From torbjorn at thep.lu.se Sat Apr 25 11:09:30 2020 From: torbjorn at thep.lu.se (=?UTF-8?Q?Torbj=c3=b6rn_Sj=c3=b6strand?=) Date: Sat, 25 Apr 2020 12:09:30 +0200 Subject: [Pythia8-announce] Pythia 8.302 now available Message-ID: ===================================================================== Dear All, PYTHIA 8.302 has been released today, and can be downloaded from http://home.thep.lu.se/Pythia specifically from the "Future (v 8.3)" frame of the left-hand index. The new version is mainly aimed at technical improvements of the PYTHIA 8.301 release. With this step the PYTHIA 8.3 series should offer a stable replacement of the PYTHIA 8.2 series. You find a summary of changes below, which is a slightly abbreviated list of the one in the Update History, found e.g. in the html manual. Wishing you an enjoyable experience with PYTHIA 8.302. Sincerely yours, The Pythia 8 Collaboration (Christian Bierlich, Nishita Desai, Ilkka Helenius, Philip Ilten, Leif L?nnblad, Stephen Mrenna, Stefan Prestel, Torbj?rn Sj?strand, Peter Skands, Marius Utheim) ===================================================================== Physics changes * None. --------------------------------------------------------------------- Technical and administrative changes * Bug fix to correct units for automated shower uncertainty weights for lhaStrategy = +-4 (similarly to 8.244 fix). In addition, the combination of weight variations, within the context of uncertainty bands, was not previously well documented and was therefore prone to misunderstandings. Now, all methods related to cross sections and weights are documented together on a single "Cross Sections and Weights" page. Further, the documentation on shower "Variations" has been improved, and the behaviour of Info::getGroupWeight() has been made more transparent. The main121.cc example has been modified accordingly. * Significant speedup of parton distribution handling, and thereby of the whole PYTHIA execution, since PDF is such a major part of the total execution time. This has been achieved by careful work by Dmitri Konstantinov and Grigory Latyshev. In detail, the main changes are: - In the LHAPDF6 interface the evaluation of the x and Q2 limits is extremely slow, such that a caching of these numbers increases execution speed by about a factor of 2 when LHAPDF is used. - A caching of info on the amount of x already used up helps speed up MPI, ISR and FSR execution times, giving gains of order 20%. - Optimization of array handling in LHAGrid1 give a slight speedup. This internal implementation of interpolation in LHAPDF6 grids runs more than 50% faster than the same PDF evaluated by LHAPDF6, at the cost of not offering facilities like PDF error bands. - The special internal routines for the NNPDF 2.3 series have been replaced by an LHAGrid1 implementation, which gives some speedup. * New base class ShowerModel introduced, as a top-level handler of parton-shower models. The default, Vincia and Dire showers inherit from it. New public method Pythia::getShowerModelPtr() is intended to provide access to public ShowerModel methods for diagnostics purposes. * A HepMC 3 interface is now included in Pythia8Plugins/HepMC3.h. All HepMC examples have been migrated from HepMC 2 accordingly, except for main44.cc and main93.cc, which are kept for legacy purposes. * New particle property directive tauCalc allows for a particle's proper lifetime to be set independently of its width. This is useful for studying the effect of lifetime for a particle when the particle width is otherwise negligible. * Fix for subscripting issue for photon beams, courtesy of Vittorio Zecca. * Extra protection against unexpected input in e+e- Les Houches events, specifically where x >= 1 by roundoff errors. Thanks to Alexander Belyaev, Alexander Pukhov and Marco Zaro. * Bug fix in SusyLesHouches::checkSpectrum(), to ensure uniform error handling when one or more spectrum self-consistency checks fails. * Replaced use of fabs() by abs() in several places (PythiaStdLib.h ensures appropriate overload). * Improvements to Vincia's handling of error messages; now issued via Info::errorMsg(). * Removed share/Pythia8/tunes directory, with Vincia reverting to the in-code way of setting tunes used elsewhere. ===================================================================== From torbjorn at thep.lu.se Tue Sep 1 17:27:02 2020 From: torbjorn at thep.lu.se (=?UTF-8?Q?Torbj=c3=b6rn_Sj=c3=b6strand?