3 <title>Update History</title>
4 <link rel="stylesheet" type="text/css" href="pythia.css"/>
5 <link rel="shortcut icon" href="pythia32.gif"/>
9 <h2>Update History</h2>
11 These update notes describe major updates relative to the baseline
12 PYTHIA 8.100 version. However, they are less extensive than the
13 corresponding update notes for PYTHIA 6. On the other hand,
14 whereas the PYTHIA 6 manual is a static document, the PYTHIA 8
15 html/php pages are kept up to date for each subversion.
18 <b>Important note:</b>version 8.160 does introduce some elements of
19 backwards incompatibility. Specifically, "multiple interactions",
20 abbreviated MI, haa been renamed "multiparton interactions", MPI.
21 This affects many parts of the code and documentation. Also some
22 features are deprecated, although remaining until the end of the
26 <h3>Main news by version</h3>
30 <li>8.105: 24 February 2008
33 <li>New option to initialize with arbitrary beam directions<br/>
34 <code>pythia.init( idA, idB, pxA, pyA, pzA, pxB, pyB, pzB)</code></li>
36 <li>Added capability to set <a href="BeamParameters.html" target="page">beam energy spread
39 <b>Warning:</b> as a consequence, the old <code>Beams</code> group of
40 settings has been moved to <code>BeamRemnants</code>, and
41 <code>Beams</code> is now instead used for machine beam parameters.
42 Therefore also some <code>Main</code> settings of this character have been
43 regrouped, as follows:
44 <table cellspacing="5">
45 <tr> <td>8.100 setting </td> <td>has been moved to </td> </tr>
46 <tr> <td><code>Main:idA </code></td>
47 <td><code>Beams:idA </code></td> </tr>
48 <tr> <td><code>Main:idB </code></td>
49 <td><code>Beams:idB </code></td> </tr>
50 <tr> <td><code>Main:inCMframe </code></td>
51 <td>(<code>Beams:frameType</code>) </td> </tr>
52 <tr> <td><code>Main:eCM </code></td>
53 <td><code>Beams:eCM </code></td> </tr>
54 <tr> <td><code>Main:eA </code></td>
55 <td><code>Beams:eA </code></td> </tr>
56 <tr> <td><code>Main:eB </code></td>
57 <td><code>Beams:eB </code></td> </tr>
58 <tr> <td><code>Main:LHEF </code></td>
59 <td><code>Beams:LHEF </code></td> </tr>
62 <li>The <code>forceHadronLevel()</code> method introduced for standalone
65 <li><code>main15.cc</code> illustrated how either full hadronization or
66 only decays of some particles can be looped over for the rest of the
69 <li>The <code>LHAevnt</code> and <code>LHAinit</code> classes have been
70 joined into a new <code>LHAup</code> one, with new options that allow
71 the writing of a Les Houches Event File.</li>
73 <li>The <code>SusyLesHouches</code> class updated to handle
76 <li>Updated HepMC conversion routine.</li>
78 <li>The static <code>ErrorMsg</code> class has been removed and
79 its functionality moved into the non-static <code>Info</code> class,
80 in the renamed Info file.</li>
82 <li>Further reduction of the use of static, with related code changes.
83 This should allow to have several almost independent <code>Pythia</code>
84 instances. Some static classes still remain, however, notably for
85 random number generation and particle properties.</li>
87 <li>Limited capability to use two different <code>Pythia</code> instances
88 for signal + pileup event generation, see <code>main19.cc</code> for an
91 <li>In the <code>Event</code> class the <code>=</code> and
92 <code>=+</code> methods have been overloaded to allow the copying
93 or appending of event records. Illustrated in <code>main19.cc</code>.</li>
95 <li>The html and php page formatting improved with
96 cascading style sheets.</li>
98 <li>Several minor improvements and new options, including updated configure
104 <li>8.108: 1 May 2008
107 <li>Correction in the event record, so that the beam particles in line
108 1 and 2 do not have any mother according to the <code>motherList</code>
109 method. Previously the "system" entry in line 0 was counted as their
110 mother, which gave rise to an unexpected extra vertex in the conversion
111 to the HepMC format.</li>
113 <li>Support for HepMC version 1 is removed, to simplify the code and
114 reflect the evolution of the field.</li>
116 <li>Status codes are stored in HepMC only as 1 for existing and 2 for
117 decayed or fragmented particles (whereas previously the original PYTHIA
118 codes were used for the latter).</li>
120 <li>Parton densities are stored in HepMC as <i>xf(x,Q^2)</i>
121 rather than the <i>f(x,Q^2)</i> used in (some) previous versions.</li>
123 <li>The SusyLesHouches class has ben updated so that reading is fully
124 compatible with the SLHA2 standard. </li>
126 <li>Improved handling of the Higgs width, relevant for massive and thereby
127 broad resonance shapes.</li>
129 <li>The matrix elements for neutralino pair production have now been
130 completed and checked.</li>
132 <li>Ensure that <i>alpha_strong</i> does not blow up, by introducing
133 a minimal scale somewhat above <i>Lambda_3</i> (roughly where
134 <i>alpha_strong = 10</i>).</li>
136 <li>New methods <code>isValence1()</code> and <code>isValence2()</code>
137 in the <code>Info</code> class.</li>
139 <li>Protection against division by zero in calculation of decay vertex
140 (for zero-mass gluons with zero lifetime, where there should be no
143 <li>A new compilation option <code>-Wshadow</code> is introduced and
144 code is rewritten at all places where this option gave warnings.</li>
146 <li>Minor library correction to allow compilation with gcc 4.3.0.</li>
151 <li>8.114: 22 October 2008
154 <li>New rescattering description operational (but still experimental)
155 for the case that FSR is not interleaved, but saved until after MPI,
156 ISR and beam remnants have been handled. This involves much new code
157 in several classes.</li>
159 <li>A new class <code>PartonSystems</code> is introduced to
160 keep track of which partons in the event record belong to which
161 subcollision system, plus some further information on each subsystem.
162 It takes over functionality previously found as part of the
163 <code>Event</code> class, but leaves room for future growth.</li>
165 <li>Add optional model, wherein an increased <i>pT0</i> turnoff scale
166 for MPI and ISR is used for above-average active events, i.e. events that
167 already have several MPI's or ISR emissions.</li>
169 <li>Freeze GRV 94L distribution at small <i>Q^2</i> to avoid blowup.</li>
171 <li>The <code>pythia.readFile(...)</code> method can now alternatively take
172 an <code>istream</code> as argument instead of a <code>filename</code>.</li>
174 <li>Minor bug correction in <code>PartonLevel.cc</code>; the bug could
175 (rarely) give a segmentation fault.</li>
180 <li>8.120: 10 March 2009
183 <li>New rescattering description further developed, but not yet
184 recommended for normal usage.</li>
186 <li>Include new processes for Large Extra Dimensions and Unparticles,
187 contributed by Stefan Ask. New test program <code>main28.cc</code>
190 <li>Include further SUSY processes: neutralino-chargino and
191 chargino-chargino pairs. The processes should be valid also
192 in the case of non-minimal flavour violation and/or CP violation.
193 Expanded machinery to keep track of SUSY parameters.</li>
195 <li>Include backwards evolution of incoming photon as part of the
196 <code>SpaceShower</code> initial-state radiation description. This
197 allows you to simulate hard collisions where one of the incoming
198 partons is a photon. New test program <code>main43.cc</code>
201 <li>Allow separate mass and transverse momentum cuts when two hard
202 subprocesses are generated in the same event.</li>
204 <li>The default value for the border between short- and long-lived
205 paticles has been changed from 1 mm to 10 mm, to better conform with
206 LHC standards, see <a href="ParticleDecays.html" target="page">here</a>.
207 The default is still to let all unstable particles decay.</li>
209 <li>New ISR matrix-element correction to <i>f -> f gamma</i>
210 in single <i>W</i> production.</li>
212 <li>New method <code>Event::statusHepMC</code> returns the status
213 code according to the HepMC conventions agreed in February 2009.
214 The interface to HepMC now writes out status according to this
217 <li>Add capability to link to FastJet, with expanded configure script
218 and Makefile, and with <code>main61.cc</code> as new example.</li>
220 <li>Update of <code>Makefile.msc</code>, with added support for latest
221 Visual C++ Express edition and use of regexp to check nmake version.</li>
223 <li>Update of <code>LHAFortran.h</code> and
224 <code>Pythia6Interface.h</code>, to make the interface to Fortran
225 routines work also under Windows. (Thanks to Anton Karneyeu.)
227 <li>Updated and expanded worksheet.</li>
229 <li>The manual pages in the <code>xmldoc</code> directory, and thereby
230 also those of the <code>htmldoc</code> and <code>phpdoc</code>
231 directories, have been significantly updated and expanded. In particular,
232 in many places the class of each method is explicitly shown, as well as
233 the type of the return value and of the arguments. This upgrade is not
234 yet completed, but already covers the more relevant sections. </li>
236 <li>The unary minus operator in the <code>Vec4()</code> returns a
237 reference to a four-vector with all components negated, but leaves
238 the original four-vector unchanged. Previously the four-vector itself
241 <li>The <code>pPlus()</code> and <code>pMinus()</code> methods of a
242 four-vector and an event-record particle are renamed <code>pPos()</code>
243 and <code>pNeg()</code>, respectively.</li>
245 <li>Include a further loop in <code>ProcessLevel</code>, so that a new
246 process is generated in case of failures of a less severe nature.</li>
248 <li>Introduce warning message for unexpected <code>meMode</code> in
249 <code>ResonanceWidths</code>.</li>
251 <li>Les Houches event reading framework has been rearranged for
252 more flexibility. Some bugs corrected. Specifically, when scale
253 is not set (<code>scale = -1.</code> in the Les Houches standard),
254 PYTHIA did not attempt to set this scale itself, which typically
255 lead to there not being any ISR or FSR. Now the
256 <a href="CouplingsAndScales.html" target="page">rules for normal
257 1-, 2- and 3-body final states</a> are applied, with a trivial
258 extension of the 3-body rules for higher multiplicities.</li>
260 <li>Correct bug in the handling of parton densities, whereby it was
261 not possible to switch to a new set, once a first initialization
264 <li>Correct bugs when several <code>Pythia::init</code> initialization
265 calls are made in the same run, specifically in the case that pointers
266 to external processes have been handed in.
268 <li>Changes in <code>main03.cmnd</code> and <code>main04.cmnd</code>
269 so that some nonstandard options are commented ou rather than active.
270 Related comments inserted also in some other <code>.cmnd</code> files,
271 but there without any change in program execution.</li>
273 <li>A few further minor bug fixes.</li>
275 <li>Update year to 2009.</li>
280 <li>8.125: 16 June 2009
283 <li>Hadronization and timlike-shower parameter default values updated
284 according to a tune to LEP1 data by Hendrik Hoeth, using the
285 Rivet + Professor framework.</li>
287 <li>Many further SUSY production processes. SLHA readin expanded to cover
288 also masses and decay modes. Example <code>main22.cc</code> updated, while
289 <code>main33.cc</code> now superfluous and removed. </li>
291 <li>Also further processes for extra dimensions.</li>
293 <li>Stefan Ask joins as coauthor.</li>
295 <li>The <code>TimeShower::shower(...)</code> method has gained
296 a new argument, that forces the shower evolution to stop after
297 a given number of branchings. A new method
298 <code>TimeShower::pTLastInShower()</code> permits the last evolution
299 <i>pT</i> to be read out. These extensions can be useful
300 for matching studies.
303 <li>New optional argument <code>isInterleaved</code> added to
304 <code>TimeShower::branch(...)</code>. Is false by default, but
305 true when called from the parton level for interleaved evolution
306 of several parton systems, optionally also with ISR and MPI.</li>
308 <li>New methods <code>UserHooks::canSetResonanceScale()</code>
309 and <code>UserHooks:scaleResonance(...)</code> allows an optional
310 user choice of the maximum shower scale in resonance decays.</li>
312 <li>A new method <code>SpaceShower::doRestart()</code> has been
313 added, to help distinguish cases when a
314 <code>SpaceShower::branch(...)</code> failure forces a complete
315 restart of the evolution from ones where only the intended
316 current branching has been vetoed.
