specified on a new line as shown above. Available  Stefan Hoeche committed Aug 03, 2009 502  parameters are listed in @mycite{Krauss2010xx}.  archibald committed Jul 28, 2009 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531  Parameters not specified get a default value, which might not make sense in specific decay channels. One may also specify often needed parameters in @code{HadronConstants.dat}, but they will get overwritten by channel specific parameters, should these exist. @item @verbatim 3.554e-11 6.956e-14 1.388e-09; @end verbatim These last three lines have quite an important meaning. If they are missing, HADRONS++ integrates this channel during the initialization and adds the result lines. If this section exists though, and @code{AlwaysIntegrate} is off (the default value, see above) then HADRONS++ reads in the maximum for the kinematics unweighting. Consequently, if some parameters are changed (also masses of incoming and outgoing particles) the maximum might change such that a new integration is needed in order to obtain correct kinematical distributions. There are two ways to enforce the integration: either by deleting the last three lines or by setting @code{AlwaysIntegrate} to 1. When a channel is re-integrated, HADRONS++ copies the old decay channel file into @code{..dat.old}. @end itemize @subsubsection HadronConstants.dat @code{HadronConstants.dat} may contain some globally needed parameters (e.g.  Stefan Hoeche committed Aug 03, 2009 532 for neutral meson mixing, see @mycite{Krauss2010xx}) and also fall-back  archibald committed Jul 28, 2009 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 values for all matrix-element parameters which one specifies in decay channel files. Here, the @code{Interference_X = 1} switch would enable rate asymmetries due to CP violation in the interference between mixing and decay (cf. @ref{Decay channel files}), and setting @code{Mixing_X = 1} enables explicit mixing in the event record according to the time evolution of the flavour states. By default, all mixing effects are turned off. @itemize @bullet @item Mixing parameters @iftex ($x = \frac{\Delta m}{\Gamma}$, $y = \frac{\Delta \Gamma}{2\Gamma}$) @end iftex with some example values @verbatim x_K = 0.946 y_K = -0.9965 qoverp2_K = 1.0 Interference_K = 0 Mixing_K = 0 x_D = 0.0 y_D = 0.0 qoverp2_D = 1.0 Interference_D = 0 Mixing_D = 0 x_B = 0.776 y_B = 0.0 qoverp2_B = 1.0 Interference_B = 1 Mixing_B = 0  Frank Siegert committed Jul 30, 2009 565 566 567 568 569 x_B(s) = 30.0 y_B(s) = 0.155 qoverp2_B(s) = 1.0 Interference_B(s) = 0 Mixing_B(s) = 0  archibald committed Jul 28, 2009 570 571 572 573 574 575 @end verbatim @end itemize @subsubsection Further remarks  Frank Siegert committed Mar 05, 2013 576 577 @cindex SOFT_SPIN_CORRELATIONS @cindex HARD_SPIN_CORRELATIONS  archibald committed Jul 28, 2009 578 579  @strong{Spin correlations:}  Frank Siegert committed Mar 05, 2013 580 581 582 583 584 585 586 587 a spin correlation algorithm is implemented. It can be switched on through the keyword @option{SOFT_SPIN_CORRELATIONS=1} in the @code{(run)} section. If spin correlations for tau leptons produced in the hard scattering process are supposed to be taken into account, one needs to specify @option{HARD_SPIN_CORRELATIONS=1} as well. If using AMEGIC++ as ME generator, note that the Process libraries have to be re-created if this is changed.  archibald committed Jul 28, 2009 588 589 590 591 592 593 594 595 596 597 598 599  @strong{Adding new channels:} if new channels are added to HADRONS++ (choosing isotropic decay kinematics) a new decay table must be defined and the corresponding hadron must be added to @code{HadronDecays.dat}. The decay table merely needs to consist of the outgoing particles and branching ratios, i.e. the last column (the one with the decay channel file name) can safely be dropped. By running Sherpa it will automatically produce the decay channel files and write their names in the decay table. @strong{Some details on tau decays:} $\tau$ decays are treated within the HADRONS++ framework, even though the $\tau$ is not a hadron. As for many hadron decays, the hadronic tau decays have form factor models implemented, for details the reader is referred to  Stefan Hoeche committed Aug 03, 2009 600 @mycite{Krauss2010xx}.  archibald committed Jul 28, 2009 601 602