3 <title>Update History</title>
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30 <h2>Update History</h2>
32 These update notes describe major updates relative to the baseline
33 PYTHIA 8.100 version. However, they are less extensive than the
34 corresponding update notes for PYTHIA 6. On the other hand,
35 whereas the PYTHIA 6 manual is a static document, the PYTHIA 8
36 html/php pages are kept up to date for each subversion.
39 <b>Important note:</b>version 8.160 does introduce some elements of
40 backwards incompatibility. Specifically, "multiple interactions",
41 abbreviated MI, haa been renamed "multiparton interactions", MPI.
42 This affects many parts of the code and documentation. Also some
43 features are deprecated, although remaining until the end of the
47 <h3>Main news by version</h3>
51 <li>8.105: 24 February 2008
54 <li>New option to initialize with arbitrary beam directions<br/>
55 <code>pythia.init( idA, idB, pxA, pyA, pzA, pxB, pyB, pzB)</code></li>
57 <li>Added capability to set <?php $filepath = $_GET["filepath"];
58 echo "<a href='BeamParameters.php?filepath=".$filepath."' target='page'>";?>beam energy spread
61 <b>Warning:</b> as a consequence, the old <code>Beams</code> group of
62 settings has been moved to <code>BeamRemnants</code>, and
63 <code>Beams</code> is now instead used for machine beam parameters.
64 Therefore also some <code>Main</code> settings of this character have been
65 regrouped, as follows:
66 <table cellspacing="5">
67 <tr> <td>8.100 setting </td> <td>has been moved to </td> </tr>
68 <tr> <td><code>Main:idA </code></td>
69 <td><code>Beams:idA </code></td> </tr>
70 <tr> <td><code>Main:idB </code></td>
71 <td><code>Beams:idB </code></td> </tr>
72 <tr> <td><code>Main:inCMframe </code></td>
73 <td>(<code>Beams:frameType</code>) </td> </tr>
74 <tr> <td><code>Main:eCM </code></td>
75 <td><code>Beams:eCM </code></td> </tr>
76 <tr> <td><code>Main:eA </code></td>
77 <td><code>Beams:eA </code></td> </tr>
78 <tr> <td><code>Main:eB </code></td>
79 <td><code>Beams:eB </code></td> </tr>
80 <tr> <td><code>Main:LHEF </code></td>
81 <td><code>Beams:LHEF </code></td> </tr>
84 <li>The <code>forceHadronLevel()</code> method introduced for standalone
87 <li><code>main15.cc</code> illustrated how either full hadronization or
88 only decays of some particles can be looped over for the rest of the
91 <li>The <code>LHAevnt</code> and <code>LHAinit</code> classes have been
92 joined into a new <code>LHAup</code> one, with new options that allow
93 the writing of a Les Houches Event File.</li>
95 <li>The <code>SusyLesHouches</code> class updated to handle
98 <li>Updated HepMC conversion routine.</li>
100 <li>The static <code>ErrorMsg</code> class has been removed and
101 its functionality moved into the non-static <code>Info</code> class,
102 in the renamed Info file.</li>
104 <li>Further reduction of the use of static, with related code changes.
105 This should allow to have several almost independent <code>Pythia</code>
106 instances. Some static classes still remain, however, notably for
107 random number generation and particle properties.</li>
109 <li>Limited capability to use two different <code>Pythia</code> instances
110 for signal + pileup event generation, see <code>main19.cc</code> for an
113 <li>In the <code>Event</code> class the <code>=</code> and
114 <code>=+</code> methods have been overloaded to allow the copying
115 or appending of event records. Illustrated in <code>main19.cc</code>.</li>
117 <li>The html and php page formatting improved with
118 cascading style sheets.</li>
120 <li>Several minor improvements and new options, including updated configure
126 <li>8.108: 1 May 2008
129 <li>Correction in the event record, so that the beam particles in line
130 1 and 2 do not have any mother according to the <code>motherList</code>
131 method. Previously the "system" entry in line 0 was counted as their
132 mother, which gave rise to an unexpected extra vertex in the conversion
133 to the HepMC format.</li>
135 <li>Support for HepMC version 1 is removed, to simplify the code and
136 reflect the evolution of the field.</li>
138 <li>Status codes are stored in HepMC only as 1 for existing and 2 for
139 decayed or fragmented particles (whereas previously the original PYTHIA
140 codes were used for the latter).</li>
142 <li>Parton densities are stored in HepMC as <i>xf(x,Q^2)</i>
143 rather than the <i>f(x,Q^2)</i> used in (some) previous versions.</li>
145 <li>The SusyLesHouches class has ben updated so that reading is fully
146 compatible with the SLHA2 standard. </li>
148 <li>Improved handling of the Higgs width, relevant for massive and thereby
149 broad resonance shapes.</li>
151 <li>The matrix elements for neutralino pair production have now been
152 completed and checked.</li>
154 <li>Ensure that <i>alpha_strong</i> does not blow up, by introducing
155 a minimal scale somewhat above <i>Lambda_3</i> (roughly where
156 <i>alpha_strong = 10</i>).</li>
158 <li>New methods <code>isValence1()</code> and <code>isValence2()</code>
159 in the <code>Info</code> class.</li>
161 <li>Protection against division by zero in calculation of decay vertex
162 (for zero-mass gluons with zero lifetime, where there should be no
165 <li>A new compilation option <code>-Wshadow</code> is introduced and
166 code is rewritten at all places where this option gave warnings.</li>
168 <li>Minor library correction to allow compilation with gcc 4.3.0.</li>
173 <li>8.114: 22 October 2008
176 <li>New rescattering description operational (but still experimental)
177 for the case that FSR is not interleaved, but saved until after MPI,
178 ISR and beam remnants have been handled. This involves much new code
179 in several classes.</li>
181 <li>A new class <code>PartonSystems</code> is introduced to
182 keep track of which partons in the event record belong to which
183 subcollision system, plus some further information on each subsystem.
184 It takes over functionality previously found as part of the
185 <code>Event</code> class, but leaves room for future growth.</li>
187 <li>Add optional model, wherein an increased <i>pT0</i> turnoff scale
188 for MPI and ISR is used for above-average active events, i.e. events that
189 already have several MPI's or ISR emissions.</li>
191 <li>Freeze GRV 94L distribution at small <i>Q^2</i> to avoid blowup.</li>
193 <li>The <code>pythia.readFile(...)</code> method can now alternatively take
194 an <code>istream</code> as argument instead of a <code>filename</code>.</li>
196 <li>Minor bug correction in <code>PartonLevel.cc</code>; the bug could
197 (rarely) give a segmentation fault.</li>
202 <li>8.120: 10 March 2009
205 <li>New rescattering description further developed, but not yet
206 recommended for normal usage.</li>
208 <li>Include new processes for Large Extra Dimensions and Unparticles,
209 contributed by Stefan Ask. New test program <code>main28.cc</code>
212 <li>Include further SUSY processes: neutralino-chargino and
213 chargino-chargino pairs. The processes should be valid also
214 in the case of non-minimal flavour violation and/or CP violation.
215 Expanded machinery to keep track of SUSY parameters.</li>
217 <li>Include backwards evolution of incoming photon as part of the
218 <code>SpaceShower</code> initial-state radiation description. This
219 allows you to simulate hard collisions where one of the incoming
220 partons is a photon. New test program <code>main43.cc</code>
223 <li>Allow separate mass and transverse momentum cuts when two hard
224 subprocesses are generated in the same event.</li>
226 <li>The default value for the border between short- and long-lived
227 paticles has been changed from 1 mm to 10 mm, to better conform with
228 LHC standards, see <?php $filepath = $_GET["filepath"];
229 echo "<a href='ParticleDecays.php?filepath=".$filepath."' target='page'>";?>here</a>.
230 The default is still to let all unstable particles decay.</li>
232 <li>New ISR matrix-element correction to <i>f -> f gamma</i>
233 in single <i>W</i> production.</li>
235 <li>New method <code>Event::statusHepMC</code> returns the status
236 code according to the HepMC conventions agreed in February 2009.
237 The interface to HepMC now writes out status according to this
240 <li>Add capability to link to FastJet, with expanded configure script
241 and Makefile, and with <code>main61.cc</code> as new example.</li>
243 <li>Update of <code>Makefile.msc</code>, with added support for latest
244 Visual C++ Express edition and use of regexp to check nmake version.</li>
246 <li>Update of <code>LHAFortran.h</code> and
247 <code>Pythia6Interface.h</code>, to make the interface to Fortran
248 routines work also under Windows. (Thanks to Anton Karneyeu.)
250 <li>Updated and expanded worksheet.</li>
252 <li>The manual pages in the <code>xmldoc</code> directory, and thereby
253 also those of the <code>htmldoc</code> and <code>phpdoc</code>
254 directories, have been significantly updated and expanded. In particular,
255 in many places the class of each method is explicitly shown, as well as
256 the type of the return value and of the arguments. This upgrade is not
257 yet completed, but already covers the more relevant sections. </li>
259 <li>The unary minus operator in the <code>Vec4()</code> returns a
260 reference to a four-vector with all components negated, but leaves
261 the original four-vector unchanged. Previously the four-vector itself
264 <li>The <code>pPlus()</code> and <code>pMinus()</code> methods of a
265 four-vector and an event-record particle are renamed <code>pPos()</code>
266 and <code>pNeg()</code>, respectively.</li>
268 <li>Include a further loop in <code>ProcessLevel</code>, so that a new
269 process is generated in case of failures of a less severe nature.</li>
271 <li>Introduce warning message for unexpected <code>meMode</code> in
272 <code>ResonanceWidths</code>.</li>
274 <li>Les Houches event reading framework has been rearranged for
275 more flexibility. Some bugs corrected. Specifically, when scale
276 is not set (<code>scale = -1.</code> in the Les Houches standard),
277 PYTHIA did not attempt to set this scale itself, which typically
278 lead to there not being any ISR or FSR. Now the
279 <?php $filepath = $_GET["filepath"];
280 echo "<a href='CouplingsAndScales.php?filepath=".$filepath."' target='page'>";?>rules for normal
281 1-, 2- and 3-body final states</a> are applied, with a trivial
282 extension of the 3-body rules for higher multiplicities.</li>
284 <li>Correct bug in the handling of parton densities, whereby it was
285 not possible to switch to a new set, once a first initialization
288 <li>Correct bugs when several <code>Pythia::init</code> initialization
289 calls are made in the same run, specifically in the case that pointers
290 to external processes have been handed in.
292 <li>Changes in <code>main03.cmnd</code> and <code>main04.cmnd</code>
293 so that some nonstandard options are commented ou rather than active.
294 Related comments inserted also in some other <code>.cmnd</code> files,
295 but there without any change in program execution.</li>
297 <li>A few further minor bug fixes.</li>
299 <li>Update year to 2009.</li>
304 <li>8.125: 16 June 2009
307 <li>Hadronization and timlike-shower parameter default values updated
308 according to a tune to LEP1 data by Hendrik Hoeth, using the
309 Rivet + Professor framework.</li>
311 <li>Many further SUSY production processes. SLHA readin expanded to cover
312 also masses and decay modes. Example <code>main22.cc</code> updated, while
313 <code>main33.cc</code> now superfluous and removed. </li>
315 <li>Also further processes for extra dimensions.</li>
317 <li>Stefan Ask joins as coauthor.</li>
319 <li>The <code>TimeShower::shower(...)</code> method has gained
320 a new argument, that forces the shower evolution to stop after
321 a given number of branchings. A new method
322 <code>TimeShower::pTLastInShower()</code> permits the last evolution
323 <i>pT</i> to be read out. These extensions can be useful
324 for matching studies.
327 <li>New optional argument <code>isInterleaved</code> added to
328 <code>TimeShower::branch(...)</code>. Is false by default, but
329 true when called from the parton level for interleaved evolution
330 of several parton systems, optionally also with ISR and MPI.</li>
332 <li>New methods <code>UserHooks::canSetResonanceScale()</code>
333 and <code>UserHooks:scaleResonance(...)</code> allows an optional
334 user choice of the maximum shower scale in resonance decays.</li>
336 <li>A new method <code>SpaceShower::doRestart()</code> has been
337 added, to help distinguish cases when a
338 <code>SpaceShower::branch(...)</code> failure forces a complete
339 restart of the evolution from ones where only the intended
340 current branching has been vetoed.
