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1<chapter name="Update History">
2
3<h2>Update History</h2>
4
5These update notes describe major updates relative to the baseline
6PYTHIA 8.100 version. However, they are less extensive than the
7corresponding update notes for PYTHIA 6. On the other hand,
8whereas the PYTHIA 6 manual is a static document, the PYTHIA 8
9html/php pages are kept up to date for each subversion.
10
11<br/><br/>
12<b>Important note:</b>version 8.160 does introduce some elements of
13backwards incompatibility. Specifically, "multiple interactions",
14abbreviated MI, haa been renamed "multiparton interactions", MPI.
15This affects many parts of the code and documentation. Also some
16features are deprecated, although remaining until the end of the
178.1xx version series.
18
19
20<h3>Main news by version</h3>
21
22<ul>
23
24<li>8.105: 24 February 2008
25<ul>
26
27<li>New option to initialize with arbitrary beam directions<br/>
28<code>pythia.init( idA, idB, pxA, pyA, pzA, pxB, pyB, pzB)</code></li>
29
30<li>Added capability to set <aloc href="BeamParameters">beam energy spread
31and beam vertex</aloc>.
32<br/>
33<b>Warning:</b> as a consequence, the old <code>Beams</code> group of
34settings has been moved to <code>BeamRemnants</code>, and
35<code>Beams</code> is now instead used for machine beam parameters.
36Therefore also some <code>Main</code> settings of this character have been
37regrouped, as follows:
38<table cellspacing="5">
39<tr> <td>8.100 setting  </td> <td>has been moved to </td> </tr>
40<tr> <td><code>Main:idA          </code></td>
41     <td><code>Beams:idA         </code></td> </tr>
42<tr> <td><code>Main:idB          </code></td>
43     <td><code>Beams:idB         </code></td> </tr>
44<tr> <td><code>Main:inCMframe    </code></td>
45     <td>(<code>Beams:frameType</code>) </td> </tr>
46<tr> <td><code>Main:eCM          </code></td>
47     <td><code>Beams:eCM         </code></td> </tr>
48<tr> <td><code>Main:eA           </code></td>
49     <td><code>Beams:eA          </code></td> </tr>
50<tr> <td><code>Main:eB           </code></td>
51     <td><code>Beams:eB          </code></td> </tr>
52<tr> <td><code>Main:LHEF         </code></td>
53     <td><code>Beams:LHEF        </code></td> </tr>
54</table></li>
55
56<li>The <code>forceHadronLevel()</code> method introduced for standalone
57hadronization.</li>
58
59<li><code>main15.cc</code> illustrated how either full hadronization or
60only decays of some particles can be looped over for the rest of the
61event retained.</li>
62
63<li>The <code>LHAevnt</code> and <code>LHAinit</code> classes have been
64joined into a new <code>LHAup</code> one, with new options that allow
65the writing of a Les Houches Event File.</li>
66
67<li>The <code>SusyLesHouches</code> class updated to handle
68SLHA version 2.</li>
69
70<li>Updated HepMC conversion routine.</li>
71
72<li>The static <code>ErrorMsg</code> class has been removed and
73its functionality moved into the non-static <code>Info</code> class,
74in the renamed Info file.</li>
75
76<li>Further reduction of the use of static, with related code changes.
77This should allow to have several almost independent <code>Pythia</code> 
78instances. Some static classes still remain, however, notably for
79random number generation and particle properties.</li>
80
81<li>Limited capability to use two different <code>Pythia</code> instances
82for signal + pileup event generation, see <code>main19.cc</code> for an
83example.</li> 
84
85<li>In the <code>Event</code> class the <code>=</code> and
86<code>=+</code> methods have been overloaded to allow the copying
87or appending of event records. Illustrated in <code>main19.cc</code>.</li>
88
89<li>The html and php page formatting improved with
90cascading style sheets.</li>
91
92<li>Several minor improvements and new options, including updated configure
93scripts.</li>
94
95</ul>
96</li>
97
98<li>8.108: 1 May 2008
99<ul>
100
101<li>Correction in the event record, so that the beam particles in line
1021 and 2 do not have any mother according to the <code>motherList</code>
103method. Previously the "system" entry in line 0 was counted as their
104mother, which gave rise to an unexpected extra vertex in the conversion
105to the HepMC format.</li>
106
107<li>Support for HepMC version 1 is removed, to simplify the code and
108reflect the evolution of the field.</li>
109
110<li>Status codes are stored in HepMC only as 1 for existing and 2 for
111decayed or fragmented particles (whereas previously the original PYTHIA
112codes were used for the latter).</li>
113
114<li>Parton densities are stored in HepMC as <ei>xf(x,Q^2)</ei> 
115rather than the <ei>f(x,Q^2)</ei> used in (some) previous versions.</li>
116
117<li>The SusyLesHouches class has ben updated so that reading is fully
118compatible with the SLHA2 standard. </li>
119
120<li>Improved handling of the Higgs width, relevant for massive and thereby
121broad resonance shapes.</li>
122
123<li>The matrix elements for neutralino pair production have now been
124completed and checked.</li>
125
126<li>Ensure that <ei>alpha_strong</ei> does not blow up, by introducing
127a minimal scale somewhat above <ei>Lambda_3</ei> (roughly where
128<ei>alpha_strong = 10</ei>).</li>
129
130<li>New methods <code>isValence1()</code> and <code>isValence2()</code> 
131in the <code>Info</code> class.</li>
132
133<li>Protection against division by zero in calculation of decay vertex
134(for zero-mass gluons with zero lifetime, where there should be no
135displacement).</li>
136
137<li>A new compilation option <code>-Wshadow</code> is introduced and
138code is rewritten at all places where this option gave warnings.</li>
139
140<li>Minor library correction to allow compilation with gcc 4.3.0.</li>
141
142</ul>
143</li>
144
145<li>8.114: 22 October 2008
146<ul>
147
148<li>New rescattering description operational (but still experimental)
149for the case that FSR is not interleaved, but saved until after MPI,
150ISR and beam remnants have been handled. This involves much new code
151in several classes.</li>
152
153<li>A new class <code>PartonSystems</code> is introduced to
154keep track of which partons in the event record belong to which
155subcollision system, plus some further information on each subsystem.
156It takes over functionality previously found as part of the
157<code>Event</code> class, but leaves room for future growth.</li>
158
159<li>Add optional model, wherein an increased <ei>pT0</ei> turnoff scale
160for MPI and ISR is used for above-average active events, i.e. events that
161already have several MPI's or ISR emissions.</li>
162
163<li>Freeze GRV 94L distribution at small <ei>Q^2</ei> to avoid blowup.</li>
164
165<li>The <code>pythia.readFile(...)</code> method can now alternatively take
166an <code>istream</code> as argument instead of a <code>filename</code>.</li>
167
168<li>Minor bug correction in <code>PartonLevel.cc</code>; the bug could
169(rarely) give a segmentation fault.</li>
170
171</ul>
172</li>
173
174<li>8.120: 10 March 2009
175<ul>
176
177<li>New rescattering description further developed, but not yet
178recommended for normal usage.</li>
179
180<li>Include new processes for Large Extra Dimensions and Unparticles,
181contributed by Stefan Ask. New test program <code>main28.cc</code> 
182illustrates.</li>
183
184<li>Include further SUSY processes: neutralino-chargino and
185chargino-chargino pairs. The processes should be valid also
186in the case of non-minimal flavour violation and/or CP violation.
187Expanded machinery to keep track of SUSY parameters.</li>
188
189<li>Include backwards evolution of incoming photon as part of the
190<code>SpaceShower</code> initial-state radiation description. This
191allows you to simulate hard collisions where one of the incoming
192partons is a photon. New test program <code>main43.cc</code> 
193illustrates.</li>
194
195<li>Allow separate mass and transverse momentum cuts when two hard
196subprocesses are generated in the same event.</li>
197
198<li>The default value for the border between short- and long-lived
199paticles has been changed from 1 mm to 10 mm, to better conform with
200LHC standards, see  <aloc href="ParticleDecays">here</aloc>.
201The default is still to let all unstable particles decay.</li>
202
203<li>New ISR matrix-element correction to <ei>f -&gt; f gamma</ei> 
204in single <ei>W</ei> production.</li>
205
206<li>New method <code>Event::statusHepMC</code> returns the status
207code according to the HepMC conventions agreed in February 2009.
208The interface to HepMC now writes out status according to this
209convention.</li>
210
211<li>Add capability to link to FastJet, with expanded configure script
212and Makefile, and with <code>main61.cc</code> as new example.</li>
213
214<li>Update of <code>Makefile.msc</code>, with added support for latest
215Visual C++ Express edition and use of regexp to check nmake version.</li>
216
217<li>Update of <code>LHAFortran.h</code> and
218<code>Pythia6Interface.h</code>, to make the interface to Fortran
219routines work also under Windows. (Thanks to Anton Karneyeu.)
220
221<li>Updated and expanded worksheet.</li>
222
223<li>The manual pages in the <code>xmldoc</code> directory, and thereby
224also those of the <code>htmldoc</code> and <code>phpdoc</code>
225directories, have been significantly updated and expanded. In particular,
226in many places the class of each method is explicitly shown, as well as
227the type of the return value and of the arguments. This upgrade is not
228yet completed, but already covers the more relevant sections. </li>
229
230<li>The unary minus operator in the <code>Vec4()</code> returns a
231reference to a four-vector with all components negated, but leaves
232the original four-vector unchanged. Previously the four-vector itself
233was flipped.</li>
234
235<li>The <code>pPlus()</code> and <code>pMinus()</code> methods of a
236four-vector and an event-record particle are renamed <code>pPos()</code> 
237and <code>pNeg()</code>, respectively.</li>
238
239<li>Include a further loop in <code>ProcessLevel</code>, so that a new
240process is generated in case of failures of a less severe nature.</li>
241
242<li>Introduce warning message for unexpected <code>meMode</code> in
243<code>ResonanceWidths</code>.</li>
244
245<li>Les Houches event reading framework has been rearranged for
246more flexibility. Some bugs corrected. Specifically, when scale
247is not set (<code>scale = -1.</code> in the Les Houches standard),
248PYTHIA did not attempt to set this scale itself, which typically
249lead to there not being any ISR or FSR. Now the
250<aloc href="CouplingsAndScales">rules for normal
2511-, 2- and 3-body final states</aloc> are applied, with a trivial
252extension of the 3-body rules for higher multiplicities.</li>
253
254<li>Correct bug in the handling of parton densities, whereby it was
255not possible to switch to a new set, once a first initialization
256had been done.</li>
257
258<li>Correct bugs when several <code>Pythia::init</code> initialization
259calls are made in the same run, specifically in the case that pointers
260to external processes have been handed in.
261
262<li>Changes in <code>main03.cmnd</code> and <code>main04.cmnd</code> 
263so that some nonstandard options are commented ou rather than active.
264Related comments inserted also in some other <code>.cmnd</code> files,
265but there without any change in program execution.</li>
266
267<li>A few further minor bug fixes.</li>
268
269<li>Update year to 2009.</li>
270
271</ul>
272</li>
273
274<li>8.125: 16 June 2009
275<ul>
276
277<li>Hadronization and timlike-shower parameter default values updated
278according to a tune to LEP1 data by Hendrik Hoeth, using the
279Rivet + Professor framework.</li>
280
281<li>Many further SUSY production processes. SLHA readin expanded to cover
282also masses and decay modes. Example <code>main22.cc</code> updated, while
283<code>main33.cc</code> now superfluous and removed. </li>
284
285<li>Also further processes for extra dimensions.</li>
286
287<li>Stefan Ask joins as coauthor.</li>
288
289<li>The <code>TimeShower::shower(...)</code> method has gained
290a new argument, that forces the shower evolution to stop after
291a given number of branchings. A new method
292<code>TimeShower::pTLastInShower()</code> permits the last evolution
293<ei>pT</ei> to be read out. These extensions can be useful
294for matching studies.