318 <li>When multiparton interactions are initialized, it is now
319 possible to reduce both <i>pT0</i> and <i>pTmin</i>
320 if necessary to find a valid solution where
321 <i>sigma_jet > sigma_nondiffractive</i>. Previously
322 only the former would be reduced, which could lead to
323 infinite loops if too large a <i>pTmin</i> was used.
324 Thanks to Sami Kama for pointing out the problem.
327 <li>The rescattering machinery is now essentially completed, and can
328 be used also by others than the authors. For now, however, it can only
329 be recommended for dedicated studies, not e.g. for generic tunes.
332 <li>Timelike and spacelike showers, and beam remnant handling,
333 are modified to handle rescattering partons. Specifically, a new machinery
334 is introduced to trace the recoils from the combination of rescattering
335 with showers and primordial <i>kT</i>. Can assign space- or timelike
336 virtualities to intermediate particles to have energy and momentum
337 conserved locally. This affects the <code>PartonLevel</code>,
338 <code>MultipartonInteractions</code>, <code>TimeShower</code>,
339 <code>SpaceShowe</code>r and <code>BeamRemnants</code> classes.
340 Further details to appear in the upcoming article on rescattering.
341 (Another change is a reversal to pre-8.114 order for non-interleaved FSR,
342 wherein also FSR is treated before beam remnants are attached.)
345 <li>Four new status codes introduced, as part of the rescattering
347 <br/>45 : incoming rescattered parton, with changed kinematics owing
348 to ISR in the mother system (cf. status 34);
349 <br/>46 : incoming copy of recoiler when this is a rescattered parton
351 <br/>54 : copy of a recoiler, when in the initial state of a different
352 system from the radiator;
353 <br/>55 : copy of a recoiler, when in the final state of a different
354 system from the radiator.
357 <li>New method <code>Info::tooLowPTmin()</code> can tell whether the
358 <i>pTmin</i> scales for showers or multiparton interactions are too low.
361 <li>Pion beams allowed, both <i>pi^+</i>, <i>pi^-</i> and
362 <i>pi^0</i>. New machinery for the latter, where the valence
363 flavour content is chosen to be either <i>d dbar</i> or
364 <i>u ubar</i> for each new event. One internal pion PDF
365 implemented, with others from LHAPDF.</li>
367 <li>Treatment of Pomeron-proton collisions begun.</li>
369 <li>Phase-space handling of hard processes and multiparton interactions
370 slightly expanded to better allow for harder PDF's than proton ones,
371 e.g. for Pomerons.</li>
373 <li>The program documentation has been expanded with an
374 alphabetical index of all methods that are described on the
375 webpages, see the <a href="ProgramMethods.html" target="page">Program Methods</a>
376 page. Also other sections of the documentation have been
377 updated and expanded, including the worksheet.</li>
379 <li>Several <code>list</code> methods have been made
380 <code>const</code>. For the listing of events two new methods
381 have been added, <code>Event::list()</code> and
382 <code>Event::list(bool showScaleAndVertex,
383 bool showMothersAndDaughters = false)</code>,
384 that correspond to special cases of the general method.</li>
386 <li>A new method <code>Pythia::LHAeventSkip(int nSkip)</code>
387 permits a skip-ahead of the reading of external Les Houches
388 Events, without the necessity to generate the intervening
389 <code>nSkip</code> events in full. Makes use of the new
390 <code>LHAup::skipEvent(int nSkip)</code> method to perform
391 the operations. Mainly intended for debug purposes.
393 <li>The <code>ClusterJet</code> jet finder now saves the last
394 five clustering scales. Also a minor bug fix. Thanks to Nils
395 Lavesson for this contribution.</li>
397 <li>The <code>Particle::m2()</code> method now returns a negative
398 number when the stored mass <i>m</i> is negative, as used to
399 indicate spacelike virtualities. Also the
400 <code>Particle::eCalc()</code>, <code>Particle::mT()</code> and
401 <code>Particle::mT2()</code> methods have been modified.
404 <li>The <code><<</code> method to print our a four-vector has
405 been expanded with a fifth number, the invariant length, with a minus
406 sign for spacelike vectors, and provided within brackets to allow
407 a simple visual distinction.</li>
409 <li>New methods <code>Rndm::dumpState(string fileName)</code> and
410 <code>Rndm::readState(string fileName)</code> allows to write or
411 read the state of the random number generator to or from a binary file.
414 <li>New method <code>double GammaReal(double x)</code> returns the
415 value of the <i>Gamma</i> function for arbitrary real argument.
416 Some cross sections for extra-dimensional processes rewritten to
420 <li>New example program <code>main29.cc</code> shows how
421 to set up a fictitious process of a heavy system decaying
422 to two particles or partons, with decays traced to stable
423 particles, as relevant for astroparticle applications.</li>
425 <li>Main programs that illustrate the HepMC interface have
426 been updated to use version 2.04, including units and excluding
427 deprecated output formats.</li>
429 <li>The <code>main32.cc</code> example extended also to handle
430 Les Houches Event Files.</li>
432 <li>The Makefile has been modified so that "make clean" only
433 removes the current compilation and library fles, while
434 "make distclean" gives a more extensive reset and cleanup.
435 Thanks to Nils Lavesson for this contribution. Some other
436 minor Makefile corrections.</li>
438 <li>Several main programs that use the
439 <code>Main:timesToShow</code> mode have been corrected so as
440 not to crash if this is set to zero. Also some other cosmetics
441 changes in main programs that do not affect the running.</li>
443 <li>Bug correction, in that previously a veto with user hooks
444 was not propagated from parton showers inside resonance decays.
447 <li>Minor bug fix in <code>TimeShower</code> for kinematics with
448 unequal beam-particle masses.</li>
450 <li>Bug fix so that <code>PartonLevel:MPI = off</code> also works for
451 minimum-bias events.</li>
453 <li>Minor bug fix in the impact-parameter selection of multiparton
454 interactions. Thanks to Sami Kama for pointing it out.</li>
456 <li>String fragmentation for junction topology protected against
457 numerical instability in boost.</li>
459 <li>Bug correction in the handling of particle decays to partons,
460 where the scale of the partons was set before the partons had been
461 added to some arrays, leading to indexation out of bounds.
462 Thanks to Vladislav Burylov for discovering this bug.
465 <li>Bug correction in the handling of particles with inhibited decay,
466 where the decay vertex would be too far displaced, which could lead to
467 infinite loop. Thanks to Sami Kama for debugging this. </li>
469 <li>Check to avoid infinite loop in matrix-element handling of
470 two-body decays.</li>
472 <li>Bug correction to avoid infinite loops in Dalitz decay treatment.
473 Some changes in the decay handling logic to allow a new try when the
474 decay of a particle fails.</li>
476 <li>Minor correction, so the pointer to the <code>Info</code> class
477 is set also for user-written classes derived from <code>LHAup</code>.
480 <li>Correction for typo in the matrix element of the
481 <code>Sigma3ff2HchgchgfftWW</code> class, for doubly charged Higgs
482 production. Thanks to Merlin Kole for spotting it.</li>
484 <li>Updated colour bookkeeping in junction-antijunction annihilation
485 avoids later problems in <code>Pythia::check()</code>. </li>
487 <li>Minor updates of the <code>Makefile.msc</code> file to work with
488 Visual Studio 2008. Thanks to David Bailey for these modifications.</li>
490 <li>Ensure that <code>nInit</code> in the <code>BeamParticle</code>
491 class is set also for unresolved lepton beams.</li>
493 <li>The <code>VetoEvolution</code> class, derived from
494 <code>UserHooks</code>, is obsolete and has been removed.</li>
499 <li>8.130: 15 September 2009
502 <li>New machinery that allows multiparton interactions inside diffractive
503 systems. Also new optional Pomeron flux factors and Pomeron PDFs.
504 New page on <a href="Diffraction.html" target="page">diffraction</a> added, where
505 further details are collected. Still not tuned, so to be used with
508 <li>Make Peter Skands' "Tune 1" parameters for ISR and MPI default.
509 The older simpler tune is still available as an option, see
510 <code><a href="Tunes.html" target="page">Tune:pp</a></code>.
513 <li>New possible choices for a second hard process: charmonium,
514 bottomonium, top pair and single top.</li>
516 <li>New code for pair production of generic colour-triplet scalar,
517 fermion or vector. Largely written by Johan Bijnens, partly recycling
520 <li>Add user hooks possibility to veto event after a given number
521 of multiparton interactions.</li>
523 <li>Add instructions how PYTHIA 8 can be used from inside ROOT.
524 Thanks to Andreas Morsch for providing the text and Rene Brun
525 for a simple example.</li>
527 <li>The <code>main21.cc</code> example extended with an option
528 for a single-particle gun.</li>
530 <li>Improvements and bug fixes in rescattering framework.</li>
532 <li>New method <code>Hist::table(string fileName)</code> provides a
533 more direct way to print a two-column table of histogram contents
534 into a file than the current <code>Hist::table(ostream& os = cout)</code>.
537 <li>Modify reading of external files so that a line only consisting of
538 control characters counts as empty, the same way as a line only consisting
539 of blanks already did. This includes carriage return, tabs and a few more,
540 the ones represented by <code>\n \t \v \b \r \f \a</code>. Applies to
541 Les Houches Event files, settings files and particle data files. </li>
543 <li>Fix it so that the read-in of a Les Houches Event File for the
544 hardest process can be combined with the faciliy to select a specified
545 second hard process.</li>
547 <li>New empty base class method <code>LHAup::fileFound()</code>
548 allows the derived class <code>LHAupLHEF</code> to signal more
549 clearly that a failed initialization is caused by a failure to open
550 the desired file. </li>
552 <li>Check that a pointer to an <code>LHAup</code> object has been set
553 in <code>Pythia::LHAeventList()</code> and
554 <code>Pythia::LHAeventSkip(...)</code> calls.</li>
556 <li>Updated configure and Makefile, e.g. to build shared libraries
559 <li>The options with a direct link to hard-process generation
560 in PYTHIA 6 has been removed. It is hardly ever used but
561 complicates the build structure. (Owing to its usefulness for some
562 debug work, it was reinstated in a limited form in version 8.135.
563 Thus <code>main51.cc</code> now contains the complete interface,
564 previously in separate files, and commented-out lines in
565 <code>examples/Makefile</code> suggest how PYTHIA 6 could be linked.)
568 <li>New argument to <code>Info::errorMsg(...)</code> allows to
569 show all error messages of a specific kind rather than only the
570 first one, e.g. for initialization.</li>
572 <li>Correction in decay table of righthanded Majorana neutrinos.
573 Thanks to Arnaud Ferrari and Vladimir Savinov.</li>
575 <li>Correction in expressions in the manual for <i>H^+-</i> couplings
576 to an <i>h^0</i>, <i>H^0</i> or <i>A^0</i> and a <i>W^+-</i>.
577 Thanks to Rikard Enberg.</li>
579 <li>Fix for accessing uninitialized memory, caused by accessing the
580 daughters of the incoming beams before these daughters actually existed.
