Update History

Main news by version

• 8.226: 26 April 2017
  • Implementation of gamma-hadron collisions and photoproduction in lepton-hadron ones. Section ";?>Photon-photon Interactions renamed to ";?>Photoproduction to cover also gamma-hadron documentation. Modified GammaKinematics class to sample photon kinematics also with one photon. Added case gamma-hadron to SigmaTotal.
  • Automatic mixing of resolved and unresolved photon-photon interactions. Implemented by introducing resolved and unresolved PDF pointers for a BeamParticle, and calling the relevant one once the process has been selected. In case of one direct photon the correct number of photon-initiated processes (PhotonParton) is set by ProcessContainer. A new method Info::photonMode() to output the type of the process. Updated sample program main69.cc.
  • Check if there is room left for photon-beam remnants also in case of softQCD processes. Very rarely fails.
  • A new partonic subprocess q gamma → q gamma, mainly to study photon production in lepton → gamma - hadron collisions.
  • Modified kinematics methods for DIS and photoproduction physics, to take beam particle masses into account where important. For DIS, e.g., the incoming lepton is kept massive, which leads to slight changes only visible at very low energies.
  • Redesigned the merging machinery to allow users to define their own ME+PS merging plugin, which can then be used by Pythia. This change does not affect the physics of Pythia's internal merging schemes. For further details see the new section on "Implementing an external ME+PS combination scheme and interfacing this plugin with Pythia" on the ";?>Matching and Merging page.
  • Added some new (optional) virtual functions to the timelike and spacelike showers, to ease ME+PS merging with shower plugin codes. The change does not impair the compatibility of existing shower plugin codes. See the description on how to ";?>Implement New Showers, the new methods allowedSplitting(...) and getRecoilers(...), and the modified getSplittingName(...) ones.
  • New method Pythia::addUserHooksPtr(...) allows the simultaneous use of several ";?>User Hooks. When several hooks are applicable for a given task the net effect is multiplicative, in weights or in veto survival. It is up to the user to ensure that such combinations are the intended ones.
  • New ";?>User Hooks added to set the space-time vertices for the ISR, FSR and MPI evolution process. New main65.cc example illustrates how to set it up. Thanks to Christian Bierlich.
  • Bug fix in the user hooks machinery for setting fragmentation parameters, and an extension of this framework also to junction topologies.
  • Four central members from the NNPDF 3.1 sets are made available, as PDF:pSet (and equivalent) codes 17 - 20: the LO ones with alpha_s = 0.130 and 0.118, and the NLO and NNLO ones with the latter alpha_s. Note that these are rather different from the default NNPDF 2.3 ones; in particular the small-x behaviour is completely changed. Therefore MPI cross sections are appreciably modified for current parameter values, and retunes will be necessary before using NNPDF 3.1 in production. Thanks to Juan Rojo.
  • Construct pi^+- PDFs so that dbar = u and d = ubar, shortcutting the returned d, dbar values since these are not always constructed correctly in LHAPDF. Thanks to Vincent Andrieux.
  • Upgrade from fjcore version 3.0.5 to 3.2.1. This removes the usage of the deprecated std::auto_ptr C++ feature. Thanks to Ivan Razumov.
  • Fix a number of harmless but annoying warnings issued in some versions of GCC 6.x, where the -Wmisleading-indentation flag appears to be on by default. Thanks to Ivan Razumov.
  • Bug fix the calculation of enhancement factor for the machinery with two hard processes. By mistake statistics was added once with the correct value for each event (accessible with Info::enhanceMPI()), and once with unity, leading to a dilution of the effect. The average enhancement factor is now also calculated at initialization, see Info::enhanceMPIavg() and Info::enhanceMPIoldavg().
  • Bug fix in SusyLesHouches.cc, in which the unitary checks of SLHA mixing matrices previously ignored imaginary components, leading to failures when reading in spectra with explicit CP violation. Thanks to M. Noormandipur for pointing to this bug. Mixing-matrix output simultaneously updated so that the magnitudes, rather than the real parts, of mixing-matrix elements are printed.
  • A new approach has been introduced to force settings values outside their allowed range, either by using the keyword FORCE after the key (= parameter name) in an readString() or readFile() command line, or by using a new optional third argument force = true (which is false by default) in the Settings methods used to change values. The latter methods also will add a new key to the database if not already there when force = true is set. The old special force methods are now redundant and will be removed in the next major release.
  • New methods Settings::getReadHistory and ParticleData::getReadHistory return a vector with all strings that have been read in by the Settings::readString() and ParticleData::readString() methods, respectively, and thereby also the information set by the Pythia::readString() and Pythia::readFile() commands.
  • Introduce possibility to make phase space cuts on the DIS Q^2 variable.
  • Add options to use the DIS Q^2 variable as factorization and/or renormalization scale.
  • Introduce some freedom to modify the default shape of the low-mass part of diffractive cross sections, and thereby also the integrated value.
  • The new LHAupHelaconia class in include/Pythia8Plugins/LHAHelaconia.h provides an interface to the HelacOnia [Sha15] package for onium production, see further the new ";?>HelacOnia Processes page. The new main35.cc example shows how to use the interface, and how to compare with corresponding internal Pythia results.
  • Modified configure and Makefiles fixes an issue with linking shared libraries on a Mac, and automatizes the selection of whether to link static or shared libraries to the example main programs.
  • Two new Vec4 methods introduced: cross4 for cross product of three four-vectors, and getTwoPerpendicular to create to four-vectors perpendicular to two given ones.
  • New main74.cc illustrates how the modified Mass Drop Tagger code in FastJet can be used to improve mass reconstruction of a resonance.
  • When using the PhaseSpace:bias2Selection to reweight high-pT events the PhaseSpace:pTHatMinDiverge value is now used as ultimate fail-safe to avoid pT = 0.
  • Bug fix in the TimeShower::findMEtype(...) for a few rare cases.
  • Bug fixes for the squark-gluino and gluino-chargino processes. The charge-conjugate processes were not handled correctly, since the PDF factors are different, and have now been separated.
  • Minor addition to Streams.cc includes to avoid problems on one platform. Thanks to Joshua Ellis.
  • Bug fix in HVStringFlav, which otherwise left some Hidden Valley particles massless. Thanks to Colleen Treado.
  • A few minor fixes when Dark Matter is used as incoming beams in Les Houches input. Thanks to Roberto Ruiz.
  • Minor bug fix where the process container for resonance decays (only) from LHE input is not initialized. This can lead to the problem where particle input without lifetimes are not corrected, even when the LesHouches:setLifetime mode is non-zero.