=) Date: Tue, 1 Sep 2020 18:27:02 +0200 Subject: [Pythia8-announce] Pythia 8.303 now available Message-ID: Dear All, PYTHIA 8.303 has been released today, and can be downloaded from http://home.thep.lu.se/Pythia as usual. This version includes several new physics modules, that extend the usefulness of the code. There is also a sprinkling of other news, and the traditional set of bug fixes. While the transition from 8.2 to 8.3 was intended to be smooth for the user, many technical changes were made under the hood. Therefore the 8.301 and 8.302 versions were still deemed slightly experimental, even if fully functional. With 8.303 we believe that the 8.3 series now offers sufficient advantages to motivate a transition from the 8.2 one. The one limitation is that some recent matching-and-merging fixes still have to find their way into 8.3. As a consequence, the Pythia webpage now lists 8.3 as the present main line, and 8.2 as the recent one, instead of future and present ones, respectively. You find a summary of changes below, based on the list in the Update History, found e.g. in the html manual. It starts with the major new features and then proceeds towards smaller news and bug fixes. Wishing you an enjoyable experience with PYTHIA 8.303. Sincerely yours, The Pythia 8 Collaboration (Christian Bierlich, Nishita Desai, Leif Gellersen, Ilkka Helenius, Philip Ilten, Leif L?nnblad, Stephen Mrenna, Stefan Prestel, Christine Rasmussen, Torbj?rn Sj?strand, Peter Skands, Marius Utheim) ===================================================================== Summary list of changes, starting with the major physics news and then proceeding towards bug fixes: * Marius Utheim and Leif Gellersen join the author team. * A new framework for Hadronic Rescattering has been developed. To enable rescattering, use HadronLevel:Rescatter = on, or see example programs main151.cc through main156.cc for use examples. Note that while the framework is ready to use, it is still being actively developed, and changes are likely in the near future. The older and much simpler rescattering models have been removed, including the related pp tunes 33 and 34, and there has been some file reorganization in code and documentation. * A new class HadronWidths has been added to handle hadrons with mass-dependent widths. This has been done primarily because of its importance in resonance formation in rescattering, but the class is also used for decays of hadrons produced in other processes. * A new class LowEnergySigma has been added to calculate cross sections of hadron-hadron interactions at low energies. These are used in rescattering and when performing primary collisions at low energies. Cross sections can be accessed using Pythia::getLowEnergySigma. * Several changes in the LowEnergyProcess and MiniStringFragmentation frameworks, in particular with several new approaches to produce nondiffractive inelastic events as close as possible to the kinematical threshold. New method StringFlav::combineToLightest attempts to form the lightest hadron for a given flavour content. Also new possibility to disable popcorn baryon production, for use in small systems. * The "decay"/mixing time of K^0/K^0bar -> K^0_S/K^0_L has been changed from 1e-15 to 1e-6 mm, such that it only happens after hadronic rescattering, but still well before K^0_S/K^0_L decays. * The Parton Vertex impact-parameter-plane assignment machinery has been completely rewritten and expanded with new options and capabilities. The default proton radius has been change from 0.7 to 0.85 fm. * Limit the amount by which transverse smearing of the space-time quark-antiquark string breakup vertices can give large shifts, see further the new HadronVertex:maxSmear parameter. The new HadronVertex:maxTau gives the possibility to reject hadrons of suspected misreconstructed systems and try again. The introduction of MPI impact parameters is compensated by a reduced transverse hadronization smearing. Also some other related changes. * The internal generation of photon-induced processes in hadronic collisions has been extended. This can be enabled with the new options PDF:beamA2gamma and PDF:beamB2gamma, which supersede the previous PDF:leptonA2gamma option. Some minor updates also for other related options, see PDF Selection for details. * New photon fluxes from hadrons implemented, see PDF Selection for details. * New example main program main78.cc to generate elastic, single- and double-dissociative photon-induced processes in proton-proton collisions, using options PDF:beamA2gamma and PDF:beamB2gamma. Also the sample programs main69.cc and main70.cc have been updated to use