295</li>
296
297<li>New optional argument <code>isInterleaved</code> added to
298<code>TimeShower::branch(...)</code>. Is false by default, but
299true when called from the parton level for interleaved evolution
300of several parton systems, optionally also with ISR and MPI.</li>
301
302<li>New methods <code>UserHooks::canSetResonanceScale()</code>
303and <code>UserHooks:scaleResonance(...)</code> allows an optional
304user choice of the maximum shower scale in resonance decays.</li>
305
306<li>A new method <code>SpaceShower::doRestart()</code> has been
307added, to help distinguish cases when a
308<code>SpaceShower::branch(...)</code> failure forces a complete
309restart of the evolution from ones where only the intended
310current branching has been vetoed.
311
312<li>When multiparton interactions are initialized, it is now
313possible to reduce both <ei>pT0</ei> and <ei>pTmin</ei>
314if necessary to find a valid solution where
315<ei>sigma_jet &gt; sigma_nondiffractive</ei>. Previously
316only the former would be reduced, which could lead to
317infinite loops if too large a <ei>pTmin</ei> was used.
318Thanks to Sami Kama for pointing out the problem.
319</li>
320
321<li>The rescattering machinery is now essentially completed, and can
322be used also by others than the authors. For now, however, it can only
323be recommended for dedicated studies, not e.g. for generic tunes.
324</li>
325
326<li>Timelike and spacelike showers, and beam remnant handling,
327are modified to handle rescattering partons. Specifically, a new machinery
328is introduced to trace the recoils from the combination of rescattering
329with showers and primordial <ei>kT</ei>. Can assign space- or timelike
330virtualities to intermediate particles to have energy and momentum
331conserved locally. This affects the <code>PartonLevel</code>,
332<code>MultipartonInteractions</code>, <code>TimeShower</code>,
333<code>SpaceShowe</code>r and <code>BeamRemnants</code> classes.
334Further details to appear in the upcoming article on rescattering.
335(Another change is a reversal to pre-8.114 order for non-interleaved FSR,
336wherein also FSR is treated before beam remnants are attached.)
337</li>
338
339<li>Four new status codes introduced, as part of the rescattering
340description:
341<br/>45 : incoming rescattered parton, with changed kinematics owing
342to ISR in the mother system (cf. status 34);
343<br/>46 : incoming copy of recoiler when this is a rescattered parton
344(cf. status 42);
345<br/>54 : copy of a recoiler, when in the initial state of a different
346system from the radiator;
347<br/>55 : copy of a recoiler, when in the final state of a different
348system from the radiator.
349</li>
350
351<li>New method <code>Info::tooLowPTmin()</code> can tell whether the
352<ei>pTmin</ei> scales for showers or multiparton interactions are too low.
353</li>
354
355<li>Pion beams allowed, both <ei>pi^+</ei>, <ei>pi^-</ei> and
356<ei>pi^0</ei>. New machinery for the latter, where the valence
357flavour content is chosen to be either <ei>d dbar</ei> or
358<ei>u ubar</ei> for each new event. One internal pion PDF
359implemented, with others from LHAPDF.</li>
360
361<li>Treatment of Pomeron-proton collisions begun.</li>
362
363<li>Phase-space handling of hard processes and multiparton interactions
364slightly expanded to better allow for harder PDF's than proton ones,
365e.g. for Pomerons.</li>
366
367<li>The program documentation has been expanded with an
368alphabetical index of all methods that are described on the
369webpages, see the <aloc href="ProgramMethods">Program Methods</aloc> 
370page. Also other sections of the documentation have been
371updated and expanded, including the worksheet.</li>
372
373<li>Several <code>list</code> methods have been made
374<code>const</code>. For the listing of events two new methods
375have been added, <code>Event::list()</code> and
376<code>Event::list(bool showScaleAndVertex,
377bool showMothersAndDaughters = false)</code>,
378that correspond to special cases of the general method.</li>
379
380<li>A new method <code>Pythia::LHAeventSkip(int nSkip)</code>
381permits a skip-ahead of the reading of external Les Houches
382Events, without the necessity to generate the intervening
383<code>nSkip</code> events in full. Makes use of the new
384<code>LHAup::skipEvent(int nSkip)</code> method to perform
385the operations. Mainly intended for debug purposes.
386
387<li>The <code>ClusterJet</code> jet finder now saves the last
388five clustering scales. Also a minor bug fix. Thanks to Nils
389Lavesson for this contribution.</li>
390
391<li>The <code>Particle::m2()</code> method now returns a negative
392number when the stored mass <ei>m</ei> is negative, as used to
393indicate spacelike virtualities. Also the
394<code>Particle::eCalc()</code>, <code>Particle::mT()</code> and
395<code>Particle::mT2()</code> methods have been modified.
396</li>
397
398<li>The <code>&lt;&lt;</code> method to print our a four-vector has
399been expanded with a fifth number, the invariant length, with a minus
400sign for spacelike vectors, and provided within brackets to allow
401a simple visual distinction.</li>
402
403<li>New methods <code>Rndm::dumpState(string fileName)</code> and
404<code>Rndm::readState(string fileName)</code> allows to write or
405read the state of the random number generator to or from a binary file.
406</li>
407
408<li>New method <code>double GammaReal(double x)</code> returns the
409value of the <ei>Gamma</ei> function for arbitrary real argument.
410Some cross sections for extra-dimensional processes rewritten to
411make use of it.
412</li>
413
414<li>New example program <code>main29.cc</code> shows how
415to set up a fictitious process of a heavy system decaying
416to two particles or partons, with decays traced to stable
417particles, as relevant for astroparticle applications.</li>
418
419<li>Main programs that illustrate the HepMC interface have
420been updated to use version 2.04, including units and excluding
421deprecated output formats.</li>
422
423<li>The <code>main32.cc</code> example extended also to handle
424Les Houches Event Files.</li>
425
426<li>The Makefile has been modified so that "make clean" only
427removes the current compilation and library fles, while
428"make distclean" gives a more extensive reset and cleanup.
429Thanks to Nils Lavesson for this contribution. Some other
430minor Makefile corrections.</li>
431
432<li>Several main programs that use the
433<code>Main:timesToShow</code> mode have been corrected so as
434not to crash if this is set to zero. Also some other cosmetics
435changes in main programs that do not affect the running.</li>
436
437<li>Bug correction, in that previously a veto with user hooks
438was not propagated from parton showers inside resonance decays.
439</li>
440
441<li>Minor bug fix in <code>TimeShower</code> for kinematics with
442unequal beam-particle masses.</li>
443
444<li>Bug fix so that <code>PartonLevel:MPI = off</code> also works for
445minimum-bias events.</li>
446
447<li>Minor bug fix in the impact-parameter selection of multiparton
448interactions. Thanks to Sami Kama for pointing it out.</li>
449
450<li>String fragmentation for junction topology protected against
451numerical instability in boost.</li>
452
453<li>Bug correction in the handling of particle decays to partons,
454where the scale of the partons was set before the partons had been
455added to some arrays, leading to indexation out of bounds.
456Thanks to Vladislav Burylov for discovering this bug.
457</li>
458
459<li>Bug correction in the handling of particles with inhibited decay,
460where the decay vertex would be too far displaced, which could lead to
461infinite loop. Thanks to Sami Kama for debugging this. </li>
462
463<li>Check to avoid infinite loop in matrix-element handling of
464two-body decays.</li>
465
466<li>Bug correction to avoid infinite loops in Dalitz decay treatment.
467Some changes in the decay handling logic to allow a new try when the
468decay of a particle fails.</li>
469
470<li>Minor correction, so the pointer to the <code>Info</code> class
471is set also for user-written classes derived from <code>LHAup</code>.
472</li>
473
474<li>Correction for typo in the matrix element of the
475<code>Sigma3ff2HchgchgfftWW</code> class, for doubly charged Higgs
476production. Thanks to Merlin Kole for spotting it.</li>
477
478<li>Updated colour bookkeeping in junction-antijunction annihilation
479avoids later problems in <code>Pythia::check()</code>. </li>
480
481<li>Minor updates of the <code>Makefile.msc</code> file to work with
482Visual Studio 2008. Thanks to David Bailey for these modifications.</li>
483
484<li>Ensure that <code>nInit</code> in the <code>BeamParticle</code>
485class is set also for unresolved lepton beams.</li>
486
487<li>The <code>VetoEvolution</code> class, derived from
488<code>UserHooks</code>, is obsolete and has been removed.</li>
489
490</ul>
491</li>
492
493<li>8.130: 15 September 2009
494<ul>
495
496<li>New machinery that allows multiparton interactions inside diffractive
497systems. Also new optional Pomeron flux factors and Pomeron PDFs.
498New page on <aloc href="Diffraction">diffraction</aloc> added, where
499further details are collected. Still not tuned, so to be used with
500caution.</li>
501
502<li>Make Peter Skands' "Tune 1" parameters for ISR and MPI default.
503The older simpler tune is still available as an option, see
504<code><aloc href="Tunes">Tune:pp</aloc></code>.
505</li>
506
507<li>New possible choices for a second hard process: charmonium,
508bottomonium, top pair and single top.</li>
509
510<li>New code for pair production of generic colour-triplet scalar,
511fermion or vector. Largely written by Johan Bijnens, partly recycling
512existing code.</li>
513
514<li>Add user hooks possibility to veto event after a given number
515of multiparton interactions.</li>
516
517<li>Add instructions how PYTHIA 8 can be used from inside ROOT.
518Thanks to Andreas Morsch for providing the text and Rene Brun
519for a simple example.</li>
520
521<li>The <code>main21.cc</code> example extended with an option
522for a single-particle gun.</li>
523
524<li>Improvements and bug fixes in rescattering framework.</li>
525
526<li>New method <code>Hist::table(string fileName)</code> provides a
527more direct way to print a two-column table of histogram contents
528into a file than the current <code>Hist::table(ostream& os = cout)</code>.
529 </li>
530
531<li>Modify reading of external files so that a line only consisting of
532control characters counts as empty, the same way as a line only consisting
533of blanks already did. This includes carriage return, tabs and a few more,
534the ones represented by <code>\n \t \v \b \r \f \a</code>. Applies to
535Les Houches Event files, settings files and particle data files. </li>
536
537<li>Fix it so that the read-in of a Les Houches Event File for the
538hardest process can be combined with the faciliy to select a specified
539second hard process.</li>
540
541<li>New empty base class method <code>LHAup::fileFound()</code> 
542allows the derived class <code>LHAupLHEF</code> to signal more
543clearly that a failed initialization is caused by a failure to open
544the desired file. </li>
545
546<li>Check that a pointer to an <code>LHAup</code> object has been set
547in <code>Pythia::LHAeventList()</code> and
548<code>Pythia::LHAeventSkip(...)</code> calls.</li>
549
550<li>Updated configure and Makefile, e.g. to build shared libraries
551on Mac OS X.</li>
552
553<li>The options with a direct link to hard-process generation
554in PYTHIA 6 has been removed. It is hardly ever used but
555complicates the build structure. (Owing to its usefulness for some
556debug work, it was reinstated in a limited form in version 8.135.
557Thus <code>main51.cc</code> now contains the complete interface,
558previously in separate files, and commented-out lines in
559<code>examples/Makefile</code> suggest how PYTHIA 6 could be linked.)
560</li>
561
562<li>New argument to <code>Info::errorMsg(...)</code> allows to
563show all error messages of a specific kind rather than only the
564first one, e.g. for initialization.</li>
565
566<li>Correction in decay table of righthanded Majorana neutrinos.
567Thanks to Arnaud Ferrari and Vladimir Savinov.</li>
568
569<li>Correction in expressions in the manual for <ei>H^+-</ei> couplings
570to an <ei>h^0</ei>, <ei>H^0</ei> or <ei>A^0</ei> and a <ei>W^+-</ei>.
571Thanks to Rikard Enberg.</li>
572
573<li>Fix for accessing uninitialized memory, caused by accessing the
574daughters of the incoming beams before these daughters actually existed.
575Thanks to David Bailey and Sami Kama.