  • Bug fix in LED/Unparticle + Z^0 production: correct cross section for allowed Z^0 decay channels. Thanks to Andreas Albert.
  • Fixed memory leak in TimeShower, for the case when the ProcessLevel is off. Thanks to Ryosuke Sato.
  • Fix that the MPI machinery did not work for the (infrequently used) MultipartonInteractions:bProfile = 0 option.
  • Minor division-by-zero bug fix in statistics calculation and harmless uninitialized bools in CoupSUSY. Thanks to Vittorio Zecca.
  • Minor numerical precision improvements in gamma-gamma kinematics and in tHat and uHat construction.
• 8.223: 5 January 2017
  • Nadine Fischer and Leif Lönnblad join as co-authors, while Jesper Roy Christiansen leaves. Nishista Desai, Ilkka Helenius and Stefan Prestel have new affiliations.
  • The machinery for resolved γγ collisions has been extended, such that now soft processes and MPIs can be simulated, also when embedded in l^+l^- collisions. (But not yet diffraction.) Also some further improvements have been introduced, see the ";?>Photon-photon Interactions description. This implies several changes in different parts of the code, mainly related to beam remnants and beam particles.
  • Also direct-resolved and direct-direct processes are included for γγ interactions, with photon beams and within lepton beams. This involves new subprocesses where one initiator is a photon and the other a parton. A new sample main program (main69.cc) illustrates how the different classes of γγ interactions are combined.
  • The kinematics of γγ have been revised to include all mass corrections and to handle also non-equal leptons. A new class GammaKinematics is introduced to handle the sampling of the kinematics. A fix for the ProcessLevel::roomForRemnants() function, which rejected a bit too many processes when photon-photon collisions were generated within lepton beams.
  • New cuts for the kinematics of γγ interactions in l^+l^- collisions are introduced, for details see ";?>Photon-photon Interactions. Matching new kinematics output methods, see ";?>Event Information.
  • A PDF for point-like photon is included. In case of lepton PDFs, the photon contribution has now restricted virtuality and also more accurate lower limit for the virtuality. A new option to use separate PDFs for hard processes, with photon PDFs obtained from LHAPDF5. CJKL PDFs are modified so that, instead of freezing the scale below its minimum, the scale evolution is approximated with log(Q^2).
  • A new alternative "thermal hadronization" option is introduced, wherein an exponential exp(-pT / T) hadronic transverse momentum spectrum replaces the default Gaussian one, with a "temperature" T as free parameter. Given this pT, the next hadron (consistent with local flavour conservation) is picked among the possibilities with an exp(-mT / T) weight. This option is accessed with StringPT:thermalModel = on. See further the ";?>Fragmentation and ";?>Flavour Selection descriptions and the article [Fis16].
  • A new option StringPT:closePacking = on allows to enhance the pT width in regions where there is a high density of partly overlapping strings. This works both for the default Gaussian and the alternative exponential (see above) pT description; in the latter case it will also enhance the rate of heavier-particle production. See further the ";?>Fragmentation description and the article [Fis16].
  • A new simple model for hadronic rescattering is introduced, with two variants, as described in [Fis16]. A new master switch HadronLevel:HadronScatter, by default off, and HadronScatter:mode to pick among them and the old one. See the ";?>Hadron Scattering page for further details and parameters. New status codes 111 and 112 introduced for rescattered hadrons.
  • A first process for Dark Matter production, for the pair production of new Dirac DM particles through an s-channel vector-like mediator.
  • New mode BeamRemnants:unresolvedHadron can be used to let original hadron remain as beam remnant, e.g. for coherent emission of photons.
  • New option with running coupling in Hidden Valley scenarios. Some other small fixes in it.
  • Fixed a check in the construction of all shower histories for the merging, which meant that not all histories were produced for squarks+jets. Included rudimentary facilities to guess the process for merging.
  • Added functionality to write Pythia events to a LHEF3-style string, e.g. for use in an external Pythia caller.
  • Improved safety checks for the presence of LHE files.
  • New status codes 49 and 59 introduced for ISR and FSR partons, respectively, to represent special states in the evolution where E^2 - p^2 = m^2 is not fulfilled.
  • New behaviour of Event::remove, where mother and daughter indices now are updated by default.
  • Fix in the setup of tunes with SpaceShower:rapidityOrder = off. The new (in 8.219) SpaceShower:rapidityOrderMPI then also ought to have been set off, but this was missed, giving small inconsistencies (around 2% reduction of the charged multiplicity). Thanks to James Monk.
  • New method string Hist::getTitle() to get the title of a histogram, while void Hist::title(string ) sets it. Thanks to Roberto Franceschini.
  • Corrected behaviour for R-hadrons produced in sequential resonance decays (for example a squark decaying to a gluino with the latter forming an R-hadron). Thanks to Jinmian Li for alerting us.
  • Minor updates so that main91 and main92 examples work also with ROOT 6, in addition to the existing ROOT 5 support. Thanks to Li Huang.
  • Include correct mass suppression for excited fermion three-body decays F^* → F Fbar f, primarily for F = t. Thanks to Olya Igonkina and Oleg Zenin.
  • Two new Hist::rivetTable methods allow histograms to be written on file in a format that Rivet understands.
  • New particle data method nQuarksInCode(int idQ) counts how many copies of the requested quark code idQ that a quark, diquark, meson or baryon code contains.
  • Bring the FJcore package inside the Pythia8 namespace to avoid potential name clashes with user code. Thanks to Andy Buckley.
  • Fixed flat_namespace issue for macOS. Thanks to Juergen Reuter.
  • Ensure that bash shell is used in Makefiles. Thanks to Inga Strumke.
  • New #define PYTHIA_VERSION_INTEGER 82xx in Pythia.h matches already existing #define PYTHIA_VERSION 8.2xx, for more convenient matching using integers. Thanks to Andrii Verbytskyi.
  • The handling of the meMode ranges 52 - 60 and 62 - 70 were incorrect, insofar as checks or not against duplication of existing channels go, and have now been set straight. Thanks to Christopher West.
  • Minor bug fix in the TimeShower machinery to optionally enhance the rate of some shower branchings.
  • A minor fix for BeamParticle::popBack() method to reset companion choice also if iComp = 0.
  • Cleanup of unmatched xml tags and other xml inconsistencies.
  • Two minor particle data fixes.
  • Small fix in the parsing code of LHEF3.h.
  • Year updated to 2017.
  • Small clarifications in the documentation.
• 8.219: 10 May 2016
  • An interface to the Python programming language has been introduced, see ";?>A Python Interface for details. Various minor changes in the C++ code have been done in order to permit the automatic generation of the interface.