581 Thanks to David Bailey and Sami Kama.
584 <li>Uninitialized photon PDF inside the proton could give crazy results
585 for processes with incoming photons. Thanks to Adam Davison.</li>
587 <li>Bug fix such that finite lifetimes can be set also for particles
588 produced in the hard process. To exemplify, the bug affected
589 <i>tau</i> leptons produced in <i>Z^0</i> and <i>W^+-</i>
590 decays. Thanks to Troels Petersen.</li>
592 <li>Bug fix in <code>TimeShower</code>, that <code>beamOffset</code>
593 could remain uninitialized. Thanks to Sami Kama.</li>
595 <li>Minor correction to resonance decays: fail if the allowed mass
596 range of a Breit-Wigner resonance is a small fraction of the total
597 area under the resonance curve.</li>
599 <li>Correction when all three valence quarks were kicked out from a
600 proton and could give false messages that beam momentum had been
603 <li>Clarify status codes needed for hadron-level standalone runs in
604 order to avoid error messages, and modify the <code>main21.cc</code>
605 example accordingly. </li>
607 <li>Minor corrections in the processes for extra dimensions.</li>
609 <li>Some other minor additions to existing facilities
610 and minor bug fixes.</li>
615 <li>8.135: 10 January 2010
618 <li>All usage of static member methods inside Pythia8 has now been
619 eliminated. This simplifies for you to have several simultaneous
620 <code>Pythia</code> instances that are run with different conditions.
621 The three main classes affected by this are the <code>Settings</code>
622 and <code>ParticleData</code> databases and the <code>Rndm</code>
623 random-number generator. You can no longer address the methods of these
624 classes directly, but have to address them via the <code>settings</code>,
625 <code>particleData</code> and <code>rndm</code> instances in the
626 respective <code>Pythia</code> object. Also some other smaller pieces
627 of code are affected, e.g. Standard Model and SUSY couplings
628 (the latter in new files).
629 <br/><b>Note 1</b>: The documentation has been updated accordingly
630 on these webpages, but the "A Brief Introduction to PYTHIA 8.1"
631 still refers to the old behaviour of version 8.100.
632 <br/><b>Note 2</b>: the interface to the external LHAPDF library remains
633 static, since LHAPDF is written in Fortran and thus by definition
635 <br/><b>Note 3:</b> if you want to have momentum smearing in
636 <code>CellJet</code> you now need to send in a pointer to a
637 random-number generator.
640 <li>Ten new proton PDF sets are made available internally:
641 MRST LO* (2007), MRST LO** (2008), MSTW 2008 LO (central member),
642 MSTW 2008 NLO (central member), CTEQ6L, CTEQ6L1, CTEQ6.6 (NLO,
643 central member), CT09MC1, CT09MC2, and CT09MCS, see
644 <a href="PDFSelection.html" target="page">PDF Selection</a>. The Pomeron PDF data
645 files have been renamed for consistency. Thanks to Tomas Kasemets
646 for help with this [<a href="Bibliography.html" target="page">Kas10</a>].
649 <li>New parameters <code>TimeShower:pTmaxFudgeMPI</code> and
650 <code>SpaceShower:pTmaxFudgeMPI</code> introduced, to give the same
651 functionality for multiparton interactions that
652 <code>TimeShower:pTmaxFudge</code> and <code>SpaceShower:pTmaxFudge</code>
653 do for the hardest.</li>
655 <li>A few extensions of the <code>UserHooks</code> framework.
656 New methods <code>UserHooks:canVetoISREmission()</code> and
657 <code>UserHooks::doVetoISREmission(...)</code> allows the latest
658 initial-state emission to be studied before being finalized,
659 with the possibility to veto it.
660 Similarly <code>Userhooks:canVetoFSREmission()</code> and
661 <code>UserHooks::doVetoFSREmission(...)</code> can be used to
662 veto the latest final-state emission.</li>
664 <li>A number of loop counters have been introduced in the
665 <code>Info</code> class, that offers some further information on
666 the progress of the event generation, for use e.g. in conjunction
667 with the <code>UserHooks</code> facility.</li>
669 <li>The <code>Pythia::initTunes(...)</code> method is made public, so that
670 it can be called before the normal call from <code>Pythia::init(...)</code>.
671 That way it is possible to start out from a given tune and change a few
675 <li>Bug corrected in <code>LHAFortran.h</code> for hard-process input
676 from Fortran commonblock. This did not work properly when the input
677 was used in combination with a second hard process generated internally.
678 Thanks to Mikhail Kirsanov and Roberto Chierici.
680 <li>Insertion of missing initialization of <code>isInit</code> in the
681 <code>Settings</code> and <code>ParticleData</code> constructors, and
682 <code>nInit</code> for <code>BeamParticle</code>.
683 Thanks to Leif Lönnblad.</li>
685 <li>Updated <code>Makefile.msc</code> for Windows users.</li>
687 <li>Fix of some non-optimal use of booleans, that give warnings on
688 a Windows compiler. Thanks to Anton Karneyeu.</li>
690 <li>New options for the <a href="SUSYLesHouchesAccord.html" target="page">
691 SUSY Les Houches Accord</a> such that, by default,
692 particle and decay data are not overwritten for known Standard Model
693 particles (including <i>Z^0</i>, <i>W^+-</i> and <i>t</i>,
694 but excluding the Higgs).</li>
696 <li>Bug fix in <code>SusyLesHouches</code>, where the reading of SLHA
697 information embedded in an LHEF would not stop at the end of the header
700 <li>Bug correction for undefined secondary widths where decay products
701 together are heavier than the mother. Also unit default secondary width
702 values in the <code>DecayChannel</code> constructor.</li>
704 <li>Documentation updated, including change of current year to 2010.</li>
709 <li>8.140: 16 July 2010
712 <li>Four new draft <a href="Tunes.html" target="page">tunes</a> available.</li>
714 <li>Introduction of a new scenario for production of Hidden-Valley
715 particles, and interleaved showering in the QCD and HV sectors, see
716 the new <a href="HiddenValleyProcesses.html" target="page">Hidden Valleys</a>
717 description. A longer physics writeup is available [<a href="Bibliography.html" target="page">Car10</a>].
720 <li>Implementation of <i>2 -> 3</i> phase space selection intended
721 for QCD processes with massless partons. A new set of matching
722 <a href="PhaseSpaceCuts.html" target="page">phase space cut parameters</a>.
723 The <a href="QCDProcesses.html" target="page">ten different QCD <i>2 -> 3</i>
724 processes</a> have been implemented making use of this new
725 possibility, so far without a complete handling of possible colour
728 <li>New processes have been added for
729 <a href="CompositenessProcesses.html" target="page">contact interactions</a> in
730 <i>q q -> q q</i> and <i>q qbar -> q qbar</i> scattering.</li>
732 <li>A process has been added for TeV^-1 Sized
733 <a href="ExtraDimensionalProcesses.html" target="page">Extra Dimensions</a>, which
734 involves the electroweak KK gauge bosons, i.e. <i>gamma_{KK}/Z_{KK}</i>,
735 in one TeV^-1 sized extra dimension; see <code>main30.cc</code> for
736 an example. This scenario is described in [<a href="Bibliography.html" target="page">Bel10</a>]. Thanks to
737 Noam Hod and coworkers for contributing this code.</li>
739 <li>In the Randall-Sundrum extra-dimensional scenario a new option has
740 been added where SM fields can exist in the bulk rather than only on
741 a brane. (Still under development.) Furthermore production of a
742 Kaluza-Klein gluon state has been added, and the <code> main28.cc</code>
743 test program extended.</li>
745 <li>The scenario for monojets in Large Extra Dimensions has been expanded
746 with an alternative for scalar graviton exchange instead of tensor one.
749 <li>New parameters for maximum scale of
750 <a href="TimelikeShowers.html" target="page">timelike showers</a>,
751 <code>TimeShower:pTmaxMatch</code>, and the dampening of hard radiation,
752 <code>TimeShower:pTdampMatch</code> and <code>TimeShower:pTdampFudge</code>,
753 by analogy with corresponding ones for spacelike showers. Also new method
754 <code>TimeShower:limitPTmax(...)</code> to implement alternative procedures.
755 For dipoles stretched to the beam the new switch
756 <code>TimeShower:dampenBeamRecoil</code> allows to dampen radiation
757 close to the beam direction, with a changed default behaviour.</li>
759 <li>Azimuthal anisotropies from coherence arguments have been introduced
760 for the spacelike parton showers, see <code>SpaceShower:phiIntAsym</code>
761 and <code>SpaceShower:strengthIntAsym</code>.
762 Also azimuthal anisotropies from gluon polarization have been introduced
763 for the spacelike parton showers, see <code>SpaceShower:phiPolAsym</code>,
764 and updated for timelike parton showers, see
765 <code>TimeShower:phiPolAsym</code>.</li>
767 <li>Improvements for the matching to POWHEG LHEF-style input illustrated
768 by the new <code>main71.cc</code> example. See also [<a href="Bibliography.html" target="page">Cor10</a>].</li>
770 <li>A set of new processes <i>gamma gamma -> f fbar</i>, with <i>f</i>
771 quarks or leptons. Code for equivalent photon flux around an unresolved
772 proton, with more to come. Thanks to Oystein Alvestad.
775 <li>A new option has been included to dampen the growth of the diffractive
776 cross sections, see <a href="TotalCrossSections.html" target="page">Total Cross
779 <li>A new method <code>virtual int SigmaProcess::idSChannel()</code>
780 has been introduced. If overloaded to return a nonzero value then a
781 <i>2 -> n</i> process will appear listed as a <i>2 -> 1 -> n</i> one.
782 That is, an intermediate resonance with the requested identity will be
783 inserted in the event record, even without appearing in the calculation
784 of the matrix element proper. Thanks to Noam Hod for idea and code.</li>
786 <li>A new method <code>SigmaProcess::convertM2()</code> has been introduced
787 to optionally allow the <code>SigmaProcess::sigmaHat()</code> to return
788 the squared matrix element rather than <i>d(sigmaHat)/d(tHat)</i> for
789 <i> 2 -> 2 </i> processes. Furthermore kinematics is stored in the new
790 <code>mME</code> and <code>pME</code> vectors for alternative cross
791 section encodings.</li>
793 <li>Different encoding of the <i>f fbar -> Z W</i> cross section,
794 contributed by Merlin Kole, based on the cross section of
795 Brown, Sahdev and Mikaelian. Gives a distinctly different cross section
796 than the previous based on EHLQ (including their bug fix).
797 In particular the problem with negative cross sections is now fixed.</li>
799 <li>Minor updates: pass <code>xmlPath</code> to new MSTW and CTEQ PDFs;
800 reset beams earlier to give cleaner documentation.</li>
802 <li>The H1 Fit B LO parametrization to the Pomeron PDF has been included,
803 and made new default for Pomerons. Thanks to Paul Newman for providing
806 <li>Three changes, in principle unrelated, but with the common objective
807 to make the generation of a given event depend only on the values
808 determined during the initialization stage and on the state of the
809 random-number generator when the event is begun. The new default
810 should ensure a reproducible stop-and-restart behaviour, convenient
811 for debug purposes. Thanks to Michael Schmelling for stressing the
812 desire for such a behaviour.
813 <br/>(i) Introduction of a new option <code><a href="PhaseSpaceCuts.html" target="page">
814 PhaseSpace:increaseMaximum</a></code> that allows to switch between
815 two strategies for handling the (hopefully rare) cases when the
816 assumed maximum of the cross section function is exceeded during the
817 event generation, with a changed default behaviour. In the old
818 default the maximum could be increased if it was exceeded during the run,
819 thereby introducing a memory of the previously generated events.
820 <br/>(ii) Updated handling of random numbers with Gaussian distributions.
821 The <code>gauss()</code> method now only generates one value at a time.
822 Instead the new <code>gauss2()</code> method returns a pair of Gauss
823 numbers, with related time savings. In the old approach one Gaussian
824 number could be buffered, which introduced a memory.
825 <br/>(iii) Minor bug fix in <code>MiniStringFragmentation</code>, where
826 the popcorn baryon state was not reset for each new system, again
827 giving a (flawed) memory.</li>
829 <li>New directory <code>rootexample</code> with a simple code example
830 how to use ROOT for histogramming in PYTHIA runs. See
831 <a href="ROOTusage.html" target="page">ROOT Usage</a> for details. Thanks to Rene Brun.
