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<h2>Update History</h2>
These update notes describe major updates relative to the baseline
PYTHIA 8.100 version. However, they are less extensive than the
corresponding update notes for PYTHIA 6. On the other hand,
whereas the PYTHIA 6 manual is a static document, the PYTHIA 8
html/php pages are kept up to date for each subversion.
<br/><br/>
<b>Important note:</b>version 8.160 does introduce some elements of
backwards incompatibility. Specifically, "multiple interactions",
abbreviated MI, has been renamed "multiparton interactions", MPI.
This affects many parts of the code and documentation. Also some
features are deprecated, although remaining until the end of the
8.1xx version series.
<h3>Main news by version</h3>
<ul>
<li>8.105: 24 February 2008
<ul>
<li>New option to initialize with arbitrary beam directions<br/>
<code>pythia.init( idA, idB, pxA, pyA, pzA, pxB, pyB, pzB)</code></li>
<li>Added capability to set <a href="BeamParameters.html" target="page">beam energy spread
and beam vertex</a>.
<br/>
<b>Warning:</b> as a consequence, the old <code>Beams</code> group of
settings has been moved to <code>BeamRemnants</code>, and
<code>Beams</code> is now instead used for machine beam parameters.
Therefore also some <code>Main</code> settings of this character have been
regrouped, as follows:
<table cellspacing="5">
<tr> <td>8.100 setting </td> <td>has been moved to </td> </tr>
<tr> <td><code>Main:idA </code></td>
<td><code>Beams:idA </code></td> </tr>
<tr> <td><code>Main:idB </code></td>
<td><code>Beams:idB </code></td> </tr>
<tr> <td><code>Main:inCMframe </code></td>
<td>(<code>Beams:frameType</code>) </td> </tr>
<tr> <td><code>Main:eCM </code></td>
<td><code>Beams:eCM </code></td> </tr>
<tr> <td><code>Main:eA </code></td>
<td><code>Beams:eA </code></td> </tr>
<tr> <td><code>Main:eB </code></td>
<td><code>Beams:eB </code></td> </tr>
<tr> <td><code>Main:LHEF </code></td>
<td><code>Beams:LHEF </code></td> </tr>
</table></li>
<li>The <code>forceHadronLevel()</code> method introduced for standalone
hadronization.</li>
<li><code>main15.cc</code> illustrated how either full hadronization or
only decays of some particles can be looped over for the rest of the
event retained.</li>
<li>The <code>LHAevnt</code> and <code>LHAinit</code> classes have been
joined into a new <code>LHAup</code> one, with new options that allow
the writing of a Les Houches Event File.</li>
<li>The <code>SusyLesHouches</code> class updated to handle
SLHA version 2.</li>
<li>Updated HepMC conversion routine.</li>
<li>The static <code>ErrorMsg</code> class has been removed and
its functionality moved into the non-static <code>Info</code> class,
in the renamed Info file.</li>
<li>Further reduction of the use of static, with related code changes.
This should allow to have several almost independent <code>Pythia</code>
instances. Some static classes still remain, however, notably for
random number generation and particle properties.</li>
<li>Limited capability to use two different <code>Pythia</code> instances
for signal + pileup event generation, see <code>main19.cc</code> for an
example.</li>
<li>In the <code>Event</code> class the <code>=</code> and
<code>=+</code> methods have been overloaded to allow the copying
or appending of event records. Illustrated in <code>main19.cc</code>.</li>
<li>The html and php page formatting improved with
cascading style sheets.</li>
<li>Several minor improvements and new options, including updated configure
scripts.</li>
</ul>
</li>
<li>8.108: 1 May 2008
<ul>
<li>Correction in the event record, so that the beam particles in line
1 and 2 do not have any mother according to the <code>motherList</code>
method. Previously the "system" entry in line 0 was counted as their
mother, which gave rise to an unexpected extra vertex in the conversion
to the HepMC format.</li>
<li>Support for HepMC version 1 is removed, to simplify the code and
reflect the evolution of the field.</li>
<li>Status codes are stored in HepMC only as 1 for existing and 2 for
decayed or fragmented particles (whereas previously the original PYTHIA
codes were used for the latter).</li>
<li>Parton densities are stored in HepMC as <i>xf(x,Q^2)</i>
rather than the <i>f(x,Q^2)</i> used in (some) previous versions.</li>
<li>The SusyLesHouches class has been updated so that reading is fully
compatible with the SLHA2 standard. </li>
<li>Improved handling of the Higgs width, relevant for massive and thereby
broad resonance shapes.</li>
<li>The matrix elements for neutralino pair production have now been
completed and checked.</li>
<li>Ensure that <i>alpha_strong</i> does not blow up, by introducing
a minimal scale somewhat above <i>Lambda_3</i> (roughly where
<i>alpha_strong = 10</i>).</li>
<li>New methods <code>isValence1()</code> and <code>isValence2()</code>
in the <code>Info</code> class.</li>
<li>Protection against division by zero in calculation of decay vertex
(for zero-mass gluons with zero lifetime, where there should be no
displacement).</li>
<li>A new compilation option <code>-Wshadow</code> is introduced and
code is rewritten at all places where this option gave warnings.</li>
<li>Minor library correction to allow compilation with gcc 4.3.0.</li>
</ul>
</li>
<li>8.114: 22 October 2008
<ul>
<li>New rescattering description operational (but still experimental)
for the case that FSR is not interleaved, but saved until after MPI,
ISR and beam remnants have been handled. This involves much new code
in several classes.</li>
<li>A new class <code>PartonSystems</code> is introduced to
keep track of which partons in the event record belong to which
subcollision system, plus some further information on each subsystem.
It takes over functionality previously found as part of the
<code>Event</code> class, but leaves room for future growth.</li>
<li>Add optional model, wherein an increased <i>pT0</i> turnoff scale
for MPI and ISR is used for above-average active events, i.e. events that
already have several MPI's or ISR emissions.</li>
<li>Freeze GRV 94L distribution at small <i>Q^2</i> to avoid blowup.</li>
<li>The <code>pythia.readFile(...)</code> method can now alternatively take
an <code>istream</code> as argument instead of a <code>filename</code>.</li>
<li>Minor bug correction in <code>PartonLevel.cc</code>; the bug could
(rarely) give a segmentation fault.</li>
</ul>
</li>
<li>8.120: 10 March 2009
<ul>
<li>New rescattering description further developed, but not yet
recommended for normal usage.</li>
<li>Include new processes for Large Extra Dimensions and Unparticles,
contributed by Stefan Ask. New test program <code>main28.cc</code>
illustrates.</li>
<li>Include further SUSY processes: neutralino-chargino and
chargino-chargino pairs. The processes should be valid also
in the case of non-minimal flavour violation and/or CP violation.
Expanded machinery to keep track of SUSY parameters.</li>
<li>Include backwards evolution of incoming photon as part of the
<code>SpaceShower</code> initial-state radiation description. This
allows you to simulate hard collisions where one of the incoming
partons is a photon. New test program <code>main43.cc</code>
illustrates.</li>
<li>Allow separate mass and transverse momentum cuts when two hard
subprocesses are generated in the same event.</li>
<li>The default value for the border between short- and long-lived
particles has been changed from 1 mm to 10 mm, to better conform with
LHC standards, see <a href="ParticleDecays.html" target="page">here</a>.
The default is still to let all unstable particles decay.</li>
<li>New ISR matrix-element correction to <i>f → f gamma</i>
in single <i>W</i> production.</li>
<li>New method <code>Event::statusHepMC</code> returns the status
code according to the HepMC conventions agreed in February 2009.
The interface to HepMC now writes out status according to this
convention.</li>
<li>Add capability to link to FastJet, with expanded configure script
and Makefile, and with <code>main61.cc</code> as new example.</li>
<li>Update of <code>Makefile.msc</code>, with added support for latest
Visual C++ Express edition and use of regexp to check nmake version.</li>
<li>Update of <code>LHAFortran.h</code> and
<code>Pythia6Interface.h</code>, to make the interface to Fortran
routines work also under Windows. (Thanks to Anton Karneyeu.)
<li>Updated and expanded worksheet.</li>
<li>The manual pages in the <code>xmldoc</code> directory, and thereby
also those of the <code>htmldoc</code> and <code>phpdoc</code>
directories, have been significantly updated and expanded. In particular,
in many places the class of each method is explicitly shown, as well as
the type of the return value and of the arguments. This upgrade is not
yet completed, but already covers the more relevant sections. </li>
<li>The unary minus operator in the <code>Vec4()</code> returns a
reference to a four-vector with all components negated, but leaves
the original four-vector unchanged. Previously the four-vector itself
was flipped.</li>
<li>The <code>pPlus()</code> and <code>pMinus()</code> methods of a
four-vector and an event-record particle are renamed <code>pPos()</code>
and <code>pNeg()</code>, respectively.</li>
<li>Include a further loop in <code>ProcessLevel</code>, so that a new
process is generated in case of failures of a less severe nature.</li>
<li>Introduce warning message for unexpected <code>meMode</code> in
<code>ResonanceWidths</code>.</li>
<li>Les Houches event reading framework has been rearranged for
more flexibility. Some bugs corrected. Specifically, when scale
is not set (<code>scale = -1.</code> in the Les Houches standard),
PYTHIA did not attempt to set this scale itself, which typically
lead to there not being any ISR or FSR. Now the
<a href="CouplingsAndScales.html" target="page">rules for normal
1-, 2- and 3-body final states</a> are applied, with a trivial
extension of the 3-body rules for higher multiplicities.</li>
<li>Correct bug in the handling of parton densities, whereby it was
not possible to switch to a new set, once a first initialization
had been done.</li>
<li>Correct bugs when several <code>Pythia::init</code> initialization
calls are made in the same run, specifically in the case that pointers
to external processes have been handed in.
<li>Changes in <code>main03.cmnd</code> and <code>main04.cmnd</code>
so that some nonstandard options are commented out rather than active.
Related comments inserted also in some other <code>.cmnd</code> files,
but there without any change in program execution.</li>
<li>A few further minor bug fixes.</li>
<li>Update year to 2009.</li>
</ul>
</li>
<li>8.125: 16 June 2009
<ul>
<li>Hadronization and timelike-shower parameter default values updated
according to a tune to LEP1 data by Hendrik Hoeth, using the
Rivet + Professor framework.</li>
<li>Many further SUSY production processes. SLHA readin expanded to cover
also masses and decay modes. Example <code>main22.cc</code> updated, while
<code>main33.cc</code> now superfluous and removed. </li>
<li>Also further processes for extra dimensions.</li>
<li>Stefan Ask joins as coauthor.</li>
<li>The <code>TimeShower::shower(...)</code> method has gained
a new argument, that forces the shower evolution to stop after
a given number of branchings. A new method
<code>TimeShower::pTLastInShower()</code> permits the last evolution
<i>pT</i> to be read out. These extensions can be useful
for matching studies.
</li>
<li>New optional argument <code>isInterleaved</code> added to
<code>TimeShower::branch(...)</code>. Is false by default, but
true when called from the parton level for interleaved evolution
of several parton systems, optionally also with ISR and MPI.</li>
<li>New methods <code>UserHooks::canSetResonanceScale()</code>
and <code>UserHooks:scaleResonance(...)</code> allows an optional
user choice of the maximum shower scale in resonance decays.</li>
<li>A new method <code>SpaceShower::doRestart()</code> has been
added, to help distinguish cases when a
<code>SpaceShower::branch(...)</code> failure forces a complete
restart of the evolution from ones where only the intended
current branching has been vetoed.
<li>When multiparton interactions are initialized, it is now
possible to reduce both <i>pT0</i> and <i>pTmin</i>
if necessary to find a valid solution where
<i>sigma_jet > sigma_nondiffractive</i>. Previously
only the former would be reduced, which could lead to
infinite loops if too large a <i>pTmin</i> was used.
Thanks to Sami Kama for pointing out the problem.
</li>
<li>The rescattering machinery is now essentially completed, and can
be used also by others than the authors. For now, however, it can only
be recommended for dedicated studies, not e.g. for generic tunes.
</li>
<li>Timelike and spacelike showers, and beam remnant handling,
are modified to handle rescattering partons. Specifically, a new machinery
is introduced to trace the recoils from the combination of rescattering
with showers and primordial <i>kT</i>. Can assign space- or timelike
virtualities to intermediate particles to have energy and momentum
conserved locally. This affects the <code>PartonLevel</code>,
<code>MultipartonInteractions</code>, <code>TimeShower</code>,
<code>SpaceShowe</code>r and <code>BeamRemnants</code> classes.
Further details to appear in the upcoming article on rescattering.
(Another change is a reversal to pre-8.114 order for non-interleaved FSR,
wherein also FSR is treated before beam remnants are attached.)
</li>
<li>Four new status codes introduced, as part of the rescattering
description:
<br/>45 : incoming rescattered parton, with changed kinematics owing
to ISR in the mother system (cf. status 34);
<br/>46 : incoming copy of recoiler when this is a rescattered parton
(cf. status 42);
<br/>54 : copy of a recoiler, when in the initial state of a different
system from the radiator;
<br/>55 : copy of a recoiler, when in the final state of a different
system from the radiator.
</li>
<li>New method <code>Info::tooLowPTmin()</code> can tell whether the
<i>pTmin</i> scales for showers or multiparton interactions are too low.
</li>
<li>Pion beams allowed, both <i>pi^+</i>, <i>pi^-</i> and
<i>pi^0</i>. New machinery for the latter, where the valence
flavour content is chosen to be either <i>d dbar</i> or
<i>u ubar</i> for each new event. One internal pion PDF
implemented, with others from LHAPDF.</li>
<li>Treatment of Pomeron-proton collisions begun.</li>
<li>Phase-space handling of hard processes and multiparton interactions
slightly expanded to better allow for harder PDF's than proton ones,
e.g. for Pomerons.</li>
<li>The program documentation has been expanded with an
alphabetical index of all methods that are described on the
webpages, see the <a href="ProgramMethods.html" target="page">Program Methods</a>
page. Also other sections of the documentation have been
updated and expanded, including the worksheet.</li>
<li>Several <code>list</code> methods have been made
<code>const</code>. For the listing of events two new methods
have been added, <code>Event::list()</code> and
<code>Event::list(bool showScaleAndVertex,
bool showMothersAndDaughters = false)</code>,
that correspond to special cases of the general method.</li>
<li>A new method <code>Pythia::LHAeventSkip(int nSkip)</code>
permits a skip-ahead of the reading of external Les Houches
Events, without the necessity to generate the intervening
<code>nSkip</code> events in full. Makes use of the new
<code>LHAup::skipEvent(int nSkip)</code> method to perform
the operations. Mainly intended for debug purposes.
<li>The <code>ClusterJet</code> jet finder now saves the last
five clustering scales. Also a minor bug fix. Thanks to Nils
Lavesson for this contribution.</li>
<li>The <code>Particle::m2()</code> method now returns a negative
number when the stored mass <i>m</i> is negative, as used to
indicate spacelike virtualities. Also the
<code>Particle::eCalc()</code>, <code>Particle::mT()</code> and
<code>Particle::mT2()</code> methods have been modified.
</li>
<li>The <code><<</code> method to print our a four-vector has
been expanded with a fifth number, the invariant length, with a minus
sign for spacelike vectors, and provided within brackets to allow
a simple visual distinction.</li>
<li>New methods <code>Rndm::dumpState(string fileName)</code> and
<code>Rndm::readState(string fileName)</code> allows to write or
read the state of the random number generator to or from a binary file.
</li>
<li>New method <code>double GammaReal(double x)</code> returns the
value of the <i>Gamma</i> function for arbitrary real argument.
Some cross sections for extra-dimensional processes rewritten to
make use of it.