576</li>
577
578<li>Uninitialized photon PDF inside the proton could give crazy results
579for processes with incoming photons. Thanks to Adam Davison.</li>
580
581<li>Bug fix such that finite lifetimes can be set also for particles
582produced in the hard process. To exemplify, the bug affected
583<ei>tau</ei> leptons produced in <ei>Z^0</ei> and <ei>W^+-</ei> 
584decays. Thanks to Troels Petersen.</li>
585
586<li>Bug fix in <code>TimeShower</code>, that <code>beamOffset</code>
587could remain uninitialized. Thanks to Sami Kama.</li>
588
589<li>Minor correction to resonance decays: fail if the allowed mass
590range of a Breit-Wigner resonance is a small fraction of the total
591area under the resonance curve.</li>
592
593<li>Correction when all three valence quarks were kicked out from a
594proton and could give false messages that beam momentum had been
595used up.</li>
596
597<li>Clarify status codes needed for hadron-level standalone runs in
598order to avoid error messages, and modify the <code>main21.cc</code>
599example accordingly. </li>
600
601<li>Minor corrections in the processes for extra dimensions.</li>
602
603<li>Some other minor additions to existing facilities
604and minor bug fixes.</li>
605
606</ul>
607</li>
608
609<li>8.135: 10 January 2010
610<ul>
611
612<li>All usage of static member methods inside Pythia8 has now been
613eliminated. This simplifies for you to have several simultaneous
614<code>Pythia</code> instances that are run with different conditions.
615The three main classes affected by this are the <code>Settings</code> 
616and <code>ParticleData</code> databases and the <code>Rndm</code> 
617random-number generator. You can no longer address the methods of these
618classes directly, but have to address them via the <code>settings</code>,
619<code>particleData</code> and <code>rndm</code> instances in the
620respective <code>Pythia</code> object. Also some other smaller pieces
621of code are affected, e.g. Standard Model and SUSY couplings
622(the latter in new files).
623<note>Note 1</note>: The documentation has been updated accordingly
624on these webpages, but the "A Brief Introduction to PYTHIA 8.1"
625still refers to the old behaviour of version 8.100.
626<note>Note 2</note>: the interface to the external LHAPDF library remains
627static, since LHAPDF is written in Fortran and thus by definition
628static.
629<note>Note 3:</note> if you want to have momentum smearing in
630<code>CellJet</code> you now need to send in a pointer to a
631random-number generator. 
632</li>
633
634<li>Ten new proton PDF sets are made available internally:
635MRST LO* (2007), MRST LO** (2008), MSTW 2008 LO (central member),
636MSTW 2008 NLO (central member), CTEQ6L, CTEQ6L1, CTEQ6.6 (NLO,
637central member), CT09MC1, CT09MC2, and CT09MCS, see
638<aloc href="PDFSelection">PDF Selection</aloc>. The Pomeron PDF data
639files have been renamed for consistency. Thanks to Tomas Kasemets
640for help with this <ref>Kas10</ref>.
641</li>
642
643<li>New parameters <code>TimeShower:pTmaxFudgeMPI</code> and
644<code>SpaceShower:pTmaxFudgeMPI</code> introduced, to give the same
645functionality for multiparton interactions that
646<code>TimeShower:pTmaxFudge</code> and <code>SpaceShower:pTmaxFudge</code> 
647do for the hardest.</li>
648
649<li>A few extensions of the <code>UserHooks</code> framework.
650New methods <code>UserHooks:canVetoISREmission()</code> and
651<code>UserHooks::doVetoISREmission(...)</code> allows the latest
652initial-state emission to be studied before being finalized,
653with the possibility to veto it.
654Similarly <code>Userhooks:canVetoFSREmission()</code> and
655<code>UserHooks::doVetoFSREmission(...)</code> can be used to
656veto the latest final-state emission.</li>
657
658<li>A number of loop counters have been introduced in the
659<code>Info</code> class, that offers some further information on
660the progress of the event generation, for use e.g. in conjunction
661with the <code>UserHooks</code> facility.</li>
662
663<li>The <code>Pythia::initTunes(...)</code> method is made public, so that
664it can be called before the normal call from <code>Pythia::init(...)</code>.
665That way it is possible to start out from a given tune and change a few
666of the parameters.
667</li>
668
669<li>Bug corrected in <code>LHAFortran.h</code> for hard-process input
670from Fortran commonblock. This did not work properly when the input
671was used in combination with a second hard process generated internally.
672Thanks to Mikhail Kirsanov and Roberto Chierici.
673
674<li>Insertion of missing initialization of <code>isInit</code> in the
675<code>Settings</code> and <code>ParticleData</code> constructors, and
676<code>nInit</code> for <code>BeamParticle</code>.
677Thanks to Leif L&ouml;nnblad.</li>
678
679<li>Updated <code>Makefile.msc</code> for Windows users.</li>
680
681<li>Fix of some non-optimal use of booleans, that give warnings on
682a Windows compiler. Thanks to Anton Karneyeu.</li>
683
684<li>New options for the <aloc href="SUSYLesHouchesAccord">
685SUSY Les Houches Accord</aloc> such that, by default,
686particle and decay data are not overwritten for known Standard Model
687particles (including <ei>Z^0</ei>, <ei>W^+-</ei> and <ei>t</ei>,
688but excluding the Higgs).</li>
689
690<li>Bug fix in <code>SusyLesHouches</code>, where the reading of SLHA
691information embedded in an LHEF would not stop at the end of the header
692section.</li> 
693 
694<li>Bug correction for undefined secondary widths where decay products
695together are heavier than the mother. Also unit default secondary width
696values in the <code>DecayChannel</code> constructor.</li>
697 
698<li>Documentation updated, including change of current year to 2010.</li>
699
700</ul>
701</li>
702
703<li>8.140: 16 July 2010
704<ul>
705
706<li>Four new draft <aloc href="Tunes">tunes</aloc> available.</li>
707
708<li>Introduction of a new scenario for production of Hidden-Valley
709particles, and interleaved showering in the QCD and HV sectors, see
710the new <aloc href="HiddenValleyProcesses">Hidden Valleys</aloc> 
711description. A longer physics writeup is available <ref>Car10</ref>.
712</li>
713
714<li>Implementation of <ei>2 -> 3</ei> phase space selection intended
715for QCD processes with massless partons. A new set of matching
716<aloc href="PhaseSpaceCuts">phase space cut parameters</aloc>.
717The <aloc href="QCDProcesses">ten different QCD <ei>2 -> 3</ei> 
718processes</aloc> have been implemented making use of this new
719possibility, so far without a complete handling of possible colour
720flows, however.</li> 
721
722<li>New processes have been added for
723<aloc href="CompositenessProcesses">contact interactions</aloc> in
724<ei>q q -> q q</ei> and <ei>q qbar -> q qbar</ei> scattering.</li>
725
726<li>A process has been added for TeV^-1 Sized
727<aloc href="ExtraDimensionalProcesses">Extra Dimensions</aloc>, which
728involves the electroweak KK gauge bosons, i.e. <ei>gamma_{KK}/Z_{KK}</ei>,
729in one TeV^-1 sized extra dimension; see <code>main30.cc</code> for
730an example. This scenario is described in <ref>Bel10</ref>. Thanks to
731Noam Hod and coworkers for contributing this code.</li>
732
733<li>In the Randall-Sundrum extra-dimensional scenario a new option has
734been added where SM fields can exist in the bulk rather than only on
735a brane. (Still under development.) Furthermore production of a
736Kaluza-Klein gluon state has been added, and the <code> main28.cc</code> 
737test program extended.</li> 
738
739<li>The scenario for monojets in Large Extra Dimensions has been expanded
740with an alternative for scalar graviton exchange instead of tensor one.
741</li> 
742
743<li>New parameters for maximum scale of
744<aloc href="TimelikeShowers">timelike showers</aloc>,
745<code>TimeShower:pTmaxMatch</code>, and the dampening of hard radiation,
746<code>TimeShower:pTdampMatch</code> and <code>TimeShower:pTdampFudge</code>,
747by analogy with corresponding ones for spacelike showers. Also new method
748<code>TimeShower:limitPTmax(...)</code> to implement alternative procedures.
749For dipoles stretched to the beam the new switch
750<code>TimeShower:dampenBeamRecoil</code> allows to dampen radiation
751close to the beam direction, with a changed default behaviour.</li> 
752
753<li>Azimuthal anisotropies from coherence arguments have been introduced
754for the spacelike parton showers, see <code>SpaceShower:phiIntAsym</code>
755and <code>SpaceShower:strengthIntAsym</code>.
756Also azimuthal anisotropies from gluon polarization have been introduced
757for the spacelike parton showers, see <code>SpaceShower:phiPolAsym</code>,
758and updated for timelike parton showers, see
759<code>TimeShower:phiPolAsym</code>.</li>
760
761<li>Improvements for the matching to POWHEG LHEF-style input illustrated
762by the new <code>main71.cc</code> example. See also <ref>Cor10</ref>.</li>
763
764<li>A set of new processes <ei>gamma gamma -> f fbar</ei>, with <ei>f</ei>
765quarks or leptons. Code for equivalent photon flux around an unresolved
766proton, with more to come. Thanks to Oystein Alvestad.
767</li>
768
769<li>A new option has been included to dampen the growth of the diffractive
770cross sections, see <aloc href="TotalCrossSections">Total Cross
771Sections</aloc>.</li>
772
773<li>A new method <code>virtual int SigmaProcess::idSChannel()</code>
774has been introduced. If overloaded to return a nonzero value then a
775<ei>2 -> n</ei> process will appear listed as a <ei>2 -> 1 -> n</ei> one.
776That is, an intermediate resonance with the requested identity will be
777inserted in the event record, even without appearing in the calculation
778of the matrix element proper. Thanks to Noam Hod for idea and code.</li> 
779
780<li>A new method <code>SigmaProcess::convertM2()</code> has been introduced
781to optionally allow the <code>SigmaProcess::sigmaHat()</code> to return
782the squared matrix element rather than <ei>d(sigmaHat)/d(tHat)</ei> for
783<ei> 2 -> 2 </ei> processes. Furthermore kinematics is stored in the new
784<code>mME</code> and <code>pME</code> vectors for alternative cross
785section encodings.</li> 
786
787<li>Different encoding of the <ei>f fbar -> Z W</ei> cross section,
788contributed by Merlin Kole, based on the cross section of
789Brown, Sahdev and Mikaelian. Gives a distinctly different cross section
790than the previous based on EHLQ (including their bug fix).
791In particular the problem with negative cross sections is now fixed.</li>
792
793<li>Minor updates: pass <code>xmlPath</code> to new MSTW and CTEQ PDFs;
794reset beams earlier to give cleaner documentation.</li>
795
796<li>The H1 Fit B LO parametrization to the Pomeron PDF has been included,
797and made new default for Pomerons. Thanks to Paul Newman for providing
798the data files.</li>
799
800<li>Three changes, in principle unrelated, but with the common objective
801to make the generation of a given event depend only on the values
802determined during the initialization stage and on the state of the
803random-number generator when the event is begun. The new default
804should ensure a reproducible stop-and-restart behaviour, convenient
805for debug purposes. Thanks to Michael Schmelling for stressing the
806desire for such a behaviour.
807<br/>(i) Introduction of a new option <code><aloc href="PhaseSpaceCuts">
808PhaseSpace:increaseMaximum</aloc></code> that allows to switch between
809two strategies for handling the (hopefully rare) cases when the
810assumed maximum of the cross section function is exceeded during the
811event generation, with a changed default behaviour. In the old
812default the maximum could be increased if it was exceeded during the run,
813thereby introducing a memory of the previously generated events.
814<br/>(ii) Updated handling of random numbers with Gaussian distributions.
815The <code>gauss()</code> method now only generates one value at a time.
816Instead the new <code>gauss2()</code> method returns a pair of Gauss
817numbers, with related time savings. In the old approach one Gaussian
818number could be buffered, which introduced a memory.
819<br/>(iii) Minor bug fix in <code>MiniStringFragmentation</code>, where
820the popcorn baryon state was not reset for each new system, again
821giving a (flawed) memory.</li> 
822
823<li>New directory <code>rootexample</code> with a simple code example
824how to use ROOT for histogramming in PYTHIA runs. See
825<aloc href="ROOTusage">ROOT Usage</aloc> for details. Thanks to Rene Brun.