834 <li>In the <code>HepMCinterface</code> the checks for unhadronized
835 quarks and gluons are not performed if hadronization has been switched
838 <li>The <code>UserHooks::initPtr(...)</code> has been expanded so that
839 pointers to more classes (beam particles, random number, couplings, etc.)
840 are sent in, thereby increasing the scope of possible user-written code.
841 Also, the <code>UserHooks::doVetoProcessLevel(Event& process)</code>
842 now allows the <code>process</code> event record to be modified,
843 even if it is not recommended. The new <code>Info::pTnow()</code>
844 method returns the current <i>pT</i> scale of the combined MPI, ISR
845 and FSR evolution, which can be useful for some user hooks decisions.
848 <li>Histograms of the <code>Hist</code> class can now be booked
849 with up to 1000 bins, instead of the previous maximum 100. All bins
850 can be written to file, but the line-printer style printing will join
851 nearby bins so at most 100 are printed, as before. </li>
853 <li>Updated <code>configure</code> and <code>Makefile</code>
854 to allow 64-bit compilation and more options. Thanks to Mikhail Kirsanov,
855 Rene Brun and Fons Rademakers.</li>
857 <li>Bug fix in <code>ProcessLevel</code> for colour flow checks of
858 junctions. Enables the decay of a neutralino to three quarks, e.g.
859 Thanks to Nils-Erik Bomark.</li>
861 <li>Bug fixes in <code>TimeShower</code>, where recoil partners in resonance
862 decays of coloured particles, and recoil partners in QED dipoles when beams
863 are not allowed to take a recoil, might not be correctly identified. </li>
865 <li>Bug fix in <code>SpaceShower</code>: when used with a fixed
866 <i>alpha_strong</i>, the threshold enhancement factor of
867 <i>g -> Q Qbar</i> became undefined. Thanks to Stefan Prestel.</li>
869 <li>Bug fix in initialization of resonance widths, where the
870 <code>minWidth</code> parameter could be used uninitialized,
871 occasionally resulting in strange initialization problems when
872 kinematics needs to force at least one resonance to be off-shell.</li>
874 <li>Minor updates of <code>main06.cc</code>, <code>main10.cc</code>
875 and <code>main23.cc</code>.</li>
877 <li>Bug fix in mother pointer of multiparton interactions in
878 diffractive systems.</li>
883 <li>8.142: 15 August 2010
886 <li>The strategy for setting up tune values has been changed.
887 Previously the <code>Tune:ee</code> and <code>Tune:pp</code>
888 settings were only interpreted during the
889 <code>Pythia::init(...)</code> stage. Now they are interpreted
890 as soon as they are read. Specifically this means that it is
891 possible to override any of the tune parameters by putting new
892 commands below <code>Tune:ee</code> and <code>Tune:pp</code>
893 in the <code>Pythia::readFile(...)</code> configuration file
894 or in the list of <code>Pythia::readString(...)</code> commands.
895 <br/>As a consequence of this change, the public
896 <code>Pythia::initTunes(...)</code> method has been replaced by
897 two private <code>Settings::initTuneEE(...)</code> and
898 <code>Settings::initTunePP(...)</code> methods.
899 <br/>If <code>Tune:ee</code> or <code>Tune:pp</code> are
900 nonvanishing by default, then the corresponding tune variables
901 are set also from the <code>Pythia</code> constructor, before any
902 user changes are possible. Currently this is not relevant.
905 <li>Bug fix in the setup of the <code>Tune:pp = 5</code> and
906 <code>= 6</code> options, which meant that diffractive cross
907 sections were not reduced as advertised.</li>
909 <li>The default value of <code>MultipartonInteractions:pT0Ref</code>
910 has been slightly reduced so as to give a somewhat improved
911 default description. It is not intended as a replacement for the
912 specific tunes, however.</li>
914 <li>Some comparisons between tunes and data, obtained with the
915 Rivet package, have been posted on
916 <a href="http://home.thep.lu.se/~richard/pythia81/">
917 http://home.thep.lu.se/~richard/pythia81/</a>.
918 Further improvements can be expected from future Professor-based
919 tunes. The current set of 2C, 2M, 3C and 3M "draft tunes" have
920 deliberately been chosen different also to explore a range of
921 possibilities. One not visible in the plots is the fraction
922 of single and double diffractive events in the inelastic cross
923 section. This is 32% in 2C and 2M, while it was reduced to
924 21% in 3C and 3M, and a recent ATLAS study (ATLAS-CONF-2010-048)
925 would suggest 28+-4%.</li>
927 <li>Minor changes in <code>TimeShower</code> and
928 <code>SpaceShower</code>, as protection if the <i>c</i> or
929 <i>b</i> masses are set small.</li>
931 <li>Bug fix in <code>SpaceShower</code>, for case when <i>phi</i>
932 angle selection is biased to take into account interference effects.
935 <li>The <code>SigmaProcess::convertM2()</code> method now has
936 been implemented also for <i>2 -> 1</i> processes, so that it is
937 possible to provide the squared matrix element instead of
938 <i>sigmaHat</i> for semi-internal processes. A fixed-width
939 Breit-Wigner is also inserted, since the matrix element is supposed
940 not to include it.</li>
942 <li>New method <code>SigmaProcess::setupForME()</code> does an
943 extended conversion from the internal kinematics to an almost
944 equivalent one, better adapted to the mass conventions of matrix-element
945 caclulation programs, such as massive incoming <i>b</i> quarks.
946 New flags allow to determine whether the <i>c</i>, <i>b</i>,
947 <i>mu</i> and <i>tau</i> should be considered massless or not
948 in the calculations.</li>
950 <li>Two new friend methods <code>table</code> of the <code>Hist</code>
951 class allow to print a table with three columns, the first for the
952 (common!) <i>x</i> values and the other two for the respective
953 histogram values. A new method <code>takeSqrt</code> for the square
954 root of histogram bin contents.
960 <li>8.145: 10 November 2010
963 <li><code>Couplings</code> is defined in <code>StandardModel.h</code>
964 as a derived class of <code>coupSM</code> and has only one extra flag:
965 <code>isSUSY</code> to check presence of extra couplings.Changed all
966 pointers <code>CoupSM*</code> to <code>Couplings*</code> and removed
967 explicit references to <code>CoupSUSY*</code>. The <code>coupSUSY</code>
968 object is only initialised if SUSY couplings are present. The new pointer
969 <code>couplingsPtr</code> points either to only SM couplings or SM+SUSY
970 couplings based on SLHA data.</li>
972 <li>New files <code>SusyResonanceWidths.h/cc</code> contains the
973 <code>SusyResonanceWidths</code> class, which inherits from
974 <code>ResonanceWidths</code> but typecasts the <code>couplingsPtr</code>
975 to <code>(CoupSUSY*) coupSUSYPtr</code>. This is the base class for
976 all SUSY resonances. It contains the <code>ResonanceSquark</code> class
977 for all squark decays. A new flag <code>SLHA:useDecayTable</code>
978 to check if internal widths should be overwritten by those read in
981 <li>Added new functionality to <code>SusyLesHouches</code> for read-in
982 of generic user blocks in the SLHA format, along with methods to
983 extract parameters from them with typecasting controlled by the user.
984 Intended for use with user-written semi-internal processes.</li>
986 <li>Added <code>Sigma1qq2antisquark</code> cross section.</li>
988 <li>Some new flags and modes in the <code>SUSY</code> and
989 <code>SLHA</code> series offer further functionality.</li>
991 <li>Several further changes as a consequence of the upgrade of the SUSY
994 <li>Bug/typo fixes in rotation matrices for SUSY couplings and for the
995 processes <code>qqbar2squarkantisquark</code>,
996 <code>qq2squarksquark</code> and more.</li>
998 <li>Improved handling of colour junctions. Added new example program
999 <code>main72.cc</code>, to illustrate read-in of color junction
1000 structures via LHEF (<code>main72.lhe</code>). The example used is SUSY
1003 <li>New Tune 4C introduced as <code>Tune:pp = 5</code>. The more crude
1004 (non-)tunes 3C and 3M are removed.</li>
1006 <li>New methods <code>Settings::getFlagMap(...)</code>,
1007 <code>Settings::getModeMap(...)</code>,
1008 <code>Settings::getParmMap(...)</code> and
1009 <code>Settings::getWordMap(...)</code> allows to return a map of all
1010 settings of the respective type that contain a specific string
1014 <li>Improved description of excited <i>g^*/KK-gluon^*</i> production
1015 in the <code>Sigma1qqbar2KKgluonStar</code> and
1016 <code>ResonanceKKgluon</code> classes.</li>
1018 <li>Possibility added to let Hidden-Valley <i>gamma_v</i> have
1019 a nonero mass and decay by mixing with the ordinary photon.
1020 Still experimental.</li>
1022 <li>Minor bug fix in handling of three-body phase space.</li>
1024 <li>Minor correction in <code>Sigma2ffbar2TEVffbar</code> class.</li>
1026 <li>Bug fix for decays of <i>W'</i> to a pair of heavy fermions when
1027 <i>gV != gA</i>. Thanks to M. Chizhov, see arXiv:0705.3944. </li>
1029 <li>Restore the older EHLQ-based encoding of the <i>f fbar -> Z W</i>
1030 cross section, which was changed in version 8.140, since comparisons
1031 with Madgraph gives much better agreement with it than with the
1032 expression of Brown, Sahdev and Mikaelian.</li>
1034 <li>The <code>HepMCInterface</code> now also stores colour flow
1035 information for coloured particles.</li>
1037 <li>Pointer to <code>Couplings</code> made available for particle
1040 <li>Minor update in <code>main61.cc</code> for more elegant usage
1041 of FastJet, as suggested by Gregory Soyez.</li>
1046 <li>8.150: 20 April 2011
1049 <li>Tune 4C is made default. It is based on first comparisons with
1050 LHC data [<a href="Bibliography.html" target="page">Cor10a</a>], and has also been checked independently
1051 [<a href="Bibliography.html" target="page">Buc11</a>] to give reasonable agreement with many distributions.
1054 <li>The description of <i>tau</i> lepton decays has been significantly
1055 enhanced, to include helicity information related to the production
1056 process and hadronic currents fitted to data. A complete writeup is
1057 in preparation [<a href="Bibliography.html" target="page">Ilt11</a>]. A new flag is introduced to revert
1058 to the old behaviour, for cross-checks, see
1059 <a href="ParticleDecays.html" target="page">Particle Decays</a>.
1060 The new tau decay machinery is on by default.
1063 <li>A new option <code>MultipartonInteractions:bProfile = 4</code> has
1064 been introduced for the impact-parameter profile of protons in the
1065 <a href="MultipartonInteractions.html" target="page">Multiparton Interactions</a>
1066 framework, wherein low-<i>x</i> partons are spread over a larger area
1067 than high-<i>x</i> ones, see [<a href="Bibliography.html" target="page">Cor11</a>]. A new method
1068 <code>Info::eMPI(i)</code> gives back the enhancement factor related to
1069 the <code>i</code>'th interaction. The impact-parameter profile can now
1070 be selected separately for <a href="Diffraction.html" target="page">diffraction</a>,
1071 but without a <code>bProfile = 4</code> option.
1074 <li>The possibility of "hadronization" in the
1075 <a href="HiddenValleyProcesses.html" target="page">Hidden Valley</a> sector
1076 has been added as a new option <code>HiddenValley:fragment = on</code>.