the new options. * For asymmetric beams (e.g. electron-proton collisions) in Les Houches event files, a boost to the event CM frame is now defined and applied for outgoing particles, as required for successful event processing. * The problem of "dangling" gluons causing changing color flows in SimpleTimeShower for top decays is now fixed. The fix is not fully validated for RPV. * For LHE processes, the width of the primordial kT distribution is now set solely by the BeamRemnants:primordialKThard parameter, ignorning BeamRemnants:primordialKTsoft. This change is so that LHE events with low-pT extra jets (e.g., in the context of POWHEG-style merging) are given the same primordial kT as their Born-level counterparts. * Improved HepMC3 multiweight output. * Added automated renormalization scale variations in CKKW-L type merging schemes. * Added UNLOPS merging scheme variations. * Added warning messages in UNLOPS merging. * Added flexible runtime plugin loading for Dire and Vincia matrix element corrections from Madgraph. These corrections can be enabled with the --enable-mg5mes flag during configuration and with the Dire:MEplugin and Vincia:MEplugin settings. * Introduced common runtime plugin loading and unloading structure. * Removed PDF set tracking for LHAPDF6 which breaks thread safety. In some cases this might cause a small penalty in memory. * Removed SLHA:keepSM as it duplicates the functionality provided by SLHA:minMassSM. * Some new methods in the Hist and HistPlot classes. Hist::plotFunc creates a histogram from the function provided as first argument, by evaluating its value in the middle of each histogram bin. Hist::normalize can rescale a histogram to an intended sum of bin contents. Methods to get x limits and lowest and highest y value. Hist::smallestAbsValue renamed Hist::getYAbsMin for consistency. HistPlot::addFile can add a file of data points, with or without errors, on to an existing histogram, for comparison purposes. A new variant of HistPlot::plot can set the frame borders. * New LinearInterpolator class in MathTools. * New RotBstMatrix methods toSameVframe and fromSameVframe sets up transformation to/from a frame where two particles move towards each other with equal-size velocities along the +-z direction. * Some new functionality accessible via PythiaStdlib.h. * It is now possible to use range-based for loops to iterate over particles in an event, e.g. for (Particle& p : pythia.event). Similarly, the particle data table can be iterated over, with each entry being a pair< int, ParticleDataEntry&>. * New possibility to redirect particle data listing output. * A configure option --obj-common='FLAGS' to add additional compiler flags to object (.o) compilation (i.e. no effect on linking). * Compilation flag -DGCCFPDEBUG enables floating point exceptions on a gcc compiler. * New index() method in the Py8Particle class of the Fastjet3 interface ensures that the location of the particle in the PYTHIA event record is returned correctly. Thanks to Gavin Salam and Priyotosh Bandyopadhyay. * A minor fix for kinematics of zero-virtuality photons to retain physical kinematics. * Protect against diffractive masses exceeding phase space bounds for hard diffraction. * A bug for propagation of space-like partons in string shoving. Thanks to Dong Jo Kim. * Several indexing bugs for the "guess" option used in CKKW-L merging have been fixed. However, this does not yet mean that "guess" is guaranteed to be stable for any BSM process. * Several fixes for problems discovered in a static code analysis, including one bug fix in LowEnergyProcess.cc. Thanks to Dmitri Konstantinov. * Mixup of ASecondHardProcess and SecondHardProcess labels resolved. Thanks to Anton Karneyeu. * Number of weights in info reset to 1 for each new init call. * Fixed issue where the dark matter mass was reset even after explicitly being set by the user, e.g. 57:m0 = X. This affects particle IDs 57 (DM+), 58 (DM2), and 59 (DM++). * An indexing bug for the scattering lepton in DIS events with photon radiation allowed has been fixed. * The redefinition of dlsym for plugin loading has now been removed as this is no longer required by modern compilers. Thanks to Chris Burr. * Several small bug fixes based on error reports by Vittorio Zecca. - In ProcessContainer.cc the error calculation for Les Houches strategy +-3 should not be renewed for each file when the event sample is split across several files. - In ProcessContainer::trialProcess() a call to phaseSpacePtr->rescaleMomenta( sHatNew); should not be done