826</li>
827
828<li>In the <code>HepMCinterface</code> the checks for unhadronized
829quarks and gluons are not performed if hadronization has been switched
830off.</li>
831
832<li>The <code>UserHooks::initPtr(...)</code> has been expanded so that
833pointers to more classes (beam particles, random number, couplings, etc.)
834are sent in, thereby increasing the scope of possible user-written code.
835Also, the <code>UserHooks::doVetoProcessLevel(Event& process)</code>
836now allows the <code>process</code> event record to be modified,
837even if it is not recommended. The new <code>Info::pTnow()</code>
838method returns the current <ei>pT</ei> scale of the combined MPI, ISR
839and FSR evolution, which can be useful for some user hooks decisions.
840</li>
841
842<li>Histograms of the <code>Hist</code> class can now be booked
843with up to 1000 bins, instead of the previous maximum 100. All bins
844can be written to file, but the line-printer style printing will join
845nearby bins so at most 100 are printed, as before.  </li>
846
847<li>Updated <code>configure</code> and <code>Makefile</code> 
848to allow 64-bit compilation and more options. Thanks to Mikhail Kirsanov,
849Rene Brun and Fons Rademakers.</li>
850
851<li>Bug fix in <code>ProcessLevel</code> for colour flow checks of
852junctions. Enables the decay of a neutralino to three quarks, e.g.
853Thanks to Nils-Erik Bomark.</li>
854
855<li>Bug fixes in <code>TimeShower</code>, where recoil partners in resonance
856decays of coloured particles, and recoil partners in QED dipoles when beams
857are not allowed to take a recoil, might not be correctly identified. </li>
858
859<li>Bug fix in <code>SpaceShower</code>: when used with a fixed
860<ei>alpha_strong</ei>, the threshold enhancement factor of
861<ei>g -> Q Qbar</ei> became undefined. Thanks to Stefan Prestel.</li>
862
863<li>Bug fix in initialization of resonance widths, where the
864<code>minWidth</code> parameter could be used uninitialized,
865occasionally resulting in strange initialization problems when
866kinematics needs to force at least one resonance to be off-shell.</li>
867
868<li>Minor updates of <code>main06.cc</code>, <code>main10.cc</code>
869and <code>main23.cc</code>.</li>
870
871<li>Bug fix in mother pointer of multiparton interactions in
872diffractive systems.</li>
873
874</ul>
875</li>
876
877<li>8.142: 15 August 2010
878<ul>
879
880<li>The strategy for setting up tune values has been changed.
881Previously the <code>Tune:ee</code> and <code>Tune:pp</code>
882settings were only interpreted during the
883<code>Pythia::init(...)</code> stage. Now they are interpreted
884as soon as they are read. Specifically this means that it is
885possible to override any of the tune parameters by putting new
886commands below <code>Tune:ee</code> and <code>Tune:pp</code>
887in the <code>Pythia::readFile(...)</code> configuration file
888or in the list of <code>Pythia::readString(...)</code> commands.
889<br/>As a consequence of this change, the public
890<code>Pythia::initTunes(...)</code> method has been replaced by
891two private <code>Settings::initTuneEE(...)</code> and
892<code>Settings::initTunePP(...)</code> methods.
893<br/>If <code>Tune:ee</code> or <code>Tune:pp</code> are
894nonvanishing by default, then the corresponding tune variables
895are set also from the <code>Pythia</code> constructor, before any
896user changes are possible. Currently this is not relevant.
897</li>
898
899<li>Bug fix in the setup of the <code>Tune:pp = 5</code> and
900<code>= 6</code> options, which meant that diffractive cross
901sections were not reduced as advertised.</li>
902
903<li>The default value of <code>MultipartonInteractions:pT0Ref</code>
904has been slightly reduced so as to give a somewhat improved
905default description. It is not intended as a replacement for the
906specific tunes, however.</li>
907
908<li>Some comparisons between tunes and data, obtained with the
909Rivet package, have been posted on
910<a href="http://home.thep.lu.se/~richard/pythia81/">   
911http://home.thep.lu.se/~richard/pythia81/</a>.
912Further improvements can be expected from future Professor-based
913tunes. The current set of 2C, 2M, 3C and 3M "draft tunes" have
914deliberately been chosen different also to explore a range of
915possibilities. One not visible in the plots is the fraction
916of single and double diffractive events in the inelastic cross
917section. This is 32% in 2C and 2M, while it was reduced to
91821% in 3C and 3M, and a recent ATLAS study (ATLAS-CONF-2010-048)
919would suggest 28+-4%.</li>
920
921<li>Minor changes in <code>TimeShower</code> and
922<code>SpaceShower</code>, as protection if the <ei>c</ei> or
923<ei>b</ei> masses are set small.</li>
924
925<li>Bug fix in <code>SpaceShower</code>, for case when <ei>phi</ei> 
926angle selection is biased to take into account interference effects.
927</li>
928
929<li>The <code>SigmaProcess::convertM2()</code> method now has
930been implemented also for <ei>2 -> 1</ei> processes, so that it is
931possible to provide the squared matrix element instead of
932<ei>sigmaHat</ei> for semi-internal processes. A fixed-width
933Breit-Wigner is also inserted, since the matrix element is supposed
934not to include it.</li> 
935
936<li>New method <code>SigmaProcess::setupForME()</code> does an
937extended conversion from the internal kinematics to an almost
938equivalent one, better adapted to the mass conventions of matrix-element
939caclulation programs, such as massive incoming <ei>b</ei> quarks.
940New flags allow to determine whether the <ei>c</ei>, <ei>b</ei>,
941<ei>mu</ei> and <ei>tau</ei> should be considered massless or not
942in the calculations.</li>
943
944<li>Two new friend methods <code>table</code> of the <code>Hist</code> 
945class allow to print a table with three columns, the first for the
946(common!) <ei>x</ei> values and the other two for the respective
947histogram values. A new method <code>takeSqrt</code> for the square
948root of histogram bin contents.
949</li>
950
951</ul>
952</li>
953
954<li>8.145: 10 November 2010
955<ul>
956
957<li><code>Couplings</code> is defined in <code>StandardModel.h</code>
958as a derived class of <code>coupSM</code> and has only one extra flag:
959<code>isSUSY</code> to check presence of extra couplings.Changed all
960pointers <code>CoupSM*</code> to <code>Couplings*</code> and removed
961explicit references to <code>CoupSUSY*</code>. The <code>coupSUSY</code>
962object is only initialised if SUSY couplings are present. The new pointer
963<code>couplingsPtr</code> points either to only SM couplings or SM+SUSY
964couplings based on SLHA data.</li>
965
966<li>New files <code>SusyResonanceWidths.h/cc</code> contains the
967<code>SusyResonanceWidths</code> class, which inherits from
968<code>ResonanceWidths</code> but typecasts the <code>couplingsPtr</code> 
969to <code>(CoupSUSY*) coupSUSYPtr</code>.  This is the base class for
970all SUSY resonances. It contains the <code>ResonanceSquark</code> class
971for all squark decays. A new flag <code>SLHA:useDecayTable</code> 
972to check if internal widths should be overwritten by those read in
973via SLHA.</li>
974
975<li>Added new functionality to <code>SusyLesHouches</code> for read-in
976of generic user blocks in the SLHA format, along with methods to
977extract parameters from them with typecasting controlled by the user.
978Intended for use with user-written semi-internal processes.</li>
979
980<li>Added <code>Sigma1qq2antisquark</code> cross section.</li>
981
982<li>Some new flags and modes in the <code>SUSY</code> and
983<code>SLHA</code> series offer further functionality.</li>
984
985<li>Several further changes as a consequence of the upgrade of the SUSY
986machinery.</li> 
987
988<li>Bug/typo fixes in rotation matrices for SUSY couplings and for the
989processes <code>qqbar2squarkantisquark</code>,
990<code>qq2squarksquark</code> and more.</li>
991
992<li>Improved handling of colour junctions. Added new example program
993<code>main72.cc</code>, to illustrate read-in of color junction
994structures via LHEF (<code>main72.lhe</code>). The example used is SUSY
995with RPV.</li>
996
997<li>New Tune 4C introduced as <code>Tune:pp = 5</code>. The more crude
998(non-)tunes 3C and 3M are removed.</li>
999
1000<li>New methods <code>Settings::getFlagMap(...)</code>,
1001<code>Settings::getModeMap(...)</code>,
1002<code>Settings::getParmMap(...)</code> and
1003<code>Settings::getWordMap(...)</code> allows to return a map of all
1004settings of the respective type that contain a specific string
1005in its name.
1006</li>
1007
1008<li>Improved description of excited <ei>g^*/KK-gluon^*</ei> production
1009in the <code>Sigma1qqbar2KKgluonStar</code> and
1010<code>ResonanceKKgluon</code> classes.</li>
1011
1012<li>Possibility added to let Hidden-Valley <ei>gamma_v</ei> have
1013a nonero mass and decay by mixing with the ordinary photon.
1014Still experimental.</li>
1015
1016<li>Minor bug fix in handling of three-body phase space.</li>
1017
1018<li>Minor correction in <code>Sigma2ffbar2TEVffbar</code> class.</li>
1019
1020<li>Bug fix for decays of <ei>W'</ei> to a pair of heavy fermions when
1021<ei>gV != gA</ei>. Thanks to M. Chizhov, see arXiv:0705.3944. </li>
1022
1023<li>Restore the older EHLQ-based encoding of the <ei>f fbar -> Z W</ei> 
1024cross section, which was changed in version 8.140, since comparisons
1025with Madgraph gives much better agreement with it than with the
1026expression of Brown, Sahdev and Mikaelian.</li>
1027
1028<li>The <code>HepMCInterface</code> now also stores colour flow
1029information for coloured particles.</li>
1030
1031<li>Pointer to <code>Couplings</code> made available for particle
1032decays.</li>
1033
1034<li>Minor update in <code>main61.cc</code> for more elegant usage
1035of FastJet, as suggested by Gregory Soyez.</li>
1036
1037</ul>
1038</li>
1039
1040<li>8.150: 20 April 2011
1041<ul>
1042
1043<li>Tune 4C is made default. It is based on first comparisons with
1044LHC data <ref>Cor10a</ref>, and has also been checked independently
1045<ref>Buc11</ref> to give reasonable agreement with many distributions.
1046</li>
1047
1048<li>The description of <ei>tau</ei> lepton decays has been significantly
1049enhanced, to include helicity information related to the production
1050process and hadronic currents fitted to data. A complete writeup is
1051in preparation <ref>Ilt11</ref>. A new flag is introduced to revert
1052to the old behaviour, for cross-checks, see
1053<aloc href="ParticleDecays">Particle Decays</aloc>.
1054The new tau decay machinery is on by default.
1055</li>
1056
1057<li>A new option <code>MultipartonInteractions:bProfile = 4</code> has
1058been introduced for the impact-parameter profile of protons in the
1059<aloc href="MultipartonInteractions">Multiparton Interactions</aloc> 
1060framework, wherein low-<ei>x</ei> partons are spread over a larger area
1061than high-<ei>x</ei> ones, see <ref>Cor11</ref>. A new method
1062<code>Info::eMPI(i)</code> gives back the enhancement factor related to
1063the <code>i</code>'th interaction. The impact-parameter profile can now
1064be selected separately for <aloc href="Diffraction">diffraction</aloc>,
1065but without a <code>bProfile = 4</code> option.
1066</li>
1067
1068<li>The possibility of "hadronization" in the
1069<aloc href="HiddenValleyProcesses">Hidden Valley</aloc> sector
1070has been added as a new option <code>HiddenValley:fragment = on</code>.