1077 This is based on a copy of the standard string fragmentation framework,
1078 but with the option of a completely separate "flavour" sector, and
1079 separately tunable longitudinal fragmentation functions and transverse
1080 momenta. For now only a simple flavour scenario is provided, where
1081 flavour-diagonal mesons can decay back into the normal visible sector
1082 while off-diagonal ones remain hidden. A writeup of the model is in
1083 preparation [<a href="Bibliography.html" target="page">Car11</a>]. Also some further Hidden Valley options
1084 have been added.</li>
1086 <li>Included possibility in <code>TimeShower</code> for QCD dipoles to
1087 have an adjustible normalization factor, via the new
1088 <code>bool isFlexible</code> and <code>double flexFactor</code>
1089 properties of <code>class TimeDipoleEnd</code>. This flexibility is used
1090 to treat radiation off colour topologies with epsilon tensors, in
1091 particular colour junctions which have all their partons in the
1092 final state. (An example is the BNV-SUSY decay ~chi0→uds.) For
1093 such topologies, the new treatment in PYTHIA 8 is that a
1094 half-strength dipole is spanned between all combinations of
1095 final-state quarks. For junctions with an incoming (anti)colour line (such
1096 as in the BNV-SUSY decay ~t*→cb), a full-strength dipole is
1097 instead spanned between the two daughters, with no radiation from the
1098 decaying object (in its CM). As will be described in a fortcoming
1099 paper with N. Desai, this should give the
1100 closest possible correspondence to the radiation patterns exhibited
1101 by higher-order matrix elements for this type of process.</li>
1103 <li>Corrected harmless bugs in <code>ProcessLevel::findJunctions</code>
1104 which caused junctions of types 3 and 4 (i.e., junctions with 1
1105 incoming color tag) to sometimes be incorrectly classified as types
1106 1 and 2 (with all color tags outgoing), respectively.
1107 Since the parity (even/odd) of the junction kind was still correct,
1108 however, this did not cause any problems at the hadronization
1111 <li>The junction-finder in <code>ProcessLevel::findJunctions</code>
1112 has been made more stable, and the following ordering of the color
1113 tags returned by <code>Event::endColJunction(iJun, iLeg)</code> is
1114 now enforced: for junction kinds 3 and 4 (one tag
1115 incoming), <code>iLeg = 0</code> will return the
1116 incoming tag, while for kinds 5 and 6 (two tags incoming),
1117 <code>iLeg = 0</code> and <code>iLeg = 1</code> will return the
1118 incoming tags. Apart from this ordering, the color tags are
1119 ordered in ascending color tag number.</li>
1121 <li>Declarations of friend functions moved to sit outside the class
1122 it befriends. Thanks to Axel Naumann for pointing out the incorrect
1123 previous construction.</li>
1125 <li>The <code>rootexample</code> subdirectory becomes
1126 <code>rootexamples</code> as the old example is split into two,
1127 with improved documentation to clarify usage. Thanks to Axel Naumann
1128 and Bernhard Meirose for the new code.</li>
1130 <li>In the Les Houches Event File machinery, input type has been
1131 changed from <code>ifstream</code> to <code>istream</code> for more
1134 <li>R-hadron handling is largely implemented, see the
1135 <a href="RHadrons.html" target="page">R-hadrons</a> page, although some aspects
1136 still need polishing. A new class <code>RHadrons</code> takes
1137 care of the hadronization and decay. Particle data have been added
1138 for R-hadrons containing a gluino, stop or sbottom, but could
1139 alternatively be used for other long-lived coloured particles.
1140 Thanks to Bernhard Meirose for support.
1143 <li>Calculations of SUSY decay widths included by
1144 N. Desai, contained in the new source
1145 files <code>SusyResonanceWidth.cc</code>
1146 and </code>.h</code>. Validation and addition of more modes is still in
1147 progress, so this implementation should be considered preliminary
1148 for now. For a list of available modes, see
1149 the <a href="SUSYProcesses.html" target="page">SUSY Processes</a> page.
1152 <li>A first implementation of the SLHA-based QNUMBERS interface for
1153 defining new exotic particles has been
1154 included. See [<a href="Bibliography.html" target="page">Alw07</a>] and
1155 the <a href="SUSYLesHouchesAccord.html" target="page">SUSY Les Houches Accord</a>
1158 <li>Read-in of LHEF events containing Baryon Number Violating vertices
1159 has been included, using colour junctions, see
1160 the <a href="EventRecord.html" target="page">Event Record</a> page. The advanced
1161 shower model taking into account the full colour structure of such
1162 events, developed by N. Desai and described above,
1163 is turned on by default in such events.
1164 Several test cases were used to
1165 validate this implementation, but it is possible that problems could
1166 still exist for some cases. Feedback is welcome. Thanks to
1167 the MadGraph authors for providing several test cases.</li>
1169 <li>Some first steps taken to allow events containing colour sextets,
1170 e.g., from semi-internal processes or LHEF interfaces, and/or from
1171 SLHA <code>DECAY</code> tables. New
1172 <code>colType</code> codes 3 and -3 are introduced to describe
1173 sextets and antisextets, respectively. The state of the current
1174 implementation is that hard processes containing such states can be
1175 read in and decays generated (via <code>DECAY</code> tables). Parton
1176 showers can be added, but the sextets themselves do not, as yet,
1177 shower, and any undecayed sextets remaining at the hadronization
1178 stage would lead to unpredictable problems if hadronization is
1179 switched on. Thanks to J. Alwall for help with testing
1180 this implementation.
1183 <li>The functionality of the SLHA SUSY/BSM interface (see
1184 the <a href="SUSYLesHouches.html" target="page">SUSY Les Houches</a> page) has been
1185 extended so that copies of all <code>BLOCK</code>s are now stored
1187 strings, regardless of whether they correspond to "official" SLHA
1188 blocks or not. Their contents can subsequently be queried by a set
1189 of new templated member functions of the
1190 class <code>SusyLesHouches</code>. Available query functions so far
1192 <br/><code>template <class T> bool getEntry(string, T&);</code>,
1193 <br/><code>template <class T> bool getEntry(string, int, T&);</code>,
1194 <br/><code>template <class T> bool getEntry(string, int, int, T&);
1196 <br/><code>template <class T> bool getEntry(string, int,
1197 int, int, T&);</code>,
1198 <br/>where the type of
1199 the argument used in the call determines how to read the block
1200 entries. Thus, if an LHEF, SLHA, or other card file is read in by
1201 PYTHIA, the contents of any <code>BLOCK</code> in that file can
1202 subsequently be queried run-time using these functions. This is
1203 used, e.g., in the new interface between MADGRAPH 5 and PYTHIA
1204 8. Thanks to the MADGRAPH team, and to J. Alwall in particular, for
1205 help and debug on this new implementation.
1211 <li>8.153: 10 August 2011
1214 <li>The setup of tunes has been modified, see the
1215 <a href="Tunes.html" target="page">Tunes</a> page for details. Specifically
1216 the <code>Tune:ee</code> and <code>Tune:pp</code> modes have
1217 acquired a new option <code>-1</code> for a forced restore to the
1218 default values of all settings used in the respective kind of
1221 <li>The code for handling multiparton interactions in the scenario with
1222 an <i>x</i>-dependent width of the Gaussian matter profile
1223 [<a href="Bibliography.html" target="page">Cor11</a>], has been improved and updated. Tune 4Cx, which
1224 is based on this option, has been added as a further tune option.</li>
1226 <li>A possibility to bias the phase-space selection has been added,
1227 whereby some phase space regions can be oversampled, which is
1228 compensated by assigning a weight to each event.
1229 A new set of methods have been added to the <code>UserHooks</code>
1230 class to allow users to program how to bias the selection.</li>
1232 <li>New options added so that matrix-element corrections can be
1233 switched off after the first branching in ISR or FSR.</li>
1235 <li>Some new <code>Info</code> methods have been added to store
1236 information on latest ISR branching. The <code>SpaceShower</code>
1237 class has also been corrected so that the latest <i>z = 1/2</i>
1238 when not defined by history. This avoids undefined values for
1239 azimuthal asymmetries. Thanks to Stefan Prestel for finding and
1240 sorting out this problem.</li>
1242 <li>The <code>Pythia::forceHadronLevel()</code> method now takes
1243 an argument that optionally means that existing junction information
1244 is not overwritten. Thanks to Leif Lönnblad for pointing out
1245 the usefulness of this.</li>
1247 <li>For particle decays to a varying number of hadrons the multiplicity
1248 increase with mass has been somewhat reduced, and especially for
1249 <code>meMode = 23</code> a separate even slower increase has been
1252 <li>New possibility to force the tau polarization.</li>
1254 <li>Bug fix for the special case in which events containing SUSY
1255 particles are generated without proper initialization of SUSY decays.
1256 This can happen, e.g., if events containing SUSY particles are read
1257 in via external LHEF files, if those files do not contain readable
1258 SLHA spectra in their headers. In this case, a failed attempt to
1259 generate sparticle decays with ill-defined couplings previously
1260 led to crashes. The program now reverts to the old behaviour,
1261 based on static decay tables, in such cases, with the default
1262 being to decay all sparticles to gravitino + particle. An error
1263 message stating that the full SUSY treatment has been switched
1264 off and why is also issued. Thanks to N. Desai for this fix.</li>
1266 <li>The R-hadron machinery has been completed.</li>
1268 <li>Minor change in timelike showers: gluons which fall below the
1269 <i>pTmin</i> cutoff by the correction for mass effects are now
1270 eliminated, while previously they were kept. This reduces the
1271 number of gluons somewhat, but has no significant effects on the
1272 hadronic final state. (Prompted by R-hadron studies, where big mass
1273 effects else give bothersome low-energy gluons.)</li>
1275 <li>Corrected typos in two of the Upsilon wave function matrix
1276 elements, <code>Bottomonium:OUpsilon3P08</code> and
1277 <code>Bottomonium:Ochib03P01</code>. Thanks to Beate Heinemann for
1278 pointing it out.</li>
1280 <li>Implemented <i>f*</i> decay angle in <i>f f -> f f*</i> processes,
1281 and fixed some bugs for the same process. Thanks to Piyali Banerjee
1284 <li>Introduce possibility to separate production channels for
1285 TeV-sized extra dimensions, and a small code correction. Thanks to
1286 Noam Hod for code contribution.</li>
1288 <li>Bug fix for neutrino beams: since neutrinos are always lefthanded
1289 there should be a factor 2 in the cross section, relative to charged
1290 leptons, from the non-need to average over incoming spin states. This
1291 is now fixed by introducing a new PDF class <code>NeutrinoPoint</code>
1292 for (unresolved) neutrinos, with normalization 2 rather than 1 for
1293 charged leptons. Thanks to Ryosuke Sato.</li>
1295 <li>Bug fix for some (rarely used) particle settings, which could not
1296 be changed by users because they were read too early. Thanks to
1297 Andrew Altheimer and Gustaaf Brooijmans.</li>
1299 <li>Bug fix in handling of <code>tau</code> decays, where setting of
1300 decay vertices could write outside memory. Thanks to Steven Schramm.</li>
1302 <li>Minor expansion of the <code>BeamParticle</code> constructor.</li>
1304 <li>Minor bug fix in CTEQ 6L for uninitialized variables.</li>
1306 <li>Minor bug fix in fragmentation flavour combination to hadron.</li>
1308 <li>Some updates of the documentation, including new pages on
1309 MadGraph 5 as a generator for semi-internal processes (thanks to
1310 Johan Alwall) and on RIVET interfacing.</li>
1312 <li>Minor improvements of ROOT- and HepMC-related code and documentation.</li>
1314 <li>Some cleanup of code.</li>
1319 <li>8.157: 10 November 2011
1322 <ii>StefanPrestel joins as new member of the PYTHIA author team.