  • Included a new framework for automated parton-shower uncertainty bands. Variations of the QCD renormalisation scale for both initial- and final-state showers can now be computed by Pythia on the fly, and are provided as a list of alternative weights for each event, representing the probability that the given event would have occurred under different shower assumptions. So-called "nonsingular terms" can also be added to the splitting kernels to estimate the possible effect of missing matrix-element corrections. Full documentation is found on the ";?>Automated Shower Variations page, and a paper is due to appear on arXiv shortly.
  • When a final-state g → g g branching happens with a massive recoiler, radiation in the recoiler direction is now by default further suppressed to respect the "dead cone" effect, see new switch TimeShower:recoilDeadCone. Furthermore a new switch, TimeShower:MEextended, on by defaults, attempts to guess the most relevant ME correction when the correct choice is not known or implemented. Thanks to Jesse Thaler, Michele Selvaggi and Fabio Maltoni.
  • The gamma-gamma hard-process machinery has been extended to convolute the partonic PDFs in a photon with the flux of photons inside a lepton. The description is intended for the region of quasireal photons, but full kinematics is implemented.
  • New constructors that take streams rather than files as input. Thus the contents of a file can be read and then broadcast to multiple instances of Pythia, eliminating the inefficiency of multiple jobs reading from the same initialization files. This facilitates running with MPIs (Message Process Interfaces). Affected areas are settings, particle data and PDF grids.
  • Small additions and fixes to the LHEF3 framework, to keep track of weight keys, and improve parsing.
  • A new class allows PDF data files in the lhagrid1 format, with some restrictions, to be read and used. This does not replace all that you can do with a complete LHAPDF6 installation, but at least permits some simple studies without LHAPDF6 + Boost. New example main55.cc illustrates this, and event properties for an intermediate spinless resonance in γ + γ → γ + γ at 750 GeV.
  • Four Pomeron PDF sets from the ACTW study [Alv99] now implemented.
  • The three Pomeron H1 Jets PDF data files have been joined to one.
  • The ";?>external decays interface has been extended by a new method that allows sequential decays to be done in one call.
  • Increased possibilities to set the epsilon and alpha' parameters of the Pomeron trajectory for hard-diffraction Pomeron fluxes.
  • Extrapolation of PDFs to small x values when PDF:extrapolate = on now extended to more cases.
  • New flag TimeShower:QEDshowerByOther allows charged resonances, like the W^+-, to radiate photons.
  • The jet matching algorithm in JetMatching.h has been extended to better handle heavy quarks, heavy colored particles (such as squarks) and "other" partons (coloured but produced from an Electroweak vertex).
  • Added a new option SpaceShower:rapidityOrderMPI, which will enforce an ordering in rapidity for emissions off secondary scattering systems. This will be enabled by default, ensuring backwards compatibility. The old SpaceShower:rapidityOrder now only refers to the hard(est) subprocess.
  • Changes to the cross section handling in the presence of user vetoes/weights, containing three changes:
    1. Counter of selected event pythia.info.nSelected() is now updated immediately after the hard process generation.
    2. More fine-grained input settings to enforce that Pythia generates (or reads) exactly a fixed number of hard process events.
    3. The Pythia "internal cross section" pythia.info.sigmaGen() and the event weight pythia.info.weight() now directly include the effect of event vetoes and event reweighting that are applied by the leading-order ME+PS merging prescriptions.
  • Changes to the merging classes to allow for a postponed CKKW-L event veto. (See end of ";?>CKKW-L Merging page for details.)
  • Small changes to virtual parton shower functions, and to the merging classes, to prepare ME+PS merging with the Vincia parton shower.
  • The ";?>HepMC interface has been modified such that the detection of unhadronized quarks or gluons leads to an exception being thrown, so that the user can decide what action to take. See further new/renamed free_parton_exception switch. The usage of exceptions for this specific task is by request from ATLAS, and does not represent a general change of programming style. Thanks to James Monk.
  • A class WVec has been introduced to store vectors of strings. The delimiters { } are introduced to provide input with embedded blanks, and broken up across several lines. See further the ";?>Settings Scheme description.
  • The Settings::toLower method used to convert a string to lowercase, and also trim it from initial or trailing blanks and special characters, now moved to PythiaStdlib.h so it can be used more generally. Other code changes accordingly.
  • Remove many rarely (if ever) used ostream& os = cout optional arguments in favour of hardcoded cout in the code. Eliminates some redundancy of methods.
  • Rename ...print(... methods to ...list(... to favour a more regular naming pattern.
  • Minor configure and Makefile updates, to address potential linking problems on some platforms for boost, gzip and promc. Thanks to Dmitri Konstantinov.
  • New --config option of pythia8-config echoes the arguments passed to configure.
  • The description of POWHEG:vetoCount = 0 has been corrected. Thanks to Florian Koenig.
  • Allow for lightest neutralino not to decay as a resonance.
  • Do not switch off the Breit-Wigner width treatment of a resonance as easily as previously, but only if the width is below 1e-6 GeV.
  • Make some SlowJet methods virtual to allow derived classes with modified properties.
  • Moved some misplaced info on parton-level choice of MPIs.
  • Corrected typos where some bottomonium long-distance matrix element had been set larger than normally assumed.
  • Fixed typo potentially giving incorrect colour flow in resonance decays.
  • Fixed an out-of-bounds array access in HelicityMatrixElements. Thanks to Vittorio Zecca.
  • Fixes in main80.cc and main89.cc.
  • Fixed problem with the SLHAinterface not being zeroed-out when using repeated subruns.
  • Minor fix for beam particles, that no default was set as to whether they are gammas or not.
  • Cleaned up error printout for the PDF classes.
  • Change a few true/false to on/off in the documentation to make the php version of the manual recognize them.
  • Some trivial code, manual and bibliography updates.
• 8.215: 4 January 2016
  • Ilkka Helenius joins as new PYTHIA co-author.
  • A new machinery for gamma-gamma collisions is now available, see ";?>Photon-photon Interactions. So far only hard processes can be generated, along with parton showers and hadronization, but without multiparton interactions. The CJKL parton distributions of the photon have been implemented and are used.
  • Double production of charmonium and bottomonium 3S1 states is now available, but with only the colour-singlet processes included, see ";?>Onia Processes for details.
  • Weak merging implemented, i.e. W gauge bosons can be produced either as part of the hard matrix element or in the parton shower, and a proper treatment merges these two possibilities consistently. See the ";?>CKKW-L page for details.
  • Running alpha_em in merging description.
  • Improved interface to external parton showers, such as VINCIA and DIRE, so that these now also can use the various matching and merging frameworks implemented in Pythia.
  • New options in the ";?>jet matching framework, such that expert users can use their own veto code for Madgraph-style jet matching.