</li>
<li>New example program <code>main29.cc</code> shows how
to set up a fictitious process of a heavy system decaying
to two particles or partons, with decays traced to stable
particles, as relevant for astroparticle applications.</li>
<li>Main programs that illustrate the HepMC interface have
been updated to use version 2.04, including units and excluding
deprecated output formats.</li>
<li>The <code>main32.cc</code> example extended also to handle
Les Houches Event Files.</li>
<li>The Makefile has been modified so that "make clean" only
removes the current compilation and library files, while
"make distclean" gives a more extensive reset and cleanup.
Thanks to Nils Lavesson for this contribution. Some other
minor Makefile corrections.</li>
<li>Several main programs that use the
<code>Main:timesToShow</code> mode have been corrected so as
not to crash if this is set to zero. Also some other cosmetics
changes in main programs that do not affect the running.</li>
<li>Bug correction, in that previously a veto with user hooks
was not propagated from parton showers inside resonance decays.
</li>
<li>Minor bug fix in <code>TimeShower</code> for kinematics with
unequal beam-particle masses.</li>
<li>Bug fix so that <code>PartonLevel:MPI = off</code> also works for
minimum-bias events.</li>
<li>Minor bug fix in the impact-parameter selection of multiparton
interactions. Thanks to Sami Kama for pointing it out.</li>
<li>String fragmentation for junction topology protected against
numerical instability in boost.</li>
<li>Bug correction in the handling of particle decays to partons,
where the scale of the partons was set before the partons had been
added to some arrays, leading to indexation out of bounds.
Thanks to Vladislav Burylov for discovering this bug.
</li>
<li>Bug correction in the handling of particles with inhibited decay,
where the decay vertex would be too far displaced, which could lead to
infinite loop. Thanks to Sami Kama for debugging this. </li>
<li>Check to avoid infinite loop in matrix-element handling of
two-body decays.</li>
<li>Bug correction to avoid infinite loops in Dalitz decay treatment.
Some changes in the decay handling logic to allow a new try when the
decay of a particle fails.</li>
<li>Minor correction, so the pointer to the <code>Info</code> class
is set also for user-written classes derived from <code>LHAup</code>.
</li>
<li>Correction for typo in the matrix element of the
<code>Sigma3ff2HchgchgfftWW</code> class, for doubly charged Higgs
production. Thanks to Merlin Kole for spotting it.</li>
<li>Updated colour bookkeeping in junction-antijunction annihilation
avoids later problems in <code>Pythia::check()</code>. </li>
<li>Minor updates of the <code>Makefile.msc</code> file to work with
Visual Studio 2008. Thanks to David Bailey for these modifications.</li>
<li>Ensure that <code>nInit</code> in the <code>BeamParticle</code>
class is set also for unresolved lepton beams.</li>
<li>The <code>VetoEvolution</code> class, derived from
<code>UserHooks</code>, is obsolete and has been removed.</li>
</ul>
</li>
<li>8.130: 15 September 2009
<ul>
<li>New machinery that allows multiparton interactions inside diffractive
systems. Also new optional Pomeron flux factors and Pomeron PDFs.
New page on <a href="Diffraction.html" target="page">diffraction</a> added, where
further details are collected. Still not tuned, so to be used with
caution.</li>
<li>Make Peter Skands' "Tune 1" parameters for ISR and MPI default.
The older simpler tune is still available as an option, see
<code><a href="Tunes.html" target="page">Tune:pp</a></code>.
</li>
<li>New possible choices for a second hard process: charmonium,
bottomonium, top pair and single top.</li>
<li>New code for pair production of generic colour-triplet scalar,
fermion or vector. Largely written by Johan Bijnens, partly recycling
existing code.</li>
<li>Add user hooks possibility to veto event after a given number
of multiparton interactions.</li>
<li>Add instructions how PYTHIA 8 can be used from inside ROOT.
Thanks to Andreas Morsch for providing the text and Rene Brun
for a simple example.</li>
<li>The <code>main21.cc</code> example extended with an option
for a single-particle gun.</li>
<li>Improvements and bug fixes in rescattering framework.</li>
<li>New method <code>Hist::table(string fileName)</code> provides a
more direct way to print a two-column table of histogram contents
into a file than the current <code>Hist::table(ostream& os = cout)</code>.
</li>
<li>Modify reading of external files so that a line only consisting of
control characters counts as empty, the same way as a line only consisting
of blanks already did. This includes carriage return, tabs and a few more,
the ones represented by <code>\n \t \v \b \r \f \a</code>. Applies to
Les Houches Event files, settings files and particle data files. </li>
<li>Fix it so that the read-in of a Les Houches Event File for the
hardest process can be combined with the facility to select a specified
second hard process.</li>
<li>New empty base class method <code>LHAup::fileFound()</code>
allows the derived class <code>LHAupLHEF</code> to signal more
clearly that a failed initialization is caused by a failure to open
the desired file. </li>
<li>Check that a pointer to an <code>LHAup</code> object has been set
in <code>Pythia::LHAeventList()</code> and
<code>Pythia::LHAeventSkip(...)</code> calls.</li>
<li>Updated configure and Makefile, e.g. to build shared libraries
on Mac OS X.</li>
<li>The options with a direct link to hard-process generation
in PYTHIA 6 has been removed. It is hardly ever used but
complicates the build structure. (Owing to its usefulness for some
debug work, it was reinstated in a limited form in version 8.135.
Thus <code>main51.cc</code> now contains the complete interface,
previously in separate files, and commented-out lines in
<code>examples/Makefile</code> suggest how PYTHIA 6 could be linked.)
</li>
<li>New argument to <code>Info::errorMsg(...)</code> allows to
show all error messages of a specific kind rather than only the
first one, e.g. for initialization.</li>
<li>Correction in decay table of righthanded Majorana neutrinos.
Thanks to Arnaud Ferrari and Vladimir Savinov.</li>
<li>Correction in expressions in the manual for <i>H^+-</i> couplings
to an <i>h^0</i>, <i>H^0</i> or <i>A^0</i> and a <i>W^+-</i>.
Thanks to Rikard Enberg.</li>
<li>Fix for accessing uninitialized memory, caused by accessing the
daughters of the incoming beams before these daughters actually existed.
Thanks to David Bailey and Sami Kama.
</li>
<li>Uninitialized photon PDF inside the proton could give crazy results
for processes with incoming photons. Thanks to Adam Davison.</li>
<li>Bug fix such that finite lifetimes can be set also for particles
produced in the hard process. To exemplify, the bug affected
<i>tau</i> leptons produced in <i>Z^0</i> and <i>W^+-</i>
decays. Thanks to Troels Petersen.</li>
<li>Bug fix in <code>TimeShower</code>, that <code>beamOffset</code>
could remain uninitialized. Thanks to Sami Kama.</li>
<li>Minor correction to resonance decays: fail if the allowed mass
range of a Breit-Wigner resonance is a small fraction of the total
area under the resonance curve.</li>
<li>Correction when all three valence quarks were kicked out from a
proton and could give false messages that beam momentum had been
used up.</li>
<li>Clarify status codes needed for hadron-level standalone runs in
order to avoid error messages, and modify the <code>main21.cc</code>
example accordingly. </li>
<li>Minor corrections in the processes for extra dimensions.</li>
<li>Some other minor additions to existing facilities
and minor bug fixes.</li>
</ul>
</li>
<li>8.135: 10 January 2010
<ul>
<li>All usage of static member methods inside Pythia8 has now been
eliminated. This simplifies for you to have several simultaneous
<code>Pythia</code> instances that are run with different conditions.
The three main classes affected by this are the <code>Settings</code>
and <code>ParticleData</code> databases and the <code>Rndm</code>
random-number generator. You can no longer address the methods of these
classes directly, but have to address them via the <code>settings</code>,
<code>particleData</code> and <code>rndm</code> instances in the
respective <code>Pythia</code> object. Also some other smaller pieces
of code are affected, e.g. Standard Model and SUSY couplings
(the latter in new files).
<br/><b>Note 1</b>: The documentation has been updated accordingly
on these webpages, but the "A Brief Introduction to PYTHIA 8.1"
still refers to the old behaviour of version 8.100.
<br/><b>Note 2</b>: the interface to the external LHAPDF library remains
static, since LHAPDF is written in Fortran and thus by definition
static.
<br/><b>Note 3:</b> if you want to have momentum smearing in
<code>CellJet</code> you now need to send in a pointer to a
random-number generator.
</li>
<li>Ten new proton PDF sets are made available internally:
MRST LO* (2007), MRST LO** (2008), MSTW 2008 LO (central member),
MSTW 2008 NLO (central member), CTEQ6L, CTEQ6L1, CTEQ6.6 (NLO,
central member), CT09MC1, CT09MC2, and CT09MCS, see
<a href="PDFSelection.html" target="page">PDF Selection</a>. The Pomeron PDF data
files have been renamed for consistency. Thanks to Tomas Kasemets
for help with this [<a href="Bibliography.html" target="page">Kas10</a>].
</li>
<li>New parameters <code>TimeShower:pTmaxFudgeMPI</code> and
<code>SpaceShower:pTmaxFudgeMPI</code> introduced, to give the same
functionality for multiparton interactions that
<code>TimeShower:pTmaxFudge</code> and <code>SpaceShower:pTmaxFudge</code>
do for the hardest.</li>
<li>A few extensions of the <code>UserHooks</code> framework.
New methods <code>UserHooks:canVetoISREmission()</code> and
<code>UserHooks::doVetoISREmission(...)</code> allows the latest
initial-state emission to be studied before being finalized,
with the possibility to veto it.
Similarly <code>Userhooks:canVetoFSREmission()</code> and
<code>UserHooks::doVetoFSREmission(...)</code> can be used to
veto the latest final-state emission.</li>
<li>A number of loop counters have been introduced in the
<code>Info</code> class, that offers some further information on
the progress of the event generation, for use e.g. in conjunction
with the <code>UserHooks</code> facility.</li>
<li>The <code>Pythia::initTunes(...)</code> method is made public, so that
it can be called before the normal call from <code>Pythia::init(...)</code>.
That way it is possible to start out from a given tune and change a few
of the parameters.
</li>
<li>Bug corrected in <code>LHAFortran.h</code> for hard-process input
from Fortran commonblock. This did not work properly when the input
was used in combination with a second hard process generated internally.
Thanks to Mikhail Kirsanov and Roberto Chierici.
<li>Insertion of missing initialization of <code>isInit</code> in the
<code>Settings</code> and <code>ParticleData</code> constructors, and
<code>nInit</code> for <code>BeamParticle</code>.
Thanks to Leif Lönnblad.</li>
<li>Updated <code>Makefile.msc</code> for Windows users.</li>
<li>Fix of some non-optimal use of booleans, that give warnings on
a Windows compiler. Thanks to Anton Karneyeu.</li>
<li>New options for the <a href="SUSYLesHouchesAccord.html" target="page">
SUSY Les Houches Accord</a> such that, by default,
particle and decay data are not overwritten for known Standard Model
particles (including <i>Z^0</i>, <i>W^+-</i> and <i>t</i>,
but excluding the Higgs).</li>
<li>Bug fix in <code>SusyLesHouches</code>, where the reading of SLHA
information embedded in an LHEF would not stop at the end of the header
section.</li>
<li>Bug correction for undefined secondary widths where decay products
together are heavier than the mother. Also unit default secondary width
values in the <code>DecayChannel</code> constructor.</li>
<li>Documentation updated, including change of current year to 2010.</li>
</ul>
</li>
<li>8.140: 16 July 2010
<ul>
<li>Four new draft <a href="Tunes.html" target="page">tunes</a> available.</li>
<li>Introduction of a new scenario for production of Hidden-Valley
particles, and interleaved showering in the QCD and HV sectors, see
the new <a href="HiddenValleyProcesses.html" target="page">Hidden Valleys</a>
description. A longer physics writeup is available [<a href="Bibliography.html" target="page">Car10</a>].
</li>
<li>Implementation of <i>2 → 3</i> phase space selection intended
for QCD processes with massless partons. A new set of matching
<a href="PhaseSpaceCuts.html" target="page">phase space cut parameters</a>.
The <a href="QCDProcesses.html" target="page">ten different QCD <i>2 → 3</i>
processes</a> have been implemented making use of this new
possibility, so far without a complete handling of possible colour
flows, however.</li>
<li>New processes have been added for
<a href="CompositenessProcesses.html" target="page">contact interactions</a> in
<i>q q → q q</i> and <i>q qbar → q qbar</i> scattering.</li>
<li>A process has been added for TeV^-1 Sized
<a href="ExtraDimensionalProcesses.html" target="page">Extra Dimensions</a>, which
involves the electroweak KK gauge bosons, i.e. <i>gamma_{KK}/Z_{KK}</i>,
in one TeV^-1 sized extra dimension; see <code>main30.cc</code> for
an example. This scenario is described in [<a href="Bibliography.html" target="page">Bel10</a>]. Thanks to
Noam Hod and coworkers for contributing this code.</li>
<li>In the Randall-Sundrum extra-dimensional scenario a new option has
been added where SM fields can exist in the bulk rather than only on
a brane. (Still under development.) Furthermore production of a
Kaluza-Klein gluon state has been added, and the <code> main28.cc</code>
test program extended.</li>
<li>The scenario for monojets in Large Extra Dimensions has been expanded
with an alternative for scalar graviton exchange instead of tensor one.
</li>
<li>New parameters for maximum scale of
<a href="TimelikeShowers.html" target="page">timelike showers</a>,
<code>TimeShower:pTmaxMatch</code>, and the dampening of hard radiation,
<code>TimeShower:pTdampMatch</code> and <code>TimeShower:pTdampFudge</code>,
by analogy with corresponding ones for spacelike showers. Also new method
<code>TimeShower:limitPTmax(...)</code> to implement alternative procedures.
For dipoles stretched to the beam the new switch
<code>TimeShower:dampenBeamRecoil</code> allows to dampen radiation
close to the beam direction, with a changed default behaviour.</li>
<li>Azimuthal anisotropies from coherence arguments have been introduced
for the spacelike parton showers, see <code>SpaceShower:phiIntAsym</code>
and <code>SpaceShower:strengthIntAsym</code>.
Also azimuthal anisotropies from gluon polarization have been introduced
for the spacelike parton showers, see <code>SpaceShower:phiPolAsym</code>,
and updated for timelike parton showers, see
<code>TimeShower:phiPolAsym</code>.</li>
<li>Improvements for the matching to POWHEG LHEF-style input illustrated
by the new <code>main71.cc</code> example. See also [<a href="Bibliography.html" target="page">Cor10</a>].</li>
<li>A set of new processes <i>gamma gamma → f fbar</i>, with <i>f</i>
quarks or leptons. Code for equivalent photon flux around an unresolved
proton, with more to come. Thanks to Oystein Alvestad.
</li>
<li>A new option has been included to dampen the growth of the diffractive
cross sections, see <a href="TotalCrossSections.html" target="page">Total Cross
Sections</a>.</li>
<li>A new method <code>virtual int SigmaProcess::idSChannel()</code>
has been introduced. If overloaded to return a nonzero value then a
<i>2 → n</i> process will appear listed as a
<i>2 → 1 → n</i> one.
That is, an intermediate resonance with the requested identity will be
inserted in the event record, even without appearing in the calculation
of the matrix element proper. Thanks to Noam Hod for idea and code.</li>
<li>A new method <code>SigmaProcess::convertM2()</code> has been introduced
to optionally allow the <code>SigmaProcess::sigmaHat()</code> to return
the squared matrix element rather than <i>d(sigmaHat)/d(tHat)</i> for
<i> 2 → 2 </i> processes. Furthermore kinematics is stored in the new
<code>mME</code> and <code>pME</code> vectors for alternative cross
section encodings.</li>
<li>Different encoding of the <i>f fbar → Z W</i> cross section,
contributed by Merlin Kole, based on the cross section of
Brown, Sahdev and Mikaelian. Gives a distinctly different cross section
than the previous based on EHLQ (including their bug fix).