342 <li>When multiparton interactions are initialized, it is now
343 possible to reduce both <i>pT0</i> and <i>pTmin</i>
344 if necessary to find a valid solution where
345 <i>sigma_jet > sigma_nondiffractive</i>. Previously
346 only the former would be reduced, which could lead to
347 infinite loops if too large a <i>pTmin</i> was used.
348 Thanks to Sami Kama for pointing out the problem.
351 <li>The rescattering machinery is now essentially completed, and can
352 be used also by others than the authors. For now, however, it can only
353 be recommended for dedicated studies, not e.g. for generic tunes.
356 <li>Timelike and spacelike showers, and beam remnant handling,
357 are modified to handle rescattering partons. Specifically, a new machinery
358 is introduced to trace the recoils from the combination of rescattering
359 with showers and primordial <i>kT</i>. Can assign space- or timelike
360 virtualities to intermediate particles to have energy and momentum
361 conserved locally. This affects the <code>PartonLevel</code>,
362 <code>MultipartonInteractions</code>, <code>TimeShower</code>,
363 <code>SpaceShowe</code>r and <code>BeamRemnants</code> classes.
364 Further details to appear in the upcoming article on rescattering.
365 (Another change is a reversal to pre-8.114 order for non-interleaved FSR,
366 wherein also FSR is treated before beam remnants are attached.)
369 <li>Four new status codes introduced, as part of the rescattering
371 <br/>45 : incoming rescattered parton, with changed kinematics owing
372 to ISR in the mother system (cf. status 34);
373 <br/>46 : incoming copy of recoiler when this is a rescattered parton
375 <br/>54 : copy of a recoiler, when in the initial state of a different
376 system from the radiator;
377 <br/>55 : copy of a recoiler, when in the final state of a different
378 system from the radiator.
381 <li>New method <code>Info::tooLowPTmin()</code> can tell whether the
382 <i>pTmin</i> scales for showers or multiparton interactions are too low.
385 <li>Pion beams allowed, both <i>pi^+</i>, <i>pi^-</i> and
386 <i>pi^0</i>. New machinery for the latter, where the valence
387 flavour content is chosen to be either <i>d dbar</i> or
388 <i>u ubar</i> for each new event. One internal pion PDF
389 implemented, with others from LHAPDF.</li>
391 <li>Treatment of Pomeron-proton collisions begun.</li>
393 <li>Phase-space handling of hard processes and multiparton interactions
394 slightly expanded to better allow for harder PDF's than proton ones,
395 e.g. for Pomerons.</li>
397 <li>The program documentation has been expanded with an
398 alphabetical index of all methods that are described on the
399 webpages, see the <?php $filepath = $_GET["filepath"];
400 echo "<a href='ProgramMethods.php?filepath=".$filepath."' target='page'>";?>Program Methods</a>
401 page. Also other sections of the documentation have been
402 updated and expanded, including the worksheet.</li>
404 <li>Several <code>list</code> methods have been made
405 <code>const</code>. For the listing of events two new methods
406 have been added, <code>Event::list()</code> and
407 <code>Event::list(bool showScaleAndVertex,
408 bool showMothersAndDaughters = false)</code>,
409 that correspond to special cases of the general method.</li>
411 <li>A new method <code>Pythia::LHAeventSkip(int nSkip)</code>
412 permits a skip-ahead of the reading of external Les Houches
413 Events, without the necessity to generate the intervening
414 <code>nSkip</code> events in full. Makes use of the new
415 <code>LHAup::skipEvent(int nSkip)</code> method to perform
416 the operations. Mainly intended for debug purposes.
418 <li>The <code>ClusterJet</code> jet finder now saves the last
419 five clustering scales. Also a minor bug fix. Thanks to Nils
420 Lavesson for this contribution.</li>
422 <li>The <code>Particle::m2()</code> method now returns a negative
423 number when the stored mass <i>m</i> is negative, as used to
424 indicate spacelike virtualities. Also the
425 <code>Particle::eCalc()</code>, <code>Particle::mT()</code> and
426 <code>Particle::mT2()</code> methods have been modified.
429 <li>The <code><<</code> method to print our a four-vector has
430 been expanded with a fifth number, the invariant length, with a minus
431 sign for spacelike vectors, and provided within brackets to allow
432 a simple visual distinction.</li>
434 <li>New methods <code>Rndm::dumpState(string fileName)</code> and
435 <code>Rndm::readState(string fileName)</code> allows to write or
436 read the state of the random number generator to or from a binary file.
439 <li>New method <code>double GammaReal(double x)</code> returns the
440 value of the <i>Gamma</i> function for arbitrary real argument.
441 Some cross sections for extra-dimensional processes rewritten to
445 <li>New example program <code>main29.cc</code> shows how
446 to set up a fictitious process of a heavy system decaying
447 to two particles or partons, with decays traced to stable
448 particles, as relevant for astroparticle applications.</li>
450 <li>Main programs that illustrate the HepMC interface have
451 been updated to use version 2.04, including units and excluding
452 deprecated output formats.</li>
454 <li>The <code>main32.cc</code> example extended also to handle
455 Les Houches Event Files.</li>
457 <li>The Makefile has been modified so that "make clean" only
458 removes the current compilation and library fles, while
459 "make distclean" gives a more extensive reset and cleanup.
460 Thanks to Nils Lavesson for this contribution. Some other
461 minor Makefile corrections.</li>
463 <li>Several main programs that use the
464 <code>Main:timesToShow</code> mode have been corrected so as
465 not to crash if this is set to zero. Also some other cosmetics
466 changes in main programs that do not affect the running.</li>
468 <li>Bug correction, in that previously a veto with user hooks
469 was not propagated from parton showers inside resonance decays.
472 <li>Minor bug fix in <code>TimeShower</code> for kinematics with
473 unequal beam-particle masses.</li>
475 <li>Bug fix so that <code>PartonLevel:MPI = off</code> also works for
476 minimum-bias events.</li>
478 <li>Minor bug fix in the impact-parameter selection of multiparton
479 interactions. Thanks to Sami Kama for pointing it out.</li>
481 <li>String fragmentation for junction topology protected against
482 numerical instability in boost.</li>
484 <li>Bug correction in the handling of particle decays to partons,
485 where the scale of the partons was set before the partons had been
486 added to some arrays, leading to indexation out of bounds.
487 Thanks to Vladislav Burylov for discovering this bug.
490 <li>Bug correction in the handling of particles with inhibited decay,
491 where the decay vertex would be too far displaced, which could lead to
492 infinite loop. Thanks to Sami Kama for debugging this. </li>
494 <li>Check to avoid infinite loop in matrix-element handling of
495 two-body decays.</li>
497 <li>Bug correction to avoid infinite loops in Dalitz decay treatment.
498 Some changes in the decay handling logic to allow a new try when the
499 decay of a particle fails.</li>
501 <li>Minor correction, so the pointer to the <code>Info</code> class
502 is set also for user-written classes derived from <code>LHAup</code>.
505 <li>Correction for typo in the matrix element of the
506 <code>Sigma3ff2HchgchgfftWW</code> class, for doubly charged Higgs
507 production. Thanks to Merlin Kole for spotting it.</li>
509 <li>Updated colour bookkeeping in junction-antijunction annihilation
510 avoids later problems in <code>Pythia::check()</code>. </li>
512 <li>Minor updates of the <code>Makefile.msc</code> file to work with
513 Visual Studio 2008. Thanks to David Bailey for these modifications.</li>
515 <li>Ensure that <code>nInit</code> in the <code>BeamParticle</code>
516 class is set also for unresolved lepton beams.</li>
518 <li>The <code>VetoEvolution</code> class, derived from
519 <code>UserHooks</code>, is obsolete and has been removed.</li>
524 <li>8.130: 15 September 2009
527 <li>New machinery that allows multiparton interactions inside diffractive
528 systems. Also new optional Pomeron flux factors and Pomeron PDFs.
529 New page on <?php $filepath = $_GET["filepath"];
530 echo "<a href='Diffraction.php?filepath=".$filepath."' target='page'>";?>diffraction</a> added, where
531 further details are collected. Still not tuned, so to be used with
534 <li>Make Peter Skands' "Tune 1" parameters for ISR and MPI default.
535 The older simpler tune is still available as an option, see
536 <code><?php $filepath = $_GET["filepath"];
537 echo "<a href='Tunes.php?filepath=".$filepath."' target='page'>";?>Tune:pp</a></code>.
540 <li>New possible choices for a second hard process: charmonium,
541 bottomonium, top pair and single top.</li>
543 <li>New code for pair production of generic colour-triplet scalar,
544 fermion or vector. Largely written by Johan Bijnens, partly recycling
547 <li>Add user hooks possibility to veto event after a given number
548 of multiparton interactions.</li>
550 <li>Add instructions how PYTHIA 8 can be used from inside ROOT.
551 Thanks to Andreas Morsch for providing the text and Rene Brun
552 for a simple example.</li>
554 <li>The <code>main21.cc</code> example extended with an option
555 for a single-particle gun.</li>
557 <li>Improvements and bug fixes in rescattering framework.</li>
559 <li>New method <code>Hist::table(string fileName)</code> provides a
560 more direct way to print a two-column table of histogram contents
561 into a file than the current <code>Hist::table(ostream& os = cout)</code>.
564 <li>Modify reading of external files so that a line only consisting of
565 control characters counts as empty, the same way as a line only consisting
566 of blanks already did. This includes carriage return, tabs and a few more,
567 the ones represented by <code>\n \t \v \b \r \f \a</code>. Applies to
568 Les Houches Event files, settings files and particle data files. </li>
570 <li>Fix it so that the read-in of a Les Houches Event File for the
571 hardest process can be combined with the faciliy to select a specified
572 second hard process.</li>
574 <li>New empty base class method <code>LHAup::fileFound()</code>
575 allows the derived class <code>LHAupLHEF</code> to signal more
576 clearly that a failed initialization is caused by a failure to open
577 the desired file. </li>
579 <li>Check that a pointer to an <code>LHAup</code> object has been set
580 in <code>Pythia::LHAeventList()</code> and
581 <code>Pythia::LHAeventSkip(...)</code> calls.</li>
583 <li>Updated configure and Makefile, e.g. to build shared libraries
586 <li>The options with a direct link to hard-process generation
587 in PYTHIA 6 has been removed. It is hardly ever used but
588 complicates the build structure. (Owing to its usefulness for some
589 debug work, it was reinstated in a limited form in version 8.135.
590 Thus <code>main51.cc</code> now contains the complete interface,
591 previously in separate files, and commented-out lines in
592 <code>examples/Makefile</code> suggest how PYTHIA 6 could be linked.)
595 <li>New argument to <code>Info::errorMsg(...)</code> allows to
596 show all error messages of a specific kind rather than only the
597 first one, e.g. for initialization.</li>
599 <li>Correction in decay table of righthanded Majorana neutrinos.
600 Thanks to Arnaud Ferrari and Vladimir Savinov.</li>
602 <li>Correction in expressions in the manual for <i>H^+-</i> couplings
603 to an <i>h^0</i>, <i>H^0</i> or <i>A^0</i> and a <i>W^+-</i>.
604 Thanks to Rikard Enberg.</li>
606 <li>Fix for accessing uninitialized memory, caused by accessing the
607 daughters of the incoming beams before these daughters actually existed.
608 Thanks to David Bailey and Sami Kama.
611 <li>Uninitialized photon PDF inside the proton could give crazy results
612 for processes with incoming photons. Thanks to Adam Davison.</li>
614 <li>Bug fix such that finite lifetimes can be set also for particles
615 produced in the hard process. To exemplify, the bug affected
616 <i>tau</i> leptons produced in <i>Z^0</i> and <i>W^+-</i>
617 decays. Thanks to Troels Petersen.</li>
619 <li>Bug fix in <code>TimeShower</code>, that <code>beamOffset</code>
620 could remain uninitialized. Thanks to Sami Kama.</li>
622 <li>Minor correction to resonance decays: fail if the allowed mass
623 range of a Breit-Wigner resonance is a small fraction of the total
624 area under the resonance curve.</li>
626 <li>Correction when all three valence quarks were kicked out from a
627 proton and could give false messages that beam momentum had been
630 <li>Clarify status codes needed for hadron-level standalone runs in
631 order to avoid error messages, and modify the <code>main21.cc</code>
632 example accordingly. </li>
634 <li>Minor corrections in the processes for extra dimensions.</li>
636 <li>Some other minor additions to existing facilities
637 and minor bug fixes.</li>
642 <li>8.135: 10 January 2010
645 <li>All usage of static member methods inside Pythia8 has now been
646 eliminated. This simplifies for you to have several simultaneous
647 <code>Pythia</code> instances that are run with different conditions.