  • New convenient possibility to run Madgraph5_aMC@NLO from within Pythia, by wrapping the Madgraph5_aMC@NLO executable inside a new LHAupMadgraph class that derives from the Pythia LHAup base class. See ";?>MadGraph5 Processes for a brief overview, and examples/main34.cc for an example how to use it. Still at an experimental stage, and only tested for Madgraph5_aMC@NLO v2.3.3.
  • By default the program will now assign the PYTHIA mass for massless c and b quarks in Les Houches input, see ";?>LesHouches:setQuarkMass. Usually a logical recoiler is found that can transfer the needed four-momentum to the quark. The already existing machinery for giving masses to massless leptons has been expanded to use the more sophisticated algorithm now in place.
  • Significant bug found in timelike and spacelike showers, whereby the azimuthal anisotropy from gluon polarization in the past has been overestimated. This does not affect multijet rates, but can influence distributions sensitive to angular correlations, although checks have not revealed any appreciable effects. New switches TimeShower:phiPolAsymHard and SpaceShower:phiPolAsymHard regulate whether the first branching after/before the hard process can correlate with the hard-process event plane. Thanks to Radek Zlebcik.
  • Some further new options and minor additions in the machinery for hard diffraction. This includes three options for setting the impact parameter for the Pomeron p subcollision, a possibility to access both it and the impact parameter both for the original p p, and options to rescale the Pomeron flux, including one that uses the MBR renormalization. Some default values changed, notably that now MPI is checked.
  • A new constructor for the Pythia class takes references to a Settings and a ParticleData object as inputs. In cases where multiple Pythia copies are created this allows the xmldoc files to be read only once. Updated examples/main19.cc illustrates.
  • New method Particle::daughterListRecursive() that uses the daughterList() method to trace consecutive generations of decay products.
  • New Vec4 friend method pShift(...) to transfer four-momentum between two four-vectors so as to bring them to have specified new masses.
  • New particle method intPol() returns the polarization as an integer if the stored double-precision number is very close to 0, +-1, +-2 or 9, and else -9.
  • Initialize the random number generator earlier, so a non-default seed choice also could benefit early external initialization making use of it.
  • Minor fix in interface to zlib.
  • Changed default setting in main89mlm.cmnd, to better agree with common practice.
  • Minor improvements and fixes in the weighting facilities for initial- and final-state showers.
  • Minor update in the beam-remnant handling for DIS.
  • Minor improvements in the handling of resonance mass selection.
  • The GetDJR function of the JetMatchingMadgraph class has been renamed getDJR to adhere to standard naming conventions. A pointer in the same class is explicitly nulled.
  • Bug fix in the selection of masses in resonance decays. In rare situations this could give wrong masses for particles. Thanks to Are Raklev and Anders Kvellestad.
  • The StringFlav::combine( int, int bool) method is renamed combineId to avoid a potential incorrect method overloading. Thanks to James Monk.
  • Bug fix: copy vertex information when a long-lived particle decays to three quarks (typically with baryon number violation), whereof two have such a small invariant mass that they collapse to a diquark. Thanks to Cristiano Alpigiani.
  • Bug fix for excited quarks q^* and leptons l^*, that if new decay channels were introduced they could incorrectly make use of the matrix element expressions for the existing decay modes. Thanks to Simone Amoroso.
  • Bug fix in the kinematics of four or more resonance decay products when kinematics is redone owing to matrix-element corrections. Thanks to Simone Amoroso.
  • Changed off-shell behaviour for squark pair production.
  • Minor fix for random number start-up in the PowhegBox interface, and inserted warning that using LHAPDF5 in both Pythia and PowhegBox can be dangerous.
  • Correct two misspelt endtags for LHEF3 output from Pythia. Minor technical changes in the LHEF3 machinery.
  • Bug fix for information on the pdf value chosen for the hardest MPI, which was reported a factor 9/4 too large for an incoming gluon. Does not affect the event generation itself.
  • Correct BeamRemnants:primordialKThard from 2.0 to 1.71 for ATLAS tune AZ. Thanks to Christian Bauer.
  • Introduce protection against (close-to-)zero-energy partons in string length calculations, and against topologies with extremely small angles between two junction legs. Thanks to Jan Fiete Grosse-Oetringhaus.
  • Check by trial whether a given LHAPDF5 set contains photons or not, therey avoiding explicit enumeration of such sets.
  • When the ARCH environment variable does not have a valid value it is set to LINUX in configure. Thanks to Alessandro Degano.
  • Make the BOOST include directory available when the LHAPDF6 plugin is used.
  • Minor corrections for the LHAPDF6 description in README. Thanks to Radek Zlebcik.
  • Fix harmless name overloading in ProcessContainer.cc.
  • Updated address for Philip Ilten.
  • A few bibliography updates.
  • Year updated to 2016.
• 8.212: 23 September 2015
  • Included new weighting facilities in initial- and final-state showers. This allows to consistently enhance rare shower branchings without impairing the no-emission probabilities, see ";?>User Hooks. A new main63.cc, together with main63.cmnd, illustrates this feature.
  • Added new functionality to time- and spacelike showers to streamline merging with external shower plugins, see ";?>Implement New Showers.
  • New possibility to access hadronization parameters in each step of the hadronization process, and to veto individual hadrons, see ";?>User Hooks. Thanks to Christian Bierlich.
  • The ";?>EvtGen interface has been expanded with the possibility to force a rare decay of some of the particle species handled by EvtGen, with an event weight compensating for this bias. New status codes 95 or 96 single out particles from a forced decay, without or with oscillation. Documentation has been expanded.
  • New option MultipartonInteractions:pTmaxMatch = 3 introduced to allow better matching for multiparton final states. Thanks to Paolo Gunnellini.
  • Added possibility to write Les Houches Event Files abiding to the latest (v. 3) standard,see ";?>Les Houches Accord. The new main64.cc illustrates how to use the LHEF3 writer.
  • Fixes in the merging machinery, related to the scales associated with final-state splittings with an initial-state recoiler. The evolution scales and energy sharing values associated with this configuration were not calculated correctly, as an incorrect recoiler momentum was used, leading to a numerical small deviation from the actual result. This issue has now been corrected. Some additional matching and merging changes, mostly to make the reclustering in the merging numerically more stable, and to make UN2LOPS possible.
  • Fix bug for the Beams:newLHEFsameInit = on option, whereby several LHE files can be read in without new initialization for each. When the gzip support was improved in 8.209 the filenames were no longer reset properly, and so no files beyond the first one were read. Thanks to Roberto Franceschini.
  • Bug fix in the junction handling for the case of gluinos.