In particular the problem with negative cross sections is now fixed.</li>
<li>Minor updates: pass <code>xmlPath</code> to new MSTW and CTEQ PDFs;
reset beams earlier to give cleaner documentation.</li>
<li>The H1 Fit B LO parametrization to the Pomeron PDF has been included,
and made new default for Pomerons. Thanks to Paul Newman for providing
the data files.</li>
<li>Three changes, in principle unrelated, but with the common objective
to make the generation of a given event depend only on the values
determined during the initialization stage and on the state of the
random-number generator when the event is begun. The new default
should ensure a reproducible stop-and-restart behaviour, convenient
for debug purposes. Thanks to Michael Schmelling for stressing the
desire for such a behaviour.
<br/>(i) Introduction of a new option <code><a href="PhaseSpaceCuts.html" target="page">
PhaseSpace:increaseMaximum</a></code> that allows to switch between
two strategies for handling the (hopefully rare) cases when the
assumed maximum of the cross section function is exceeded during the
event generation, with a changed default behaviour. In the old
default the maximum could be increased if it was exceeded during the run,
thereby introducing a memory of the previously generated events.
<br/>(ii) Updated handling of random numbers with Gaussian distributions.
The <code>gauss()</code> method now only generates one value at a time.
Instead the new <code>gauss2()</code> method returns a pair of Gauss
numbers, with related time savings. In the old approach one Gaussian
number could be buffered, which introduced a memory.
<br/>(iii) Minor bug fix in <code>MiniStringFragmentation</code>, where
the popcorn baryon state was not reset for each new system, again
giving a (flawed) memory.</li>
<li>New directory <code>rootexample</code> with a simple code example
how to use ROOT for histogramming in PYTHIA runs. See
<a href="ROOTusage.html" target="page">ROOT Usage</a> for details. Thanks to Rene Brun.
</li>
<li>In the <code>HepMCinterface</code> the checks for unhadronized
quarks and gluons are not performed if hadronization has been switched
off.</li>
<li>The <code>UserHooks::initPtr(...)</code> has been expanded so that
pointers to more classes (beam particles, random number, couplings, etc.)
are sent in, thereby increasing the scope of possible user-written code.
Also, the <code>UserHooks::doVetoProcessLevel(Event& process)</code>
now allows the <code>process</code> event record to be modified,
even if it is not recommended. The new <code>Info::pTnow()</code>
method returns the current <i>pT</i> scale of the combined MPI, ISR
and FSR evolution, which can be useful for some user hooks decisions.
</li>
<li>Histograms of the <code>Hist</code> class can now be booked
with up to 1000 bins, instead of the previous maximum 100. All bins
can be written to file, but the line-printer style printing will join
nearby bins so at most 100 are printed, as before. </li>
<li>Updated <code>configure</code> and <code>Makefile</code>
to allow 64-bit compilation and more options. Thanks to Mikhail Kirsanov,
Rene Brun and Fons Rademakers.</li>
<li>Bug fix in <code>ProcessLevel</code> for colour flow checks of
junctions. Enables the decay of a neutralino to three quarks, e.g.
Thanks to Nils-Erik Bomark.</li>
<li>Bug fixes in <code>TimeShower</code>, where recoil partners in resonance
decays of coloured particles, and recoil partners in QED dipoles when beams
are not allowed to take a recoil, might not be correctly identified. </li>
<li>Bug fix in <code>SpaceShower</code>: when used with a fixed
<i>alpha_strong</i>, the threshold enhancement factor of
<i>g → Q Qbar</i> became undefined. Thanks to Stefan Prestel.</li>
<li>Bug fix in initialization of resonance widths, where the
<code>minWidth</code> parameter could be used uninitialized,
occasionally resulting in strange initialization problems when
kinematics needs to force at least one resonance to be off-shell.</li>
<li>Minor updates of <code>main06.cc</code>, <code>main10.cc</code>
and <code>main23.cc</code>.</li>
<li>Bug fix in mother pointer of multiparton interactions in
diffractive systems.</li>
</ul>
</li>
<li>8.142: 15 August 2010
<ul>
<li>The strategy for setting up tune values has been changed.
Previously the <code>Tune:ee</code> and <code>Tune:pp</code>
settings were only interpreted during the
<code>Pythia::init(...)</code> stage. Now they are interpreted
as soon as they are read. Specifically this means that it is
possible to override any of the tune parameters by putting new
commands below <code>Tune:ee</code> and <code>Tune:pp</code>
in the <code>Pythia::readFile(...)</code> configuration file
or in the list of <code>Pythia::readString(...)</code> commands.
<br/>As a consequence of this change, the public
<code>Pythia::initTunes(...)</code> method has been replaced by
two private <code>Settings::initTuneEE(...)</code> and
<code>Settings::initTunePP(...)</code> methods.
<br/>If <code>Tune:ee</code> or <code>Tune:pp</code> are
nonvanishing by default, then the corresponding tune variables
are set also from the <code>Pythia</code> constructor, before any
user changes are possible. Currently this is not relevant.
</li>
<li>Bug fix in the setup of the <code>Tune:pp = 5</code> and
<code>= 6</code> options, which meant that diffractive cross
sections were not reduced as advertised.</li>
<li>The default value of <code>MultipartonInteractions:pT0Ref</code>
has been slightly reduced so as to give a somewhat improved
default description. It is not intended as a replacement for the
specific tunes, however.</li>
<li>Some comparisons between tunes and data, obtained with the
Rivet package, have been posted on
<a href="http://home.thep.lu.se/~richard/pythia81/">
http://home.thep.lu.se/~richard/pythia81/</a>.
Further improvements can be expected from future Professor-based
tunes. The current set of 2C, 2M, 3C and 3M "draft tunes" have
deliberately been chosen different also to explore a range of
possibilities. One not visible in the plots is the fraction
of single and double diffractive events in the inelastic cross
section. This is 32% in 2C and 2M, while it was reduced to
21% in 3C and 3M, and a recent ATLAS study (ATLAS-CONF-2010-048)
would suggest 28+-4%.</li>
<li>Minor changes in <code>TimeShower</code> and
<code>SpaceShower</code>, as protection if the <i>c</i> or
<i>b</i> masses are set small.</li>
<li>Bug fix in <code>SpaceShower</code>, for case when <i>phi</i>
angle selection is biased to take into account interference effects.
</li>
<li>The <code>SigmaProcess::convertM2()</code> method now has
been implemented also for <i>2 → 1</i> processes, so that it is
possible to provide the squared matrix element instead of
<i>sigmaHat</i> for semi-internal processes. A fixed-width
Breit-Wigner is also inserted, since the matrix element is supposed
not to include it.</li>
<li>New method <code>SigmaProcess::setupForME()</code> does an
extended conversion from the internal kinematics to an almost
equivalent one, better adapted to the mass conventions of matrix-element
calculation programs, such as massive incoming <i>b</i> quarks.
New flags allow to determine whether the <i>c</i>, <i>b</i>,
<i>mu</i> and <i>tau</i> should be considered massless or not
in the calculations.</li>
<li>Two new friend methods <code>table</code> of the <code>Hist</code>
class allow to print a table with three columns, the first for the
(common!) <i>x</i> values and the other two for the respective
histogram values. A new method <code>takeSqrt</code> for the square
root of histogram bin contents.
</li>
</ul>
</li>
<li>8.145: 10 November 2010
<ul>
<li><code>Couplings</code> is defined in <code>StandardModel.h</code>
as a derived class of <code>coupSM</code> and has only one extra flag:
<code>isSUSY</code> to check presence of extra couplings.Changed all
pointers <code>CoupSM*</code> to <code>Couplings*</code> and removed
explicit references to <code>CoupSUSY*</code>. The <code>coupSUSY</code>
object is only initialised if SUSY couplings are present. The new pointer
<code>couplingsPtr</code> points either to only SM couplings or SM+SUSY
couplings based on SLHA data.</li>
<li>New files <code>SusyResonanceWidths.h/cc</code> contains the
<code>SusyResonanceWidths</code> class, which inherits from
<code>ResonanceWidths</code> but typecasts the <code>couplingsPtr</code>
to <code>(CoupSUSY*) coupSUSYPtr</code>. This is the base class for
all SUSY resonances. It contains the <code>ResonanceSquark</code> class
for all squark decays. A new flag <code>SLHA:useDecayTable</code>
to check if internal widths should be overwritten by those read in
via SLHA.</li>
<li>Added new functionality to <code>SusyLesHouches</code> for read-in
of generic user blocks in the SLHA format, along with methods to
extract parameters from them with typecasting controlled by the user.
Intended for use with user-written semi-internal processes.</li>
<li>Added <code>Sigma1qq2antisquark</code> cross section.</li>
<li>Some new flags and modes in the <code>SUSY</code> and
<code>SLHA</code> series offer further functionality.</li>
<li>Several further changes as a consequence of the upgrade of the SUSY
machinery.</li>
<li>Bug/typo fixes in rotation matrices for SUSY couplings and for the
processes <code>qqbar2squarkantisquark</code>,
<code>qq2squarksquark</code> and more.</li>
<li>Improved handling of colour junctions. Added new example program
<code>main72.cc</code>, to illustrate read-in of color junction
structures via LHEF (<code>main72.lhe</code>). The example used is SUSY
with RPV.</li>
<li>New Tune 4C introduced as <code>Tune:pp = 5</code>. The more crude
(non-)tunes 3C and 3M are removed.</li>
<li>New methods <code>Settings::getFlagMap(...)</code>,
<code>Settings::getModeMap(...)</code>,
<code>Settings::getParmMap(...)</code> and
<code>Settings::getWordMap(...)</code> allows to return a map of all
settings of the respective type that contain a specific string
in its name.
</li>
<li>Improved description of excited <i>g^*/KK-gluon^*</i> production
in the <code>Sigma1qqbar2KKgluonStar</code> and
<code>ResonanceKKgluon</code> classes.</li>
<li>Possibility added to let Hidden-Valley <i>gamma_v</i> have
a nonzero mass and decay by mixing with the ordinary photon.
Still experimental.</li>
<li>Minor bug fix in handling of three-body phase space.</li>
<li>Minor correction in <code>Sigma2ffbar2TEVffbar</code> class.</li>
<li>Bug fix for decays of <i>W'</i> to a pair of heavy fermions when
<i>gV != gA</i>. Thanks to M. Chizhov, see arXiv:0705.3944. </li>
<li>Restore the older EHLQ-based encoding of the <i>f fbar → Z W</i>
cross section, which was changed in version 8.140, since comparisons
with Madgraph gives much better agreement with it than with the
expression of Brown, Sahdev and Mikaelian.</li>
<li>The <code>HepMCInterface</code> now also stores colour flow
information for coloured particles.</li>
<li>Pointer to <code>Couplings</code> made available for particle
decays.</li>
<li>Minor update in <code>main61.cc</code> for more elegant usage
of FastJet, as suggested by Gregory Soyez.</li>
</ul>
</li>
<li>8.150: 20 April 2011
<ul>
<li>Tune 4C is made default. It is based on first comparisons with
LHC data [<a href="Bibliography.html" target="page">Cor10a</a>], and has also been checked independently
[<a href="Bibliography.html" target="page">Buc11</a>] to give reasonable agreement with many distributions.
</li>
<li>The description of <i>tau</i> lepton decays has been significantly
enhanced, to include helicity information related to the production
process and hadronic currents fitted to data. A complete writeup is
in preparation, while a summary can be found in [<a href="Bibliography.html" target="page">Ilt12</a>].
A new flag is introduced to revert to the old behaviour, for
cross-checks, see <a href="ParticleDecays.html" target="page">Particle Decays</a>.
The new tau decay machinery is on by default.
</li>
<li>A new option <code>MultipartonInteractions:bProfile = 4</code> has
been introduced for the impact-parameter profile of protons in the
<a href="MultipartonInteractions.html" target="page">Multiparton Interactions</a>
framework, wherein low-<i>x</i> partons are spread over a larger area
than high-<i>x</i> ones, see [<a href="Bibliography.html" target="page">Cor11</a>]. A new method
<code>Info::eMPI(i)</code> gives back the enhancement factor related to
the <code>i</code>'th interaction. The impact-parameter profile can now
be selected separately for <a href="Diffraction.html" target="page">diffraction</a>,
but without a <code>bProfile = 4</code> option.
</li>
<li>The possibility of "hadronization" in the
<a href="HiddenValleyProcesses.html" target="page">Hidden Valley</a> sector
has been added as a new option <code>HiddenValley:fragment = on</code>.
This is based on a copy of the standard string fragmentation framework,
but with the option of a completely separate "flavour" sector, and
separately tunable longitudinal fragmentation functions and transverse
momenta. For now only a simple flavour scenario is provided, where
flavour-diagonal mesons can decay back into the normal visible sector
while off-diagonal ones remain hidden. A writeup of the model is in
preparation [<a href="Bibliography.html" target="page">Car11</a>]. Also some further Hidden Valley options
have been added.</li>
<li>Included possibility in <code>TimeShower</code> for QCD dipoles to
have an adjustable normalization factor, via the new
<code>bool isFlexible</code> and <code>double flexFactor</code>
properties of <code>class TimeDipoleEnd</code>. This flexibility is used
to treat radiation off colour topologies with epsilon tensors, in
particular colour junctions which have all their partons in the
final state. (An example is the BNV-SUSY decay ~chi0→uds.) For
such topologies, the new treatment in PYTHIA 8 is that a
half-strength dipole is spanned between all combinations of
final-state quarks. For junctions with an incoming (anti)colour line (such
as in the BNV-SUSY decay ~t*→cb), a full-strength dipole is
instead spanned between the two daughters, with no radiation from the
decaying object (in its CM). As will be described in a forthcoming
paper with N. Desai, this should give the
closest possible correspondence to the radiation patterns exhibited
by higher-order matrix elements for this type of process.</li>
<li>Corrected harmless bugs in <code>ProcessLevel::findJunctions</code>
which caused junctions of types 3 and 4 (i.e., junctions with 1
incoming color tag) to sometimes be incorrectly classified as types
1 and 2 (with all color tags outgoing), respectively.
Since the parity (even/odd) of the junction kind was still correct,
however, this did not cause any problems at the hadronization
stage.</li>
<li>The junction-finder in <code>ProcessLevel::findJunctions</code>
has been made more stable, and the following ordering of the color
tags returned by <code>Event::endColJunction(iJun, iLeg)</code> is
now enforced: for junction kinds 3 and 4 (one tag
incoming), <code>iLeg = 0</code> will return the
incoming tag, while for kinds 5 and 6 (two tags incoming),
<code>iLeg = 0</code> and <code>iLeg = 1</code> will return the
incoming tags. Apart from this ordering, the color tags are
ordered in ascending color tag number.</li>
<li>Declarations of friend functions moved to sit outside the class
it befriends. Thanks to Axel Naumann for pointing out the incorrect
previous construction.</li>
<li>The <code>rootexample</code> subdirectory becomes
<code>rootexamples</code> as the old example is split into two,
with improved documentation to clarify usage. Thanks to Axel Naumann
and Bernhard Meirose for the new code.</li>
<li>In the Les Houches Event File machinery, input type has been
changed from <code>ifstream</code> to <code>istream</code> for more
flexibility.</li>
<li>R-hadron handling is largely implemented, see the
<a href="RHadrons.html" target="page">R-hadrons</a> page, although some aspects
still need polishing. A new class <code>RHadrons</code> takes
care of the hadronization and decay. Particle data have been added
for R-hadrons containing a gluino, stop or sbottom, but could
alternatively be used for other long-lived coloured particles.