648 The three main classes affected by this are the <code>Settings</code>
649 and <code>ParticleData</code> databases and the <code>Rndm</code>
650 random-number generator. You can no longer address the methods of these
651 classes directly, but have to address them via the <code>settings</code>,
652 <code>particleData</code> and <code>rndm</code> instances in the
653 respective <code>Pythia</code> object. Also some other smaller pieces
654 of code are affected, e.g. Standard Model and SUSY couplings
655 (the latter in new files).
656 <br/><b>Note 1</b>: The documentation has been updated accordingly
657 on these webpages, but the "A Brief Introduction to PYTHIA 8.1"
658 still refers to the old behaviour of version 8.100.
659 <br/><b>Note 2</b>: the interface to the external LHAPDF library remains
660 static, since LHAPDF is written in Fortran and thus by definition
662 <br/><b>Note 3:</b> if you want to have momentum smearing in
663 <code>CellJet</code> you now need to send in a pointer to a
664 random-number generator.
667 <li>Ten new proton PDF sets are made available internally:
668 MRST LO* (2007), MRST LO** (2008), MSTW 2008 LO (central member),
669 MSTW 2008 NLO (central member), CTEQ6L, CTEQ6L1, CTEQ6.6 (NLO,
670 central member), CT09MC1, CT09MC2, and CT09MCS, see
671 <?php $filepath = $_GET["filepath"];
672 echo "<a href='PDFSelection.php?filepath=".$filepath."' target='page'>";?>PDF Selection</a>. The Pomeron PDF data
673 files have been renamed for consistency. Thanks to Tomas Kasemets
674 for help with this [<a href="Bibliography.php" target="page">Kas10</a>].
677 <li>New parameters <code>TimeShower:pTmaxFudgeMPI</code> and
678 <code>SpaceShower:pTmaxFudgeMPI</code> introduced, to give the same
679 functionality for multiparton interactions that
680 <code>TimeShower:pTmaxFudge</code> and <code>SpaceShower:pTmaxFudge</code>
681 do for the hardest.</li>
683 <li>A few extensions of the <code>UserHooks</code> framework.
684 New methods <code>UserHooks:canVetoISREmission()</code> and
685 <code>UserHooks::doVetoISREmission(...)</code> allows the latest
686 initial-state emission to be studied before being finalized,
687 with the possibility to veto it.
688 Similarly <code>Userhooks:canVetoFSREmission()</code> and
689 <code>UserHooks::doVetoFSREmission(...)</code> can be used to
690 veto the latest final-state emission.</li>
692 <li>A number of loop counters have been introduced in the
693 <code>Info</code> class, that offers some further information on
694 the progress of the event generation, for use e.g. in conjunction
695 with the <code>UserHooks</code> facility.</li>
697 <li>The <code>Pythia::initTunes(...)</code> method is made public, so that
698 it can be called before the normal call from <code>Pythia::init(...)</code>.
699 That way it is possible to start out from a given tune and change a few
703 <li>Bug corrected in <code>LHAFortran.h</code> for hard-process input
704 from Fortran commonblock. This did not work properly when the input
705 was used in combination with a second hard process generated internally.
706 Thanks to Mikhail Kirsanov and Roberto Chierici.
708 <li>Insertion of missing initialization of <code>isInit</code> in the
709 <code>Settings</code> and <code>ParticleData</code> constructors, and
710 <code>nInit</code> for <code>BeamParticle</code>.
711 Thanks to Leif Lönnblad.</li>
713 <li>Updated <code>Makefile.msc</code> for Windows users.</li>
715 <li>Fix of some non-optimal use of booleans, that give warnings on
716 a Windows compiler. Thanks to Anton Karneyeu.</li>
718 <li>New options for the <?php $filepath = $_GET["filepath"];
719 echo "<a href='SUSYLesHouchesAccord.php?filepath=".$filepath."' target='page'>";?>
720 SUSY Les Houches Accord</a> such that, by default,
721 particle and decay data are not overwritten for known Standard Model
722 particles (including <i>Z^0</i>, <i>W^+-</i> and <i>t</i>,
723 but excluding the Higgs).</li>
725 <li>Bug fix in <code>SusyLesHouches</code>, where the reading of SLHA
726 information embedded in an LHEF would not stop at the end of the header
729 <li>Bug correction for undefined secondary widths where decay products
730 together are heavier than the mother. Also unit default secondary width
731 values in the <code>DecayChannel</code> constructor.</li>
733 <li>Documentation updated, including change of current year to 2010.</li>
738 <li>8.140: 16 July 2010
741 <li>Four new draft <?php $filepath = $_GET["filepath"];
742 echo "<a href='Tunes.php?filepath=".$filepath."' target='page'>";?>tunes</a> available.</li>
744 <li>Introduction of a new scenario for production of Hidden-Valley
745 particles, and interleaved showering in the QCD and HV sectors, see
746 the new <?php $filepath = $_GET["filepath"];
747 echo "<a href='HiddenValleyProcesses.php?filepath=".$filepath."' target='page'>";?>Hidden Valleys</a>
748 description. A longer physics writeup is available [<a href="Bibliography.php" target="page">Car10</a>].
751 <li>Implementation of <i>2 -> 3</i> phase space selection intended
752 for QCD processes with massless partons. A new set of matching
753 <?php $filepath = $_GET["filepath"];
754 echo "<a href='PhaseSpaceCuts.php?filepath=".$filepath."' target='page'>";?>phase space cut parameters</a>.
755 The <?php $filepath = $_GET["filepath"];
756 echo "<a href='QCDProcesses.php?filepath=".$filepath."' target='page'>";?>ten different QCD <i>2 -> 3</i>
757 processes</a> have been implemented making use of this new
758 possibility, so far without a complete handling of possible colour
761 <li>New processes have been added for
762 <?php $filepath = $_GET["filepath"];
763 echo "<a href='CompositenessProcesses.php?filepath=".$filepath."' target='page'>";?>contact interactions</a> in
764 <i>q q -> q q</i> and <i>q qbar -> q qbar</i> scattering.</li>
766 <li>A process has been added for TeV^-1 Sized
767 <?php $filepath = $_GET["filepath"];
768 echo "<a href='ExtraDimensionalProcesses.php?filepath=".$filepath."' target='page'>";?>Extra Dimensions</a>, which
769 involves the electroweak KK gauge bosons, i.e. <i>gamma_{KK}/Z_{KK}</i>,
770 in one TeV^-1 sized extra dimension; see <code>main30.cc</code> for
771 an example. This scenario is described in [<a href="Bibliography.php" target="page">Bel10</a>]. Thanks to
772 Noam Hod and coworkers for contributing this code.</li>
774 <li>In the Randall-Sundrum extra-dimensional scenario a new option has
775 been added where SM fields can exist in the bulk rather than only on
776 a brane. (Still under development.) Furthermore production of a
777 Kaluza-Klein gluon state has been added, and the <code> main28.cc</code>
778 test program extended.</li>
780 <li>The scenario for monojets in Large Extra Dimensions has been expanded
781 with an alternative for scalar graviton exchange instead of tensor one.
784 <li>New parameters for maximum scale of
785 <?php $filepath = $_GET["filepath"];
786 echo "<a href='TimelikeShowers.php?filepath=".$filepath."' target='page'>";?>timelike showers</a>,
787 <code>TimeShower:pTmaxMatch</code>, and the dampening of hard radiation,
788 <code>TimeShower:pTdampMatch</code> and <code>TimeShower:pTdampFudge</code>,
789 by analogy with corresponding ones for spacelike showers. Also new method
790 <code>TimeShower:limitPTmax(...)</code> to implement alternative procedures.
791 For dipoles stretched to the beam the new switch
792 <code>TimeShower:dampenBeamRecoil</code> allows to dampen radiation
793 close to the beam direction, with a changed default behaviour.</li>
795 <li>Azimuthal anisotropies from coherence arguments have been introduced
796 for the spacelike parton showers, see <code>SpaceShower:phiIntAsym</code>
797 and <code>SpaceShower:strengthIntAsym</code>.
798 Also azimuthal anisotropies from gluon polarization have been introduced
799 for the spacelike parton showers, see <code>SpaceShower:phiPolAsym</code>,
800 and updated for timelike parton showers, see
801 <code>TimeShower:phiPolAsym</code>.</li>
803 <li>Improvements for the matching to POWHEG LHEF-style input illustrated
804 by the new <code>main71.cc</code> example. See also [<a href="Bibliography.php" target="page">Cor10</a>].</li>
806 <li>A set of new processes <i>gamma gamma -> f fbar</i>, with <i>f</i>
807 quarks or leptons. Code for equivalent photon flux around an unresolved
808 proton, with more to come. Thanks to Oystein Alvestad.
811 <li>A new option has been included to dampen the growth of the diffractive
812 cross sections, see <?php $filepath = $_GET["filepath"];
813 echo "<a href='TotalCrossSections.php?filepath=".$filepath."' target='page'>";?>Total Cross
816 <li>A new method <code>virtual int SigmaProcess::idSChannel()</code>
817 has been introduced. If overloaded to return a nonzero value then a
818 <i>2 -> n</i> process will appear listed as a <i>2 -> 1 -> n</i> one.
819 That is, an intermediate resonance with the requested identity will be
820 inserted in the event record, even without appearing in the calculation
821 of the matrix element proper. Thanks to Noam Hod for idea and code.</li>
823 <li>A new method <code>SigmaProcess::convertM2()</code> has been introduced
824 to optionally allow the <code>SigmaProcess::sigmaHat()</code> to return
825 the squared matrix element rather than <i>d(sigmaHat)/d(tHat)</i> for
826 <i> 2 -> 2 </i> processes. Furthermore kinematics is stored in the new
827 <code>mME</code> and <code>pME</code> vectors for alternative cross
828 section encodings.</li>
830 <li>Different encoding of the <i>f fbar -> Z W</i> cross section,
831 contributed by Merlin Kole, based on the cross section of
832 Brown, Sahdev and Mikaelian. Gives a distinctly different cross section
833 than the previous based on EHLQ (including their bug fix).
834 In particular the problem with negative cross sections is now fixed.</li>
836 <li>Minor updates: pass <code>xmlPath</code> to new MSTW and CTEQ PDFs;
837 reset beams earlier to give cleaner documentation.</li>
839 <li>The H1 Fit B LO parametrization to the Pomeron PDF has been included,
840 and made new default for Pomerons. Thanks to Paul Newman for providing
843 <li>Three changes, in principle unrelated, but with the common objective
844 to make the generation of a given event depend only on the values
845 determined during the initialization stage and on the state of the
846 random-number generator when the event is begun. The new default
847 should ensure a reproducible stop-and-restart behaviour, convenient
848 for debug purposes. Thanks to Michael Schmelling for stressing the
849 desire for such a behaviour.
850 <br/>(i) Introduction of a new option <code><?php $filepath = $_GET["filepath"];
851 echo "<a href='PhaseSpaceCuts.php?filepath=".$filepath."' target='page'>";?>
852 PhaseSpace:increaseMaximum</a></code> that allows to switch between
853 two strategies for handling the (hopefully rare) cases when the
854 assumed maximum of the cross section function is exceeded during the
855 event generation, with a changed default behaviour. In the old
856 default the maximum could be increased if it was exceeded during the run,
857 thereby introducing a memory of the previously generated events.
858 <br/>(ii) Updated handling of random numbers with Gaussian distributions.
859 The <code>gauss()</code> method now only generates one value at a time.
860 Instead the new <code>gauss2()</code> method returns a pair of Gauss
861 numbers, with related time savings. In the old approach one Gaussian
862 number could be buffered, which introduced a memory.
863 <br/>(iii) Minor bug fix in <code>MiniStringFragmentation</code>, where
864 the popcorn baryon state was not reset for each new system, again
865 giving a (flawed) memory.</li>
867 <li>New directory <code>rootexample</code> with a simple code example
868 how to use ROOT for histogramming in PYTHIA runs. See
869 <?php $filepath = $_GET["filepath"];
870 echo "<a href='ROOTusage.php?filepath=".$filepath."' target='page'>";?>ROOT Usage</a> for details. Thanks to Rene Brun.
873 <li>In the <code>HepMCinterface</code> the checks for unhadronized
874 quarks and gluons are not performed if hadronization has been switched
877 <li>The <code>UserHooks::initPtr(...)</code> has been expanded so that
878 pointers to more classes (beam particles, random number, couplings, etc.)