1071This is based on a copy of the standard string fragmentation framework,
1072but with the option of a completely separate "flavour" sector, and
1073separately tunable longitudinal fragmentation functions and transverse
1074momenta. For now only a simple flavour scenario is provided, where
1075flavour-diagonal mesons can decay back into the normal visible sector
1076while off-diagonal ones remain hidden. A writeup of the model is in
1077preparation <ref>Car11</ref>. Also some further Hidden Valley options
1078have been added.</li> 
1079
1080<li>Included possibility in <code>TimeShower</code> for QCD dipoles to
1081have an adjustible normalization factor, via the new
1082<code>bool isFlexible</code> and <code>double flexFactor</code>
1083properties of <code>class TimeDipoleEnd</code>. This flexibility is used
1084to treat radiation off colour topologies with epsilon tensors, in
1085particular colour junctions which have all their partons in the
1086final state. (An example is the BNV-SUSY decay ~chi0&rarr;uds.) For
1087such topologies, the new treatment in PYTHIA 8 is that a
1088half-strength dipole is spanned between all combinations of
1089final-state quarks. For junctions with an incoming (anti)colour line (such
1090as in the BNV-SUSY decay ~t*&rarr;cb), a full-strength dipole is
1091instead spanned between the two daughters, with no radiation from the
1092decaying object (in its CM). As will be described in a fortcoming
1093paper with N. Desai, this should give the
1094closest possible correspondence to the radiation patterns exhibited
1095by higher-order matrix elements for this type of process.</li>
1096
1097<li>Corrected harmless bugs in <code>ProcessLevel::findJunctions</code>
1098which caused junctions of types 3 and 4 (i.e., junctions with 1
1099incoming color tag) to sometimes be incorrectly classified as types
11001 and 2 (with all color tags outgoing), respectively.
1101Since the parity (even/odd) of the junction kind was still correct,
1102however, this did not cause any problems at the hadronization
1103stage.</li>
1104
1105<li>The junction-finder in <code>ProcessLevel::findJunctions</code>
1106has been made more stable, and the following ordering of the color
1107tags returned by <code>Event::endColJunction(iJun, iLeg)</code>  is
1108now enforced: for junction kinds 3 and 4 (one tag
1109incoming), <code>iLeg = 0</code> will return the
1110incoming tag, while for kinds 5 and 6 (two tags incoming),
1111<code>iLeg = 0</code> and <code>iLeg = 1</code> will return the
1112incoming tags. Apart from this ordering, the color tags are
1113ordered in ascending color tag number.</li>
1114
1115<li>Declarations of friend functions moved to sit outside the class
1116it befriends. Thanks to Axel Naumann for pointing out the incorrect
1117previous construction.</li>
1118
1119<li>The <code>rootexample</code> subdirectory becomes
1120<code>rootexamples</code> as the old example is split into two,
1121with improved documentation to clarify usage. Thanks to Axel Naumann
1122and Bernhard Meirose for the new code.</li>
1123
1124<li>In the Les Houches Event File machinery, input type has been
1125changed from <code>ifstream</code> to <code>istream</code> for more
1126flexibility.</li>
1127
1128<li>R-hadron  handling is largely implemented, see the
1129<aloc href="RHadrons">R-hadrons</aloc> page, although some aspects
1130still need polishing. A new class <code>RHadrons</code> takes
1131care of the hadronization and decay. Particle data have been added
1132for R-hadrons containing a gluino, stop or sbottom, but could
1133alternatively be used for other long-lived coloured particles.
1134Thanks to Bernhard Meirose for support.
1135</li>
1136
1137<li>Calculations of SUSY decay widths included by
1138  N. Desai, contained in the new source
1139files <code>SusyResonanceWidth.cc</code>
1140  and </code>.h</code>. Validation and addition of more modes is still in
1141  progress, so this implementation should be considered preliminary
1142  for now. For a list of available modes, see
1143  the <aloc href="SUSYProcesses">SUSY Processes</aloc> page.
1144</li>
1145
1146<li>A first implementation of the SLHA-based QNUMBERS interface for
1147  defining new exotic particles has been
1148  included. See <ref>Alw07</ref> and
1149  the <aloc href="SUSYLesHouchesAccord">SUSY Les Houches Accord</aloc>
1150  page. </li>
1151
1152<li>Read-in of LHEF events containing Baryon Number Violating vertices
1153  has been included, using colour junctions, see
1154  the <aloc href="EventRecord">Event Record</aloc> page. The advanced
1155  shower model taking into account the full colour structure of such
1156  events, developed by N. Desai and described above,
1157  is turned on by default in such events.
1158  Several test cases were used to
1159  validate this implementation, but it is possible that problems could
1160  still exist for some cases. Feedback is welcome. Thanks to
1161  the MadGraph authors for providing several test cases.</li>
1162
1163<li>Some first steps taken to allow events containing colour sextets,
1164  e.g., from semi-internal processes or LHEF interfaces, and/or from
1165  SLHA <code>DECAY</code> tables. New
1166  <code>colType</code> codes 3 and -3 are introduced to describe
1167  sextets and antisextets, respectively. The state of the current
1168  implementation is that hard processes containing such states can be
1169  read in and decays generated (via <code>DECAY</code> tables). Parton
1170  showers can be added, but the sextets themselves do not, as yet,
1171  shower, and any undecayed sextets remaining at the hadronization
1172  stage would lead to unpredictable problems if hadronization is
1173  switched on. Thanks to J. Alwall for help with testing
1174  this implementation.
1175</li>
1176
1177<li>The functionality of the SLHA SUSY/BSM interface (see
1178  the <aloc href="SUSYLesHouches">SUSY Les Houches</aloc> page) has been
1179  extended so that copies of all <code>BLOCK</code>s are now stored
1180  internally as
1181  strings, regardless of whether they correspond to "official" SLHA
1182  blocks or not. Their contents can subsequently be queried by a set
1183  of new templated member functions of the
1184  class <code>SusyLesHouches</code>. Available query functions so far
1185  include
1186  <br/><code>template &lt;class T&gt; bool getEntry(string, T&);</code>,
1187  <br/><code>template &lt;class T&gt; bool getEntry(string, int, T&);</code>,
1188  <br/><code>template &lt;class T&gt; bool getEntry(string, int, int, T&);
1189  </code>, and
1190  <br/><code>template &lt;class T&gt; bool getEntry(string, int,
1191  int, int, T&);</code>,
1192  <br/>where the type of
1193  the argument used in the call determines how to read the block
1194  entries. Thus, if an LHEF, SLHA, or other card file is read in by
1195  PYTHIA, the contents of any <code>BLOCK</code> in that file can
1196  subsequently be queried run-time using these functions. This is
1197  used, e.g., in the new interface between MADGRAPH 5 and PYTHIA
1198  8. Thanks to the MADGRAPH team, and to J. Alwall in particular, for
1199  help and debug on this new implementation.
1200</li>
1201
1202</ul>
1203</li>
1204
1205<li>8.153: 10 August 2011
1206<ul>
1207
1208<li>The setup of tunes has been modified, see the
1209<aloc href="Tunes">Tunes</aloc> page for details. Specifically
1210the <code>Tune:ee</code> and <code>Tune:pp</code> modes have
1211acquired a new option <code>-1</code> for a forced restore to the
1212default values of all settings used in the respective kind of
1213tunes.</li>
1214
1215<li>The code for handling multiparton interactions in the scenario with
1216an <ei>x</ei>-dependent width of the Gaussian matter profile
1217<ref>Cor11</ref>, has been improved and updated. Tune 4Cx, which
1218is based on this option, has been added as a further tune option.</li>
1219
1220<li>A possibility to bias the phase-space selection has been added,
1221whereby some phase space regions can be oversampled, which is
1222compensated by assigning a weight to each event.
1223A new set of methods have been added to the <code>UserHooks</code>
1224class to allow users to program how to bias the selection.</li>
1225
1226<li>New options added so that matrix-element corrections can be
1227switched off after the first branching in ISR or FSR.</li>
1228
1229<li>Some new <code>Info</code> methods have been added to store
1230information on latest ISR branching.  The <code>SpaceShower</code>
1231class has also been corrected so that the latest <ei>z = 1/2</ei>
1232when not defined by history. This avoids undefined values for
1233azimuthal asymmetries. Thanks to Stefan Prestel for finding and
1234sorting out this problem.</li>
1235
1236<li>The <code>Pythia::forceHadronLevel()</code> method now takes
1237an argument that optionally means that existing junction information
1238is not overwritten. Thanks to Leif L&ouml;nnblad for pointing out
1239the usefulness of this.</li>
1240
1241<li>For particle decays to a varying number of hadrons the multiplicity
1242increase with mass has been somewhat reduced, and especially for
1243<code>meMode = 23</code> a separate even slower increase has been
1244introduced.</li>
1245
1246<li>New possibility to force the tau polarization.</li>
1247
1248<li>Bug fix for the special case in which events containing SUSY
1249particles are generated without proper initialization of SUSY decays.
1250This can happen, e.g., if events containing SUSY particles are read
1251in via external LHEF files, if those files do not contain readable
1252SLHA spectra in their headers. In this case, a failed attempt to
1253generate sparticle decays with ill-defined couplings previously
1254led to crashes. The program now reverts to the old behaviour,
1255based on static decay tables, in such cases, with the default
1256being to decay all sparticles to gravitino + particle. An error
1257message stating that the full SUSY treatment has been switched
1258off and why is also issued. Thanks to N. Desai for this fix.</li>
1259
1260<li>The R-hadron machinery has been completed.</li>
1261
1262<li>Minor change in timelike showers: gluons which fall below the
1263<ei>pTmin</ei> cutoff by the correction for mass effects are now
1264eliminated, while previously they were kept. This reduces the
1265number of gluons somewhat, but has no significant effects on the
1266hadronic final state. (Prompted by R-hadron studies, where big mass
1267effects else give bothersome low-energy gluons.)</li>
1268
1269<li>Corrected typos in two of the Upsilon wave function matrix
1270elements, <code>Bottomonium:OUpsilon3P08</code> and
1271<code>Bottomonium:Ochib03P01</code>. Thanks to Beate Heinemann for
1272pointing it out.</li>
1273
1274<li>Implemented <ei>f*</ei> decay angle in <ei>f f -> f f*</ei> processes,
1275and fixed some bugs for the same process. Thanks to Piyali Banerjee
1276for tests.</li>
1277
1278<li>Introduce possibility to separate production channels for
1279TeV-sized extra dimensions, and a small code correction. Thanks to
1280Noam Hod for code contribution.</li>
1281
1282<li>Bug fix for neutrino beams: since neutrinos are always lefthanded
1283there should be a factor 2 in the cross section, relative to charged
1284leptons, from the non-need to average over incoming spin states. This
1285is now fixed by introducing a new PDF class <code>NeutrinoPoint</code> 
1286for (unresolved) neutrinos, with normalization 2 rather than 1 for
1287charged leptons. Thanks to Ryosuke Sato.</li>
1288
1289<li>Bug fix for some (rarely used) particle settings, which could not
1290be changed by users because they were read too early. Thanks to
1291Andrew Altheimer and Gustaaf Brooijmans.</li>
1292
1293<li>Bug fix in handling of <code>tau</code> decays, where setting of
1294decay vertices could write outside memory. Thanks to Steven Schramm.</li>
1295
1296<li>Minor expansion of the <code>BeamParticle</code> constructor.</li>
1297
1298<li>Minor bug fix in CTEQ 6L for uninitialized variables.</li>
1299
1300<li>Minor bug fix in fragmentation flavour combination to hadron.</li>
1301
1302<li>Some updates of the documentation, including new pages on
1303MadGraph 5 as a generator for semi-internal processes (thanks to
1304Johan Alwall) and on RIVET interfacing.</li> 
1305 
1306<li>Minor improvements of ROOT- and HepMC-related code and documentation.</li>
1307
1308<li>Some cleanup of code.</li>
1309
1310</ul>
1311</li>
1312
1313<li>8.157: 10 November 2011
1314<ul>
1315
1316<ii>StefanPrestel joins as new member of the PYTHIA author team.
1317He is mainly working on matching/merging issues, and has contributed
1318the CKKW-L machinery mentioned below.</li>
1319
1320<li>Merging capabilities according to the CKKW-L scheme <ref>Lon11</ref>
1321have been added, see the new
1322<aloc href="MatrixElementMerging">Matrix Element Merging</aloc>
1323page. It involves new classes to reconstruct and select how a
1324matrix-element-generated partonic configuration could have been obtained
1325by the PYTHIA evolution, and to perform trial showers (using a new
1326copy of the normal parton-level machinery) that introduce the appropriate
1327Sudakov suppression factors. New examples to illustrate various
1328common tasks are found in <code>main81.cc</code>, <code>main82.cc</code>,
1329<code>main83.cc</code> and <code>main84.cc</code>.</li> 
1330
1331<li>The <code>main71.cc</code> program is now generalised for reading
1332in arbitrary POWHEG LHE files, to implement a smooth matching between NLO
1333matrix elements and the PYTHIA parton showers. Cuts are made on both
1334ISR and FSR emissions, while previously only ISR was covered. The key
1335assumptions are the <ei>pT</ei> definitions used for ISR and FSR, but several
1336further options are available, as documented in the <code>main71.cmnd</code> 
1337file. Work is still ongoing to pick the best default options. </li>
1338
1339<li>Several expansions of the <code>UserHooks</code> class.