Thanks to Bernhard Meirose for support.
</li>
<li>Calculations of SUSY decay widths included by
N. Desai, contained in the new source
files <code>SusyResonanceWidth.cc</code>
and </code>.h</code>. Validation and addition of more modes is still in
progress, so this implementation should be considered preliminary
for now. For a list of available modes, see
the <a href="SUSYProcesses.html" target="page">SUSY Processes</a> page.
</li>
<li>A first implementation of the SLHA-based QNUMBERS interface for
defining new exotic particles has been
included. See [<a href="Bibliography.html" target="page">Alw07</a>] and
the <a href="SUSYLesHouchesAccord.html" target="page">SUSY Les Houches Accord</a>
page. </li>
<li>Read-in of LHEF events containing Baryon Number Violating vertices
has been included, using colour junctions, see
the <a href="EventRecord.html" target="page">Event Record</a> page. The advanced
shower model taking into account the full colour structure of such
events, developed by N. Desai and described above,
is turned on by default in such events.
Several test cases were used to
validate this implementation, but it is possible that problems could
still exist for some cases. Feedback is welcome. Thanks to
the MadGraph authors for providing several test cases.</li>
<li>Some first steps taken to allow events containing colour sextets,
e.g., from semi-internal processes or LHEF interfaces, and/or from
SLHA <code>DECAY</code> tables. New
<code>colType</code> codes 3 and -3 are introduced to describe
sextets and antisextets, respectively. The state of the current
implementation is that hard processes containing such states can be
read in and decays generated (via <code>DECAY</code> tables). Parton
showers can be added, but the sextets themselves do not, as yet,
shower, and any undecayed sextets remaining at the hadronization
stage would lead to unpredictable problems if hadronization is
switched on. Thanks to J. Alwall for help with testing
this implementation.
</li>
<li>The functionality of the SLHA SUSY/BSM interface (see
the <a href="SUSYLesHouches.html" target="page">SUSY Les Houches</a> page) has been
extended so that copies of all <code>BLOCK</code>s are now stored
internally as
strings, regardless of whether they correspond to "official" SLHA
blocks or not. Their contents can subsequently be queried by a set
of new templated member functions of the
class <code>SusyLesHouches</code>. Available query functions so far
include
<br/><code>template <class T> bool getEntry(string, T&);</code>,
<br/><code>template <class T> bool getEntry(string, int, T&);</code>,
<br/><code>template <class T> bool getEntry(string, int, int, T&);
</code>, and
<br/><code>template <class T> bool getEntry(string, int,
int, int, T&);</code>,
<br/>where the type of
the argument used in the call determines how to read the block
entries. Thus, if an LHEF, SLHA, or other card file is read in by
PYTHIA, the contents of any <code>BLOCK</code> in that file can
subsequently be queried run-time using these functions. This is
used, e.g., in the new interface between MADGRAPH 5 and PYTHIA
8. Thanks to the MADGRAPH team, and to J. Alwall in particular, for
help and debug on this new implementation.
</li>
</ul>
</li>
<li>8.153: 10 August 2011
<ul>
<li>The setup of tunes has been modified, see the
<a href="Tunes.html" target="page">Tunes</a> page for details. Specifically
the <code>Tune:ee</code> and <code>Tune:pp</code> modes have
acquired a new option <code>-1</code> for a forced restore to the
default values of all settings used in the respective kind of
tunes.</li>
<li>The code for handling multiparton interactions in the scenario with
an <i>x</i>-dependent width of the Gaussian matter profile
[<a href="Bibliography.html" target="page">Cor11</a>], has been improved and updated. Tune 4Cx, which
is based on this option, has been added as a further tune option.</li>
<li>A possibility to bias the phase-space selection has been added,
whereby some phase space regions can be oversampled, which is
compensated by assigning a weight to each event.
A new set of methods have been added to the <code>UserHooks</code>
class to allow users to program how to bias the selection.</li>
<li>New options added so that matrix-element corrections can be
switched off after the first branching in ISR or FSR.</li>
<li>Some new <code>Info</code> methods have been added to store
information on latest ISR branching. The <code>SpaceShower</code>
class has also been corrected so that the latest <i>z = 1/2</i>
when not defined by history. This avoids undefined values for
azimuthal asymmetries. Thanks to Stefan Prestel for finding and
sorting out this problem.</li>
<li>The <code>Pythia::forceHadronLevel()</code> method now takes
an argument that optionally means that existing junction information
is not overwritten. Thanks to Leif Lönnblad for pointing out
the usefulness of this.</li>
<li>For particle decays to a varying number of hadrons the multiplicity
increase with mass has been somewhat reduced, and especially for
<code>meMode = 23</code> a separate even slower increase has been
introduced.</li>
<li>New possibility to force the tau polarization.</li>
<li>Bug fix for the special case in which events containing SUSY
particles are generated without proper initialization of SUSY decays.
This can happen, e.g., if events containing SUSY particles are read
in via external LHEF files, if those files do not contain readable
SLHA spectra in their headers. In this case, a failed attempt to
generate sparticle decays with ill-defined couplings previously
led to crashes. The program now reverts to the old behaviour,
based on static decay tables, in such cases, with the default
being to decay all sparticles to gravitino + particle. An error
message stating that the full SUSY treatment has been switched
off and why is also issued. Thanks to N. Desai for this fix.</li>
<li>The R-hadron machinery has been completed.</li>
<li>Minor change in timelike showers: gluons which fall below the
<i>pTmin</i> cutoff by the correction for mass effects are now
eliminated, while previously they were kept. This reduces the
number of gluons somewhat, but has no significant effects on the
hadronic final state. (Prompted by R-hadron studies, where big mass
effects else give bothersome low-energy gluons.)</li>
<li>Corrected typos in two of the Upsilon wave function matrix
elements, <code>Bottomonium:OUpsilon3P08</code> and
<code>Bottomonium:Ochib03P01</code>. Thanks to Beate Heinemann for
pointing it out.</li>
<li>Implemented <i>f*</i> decay angle in <i>f f → f f*</i> processes,
and fixed some bugs for the same process. Thanks to Piyali Banerjee
for tests.</li>
<li>Introduce possibility to separate production channels for
TeV-sized extra dimensions, and a small code correction. Thanks to
Noam Hod for code contribution.</li>
<li>Bug fix for neutrino beams: since neutrinos are always lefthanded
there should be a factor 2 in the cross section, relative to charged
leptons, from the non-need to average over incoming spin states. This
is now fixed by introducing a new PDF class <code>NeutrinoPoint</code>
for (unresolved) neutrinos, with normalization 2 rather than 1 for
charged leptons. Thanks to Ryosuke Sato.</li>
<li>Bug fix for some (rarely used) particle settings, which could not
be changed by users because they were read too early. Thanks to
Andrew Altheimer and Gustaaf Brooijmans.</li>
<li>Bug fix in handling of <code>tau</code> decays, where setting of
decay vertices could write outside memory. Thanks to Steven Schramm.</li>
<li>Minor expansion of the <code>BeamParticle</code> constructor.</li>
<li>Minor bug fix in CTEQ 6L for uninitialized variables.</li>
<li>Minor bug fix in fragmentation flavour combination to hadron.</li>
<li>Some updates of the documentation, including new pages on
MadGraph 5 as a generator for semi-internal processes (thanks to
Johan Alwall) and on RIVET interfacing.</li>
<li>Minor improvements of ROOT- and HepMC-related code and documentation.</li>
<li>Some cleanup of code.</li>
</ul>
</li>
<li>8.157: 10 November 2011
<ul>
<ii>Stefan Prestel joins as new member of the PYTHIA author team.
He is mainly working on matching/merging issues, and has contributed
the CKKW-L machinery mentioned below.</li>
<li>Merging capabilities according to the CKKW-L scheme [<a href="Bibliography.html" target="page">Lon11</a>]
have been added, see the new
<a href="MatrixElementMerging.html" target="page">Matrix Element Merging</a>
page. It involves new classes to reconstruct and select how a
matrix-element-generated partonic configuration could have been obtained
by the PYTHIA evolution, and to perform trial showers (using a new
copy of the normal parton-level machinery) that introduce the appropriate
Sudakov suppression factors. New examples to illustrate various
common tasks are found in <code>main81.cc</code>, <code>main82.cc</code>,
<code>main83.cc</code> and <code>main84.cc</code>.</li>
<li>The <code>main71.cc</code> program is now generalised for reading
in arbitrary POWHEG LHE files, to implement a smooth matching between NLO
matrix elements and the PYTHIA parton showers. Cuts are made on both
ISR and FSR emissions, while previously only ISR was covered. The key
assumptions are the <i>pT</i> definitions used for ISR and FSR, but several
further options are available, as documented in the <code>main71.cmnd</code>
file. Work is still ongoing to pick the best default options. </li>
<li>Several expansions of the <code>UserHooks</code> class.
For both <code>doVetoFSREmission</code> and <code>doVetoISREmission</code>
a new argument <code>iSys</code> labels the system within which the
radiation occurs. For <code>doVetoFSREmission</code> a further argument
<code>inResonance</code> distinguishes FSR in resonance
decays from that in the hard process itself. New methods
<code>canVetoMPIEmission</code> and <code>doVetoMPIEmission</code>
have been added to veto multiparton interactions in the same way as
FSR and ISR. In <code>biasSelectionBy</code> at times incorrect values
for <code>inEvent</code> has been corrected. Also some systematization
of the use of <code>const</code>.</li>
<li>A new model for hadron scattering is introduced, still at an early
stage and therefore more intended for internal development than for the
normal user. The basic idea is that a high-energy <i>pp</i> collision
involves the fragmentation of multiparton strings that overlap in space
(and time). Also the produced hadrons therefore initially overlap, and
there is a strong likelihood that hadrons can scatter against each other
until the system has expanded sufficiently. This can e.g. increase the
transverse momentum of heavier hadrons at the expense of lighter ones.
</li>
<li>A new jet finder <code>SlowJet</code> offers simple access to the
inclusive <i>kT</i>, anti-<i>kT</i>, and Cambridge/Aachen
algorithms in a cylindrical coordinate frame. The jet reconstruction
is then based on sequential recombination with progressive removal,
using the <i>E</i> recombination scheme. The minimalistic
<code>SlowJet</code> code is much slower than <code>FastJet</code>
[<a href="Bibliography.html" target="page">Cac06</a>], and contains less options, but reconstructs the same
jets if run under identical conditions. For details see the
<a href="EventAnalysis.html" target="page">Event Analysis</a> page.</li>
<li>Starting in gcc 4.6, it is possible to switch off specific warnings
around specific blocks of code. Although version 4.6 is some way off
from being commonly found, this option has now been introduced to switch
off <code>-Wshadow</code> warnings in <code>HepMCInterface.cc</code>.
For other compilers, or earlier versions of gcc, the old behaviour
is retained.</li>
<li>Support for reading in gzipped LHEFs has been added in the
<code>LesHouches</code> and <code>SusyLesHouches</code> classes.
This also affects <code>configure</code> and <code>Makefile</code>s.
Unless explicitly enabled, it should not affect anything.
If enabled, it relies on the Boost and zlib libraries to function,
so paths to these must be set appropriately, see the
<code>README</code> file for details. The Boost header files can
give very many shadow warnings, so <code>-Wshadow</code> is disabled
if gzip support is enabled, as described above.</li>
<li>Introduce use of the <code>HEPMC_HAS_UNITS</code> environment
variable in the <code>HepMCInterface.cc</code> and <code>main32.cc</code>
codes to automatically check whether GeV and mm can be set as relevant
units. If yes, then it is set in <code>main32.cc</code>. If no,
a conversion from GeV to MeV is done explicitly in
<code>HepMCInterface.cc</code>. Note that, for early HepMC versions,
this means a change of behaviour. Thanks to Andy Buckley.</li>
<li>A new method <code>Info::lhaStrategy()</code> returns the
Les Houches event weighting strategy where relevant, and 0 where not.
For the strategies <i>+-4</i> the event weight and sum,
<code>Info::weight()</code> and <code>Info::weightSum()</code>,
is now in units of pb at output, as it should be at input.
(While internally mb is used.)</li>
<li>New flag <code>Check:abortIfVeto</code> allows the user to
resume control over execution in case of a veto in the event
generation process.</li>
<li>New method <code>Event::at(i)</code> returns reference to
<code>i</code>'th particle in the event record.</li>
<li>Introduce the Fermi constant as one of the Standard Model
parameters.</li>
<li>Included automatic pre-initialization of SLHA blocks MASS and
SMINPUTS using PYTHIA's SM parameters and particle data table
values.</li>
<li>SUSY: added sleptons (and sneutrinos) as resonances.
Corrected 2-body decay widths of gluinos, squarks and gauginos.
Added sleptonic decay modes to gaugino decays.
Implemented 2-body decays of sleptons (and sneutrinos)
into sleptons/leptons/gauginos. Corrected slepton couplings (they
now look exactly like squark couplings, using a 6x6 slepton mixing
matrix).</li>
<li>New parameter <code>Diffraction:probMaxPert</code> introduce to
give more flexibility in transition from a nonperturbative to a
perturbative description of a diffractive system.</li>
<li>Bug corrected in <code>SigmaEW.cc</code>, for the process
<code>WeakSingleBoson:ffbar2ffbar(s:gm)</code>. Previously, all outgoing
quark flavours in this process were erroneously assigned ID code 5
(b quarks). This has now been corrected so the proper ratios are
obtained, with <i>u : c : d : s : b = 4 : 4 : 1 : 1 : 1</i>,
according to the squared quark charges.</li>
<li>Changes in <code>FragmentationSystems</code> and
<code>StringFragmentation</code> to reject systems with three or more
interconnected junctions. This may happen in baryon-number-violating
scenarios in pp collisions, if both of the beam baryon junctions are
resolved and get connected via an antijunction created by a
hard-process BNV vertex. In principle, this could be addressed by an
extension of the existing junction fragmentation framework. However,
since it happens rarely, for the time being an error message is printed
and the fragmentation restarted.
</li>
<li>Change in <code>Event::copy</code> to safeguard against attempting
to copy out-of-range entries. An attempt to copy a non-existing entry
will now return -1.</li>
<li>Bug fix in the machinery for the user to force the setting of
tau polarization.</li>
<li>Bug fix in the initial search for a maximum of the process
cross section (only affecting rare cases).</li>
<li>Corrected angular decay distributions for two compositeness
processes, <code>Sigma2qq2qStarq</code> and
<code>Sigma2qqbar2lStarlbar</code>.</li>
<li>Extra check in <code>HiddenValleyFragmentation</code> to make sure
that pointers which have not been assigned with <code>new</code> are not
deleted.</li>
<li>Some further minor changes.</li>
</ul>
</li>
<li>8.160: 23 January 2012
<ul>
<li>The older term "multiple interactions" has been replaced by the
new standard "multiparton interactions" one, and correspondingly the
abbreviation MI by MPI. This affects everything: settings, class and
method names, documentation, etc. It therefore becomes necessary to
rewrite user code. However, so as to keep the immediate effort at a
reasonable level, the old settings names are kept as aliases. Thus
<code>PartonLevel:MI</code> and <code>PartonLevel:MPI</code> are
equivalent, and similarly <code>MultipleInteractions:pT0Ref</code>
and <code>MultipartonInteractions:pT0Ref</code>. Should you be using
methods such as <code>double Info::pTMI(int i)</code> you need to
edit the code, however. All the <code>example/main*</code> files
have been updated accordingly.</li>
<li>A new option <code>Beams:frameType = 5</code> has been added
for the case where an external generator should provide LHA process
information. The new <code>Pythia::setLHAupPtr(...)</code> method
should then be used to link in this generator. The new switch
<code>Beams:newLHEFsameInit</code> can be used to tell that a new
LHEF should be used, but without the need for a new initialization.