879 are sent in, thereby increasing the scope of possible user-written code.
880 Also, the <code>UserHooks::doVetoProcessLevel(Event& process)</code>
881 now allows the <code>process</code> event record to be modified,
882 even if it is not recommended. The new <code>Info::pTnow()</code>
883 method returns the current <i>pT</i> scale of the combined MPI, ISR
884 and FSR evolution, which can be useful for some user hooks decisions.
887 <li>Histograms of the <code>Hist</code> class can now be booked
888 with up to 1000 bins, instead of the previous maximum 100. All bins
889 can be written to file, but the line-printer style printing will join
890 nearby bins so at most 100 are printed, as before. </li>
892 <li>Updated <code>configure</code> and <code>Makefile</code>
893 to allow 64-bit compilation and more options. Thanks to Mikhail Kirsanov,
894 Rene Brun and Fons Rademakers.</li>
896 <li>Bug fix in <code>ProcessLevel</code> for colour flow checks of
897 junctions. Enables the decay of a neutralino to three quarks, e.g.
898 Thanks to Nils-Erik Bomark.</li>
900 <li>Bug fixes in <code>TimeShower</code>, where recoil partners in resonance
901 decays of coloured particles, and recoil partners in QED dipoles when beams
902 are not allowed to take a recoil, might not be correctly identified. </li>
904 <li>Bug fix in <code>SpaceShower</code>: when used with a fixed
905 <i>alpha_strong</i>, the threshold enhancement factor of
906 <i>g -> Q Qbar</i> became undefined. Thanks to Stefan Prestel.</li>
908 <li>Bug fix in initialization of resonance widths, where the
909 <code>minWidth</code> parameter could be used uninitialized,
910 occasionally resulting in strange initialization problems when
911 kinematics needs to force at least one resonance to be off-shell.</li>
913 <li>Minor updates of <code>main06.cc</code>, <code>main10.cc</code>
914 and <code>main23.cc</code>.</li>
916 <li>Bug fix in mother pointer of multiparton interactions in
917 diffractive systems.</li>
922 <li>8.142: 15 August 2010
925 <li>The strategy for setting up tune values has been changed.
926 Previously the <code>Tune:ee</code> and <code>Tune:pp</code>
927 settings were only interpreted during the
928 <code>Pythia::init(...)</code> stage. Now they are interpreted
929 as soon as they are read. Specifically this means that it is
930 possible to override any of the tune parameters by putting new
931 commands below <code>Tune:ee</code> and <code>Tune:pp</code>
932 in the <code>Pythia::readFile(...)</code> configuration file
933 or in the list of <code>Pythia::readString(...)</code> commands.
934 <br/>As a consequence of this change, the public
935 <code>Pythia::initTunes(...)</code> method has been replaced by
936 two private <code>Settings::initTuneEE(...)</code> and
937 <code>Settings::initTunePP(...)</code> methods.
938 <br/>If <code>Tune:ee</code> or <code>Tune:pp</code> are
939 nonvanishing by default, then the corresponding tune variables
940 are set also from the <code>Pythia</code> constructor, before any
941 user changes are possible. Currently this is not relevant.
944 <li>Bug fix in the setup of the <code>Tune:pp = 5</code> and
945 <code>= 6</code> options, which meant that diffractive cross
946 sections were not reduced as advertised.</li>
948 <li>The default value of <code>MultipartonInteractions:pT0Ref</code>
949 has been slightly reduced so as to give a somewhat improved
950 default description. It is not intended as a replacement for the
951 specific tunes, however.</li>
953 <li>Some comparisons between tunes and data, obtained with the
954 Rivet package, have been posted on
955 <a href="http://home.thep.lu.se/~richard/pythia81/">
956 http://home.thep.lu.se/~richard/pythia81/</a>.
957 Further improvements can be expected from future Professor-based
958 tunes. The current set of 2C, 2M, 3C and 3M "draft tunes" have
959 deliberately been chosen different also to explore a range of
960 possibilities. One not visible in the plots is the fraction
961 of single and double diffractive events in the inelastic cross
962 section. This is 32% in 2C and 2M, while it was reduced to
963 21% in 3C and 3M, and a recent ATLAS study (ATLAS-CONF-2010-048)
964 would suggest 28+-4%.</li>
966 <li>Minor changes in <code>TimeShower</code> and
967 <code>SpaceShower</code>, as protection if the <i>c</i> or
968 <i>b</i> masses are set small.</li>
970 <li>Bug fix in <code>SpaceShower</code>, for case when <i>phi</i>
971 angle selection is biased to take into account interference effects.
974 <li>The <code>SigmaProcess::convertM2()</code> method now has
975 been implemented also for <i>2 -> 1</i> processes, so that it is
976 possible to provide the squared matrix element instead of
977 <i>sigmaHat</i> for semi-internal processes. A fixed-width
978 Breit-Wigner is also inserted, since the matrix element is supposed
979 not to include it.</li>
981 <li>New method <code>SigmaProcess::setupForME()</code> does an
982 extended conversion from the internal kinematics to an almost
983 equivalent one, better adapted to the mass conventions of matrix-element
984 caclulation programs, such as massive incoming <i>b</i> quarks.
985 New flags allow to determine whether the <i>c</i>, <i>b</i>,
986 <i>mu</i> and <i>tau</i> should be considered massless or not
987 in the calculations.</li>
989 <li>Two new friend methods <code>table</code> of the <code>Hist</code>
990 class allow to print a table with three columns, the first for the
991 (common!) <i>x</i> values and the other two for the respective
992 histogram values. A new method <code>takeSqrt</code> for the square
993 root of histogram bin contents.
999 <li>8.145: 10 November 2010
1002 <li><code>Couplings</code> is defined in <code>StandardModel.h</code>
1003 as a derived class of <code>coupSM</code> and has only one extra flag:
1004 <code>isSUSY</code> to check presence of extra couplings.Changed all
1005 pointers <code>CoupSM*</code> to <code>Couplings*</code> and removed
1006 explicit references to <code>CoupSUSY*</code>. The <code>coupSUSY</code>
1007 object is only initialised if SUSY couplings are present. The new pointer
1008 <code>couplingsPtr</code> points either to only SM couplings or SM+SUSY
1009 couplings based on SLHA data.</li>
1011 <li>New files <code>SusyResonanceWidths.h/cc</code> contains the
1012 <code>SusyResonanceWidths</code> class, which inherits from
1013 <code>ResonanceWidths</code> but typecasts the <code>couplingsPtr</code>
1014 to <code>(CoupSUSY*) coupSUSYPtr</code>. This is the base class for
1015 all SUSY resonances. It contains the <code>ResonanceSquark</code> class
1016 for all squark decays. A new flag <code>SLHA:useDecayTable</code>
1017 to check if internal widths should be overwritten by those read in
1020 <li>Added new functionality to <code>SusyLesHouches</code> for read-in
1021 of generic user blocks in the SLHA format, along with methods to
1022 extract parameters from them with typecasting controlled by the user.
1023 Intended for use with user-written semi-internal processes.</li>
1025 <li>Added <code>Sigma1qq2antisquark</code> cross section.</li>
1027 <li>Some new flags and modes in the <code>SUSY</code> and
1028 <code>SLHA</code> series offer further functionality.</li>
1030 <li>Several further changes as a consequence of the upgrade of the SUSY
1033 <li>Bug/typo fixes in rotation matrices for SUSY couplings and for the
1034 processes <code>qqbar2squarkantisquark</code>,
1035 <code>qq2squarksquark</code> and more.</li>
1037 <li>Improved handling of colour junctions. Added new example program
1038 <code>main72.cc</code>, to illustrate read-in of color junction
1039 structures via LHEF (<code>main72.lhe</code>). The example used is SUSY
1042 <li>New Tune 4C introduced as <code>Tune:pp = 5</code>. The more crude
1043 (non-)tunes 3C and 3M are removed.</li>
1045 <li>New methods <code>Settings::getFlagMap(...)</code>,
1046 <code>Settings::getModeMap(...)</code>,
1047 <code>Settings::getParmMap(...)</code> and
1048 <code>Settings::getWordMap(...)</code> allows to return a map of all
1049 settings of the respective type that contain a specific string
1053 <li>Improved description of excited <i>g^*/KK-gluon^*</i> production
1054 in the <code>Sigma1qqbar2KKgluonStar</code> and
1055 <code>ResonanceKKgluon</code> classes.</li>
1057 <li>Possibility added to let Hidden-Valley <i>gamma_v</i> have
1058 a nonero mass and decay by mixing with the ordinary photon.
1059 Still experimental.</li>
1061 <li>Minor bug fix in handling of three-body phase space.</li>
1063 <li>Minor correction in <code>Sigma2ffbar2TEVffbar</code> class.</li>
1065 <li>Bug fix for decays of <i>W'</i> to a pair of heavy fermions when
1066 <i>gV != gA</i>. Thanks to M. Chizhov, see arXiv:0705.3944. </li>
1068 <li>Restore the older EHLQ-based encoding of the <i>f fbar -> Z W</i>
1069 cross section, which was changed in version 8.140, since comparisons
1070 with Madgraph gives much better agreement with it than with the
1071 expression of Brown, Sahdev and Mikaelian.</li>
1073 <li>The <code>HepMCInterface</code> now also stores colour flow
1074 information for coloured particles.</li>
1076 <li>Pointer to <code>Couplings</code> made available for particle
1079 <li>Minor update in <code>main61.cc</code> for more elegant usage
1080 of FastJet, as suggested by Gregory Soyez.</li>
1085 <li>8.150: 20 April 2011
1088 <li>Tune 4C is made default. It is based on first comparisons with
1089 LHC data [<a href="Bibliography.php" target="page">Cor10a</a>], and has also been checked independently
1090 [<a href="Bibliography.php" target="page">Buc11</a>] to give reasonable agreement with many distributions.
1093 <li>The description of <i>tau</i> lepton decays has been significantly
1094 enhanced, to include helicity information related to the production
1095 process and hadronic currents fitted to data. A complete writeup is
1096 in preparation [<a href="Bibliography.php" target="page">Ilt11</a>]. A new flag is introduced to revert
1097 to the old behaviour, for cross-checks, see
1098 <?php $filepath = $_GET["filepath"];
1099 echo "<a href='ParticleDecays.php?filepath=".$filepath."' target='page'>";?>Particle Decays</a>.
1100 The new tau decay machinery is on by default.
1103 <li>A new option <code>MultipartonInteractions:bProfile = 4</code> has
1104 been introduced for the impact-parameter profile of protons in the
1105 <?php $filepath = $_GET["filepath"];
1106 echo "<a href='MultipartonInteractions.php?filepath=".$filepath."' target='page'>";?>Multiparton Interactions</a>
1107 framework, wherein low-<i>x</i> partons are spread over a larger area
1108 than high-<i>x</i> ones, see [<a href="Bibliography.php" target="page">Cor11</a>]. A new method
1109 <code>Info::eMPI(i)</code> gives back the enhancement factor related to
1110 the <code>i</code>'th interaction. The impact-parameter profile can now
1111 be selected separately for <?php $filepath = $_GET["filepath"];
1112 echo "<a href='Diffraction.php?filepath=".$filepath."' target='page'>";?>diffraction</a>,
1113 but without a <code>bProfile = 4</code> option.
1116 <li>The possibility of "hadronization" in the
1117 <?php $filepath = $_GET["filepath"];
1118 echo "<a href='HiddenValleyProcesses.php?filepath=".$filepath."' target='page'>";?>Hidden Valley</a> sector
1119 has been added as a new option <code>HiddenValley:fragment = on</code>.