1323 He is mainly working on matching/merging issues, and has contributed
1324 the CKKW-L machinery mentioned below.</li>
1326 <li>Merging capabilities according to the CKKW-L scheme [<a href="Bibliography.html" target="page">Lon11</a>]
1327 have been added, see the new
1328 <a href="MatrixElementMerging.html" target="page">Matrix Element Merging</a>
1329 page. It involves new classes to reconstruct and select how a
1330 matrix-element-generated partonic configuration could have been obtained
1331 by the PYTHIA evolution, and to perform trial showers (using a new
1332 copy of the normal parton-level machinery) that introduce the appropriate
1333 Sudakov suppression factors. New examples to illustrate various
1334 common tasks are found in <code>main81.cc</code>, <code>main82.cc</code>,
1335 <code>main83.cc</code> and <code>main84.cc</code>.</li>
1337 <li>The <code>main71.cc</code> program is now generalised for reading
1338 in arbitrary POWHEG LHE files, to implement a smooth matching between NLO
1339 matrix elements and the PYTHIA parton showers. Cuts are made on both
1340 ISR and FSR emissions, while previously only ISR was covered. The key
1341 assumptions are the <i>pT</i> definitions used for ISR and FSR, but several
1342 further options are available, as documented in the <code>main71.cmnd</code>
1343 file. Work is still ongoing to pick the best default options. </li>
1345 <li>Several expansions of the <code>UserHooks</code> class.
1346 For both <code>doVetoFSREmission</code> and <code>doVetoISREmission</code>
1347 a new argument <code>iSys</code> labels the system within which the
1348 radiation occurs. For <code>doVetoFSREmission</code> a further argument
1349 <code>inResonance</code> distinguishes FSR in resonance
1350 decays from that in the hard process itself. New methods
1351 <code>canVetoMPIEmission</code> and <code>doVetoMPIEmission</code>
1352 have been added to veto multiparton interactions in the same way as
1353 FSR and ISR. In <code>biasSelectionBy</code> at times incorrect values
1354 for <code>inEvent</code> has been corrected. Also some systematization
1355 of the use of <code>const</code>.</li>
1357 <li>A new model for hadron scattering is introduced, still at an early
1358 stage and therefore more intended for internal development than for the
1359 normal user. The basic idea is that a high-energy <i>pp</i> collision
1360 involves the fragmentation of multiparton strings that overlap in space
1361 (and time). Also the produced hadrons therefore initially overlap, and
1362 there is a strong likelihood that hadrons can scatter against each other
1363 until the system has expanded sufficiently. This can e.g. increase the
1364 transverse momentum of heavier hadrons at the expense of lighter ones.
1367 <li>A new jet finder <code>SlowJet</code> offers simple access to the
1368 inclusive <i>kT</i>, anti-<i>kT</i>, and Cambridge/Aachen
1369 algorithms in a cylindrical coordinate frame. The jet reconstruction
1370 is then based on sequential recombination with progressive removal,
1371 using the <i>E</i> recombination scheme. The minimalistic
1372 <code>SlowJet</code> code is much slower than <code>FastJet</code>
1373 [<a href="Bibliography.html" target="page">Cac06</a>], and contains less options, but reconstructs the same
1374 jets if run under identical conditions. For details see the
1375 <a href="EventAnalysis.html" target="page">Event Analysis</a> page.</li>
1377 <li>Starting in gcc 4.6, it is possible to switch off specific warnings
1378 around specific blocks of code. Although version 4.6 is some way off
1379 from being commonly found, this option has now been introduced to switch
1380 off <code>-Wshadow</code> warnings in <code>HepMCInterface.cc</code>.
1381 For other compilers, or earlier versions of gcc, the old behaviour
1384 <li>Support for reading in gzipped LHEFs has been added in the
1385 <code>LesHouches</code> and <code>SusyLesHouches</code> classes.
1386 This also affects <code>configure</code> and <code>Makefile</code>s.
1387 Unless explicitly enabled, it should not affect anything.
1388 If enabled, it relies on the Boost and zlib libraries to function,
1389 so paths to these must be set appropriately, see the
1390 <code>README</code> file for details. The Boost header files can
1391 give very many shadow warnings, so <code>-Wshadow</code> is disabled
1392 if gzip support is enabled, as described above.</li>
1394 <li>Introduce use of the <code>HEPMC_HAS_UNITS</code> environment
1395 variable in the <code>HepMCInterface.cc</code> and <code>main32.cc</code>
1396 codes to automatically check whether GeV and mm can be set as relevant
1397 units. If yes, then it is set in <code>main32.cc</code>. If no,
1398 a conversion from GeV to MeV is done explicitly in
1399 <code>HepMCInterface.cc</code>. Note that, for early HepMC versions,
1400 this means a change of behaviour. Thanks to Andy Buckley.</li>
1402 <li>A new method <code>Info::lhaStrategy()</code> returns the
1403 Les Houches event weighting strategy where relevant, and 0 where not.
1404 For the strategies <i>+-4</i> the event weight and sum,
1405 <code>Info::weight()</code> and <code>Info::weightSum()</code>,
1406 is now in units of pb at output, as it should be at input.
1407 (While internally mb is used.)</li>
1409 <li>New flag <code>Check:abortIfVeto</code> allows the user to
1410 resume control over execution in case of a veto in the event
1411 generation process.</li>
1413 <li>New method <code>Event::at(i)</code> returns reference to
1414 <code>i</code>'th particle in the event record.</li>
1416 <li>Introduce the Fermi constant as one of the Standard Model
1419 <li>Included automatic pre-initialization of SLHA blocks MASS and
1420 SMINPUTS using PYTHIA's SM parameters and particle data table
1423 <li>SUSY: added sleptons (and sneutrinos) as resonances.
1424 Corrected 2-body decay widths of gluinos, squarks and gauginos.
1425 Added sleptonic decay modes to gaugino decays.
1426 Implemented 2-body decays of sleptons (and sneutrinos)
1427 into sleptons/leptons/gauginos. Corrected slepton couplings (they
1428 now look exactly like squark couplings, using a 6x6 slepton mixing
1431 <li>New parameter <code>Diffraction:probMaxPert</code> introduce to
1432 give more flexibility in transition from a nonperturbative to a
1433 perturbative description of a diffractive system.</li>
1435 <li>Bug corrected in <code>SigmaEW.cc</code>, for the process
1436 <code>WeakSingleBoson:ffbar2ffbar(s:gm)</code>. Previously, all outgoing
1437 quark flavours in this process were erroneously assigned ID code 5
1438 (b quarks). This has now been corrected so the proper ratios are
1439 obtained, with <i>u : c : d : s : b = 4 : 4 : 1 : 1 : 1</i>,
1440 according to the squared quark charges.</li>
1442 <li>Changes in <code>FragmentationSystems</code> and
1443 <code>StringFragmentation</code> to reject systems with three or more
1444 interconnected junctions. This may happen in baryon-number-violating
1445 scenarios in pp collisions, if both of the beam baryon junctions are
1446 resolved and get connected via an antijunction created by a
1447 hard-process BNV vertex. In principle, this could be addressed by an
1448 extension of the existing junction fragmentation framework. However,
1449 since it happens rarely, for the time being an error message is printed
1450 and the fragmentation restarted.
1453 <li>Change in <code>Event::copy</code> to safeguard against attempting
1454 to copy out-of-range entries. An attempt to copy a non-existing entry
1455 will now return -1.</li>
1457 <li>Bug fix in the machinery for the user to force the setting of
1458 tau polarization.</li>
1460 <li>Bug fix in the initial search for a maximum of the process
1461 cross section (only affecting rare cases).</li>
1463 <li>Corrected angular decay distributions for two compositeness
1464 processes, <code>Sigma2qq2qStarq</code> and
1465 <code>Sigma2qqbar2lStarlbar</code>.</li>
1467 <li>Extra check in <code>HiddenValleyFragmentation</code> to make sure
1468 that pointers which have not been assigned with <code>new</code> are not
1471 <li>Some further minor changes.</li>
1476 <li>8.160: 23 January 2012
1479 <li>The older term "multiple interactions" has been replaced by the
1480 new standard "multiparton interactions" one, and correspondingly the
1481 abbreviation MI by MPI. This affects everything: settings, class and
1482 method names, documentation, etc. It therefore becomes necessary to
1483 rewrite user code. However, so as to keep the immediate effort at a
1484 reasonable level, the old settings names are kept as aliases. Thus
1485 <code>PartonLevel:MI</code> and <code>PartonLevel:MPI</code> are
1486 equivalent, and similarly <code>MultipleInteractions:pT0Ref</code>
1487 and <code>MultipartonInteractions:pT0Ref</code>. Should you be using
1488 methods such as <code>double Info::pTMI(int i)</code> you need to
1489 edit the code, however. All the <code>example/main*</code> files
1490 have been uopdated accordingly.</li>
1492 <li>A new option <code>Beams:frameType = 5</code> has been added
1493 for the case where an external generator should provide LHA process
1494 information. The new <code>Pythia::setLHAupPtr(...)</code> method
1495 should then be used to link in this generator. The new switch
1496 <code>Beams:newLHEFsameInit</code> can be used to tell that a new
1497 LHEF should be used, but without the need for a new initialization.
1498 With these two changes, all the different ways of initializing
1499 can be covered by the <code>Pythia::init()</code> call with no
1500 arguments. The various <code>init(...)</code>options with arguments
1501 are deprecated and will be removed for PYTHIA 8.2.</li>
1503 <li> The <code>Pythia::stat()</code> method, with no arguments,
1504 replaces <code>Pythia::statistics(...)</code>, although the latter
1505 remains as a deprecated alternative.</li>
1507 <li>New settings <code>Init:...</code>, <code>Next:...</code>,
1508 and <code>Stat:...</code> can be used to steer some details of
1509 the operation of the <code>Pythia::init()</code>,
1510 <code>Pythia::next()</code> and <code>Pythia::stat()</code>,
1511 respectively. In particular it affects the amount of printout
1512 at the various stages of operation. See
1513 <a href="MainProgramSettings.html" target="page">here</a> for further details.
1514 This change involves several code changes, but in documentation
1515 rather than physics. Most of the <code>Main:...</code> settings
1516 are deprecated as a consequence.</li>
1518 <li>The sample main programs in the <code>examples</code> subdirectory
1519 have been updated. This includes a change to the new favoured
1520 methods and settings outlined above, plus some update of the
1521 physics contents. Some of the examples have been combined,
1522 some others have been added (e.g. for R-hadroms), and as a consequence
1523 some renumbering has been made. See the modified list of
1524 <a href="SampleMainPrograms.html" target="page">sample main programs</a> for
1525 the new status. In particular note that (the new) <code>main61.cc</code>
1526 allows streamlined input and output in HepMC, like <code>main42.cc</code>
1527 (previously <code>main32.cc</code>), but additionally links to LHAPDF. </li>
1529 <li>The <code>examples/configure</code> script has new optional argument
1530 <code>--with-pythia8</code>. It can be used to set the new
1531 <code>PYTHIA8LOCATION</code> environment variable, which then is used
1532 in <code>examples/Makefile</code> to give the path to the PYTHIA
1533 library. Thereby it becomes possible to relocate (parts of) the
1534 <code>examples</code> directory and still obtain the correct path.
1535 Thanks to Mikhail Kirsanov.</li>
1537 <li>Polarization information has been included as a new
1538 <code>Particle</code> property, that can be set by
1539 <code>void pol(double polIn)</code> and obtained by
1540 <code>double pol()</code>. Default value is <code>9.</code>,
1541 in agreement with the Les Houches standard. Event listings have
1542 been expanded to optionally display this information. Currently
1543 polarization is not used internally.</li>
1545 <li>The matrix element merging machinery has been modified as follows.
1546 <br/>- Improved handling of the hard process, so that MadGraph5-produced
1547 LHE files do not produce problems (sometimes, the choices of MG4 on what
1548 to put into a LHEF have changed in MG5).
1549 <br/>- Improved handling of colour for easier handling of states with
1550 many quarks (the code has been tested for states with up to 5
1551 <i>q qbar</i> pairs and some gluons).
1552 <br/>- Improved checking which clusterings are allowed. Now, clusterings
1553 should immediately be rejected if they lead to unphysical states,
1554 without the need to explicitly construct these states. This was needed
1555 to get <i>t tbar</i> production, VBF and some simple SUSY processes
1556 running with reasonable generality.
1557 <br/>- Improved handling of incomplete histories. Now there is an
1558 additional switch allowing code to try to swap some colours when fewer
1559 clusterings than requested have been found.