With these two changes, all the different ways of initializing
can be covered by the <code>Pythia::init()</code> call with no
arguments. The various <code>init(...)</code>options with arguments
are deprecated and will be removed for PYTHIA 8.2.</li>
<li> The <code>Pythia::stat()</code> method, with no arguments,
replaces <code>Pythia::statistics(...)</code>, although the latter
remains as a deprecated alternative.</li>
<li>New settings <code>Init:...</code>, <code>Next:...</code>,
and <code>Stat:...</code> can be used to steer some details of
the operation of the <code>Pythia::init()</code>,
<code>Pythia::next()</code> and <code>Pythia::stat()</code>,
respectively. In particular it affects the amount of printout
at the various stages of operation. See
<a href="MainProgramSettings.html" target="page">here</a> for further details.
This change involves several code changes, but in documentation
rather than physics. Most of the <code>Main:...</code> settings
are deprecated as a consequence.</li>
<li>The sample main programs in the <code>examples</code> subdirectory
have been updated. This includes a change to the new favoured
methods and settings outlined above, plus some update of the
physics contents. Some of the examples have been combined,
some others have been added (e.g. for R-hadrons), and as a consequence
some renumbering has been made. See the modified list of
<a href="SampleMainPrograms.html" target="page">sample main programs</a> for
the new status. In particular note that (the new) <code>main61.cc</code>
allows streamlined input and output in HepMC, like <code>main42.cc</code>
(previously <code>main32.cc</code>), but additionally links to LHAPDF. </li>
<li>The <code>examples/configure</code> script has new optional argument
<code>--with-pythia8</code>. It can be used to set the new
<code>PYTHIA8LOCATION</code> environment variable, which then is used
in <code>examples/Makefile</code> to give the path to the PYTHIA
library. Thereby it becomes possible to relocate (parts of) the
<code>examples</code> directory and still obtain the correct path.
Thanks to Mikhail Kirsanov.</li>
<li>Polarization information has been included as a new
<code>Particle</code> property, that can be set by
<code>void pol(double polIn)</code> and obtained by
<code>double pol()</code>. Default value is <code>9.</code>,
in agreement with the Les Houches standard. Event listings have
been expanded to optionally display this information. Currently
polarization is not used internally.</li>
<li>The matrix element merging machinery has been modified as follows.
<br/>- Improved handling of the hard process, so that MadGraph5-produced
LHE files do not produce problems (sometimes, the choices of MG4 on what
to put into a LHEF have changed in MG5).
<br/>- Improved handling of colour for easier handling of states with
many quarks (the code has been tested for states with up to 5
<i>q qbar</i> pairs and some gluons).
<br/>- Improved checking which clusterings are allowed. Now, clusterings
should immediately be rejected if they lead to unphysical states,
without the need to explicitly construct these states. This was needed
to get <i>t tbar</i> production, VBF and some simple SUSY processes
running with reasonable generality.
<br/>- Improved handling of incomplete histories. Now there is an
additional switch allowing code to try to swap some colours when fewer
clusterings than requested have been found.
</li>
<li>Updates in the handling of graviton resonances in scenarios with
extra dimensions.
<br/>- Now all G decays have correct angular distribution, which was not
the case before for W/Z decays.
<br/>- Added the possibility for G to only couple to longitudinal
W/Z bosons, which affects both the width and angular distributions.
<br/>- Added decays to Higgs pairs, <i>G → hh</i>.
</li>
<li>Bug fix in the <code>findJunctions()</code> function in
<code>ProcessLevel.cc</code>. Changes introduced in version
8.145 (to allow for junctions in baryon-number-violating
processes) did not correctly handle the remapping of color
tags that can be applied when adding beam remnants to events with
multiparton interactions. A simpler and more stable algorithm is
now applied for the simplest cases, with the more complex one only
invoked for cases such as BNV, which are normally considered before
remnants are added, hence avoiding this particular problem. Also some
other changes in the handling of junction, including a safeguard to
reject systems with three or more interconnected junctions.</li>
<li>Bug fix and updates to the SLHA interface. Possibility of infinite
loop during <code>ProcessLevel::initSLHA</code> corrected. Modifications
to <code>SusyLesHouches</code> to allow interpretation of SLHA1 spectra
with R-parity violation. Rather than reject spectra that do not conform
fully to the SLHA2 standard for RPV, the interface will now first look
for SLHA1 mixing matrices and attempt to translate those into SLHA2 ones
if possible. In this case, warnings that the expected SLHA2 blocks were
not found will be printed. It is up to the user to check that the
derived SLHA2 information is correct. Corresponding additions to
<code>SusyCouplings.cc</code> to extract mixing-matrix information
from the relevant SLHA2 RPV blocks when RPV is switched on.</li>
<li>Updated SLHA example <code>main24.cmnd</code> to use new example
spectrum, <code>cmssm.spc</code>, corresponding to CMSSM point
10.1.1, obtained with SOFTSUSY 3.3.0. Thanks to B. Allanach for
providing the new spectrum file.</li>
<li>A new <code>include/FastJet3.h</code> header file simplifies
interfacing of FastJet to Pythia. For details see documentation in
the file itself. Thanks to Gavin Salam for this contribution.</li>
<li>The handling of diffraction has been made more flexible.
Specifically the "total" Pomeron-proton cross section can now be made
to depend on the mass of the diffractive system. This does not affect
the diffractive cross section in pp collisions, which is set separately,
but is used in the MPI machinery to affect the average number of
interactions per Pomeron-proton collision. Furthermore, the allowed
range for some parameters has been expanded. Thanks to Robert
Ciesielski.</li>
<li>New method <code>Pythia::forceTimeShower(...)</code> can be used to
generate a single final-state cascade from a set of partons, without
any knowledge of prior history. This is mainly intended for toy studies.
The meaning of the <code>ProcessLevel:all</code> switch has been modified
so that this parton-level function is available, but not any others
at this level.
</li>
<li>ATLAS tune A2 now included. Thanks to Deepak Kar for
providing it.</li>
<li>Change in the handling of recoils of timelike showers in resonance
decays, in cases of coloured resonances such as <i>t → b W</i>. In
the first step the <i>W</i> always acts as recoiler to the <i>b</i>,
but in subsequent step previously the <i>W</i> remained as recoiler to
one dipole, while now all QCD-radiating partons recoil against another
coloured parton. The old behaviour could give a (small) unphysical spike
of radiation collinear with the colourless recoiler in the subsequent
emissions (while the pattern of the first was and remains correct).
The old behaviour can be recovered for checks, see
<code>TimeShower:recoilToColoured</code>.
Thanks to Yevgeny Kats for pointing out this issue (previously noted
for Pythia 6 by several persons).
</li>
<li>Bug fixes for <code>rootexamples/Makefile</code> and restoration
of some deleted information in <code>rootexamples/README</code>.
Thanks to Axel Naumann and Bernhard Meirose.</li>
<li>Bug fix, so that displaced vertices are possible in resonance
decay chains. Thanks to Daniel Blackburn and Andy Buckley for
pointing this out.</li>
<li>Bug fix for <code>Info</code> counter 2.</li>
<li>Bug fix so that sextet quarks now are read in correctly from
Les Houches Event files; previously the (anti)colours were set
to 0.</li>
<li>Year updated to 2012 in copyright statements etc.</li>
<li>Reformatting to reduce the number of code lines with more
than 79 characters.</li>
<li><code>Pythia::initSLHA()</code> moved from <code>public</code>
to <code>private</code>.
</li>
<li>Remove warning message when tau polarization is set by hand.</li>
<li>Several minor changes to reduce the number of warnings issued
by the clang compiler. The origin of some warnings remains unclear
so those remain to track down (could also be compiler bugs; note that
we discuss warnings, not errors). Thanks to Randy MacLeod for bringing
this up.</li>
<li>The worksheet has been updated to be in step with Pythia 8.160.</li>
<li>Several other minor corrections in the code and documentation.</li>
</ul>
</li>
<li>8.162: 12 March 2012
<ul>
<li>A new option allows for several partons to share the recoil in
final-state radiation, see<a href="TimelikeShowers.html" target="page">Timelike
Showers</a>. It is mainly intended to be used in the context of
matching to matrix elements, and so only to be used in the first
few branchings.</li>
<li>Several new processes for LED dijet production, see
<a href="ExtraDimensionalProcesses.html" target="page">Extra Dimensions</a>.</li>
<li>Small update of the <code>Sigma2ffbar2LEDllbar</code> and
<code>Sigma2ffbar2LEDgammagamma</code> LED processes.</li>
<li>New <code>Sigma2QCffbar2llbar</code>
<a href="CompositenessProcesses.html" target="page">contact interaction</a>
process.</li>
<li>Inclusion of a new method in the
<a href="MatrixElementMerging.html" target="page">matrix-element merging</a>
framework to influence the construction of histories, e.g. to already
in the construction of histories disallow paths that fail the
<i>2 → 2</i> cuts.</li>
<li>Further minor updates of the matrix-element merging code,
mainly for improved clarity.</li>
<li>Minor bug fix in the handling of beam and event information fed
in from an <code>LHAup</code> instance.</li>
<li>Minor bug fix for potential crashes from uninitialized variables
for the merging machinery when merging is not used.</li>
<li>Updated History class for matrix element merging,
also avoiding some compiler warnings.</li>
<li>Bug fixes in the handling of correlated mass choices in resonance
decays, such as <i>H → Z^*0 Z^*0</i>.</li>
<li>Bug fix when the process-level execution is switched off,
where <code>Info::isResolved()</code> could be called before its
value was initialized. Thanks to Christian Pulvermacher
for finding this.</li>
<li>Corrected matrix-element expression for mass selection in
<i>A^0 → Z^*0 Z^*0</i> and <i>A^0 → W^*+ W^*-</i>.</li>
<li>SM Higgs mass updated to 125 GeV and default width and branching
ratios modified accordingly. Minor technical improvements of width
calculation.</li>
<li>The usage of nested classes has been removed from
<code>SusyLesHouches</code>, since it could give compilation errors
on some platforms. The new class names begin with <code>LH</code>
and all classes have been put inside the <code>Pythia8</code>
namespace.</li>
<li>Minor Makefile updates. Thanks to Mikhail Kirsanov.</li>
<li>Minor changes to avoid some clang compiler warnings on the
Mac OS X platform.</li>
</ul>
</li>
<li>8.163: 27 March 2012
<ul>
<li>New methods in the
<a href="EventInformation.html" target="page"><code>Info</code></a> class,
<code>id1pdf()</code>, <code>id2pdf()</code>, <code>x1pdf()</code>
and <code>x2pdf()</code>, to denote the partons for which parton
distribution values have been defined. Previously this was assumed
to agree with the incoming partons to the hard process, the same
methods without the <code>pdf</code> qualifier. However, now the
POWHEG approach offers a counterexample. Also the reading and
handling of Les Houches (and other) events, and the interface
to HepMC, has been modified accordingly.
</li>
<li>The decay of Higgs and top resonances read in from Les Houches
Event files is now performed with angular correlations as for
internal processes. LHE files should normally contain all process-specific
resonance decay chains and, if not, decays are made isotropic.
The <i>H → WW/ZZ → f fbar f' fbar'</i> and
<i>t → b W → b f fbar</i> correlations are process-independent,
however, and thus can be handled internally. If part of the decay
chain has already been set, e.g. <i>H → WW/Z></i> or
<i>t → b W</i>, then the subsequent decays are still isotropic.</li>
<li>Updated instructions how to link to HepMC,
in <code>README.HepMC</code>.</li>
<li>Bug fix in the turn-on of resolved diffraction for low
CM energies. Thanks to Erwin Visser.</li>
<li>Bug fix in the handling of string junctions at very high energies,
caused by numerical errors. Thanks to Erwin Visser.</li>
<li>Some other small changes, mainly aesthetics.</li>
</ul>
</li>
<li>8.165: 8 May 2012
<ul>
<li>The MBR (Minimum Bias Rockefeller) model for single, double and
central diffraction [<a href="Bibliography.html" target="page">Cie12</a>] is included as new option
<a href="Diffraction.html" target="page"><code>Diffraction:PomFlux = 5</code></a>.
It is specifically intended for <i>p p</i> and <i>pbar p</i>
interactions, and is currently the only option that also supports
central diffraction. Thus the basic machinery for Central Diffraction
(a.k.a. Double Pomeron Exchange) has now been implemented.
See <code>examples/main04.cc</code> for an example.
Thanks to Robert Ciesielski for contributing the new code.
</li>
<li>For a <i>tau</i> lepton in an external process, by default the
SPINUP number in the Les Houches Accord now is interpreted as giving
the <i>tau</i> helicity, and is used for its decay.</li>
<li>A <i>tau</i> coming from a <i>W</i> now defaults to being purely
lefthanded when neither of the existing matrix elements apply.</li>
<li>Decay mode <i>t → H+ b</i> included as an option.</li>
<li>Four ATLAS tunes have been implemented as options for
<code>Tune:pp</code>: A2-minbias-mstw2008lo, AU2-cteq6l1, AU2-mstw2008lo,
and AU2-ct10. The new flag <code>Tune:preferLHAPDF</code> can be used
to switch between the LHAPDF and the internal implementation of a
PDF set, in cases where both are available.</li>
<li>Reorder libraries in <code>examples/Makefile</code>, specifically
move <code>LIBGZIP</code> so that it is properly linked when used.
Thanks to Erik Schnetter.</li>
<li>Minor modification so that LHAPDF can be used for PDFs in the hard
process, with one of the built-in PDFs for the rest, even if LHAPDF is
compiled so as to handle only one concurrent PDF set.</Li>
<li>Bug fix, that <code>ParticleDecays:mixB = off</code> did not
switch off <i>B0 - B0bar</i> and <i>Bs0 - Bs0bar</i> mixing.
Thanks to James Catmore.</li>
<li>Bug fix for the handling of gluon polarization of initial-state
radiation, where an anisotropic azimuthal distribution was inadvertently
generated in some <i>2 → 1</i> processes. The update also includes
always setting the second daughter zero for the two partons coming in to
a hard <i>2 → 1</i> process. Thanks to Antonio Policicchio.</li>
<li>Bug fix, that the setting of the number of user hooks MPI steps did
not use <code>UserHooks::canVetoMPIStep()</code> properly.</li>
<li>Some other small changes, mainly documentation and aesthetics.</li>
</ul>
</li>
<li>8.170: 21 September 2012
<ul>
<li>Streamline default behaviour and options for choice of GeV or MeV
for output to the HepMC event format, see
<a href="HepMCInterface.html" target="page">HepMC Interface</a>.
Also set the mass of HepMC particles explicitly, rather than having
it calculated implicitly. Thanks to James Monk and Andy Buckley.</li>
<li>The <i>tau</i> decay machinery has been further augmented with
matrix elements and form factors for a variety of decay modes, such
that all modes with a branching ratio above 0.1% are fully modeled.
Several new classes and methods have been added to this end,
Also, a <i>tau</i> pair coming from a <i>Z^0</i> decay is now
handled by assuming the <i>Z^0</i> to be unpolarized when neither
of the existing matrix elements apply. Taus coming from B baryons are
handed as for B mesons.</li>
<li>Flavour violating decays have been added to the squark, gluino,
neutralino and chargino decay tables.</li>
<li>Extend the <code>UserHooks::subEvent(...)</code> method so that it
also works passably at the process level. Also new option for
<code>UserHooks::omitResonanceDecays(...)</code>.</li>
<li>New methods <code>UserHooks::canVetoPartonLevelEarly()</code>
and <code>UserHooks::doVetoPartonLevelEarly( const Event&)</code>
are intended to be used the same way as the existing ones without
<code>Early</code> in their names, but allow veto right after
the ISR + FSR + MPI evolution, before beam remnants are added and
resonance decays are considered.</li>
<li>Central diffraction now available for all
<code><a href="Diffraction.html" target="page">PomFlux</a></code>
options, not only the MBR model. This has been constructed by analogy
with the respective assumptions made for single diffraction, but
includes some arbitrariness. Therefore the cross section is left
easily rescaleable and, for backwards compatibility with tunes
that does not contain it, easily possible to switch off, see
the <a href="TotalCrossSections.html" target="page">relevant section</a>.