1120 This is based on a copy of the standard string fragmentation framework,
1121 but with the option of a completely separate "flavour" sector, and
1122 separately tunable longitudinal fragmentation functions and transverse
1123 momenta. For now only a simple flavour scenario is provided, where
1124 flavour-diagonal mesons can decay back into the normal visible sector
1125 while off-diagonal ones remain hidden. A writeup of the model is in
1126 preparation [<a href="Bibliography.php" target="page">Car11</a>]. Also some further Hidden Valley options
1127 have been added.</li>
1129 <li>Included possibility in <code>TimeShower</code> for QCD dipoles to
1130 have an adjustible normalization factor, via the new
1131 <code>bool isFlexible</code> and <code>double flexFactor</code>
1132 properties of <code>class TimeDipoleEnd</code>. This flexibility is used
1133 to treat radiation off colour topologies with epsilon tensors, in
1134 particular colour junctions which have all their partons in the
1135 final state. (An example is the BNV-SUSY decay ~chi0→uds.) For
1136 such topologies, the new treatment in PYTHIA 8 is that a
1137 half-strength dipole is spanned between all combinations of
1138 final-state quarks. For junctions with an incoming (anti)colour line (such
1139 as in the BNV-SUSY decay ~t*→cb), a full-strength dipole is
1140 instead spanned between the two daughters, with no radiation from the
1141 decaying object (in its CM). As will be described in a fortcoming
1142 paper with N. Desai, this should give the
1143 closest possible correspondence to the radiation patterns exhibited
1144 by higher-order matrix elements for this type of process.</li>
1146 <li>Corrected harmless bugs in <code>ProcessLevel::findJunctions</code>
1147 which caused junctions of types 3 and 4 (i.e., junctions with 1
1148 incoming color tag) to sometimes be incorrectly classified as types
1149 1 and 2 (with all color tags outgoing), respectively.
1150 Since the parity (even/odd) of the junction kind was still correct,
1151 however, this did not cause any problems at the hadronization
1154 <li>The junction-finder in <code>ProcessLevel::findJunctions</code>
1155 has been made more stable, and the following ordering of the color
1156 tags returned by <code>Event::endColJunction(iJun, iLeg)</code> is
1157 now enforced: for junction kinds 3 and 4 (one tag
1158 incoming), <code>iLeg = 0</code> will return the
1159 incoming tag, while for kinds 5 and 6 (two tags incoming),
1160 <code>iLeg = 0</code> and <code>iLeg = 1</code> will return the
1161 incoming tags. Apart from this ordering, the color tags are
1162 ordered in ascending color tag number.</li>
1164 <li>Declarations of friend functions moved to sit outside the class
1165 it befriends. Thanks to Axel Naumann for pointing out the incorrect
1166 previous construction.</li>
1168 <li>The <code>rootexample</code> subdirectory becomes
1169 <code>rootexamples</code> as the old example is split into two,
1170 with improved documentation to clarify usage. Thanks to Axel Naumann
1171 and Bernhard Meirose for the new code.</li>
1173 <li>In the Les Houches Event File machinery, input type has been
1174 changed from <code>ifstream</code> to <code>istream</code> for more
1177 <li>R-hadron handling is largely implemented, see the
1178 <?php $filepath = $_GET["filepath"];
1179 echo "<a href='RHadrons.php?filepath=".$filepath."' target='page'>";?>R-hadrons</a> page, although some aspects
1180 still need polishing. A new class <code>RHadrons</code> takes
1181 care of the hadronization and decay. Particle data have been added
1182 for R-hadrons containing a gluino, stop or sbottom, but could
1183 alternatively be used for other long-lived coloured particles.
1184 Thanks to Bernhard Meirose for support.
1187 <li>Calculations of SUSY decay widths included by
1188 N. Desai, contained in the new source
1189 files <code>SusyResonanceWidth.cc</code>
1190 and </code>.h</code>. Validation and addition of more modes is still in
1191 progress, so this implementation should be considered preliminary
1192 for now. For a list of available modes, see
1193 the <?php $filepath = $_GET["filepath"];
1194 echo "<a href='SUSYProcesses.php?filepath=".$filepath."' target='page'>";?>SUSY Processes</a> page.
1197 <li>A first implementation of the SLHA-based QNUMBERS interface for
1198 defining new exotic particles has been
1199 included. See [<a href="Bibliography.php" target="page">Alw07</a>] and
1200 the <?php $filepath = $_GET["filepath"];
1201 echo "<a href='SUSYLesHouchesAccord.php?filepath=".$filepath."' target='page'>";?>SUSY Les Houches Accord</a>
1204 <li>Read-in of LHEF events containing Baryon Number Violating vertices
1205 has been included, using colour junctions, see
1206 the <?php $filepath = $_GET["filepath"];
1207 echo "<a href='EventRecord.php?filepath=".$filepath."' target='page'>";?>Event Record</a> page. The advanced
1208 shower model taking into account the full colour structure of such
1209 events, developed by N. Desai and described above,
1210 is turned on by default in such events.
1211 Several test cases were used to
1212 validate this implementation, but it is possible that problems could
1213 still exist for some cases. Feedback is welcome. Thanks to
1214 the MadGraph authors for providing several test cases.</li>
1216 <li>Some first steps taken to allow events containing colour sextets,
1217 e.g., from semi-internal processes or LHEF interfaces, and/or from
1218 SLHA <code>DECAY</code> tables. New
1219 <code>colType</code> codes 3 and -3 are introduced to describe
1220 sextets and antisextets, respectively. The state of the current
1221 implementation is that hard processes containing such states can be
1222 read in and decays generated (via <code>DECAY</code> tables). Parton
1223 showers can be added, but the sextets themselves do not, as yet,
1224 shower, and any undecayed sextets remaining at the hadronization
1225 stage would lead to unpredictable problems if hadronization is
1226 switched on. Thanks to J. Alwall for help with testing
1227 this implementation.
1230 <li>The functionality of the SLHA SUSY/BSM interface (see
1231 the <?php $filepath = $_GET["filepath"];
1232 echo "<a href='SUSYLesHouches.php?filepath=".$filepath."' target='page'>";?>SUSY Les Houches</a> page) has been
1233 extended so that copies of all <code>BLOCK</code>s are now stored
1235 strings, regardless of whether they correspond to "official" SLHA
1236 blocks or not. Their contents can subsequently be queried by a set
1237 of new templated member functions of the
1238 class <code>SusyLesHouches</code>. Available query functions so far
1240 <br/><code>template <class T> bool getEntry(string, T&);</code>,
1241 <br/><code>template <class T> bool getEntry(string, int, T&);</code>,
1242 <br/><code>template <class T> bool getEntry(string, int, int, T&);
1244 <br/><code>template <class T> bool getEntry(string, int,
1245 int, int, T&);</code>,
1246 <br/>where the type of
1247 the argument used in the call determines how to read the block
1248 entries. Thus, if an LHEF, SLHA, or other card file is read in by
1249 PYTHIA, the contents of any <code>BLOCK</code> in that file can
1250 subsequently be queried run-time using these functions. This is
1251 used, e.g., in the new interface between MADGRAPH 5 and PYTHIA
1252 8. Thanks to the MADGRAPH team, and to J. Alwall in particular, for
1253 help and debug on this new implementation.
1259 <li>8.153: 10 August 2011
1262 <li>The setup of tunes has been modified, see the
1263 <?php $filepath = $_GET["filepath"];
1264 echo "<a href='Tunes.php?filepath=".$filepath."' target='page'>";?>Tunes</a> page for details. Specifically
1265 the <code>Tune:ee</code> and <code>Tune:pp</code> modes have
1266 acquired a new option <code>-1</code> for a forced restore to the
1267 default values of all settings used in the respective kind of
1270 <li>The code for handling multiparton interactions in the scenario with
1271 an <i>x</i>-dependent width of the Gaussian matter profile
1272 [<a href="Bibliography.php" target="page">Cor11</a>], has been improved and updated. Tune 4Cx, which
1273 is based on this option, has been added as a further tune option.</li>
1275 <li>A possibility to bias the phase-space selection has been added,
1276 whereby some phase space regions can be oversampled, which is
1277 compensated by assigning a weight to each event.
1278 A new set of methods have been added to the <code>UserHooks</code>
1279 class to allow users to program how to bias the selection.</li>
1281 <li>New options added so that matrix-element corrections can be
1282 switched off after the first branching in ISR or FSR.</li>
1284 <li>Some new <code>Info</code> methods have been added to store
1285 information on latest ISR branching. The <code>SpaceShower</code>
1286 class has also been corrected so that the latest <i>z = 1/2</i>
1287 when not defined by history. This avoids undefined values for
1288 azimuthal asymmetries. Thanks to Stefan Prestel for finding and
1289 sorting out this problem.</li>
1291 <li>The <code>Pythia::forceHadronLevel()</code> method now takes
1292 an argument that optionally means that existing junction information
1293 is not overwritten. Thanks to Leif Lönnblad for pointing out
1294 the usefulness of this.</li>
1296 <li>For particle decays to a varying number of hadrons the multiplicity
1297 increase with mass has been somewhat reduced, and especially for
1298 <code>meMode = 23</code> a separate even slower increase has been
1301 <li>New possibility to force the tau polarization.</li>
1303 <li>Bug fix for the special case in which events containing SUSY
1304 particles are generated without proper initialization of SUSY decays.
1305 This can happen, e.g., if events containing SUSY particles are read
1306 in via external LHEF files, if those files do not contain readable
1307 SLHA spectra in their headers. In this case, a failed attempt to
1308 generate sparticle decays with ill-defined couplings previously
1309 led to crashes. The program now reverts to the old behaviour,
1310 based on static decay tables, in such cases, with the default
1311 being to decay all sparticles to gravitino + particle. An error
1312 message stating that the full SUSY treatment has been switched
1313 off and why is also issued. Thanks to N. Desai for this fix.</li>
1315 <li>The R-hadron machinery has been completed.</li>
1317 <li>Minor change in timelike showers: gluons which fall below the
1318 <i>pTmin</i> cutoff by the correction for mass effects are now
1319 eliminated, while previously they were kept. This reduces the
1320 number of gluons somewhat, but has no significant effects on the
1321 hadronic final state. (Prompted by R-hadron studies, where big mass
1322 effects else give bothersome low-energy gluons.)</li>
1324 <li>Corrected typos in two of the Upsilon wave function matrix
1325 elements, <code>Bottomonium:OUpsilon3P08</code> and
1326 <code>Bottomonium:Ochib03P01</code>. Thanks to Beate Heinemann for
1327 pointing it out.</li>
1329 <li>Implemented <i>f*</i> decay angle in <i>f f -> f f*</i> processes,
1330 and fixed some bugs for the same process. Thanks to Piyali Banerjee
1333 <li>Introduce possibility to separate production channels for
1334 TeV-sized extra dimensions, and a small code correction. Thanks to
1335 Noam Hod for code contribution.</li>
1337 <li>Bug fix for neutrino beams: since neutrinos are always lefthanded
1338 there should be a factor 2 in the cross section, relative to charged
1339 leptons, from the non-need to average over incoming spin states. This
1340 is now fixed by introducing a new PDF class <code>NeutrinoPoint</code>
1341 for (unresolved) neutrinos, with normalization 2 rather than 1 for
1342 charged leptons. Thanks to Ryosuke Sato.</li>
1344 <li>Bug fix for some (rarely used) particle settings, which could not
1345 be changed by users because they were read too early. Thanks to
1346 Andrew Altheimer and Gustaaf Brooijmans.</li>
1348 <li>Bug fix in handling of <code>tau</code> decays, where setting of
1349 decay vertices could write outside memory. Thanks to Steven Schramm.</li>
1351 <li>Minor expansion of the <code>BeamParticle</code> constructor.</li>
1353 <li>Minor bug fix in CTEQ 6L for uninitialized variables.</li>
1355 <li>Minor bug fix in fragmentation flavour combination to hadron.</li>
1357 <li>Some updates of the documentation, including new pages on
1358 MadGraph 5 as a generator for semi-internal processes (thanks to
1359 Johan Alwall) and on RIVET interfacing.</li>
1361 <li>Minor improvements of ROOT- and HepMC-related code and documentation.</li>
1363 <li>Some cleanup of code.</li>
1368 <li>8.157: 10 November 2011
1371 <ii>StefanPrestel joins as new member of the PYTHIA author team.
1372 He is mainly working on matching/merging issues, and has contributed
1373 the CKKW-L machinery mentioned below.</li>
1375 <li>Merging capabilities according to the CKKW-L scheme [<a href="Bibliography.php" target="page">Lon11</a>]
1376 have been added, see the new
1377 <?php $filepath = $_GET["filepath"];
1378 echo "<a href='MatrixElementMerging.php?filepath=".$filepath."' target='page'>";?>Matrix Element Merging</a>
1379 page. It involves new classes to reconstruct and select how a
1380 matrix-element-generated partonic configuration could have been obtained
1381 by the PYTHIA evolution, and to perform trial showers (using a new
1382 copy of the normal parton-level machinery) that introduce the appropriate
1383 Sudakov suppression factors. New examples to illustrate various
1384 common tasks are found in <code>main81.cc</code>, <code>main82.cc</code>,
1385 <code>main83.cc</code> and <code>main84.cc</code>.</li>
1387 <li>The <code>main71.cc</code> program is now generalised for reading
1388 in arbitrary POWHEG LHE files, to implement a smooth matching between NLO
1389 matrix elements and the PYTHIA parton showers. Cuts are made on both
1390 ISR and FSR emissions, while previously only ISR was covered. The key
1391 assumptions are the <i>pT</i> definitions used for ISR and FSR, but several
1392 further options are available, as documented in the <code>main71.cmnd</code>
1393 file. Work is still ongoing to pick the best default options. </li>
1395 <li>Several expansions of the <code>UserHooks</code> class.