  • Avoid segmentation fault for some rare junction topologies. Thanks to Gabriel Magill.
  • Minor fix for the path to the PowhegBox plugin, as used in the Makefile.
  • Minor fix for the configure script, for the case of building a shared library on Mac OS X. Thanks to Mikhail Kirsanov.
  • Several minor changes in the hard diffractive machinery.
  • PDG codes 51 - 60 have been reserved for Dark Matter (DM) particles. 51, 52 and 53 are intended for spin 0, 1/2 and 1 stable DM particles, respectively. 54 and 55 are for spin 0 and 1 unstable mediators of s-channel DM pair creation or annihilation. The rest can be used freely, say in models with several DM particles. Masses should be set appropriately. Particles 54 and 55 come equipped with a fictitious mix of potential decay modes, to be modified according to the specific model. By default all have separate antiparticles, with negative codes. These can be removed by setting the antiparticle name to be "void". The ParticleData::antiName(...) method has been fixed to accept this, just like ParticleData::names(...) already did.
  • Several processes have been set up with wrong process codes, and are now fixed. The corrections are 4003 → 4203, 4004 → 4204, 4005 → 4205, 961 → 1061, 3124 → 3123, 3126 → 3124, 3144 → 3143, and 3146 → 3144.
  • For tau decay spin correlations the f fbar → V → f fbar matrix element, V = gamma/Z^0 or W^+-, is now only used when the incoming fermion pair has no other daughters. Else the simpler V → f fbar matrix element is used.
  • Minor technical changes, to allow for external pT-unordered parton showers. No effect for the internal showers.
  • The SLHA reading operation has become significantly less verbose: where previously identical warning messages could be issued for many particle codes, now these codes are collected into a single list that is written once.
  • Bug fix in the input of SLHA decay tables. Previously, the first DECAY entry could be ignored under certain conditions, so that the internal SUSY machinery was used to calculate decay properties. This was the case, in particular, when internal SUSY processes were invoked to generate events.
  • Minor correction in the cross section for f fbar → G* for extra-dimensional processes.
  • main85.cc has been updated so it can handle weighted events.
  • main89mlm.cmnd contained misleading instructions which are now changed.
  • Protect against rare but disastrous negative mass-squared by numerical roundoff in string fragmentation.
  • Introduce protection against numerical instability of companion quark distribution in x → 1 limit.
  • Use the PythiaStdlib.h header rather than accessing Stdlib directly in SusyLesHouches.h.
  • Output to cerr replaced by ditto to cout. Excepted is the examples main programs, where it serves a pedagogical function, while a separate cerr is less relevant for big batch runs. (Also FJcore code is excepted).
  • Give final-state showers used for decays access to the beams; not needed for PYTHIA itself but for some plugin showers.
  • Fix minor typo in README, in instruction for enabling 64 bit compilation.
  • Insert two missing std:: in Pythia8Plugins/GeneratorInputs.h.
  • Minor update in histogram overflow handling.
  • Add to the documentation that TimeShower:weightGluonToQuark = 1 is required for consistent aMC@NLO merging.
  • Clarify documentation on which particles are stable by default.
• 8.210: 29 June 2015
  • Bug fix in CKKW-L merging for LHE files, such that the factorization and renormalization scales are set by the SCALUP value if the muf2 and mur2 LHEF3 attributes have not been set, and the user has not set any explicit values. This change restores the PYTHIA 8.1 behaviour.
  • Various technical improvements in the machinery for hard diffraction.
  • Correct quark flavour selection when a string spanned directly between two junctions is split up.
  • Check that SK-I and SK-II colour reconnection machineries only are called for event topologies they are set up to handle.
  • Bug fixes in partial widths of the W' boson. Results are correct when the W' is a simply rescaled copy of the W, but not for more general couplings. Thanks to Mihail Chizhov.
  • Minor fix in default location of PDF data files in the constructors. No practical consequence since correct non-default values are used.
  • Tiny fix in the configure script, so that CXX options containing an equal sign are parsed correctly.
• 8.209: 25 May 2015
  • The "An Introduction to PYTHIA 8.2", arXiv:1410.3012 [hep-ph], has now been published in Comput. Phys.Commun. 191 (2015) 159.
  • The new QCD-based colour reconnection machinery has been expanded with checks whether reconnecting dipoles are causally connected. This cannot be defined exactly, and therefore several different options are available. Also some other minor changes in this part of the code, including updates of parameter default values.
  • New options for ColourReconnection:flipMode allows to sidestep the gluon-move handling but still retain the final flip step.
  • New ColourReconnection:forceResonance switch allows an additional colour reconnection step after late resonance decays. This is especially relevant for H^0 → W^+ W^- / Z^0 Z^0 → q_1 qbar_2 q_3 qbar_4, since the Higgs is so long-lived that its decay is well separated from the rest of the event.
  • The old SK I and SK II colour reconnection models are now available. These are specially aimed at the processes e^+ e^- → W^+ W^- / Z^0 Z^0, but are also relevant for H^0 → W^+ W^- / Z^0 Z^0.
  • Colour reconnection also made possible, optionally, for the forceHadronLevel method.
  • A new switch POWHEG:QEDveto has been introduced to steer the treatment of non-QCD radiation in the POWHEG implementation of include/Pythia8Plugins/PowhegHooks.h.
  • The need to link to the Boost library to read gzipped files has been eliminated by including iostream classes wrapping the zlib compression library, see new files Streams.h and Streams.cc.
  • Linkage to LHAPDF6 so far has been based on the LHAPDF5 compatibility mode, which requires no Boost headers. The new configure option --with-lhapdf6-plugin=LHAPDF6.h uses native mode, and then requires Boost headers.
  • The LHAPDF6 PDF values are frozen at the respective x and Q^2 boundary if the (x, Q^2) pair falls outside the fit region.
  • New functions to extract the fit boundaries, the current alpha_s value, and the quark masses from LHADPF6.
  • New option in the HepMC interface, whereby PYTHIA particles can be appended to an existing HepMC event. Thanks to Mikhail Kirsanov.
  • A new runtime interface to the POWHEGBOX matrix element programs, bypassing the need for intermediate LHE files. The new files include/Pythia8Plugins/LHAPowheg.h and include/Pythia8Plugins/PowhegProcs.h contain the LHAup class wrapper used to build the POWHEG plugin libraries and the simple class that facilitates loading the POWHEG plugins, respectively. The new examples/main33.cc demonstrates how to use these plugins, and examples/main33.cmnd contains the commands needed for POWHEGBOX to run the example.
  • When reading in particle data from the SLHA interface, changes done by the user takes precedence over the SLHA input ones. To be more specific, particle data changes by the Pythia::readString and readFile methods are buffered and repeated after the SLHA initialization.