1340For both <code>doVetoFSREmission</code> and <code>doVetoISREmission</code>
1341a new argument <code>iSys</code> labels the system within which the
1342radiation occurs. For <code>doVetoFSREmission</code> a further argument
1343<code>inResonance</code> distinguishes FSR in resonance
1344decays from that in the hard process itself. New methods
1345<code>canVetoMPIEmission</code> and <code>doVetoMPIEmission</code>
1346have been added to veto multiparton interactions in the same way as
1347FSR and ISR. In <code>biasSelectionBy</code> at times incorrect values
1348for <code>inEvent</code> has been corrected. Also some systematization
1349of the use of <code>const</code>.</li> 
1350
1351<li>A new model for hadron scattering is introduced, still at an early
1352stage and therefore more intended for internal development than for the
1353normal user. The basic idea is that a high-energy <ei>pp</ei> collision
1354involves the fragmentation of multiparton strings that overlap in space
1355(and time). Also the produced hadrons therefore initially overlap, and
1356there is a strong likelihood that hadrons can scatter against each other
1357until the system has expanded sufficiently. This can e.g. increase the
1358transverse momentum of heavier hadrons at the expense of lighter ones.
1359</li>
1360
1361<li>A new jet finder <code>SlowJet</code> offers simple access to the
1362inclusive <ei>kT</ei>, anti-<ei>kT</ei>, and Cambridge/Aachen
1363algorithms in a cylindrical coordinate frame. The jet reconstruction
1364is then based on sequential recombination with progressive removal,
1365using the <ei>E</ei> recombination scheme. The minimalistic
1366<code>SlowJet</code> code is much slower than <code>FastJet</code> 
1367<ref>Cac06</ref>, and contains less options, but reconstructs the same
1368jets if run under identical conditions. For details see the
1369<aloc href="EventAnalysis">Event Analysis</aloc> page.</li>
1370
1371<li>Starting in gcc 4.6, it is possible to switch off specific warnings
1372around specific blocks of code. Although version 4.6 is some way off
1373from being commonly found, this option has now been introduced to switch
1374off <code>-Wshadow</code> warnings in <code>HepMCInterface.cc</code>.
1375For other compilers, or earlier versions of gcc, the old behaviour
1376is retained.</li> 
1377
1378<li>Support for reading in gzipped LHEFs has been added in the
1379<code>LesHouches</code> and <code>SusyLesHouches</code> classes.
1380This also affects <code>configure</code> and <code>Makefile</code>s.
1381Unless explicitly enabled, it should not affect anything.
1382If enabled, it relies on the Boost and zlib libraries to function,
1383so paths to these must be set appropriately, see the
1384<code>README</code> file for details. The Boost header files can
1385give very many shadow warnings, so <code>-Wshadow</code> is disabled
1386if gzip support is enabled, as described above.</li> 
1387
1388<li>Introduce use of the <code>HEPMC_HAS_UNITS</code> environment
1389variable in the <code>HepMCInterface.cc</code> and <code>main32.cc</code> 
1390codes to automatically check whether GeV and mm can be set as relevant
1391units. If yes, then it is set in <code>main32.cc</code>. If no,
1392a conversion from GeV to MeV is done explicitly in
1393<code>HepMCInterface.cc</code>. Note that, for early HepMC versions,
1394this means a change of behaviour. Thanks to Andy Buckley.</li>
1395
1396<li>A new method <code>Info::lhaStrategy()</code> returns the
1397Les Houches event weighting strategy where relevant, and 0 where not.
1398For the strategies <ei>+-4</ei> the event weight and sum,
1399<code>Info::weight()</code> and <code>Info::weightSum()</code>,
1400is now in units of pb at output, as it should be at input.
1401(While internally mb is used.)</li>
1402
1403<li>New flag <code>Check:abortIfVeto</code> allows the user to
1404resume control over execution in case of a veto in the event
1405generation process.</li>
1406
1407<li>New method <code>Event::at(i)</code> returns reference to
1408<code>i</code>'th particle in the event record.</li>
1409
1410<li>Introduce the Fermi constant as one of the Standard Model
1411parameters.</li>
1412
1413<li>Included automatic pre-initialization of SLHA blocks MASS and
1414SMINPUTS using PYTHIA's SM parameters and particle data table
1415values.</li>
1416
1417<li>SUSY: added sleptons (and sneutrinos) as resonances.
1418Corrected 2-body decay widths of gluinos, squarks and gauginos.
1419Added sleptonic decay modes to gaugino decays.
1420Implemented 2-body decays of sleptons (and sneutrinos)
1421into sleptons/leptons/gauginos. Corrected slepton couplings (they
1422now look exactly like squark couplings, using a 6x6 slepton mixing
1423matrix).</li>
1424
1425<li>New parameter <code>Diffraction:probMaxPert</code> introduce to
1426give more flexibility in transition from a nonperturbative to a
1427perturbative description of a diffractive system.</li>
1428
1429<li>Bug corrected in <code>SigmaEW.cc</code>, for the process
1430<code>WeakSingleBoson:ffbar2ffbar(s:gm)</code>. Previously, all outgoing
1431quark flavours in this process were erroneously assigned ID code 5
1432(b quarks). This has now been corrected so the proper ratios are
1433obtained, with <ei>u : c : d : s : b = 4 : 4 : 1 : 1 : 1</ei>,
1434according to the squared quark charges.</li>
1435 
1436<li>Changes in <code>FragmentationSystems</code> and
1437<code>StringFragmentation</code> to reject systems with three or more
1438interconnected junctions. This may happen in baryon-number-violating
1439scenarios in pp collisions, if both of the beam baryon junctions are
1440resolved and get connected via an antijunction created by a
1441hard-process BNV vertex. In principle, this could be addressed by an
1442extension of the existing junction fragmentation framework. However,
1443since it happens rarely, for the time being an error message is printed
1444and the fragmentation restarted.
1445</li>
1446
1447<li>Change in <code>Event::copy</code> to safeguard against attempting
1448to copy out-of-range entries. An attempt to copy a non-existing entry
1449will now return -1.</li>
1450
1451<li>Bug fix in the machinery for the user to force the setting of
1452tau polarization.</li>
1453
1454<li>Bug fix in the initial search for a maximum of the process
1455cross section (only affecting rare cases).</li>
1456
1457<li>Corrected angular decay distributions for two compositeness
1458processes, <code>Sigma2qq2qStarq</code> and
1459<code>Sigma2qqbar2lStarlbar</code>.</li> 
1460   
1461<li>Extra check in <code>HiddenValleyFragmentation</code> to make sure
1462that pointers which have not been assigned with <code>new</code> are not
1463deleted.</li>
1464
1465<li>Some further minor changes.</li>
1466
1467</ul>
1468</li>
1469
1470<li>8.160: 23 January 2012
1471<ul>
1472
1473<li>The older term "multiple interactions" has been replaced by the
1474new standard "multiparton interactions" one, and correspondingly the
1475abbreviation MI by MPI. This affects everything: settings, class and
1476method names, documentation, etc. It therefore becomes necessary to
1477rewrite user code. However, so as to keep the immediate effort at a
1478reasonable level, the old settings names are kept as aliases. Thus
1479<code>PartonLevel:MI</code> and <code>PartonLevel:MPI</code> are
1480equivalent, and similarly <code>MultipleInteractions:pT0Ref</code> 
1481and <code>MultipartonInteractions:pT0Ref</code>. Should you be using
1482methods such as <code>double Info::pTMI(int i)</code> you need to
1483edit the code, however. All the <code>example/main*</code> files
1484have been uopdated accordingly.</li>
1485
1486<li>A new option <code>Beams:frameType = 5</code> has been added
1487for the case where an external generator should provide LHA process
1488information. The new <code>Pythia::setLHAupPtr(...)</code> method
1489should then be used to link in this generator. The new switch
1490<code>Beams:newLHEFsameInit</code> can be used to tell that a new
1491LHEF should be used, but without the need for a new initialization.
1492With these two changes, all the different ways of initializing
1493can be covered by the <code>Pythia::init()</code> call with no
1494arguments. The various <code>init(...)</code>options with arguments
1495are deprecated and will be removed for PYTHIA 8.2.</li>
1496
1497<li> The <code>Pythia::stat()</code> method, with no arguments,
1498replaces <code>Pythia::statistics(...)</code>, although the latter
1499remains as a deprecated alternative.</li>
1500
1501<li>New settings <code>Init:...</code>, <code>Next:...</code>,
1502and <code>Stat:...</code> can be used to steer some details of
1503the operation of the <code>Pythia::init()</code>
1504<code>Pythia::next()</code> and  <code>Pythia::stat()</code>,
1505respectively. In particular it affects the amount of printout
1506at the various stages of operation. See
1507<aloc href="MainProgramSettings">here</aloc> for further details.
1508This change involves several code changes, but in documentation
1509rather than physics. Most of the <code>Main:...</code> settings
1510are deprecated as a consequence.</li>
1511
1512<li>The sample main programs in the <code>examples</code> subdirectory
1513have been updated. This includes a change to the new favoured
1514methods and settings outlined above, plus some update of the
1515physics contents. Some of the examples have been combined,
1516some others have been added (e.g. for R-hadroms), and as a consequence
1517some renumbering has been made. See the modified list of
1518<aloc href="SampleMainPrograms">sample main programs</aloc> for
1519the new status. In particular note that (the new) <code>main61.cc</code>
1520allows streamlined input and output in HepMC, like <code>main42.cc</code>
1521(previously <code>main32.cc</code>), but additionally links to LHAPDF. </li>
1522
1523<li>The <code>examples/configure</code> script has new optional argument
1524<code>--with-pythia8</code>. It can be used to set the new
1525<code>PYTHIA8LOCATION</code> environment variable, which then is used
1526in <code>examples/Makefile</code> to give the path to the PYTHIA
1527library. Thereby it becomes possible to relocate (parts of) the
1528<code>examples</code> directory and still obtain the correct path.
1529Thanks to Mikhail Kirsanov.</li>
1530
1531<li>Polarization information has been included as a new
1532<code>Particle</code> property, that can be set by
1533<code>void pol(double polIn)</code> and obtained by
1534<code>double pol()</code>. Default value is <code>9.</code>,
1535in agreement with the Les Houches standard. Event listings have
1536been expanded to optionally display this information. Currently
1537polarization is not used internally.</li>
1538
1539<li>The matrix element merging machinery has been modified as follows.
1540<br/>- Improved handling of the hard process, so that MadGraph5-produced
1541LHE files do not produce problems (sometimes, the choices of MG4 on what
1542to put into a LHEF have changed in MG5).
1543<br/>- Improved handling of colour for easier handling of states with
1544many quarks (the code has been tested for states with up to 5
1545<ei>q qbar</ei> pairs and some gluons).
1546<br/>- Improved checking which clusterings are allowed. Now, clusterings
1547should immediately be rejected if they lead to unphysical states,
1548without the need to explicitly construct these states. This was needed
1549to get <ei>t tbar</ei> production, VBF and some simple SUSY processes
1550running with reasonable generality.
1551<br/>- Improved handling of incomplete histories. Now there is an
1552additional switch allowing code to try to swap some colours when fewer
1553clusterings than requested have been found.
1554</li>
1555
1556<li>Updates in the handling of graviton resonances in scenarios with
1557extra dimensions.
1558<br/>- Now all G decays have correct angular distribution, which was not
1559the case before for W/Z decays.
1560<br/>- Added the possibility for G to only couple to longitudinal
1561W/Z bosons, which affects both the width and angular distributions.