1396 For both <code>doVetoFSREmission</code> and <code>doVetoISREmission</code>
1397 a new argument <code>iSys</code> labels the system within which the
1398 radiation occurs. For <code>doVetoFSREmission</code> a further argument
1399 <code>inResonance</code> distinguishes FSR in resonance
1400 decays from that in the hard process itself. New methods
1401 <code>canVetoMPIEmission</code> and <code>doVetoMPIEmission</code>
1402 have been added to veto multiparton interactions in the same way as
1403 FSR and ISR. In <code>biasSelectionBy</code> at times incorrect values
1404 for <code>inEvent</code> has been corrected. Also some systematization
1405 of the use of <code>const</code>.</li>
1407 <li>A new model for hadron scattering is introduced, still at an early
1408 stage and therefore more intended for internal development than for the
1409 normal user. The basic idea is that a high-energy <i>pp</i> collision
1410 involves the fragmentation of multiparton strings that overlap in space
1411 (and time). Also the produced hadrons therefore initially overlap, and
1412 there is a strong likelihood that hadrons can scatter against each other
1413 until the system has expanded sufficiently. This can e.g. increase the
1414 transverse momentum of heavier hadrons at the expense of lighter ones.
1417 <li>A new jet finder <code>SlowJet</code> offers simple access to the
1418 inclusive <i>kT</i>, anti-<i>kT</i>, and Cambridge/Aachen
1419 algorithms in a cylindrical coordinate frame. The jet reconstruction
1420 is then based on sequential recombination with progressive removal,
1421 using the <i>E</i> recombination scheme. The minimalistic
1422 <code>SlowJet</code> code is much slower than <code>FastJet</code>
1423 [<a href="Bibliography.php" target="page">Cac06</a>], and contains less options, but reconstructs the same
1424 jets if run under identical conditions. For details see the
1425 <?php $filepath = $_GET["filepath"];
1426 echo "<a href='EventAnalysis.php?filepath=".$filepath."' target='page'>";?>Event Analysis</a> page.</li>
1428 <li>Starting in gcc 4.6, it is possible to switch off specific warnings
1429 around specific blocks of code. Although version 4.6 is some way off
1430 from being commonly found, this option has now been introduced to switch
1431 off <code>-Wshadow</code> warnings in <code>HepMCInterface.cc</code>.
1432 For other compilers, or earlier versions of gcc, the old behaviour
1435 <li>Support for reading in gzipped LHEFs has been added in the
1436 <code>LesHouches</code> and <code>SusyLesHouches</code> classes.
1437 This also affects <code>configure</code> and <code>Makefile</code>s.
1438 Unless explicitly enabled, it should not affect anything.
1439 If enabled, it relies on the Boost and zlib libraries to function,
1440 so paths to these must be set appropriately, see the
1441 <code>README</code> file for details. The Boost header files can
1442 give very many shadow warnings, so <code>-Wshadow</code> is disabled
1443 if gzip support is enabled, as described above.</li>
1445 <li>Introduce use of the <code>HEPMC_HAS_UNITS</code> environment
1446 variable in the <code>HepMCInterface.cc</code> and <code>main32.cc</code>
1447 codes to automatically check whether GeV and mm can be set as relevant
1448 units. If yes, then it is set in <code>main32.cc</code>. If no,
1449 a conversion from GeV to MeV is done explicitly in
1450 <code>HepMCInterface.cc</code>. Note that, for early HepMC versions,
1451 this means a change of behaviour. Thanks to Andy Buckley.</li>
1453 <li>A new method <code>Info::lhaStrategy()</code> returns the
1454 Les Houches event weighting strategy where relevant, and 0 where not.
1455 For the strategies <i>+-4</i> the event weight and sum,
1456 <code>Info::weight()</code> and <code>Info::weightSum()</code>,
1457 is now in units of pb at output, as it should be at input.
1458 (While internally mb is used.)</li>
1460 <li>New flag <code>Check:abortIfVeto</code> allows the user to
1461 resume control over execution in case of a veto in the event
1462 generation process.</li>
1464 <li>New method <code>Event::at(i)</code> returns reference to
1465 <code>i</code>'th particle in the event record.</li>
1467 <li>Introduce the Fermi constant as one of the Standard Model
1470 <li>Included automatic pre-initialization of SLHA blocks MASS and
1471 SMINPUTS using PYTHIA's SM parameters and particle data table
1474 <li>SUSY: added sleptons (and sneutrinos) as resonances.
1475 Corrected 2-body decay widths of gluinos, squarks and gauginos.
1476 Added sleptonic decay modes to gaugino decays.
1477 Implemented 2-body decays of sleptons (and sneutrinos)
1478 into sleptons/leptons/gauginos. Corrected slepton couplings (they
1479 now look exactly like squark couplings, using a 6x6 slepton mixing
1482 <li>New parameter <code>Diffraction:probMaxPert</code> introduce to
1483 give more flexibility in transition from a nonperturbative to a
1484 perturbative description of a diffractive system.</li>
1486 <li>Bug corrected in <code>SigmaEW.cc</code>, for the process
1487 <code>WeakSingleBoson:ffbar2ffbar(s:gm)</code>. Previously, all outgoing
1488 quark flavours in this process were erroneously assigned ID code 5
1489 (b quarks). This has now been corrected so the proper ratios are
1490 obtained, with <i>u : c : d : s : b = 4 : 4 : 1 : 1 : 1</i>,
1491 according to the squared quark charges.</li>
1493 <li>Changes in <code>FragmentationSystems</code> and
1494 <code>StringFragmentation</code> to reject systems with three or more
1495 interconnected junctions. This may happen in baryon-number-violating
1496 scenarios in pp collisions, if both of the beam baryon junctions are
1497 resolved and get connected via an antijunction created by a
1498 hard-process BNV vertex. In principle, this could be addressed by an
1499 extension of the existing junction fragmentation framework. However,
1500 since it happens rarely, for the time being an error message is printed
1501 and the fragmentation restarted.
1504 <li>Change in <code>Event::copy</code> to safeguard against attempting
1505 to copy out-of-range entries. An attempt to copy a non-existing entry
1506 will now return -1.</li>
1508 <li>Bug fix in the machinery for the user to force the setting of
1509 tau polarization.</li>
1511 <li>Bug fix in the initial search for a maximum of the process
1512 cross section (only affecting rare cases).</li>
1514 <li>Corrected angular decay distributions for two compositeness
1515 processes, <code>Sigma2qq2qStarq</code> and
1516 <code>Sigma2qqbar2lStarlbar</code>.</li>
1518 <li>Extra check in <code>HiddenValleyFragmentation</code> to make sure
1519 that pointers which have not been assigned with <code>new</code> are not
1522 <li>Some further minor changes.</li>
1527 <li>8.160: 23 January 2012
1530 <li>The older term "multiple interactions" has been replaced by the
1531 new standard "multiparton interactions" one, and correspondingly the
1532 abbreviation MI by MPI. This affects everything: settings, class and
1533 method names, documentation, etc. It therefore becomes necessary to
1534 rewrite user code. However, so as to keep the immediate effort at a
1535 reasonable level, the old settings names are kept as aliases. Thus
1536 <code>PartonLevel:MI</code> and <code>PartonLevel:MPI</code> are
1537 equivalent, and similarly <code>MultipleInteractions:pT0Ref</code>
1538 and <code>MultipartonInteractions:pT0Ref</code>. Should you be using
1539 methods such as <code>double Info::pTMI(int i)</code> you need to
1540 edit the code, however. All the <code>example/main*</code> files
1541 have been uopdated accordingly.</li>
1543 <li>A new option <code>Beams:frameType = 5</code> has been added
1544 for the case where an external generator should provide LHA process
1545 information. The new <code>Pythia::setLHAupPtr(...)</code> method
1546 should then be used to link in this generator. The new switch
1547 <code>Beams:newLHEFsameInit</code> can be used to tell that a new
1548 LHEF should be used, but without the need for a new initialization.
1549 With these two changes, all the different ways of initializing
1550 can be covered by the <code>Pythia::init()</code> call with no
1551 arguments. The various <code>init(...)</code>options with arguments
1552 are deprecated and will be removed for PYTHIA 8.2.</li>
1554 <li> The <code>Pythia::stat()</code> method, with no arguments,
1555 replaces <code>Pythia::statistics(...)</code>, although the latter
1556 remains as a deprecated alternative.</li>
1558 <li>New settings <code>Init:...</code>, <code>Next:...</code>,
1559 and <code>Stat:...</code> can be used to steer some details of
1560 the operation of the <code>Pythia::init()</code>,
1561 <code>Pythia::next()</code> and <code>Pythia::stat()</code>,
1562 respectively. In particular it affects the amount of printout
1563 at the various stages of operation. See
1564 <?php $filepath = $_GET["filepath"];
1565 echo "<a href='MainProgramSettings.php?filepath=".$filepath."' target='page'>";?>here</a> for further details.
1566 This change involves several code changes, but in documentation
1567 rather than physics. Most of the <code>Main:...</code> settings
1568 are deprecated as a consequence.</li>
1570 <li>The sample main programs in the <code>examples</code> subdirectory
1571 have been updated. This includes a change to the new favoured
1572 methods and settings outlined above, plus some update of the
1573 physics contents. Some of the examples have been combined,
1574 some others have been added (e.g. for R-hadroms), and as a consequence
1575 some renumbering has been made. See the modified list of
1576 <?php $filepath = $_GET["filepath"];
1577 echo "<a href='SampleMainPrograms.php?filepath=".$filepath."' target='page'>";?>sample main programs</a> for
1578 the new status. In particular note that (the new) <code>main61.cc</code>
1579 allows streamlined input and output in HepMC, like <code>main42.cc</code>
1580 (previously <code>main32.cc</code>), but additionally links to LHAPDF. </li>
1582 <li>The <code>examples/configure</code> script has new optional argument
1583 <code>--with-pythia8</code>. It can be used to set the new
1584 <code>PYTHIA8LOCATION</code> environment variable, which then is used
1585 in <code>examples/Makefile</code> to give the path to the PYTHIA
1586 library. Thereby it becomes possible to relocate (parts of) the
1587 <code>examples</code> directory and still obtain the correct path.
1588 Thanks to Mikhail Kirsanov.</li>
1590 <li>Polarization information has been included as a new
1591 <code>Particle</code> property, that can be set by
1592 <code>void pol(double polIn)</code> and obtained by
1593 <code>double pol()</code>. Default value is <code>9.</code>,
1594 in agreement with the Les Houches standard. Event listings have
1595 been expanded to optionally display this information. Currently
1596 polarization is not used internally.</li>
1598 <li>The matrix element merging machinery has been modified as follows.
1599 <br/>- Improved handling of the hard process, so that MadGraph5-produced
1600 LHE files do not produce problems (sometimes, the choices of MG4 on what
1601 to put into a LHEF have changed in MG5).
1602 <br/>- Improved handling of colour for easier handling of states with
1603 many quarks (the code has been tested for states with up to 5
1604 <i>q qbar</i> pairs and some gluons).
1605 <br/>- Improved checking which clusterings are allowed. Now, clusterings
1606 should immediately be rejected if they lead to unphysical states,
1607 without the need to explicitly construct these states. This was needed
1608 to get <i>t tbar</i> production, VBF and some simple SUSY processes
1609 running with reasonable generality.
1610 <br/>- Improved handling of incomplete histories. Now there is an
1611 additional switch allowing code to try to swap some colours when fewer
1612 clusterings than requested have been found.
1615 <li>Updates in the handling of graviton resonances in scenarios with
1617 <br/>- Now all G decays have correct angular distribution, which was not
1618 the case before for W/Z decays.
1619 <br/>- Added the possibility for G to only couple to longitudinal
1620 W/Z bosons, which affects both the width and angular distributions.
1621 <br/>- Added decays to Higgs pairs, <i>G -> hh</i>.