since the momenta have not been set yet. - In the CT14qed PDF grid (and others?) the first two x grid values coincide, so one must not divide by their difference. - Default initialization of hasOwnEventAttributes in Info.h is necessary. - Protected against explicit evaluation of alphaS(LambdaQCD) in VinciaISR. Also added explicit member-variable initialisations for the QEDemitElemental class in VinciaQED. - Protected against floating point exceptions caused by dividing by zero in PhaseSpace for zero-width resonances. - Corrected a floating point exception in Ropewalk.cc. - Protected against out of range renormalization scale access for diffractive systems. * Some further replacements of fabs by abs. * Fix missing-pointer bug when colour reconnection is switched off for diffraction. Thanks to Valentina Zaccolo. From torbjorn at thep.lu.se Thu Nov 5 08:26:31 2020 From: torbjorn at thep.lu.se (=?UTF-8?Q?Torbj=c3=b6rn_Sj=c3=b6strand?=) Date: Thu, 5 Nov 2020 09:26:31 +0100 Subject: [Pythia8-announce] PYTHIA 8.245 now available Message-ID: <4de14fc0-4a51-ac8c-5700-06ddcfe820c5@thep.lu.se> Dear All, The main Pythia development effort now is in the Pythia 8.3 branch, as you know. There still are several experiments that use Pythia 8.2, however, and that have noted issues they need fixed. For that reason a new Pythia 8.245 release can now be downloaded from http://home.thep.lu.se/Pythia This may well be the final release in the 8.2 series. In addition to the requested changes, you will also find some upgrades that work equally well for 8.2 and 8.3, and for various reasons were implemented in both contexts. On the other hand, some peripheral add-ons have not been updated, such as the Doxygen manual or the Python interface. The slightly compressed list from the update notes contain the following main points. --------------------------------------------------------------------- Physics news * Significant speedup of parton distribution handling, and thereby of the whole PYTHIA execution, since PDF is such a major part of the total execution time. This has been achieved by careful work by Dmitri Konstantinov and Grigory Latyshev. * Include the functionality for MC at NLO-Delta matching with aMC at NLO. This requires runtime interfacing of Pythia and aMC at NLO, and can not be employed by inexperienced users. --------------------------------------------------------------------- Bug fixes * Bug fixed in the new possibility to let particles with narrow widths (such as onia states) obtain a simple Breit-Wigner distribution, specifically for MPIs, introduced in 8.240. This bug led to excessive rejection of low-invariant-mass interactions. Thanks to Albert De Roeck. * Several fixes to avoid out-of-bound evaluation of vectors in the merging code. * Several fixes to correctly handle CKKW-L merging of EWkino- and higgsino-processes have been included. * Further bug fixes for the hard process name handling for weak-boson-fusion-like processes, that led to an incorrect counting of additional emissions. * Small fixes to history construction in the presence of multiple resonances. * The primordial kT for LHE files is now set by the BeamRemnants:primordialKThard average value, rather than the LHE scale, since the latter may be quite low e.g. in the POWHEG approach. * The problem of "dangling" gluons causing changing color flows in SimpleTimeShower for top decays is now fixed. The fix is not fully validated for RPV. * Extra check added to SimpleSpaceShower for the case where a small daughter PDF value can lead to an infinite loop if PDF variations are switched on. * An indexing bug, for the scattering lepton in DIS events with photon radiation allowed, has been fixed. * Added a few copy constructors to match corresponding assignment operators, to avoid warnings for some compilers. * Fixes in configure and examples/Makefile, to have ROOT examples work again. * Small fix in cross section calculation of main89.cc. * main**.cmnd, ** = 81-84, 87-88 have been slightly modified such that linking to LHAPDF6 is not required by default. * A bug in the XML-to-HTML conversion has led to the indiscriminate removal of "more" from the HTML manual, notably in Pythia::moreDecays(). --------------------------------------------------------------------- Wishing you an enjoyable experience with Pythia 8.245. Sincerely yours, The Pythia 8 Collaboration (Christian Bierlich, Nishita Desai, Leif Gellersen, Ilkka Helenius, Philip Ilten, Leif L?nnblad, Stephen Mrenna, Stefan Prestel, Torbj?rn Sj?strand, Peter Skands, Marius Utheim)