  • New #define PYTHIA_VERSION 8.2xx in Pythia.h allows user-code preprecessors to make version-specific choices, and allows the Pythia class constructor to check that the header-file version number matches those of the source code and the XML files. Thanks to Pere Mato.
  • User-defined semi-internal processes can now be accompanied by user-defined phase-space generators, via a second optional argument to Pythia::setSigmaPtr(SigmaProcess*, PhaseSpace* = 0). Default is the old behaviour, with PYTHIA selecting the phase-space generator itself, based on the process type. Alternatively, the user may provide a pointer to an instance of an object inheriting from the PhaseSpace class. Sufficiently well-tested and general such generators could be communicated to the PYTHIA authors for possible inclusion in a future release.
  • Updated initialization of LHEF files in LesHouches.cc to ignore file contents enclosed in comment tags, <!-- .. --> and/or the special CDATA statement, <![CDATA[ .. ]]>. The latter occurs, e.g., in LHEF files produced by CalcHep. (It is generally used to store content that contains XML-illegal characters like "<" or "&", such as JavaScript source.) Thanks to A. Belyaev and A. Pukhov for help with this update.
  • New flag LesHouches:matchInOut, by default on, to recalculate the energies and longitudinal momenta of the incoming particles from the outgoing ones for Les Houches input. Reduces effect of numerical inconsistencies in input.
  • Updated EvtGen interface, to allow a pointer to an FSR engine to be passed. Thanks to Torben Ferber.
  • Spin information for tau leptons now also set up for Z' and W' decays.
  • New methodAlphaStrong::setThresholds(...) allows to set the charm, bottom and top flavour-threshold masses used for the running of alpha_strong.
  • New option for the Event::list() methods allows to show momenta with more decimal digits.
  • New Particle::isFinalPartonLevel() method to tell whether a particle belonged to the final state on the parton level of generation or not. New main73.cc example illustrates usefulness.
  • The [] operator is implemented for the Vec4 class to return its components by index.
  • New method string Settings::output(string key) returns the value of a variable as a string. In Pythia::readString() or readFile() calls this can now be used to print a current setting value by the command key = ?.
  • The role of the pythia.forceTimeShower(...) method is better explained in the hadron-level standalone documentation, and main21.cc has been extended with an example.
  • The TimeShower::enhancePTmax() method is made virtual.
  • The iTopCopyId() and iBotCopyId() methods now scan all mothers/daughters, rather than only the first and last, when searching for a unique flavour match.
  • New example main62.cc illustrates how a user hook can steer the selection of angles in a resonance decay.
  • Minor correction in the treatment of the highest multiplicity in FxFx jet matching.
  • Minor correction in the interface to aMC@NLO for dijet and photon+jet processes.
  • Inserted missing endtag that corrupted the Tunes.php page. Thanks to Tim Martin.
  • Minor fix for polarization sign when the tau polarization is forced.
  • The meaning of the HiggsXX:parity options for CP mixing has been slightly modified and is better described.
  • Clarification in the documentation that impact-parameter-enhancement factor calculation for two hard processes does not work for the x-dependent impact-parameter profile option.
  • Fixed a factor sqrt(2) error in couplings for chargino + squark pair production. Thanks to Michihisa Takeuchi.
  • Some minor bug fixes in the SUSY code, and some speed optimization suggested by Martin White.
  • Fixed incorrect indexing in the SLHA interface.
  • Removed misleading flavour setup for unused Pomeron.
  • Fixed possible unwarranted destruction of pointer to external timelike shower by the Pythia destructor.
  • Initialized pointers to NULL in the Info class, to avoid some problems. Thanks to Keno Fischer.
  • Minor Makefile improvements for LHAPDF linking.
  • Minor improvement to the main89.cc example program.
  • Mildly modified warning/error messages when junction splitting fails.
  • Minor fixes in LHAFortran.h, which is also moved to include/Pythia8Plugins to better reflect its peripheral role.
  • New machinery for hard diffraction now in place. Still being debugged and tested, so not yet ready for public usage.
• 8.205: 23 January 2015
  • Unfortunate tiny typo made the new A14 tunes inaccessible. Now fixed.
  • Resolved an inconsistency between MLM and FxFx merging that was introduced in 8.201 upon answering a user request. The effect should be minimal. Thanks to Josh Bendavid for bringing this to our attention.
  • Amended the automated reading of the (optional) "TimeShower:nPartonsInBorn" setting from Les Houches Event files produced with aMC@NLO. Heavy coloured objects are now handled correctly when the information in the Les Houches event does not include heavy partons of the lowest-multiplicity state into its counting (as is conventional). Thanks to Josh Bendavid for pointing this out.
• 8.204: 22 January 2015
  • The examples directory has been moved back from the share/Pythia8/ subdirectory to the main directory, as was the case in PYTHIA 8.1, to make it more visible to newcomers. The optional make install step will create a copy of examples in share/Pythia8/. The rarely used examples/outref subdirectory is moved to share/Pythia8/outref.
  • Fifteen new ";?>tunes have been added, the MonashStar tune from CMS and fourteen A14 tunes from ATLAS [ATL14a]. The latter correspond to central tunes for four different PDF sets and ten variations in five (approximate) eigenvector directions. Furthermore, now the chosen Tune:pp implies the Tune:ee value to which it is related, and thus the latter need not be set separately.
  • Default settings values have been updated to agree with the Monash 2013 tune. Thus typically the list of changed settings is significantly reduced. Thanks to Mikhail Kirsanov for suggestion.
  • The compositeness section has been expanded with six further processes, describing the pair production of excited leptons or neutrinos. Three-body contact-interaction decay modes of these excited states have been introduced. A bug has been fixed that gave the wrong helicity in decays for excited quarks, leptons and neutrinos. Further, the gamma^*/Z^0/Z'^0 can decay to a pair of excited fermions provided that the channels are added to the list of allowed ones. Based on code provided by Olga Igonkina.
  • A new interface to the EvtGen decay package, primarily intended for bottom and charm decays, has been implemented. It is available in include/Pythia8Plugins/EvtGen.h and an example how to set it up is found in main48.
  • Several minor changes in the examples subdirectory. This includes the README, Makefile an runmains files. The main61 example program has been removed, since now LHAPDF can be loaded dynamically for main42, so that the two become equivalent. Further main62 has been renamed main43, to gather HepMC-related examples, and testlhef3.lhe has been renamed wbj_lhef3.lhe.
  • A new example main30 how to create a tailormade copy of the ordinary event record, here with a history tracing of the hard process closer to the PYTHIA 6 conventions.