1624 <li>Bug fix in the <code>findJunctions()</code> function in
1625 <code>ProcessLevel.cc</code>. Changes introduced in version
1626 8.145 (to allow for junctions in baryon-number-violating
1627 processes) did not correctly handle the remapping of color
1628 tags that can be applied when adding beam remnants to events with
1629 multiparton interactions. A simpler and more stable algorithm is
1630 now applied for the simplest cases, with the more complex one only
1631 invoked for cases such as BNV, which are normally considered before
1632 remnants are added, hence avoiding this particular problem. Also some
1633 other changes in the handling of junction, including a safeguard to
1634 reject systems with three or more interconnected junctions.</li>
1636 <li>Bug fix and updates to the SLHA interface. Possibility of infinite
1637 loop during <code>ProcessLevel::initSLHA</code> corrected. Modifications
1638 to <code>SusyLesHouches</code> to allow interpretation of SLHA1 spectra
1639 with R-parity violation. Rather than reject spectra that do not conform
1640 fully to the SLHA2 standard for RPV, the interface will now first look
1641 for SLHA1 mixing matrices and attempt to translate those into SLHA2 ones
1642 if possible. In this case, warnings that the expected SLHA2 blocks were
1643 not found will be printed. It is up to the user to check that the
1644 derived SLHA2 information is correct. Corresponding additions to
1645 <code>SusyCouplings.cc</code> to extract mixing-matrix information
1646 from the relevant SLHA2 RPV blocks when RPV is switched on.</li>
1648 <li>Updated SLHA example <code>main24.cmnd</code> to use new example
1649 spectrum, <code>cmssm.spc</code>, corresponding to CMSSM point
1650 10.1.1, obtained with SOFTSUSY 3.3.0. Thanks to B. Allanach for
1651 providing the new spectrum file.</li>
1653 <li>A new <code>include/FastJet3.h</code> header file simplifies
1654 interfacing of FastJet to Pythia. For details see documentation in
1655 the file itself. Thanks to Gavin Salam for this contribution.</li>
1657 <li>The handling of diffraction has been made more flexible.
1658 Specifically the "total" Pomeron-proton cross section can now be made
1659 to depend on the mass of the diffractive system. This does not affect
1660 the diffractive cross section in pp collisions, which is set separately,
1661 but is used in the MPI machinery to affect the average number of
1662 interactions per Pomeron-proton collision. Furthermore, the allowed
1663 range for some parameters has been expanded. Thanks to Robert
1666 <li>New method <code>Pythia::forceTimeShower(...)</code> can be used to
1667 generate a single final-state cascade from a set of partons, without
1668 any knowledge of prior history. This is mainly intended for toy studies.
1669 The meaning of the <code>ProcessLevel:all</code> switch has been modified
1670 so that this parton-level function is available, but not any others
1674 <li>ATLAS tune A2 now included. Thanks to Deepak Kar for
1677 <li>Change in the handling of recoils of timelike showers in resonance
1678 decays, in cases of coloured resonances such as <i>t -> b W</i>. In
1679 the first step the <i>W</i> always acts as recoiler to the <i>b</i>,
1680 but in subsequent step previously the <i>W</i> remained as recoiler to
1681 one dipole, while now all QCD-radiating partons recoil against another
1682 coloured parton. The old behaviour could give a (small) unphysical spike
1683 of radition collinear with the colourless recoiler in the subsequent
1684 emissions (while the pattern of the first was and remains correct).
1685 The old behaviour can be recovered for checks, see
1686 <code>TimeShower:recoilToColoured</code>.
1687 Thanks to Yevgeny Kats for pointing out this issue (previously noted
1688 for Pythia 6 by several persons).
1691 <li>Bug fixes for <code>rootexamples/Makefile</code> and restoration
1692 of some deleted information in <code>rootexamples/README</code>.
1693 Thanks to Axel Naumann and Bernhard Meirose.</li>
1695 <li>Bug fix, so that displaced vertices are possible in resonance
1696 decay chains. Thanks to Daniel Blackburn and Andy Buckley for
1697 pointing this out.</li>
1699 <li>Bug fix for <code>Info</code> counter 2.</li>
1701 <li>Bug fix so that sextet quarks now are read in correctly from
1702 Les Houches Event files; previously the (anti)colours were set
1705 <li>Year updated to 2012 in copyright statements etc.</li>
1707 <li>Reformatting to reduce the number of code lines with more
1708 than 79 characters.</li>
1710 <li><code>Pythia::initSLHA()</code> moved from <code>public</code>
1711 to <code>private</code>.
1714 <li>Remove warning message when tau polarization is set by hand.</li>
1716 <li>Several minor changes to reduce the number of warnings issued
1717 by the clang compiler. The origin of some warnings remains unclear
1718 so those remain to track down (could also be compiler bugs; note that
1719 we discuss warnings, not errors). Thanks to Randy MacLeod for bringing
1722 <li>The worksheet has been updated to be in step with Pythia 8.160.</li>
1724 <li>Several other minor corrections in the code and documentation.</li>
1729 <li>8.162: 12 March 2012
1732 <li>A new option allows for several partons to share the recoil in
1733 final-state radiation, see<?php $filepath = $_GET["filepath"];
1734 echo "<a href='TimelikeShowers.php?filepath=".$filepath."' target='page'>";?>Timelike
1735 Showers</a>. It is mainly intended to be used in the context of
1736 matching to matrix elements, and so only to be used in the first
1737 few branchings.</li>
1739 <li>Several new processes for LED dijet production, see
1740 <?php $filepath = $_GET["filepath"];
1741 echo "<a href='ExtraDimensionalProcesses.php?filepath=".$filepath."' target='page'>";?>Extra Dimensions</a>.</li>
1743 <li>Small update of the <code>Sigma2ffbar2LEDllbar</code> and
1744 <code>Sigma2ffbar2LEDgammagamma</code> LED processes.</li>
1746 <li>New <code>Sigma2QCffbar2llbar</code>
1747 <?php $filepath = $_GET["filepath"];
1748 echo "<a href='CompositenessProcesses.php?filepath=".$filepath."' target='page'>";?>contact interaction</a>
1751 <li>Inclusion of a new method in the
1752 <?php $filepath = $_GET["filepath"];
1753 echo "<a href='MatrixElementMerging.php?filepath=".$filepath."' target='page'>";?>matrix-element merging</a>
1754 framework to influence the construction of histories, e.g. to already
1755 in the construction of histories disallow paths that fail the
1756 <i>2 -> 2</i> cuts.</li>
1758 <li>Further minor updates of the matrix-element merging code,
1759 mainly for improved clarity.</li>
1761 <li>Minor bug fix in the handling of beam and event information fed
1762 in from an <code>LHAup</code> instance.</li>
1764 <li>Minor bug fix for potential crashes from uninitialized variables
1765 for the merging machinery when merging is not used.</li>
1767 <li>Updated History class for matrix element merging,
1768 also avoiding some compiler warnings.</li>
1770 <li>Bug fixes in the handling of correlated mass choices in resonance
1771 decays, such as <i>H -> Z^*0 Z^*0</i>.</li>
1773 <li>Bug fix when the process-level execution is switched off,
1774 where <code>Info::isResolved()</code> could be called before its
1775 value was initialized. Thanks to Christian Pulvermacher
1776 for finding this.</li>
1778 <li>Corrected matrix-element expression for mass selection in
1779 <i>A^0 -> Z^*0 Z^*0</i> and <i>A^0 -> W^*+ W^*-</i>.</li>
1781 <li>SM Higgs mass updated to 125 GeV and default width and branching
1782 ratios modified accordingly. Minor technical improvements of width
1785 <li>The usage of nested classes has been removed from
1786 <code>SusyLesHouches</code>, since it could give compilation errors
1787 on some platforms. The new class names begin with <code>LH</code>
1788 and all classes have been put inside the <code>Pythia8</code>
1791 <li>Minor Makefile updates. Thanks to Mikhail Kirsanov.</li>
1793 <li>Minor changes to avoid some clang compiler warnings on the
1794 Mac OS X platform.</li>
1799 <li>8.163: 27 March 2012
1802 <li>New methods in the
1803 <?php $filepath = $_GET["filepath"];
1804 echo "<a href='EventInformation.php?filepath=".$filepath."' target='page'>";?><code>Info</code></a> class,
1805 <code>id1pdf()</code>, <code>id2pdf()</code>, <code>x1pdf()</code>
1806 and <code>x2pdf()</code>, to denote the partons for which parton
1807 distribution values have been defined. Previously this was assumed
1808 to agree with the incoming partons to the hard process, the same
1809 methods without the <code>pdf</code> qualifier. However, now the
1810 POWHEG approach offers a counterexample. Also the reading and
1811 handling of Les Houches (and other) events, and the interface
1812 to HepMC, has been modified accordingly.
1815 <li>The decay of Higgs and top resonances read in from Les Houches
1816 Event files is now performed with angular correlations as for
1817 internal processes. LHE files should normally contain all process-specific
1818 resonance decay chains and, if not, decays are made isotropic.
1819 The <i>H -> WW/ZZ -> f fbar f' fbar'</i> and
1820 <i>t -> b W -> b f fbar</i> correlations are process-independent,
1821 however, and thus can be handled internally. If part of the decay
1822 chain has already been set, e.g. <i>H -> WW/Z></i> or <i>t -> b W</i>,
1823 then the subsequent decays are still isotropic.</li>
1825 <li>Updated instructions how to link to HepMC,
1826 in <code>README.HepMC</code>.</li>
1828 <li>Bug fix in the turn-on of resolved diffraction for low
1829 CM energies. Thanks to Erwin Visser.</li>
1831 <li>Bug fix in the handling of string junctions at very high energies,
1832 caused by numerical errors. Thanks to Erwin Visser.</li>
1834 <li>Some other small changes, mainly aesthetics.</li>
1839 <li>8.165: 8 May 2012
1842 <li>The MBR (Minimum Bias Rockefeller) model for single, double and
1843 central diffraction [<a href="Bibliography.php" target="page">Cie12</a>] is included as new option
1844 <?php $filepath = $_GET["filepath"];
1845 echo "<a href='Diffraction.php?filepath=".$filepath."' target='page'>";?><code>Diffraction:PomFlux = 5</code></a>.
1846 It is specifically intended for <i>p p</i> and <i>pbar p</i>
1847 interactions, and is currently the only option that also supports
1848 central diffraction. Thus the basic machinery for Central Diffraction
1849 (a.k.a. Double Pomeron Exchange) has now been implemented.
1850 See <code>examples/main04.cc</code> for an example.
1851 Thanks to Robert Ciesielski for contributing the new code.
1854 <li>For a <i>tau</i> lepton in an external process, by default the
1855 SPINUP number in the Les Houches Accord now is interpreted as giving
1856 the <i>tau</i> helicity, and is used for its decay.</li>
1858 <li>A <i>tau</i> coming from a <i>W</i> now defaults to being purely
1859 lefthanded when neither of the existing matrix elements apply.</li>
1861 <li>Decay mode <i>t -> H+ b</i> included as an option.</li>
1863 <li>Four ATLAS tunes have been implemented as options for
1864 <code>Tune:pp</code>: A2-minbias-mstw2008lo, AU2-cteq6l1, AU2-mstw2008lo,
1865 and AU2-ct10. The new flag <code>Tune:preferLHAPDF</code> can be used
1866 to switch between the LHAPDF and the internal implementation of a
1867 PDF set, in cases where both are available.</li>
1869 <li>Reorder libraries in <code>examples/Makefile</code>, specifically
1870 move <code>LIBGZIP</code> so that it is properly linked when used.
1871 Thanks to Erik Schnetter.</li>
1873 <li>Minor modification so that LHAPDF can be used for PDFs in the hard
1874 process, with one of the built-in PDFs for the rest, even if LHAPDF is
1875 compiled so as to handle only one concurrent PDF set.</Li>
1877 <li>Bug fix, that <code>ParticleDecays:mixB = off</code> did not
1878 switch off <i>B0 - B0bar</i> and <i>Bs0 - Bs0bar</i> mixing.