</li>
<li>Reading of ALPGEN parameter and event files has been added,
see <a href="AlpgenAndMLM.html" target="page">ALPGEN and MLM Merging</a>.
</li>
<li>MLM matching has been added, as a first step for ALPGEN events,
see <a href="AlpgenAndMLM.html" target="page">ALPGEN and MLM Merging</a>.
</li>
<li>The CKKW-L merging machinery has been upgraded in a number of respects.
<br/>- More thorough treatment of <code>pp>bb~e+e-veve~</code> with
additional <i>b</i>-jets.
<br/>- Corrected hard <i>mu_r</i> and <i>mu_f</i> choices for
dijet and prompt photon.
<br/>- More ways to define a hard process, e.g. with the LEPTONS and
NEUTRINO tags. The merging will understand LHE files for mixed processes
(e.g. <i>W+</i> and <i>W-</i> production together).
<br/>- More merging scale definitions.
<br/>- More freedom to generate all possible histories.
<br/>- Internal check (and cut) on Les Houches events in
<code>Pythia::mergeProcess</code> if merging scale value of the events
is below the value given to Pythia by setting <code>Merging::TMS</code>.
</li>
<li>It now works to have R-parity violating decays of R-hadrons,
i.e. baryon number violation in a vertex displaced from the primary
one.</li>
<li>The documentation of diffractive processes by the
<code><a href="EventInformation.html" target="page">Info</a></code>
methods has been expanded and corrected. This also include the
<code>list()</code> method.</li>
<li>Particle masses and widths have been updated to agree with the
2012 RPP values [<a href="Bibliography.html" target="page">Ber12</a>]. Thanks to Piotr Zyla for data file
and James Catmore for program to update the PYTHIA tables from this
input.</li>
<li>New methods <code>jetAssignment</code> and <code>removeJet</code>
added to the <code>SlowJet</code> class.</li>
<li>Introduce angular correlation in decay chain
<i>H → gamma Z0 → gamma f fbar</i>. Thanks to Tim Barklow and
Michael Peskin.</li>
<li>Introduce simple way to bias the selection of <i>2 → 2</i>
processes towards larger <i>pT</i> values, with a compensatingly
decreasing event weight, see
<a href="PhaseSpaceCuts.html" target="page">Phase Space Cuts</a>. Only offers a
subset of the possibilities allowed by <code>UserHooks</code>,
but simpler to use. The <code>main08.cc</code> program has been
expanded to illustrate this possibility, and also expanded to
include low-<i>pT</i> subsamples.</li>
<li>The two remaining non-NLO tunes from [<a href="Bibliography.html" target="page">ATL12</a>] are now
included.</li>
<li>The <code><a href="EventInformation.html" target="page">Info</a></code> methods
<code>nTried, nSelected, nAccepted, sigmaGen</code> and
<code>SigmaErr</code> now takes the code of an individual process
as an optional argument.</li>
<li>It is now possible to generate resonance decays, followed by
showers and hadronization, without having them associated with any
specific process. This is part of an expanded
<a href="HadronLevelStandalone.html" target="page">Hadron-Level Standalone</a>
machinery, as before triggered by <code>ProcessLevel = off</code>,
but additionally requiring <code>Standalone:allowResDec = on</code>.
Input can either be directly into the <code>event</code>
event record or via a (simplified) Les Houches Event File.</li>
<li>New <code>configure</code> script options <code>--installdir</code>,
<code>--prefix</code> and <code>--datadir</code> can be used to set the
location(s) to which the library, header and data directories
will be copied by a <code>make install</code> subsequent to the
<code>make</code>. Thanks to Mikhail Kirsanov.</li>
<li>Fix charge in antiparticle name when particle read in from SLHA
file. Thanks to Johan Alwall.</li>
<li>Pointers now only compared with == and != (not e.g. > 0), to avoid
warnings in gcc 4.7.</li>
<li>New check that version number of the code matches that of the
XML files. If not, no events can be generated. Thanks to James Monk
for suggestion.</li>
<li>New check that mother and daughter indices have been set to give
a consistent event history. Can be switched on/off with the new
<code>Check:history</code> flag.</li>
<li>A new method <code>LHAup::newEventFile</code> has been added to
switch to reading in events from another LHE file without having to
reinitialize the whole class. Lower-level routines like
<code>openFile</code> and <code>closeFile</code> have been added to
handle correct order of operations also when an intermediate gzip
decompression step is involved.</li>
<li><code>LHAup::eventLHEF()</code> can now be called with an optional
argument <code>false</code>, to make event files somewhat smaller by
reducing the amount of blanks.</li>
<li>A new mode <code>Beams:nSkipLHEFatInit</code> introduced to
skip ahead the first few events in a Les Houches Event File (cf. the
<code>LHAup::skipEvent(nSkip)</code> method).</li>
<li>Introduce a new pair of user hooks that can be used to reject
the sequence of hard-process resonance decays, without rejecting
the production of the primary resonances.</li>
<li>The possibility of separate multiplicative prefactors to the
renormalization and factorization default <i>pT^2</i> scale has been
introduced for both timelike and spacelike showers.</li>
<li>Bug fixes in history information for R-hadron production, which also
fixes HepMC conversion in this case.</li>
<li>Bug corrected in <code>SigmaSusy.cc</code>, for chargino+neutralino
production. Indexing error for incoming quark states in the process
<code>Sigma2qqbar2charchi0</code>, resulted in incorrect CKM factors.</li>
<li>Corrected a bug in <code>SusyLesHouches.cc</code>, for NMSSM spectra.
The unitarity check on the neutralino mixing matrix was faulty, leading
to erroneous messages about unitarity violations and SUSY being switched
off.</li>
<li>Bug fixes in the handling of resolved and unresolved diffractive events.
Thanks to Robert Ciesielski for debug.</li>
<li>Do not set up FSR dipoles for <i>2 → 1</i> processes.</li>
<li>Check that some channel open for resonance decays. Also further
check whether resonance decay treatment should be invoked.</li>
<li>Bug fix in reading of particle names from SLHA input.</li>
<li>Change mass, width and decay mode(s) of D*_s(10431). Thanks to
Michal Petran.</li>
<li>Bug fix in leptoquark production (lepton sign in
<i>q g → LQ l</i>).</li>
<li>New argument added to <code>SpaceShower::reassignBeamPtrs</code>
for diffractive event processing, as already available for
<code>TimeShower</code>.</li>
<li>Do not write warnings in <code>SpaceShower</code> for weights
above unity if the evolution scale is below 1 GeV^2.</li>
<li>Add default values for member variables in some constructors,
and some related changes for <code>AlphaStrong</code> code.</li>
<li>Warn if negative-energy parton in hadronization.</li>
<li>The MPI <i>pT</i> values assumed in the beam remnant setting
of primordial <i>kT</i> and colour reconnection probability were
incorrect for diffractive events.</li>
<li>The arrays with MPI information were not reset when parton or
hadron level fails and a new try is made. Only affected few events.</li>
<li>MPI statistics can not yet be accumulated for diffractive events,
and therefore the relevant routine is no longer called.</li>
<li>Bug fix in the double parton scattering suppression from
energy-momentum conservation.</li>
<li>Outgoing proton masses were not set in the event record for
elastic scattering (but kinematics handling was correct).</li>
<li>Bug fixes in the identification and documentation of junctions,
previously leading to some unnecessarily rejected events. Also
other improvements leading to fewer errors.</li>
<li>Slightly increased values for FragmentationSystems:mJoin and
StringFragmentation::FACSTOPMASS to reduce failure rate, without
noticeably affecting event properties.</li>
<li>The Les Houches cross section error is now taken into account
in the final Pythia error for strategies +-3. New methods
<code>LHAup::xSecSum()</code> and <code>LHAup::xErrSum()</code>
provide the necessary information.
</li>
<li>When a tau pair comes from a massless photon, in dipole shower
evolution, for the decay description the mother photon is reassigned
to have the sum of the tau momenta.</li>
<li>Minor change in initialization sequence for user hooks,
to allow for more flexibility.</li>
<li>Do not print warnings when multiparton interaction weights are
only slightly above unity.</li>
<li>Do not write warnings for three known particles that are so close
to threshold that widths are switched off to avoid trouble.</li>
<li>Some minor typographical changes.</li>
</ul>
</li>
<li>8.175: 18 February 2013
<ul>
<li>Richard Corke and Stefan Ask leave as active authors, and have
new e-mail addresses.</li>
<li>Jesper Roy Christiansen and Philip Ilten join as new authors.</li>
<li>A severe bug found and corrected in the handling of junction
fragmentation. For some string topologies it could lead to parts of
partonic systems mainly aligned along the beam axis to obtain an
effective tilt, thereby giving rise to a pair of opposing jets that
should not be there. The bug was an unfortunate side consequence
of the improvement of junction handling introduced in version 8.170,
and do not affect versions prior to that. To the largest extent
possible, it is recommended to avoid this version. Potential errors
are likely to be most relevant for processes at low <i>pT</i>,
whereas processes that already have a large scale proportionately
are less affected. Sincere apologies, and thanks to Hannes Jung for
discovering it.</li>
<li>The initialization is aborted when the user tries to change
the value of a non-existing variable in the Settings or
ParticleData databases, and it becomes impossible to generate events.
This may be rather brutal, as opposed to the former policy of
ignoring such commands (except for a warning), but avoids that
the user wastes time on a run that is likely not to give the wanted
results. Thanks to Gavin Salam for stressing this point.</li>
<li> Major updates of the merging code. CKKW-L code is made more flexible,
and now includes additional options to facilitate merging of additional
jets in MSSM processes. Unitarised ME+PS merging (UMEPS) is introduced
as a new merging scheme for tree-level input. An example main program
for UMEPS is added. UMEPS is documented in the new section
<a href="UMEPSMerging.html" target="page">UMEPS Merging</a>.
NLO merging methods are now functional. Two NLO merging schemes are
implemented: NL<sup>3</sup> and unitarised NLO+PS merging (UNLOPS),
both of which are illustrated with example main programs. NLO merging
is documented in <a href="NLOMerging.html" target="page">NLO Merging</a>.
</li>
<li>The machinery for the MLM-style matching of jets has been
expanded to cover input either from ALPGEN, as before, or from
Madgraph (or other LHEF input), and expanded to cover either a
matching algorithm based on the one in ALPGEN or the one in Madgraph.
See <a href="JetMatching.html" target="page">Jet Matching</a> for
details.</li>
<li>Neutrons and antineutrons are now allowed as incoming
beam particles. The neutron PDF is derived from the chosen proton
PDF by simple isospin conjugation, and total/elastic/diffractive
cross sections are assumed the same as for protons.</li>
<li>Update in <code>Pythia.cc</code>, to allow user to override
SLHA mass values by hand, controlled by the new flag
<code>SLHA:allowUserOverride</code>. This was motivated by people
wanting to be able to read in a base SLHA spectrum and then quickly
scan over particular mass values manually. Corresponding documentation
update in <code>SUSYLesHouchesAccord.xml</code>.</li>
<li>Updates to the <code>ResonanceWidths</code> and
<code>SUSYResonanceWidths</code> classes, to merge common
initialization steps into the base class. Corresponding documentation
update in <code>SemiInternalResonances.xml</code>. Also some cosmetic
changes in <code>SUSYResonanceWidths</code> to improve conformity
with <code>CODINGSTYLE</code> rules.</li>
<li>The <code>SlowJet</code> jet finder is updated with an option
for an alternative <i>R</i> separation based on
<i>cosh(Delta y)-cos(Delta phi)</i>.</li>
<li>Statistics information on the separate subprocesses among
the Les Houches external input is improved.</li>
<li>The sophisticated tau decay machinery has been expanded so that
it can also handle production of taus in hypothetical
lepton-number-violating processes, such as <i>H0 → tau+ mu-</i>.
</li>
<li>Branching ratios for most light hadrons, and the tau lepton,
have been updated to agree with the 2012 Review of Particle Physics
[<a href="Bibliography.html" target="page">Ber12</a>], by Anil Pratap Singh.</li>
<li>Photon radiation can now be included in leptonic two-body decays
of hadrons by setting the new switch
<code>ParticleDecays:allowPhotonRadiation = on</code>.
The lower shower cutoff <code>TimeShower:pTminChgL</code> has been
reduced so as to let the simulated photon spectrum extend to lower
energies.
</li>
<li>A new switch <code>MultipartonInteractions:bSelScale</code> has
been introduced, to determine the relevant mass or <i>pT</i> scale
of an event for the selection of impact parameter in the MPI
framework. In spite of a changed default behaviour (the old being
option 3), practical consequences are small for most processes.
</li>
<li>The new <code>UserHooks::retryPartonLevel()</code> method can be
overloaded, so that the same hard process is reused for a new try
on the parton level, rather than being rejected completely.
Thanks to Christian Bauer for suggestion.</li>
<li>A new method <code>Event::undoDecay(int i)</code> can be used
to remove the daughters of a particle, and further descendents.
Does not work for removing the daughters of a parton.</li>
<li>The interface to <code>HepMC</code> has been updated. In particular
the support for old version has been removed, thereby allowing
significant simplifications. The list of methods to set and get the
behaviour of the conversion routine has also been updated. The
<code>set_event_scale</code> method now stores the renormalization
scale (rather than the <i>pT</i> stored previously).
The examples <code>main41</code>, <code>main42</code>,
<code>main61</code>, <code>main62</code> and <code>main84</code>
have been updated accordingly.</li>
<li>Four new methods to interrogate the default values of the
four different kinds of settings.</li>
<li>The <code>Vec4</code> class has been expanded with methods to
return true rapidity or pseudorapidity, and the <i>R</i> distance
in <i>(y, phi)</i> or <i>(eta, phi)</i> cylindrical coordinates.
Thanks to Andy Buckley.</li>
<li>The copy and = constructors of the <code>Pythia</code> class
are made private so that compilers will block use of them.
Thanks to Andy Buckley.</li>
<li>New option of the <code>Pythia</code> constructor, to omit
the banner printout where necessary. Also new master switch
<code>Print:quiet</code> to switch off most runtime program
messages. Thanks to Andy Buckley.</li>
<li>Updates in the machinery that restores all affected values
to their defaults before setting a new tune.</li>
<li>A new <code>Vect</code> class has been introduced for the
<a href="SettingsScheme.html" target="page">Settings</a> database.
It can be used to store a vector of double-precision real values.
</li>
<li>Three new groupings of existing QCD processes:
<code>SoftQCD:inelastic</code>, <code>HardQCD:hardccbar</code>
and <code>HardQCD:hardbbbar</code>. </li>
<li>New possibility to set the <i>a</i> and <i>b</i> parameters
of the Lund fragmentation function separately for heavy flavour.