  • The ";?>ProMC input-output file format is now implemented among the libraries that can be configured to run with PYTHIA. An examples is provided in main46.cc. Thanks to Sergei Chekanov.
  • Change in the setup of final-state-shower colour dipoles for the non-default case of no interleaving, whereby it becomes less likely to pick a colourless final-state particle as recoiler. New option TimeShower:allowMPIdipole gives more flexibility. Thanks to Mihoko Nojiri and Bryan Webber.
  • New options 3 and 4 for TimeShower:pTdampMatch and SpaceShower:pTdampMatch, with new default 3 for the latter. The main effect is that, by default, t tbar production (as a 2 → 2 process) obtains damped radiation above the process scale. Thanks to Andy Buckley for suggestion.
  • Initialization will now abort if a mode has been chosen with a non-allowed value. This applies to those modes that have been defined with the modepick or modefix labels in the xmldoc/*.xml files and, for the former, where maximal and minimal values have been specified. The former label is used to represent a discrete set of options, and so any value outside the allowed range is just plain wrong. Thanks to James Monk for suggestion.
  • Added getChannels() in SusyResonanceWidths to dynamically create the decay table for SUSY particles and thereby to remove duplication in the XML file.
  • New file SusyWidthfunctions. Added new class WidthFunction to handle calculation of three- and four-body decay widths.
  • In main24.cc the example spectrum file format has been updated from SLHA1 to SLHA2, obtained from SoftSusy 3.5.1. The two new slha1-example.spc and slha2-example.spc files replace the older cmssm.spc, snowmass2.spc and softsusy.spc ones.
  • In LesHouches.cc the read-in of LHEF headers containing tags that open and close on the same line (e.g., a single line containing <tag>blabla</tag>) has been enabled. This could previously lead to improper initialization and crashes. Also implemented a check for forgotten close-tag statements, with a warning issued to the user. Thanks to Alexander Belyaev and Alexander Pukhov.
  • Bug fix in the conversion from the xml settings files to their php radio-button equivalents, whereby the text describing some options was not set properly. (Typically the text of the previous option was repeated.) Thanks to Radek Zlebcik.
  • Minor fixes in the LHEF version 3 reader. Introduce a new matching writer of LHEF version 1 or 3 files.
  • Introduction of a new mode LesHouches:setLeptonMass, such that by default final-state charged leptons acquire sensible masses, even when the matrix-element calculations have been performed with massless leptons. This and other energy-momentum adjustments, e.g. for limited-precision storage, are now located in ProcessContainer::constructProcess.
  • http://home.thep.lu.se/Pythia has been introduced as a simpler but (hopefully) equivalent address to http://home.thep.lu.se/~torbjorn/Pythia.html, and various documentation has been updated accordingly. Thanks to Leif Lönnblad.
  • New file include/Pythia8Plugins/execinfo.h contains trivial copies of three backtrace methods needed to be able to compile PYTHIA under Cygwin. The README file and the worksheet updated with brief information on three (non-supported) ways of working with PYTHIA under Windows. Thanks to and Theo Hughes and Gordon Watts.
  • Bug fix in check for colour sextets and transfer of such colour information. Thanks to Alexander Belyaev and Alexander Pukhov.
  • Improved handling of stray characters in the SUSY Les Houches code. The check on the consistency of decay tables has been removed. Improved warning/error printing in the SLHA interface.
  • Bug fix in new beam remnant model, so that it basically operates like the old one for e^+e^- annihilation.
  • Two bug fixes in the new colour reconnection model, one for diquarks at the ends of junction strings, and another to check that coloured resonances are processes with early resonance decays option.
  • Bug fix for multiple Pythia::init() calls, where beam contents were not properly reset. Thanks to Josh Bendavid.
  • Bug fix such that the valence content of a pi^0, K^0_S, K^0_L and Pomeron is reselected for each new event. Thanks to Radek Zlebcik.
  • Fix typo in constants of the tau → 3 pi current for the amplitudes of the rho, rho(1450), and f2. Thanks to Ian Nugent.
  • Small bug fixes for string and ministring fragmentation, for the case when a low-mass (order 2 GeV) system contains at least three partons, which fail to define a unique direction for the final string region.
  • New parameter BeamRemnants:reducedKTatHighY introduced to reduce technical problems with low-mass MPIs produced at high rapidities when primordial kT is introduced.
  • Small bug fix in the global-recoil option for timelike showers.
  • Update year to 2015, remove tabs and superfluous blanks, break long lines where meaningful, and some further minor changes.
• 8.201: 14 October 2014
  • The Introduction to PYTHIA 8.2 has now been assigned the arXiv:1410.3012 [hep-ph] identifier, which has been introduced in code and text.
  • The enable-shared by mistake was not listed among allowed configure options.
  • Corrected a few tiny documentation typos.
• 8.200: 11 October 2014
  • A new share/Pythia8 directory collects all documentation and example code. The examples, htmldoc, phpdoc and xmldoc directories have been moved here. The main-directory files AUTHORS, COPYING, GUIDELINE and README are also copied here during installation.
  • A new share/Pythia8/pdfdoc directory collects pdf documents that are linked from the htmldoc and phpdoc directories. Over time it will provide more in-depth descriptions of various physics aspects than offered in the html/php-formatted documentation. In addition to the official main publication and the worksheet, currently notes on LO vs. NLO PDFs and on the g → q qbar branching kernel are included.
  • A new include/Pythia8Plugins directory collects code that does not form part of the core PYTHIA functionality but still has a general usefulness. Code in this directory will not be compiled as part of the Pythia library, but can be linked where needed. This new directory contains
    • the jet matching classes in CombineMatchingInput.h, GeneratorInput.h and JetMatching.h, moved from the examples directory;
    • the PowhegHooks user hook, to veto shower emissions above the POWHEG scale, formerly found in examples/main31.cc;
    • the Pythia8ToHepMC interface for output of PYTHIA events into the HepMC format, combining the code previously in include/Pythia8ToHepMC.h and pythia8tohepmc/Pythia8ToHepMC.cc into a new HepMC2.h file;
    • the FastJet3.h interface of PYTHIA particles to the FastJet 3 library of jet finders, formerly found in include/FastJet3.h; and
    • the LHAPDF5.h and LHAPDF6.h files for interfaces to the LHAPDF library (see further below).
  • The configure/make structure has been considerably rewritten. Now all external libraries to be linked are specified in the main-directory configure step, along with other options, so there is no longer an examples/configure. The make step will, as before, compile and install libraries inside the current directory, such that the main programs in the examples directory can be run. One small difference is that also the archive libraries are installed in lib and not in lib/archive.