1562<br/>- Added decays to Higgs pairs, <ei>G -> hh</ei>.
1563</li>
1564
1565<li>Bug fix in the <code>findJunctions()</code> function in
1566<code>ProcessLevel.cc</code>. Changes introduced in version
15678.145 (to allow for junctions in baryon-number-violating
1568processes) did not correctly handle the remapping of color
1569tags that can be applied when adding beam remnants to events with
1570multiparton interactions. A simpler and more stable algorithm is
1571now applied for the simplest cases, with the more complex one only
1572invoked for cases such as BNV, which are normally considered before
1573remnants are added, hence avoiding this particular problem. Also some
1574other changes in the handling of junction, including a safeguard to
1575reject systems with three or more interconnected junctions.</li>
1576
1577<li>Bug fix and updates to the SLHA interface. Possibility of infinite
1578loop during <code>ProcessLevel::initSLHA</code> corrected. Modifications
1579to <code>SusyLesHouches</code> to allow interpretation of SLHA1 spectra
1580with R-parity violation. Rather than reject spectra that do not conform
1581fully to the SLHA2 standard for RPV, the interface will now first look
1582for SLHA1 mixing matrices and attempt to translate those into SLHA2 ones
1583if possible. In this case, warnings that the expected SLHA2 blocks were
1584not found will be printed. It is up to the user to check that the
1585derived SLHA2 information is correct. Corresponding additions to
1586<code>SusyCouplings.cc</code> to extract mixing-matrix information
1587from the relevant SLHA2 RPV blocks when RPV is switched on.</li>
1588
1589<li>Updated SLHA example <code>main24.cmnd</code> to use new example
1590spectrum, <code>cmssm.spc</code>, corresponding to CMSSM point
159110.1.1, obtained with SOFTSUSY 3.3.0. Thanks to B. Allanach for
1592providing the new spectrum file.</li>
1593
1594<li>A new <code>include/FastJet3.h</code> header file simplifies
1595interfacing of FastJet to Pythia. For details see documentation in
1596the file itself. Thanks to Gavin Salam for this contribution.</li>
1597
1598<li>The handling of diffraction has been made more flexible.
1599Specifically the "total" Pomeron-proton cross section can now be made
1600to depend on the mass of the diffractive system. This does not affect
1601the diffractive cross section in pp collisions, which is set separately,
1602but is used in the MPI machinery to affect the average number of
1603interactions per Pomeron-proton collision. Furthermore, the allowed
1604range for some parameters has been expanded. Thanks to Robert
1605Ciesielski.</li> 
1606
1607<li>New method <code>Pythia::forceTimeShower(...)</code> can be used to
1608generate a single final-state cascade from a set of partons, without
1609any knowledge of prior history. This is mainly intended for toy studies.
1610The meaning of the <code>ProcessLevel:all</code> switch has been modified
1611so that this parton-level function is available, but not any others
1612at this level.
1613</li>
1614
1615<li>ATLAS tune A2 now included. Thanks to Deepak Kar for
1616providing it.</li>
1617
1618<li>Change in the handling of recoils of timelike showers in resonance
1619decays, in cases of coloured resonances such as <ei>t -> b W</ei>. In
1620the first step the <ei>W</ei> always acts as recoiler to the <ei>b</ei>,
1621but in subsequent step previously the <ei>W</ei> remained as recoiler to
1622one dipole, while now all QCD-radiating partons recoil against another
1623coloured parton. The old behaviour could give a (small) unphysical spike
1624of radition collinear with the colourless recoiler in the subsequent
1625emissions (while the pattern of the first was and remains correct).
1626The old behaviour can be recovered for checks, see
1627<code>TimeShower:recoilToColoured</code>.
1628Thanks to Yevgeny Kats for pointing out this issue (previously noted
1629for Pythia 6 by several persons).
1630</li>
1631
1632<li>Bug fixes for <code>rootexamples/Makefile</code> and restoration
1633of some deleted information in <code>rootexamples/README</code>.
1634Thanks to Axel Naumann and Bernhard Meirose.</li>
1635
1636<li>Bug fix, so that displaced vertices are possible in resonance
1637decay chains. Thanks to Daniel Blackburn and Andy Buckley for
1638pointing this out.</li>
1639
1640<li>Bug fix for <code>Info</code> counter 2.</li>
1641
1642<li>Bug fix so that sextet quarks now are read in correctly from
1643Les Houches Event files; previously the (anti)colours were set
1644to 0.</li>
1645
1646<li>Year updated to 2012 in copyright statements etc.</li>
1647
1648<li>Reformatting to reduce the number of code lines with more
1649than 79 characters.</li>
1650
1651<li><code>Pythia::initSLHA()</code> moved from <code>public</code>
1652to <code>private</code>.
1653</li>
1654
1655<li>Remove warning message when tau polarization is set by hand.</li>
1656
1657<li>Several minor changes to reduce the number of warnings issued
1658by the clang compiler. The origin of some warnings remains unclear
1659so those remain to track down (could also be compiler bugs; note that
1660we discuss warnings, not errors). Thanks to Randy MacLeod for bringing
1661this up.</li>
1662
1663<li>The worksheet has been updated to be in step with Pythia 8.160.</li>
1664
1665<li>Several other minor corrections in the code and documentation.</li>
1666
1667</ul>
1668</li>
1669
1670<li>8.162: 12 March 2012
1671<ul>
1672
1673<li>A new option allows for several partons to share the recoil in
1674final-state radiation, see<aloc href="TimelikeShowers">Timelike
1675Showers</aloc>. It is mainly intended to be used in the context of
1676matching to matrix elements, and so only to be used in the first
1677few branchings.</li>
1678
1679<li>Several new processes for LED dijet production, see
1680<aloc href="ExtraDimensionalProcesses">Extra Dimensions</aloc>.</li>
1681
1682<li>Small update of the <code>Sigma2ffbar2LEDllbar</code> and
1683<code>Sigma2ffbar2LEDgammagamma</code> LED processes.</li>
1684
1685<li>New <code>Sigma2QCffbar2llbar</code> 
1686<aloc href="CompositenessProcesses">contact interaction</aloc> 
1687process.</li>
1688
1689<li>Inclusion of a new method in the
1690<aloc href="MatrixElementMerging">matrix-element merging</aloc> 
1691framework to influence the construction of histories, e.g. to already
1692in the construction of histories disallow paths that fail the
1693<ei>2 -> 2</ei> cuts.</li>
1694
1695<li>Further minor updates of the matrix-element merging code,
1696mainly for improved clarity.</li>
1697
1698<li>Minor bug fix in the handling of beam and event information fed
1699in from an <code>LHAup</code> instance.</li>
1700
1701<li>Minor bug fix for potential crashes from uninitialized variables
1702for the merging machinery when merging is not used.</li>
1703
1704<li>Updated History class for matrix element merging,
1705also avoiding some compiler warnings.</li>
1706
1707<li>Bug fixes in the handling of correlated mass choices in resonance
1708decays, such as <ei>H -> Z^*0 Z^*0</ei>.</li>
1709
1710<li>Bug fix when the process-level execution is switched off,
1711where <code>Info::isResolved()</code> could be called before its
1712value was initialized. Thanks to Christian Pulvermacher
1713for finding this.</li>
1714
1715<li>Corrected matrix-element expression for mass selection in
1716<ei>A^0 -> Z^*0 Z^*0</ei> and <ei>A^0 -> W^*+ W^*-</ei>.</li>
1717
1718<li>SM Higgs mass updated to 125 GeV and default width and branching
1719ratios modified accordingly. Minor technical improvements of width
1720calculation.</li>
1721
1722<li>The usage of nested classes has been removed from
1723<code>SusyLesHouches</code>, since it could give compilation errors
1724on some platforms. The new class names begin with <code>LH</code>
1725and all classes have been put inside the <code>Pythia8</code> 
1726namespace.</li>
1727
1728<li>Minor Makefile updates. Thanks to Mikhail Kirsanov.</li>
1729
1730<li>Minor changes to avoid some clang compiler warnings on the
1731Mac OS X platform.</li>
1732
1733</ul>
1734</li>
1735
1736<li>8.163: 27 March 2012
1737<ul>
1738
1739<li>New methods in the
1740<aloc href="EventInformation"><code>Info</code></aloc> class,
1741<code>id1pdf()</code>, <code>id2pdf()</code>, <code>x1pdf()</code> 
1742and <code>x2pdf()</code>, to denote the partons for which parton
1743distribution values have been defined. Previously this was assumed
1744to agree with the incoming partons to the hard process, the same
1745methods without the <code>pdf</code> qualifier. However, now the
1746POWHEG approach offers a counterexample. Also the reading and
1747handling of Les Houches (and other) events, and the interface
1748to HepMC, has been modified accordingly.
1749</li>
1750
1751<li>The decay of Higgs and top resonances read in from Les Houches
1752Event files is now performed with angular correlations as for
1753internal processes. LHE files should normally contain all process-specific
1754resonance decay chains and, if not, decays are made isotropic.
1755The <ei>H -> WW/ZZ -> f fbar f' fbar'</ei> and
1756<ei>t -> b W -> b f fbar</ei> correlations are process-independent,
1757however, and thus can be handled internally. If part of the decay
1758chain has already been set, e.g. <ei>H -> WW/Z></ei> or <ei>t -> b W</ei>,
1759then the subsequent decays are still isotropic.</li>
1760
1761<li>Updated instructions how to link to HepMC,
1762in <code>README.HepMC</code>.</li>
1763
1764<li>Bug fix in the turn-on of resolved diffraction for low
1765CM energies. Thanks to Erwin Visser.</li>
1766
1767<li>Bug fix in the handling of string junctions at very high energies,
1768caused by numerical errors. Thanks to Erwin Visser.</li>
1769
1770<li>Some other small changes, mainly aesthetics.</li>
1771
1772</ul>
1773</li>
1774
1775<li>8.165: 8 May 2012
1776<ul>
1777
1778<li>The MBR (Minimum Bias Rockefeller) model for single, double and
1779central diffraction <ref>Cie12</ref> is included as new option
1780<aloc href="Diffraction"><code>Diffraction:PomFlux = 5</code></aloc>.
1781It is specifically intended for <ei>p p</ei> and <ei>pbar p</ei>
1782interactions, and is currently the only option that also supports
1783central diffraction. Thus the basic machinery for Central Diffraction
1784(a.k.a. Double Pomeron Exchange) has now been implemented.
1785See <code>examples/main04.cc</code> for an example.
1786Thanks to Robert Ciesielski for contributing the new code.
1787</li>
1788
1789<li>For a <ei>tau</ei> lepton in an external process, by default the
1790SPINUP number in the Les Houches Accord now is interpreted as giving
1791the <ei>tau</ei> helicity, and is used for its decay.</li> 
1792
1793<li>A <ei>tau</ei> coming from a <ei>W</ei> now defaults to being purely
1794lefthanded when neither of the existing matrix elements apply.</li>
1795
1796<li>Decay mode <ei>t -> H+ b</ei> included as an option.</li>
1797
1798<li>Four ATLAS tunes have been implemented as options for
1799<code>Tune:pp</code>: A2-minbias-mstw2008lo, AU2-cteq6l1, AU2-mstw2008lo,
1800and AU2-ct10. The new flag <code>Tune:preferLHAPDF</code> can be used
1801to switch between the LHAPDF and the internal implementation of a
1802PDF set, in cases where both are available.</li>
1803
1804<li>Reorder libraries in <code>examples/Makefile</code>, specifically
1805move <code>LIBGZIP</code> so that it is properly linked when used.
1806Thanks to Erik Schnetter.</li>
1807
1808<li>Minor modification so that LHAPDF can be used for PDFs in the hard
1809process, with one of the built-in PDFs for the rest, even if LHAPDF is
1810compiled so as to handle only one concurrent PDF set.</Li>
1811
1812<li>Bug fix, that <code>ParticleDecays:mixB = off</code> did not
1813switch off <ei>B0 - B0bar</ei> and <ei>Bs0 - Bs0bar</ei> mixing.
