[Pythia8-announce] Pythia 8.185 now released

[Torbjorn Sjostrand]

Dear All,

Pythia 8.185 has now been released, and can be downloaded from

http://home.thep.lu.se/~torbjorn/Pythia.html

Some of the main changes are summarized below. For a more
extensive listing, see the "Update History" in the online
html/php manual. Most changes will not affect the normal user.

A sincere thank to all the persons who have contributed with
new code, bug reports or suggestions for improvements.

As always, we look forward to constructive feedback.

Sincerely yours,
The Pythia 8 Collaboration
(Torbjörn Sjöstrand, Jesper Roy Christiansen, Nishita Desai,
Philip Ilten, Stephen Mrenna, Stefan Prestel, Peter Skands)

MAIN NEWS

* 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 pT 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-pT
   particles, and also a bit too high multiplicity. In versions up to
   and including 8.180, instead the pT of the second MPI was not
   strictly limited by the pT of the first, which also gave an
   overestimate, but smaller.

* Added the FxFx matching and shower-kT matching schemes as new
   options. Still under validation, though.

* 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 K factors for main88.cc.

* New documentation on the POWHEG merging implemented in main31.cc.

* Higgs particle names (re)simplified to MSSM standard. New
   SLHAInterface code added to reset the names appropriately
   (SLHA2 conventions) when in the NMSSM, CPV or RPV scenarios.

* SUSY decay channels now have meMode = 0, except those to Gravitinos,
   for which no code has been implemented (they stay 103).

* Expanded SLHA input support for NMSSM type models, plus a few
   further minor SUSY improvements and fixes.

* Significant extensions to the charmonium and bottomonium machineries:
   - Many more colour-octet states.
   - Data on processes which only differ by the radial excitation
     number are grouped into vectors for on/off switches and
     long-dinstance matrix elements, but share the same process code
     and short-distance matrix elements.
   - Matrix elements for 3DJ processes are now implemented.
   - The mass splitting between all colour octet and singlet state
     pairs can be set by one common parameter.

* Introduce new switch TimeShower:weightGluonToQuark that allows
   a few alternative approaches to set the g -> q qbar branching rate,
   notably for heavy quarks, and similarly for gamma -> f fbar.

* 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.

* New possibility to comment out a section of lines in a command file,
   when read in by Pythia::readFile(...).

* Implement (some of the) functionality of the doForceWidth
   switch for resonances, that has been missing so far.