    A new optional make install step allows you to copy files to more convenient locations. The default option, with no directories specified in the configure step, requires you to have superuser privileges. Then files will be copied to standard locations as follows:

    lib/	→	/usr/lib/
    include/	→	/usr/include/
    share/	→	/usr/share/
    pythia-config	→	/usr/bin/

  • The pythia8-config.in script has been replaced by a new bin/pythia8-config script. See the README file for details. The make install step by default will put a copy of it in /usr/bin.
  • The interface to LHAPDF is now dynamically loaded when requested, and can be either to version 5 or 6 of the library. The dummy code previously in lhapdfdummy/LHAPDFDummy.cc, to be linked when LHAPDF is not, is no longer required. The two new files LHAPDF5.h and LHAPDF6.h in the include/Pythia8Plugins directory contain the necessary interface code. The selection of PDF sets, notably for the proton, has been extended to simplify mixing of internal and external PDF sets, and it is now possible to specify different PDFs for the two incoming protons at the LHC, see the ";?>PDF Selection description.
  • The new LHEF3.h file contains a generic interface for reading Les Houches Event Files of versions 1.0, 2.0 and 3.0. This allows more information to be read and studied by the author. Currently PYTHIA itself makes little use of the information beyond the one in 1.0, but it is available among the ";?>Event Information. Examples are found in main37.cc and main38.cc.
  • The new Beams:strictLHEFscale switch can be used to restrict parton showers in resonance decays to be below the input Les Houches scale, not only the hard process itself. The new Beams:setProductionScalesFromLHEF switch can be used to restrict the emission off each separate parton to be below its specific scale.
  • The rootexamples directory has been removed, and the two programs examples/main91 and examples/main92 now illustrate how ROOT can be used in conjunction with PYTHIA.
  • The executable built from examples/mainxx.cc is now named examples/mainxx, while previously it was named examples/mainxx.exe.
  • The rudimentary support for compilation on Windows platforms, present in PYTHIA 8.1, has not yet been updated for 8.2 and so is omitted. Also the README.HepMC file is omitted for now.
  • The ProMC interface is broken, and has been removed for now.
  • Several methods have been removed from the Event class since the properties now instead can be accessed from the individual Particle instance, if this particle belongs to an event. These include iTopCopy, iBotCopy, iTopCopyId, iBotCopyId,motherList, daughterList, sisterList, sisterListTopBot, isAncestor, statusHepMC and undoDecay.
  • A number of deprecated Pythia::init(...) methods with varying arguments have been removed. Instead call init() without any arguments and use ";?>Beam Parameters settings to specify beams and energies in different ways.
  • The deprecated Pythia::statistics(...) method has been removed; instead use Pythia::stat(...).
  • Several settings in the Main: series have been removed. Most of these have already found replacements in the Init:, Next: and Stat: ones, and have been marked as deprecated. Four further ones were deemed so peripheral that they were removed altogether, but of course the underlying functionality remains.
  • A few aliases for (parts of) settings names have been removed. Previously "Multiple" was mapped to "Multiparton", "MI" to "MPI" and "minBias" to "nonDiffractive" if a settings name was not found for the original input string.
  • The default tune has been changed from 4C to Monash 2013, meaning Tune:ee = 7 and Tune:pp = 14. The old 4C tune that was default in 8.1 can be recovered with Tune:ee = 3 and Tune:pp = 5. Also most other older tunes are based on Tune:ee = 3.
  • Two new CMS underlying-event tunes [CMS14] and the ATLAS AZ tune [ATL14] have been added as options.
  • The default handling of the g → q qbar splitting kernel has been changed, affecting in particular heavy-flavour production. TimeShower:weightGluonToQuark has been changed from 1 to 4 to do this. All old tunes are with the 1 value but, since the tunes are not probing the detailed g → q qbar behaviour, this is not set as part of the tune options.
  • Christine O. Rasmussen joins as new PYTHIA collaboration member.
  • A new model for the handling of ";?>beam remnants as an option to the old one, which remains as default for now.
  • Two new models for ";?>colour reconnection, one quite sophisticated and one simpler. This involves several new classes and files. It also includes some changes in the hadronization framework, notably for the handling of junctions. The old model remains as default for now. The BeamRemnants:reconnectColours flag to switch on/off reconnection has been renamed ColourReconnection:reconnect, the main parameter BeamRemnants:reconnectRange of the old model has been renamed ColourReconnection:range, and several new settings have been introduced, notably ColourReconnection:mode to switch among the three models.
  • A new include/Pythia8Plugins/ColourReconnectionHooks.h makes available an even larger selection of toy colour reconnection models, via user hooks. Some of them are only intended for top decays, for top mass uncertainty studies, whereas others can be used more generally. The examples/main29.cc program illustrates how the different options should be set up.
  • Several new features and improvements in the matching/merging machinery. Notably the aMC@NLO matching scheme has been implemented, see the ";?>aMC@NLO Matching description. To this end the global-recoil option of timelike showers has been improved, and security checks have been introduced for inaccurate LHEF input. A new main89.cc example has been introduced, where different .cmnd files show how to set up either CKKW-L, FxFx, MLM, UMEPS or UNLOPS merging.
  • Improved capability for the LHAup Les Houches interface to read SLHA information embedded in the input file or stream.
  • The Makefiles have been updated to take into account the changed structure of the HepMC interface.
  • The Z' production process has been updated to optionally allow decay to a fourth generation of fermions, with universal or non-universal couplings.
  • Introduction of a new Higgs CP-mixing parametrization via a mixing angle phi as described in ";?>Higgs Processes. The choice of the Higgs CP-mixing parametrization now also affects the distributions of the tau decay products from the processes H^0 → tau^+ tau^-.
  • Bug fix in H^0 → W^+ W^- → 4 f matrix element for mixed CP-state case.
  • Various improvements and finer grain control for the determination of tau decay correlations and tau polarizations. By default the decays of tau pairs from known resonance decays in Les Houches input are now correlated. The ParticleDecays:sophisticatedTau mode in ";?>Particle Decays has been renamed TauDecays:mode, as well as all tau-related ParticleDecay options, with two new options of using only the internal machinery to determine correlations and polarizations, and only using the provided SPINUP digit from Les Houches input. The option TauDecays:externalMode has been introduced to control the interpretation of the SPINUP digit.
  • For Les Houches Event input the energy of a particle is recalculated from its three-momentum and mass, in order to limit mismatches from limited numerical precision in the input values.
  • Bug fix in the two-loop running alpha_s, for the matching to six flavours at the top mass.
  • Eliminate harmless compiler warnings for FJcore.
  • Updated Introduction (= the official 8.2 article) and Worksheet.