1879 Thanks to James Catmore.</li>
1881 <li>Bug fix for the handling of gluon polarization of initial-state
1882 radiation, where an anisotropic azimuthal distribution was inadvertently
1883 generated in some <i>2 -> 1</i> processes. The update also includes
1884 always setting the second daughter zero for the two partons coming in to
1885 a hard <i>2 -> 1</i> process. Thanks to Antonio Policicchio.</li>
1887 <li>Bug fix, that the setting of the number of user hooks MPI steps did
1888 not use <code>UserHooks::canVetoMPIStep()</code> properly.</li>
1890 <li>Some other small changes, mainly documentation and aesthetics.</li>
1895 <li>8.170: 21 September 2012
1898 <li>Streamline default behaviour and options for choice of GeV or MeV
1899 for output to the HepMC event format, see
1900 <?php $filepath = $_GET["filepath"];
1901 echo "<a href='HepMCInterface.php?filepath=".$filepath."' target='page'>";?>HepMC Interface</a>.
1902 Also set the mass of HepMC particles explicitly, rather than having
1903 it calculated implicitly. Thanks to James Monk and Andy Buckley.</li>
1905 <li>The <i>tau</i> decay machinery has been further augmented with
1906 matrix elements and form factors for a variety of decay modes, such
1907 that all modes with a branching ratio above 0.1% are fully modelled.
1908 Several new classes and methods have been added to this end,
1909 Also, a <i>tau</i> pair coming from a <i>Z^0</i> decay is now
1910 handled by assuming the <i>Z^0</i> to be unpolarized when neither
1911 of the existing matrix elements apply. Taus coming from B baryons are
1912 handed as for B mesons.</li>
1914 <li>Flavour violating decays have been added to the squark, gluino,
1915 neutralino and chargino decay tables.</li>
1917 <li>Extend the <code>UserHooks::subEvent(...)</code> method so that it
1918 also works passably at the process level. Also new option for
1919 <code>UserHooks::omitResonanceDecays(...)</code>.</li>
1921 <li>New methods <code>UserHooks::canVetoPartonLevelEarly()</code>
1922 and <code>UserHooks::doVetoPartonLevelEarly( const Event&)</code>
1923 are intended to be used the same way as the existing ones without
1924 <code>Early</code> in their names, but allow veto right after
1925 the ISR + FSR + MPI evolution, before beam remnants are added and
1926 resonance decays are considered.</li>
1928 <li>Central diffraction now available for all
1929 <code><?php $filepath = $_GET["filepath"];
1930 echo "<a href='Diffraction.php?filepath=".$filepath."' target='page'>";?>PomFlux</a></code>
1931 options, not only the MBR model. This has been constructed by analogy
1932 with the respective assumptions made for single diffraction, but
1933 includes some arbitrariness. Therefore the cross section is left
1934 easily rescaleable and, for backwards compatibility with tunes
1935 that does not contain it, easily possible to switch off, see
1936 the <?php $filepath = $_GET["filepath"];
1937 echo "<a href='TotalCrossSections.php?filepath=".$filepath."' target='page'>";?>relevant section</a>.
1940 <li>Reading of ALPGEN parameter and event files has been added,
1941 see <?php $filepath = $_GET["filepath"];
1942 echo "<a href='AlpgenAndMLM.php?filepath=".$filepath."' target='page'>";?>ALPGEN and MLM Merging</a>.
1945 <li>MLM matching has been added, as a first step for ALPGEN events,
1946 see <?php $filepath = $_GET["filepath"];
1947 echo "<a href='AlpgenAndMLM.php?filepath=".$filepath."' target='page'>";?>ALPGEN and MLM Merging</a>.
1950 <li>The CKKW-L merging machinery has been upgraded in a number of respects.
1951 <br/>- More thorough treatment of <code>pp>bb~e+e-veve~</code> with
1952 additional <i>b</i>-jets.
1953 <br/>- Corrected hard <i>mu_r</i> and <i>mu_f</i> choices for
1954 dijet and promt photon.
1955 <br/>- More ways to define a hard process, e.g. with the LEPTONS and
1956 NEUTRINO tags. The merging will understand LHE files for mixed processes
1957 (e.g. <i>W+</i> and <i>W-</i> production together).
1958 <br/>- More merging scale definitions.
1959 <br/>- More freedom to generate all possible histories.
1960 <br/>- Internal check (and cut) on Les Houches events in
1961 <code>Pythia::mergeProcess</code> if merging scale value of the events
1962 is below the value given to Pythia by setting <code>Merging::TMS</code>.
1965 <li>It now works to have R-parity violating decays of R-hadrons,
1966 i.e. baryon number violation in a vertex displaced from the primary
1969 <li>The documentation of diffractive processes by the
1970 <code><?php $filepath = $_GET["filepath"];
1971 echo "<a href='EventInformation.php?filepath=".$filepath."' target='page'>";?>Info</a></code>
1972 methods has been expanded and corrected. This also include the
1973 <code>list()</code> method.</li>
1975 <li>Particle masses and widths have been updated to agree with the
1976 2012 RPP values [<a href="Bibliography.php" target="page">Ber12</a>]. Thanks to Piotr Zyla for data file
1977 and James Catmore for program to update the PYTHIA tables from this
1980 <li>New methods <code>jetAssignment</code> and <code>removeJet</code>
1981 added to the <code>SlowJet</code> class.</li>
1983 <li>Introduce angular correlation in decay chain
1984 <i>H -> gamma Z0 -> gamma f fbar</i>. Thanks to Tim Barklow and
1985 Michael Peskin.</li>
1987 <li>Introduce simple way to bias the selection of <i>2 -> 2</i>
1988 processes towards larger <i>pT</i> values, with a compensatingly
1989 decreasing event weight, see
1990 <?php $filepath = $_GET["filepath"];
1991 echo "<a href='PhaseSpaceCuts.php?filepath=".$filepath."' target='page'>";?>Phase Space Cuts</a>. Only offers a
1992 subset of the possibilities allowed by <code>UserHooks</code>,
1993 but simpler to use. The <code>main08.cc</code> program has been
1994 expanded to illustrate this possibility, and also expanded to
1995 include low-<i>pT</i> subsamples.</li>
1997 <li>The two remaining non-NLO tunes from [<a href="Bibliography.php" target="page">ATL12</a>] are now
2000 <li>The <code><?php $filepath = $_GET["filepath"];
2001 echo "<a href='EventInformation.php?filepath=".$filepath."' target='page'>";?>Info</a></code> methods
2002 <code>nTried, nSelected, nAccepted, sigmaGen</code> and
2003 <code>SigmaErr</code> now takes the code of an individual process
2004 as an optional argument.</li>
2006 <li>It is now possible to generate resonance decays, followed by
2007 showers and hadronization, without having them associated with any
2008 specific process. This is part of an expanded
2009 <?php $filepath = $_GET["filepath"];
2010 echo "<a href='HadronLevelStandalone.php?filepath=".$filepath."' target='page'>";?>Hadron-Level Standalone</a>
2011 machinery, as before triggered by <code>ProcessLevel = off</code>,
2012 but additionally requiring <code>Standalone:allowResDec = on</code>.
2013 Input can either be directly into the <code>event</code>
2014 event record or via a (simplified) Les Houches Event File.</li>
2016 <li>New <code>configure</code> script options <code>--installdir</code>,
2017 <code>--prefix</code> and <code>--datadir</code> can be used to set the
2018 location(s) to which the library, header and data directories
2019 will be copied by a <code>make install</code> subsequent to the
2020 <code>make</code>. Thanks to Mikhail Kirsanov.</li>
2022 <li>Fix charge in antiparticle name when particle read in from SLHA
2023 file. Thanks to Johan Alwall.</li>
2025 <li>Pointers now only compared with == and != (not e.g. > 0), to avoid
2026 warnings in gcc 4.7.</li>
2028 <li>New check that version number of the code matches that of the
2029 XML files. If not, no events can be generated. Thanks to James Monk
2030 for suggestion.</li>
2032 <li>New check that mother and daughter indices have been set to give
2033 a consistent event history. Can be switched on/off with the new
2034 <code>Check:history</code> flag.</li>
2036 <li>A new method <code>LHAup::newEventFile</code> has been added to
2037 switch to reading in events from another LHE file without having to
2038 reinitialize the whole class. Lower-level routines like
2039 <code>openFile</code> and <code>closeFile</code> have been added to
2040 handle correct order of operations also when an intermediate gzip
2041 decompression step is involved.</li>
2043 <li><code>LHAup::eventLHEF()</code> can now be called with an optional
2044 argument <code>false</code>, to make event files somewhat smaller by
2045 reducing the amount of blanks.</li>
2047 <li>A new mode <code>Beams:nSkipLHEFatInit</code> introduced to
2048 skip ahead the first few events in a Les Houches Event File (cf. the
2049 <code>LHAup::skipEvent(nSkip)</code> method).</li>
2051 <li>Introduce a new pair of user hooks that can be used to reject
2052 the sequence of hard-process resonance decays, without rejecting
2053 the production of the primary resonances.</li>
2055 <li>The possibility of separate multiplicative prefactors to the
2056 renormalization and factorization default <i>pT^2</i> scale has been
2057 introduced for both timelike and spacelike showers.</li>
2059 <li>Bug fixes in history information for R-hadron production, which also
2060 fixes HepMC conversion in this case.</li>
2062 <li>Bug corrected in <code>SigmaSusy.cc</code>, for chargino+neutralino
2063 production. Indexing error for incoming quark states in the process
2064 <code>Sigma2qqbar2charchi0</code>, resulted in incorrect CKM factors.</li>
2066 <li>Corrected a bug in <code>SusyLesHouches.cc</code>, for NMSSM spectra.
2067 The unitarity check on the neutralino mixing matrix was faulty, leading
2068 to erroneous messages about unitarity violations and SUSY being switched
2071 <li>Bug fixes in the handling of resolved and unresolved diffractive events.
2072 Thanks to Robert Ciesielski for debug.</li>
2074 <li>Do not set up FSR dipoles for <i>2 -> 1</i> processes.</li>
2076 <li>Check that some channel open for resonance decays. Also further
2077 check whether resonance decay treatment should be invoked.</li>
2079 <li>Bug fix in reading of particle names from SLHA input.</li>
2081 <li>Change mass, width and decay mode(s) of D*_s(10431). Thanks to
2084 <li>Bug fix in leptoquark production (lepton sign in
2085 <i>q g -> LQ l</i>).</li>
2087 <li>New argument added to <code>SpaceShower::reassignBeamPtrs</code>
2088 for diffractive event processing, as already available for
2089 <code>TimeShower</code>.</li>
2091 <li>Do not write warnings in <code>SpaceShower</code> for weights
2092 above unity if the evolution scale is below 1 GeV^2.</li>
2094 <li>Add default values for member variables in some constructors,
2095 and some related changes for <code>AlphaStrong</code> code.</li>
2097 <li>Warn if negative-energy parton in hadronization.</li>
2099 <li>The MPI <i>pT</i> values assumed in the beam remnant setting
2100 of primordial <i>kT</i> and colour reconnection probability were
2101 incorrect for diffractive events.</li>
2103 <li>The arrays with MPI information were not reset when parton or
2104 hadron level fails and a new try is made. Only affected few events.</li>
2106 <li>MPI statistics can not yet be accumulated for diffractive events,
2107 and therefore the relevant routine is no longer called.</li>
2109 <li>Bug fix in the double parton scattering suppression from
2110 energy-momentum conservation.</li>
2112 <li>Outgoing proton masses were not set in the event record for
2113 elastic scattering (but kinematics handling was correct).</li>
2115 <li>Bug fixes in the identification and documentation of junctions,
2116 previously leading to some unnecessarily rejected events. Also
2117 other improvements leading to fewer errors.</li>
2119 <li>Slightly increased values for FragmentationSystems:mJoin and
2120 StringFragmentation::FACSTOPMASS to reduce failure rate, without
2121 noticeably affecting event properties.</li>
2123 <li>The Les Houches cross section error is now taken into account
2124 in the final Pythia error for strategies +-3. New methods
2125 <code>LHAup::xSecSum()</code> and <code>LHAup::xErrSum()</code>
2126 provide the necessary information.
2129 <li>When a tau pair comes from a massless photon, in dipole shower
2130 evolution, for the decay description the mother photon is reassigned
2131 to have the sum of the tau momenta.</li>
2133 <li>Minor change in initialization sequence for user hooks,
2134 to allow for more flexibility.</li>
2136 <li>Do not print warnings when multiparton interaction weights are
2137 only slightly above unity.</li>
2139 <li>Do not write warnings for three known particles that are so close
2140 to threshold that widths are switched off to avoid trouble.</li>
2142 <li>Some minor typographical changes.</li>
2151 <!-- Copyright (C) 2012 Torbjorn Sjostrand -->