Especially the <i>b</i> is expected to be universal, but
Aurelien Martens and Eli Ben-Haim have found improved fits by
relaxing this condition, so we formalize this possibility without
recommeding it.</li>
<li>Method <code>Pythia::getPDFPtr</code> is made public so it can
be used also outside the <code>Pythia</code> class to access PDF
sets. Internally the PDF bookkeeping is modified to allow for
the simultaneous handling of several PDF sets. Thanks to
Mathias Ritzmann for providing code changes.</li>
<li>It is now possible to read the separate scale values of all
outgoing particles, if this info is stored as a single line in
an LHEF, begun by a single hashtag character. This is currently
nonstandard and may evolve.</li>
<li>Some improvements to the install targets code in the
<code>Makefile</code> and error detection in
<code>examples/configure</code>. Thanks to Mikhail Kirsanov.</li>
<li>The CC and FC global environment variables can be set to specify
the C++ and Fortran 77/90 compilers, otherwise set in
<code>configure</code> and <code>examples/configure</code>.
Thanks to Mikhail Kirsanov.</li>
<li>Check of shell choice in <code>configure</code> removed.
Thanks to Andy Buckley.</li>
<li>Minor modifications in the Makefile and text for Root examples,
relevant if shared libraries are used.</li>
<li>Previously the whole <code>std</code> namespace has been made
available in <code>PythiaStdlib.h</code>. Now this behaviour has
been replaced by the already-existing alternative, where only a
part of <code>std</code> is made available, and only inside the
<code>Pythia8</code> namespace. Thus user code does not become
reliant on the choices in PYTHIA. Some related smaller code
rearrangements. Thanks to Andy Buckley.</li>
<li>When the "second hard" machinery is used to set two hard processes,
the old behaviour for the <code>SpaceShower:pTmaxMatch = 0</code> and
<code>TimeShower:pTmaxMatch = 0</code> options was to use the combined
final state of the two processes to decide what <i>pT_max</i>
scale to use. This could have unexpected consequences. Now each process
is analyzed separately, and therefore has a separate scale. Also
for <code>MultipartonInteractions:pTmaxMatch = 0</code> the two
interactions now are analyzed separately. It is then enough that
one of them should limit <i>pT_max</i> of subsequent MPI's for
such a restriction to be imposed. Thanks to Monika Jindal for
discovering this bug.</li>
<li>The <code>TimeShower:pTdampMatch</code> option had no effect if
switched on, since some code was missing. The manual description
of it and the more relevant <code>SpaceShower:pTdampMatch</code>
has been updated.</li>
<li>One minor bug fix and some corrections to make the code compile
on Windows/VisualC++-2010. A simple error function parametrization
has been added to <code>PhaseSpace.h</code> and
<code>SigmaTotal.h</code>, to be uncommented in case
<code>erf(x)</code> is not available by default. Thanks to Guy Barrand
for providing the information.</li>
<li>Break a closed dependency loop between <code>ParticleData.h</code>
and <code>ResonanceWidths.h</code>. Thanks to Andreas Schaelicke and
Andy Buckley.</li>
<li>In the <code>examples/mainXX.cc</code> programs, class instances
that have been created with a <code>new</code> are explicitly
<code>delete</code>d at the end of the run. Useful if trying to track
memory leaks.</li>
<li>Bug fix for R-parity violating decays of R-hadrons, to treat the
special case of sequential resonance decays after the RPV one.
Thanks to Mariangela Lisanti for pointing out this bug.</li>
<li>Changed the maximum allowed value for <code>Tune:pp</code>.
Thanks to Yevgeny Kats.</li>
<li>Bug fix in the <i>z</i>-value weight for QED ISR emissions.</li>
<li>Some destructors moved for improved consistency.</li>
<li>Constants <code>DEBUG</code> renamed <code>DBSUSY</code> in the
<code>SusyCouplings</code> and <code>SusyResonanceWidths</code>
classes to avoid confusion. Thanks to Guy Barrand.</li>
<li>Many typos corrected and some other minor improvements of the
online documentation.</li>
<li>The year has been updated to 2013 in files.</li>
</ul>
</li>
<li>8.176: 18 April 2013
<ul>
<li>Introduce weak shower, whereby <i>W^+-</i> and <i>Z^0</i>
gauge bosons can be produced interleaved with ordinary QCD and
QED emissions. Currently only available for final-state radiation,
and off by default, see
<a href="TimelikeShowers.html" target="page">Timelike Showers</a>.
A new status code 56 denotes <i>W^+-</i> and <i>Z^0</i> gauge
bosons produced by the FSR parton showers.</li>
<li>The gauge bosons produced by showers decay at the end of the
parton-level step. New identity codes 93 for a <code>Zcopy</code>
and 94 for a <code>Wcopy</code> can be used to set the decay modes
of shower-produced gauge bosons separately from hard-process ones,
but do not appear in event listings.</li>
<li>The <code>Particle</code> class has been updated with a pointer
to the mother <code>Event</code> class, replacing the previous pointer
to the <code>ParticleData</code> class. Thereby several old methods
in the <code>Event</code> class can obtain new equivalents for the
<code>Particle</code> one. That is, a call <code>event.method(i)</code>
instead can be written <code>event[i].method()</code>. The duplicated
methods are <code>statusHepMC</code>, <code>iTopCopy</code>,
<code>iBotCopy</code>, <code>iTopCopyId</code>, <code>iBotCopyId</code>,
<code>motherList</code>, <code>daughterList</code>, <code>sisterList</code>,
<code>isAncestor</code> and <code>undoDecay</code>. Omitted is
<code>sisterListTopBot</code>, while <code>sisterList</code> obtains an
optional argument. A new method <code>index</code> is introduced.
The now redundant <code>Event</code> class methods will be removed in
PYTHIA version 8.2. Thanks to Andy Buckley for suggestion.
</li>
<li>The initialization of SUSY couplings and particle data has been
moved from the <code>Pythia</code> and <code>ProcessLevel</code> classes
to a new dedicated <code>SLHAinterface</code> class.</li>
<li>Some SUSY 3-body decays have been implemented with Matrix Element
weighting.</li>
<li>New method <code>Info::scalup()</code> returns the Les Houches
<code>SCALUP</code> variable. This method is now used instead of
<code>QFac()</code> in <code>main31.cc</code>, to set maximal scale for
shower radiation in case that the event contains no POWHEG emission, and
thereby sidesteps a potential bug when PDF information is provided in the
Les Houches Event File. Also some default values have been changed in
<code>main31.cmnd</code>. Thanks to James Monk.</li>
<li>New parameter <code>LesHouches:mRecalculate</code> can be used to
prompt the recalculation of a particle mass from its four-momentum.
This may be required for Les Houches input events where the nominal
mass of the particle species is stored in the mass slot, rather than
the actual mass of the current particle, as foreseen.</li>
<li>Extra checks that tracing of junctions in particular and partonic
colour singlets in general are only performed when the event record
contains coloured unhadronized partons. Thanks to James Catmore.</li>
<li>Minor correction related to GZIP support. Thanks to James Monk.</li>
<li>Recalculate the phase space of diffractive processes for each event
when variable beam energies are allowed. Thanks to Oldrich Kepka for
finding the bug.</li>
<li>Fix a bug whereby a gluon in diffractive systems would obtain a
light-quark mass.</li>
<li>The <code>Pythia::check()</code> method can also check that each
particle obeys <i>E^2 - p^2 = m^2</i> (within numerical precision).
Speed up the checks on mother-daughter history by streamlining the
handling of simple cases.</li>
</ul>
</li>
<li>8.180: 20 September 2013
<ul>
<li>Nishita Desai joins as new author.</li>
<li>All the header files <code>include/*.h</code> have been moved to
<code>include/Pythia8/*.h</code> to better comply with conventions
in other libraries (<code>*</code> = generic name). Thus also all
code lines <code>#include "*.h"</code> that refer to PYTHIA files
have been changed to <code>#include "Pythia8/*.h"</code>. Thanks to
Andy Buckley for suggestion.</li>
<li>The class that converts PYTHIA events to the HepMC format
is renamed from <code>I_Pythia8</code> to <code>Pythia8ToHepMC</code>,
the files where the class resides from <code>HepMCInterface.h/.cc</code>
to <code>Pythia8ToHepMC.h/.cc</code>, and the subdirectory of the
<code>.cc</code> file from <code>hepmcinterface</code> to
<code>pythia8tohepmc</code>. This clarifies the role of the class
and avoids potential future name clashes with other interfaces.
Makefiles and example main runs have been modified accordingly.
Thanks to Andy Buckley.</li>
<li>The configure/Makefile step has been extended such that a
<code>bin/pythia8-config</code> script is constructed, to simplify
subsequent linking of PYTHIA 8 and other libraries to your main
program. See the <code>README</code> file for further instructions,
the new "Compling programs against PYTHIA 8" section.
Thanks to Andy Buckley for code and text.</li>
<li>The "minbias" event class has been renamed into the
(inelastic) "nondiffractive" one, since the "minbias" denomination
should be reserved for an experimental procedure. Needless to say,
also the separation into diffraction or not could be made by
experimental procedures, but here it is more generally accepted that
there is an underlying theoretical description that takes precedence
in cases of conflict. Thus the <code>SoftQCD:minBias</code> flag
has been remaned <code>SoftQCD:nonDiffractive</code>, and the
<code>Info::isMinBias()</code> method has been renamed
<code>Info::isNonDiffractive()</code>. The old names have been retained
as alternatives for now. Thanks to Andy Buckley.</li>
<li>Four PDF sets have been added from the NNPDF2.3 QCD+QED family:
the central sets for LO with <i>alpha_s(M_Z) = 0.130</i>,
LO with <i>alpha_s(M_Z) = 0.119</i>, NLO with <i>alpha_s(M_Z) = 0.119</i>,
and NNLO with <i>alpha_s(M_Z) = 0.119</i>.
Thanks to Juan Rojo and Stefano Carrazza for providing the code.</li>
<li>The <code>fjcore</code> version 3.0.5 code from <code>FastJet</code>
has been included with the PYTHIA distribution. <code>SlowJet</code> now
by default becomes a front end to <code>fjcore</code>, but the old
behaviour is retained as an option. The new approach is faster,
but the older one still offers a few extra possibilities. Note that
the new <code>useFJcore</code> argument to the <code>SlowJet</code>
constructor has been included as a new last-but-one argument,
since the last one is likely to be used much more infrequently
and logically depends on the value set for <code>useFJcore</code>.
Thanks to Matteo Cacciari, Gavin Salam and Gregory Soyez for making
the <code>fjcore</code> code freely distributable.</li>
<li>New method <code>constituents(i)</code> in <code>FastJet</code>
returns a vector with the indices of the particles belonging to the
<i>i</i>'th jet.</li>
<li>The global recoil option for final-state showers has been extended
with a few more options to improve possibility for matching to
output from other programs, such as aMC@NLO.</li>
<li>Further extensions of the weak-showering machinery, but still
experimental. Now also includes <i>W/Z</i> emission in the initial
state.</li>
<li>Introduce new <code>qqbar</code> option for
<code>SigmaProcess::inFlux()</code> and update documentation.</li>
<li>Improve the description of <code>meMode</code> for resonances
and illustrate how to force specific Higgs branching ratios in
<code>main16.cmnd</code>.</li>
<li>Added two previously missing SUSY processes for associated
production of a gluino with a neutralino or chargino:
<code>SUSY:qqbar2chi0gluino</code> and
<code>SUSY:qqbar2chi+-gluino</code>, using the cross section
expressions in [<a href="Bibliography.html" target="page">Fuk11</a>]. Validated against PYTHIA 6 and
XSUSY.</li>
<li>Added direct slepton production from <i>q qbar</i> annihilation,
<code>SUSY:qqbar2sleptonantislepton</code>. Validated against
PYTHIA 6.</li>
<li>Corrected some slepton and squark EW couplings in
<code>SusyCouplings</code>.</li>
<li>Generalized the cross section formulae for
<code>SUSY:qg2squarkgluino</code> to the case of non-minimal flavor
violation, using the expressions in [<a href="Bibliography.html" target="page">Fuk11</a>]. Validated
against PYTHIA 6 and XSUSY. The new implementation is compatible
with both SLHA2 and SLHA1, whereas the older was only compatible
with SLHA1.</li>
<li>Generalized the cross section formulae for
<code>SUSY:qqbar2gluinogluino</code> to the case of non-minimal
flavour violation, using the expressions in [<a href="Bibliography.html" target="page">Fuk11</a>].
(Also corrected a factor 2 in that paper on the color factor for
<i>st</i> and <i>su</i> interference terms.) The new
implementation is compatible with both SLHA2 and SLHA1, whereas
the older was only compatible with SLHA1.</li>
<li>Changed the default <code>meMode</code> for SLHA DECAY modes to 100,
to allow off-shell decays. Enabled the user to choose a different
<code>meMode</code> if desired, via a new mode, <code>SLHA:meMode</code>.
If values different from 100 are selected (e.g., 103), modes that are
extremely far off shell (defined as needing a fluctuation of more than
100 times the root-sum-square of the widths of the mother and daughter
particles) will still default back to 100, though the user may of course
still switch them off if so desired. Added documentation about this in
<code>SusyLesHouchesAccord.xml</code>. Deleted the parameter
<code>SLHA:minDecayDeltaM</code>, which would prevent the possibility
of off-shell decays unless set to a large negative value.</li>
<li>Added calculation of decay lengths to SLHA DECAY modes.</li>
<li>Updated documentation of SUSY processes and SLHA-related
parameters. Additional reference to the new cross sections included in
the bibliography.</li>
<li>Allow six-flavour running of <i>alpha_s</i> above the top threshold,
and implement option with CMW rescaling of the Lambda values, for use
in coherent showers.</li>
<li>The merging code has been updated, with corrected handling of massive
partons. This amends problems in <i>tt̄</i>, and makes clusterings of
massive emissions <i>W, Z, ~g</i> possible. The bookkeeping for the hard
process has been upgraded to accommodate more general BSM processes. The
treatment of incomplete histories has been upgraded, so that histories which
allow for at least one clustering will be used in the unitarisation. Also,
states that do not allow for any clustering will not be subject to the
(internal, optional) cut on the input events any longer, to guarantee full
phase space coverage. This is important for processes for which a
non-negligible fraction of states lead to incomplete histories, e.g.
<i>tt̄W</i> production. Further, functionality for reclustering
FSR off SUSY particles has been added. A new setting allows more easily
to switch between 4-flavour and 5-flavour merging schemes.</li>
<li>The <code>main85.cc</code> - <code>main88.cc</code> have obtained
support for zipped LHE input files, and have nicer printing of the
inclusive cross section at the end.</li>
<li>Introduced new mode <code>LesHouches:setLifetime</code> so that
the lifetime information in Les Houches input can be replaced by
the standard PYTHIA selection procedure. By default this is applied to
<i>tau</i> leptons, since some matrix-element generators do not set
this lifetime. Thanks to James Monk and Thorsten Kuhl.</li>
<li>A new <code>examples/main46.cc</code> illustrates how to write a
ProMC file with PYTHIA events. Thanks to Sergei Chekanov.</li>
<li>The <code>Vect</code> class has been renamed <code>PVec</code>
and a new <code>MVec</code> class has been introduced along the same
lines, see the <a href="SettingsScheme.html" target="page">Settings</a> database.
They can be used to store a vector of double-precision real or integer
values, respectively, i.e. of parms or modes, hence the names.
Thanks to Abram Krislock.</li>
<li>Two new vectors of integers <code>SUSY:idVecA</code> and
<code>SUSY:idVecB</code> have been introduced to allow a more flexible
selection of final states in SUSY processes, see the
<a href="SUSYProcesses.html" target="page">SUSY process selection</a> page.
The selection machinery has been expanded to cope.
