<html xmlns="http://www.w3.org/1999/xhtml"> <head> <title></title> </head> <body> <div name="messageBodySection"> <div dir="auto">===================================================================== Dear All, PYTHIA 8.307 has been released, and can be downloaded from • http://pythia.org Main physics updates include extensions to the hadronic cross sections and beam types used for hadronic rescattering and cascades in the atmosphere, improvements for hidden valley scenarios, and a new framework for parallelisation (in addition to the existing openMP option). The release also contains a number of other technical improvements and bug fixes. A brief summary of all changes is included below and in the Update History part of the HTML manual. Wishing you an enjoyable experience with PYTHIA 8.307. Sincerely, The Pythia 8 Collaboration (Christian Bierlich, Nishita Desai, Leif Gellersen, Ilkka Helenius, Philip Ilten, Leif Lönnblad, Stephen Mrenna, Stefan Prestel, Christian Preuss, Torbjörn Sjöstrand, Peter Skands, Marius Utheim, Rob Verheyen) -------------------------------------------------------------------- CONTACT: write to authors@pythia.org if you need to contact any of the authors. This allows us to coordinate replies. You may also include the individual addresses of authors that are relevant for a specific issue. Never contact several persons independently on the same topic, thereby potentially leading to double work. Abuse will have consequences. When responding to emails from us at authors@pythia.org, please reply directly to the email, which has a unique return address of the form incoming+<hash>@incoming.gitlab.com. Do _not_ reply to authors@pythia.org, as this would start a new issue. Please consider allowing your correspondence to be made publicly available to other users via our issue tracker, by replying at any point with your express permission, e.g. "this correspondence can be made public". ===================================================================== Summary list of changes for 8.307: * New option with interpolation between the low-energy hadronic cross sections, used for rescattering, and the more traditional SaS/DL cross sections, used at high energies. The latter framework has also been extended to include many more collinding hadron pairs. The Pythia::getSigmaTotal and Pythia::getSigmaPartial methods give the user direct access to these cross sections. These extend and replace the Pythia::getLowEnergySigma methods. * New "SU21" PDFs for some 20 mesons and baryons, to be used e.g. in the MPI scenarios in hadron-hadron collisions, e.g. in a cascade in the atmosphere. The pi+ default PDF has been upgraded from GRV92 LO to GRS99 LO. The GJR07 LO set has been included as an option for the proton. The default value of BeamRemnants:maxValQuark has been updated to allow also charm and bottom hadrons as incoming beam particles. * The framework for changing the beam kinematics between subsequent Pythia::next calls when using variable collision energies has been expanded. The Pythia::setKinematics methods mirror the frame type options for the beams. * As a further extension of the above, a new option exists wherein the first beam particle is initialized so it can be switched event-by-event between essentially any incoming hadron, while the second beam is restricted to be a proton or neutron. Again only SoftQCD and LowEnergyQCD processes are possible. To handle this feature, the code has been extended so that some 20 different PDFs are initialized, each with a corresponding MPI initialization and storage of required coefficients. * Extended and improved handling of the Hidden Valley (HV) scenario. Thanks to Matt Strassler and Suchita Kulkarni for useful input. Improved tracing of hidden-valley colours through a hidden-valley shower evolution history, thereby avoiding problems for some topologies. Introduced the possibility to bookkeep individual HV hadron types, in particular HV-mesons, and thereby manange masses and decay properties. The default remains the simpler scheme, where only a smaller set of HV-hadron properties need to be defined. The detailed scenario also involves a mass-dependent handling of the joining of hadronization chains, or the collapse into a single hadron. The list of Zv decays has been expanded to include further HV-quarks. Some default masses have been modified. It is possible to set different production rates for HV-quarks during hadronization, and for HV-diquarks leading to HV-baryon production. Introduced an option to suppress production of one flavour-diagonal pseudoscalar state, representing the eta_1 flavour singlet. The HiddenValley:spinFv default value has been changed from 1 to 0, to