[Pythia8-announce] PYTHIA 8.245 now available

[Torbjörn Sjöstrand]

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.

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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.

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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().

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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 Lönnblad, Stephen Mrenna, Stefan Prestel,
Torbjörn Sjöstrand, Peter Skands, Marius Utheim)