Thanks to Abram Krislock.</li>
<li>New switch <code>PartonLevel:earlyResDec</code> to give
first simple option where resonances are allowed ro decay before
colour reconnection and beam remnants are added.</li>
<li>Renamed the <code>mass(...)</code> methods to <code>mSel(...)</code>
in the <code>Particle</code>, <code>ParticleData</code> and
<code>ParticleDataEntry</code> classes, to avoid users mistaking
<code>Particle::mass()</code> for <code>Particle::m()</code>.</li>
<li>Fixed a missing (unused) argument in some derived classes when
the <code>mRecalculate</code> parameter was introduced in Les Houches
code in version 8.176.</li>
<li>Removed several unused class variables from header files, based
on new compiler information.</li>
<li>Fixed a bug in <code>Sigma2ffbar2HposHneg</code>, where
<code>int(...)</code> was used instead of <code>abs.(...)</code>.
Thanks to Vittorio Zecca.</li>
<li>Fixed missing re-initialization of Breit-Wigner mass generation
parameters for externally set new resonance widths.
Thanks to Vittorio Zecca.</li>
<li>Fixed several places where division by zero or adressing of
arrays out-of-bounds could occur. While some were trivial, others
revealed underlying errors, notably in the handling of some SUSY
processes and resonances. New checks against unphysical SLHA input
have been implemented. Also some bug fixes in the new weak-shower
ISR component, the sphericity analysis, the event undo-decay option,
and more. Thanks to Vittorio Zecca.</li>
<li>Bug fix in the <i>tau</i> decay description for decay chains like
<i>H0 → A0 A0 → 4 tau</i>, caused by an erroneous assignment of
the number of spin states. Thanks to Brock Tweedie.</li>
<li>Add setting of some <code>TimeShower</code> variables that might
remain uninitialized. Thanks to Christian Pulvermacher.
</li>
<li>Extra check in <code>TimeShower</code> for incoming massive
particles, where a recalculation of kinematics to an equivalent
massless case could give a slightly negative effective dipole mass
(with endpoint masses subtracted). Thanks to Paolo Torrielli.
</li>
<li>Updated manual on how to implement new showers, mainly detailing
new optional method arguments. Thanks to Mathias Ritzmann.
</li>
<li>Corrected bug in <code>SigmaSUSY</code> which caused flavour violating
slepton production (for R-parity conserving cases too).</li>
<li>Corrected bug in <code>SusyCouplings</code> where <i>tan(beta)</i>
was not read from LHA file for RPV spectrum.</li>
<li>Modified the contact interaction term normalization of the
<i>f fbar → l lbar</i> process to agree with the one used in
PYTHIA 6. Documentation of the <code>ContactInteractions:Lambda</code>
updated to reflect this. Thanks to Daniel Hayden.</li>
<li>Introduced copy constroctor for the <code>Event</code> class.</li>
<li>Reset the Higgs mass range when its mass is changed in
<code>examples/main14.cc</code>.</li>
<li>Remove obsolete <code>examples/main91.cc</code> and associated
<code>Makefile</code> code.
</li>
<li>Catch cases where junction topologies are sent to the ministring
machinery, which is not set up to handle it, and therefore could
give segmentation faults. Very rare.</li>
</ul>
</li>
<li>8.183: 23 January 2014
<ul>
<li>A potentially severe bug has been found in version 8.180,
in that by mistake the <code>SpaceShower:vetoWeakJets</code>,
<code>SpaceShower:dopTDampMass</code>, <code>TimeShower:dopTDampMass</code>
were given a default <code>on</code> value rather than <code>off</code>.
Its main effect is to reduce the emission of two or more hard
jets for processes 221 and 222, i.e. <i>gamma^*/Z^0/W^+-</i>
production: implicitly it thereby also softens the <i>pT</i>
spectrum of the gauge boson. Other processes should be unaffected.
</li>
<Li>The emission of <i>W</i> and <i>Z</i> weak gauge bosons in
ISR and FSR parton showers is now fully implemented [<a href="Bibliography.html" target="page">Chr14</a>].
Note extra optional arguments for a few <code>TimeShower</code> and
<code>SpaceShower</code> methods.</li>
<li>The worksheet, intended to help beginners get going, has been
updated and expanded. Notably with new exercises on CKKW-L merging
and Higgs production and decay. Also some new comments on platform
requirements and how to meet them. An <code>examples/main80</code>
program has been added for the merging exercise.</li>
</li>
<li>The LO PDF sets in the NNPDF2.3 QCD+QED family are now valid down to
<i>Q^2 = 1 GeV^2</i>, the NLO and NNLO sets are positive definite,
and all go down to <i>x = 10^-9</i>. Grid file names have been updated
to agree with the LHAPDF ones. New <code>main54.cc</code> test program.
Thanks to Juan Rojo and Stefano Carrazza for the updates.</li>
<li>Three new <a href="Tunes.html" target="page"><i>e^+e^-</i> tunes</a> to some
LEP data, one by Peter Skands and two by Nadine Fischer. Also the
more comprehensive <a href="Tunes.html" target="page">Monash 2013 tune</a>
[<a href="Bibliography.html" target="page">Ska14</a>], which covers both <i>e^+e^-</i> and
<i>pp/pbarp</i> data.</li>
<li>Some moderate changes in the merging machinery, as follows.
Added the D-parameter of the <i>kT</i> measure as an input. Added
flag to not remove states with incomplete histories from NLO input
(normally, these are taken from tree-level samples instead). This is
necessary for a correct treatment of inputs with "diagram subtraction",
as is e.g. needed for the definition of <i>p p → tW</i>.
Updated the bookkeeping of the hard process in the merging again, so
that the "hard process candidates" are not switched around too often.
Updated the main files with proper header for the standard
<code>access( string, F_OK)</code> function.</li>
<li>Changed status code for partons in the hardest interaction of
the <code>SoftQCD</code> processes, from being in the 30'ies range
to being in the 20'ies range. Thus a nondiffractive event is always
set to have one 20'ies hard interaction. Diffractive events can have
zero, one or two hard interactions, the latter possible only for
double diffraction. A low-mass diffractive system need not contain
any perturbative interaction, but a nonperturbatively kicked-out
quark or gluon is defined by the new 24 status code.</li>
<li>New flag <code>HiggsSM:NLOWidths</code>, on by default, enables
rescaling of the internal PYTHIA partial widths of the SM Higgs
to the values recommended by the LHCXSWG.</li>
<li>New possibility to pick a fixed factorization scale for ISR
(and also for FSR) for debug purposes.</li>
<li>New processes for s-channel exchange of a <i>gamma^*/Z^0</i>
or <i>W^+-</i>, written as <i>2 → 2</i> processes, whereas the
already existing processes separate production and decay of a resonance.
</li>
<li>New parameter <code>StringZ:aExtraSQuark</code> allows an optional
softening in hadronization for strange quarks.</li>
<li>New method <code>vector<int> Info::codesHard()</code> returns a
vector of the hard-process codes set up for current run.</li>
<li>New optional extra argument for the <code>Hist::table</code> methods
allow output of underflow and overflow. Thanks to Mathias Ritzmann.</li>
<li>Two extra safety checks for the <code>Event</code> class.
Thanks to Mathias Ritzmann.</li>
<li>Allow a leptoquark also to couple to the top quark. Thanks to
Katherine Leney.</li>
<li>Updated problematic return statement in <code>JetMatching.h</code>.
Thanks to Simon de Visscher.</li>
<li>New addresses for Nishita Desai and Philip Ilten.</li>
<li>Changes in <code>TimeShower</code>, <code>(Susy)ResonanceWidths</code>,
<code>SigmaProcess</code> and other classes to avoid undefined variables.
Thanks to Vittorio Zecca.</li>
<li>Major cleanup of code and documentation files: replace tabs, remove
blank characters at the end of code lines, keep one blank character at the
end of documentation lines, restrict to a maximum of 79 characters per line
wherever feasible, and update year to 2014.</li>
</ul>
</li>
<li>8.185: 15 March 2014
<ul>
<li>Bug found in the handling of ISR in diffractive systems, whereby the
maximal scale of shower emissions was set to the mass of the diffractive
system, rather than the <i>pT</i> of the hardest interaction. This bug
was introduced in version 8.183, when the status code of the hardest MPI
was changed, and notably gave too many high-<i>pT</i> particles, and
also a bit too high multiplicity. In versions up to and including 8.180,
instead the <i>pT</i> of the second MPI was not strictly limited by the
<i>pT</i> of the first, which also gave an overestimate, but smaller.</li>
<li>Added the FxFx matching and shower-kT matching schemes as new options,
see <a href="JetMatching.html" target="page">Jet Matching</a>. Still under validation,
though. Part of the new code is contributed by Simon de Visscher.</li>
<li>A number of minor improvements of the merging machineries for
increased flexibility, including removed hardcoded maximum number of jets,
updated bookkeeping to allow for a event-by-event definition of the
hard process for merging, removed incomplete histories warning, small
change in mass treatment for reclustering, and more. Also removed internal
setting of <i>K</i> factors for <code>main88.cc</code>.</li>
<li>New documentation on the
<a href="POWHEGMerging.html" target="page">POWHEG Merging</a> implemented in
<code>examples/main31.cc</code>.</li>
<li>Higgs particle names (re)simplified to MSSM standard. New
<code>SLHAInterface</code> code added to reset the names appropriately
(SLHA2 conventions) when in the NMSSM, CPV or RPV scenarios. PDG codes
45 and 46 reserved as placeholders for further Higgs states.</li>
<li>SUSY decay channels now have <code>meMode = 0</code>, except those to
Gravitinos, for which no code has been implemented (they stay 103).
By default, the width of SUSY particles is formally set to 1.0, but all
decay channels start out with zero branching fractions. The proper BRs
should then be calculated by PYTHIA, and/or read in via SLHA decay tables,
and/or set by hand by the user.</li>
<li>Expanded SLHA input support for NMSSM type models, plus a few
further minor SUSY improvements and fixes.</li>
<li>Significant extensions to the
<a href="OniaProcesses.html" target="page">charmonium and bottomonium</a>
machineries, as follows.
<br/>Many more colour-octet states, according to a new labelling
convention <i>9 9 n_Q n_state n_r n_L n_J</i>, where <i>n_Q</i> is
the flavour of the state (4 or 5), <i>n_state</i> is 0 for 3S1,
1 for 1S0 and 2 for 3PJ states, while <i>n_r</i>, <i>n_L</i>
and <i>n_J</i> are the same as in the PDG convention. They are
assigned masses 10 MeV above the respective colour singlet state.
<br/>Data on processes which only differ by the radial excitation
number <i>n_r</i> are grouped into vectors for on/off switches
and long-dinstance matrix elements, but share the same process code
and short-distance matrix elements. This grouping involves some upgrades
to the cross section bookkeeping machinery.
<br/>Matrix elements for 3DJ processes are now implemented.
<br/>The mass splitting between all colour octet and singlet state pairs
can be set by one common parameter.
</li>
<li>Introduce new switch <code>TimeShower:weightGluonToQuark</code> that
allows a few alternative approaches to set the <i>g → q qbar</i>
branching rate, notably for heavy quarks, and similarly for
<i>gamma → f fbar</i>. Associated scale-setting freedom regulated
by new <code>TimeShower:scaleGluonToQuark</code> parameter.
</li>
<li>New/improved capabilities to accept LesHouches input of events
without any incoming beams, e.g. for resonances with decay chains,
where PYTHIA should add showers and hadronization, see
<a href="LesHouchesAccord.html" target="page">Les Houches Accord</a> and
<a href="HadronLevelStandalone.html" target="page">Hadron-Level Standalone</a>.
The <code>Standalone:allowResDec</code> switch is removed and its
functionality largely taken over by the
<code>ProcessLevel:resonanceDecays</code> one.</li>
<li>New possibility to comment out a section of lines in a command file,
when read in by <code>Pythia::readFile(...)</code>. The first line of
the commented section should begin by <code>/*</code> and the last
begin by <code>*/</code>. Best is to keep them on separate lines,
optionally followed by comments, but no commands.</li>
<li>A new <code>FVec</code> class has been introduced to store a vector
of flags, see the <a href="SettingsScheme.html" target="page">Settings</a> database.
</li>
<li>Minor update in <code>configure</code> to be used by
<code>pythia8-config</code>. Thanks to Andy Buckley.</li>
<li>Minor update in the <code>configure</code> options for FastJet.</li>
<li>Minor update of the Monash 2013 tune.</li>
<li>In the joining of nearby partons, <i>q + g → q</i> ,
in preparation of the hadronization step, it is ensured that the quark
mother is listed as <code>mother1()</code>, even when this is not the
order of the mothers in the event record.</li>
<li>The histogram table printing routines have acquired a new argument
that allows the <i>x</i> value at the beginning of each bin to be
printed, instead of the midpoint one.</li>
<li>Implement (some of the) functionality of the <code>doForceWidth</code>
switch for resonances, that has been missing so far, and improve the
documentation thereof. Thanks to Xiaohu Sun.</li>
<li>Update some of the hadron-level code to handle several
junction-antijunction topologies in a single event.</li>
<li>Bug fix for MPI's with an <i>x</i>-dependent impact parameter profile
(<code>bProfile = 4</code>) and the factorization scale of a hard process as
the maximal scale (<code>pTmaxMatch = 1</code>), that this maximum was not
respected, so that an MPI could be harder than the hard process.
Thanks to Stefano Camarda.</li>
<li>A few minor bug fixes in the new weak-shower machinery.</li>
<li>Minor fix in the setting of the pointer of a particle data entry to
the full particle data table.</li>
<li>Some other minor fixes.</li>
</ul>
</li>
<li>8.186: 8 July 2014
<ul>
<li>A new user hook to help experimentation with colour reconnection,
in particular in relation to resonance decays.</li>
<li>New set of parameters <code>StringFlav:probQQ1toQQ0join</code>,
used to pick diquark spin when two already produced quarks are to be
joined into a diquark.</li>
<li>Possibility to map the bookkeeping of exotic unresolved incoming
beams in Les Houches event files onto neutrino beams, see
<code>LesHouches:idRenameBeams</code>. Primarily intended for dark matter
annihilation. Thanks to Leila Ali Cavasonza and Jiang-Hao Yu.
</li>
<li>A correction to the graviton (<i>G^*</i>) + parton hard processes
(5003-5005) to account for off-shell <i>G^*</i> production.
The previous formula assumed the graviton was on-shell and could
greatly overestimate the low-mass tail of the <i>G^*</i>.</li>
<li>Bug fixes in <code>examples/JetMatching.h</code>, for uninitialized
boolean, and number of partons to match for heavy flavour handling.
The former bug was introduced with the new matching schemes in version
8.185 and affected matching to ALPGEN, since no events were rejected.
Thanks to Chris Brust.</li>
<li>Differentiate the reading of ALPGEN masses, so that vanishing
<i>c</i> or <i>b</i> masses in ALPGEN are not unwittingly used
where inappropriate. Also protect the <i>c</i> and <i>b</i> masses
from being set too low in <code>TimeShower</code> and
<code>SpaceShower</code>, so that flavour thresholds are not messed up.</li>
<li>Reduce number of maximum violation warnings in <code>SpaceShower</code>
by leaving some headroom for branching weights.</li>
<li>Bug fix that <code>hasVetoed</code> in <code>Pythia.cc</code> was not
reset correctly in some specific cases. Thanks to Christian Bauer and
Calvin Berggren.</li>
<li>Bug fix in PartonLevel.cc where a reference could become invalid.
Thanks to Thomas Rössler.</li>
<li>Improvements and bug fixes in junction handling.</li>
<li>Bug fix to not reuse colour indices in double diffraction.</li>
<li>Bug fix in the calculation of the average mass threshold of
open decay channels of a resonance. Reduced
<code>ResonanceWidths::MASSMIN</code> parameter value.</li>
<li>Correct typo in left-right symmetry documentation. Thanks to
Nady Bakhet.</li>
<li>Some other minor fixes. Thanks to Pere Mato for two of them.</li>
</ul>
</li>
</ul>
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