make it transparent that HV-quarks have spin 1/2 by default. Expanded the list of invisible particles accordingly. A few minor bug fixes. A significantly expanded description in Hidden Valley Processes. * Added a new class PythiaParallel for easily making runs in parallel. See main161, main162 and main163 for usage examples. NOTE: this is an experimental feature. Feedback and bug reports should be sent to authors@pythia.org. * New option introduced, where MPI initialization data can be stored on file and reused in a later run, to save time. Also option to symmetrize the MPI rate between e.g. pi^+ p and pi^- p. * New options allow a harder fragmentation function for a beam-remnant diquark, by a separate choice of the a and b parameters, and also forbid the popcorn mechanism for it. * New diffractive states introduced, to cover all five-flavour mesonic states, and all baryonic ones with at most one c or b quarks. Furthermore, nitrogen and oxygen have been added to the set of nuclei * New processes SoftQCD:singleDiffractiveXB and SoftQCD:singleDiffractiveAX allow to set single diffraction to occur only by A B → X B or only by A B → A X. * Reorganised and consolidated the interface to external matrix element generators. Renamed ShowerMEs to ExternalMEs and ShowerMEsMadgraph to ExternalMEsMadgraph. Introduced new HelicitySampler class to sample helicities using external matrix elements. * New options to get and set the state of the random number generator, Rndm::getState and Rndm::setState, as a direct-transfer option to the file-based dumpState/readState methods. * New methods Hist::fillTable to read back in a table of histogram data, specifically as written by the Hist::table methods. * Some minor rearrangements in HadronLevel to better structure the interleaving of hadronic rescattering and particle decays. New method Pythia::moreDecays(int i) to perform the decay of a single specified particle. * Switched tunes to by default prefer LHAPDF 6 PDFs over LHAPDF 5 ones, via the setting Tune:preferLHAPDF. * New LHAPDF:xSymmetric parameters allow the user to choose to use symmetric PDFs for s, c, and b quarks when using LHAPDF for a performance boost. By default, c and b are taken as symmetric (this matches the previous behaviour). * Info::pTnow() can now also be used for showers during resonance decays, and when using the shower() method. The latter so far only for the Simple and Vincia shower models. * New switch "SLHA:allowOnlyOffShell” to allow SLHA decay tables with only off-shell decays. * Corrected a bug that mainly affects beam-remnant fragmentation in the QCD CR model. Previously, diquark-antidiquark systems with invariant masses below the threshold for baryon-antibaryon production would be combined into tetraquark-like states that do not exist in PYTHIA, resulting in errors with unknown particle codes and charge non-conservation. Now, MiniStringFragmentation::ministring2two() instead reconnects such topologies into two mesons, noting that this is consistent with the colour structure. Further motivation comes from studies of low-mass junction-antijunction systems. * Introduced fix to prevent the central description of Les Houches events showered with global recoil from shifting when shower variations are enabled. * Fixed a few issues in Vincia's sector merging. Specifically, while the merging itself still only handles QCD corrections, Vincia's QED showers can now be left on during merging. Also corrected a bug leading to incomplete histories replacing complete ones with smaller probability, and fixed an inconsistent treatment of trial showers in systems with coloured resonances. * When running Angantyr at very low energies, initialization would abort due to an incorrect initialization of the high-mass diffraction MPI machinery. Logic has been introduced to prevent this initializatoin. * Fixed memory leaks in the ColourReconnection class. * Fixed some recent compiler warnings and errors; thanks to Mattias Ellert * Removed the deprecated SubCollisionModel called MultiRadial from the heavy ion machinery. * Added an abort in Pythia initialization to prevent using a low energy process with a hard process. Thanks to Jenna Bacon. * Broke a circular shared pointer reference in ResonanceWidths and ParticleDataEntry which caused a small memory leak. Thanks to Gabriele Inghirami. * Minor fix to avoid unnecessary (attempted) MPI initialization. * Fixed issue with Dire getting stuck when showering soft QCD events. Note, Dire has not been validated for these types of events. Thanks to Giancarlo Panizzo and Marvin Flores for reporting the issue. =====================================================================</div> </div> </body> </html>