1562 <li>Updates in the handling of graviton resonances in scenarios with
1564 <br/>- Now all G decays have correct angular distribution, which was not
1565 the case before for W/Z decays.
1566 <br/>- Added the possibility for G to only couple to longitudinal
1567 W/Z bosons, which affects both the width and angular distributions.
1568 <br/>- Added decays to Higgs pairs, <i>G -> hh</i>.
1571 <li>Bug fix in the <code>findJunctions()</code> function in
1572 <code>ProcessLevel.cc</code>. Changes introduced in version
1573 8.145 (to allow for junctions in baryon-number-violating
1574 processes) did not correctly handle the remapping of color
1575 tags that can be applied when adding beam remnants to events with
1576 multiparton interactions. A simpler and more stable algorithm is
1577 now applied for the simplest cases, with the more complex one only
1578 invoked for cases such as BNV, which are normally considered before
1579 remnants are added, hence avoiding this particular problem. Also some
1580 other changes in the handling of junction, including a safeguard to
1581 reject systems with three or more interconnected junctions.</li>
1583 <li>Bug fix and updates to the SLHA interface. Possibility of infinite
1584 loop during <code>ProcessLevel::initSLHA</code> corrected. Modifications
1585 to <code>SusyLesHouches</code> to allow interpretation of SLHA1 spectra
1586 with R-parity violation. Rather than reject spectra that do not conform
1587 fully to the SLHA2 standard for RPV, the interface will now first look
1588 for SLHA1 mixing matrices and attempt to translate those into SLHA2 ones
1589 if possible. In this case, warnings that the expected SLHA2 blocks were
1590 not found will be printed. It is up to the user to check that the
1591 derived SLHA2 information is correct. Corresponding additions to
1592 <code>SusyCouplings.cc</code> to extract mixing-matrix information
1593 from the relevant SLHA2 RPV blocks when RPV is switched on.</li>
1595 <li>Updated SLHA example <code>main24.cmnd</code> to use new example
1596 spectrum, <code>cmssm.spc</code>, corresponding to CMSSM point
1597 10.1.1, obtained with SOFTSUSY 3.3.0. Thanks to B. Allanach for
1598 providing the new spectrum file.</li>
1600 <li>A new <code>include/FastJet3.h</code> header file simplifies
1601 interfacing of FastJet to Pythia. For details see documentation in
1602 the file itself. Thanks to Gavin Salam for this contribution.</li>
1604 <li>The handling of diffraction has been made more flexible.
1605 Specifically the "total" Pomeron-proton cross section can now be made
1606 to depend on the mass of the diffractive system. This does not affect
1607 the diffractive cross section in pp collisions, which is set separately,
1608 but is used in the MPI machinery to affect the average number of
1609 interactions per Pomeron-proton collision. Furthermore, the allowed
1610 range for some parameters has been expanded. Thanks to Robert
1613 <li>New method <code>Pythia::forceTimeShower(...)</code> can be used to
1614 generate a single final-state cascade from a set of partons, without
1615 any knowledge of prior history. This is mainly intended for toy studies.
1616 The meaning of the <code>ProcessLevel:all</code> switch has been modified
1617 so that this parton-level function is available, but not any others
1621 <li>ATLAS tune A2 now included. Thanks to Deepak Kar for
1624 <li>Change in the handling of recoils of timelike showers in resonance
1625 decays, in cases of coloured resonances such as <i>t -> b W</i>. In
1626 the first step the <i>W</i> always acts as recoiler to the <i>b</i>,
1627 but in subsequent step previously the <i>W</i> remained as recoiler to
1628 one dipole, while now all QCD-radiating partons recoil against another
1629 coloured parton. The old behaviour could give a (small) unphysical spike
1630 of radition collinear with the colourless recoiler in the subsequent
1631 emissions (while the pattern of the first was and remains correct).
1632 The old behaviour can be recovered for checks, see
1633 <code>TimeShower:recoilToColoured</code>.
1634 Thanks to Yevgeny Kats for pointing out this issue (previously noted
1635 for Pythia 6 by several persons).
1638 <li>Bug fixes for <code>rootexamples/Makefile</code> and restoration
1639 of some deleted information in <code>rootexamples/README</code>.
1640 Thanks to Axel Naumann and Bernhard Meirose.</li>
1642 <li>Bug fix, so that displaced vertices are possible in resonance
1643 decay chains. Thanks to Daniel Blackburn and Andy Buckley for
1644 pointing this out.</li>
1646 <li>Bug fix for <code>Info</code> counter 2.</li>
1648 <li>Bug fix so that sextet quarks now are read in correctly from
1649 Les Houches Event files; previously the (anti)colours were set
1652 <li>Year updated to 2012 in copyright statements etc.</li>
1654 <li>Reformatting to reduce the number of code lines with more
1655 than 79 characters.</li>
1657 <li><code>Pythia::initSLHA()</code> moved from <code>public</code>
1658 to <code>private</code>.
1661 <li>Remove warning message when tau polarization is set by hand.</li>
1663 <li>Several minor changes to reduce the number of warnings issued
1664 by the clang compiler. The origin of some warnings remains unclear
1665 so those remain to track down (could also be compiler bugs; note that
1666 we discuss warnings, not errors). Thanks to Randy MacLeod for bringing
1669 <li>The worksheet has been updated to be in step with Pythia 8.160.</li>
1671 <li>Several other minor corrections in the code and documentation.</li>
1676 <li>8.162: 12 March 2012
1679 <li>A new option allows for several partons to share the recoil in
1680 final-state radiation, see<a href="TimelikeShowers.html" target="page">Timelike
1681 Showers</a>. It is mainly intended to be used in the context of
1682 matching to matrix elements, and so only to be used in the first
1683 few branchings.</li>
1685 <li>Several new processes for LED dijet production, see
1686 <a href="ExtraDimensionalProcesses.html" target="page">Extra Dimensions</a>.</li>
1688 <li>Small update of the <code>Sigma2ffbar2LEDllbar</code> and
1689 <code>Sigma2ffbar2LEDgammagamma</code> LED processes.</li>
1691 <li>New <code>Sigma2QCffbar2llbar</code>
1692 <a href="CompositenessProcesses.html" target="page">contact interaction</a>
1695 <li>Inclusion of a new method in the
1696 <a href="MatrixElementMerging.html" target="page">matrix-element merging</a>
1697 framework to influence the construction of histories, e.g. to already
1698 in the construction of histories disallow paths that fail the
1699 <i>2 -> 2</i> cuts.</li>
1701 <li>Further minor updates of the matrix-element merging code,
1702 mainly for improved clarity.</li>
1704 <li>Minor bug fix in the handling of beam and event information fed
1705 in from an <code>LHAup</code> instance.</li>
1707 <li>Minor bug fix for potential crashes from uninitialized variables
1708 for the merging machinery when merging is not used.</li>
1710 <li>Updated History class for matrix element merging,
1711 also avoiding some compiler warnings.</li>
1713 <li>Bug fixes in the handling of correlated mass choices in resonance
1714 decays, such as <i>H -> Z^*0 Z^*0</i>.</li>
1716 <li>Bug fix when the process-level execution is switched off,
1717 where <code>Info::isResolved()</code> could be called before its
1718 value was initialized. Thanks to Christian Pulvermacher
1719 for finding this.</li>
1721 <li>Corrected matrix-element expression for mass selection in
1722 <i>A^0 -> Z^*0 Z^*0</i> and <i>A^0 -> W^*+ W^*-</i>.</li>
1724 <li>SM Higgs mass updated to 125 GeV and default width and branching
1725 ratios modified accordingly. Minor technical improvements of width
1728 <li>The usage of nested classes has been removed from
1729 <code>SusyLesHouches</code>, since it could give compilation errors
1730 on some platforms. The new class names begin with <code>LH</code>
1731 and all classes have been put inside the <code>Pythia8</code>
1734 <li>Minor Makefile updates. Thanks to Mikhail Kirsanov.</li>
1736 <li>Minor changes to avoid some clang compiler warnings on the
1737 Mac OS X platform.</li>
1742 <li>8.163: 27 March 2012
1745 <li>New methods in the
1746 <a href="EventInformation.html" target="page"><code>Info</code></a> class,
1747 <code>id1pdf()</code>, <code>id2pdf()</code>, <code>x1pdf()</code>
1748 and <code>x2pdf()</code>, to denote the partons for which parton
1749 distribution values have been defined. Previously this was assumed
1750 to agree with the incoming partons to the hard process, the same
1751 methods without the <code>pdf</code> qualifier. However, now the
1752 POWHEG approach offers a counterexample. Also the reading and
1753 handling of Les Houches (and other) events, and the interface
1754 to HepMC, has been modified accordingly.
1757 <li>The decay of Higgs and top resonances read in from Les Houches
1758 Event files is now performed with angular correlations as for
1759 internal processes. LHE files should normally contain all process-specific
1760 resonance decay chains and, if not, decays are made isotropic.
1761 The <i>H -> WW/ZZ -> f fbar f' fbar'</i> and
1762 <i>t -> b W -> b f fbar</i> correlations are process-independent,
1763 however, and thus can be handled internally. If part of the decay
1764 chain has already been set, e.g. <i>H -> WW/Z></i> or <i>t -> b W</i>,
1765 then the subsequent decays are still isotropic.</li>
1767 <li>Updated instructions how to link to HepMC,
1768 in <code>README.HepMC</code>.</li>
1770 <li>Bug fix in the turn-on of resolved diffraction for low
1771 CM energies. Thanks to Erwin Visser.</li>
1773 <li>Bug fix in the handling of string junctions at very high energies,
1774 caused by numerical errors. Thanks to Erwin Visser.</li>
1776 <li>Some other small changes, mainly aesthetics.</li>
1781 <li>8.165: 8 May 2012
1784 <li>The MBR (Minimum Bias Rockefeller) model for single, double and
1785 central diffraction [<a href="Bibliography.html" target="page">Cie12</a>] is included as new option
1786 <a href="Diffraction.html" target="page"><code>Diffraction:PomFlux = 5</code></a>.
1787 It is specifically intended for <i>p p</i> and <i>pbar p</i>
1788 interactions, and is currently the only option that also supports
1789 central diffraction. Thus the basic machinery for Central Diffraction
1790 (a.k.a. Double Pomeron Exchange) has now been implemented.
1791 See <code>examples/main04.cc</code> for an example.
1792 Thanks to Robert Ciesielski for contributing the new code.
1795 <li>For a <i>tau</i> lepton in an external process, by default the
1796 SPINUP number in the Les Houches Accord now is interpreted as giving
1797 the <i>tau</i> helicity, and is used for its decay.</li>
1799 <li>A <i>tau</i> coming from a <i>W</i> now defaults to being purely
1800 lefthanded when neither of the existing matrix elements apply.</li>
1802 <li>Decay mode <i>t -> H+ b</i> included as an option.</li>
1804 <li>Four ATLAS tunes have been implemented as options for
1805 <code>Tune:pp</code>: A2-minbias-mstw2008lo, AU2-cteq6l1, AU2-mstw2008lo,
1806 and AU2-ct10. The new flag <code>Tune:preferLHAPDF</code> can be used
1807 to switch between the LHAPDF and the internal implementation of a
1808 PDF set, in cases where both are available.</li>
1810 <li>Reorder libraries in <code>examples/Makefile</code>, specifically
1811 move <code>LIBGZIP</code> so that it is properly linked when used.
1812 Thanks to Erik Schnetter.</li>
1814 <li>Minor modification so that LHAPDF can be used for PDFs in the hard
1815 process, with one of the built-in PDFs for the rest, even if LHAPDF is
1816 compiled so as to handle only one concurrent PDF set.</Li>
1818 <li>Bug fix, that <code>ParticleDecays:mixB = off</code> did not
1819 switch off <i>B0 - B0bar</i> and <i>Bs0 - Bs0bar</i> mixing.