1814Thanks to James Catmore.</li>
1815
1816<li>Bug fix for the handling of gluon polarization of initial-state
1817radiation, where an anisotropic azimuthal distribution was inadvertently
1818generated in some <ei>2 -> 1</ei> processes. The update also includes
1819always setting the second daughter zero for the two partons coming in to
1820a hard <ei>2 -> 1</ei> process. Thanks to Antonio Policicchio.</li>
1821
1822<li>Bug fix, that the setting of the number of user hooks MPI steps did
1823not use <code>UserHooks::canVetoMPIStep()</code> properly.</li>
1824
1825<li>Some other small changes, mainly documentation and aesthetics.</li>
1826
1827</ul>
1828</li>
1829
1830<li>8.170: 21 September 2012
1831<ul>
1832
1833<li>Streamline default behaviour and options for choice of GeV or MeV
1834for output to the HepMC event format, see
1835<aloc href="HepMCInterface">HepMC Interface</aloc>.
1836Also set the mass of HepMC particles explicitly, rather than having
1837it calculated implicitly. Thanks to James Monk and Andy Buckley.</li>
1838
1839<li>The <ei>tau</ei> decay machinery has been further augmented with
1840matrix elements and form factors for a variety of decay modes, such
1841that all modes with a branching ratio above 0.1% are fully modelled.
1842Several new classes and methods have been added to this end,
1843Also, a <ei>tau</ei> pair coming from a <ei>Z^0</ei> decay is now
1844handled by assuming the <ei>Z^0</ei> to be unpolarized when neither
1845of the existing matrix elements apply. Taus coming from B baryons are
1846handed as for B mesons.</li>
1847
1848<li>Flavour violating decays have been added to the squark, gluino,
1849neutralino and chargino decay tables.</li>
1850
1851<li>Extend the <code>UserHooks::subEvent(...)</code> method so that it
1852also works passably at the process level. Also new option for
1853<code>UserHooks::omitResonanceDecays(...)</code>.</li>
1854
1855<li>New methods <code>UserHooks::canVetoPartonLevelEarly()</code> 
1856and <code>UserHooks::doVetoPartonLevelEarly( const Event&)</code> 
1857are intended to be used the same way as the existing ones without
1858<code>Early</code> in their names, but allow veto right after
1859the ISR + FSR + MPI evolution, before beam remnants are added and
1860resonance decays are considered.</li>
1861
1862<li>Central diffraction now available for all
1863<code><aloc href="Diffraction">PomFlux</aloc></code> 
1864options, not only the MBR model. This has been constructed by analogy
1865with the respective assumptions made for single diffraction, but
1866includes some arbitrariness. Therefore the cross section is left
1867easily rescaleable and, for backwards compatibility with tunes
1868that does not contain it, easily possible to switch off, see
1869the <aloc href="TotalCrossSections">relevant section</aloc>.
1870</li> 
1871
1872<li>Reading of ALPGEN parameter and event files has been added,
1873see <aloc href="AlpgenAndMLM">ALPGEN and MLM Merging</aloc>.
1874</li>
1875
1876<li>MLM matching has been added, as a first step for ALPGEN events,
1877see <aloc href="AlpgenAndMLM">ALPGEN and MLM Merging</aloc>.
1878</li>
1879
1880<li>The CKKW-L merging machinery has been upgraded in a number of respects.
1881<br/>- More thorough treatment of <code>pp>bb~e+e-veve~</code> with
1882additional <ei>b</ei>-jets.
1883<br/>- Corrected hard <ei>mu_r</ei> and <ei>mu_f</ei> choices for
1884dijet and promt photon.
1885<br/>- More ways to define a hard process, e.g. with the LEPTONS and
1886NEUTRINO tags. The merging will understand LHE files for mixed processes
1887(e.g. <ei>W+</ei> and <ei>W-</ei> production together).
1888<br/>- More merging scale definitions.
1889<br/>- More freedom to generate all possible histories.
1890<br/>- Internal check (and cut) on Les Houches events in
1891<code>Pythia::mergeProcess</code> if merging scale value of the events
1892is below the value given to Pythia by setting <code>Merging::TMS</code>.
1893</li>
1894
1895<li>It now works to have R-parity violating decays of R-hadrons,
1896i.e. baryon number violation in a vertex displaced from the primary
1897one.</li>
1898
1899<li>The documentation of diffractive processes by the
1900<code><aloc href="EventInformation">Info</aloc></code> 
1901methods has been expanded and corrected. This also include the
1902<code>list()</code> method.</li> 
1903
1904<li>Particle masses and widths have been updated to agree with the
19052012 RPP values <ref>Ber12</ref>. Thanks to Piotr Zyla for data file
1906and James Catmore for program to update the PYTHIA tables from this
1907input.</li>
1908
1909<li>New methods <code>jetAssignment</code> and <code>removeJet</code>
1910added to the <code>SlowJet</code> class.</li>
1911
1912<li>Introduce angular correlation in decay chain
1913<ei>H -> gamma Z0 -> gamma f fbar</ei>. Thanks to Tim Barklow and
1914Michael Peskin.</li>
1915
1916<li>Introduce simple way to bias the selection of <ei>2 -> 2</ei> 
1917processes towards larger <ei>pT</ei> values, with a compensatingly
1918decreasing event weight, see
1919<aloc href="PhaseSpaceCuts">Phase Space Cuts</aloc>. Only offers a
1920subset of the possibilities allowed by <code>UserHooks</code>,
1921but simpler to use. The <code>main08.cc</code> program has been
1922expanded to illustrate this possibility, and also expanded to
1923include low-<ei>pT</ei> subsamples.</li>
1924
1925<li>The two remaining non-NLO tunes from <ref>ATL12</ref> are now
1926included.</li>
1927
1928<li>The <code><aloc href="EventInformation">Info</aloc></code> methods
1929<code>nTried, nSelected, nAccepted, sigmaGen</code> and
1930<code>SigmaErr</code> now takes the code of an individual process
1931as an optional argument.</li>
1932
1933<li>It is now possible to generate resonance decays, followed by
1934showers and hadronization, without having them associated with any
1935specific process. This is part of an expanded 
1936<aloc href="HadronLevelStandalone">Hadron-Level Standalone</aloc>
1937machinery, as before triggered by <code>ProcessLevel = off</code>,
1938but additionally requiring <code>Standalone:allowResDec = on</code>.
1939Input can either be directly into the <code>event</code> 
1940event record or via a (simplified) Les Houches Event File.</li>
1941
1942<li>New <code>configure</code> script options <code>--installdir</code>,
1943<code>--prefix</code> and <code>--datadir</code> can be used to set the
1944location(s) to which the library, header and data directories
1945will be copied by a <code>make install</code> subsequent to the
1946<code>make</code>. Thanks to Mikhail Kirsanov.</li>
1947
1948<li>Fix charge in antiparticle name when particle read in from SLHA
1949file. Thanks to Johan Alwall.</li>
1950
1951<li>Pointers now only compared with == and != (not e.g. > 0), to avoid
1952warnings in gcc 4.7.</li>
1953
1954<li>New check that version number of the code matches that of the
1955XML files. If not, no events can be generated. Thanks to James Monk
1956for suggestion.</li>
1957 
1958<li>New check that mother and daughter indices have been set to give
1959a consistent event history. Can be switched on/off with the new
1960<code>Check:history</code> flag.</li>
1961
1962<li>A new method <code>LHAup::newEventFile</code> has been added to
1963switch to reading in events from another LHE file without having to
1964reinitialize the whole class. Lower-level routines like
1965<code>openFile</code> and <code>closeFile</code> have been added to
1966handle correct order of operations also when an intermediate gzip
1967decompression step is involved.</li>
1968
1969<li><code>LHAup::eventLHEF()</code> can now be called with an optional
1970argument <code>false</code>, to make event files somewhat smaller by
1971reducing the amount of blanks.</li>
1972
1973<li>A new mode <code>Beams:nSkipLHEFatInit</code> introduced to
1974skip ahead the first few events in a Les Houches Event File (cf. the
1975<code>LHAup::skipEvent(nSkip)</code> method).</li>
1976
1977<li>Introduce a new pair of user hooks that can be used to reject
1978the sequence of hard-process resonance decays, without rejecting
1979the production of the primary resonances.</li>
1980
1981<li>The possibility of separate multiplicative prefactors to the
1982renormalization and factorization default <ei>pT^2</ei> scale has been
1983introduced for both timelike and spacelike showers.</li>
1984
1985<li>Bug fixes in history information for R-hadron production, which also
1986fixes HepMC conversion in this case.</li>
1987
1988<li>Bug corrected in <code>SigmaSusy.cc</code>, for chargino+neutralino
1989production. Indexing error for incoming quark states in the process
1990<code>Sigma2qqbar2charchi0</code>, resulted in incorrect CKM factors.</li>
1991
1992<li>Corrected a bug in <code>SusyLesHouches.cc</code>, for NMSSM spectra.
1993The unitarity check on the neutralino mixing matrix was faulty, leading
1994to erroneous messages about unitarity violations and SUSY being switched
1995off.</li>
1996
1997<li>Bug fixes in the handling of resolved and unresolved diffractive events.
1998Thanks to Robert Ciesielski for debug.</li>
1999
2000<li>Do not set up FSR dipoles for <ei>2 -> 1</ei> processes.</li>
2001
2002<li>Check that some channel open for resonance decays. Also further
2003check whether resonance decay treatment should be invoked.</li>
2004
2005<li>Bug fix in reading of particle names from SLHA input.</li>
2006
2007<li>Change mass, width and decay mode(s) of D*_s(10431). Thanks to
2008Michal Petran.</li>
2009
2010<li>Bug fix in leptoquark production (lepton sign in
2011<ei>q g -> LQ l</ei>).</li>
2012
2013<li>New argument added to <code>SpaceShower::reassignBeamPtrs</code>
2014for diffractive event processing, as already available for
2015<code>TimeShower</code>.</li>
2016
2017<li>Do not write warnings in <code>SpaceShower</code> for weights
2018above unity if the evolution scale is below 1 GeV^2.</li>
2019
2020<li>Add default values for member variables in some constructors,
2021and some related changes for <code>AlphaStrong</code> code.</li>
2022
2023<li>Warn if negative-energy parton in hadronization.</li>
2024
2025<li>The MPI <ei>pT</ei> values assumed in the beam remnant setting
2026of primordial <ei>kT</ei> and colour reconnection probability were
2027incorrect for diffractive events.</li>
2028
2029<li>The arrays with MPI information were not reset when parton or
2030hadron level fails and a new try is made. Only affected few events.</li>
2031
2032<li>MPI statistics can not yet be accumulated for diffractive events,
2033and therefore the relevant routine is no longer called.</li>
2034
2035<li>Bug fix in the double parton scattering suppression from
2036energy-momentum conservation.</li>
2037
2038<li>Outgoing proton masses were not set in the event record for
2039elastic scattering (but kinematics handling was correct).</li>
2040
2041<li>Bug fixes in the identification and documentation of junctions,
2042previously leading to some unnecessarily rejected events. Also
2043other improvements leading to fewer errors.</li>
2044
2045<li>Slightly increased values for FragmentationSystems:mJoin and
2046StringFragmentation::FACSTOPMASS to reduce failure rate, without
2047noticeably affecting event properties.</li>
2048
2049<li>The Les Houches cross section error is now taken into account
2050in the final Pythia error for strategies +-3.  New methods
2051<code>LHAup::xSecSum()</code> and <code>LHAup::xErrSum()</code>
2052provide the necessary information.
2053</li>
2054
2055<li>When a tau pair comes from a massless photon, in dipole shower
2056evolution, for the decay description the mother photon is reassigned
2057to have the sum of the tau momenta.</li>
2058
2059<li>Minor change in initialization sequence for user hooks,
2060to allow for more flexibility.</li>
2061
2062<li>Do not print warnings when multiparton interaction weights are
2063only slightly above unity.</li>
2064
2065<li>Do not write warnings for three known particles that are so close
2066to threshold that widths are switched off to avoid trouble.</li>
2067
2068<li>Some minor typographical changes.</li>
2069
2070</ul>
2071</li>
2072</ul>
2073
2074</chapter>
2075
2076<!-- Copyright (C) 2012 Torbjorn Sjostrand -->
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