1820 Thanks to James Catmore.</li>
1822 <li>Bug fix for the handling of gluon polarization of initial-state
1823 radiation, where an anisotropic azimuthal distribution was inadvertently
1824 generated in some <i>2 -> 1</i> processes. The update also includes
1825 always setting the second daughter zero for the two partons coming in to
1826 a hard <i>2 -> 1</i> process. Thanks to Antonio Policicchio.</li>
1828 <li>Bug fix, that the setting of the number of user hooks MPI steps did
1829 not use <code>UserHooks::canVetoMPIStep()</code> properly.</li>
1831 <li>Some other small changes, mainly documentation and aesthetics.</li>
1836 <li>8.170: 21 September 2012
1839 <li>Streamline default behaviour and options for choice of GeV or MeV
1840 for output to the HepMC event format, see
1841 <a href="HepMCInterface.html" target="page">HepMC Interface</a>.
1842 Also set the mass of HepMC particles explicitly, rather than having
1843 it calculated implicitly. Thanks to James Monk and Andy Buckley.</li>
1845 <li>The <i>tau</i> decay machinery has been further augmented with
1846 matrix elements and form factors for a variety of decay modes, such
1847 that all modes with a branching ratio above 0.1% are fully modelled.
1848 Several new classes and methods have been added to this end,
1849 Also, a <i>tau</i> pair coming from a <i>Z^0</i> decay is now
1850 handled by assuming the <i>Z^0</i> to be unpolarized when neither
1851 of the existing matrix elements apply. Taus coming from B baryons are
1852 handed as for B mesons.</li>
1854 <li>Flavour violating decays have been added to the squark, gluino,
1855 neutralino and chargino decay tables.</li>
1857 <li>Extend the <code>UserHooks::subEvent(...)</code> method so that it
1858 also works passably at the process level. Also new option for
1859 <code>UserHooks::omitResonanceDecays(...)</code>.</li>
1861 <li>New methods <code>UserHooks::canVetoPartonLevelEarly()</code>
1862 and <code>UserHooks::doVetoPartonLevelEarly( const Event&)</code>
1863 are intended to be used the same way as the existing ones without
1864 <code>Early</code> in their names, but allow veto right after
1865 the ISR + FSR + MPI evolution, before beam remnants are added and
1866 resonance decays are considered.</li>
1868 <li>Central diffraction now available for all
1869 <code><a href="Diffraction.html" target="page">PomFlux</a></code>
1870 options, not only the MBR model. This has been constructed by analogy
1871 with the respective assumptions made for single diffraction, but
1872 includes some arbitrariness. Therefore the cross section is left
1873 easily rescaleable and, for backwards compatibility with tunes
1874 that does not contain it, easily possible to switch off, see
1875 the <a href="TotalCrossSections.html" target="page">relevant section</a>.
1878 <li>Reading of ALPGEN parameter and event files has been added,
1879 see <a href="AlpgenAndMLM.html" target="page">ALPGEN and MLM Merging</a>.
1882 <li>MLM matching has been added, as a first step for ALPGEN events,
1883 see <a href="AlpgenAndMLM.html" target="page">ALPGEN and MLM Merging</a>.
1886 <li>The CKKW-L merging machinery has been upgraded in a number of respects.
1887 <br/>- More thorough treatment of <code>pp>bb~e+e-veve~</code> with
1888 additional <i>b</i>-jets.
1889 <br/>- Corrected hard <i>mu_r</i> and <i>mu_f</i> choices for
1890 dijet and promt photon.
1891 <br/>- More ways to define a hard process, e.g. with the LEPTONS and
1892 NEUTRINO tags. The merging will understand LHE files for mixed processes
1893 (e.g. <i>W+</i> and <i>W-</i> production together).
1894 <br/>- More merging scale definitions.
1895 <br/>- More freedom to generate all possible histories.
1896 <br/>- Internal check (and cut) on Les Houches events in
1897 <code>Pythia::mergeProcess</code> if merging scale value of the events
1898 is below the value given to Pythia by setting <code>Merging::TMS</code>.
1901 <li>It now works to have R-parity violating decays of R-hadrons,
1902 i.e. baryon number violation in a vertex displaced from the primary
1905 <li>The documentation of diffractive processes by the
1906 <code><a href="EventInformation.html" target="page">Info</a></code>
1907 methods has been expanded and corrected. This also include the
1908 <code>list()</code> method.</li>
1910 <li>Particle masses and widths have been updated to agree with the
1911 2012 RPP values [<a href="Bibliography.html" target="page">Ber12</a>]. Thanks to Piotr Zyla for data file
1912 and James Catmore for program to update the PYTHIA tables from this
1915 <li>New methods <code>jetAssignment</code> and <code>removeJet</code>
1916 added to the <code>SlowJet</code> class.</li>
1918 <li>Introduce angular correlation in decay chain
1919 <i>H -> gamma Z0 -> gamma f fbar</i>. Thanks to Tim Barklow and
1920 Michael Peskin.</li>
1922 <li>Introduce simple way to bias the selection of <i>2 -> 2</i>
1923 processes towards larger <i>pT</i> values, with a compensatingly
1924 decreasing event weight, see
1925 <a href="PhaseSpaceCuts.html" target="page">Phase Space Cuts</a>. Only offers a
1926 subset of the possibilities allowed by <code>UserHooks</code>,
1927 but simpler to use. The <code>main08.cc</code> program has been
1928 expanded to illustrate this possibility, and also expanded to
1929 include low-<i>pT</i> subsamples.</li>
1931 <li>The two remaining non-NLO tunes from [<a href="Bibliography.html" target="page">ATL12</a>] are now
1934 <li>The <code><a href="EventInformation.html" target="page">Info</a></code> methods
1935 <code>nTried, nSelected, nAccepted, sigmaGen</code> and
1936 <code>SigmaErr</code> now takes the code of an individual process
1937 as an optional argument.</li>
1939 <li>It is now possible to generate resonance decays, followed by
1940 showers and hadronization, without having them associated with any
1941 specific process. This is part of an expanded
1942 <a href="HadronLevelStandalone.html" target="page">Hadron-Level Standalone</a>
1943 machinery, as before triggered by <code>ProcessLevel = off</code>,
1944 but additionally requiring <code>Standalone:allowResDec = on</code>.
1945 Input can either be directly into the <code>event</code>
1946 event record or via a (simplified) Les Houches Event File.</li>
1948 <li>New <code>configure</code> script options <code>--installdir</code>,
1949 <code>--prefix</code> and <code>--datadir</code> can be used to set the
1950 location(s) to which the library, header and data directories
1951 will be copied by a <code>make install</code> subsequent to the
1952 <code>make</code>. Thanks to Mikhail Kirsanov.</li>
1954 <li>Fix charge in antiparticle name when particle read in from SLHA
1955 file. Thanks to Johan Alwall.</li>
1957 <li>Pointers now only compared with == and != (not e.g. > 0), to avoid
1958 warnings in gcc 4.7.</li>
1960 <li>New check that version number of the code matches that of the
1961 XML files. If not, no events can be generated. Thanks to James Monk
1962 for suggestion.</li>
1964 <li>New check that mother and daughter indices have been set to give
1965 a consistent event history. Can be switched on/off with the new
1966 <code>Check:history</code> flag.</li>
1968 <li>A new method <code>LHAup::newEventFile</code> has been added to
1969 switch to reading in events from another LHE file without having to
1970 reinitialize the whole class. Lower-level routines like
1971 <code>openFile</code> and <code>closeFile</code> have been added to
1972 handle correct order of operations also when an intermediate gzip
1973 decompression step is involved.</li>
1975 <li><code>LHAup::eventLHEF()</code> can now be called with an optional
1976 argument <code>false</code>, to make event files somewhat smaller by
1977 reducing the amount of blanks.</li>
1979 <li>A new mode <code>Beams:nSkipLHEFatInit</code> introduced to
1980 skip ahead the first few events in a Les Houches Event File (cf. the
1981 <code>LHAup::skipEvent(nSkip)</code> method).</li>
1983 <li>Introduce a new pair of user hooks that can be used to reject
1984 the sequence of hard-process resonance decays, without rejecting
1985 the production of the primary resonances.</li>
1987 <li>The possibility of separate multiplicative prefactors to the
1988 renormalization and factorization default <i>pT^2</i> scale has been
1989 introduced for both timelike and spacelike showers.</li>
1991 <li>Bug fixes in history information for R-hadron production, which also
1992 fixes HepMC conversion in this case.</li>
1994 <li>Bug corrected in <code>SigmaSusy.cc</code>, for chargino+neutralino
1995 production. Indexing error for incoming quark states in the process
1996 <code>Sigma2qqbar2charchi0</code>, resulted in incorrect CKM factors.</li>
1998 <li>Corrected a bug in <code>SusyLesHouches.cc</code>, for NMSSM spectra.
1999 The unitarity check on the neutralino mixing matrix was faulty, leading
2000 to erroneous messages about unitarity violations and SUSY being switched
2003 <li>Bug fixes in the handling of resolved and unresolved diffractive events.
2004 Thanks to Robert Ciesielski for debug.</li>
2006 <li>Do not set up FSR dipoles for <i>2 -> 1</i> processes.</li>
2008 <li>Check that some channel open for resonance decays. Also further
2009 check whether resonance decay treatment should be invoked.</li>
2011 <li>Bug fix in reading of particle names from SLHA input.</li>
2013 <li>Change mass, width and decay mode(s) of D*_s(10431). Thanks to
2016 <li>Bug fix in leptoquark production (lepton sign in
2017 <i>q g -> LQ l</i>).</li>
2019 <li>New argument added to <code>SpaceShower::reassignBeamPtrs</code>
2020 for diffractive event processing, as already available for
2021 <code>TimeShower</code>.</li>
2023 <li>Do not write warnings in <code>SpaceShower</code> for weights
2024 above unity if the evolution scale is below 1 GeV^2.</li>
2026 <li>Add default values for member variables in some constructors,
2027 and some related changes for <code>AlphaStrong</code> code.</li>
2029 <li>Warn if negative-energy parton in hadronization.</li>
2031 <li>The MPI <i>pT</i> values assumed in the beam remnant setting
2032 of primordial <i>kT</i> and colour reconnection probability were
2033 incorrect for diffractive events.</li>
2035 <li>The arrays with MPI information were not reset when parton or
2036 hadron level fails and a new try is made. Only affected few events.</li>
2038 <li>MPI statistics can not yet be accumulated for diffractive events,
2039 and therefore the relevant routine is no longer called.</li>
2041 <li>Bug fix in the double parton scattering suppression from
2042 energy-momentum conservation.</li>
2044 <li>Outgoing proton masses were not set in the event record for
2045 elastic scattering (but kinematics handling was correct).</li>
2047 <li>Bug fixes in the identification and documentation of junctions,
2048 previously leading to some unnecessarily rejected events. Also
2049 other improvements leading to fewer errors.</li>
2051 <li>Slightly increased values for FragmentationSystems:mJoin and
2052 StringFragmentation::FACSTOPMASS to reduce failure rate, without
2053 noticeably affecting event properties.</li>
2055 <li>The Les Houches cross section error is now taken into account
2056 in the final Pythia error for strategies +-3. New methods
2057 <code>LHAup::xSecSum()</code> and <code>LHAup::xErrSum()</code>
2058 provide the necessary information.
2061 <li>When a tau pair comes from a massless photon, in dipole shower
2062 evolution, for the decay description the mother photon is reassigned
2063 to have the sum of the tau momenta.</li>
2065 <li>Minor change in initialization sequence for user hooks,
2066 to allow for more flexibility.</li>
2068 <li>Do not print warnings when multiparton interaction weights are
2069 only slightly above unity.</li>
2071 <li>Do not write warnings for three known particles that are so close
2072 to threshold that widths are switched off to avoid trouble.</li>
2074 <li>Some minor typographical changes.</li>
2083 <!-- Copyright (C) 2012 Torbjorn Sjostrand -->