[Pythia8-announce] Pythia 8.175 now available

[Torbjorn Sjostrand]

Dear All,

Pythia 8.175 has now been released, and can be downloaded from

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

This time we call for a more rapid-than-usual transition to
the new version, since unfortunately 8.170 introduced an
embarrassing bug that could give spurious extra jets,
skewing results especially for min-bias runs.

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

The list of news and improvements include:

* Stefan Ask and Richard Corke have left the Pythia collaboration,
   while Jesper Roy Christiansen and Philip Ilten have joined.

* The CKKW-L merging algorithm has been improved, and three new
   related algorithms introduced: UMEPS, NL^3 and UNLOPS, the latter
   two of NLO accuracy. Extensive examples are provided.

* The parton-jet "MLM" matching machinery has been expanded to
   allow either the Alpgen or Madgraph algorithms to be applied
   to either Alpgen or Madgraph input.

* Improvements in the SLHA framework and handling of SUSY processes.

* Improvements in the tau production and decay machinery.

* Branching ratios of light hadrons and the tau lepton updated to
   the 2012 RPP.

* Neutrons and antineutron allowed as incoming beams.

* Optional photon radiation in hadronic decays to lepton pairs.

* Better default scale choice for impact-parameter selection.

* Streamlined HepMC interface, no longer supporting obsolete versions.

* Several improvements on the configure and Makefile capabilities,
   as well as fixes for some compiler-specific issues.

* Abort initialization when user tries to change non-existing
   settings or particle data.

* A new Vect kind of allowed settings, and other new settings methods.

* The Vec4 class also has new methods, e.g. to give rapidity.

* New method to undo the decay of a particle in the event record.

* External access to Pythia PDF's, and improved internal flexibility.

* Further extension of the UserHooks facility.

* New options to reduce Pythia printing.

* Improved statistics information for external Les Houches input.

* New options for the fragmentation function of heavy flavours.

* Possibility to read in and use parton-specific scale from LHEF input.

* The std namespace now only made available inside the Pythia8 namespace.

* Bug fix, mentioned at the beginning, wherein an intended improvement
   of the junction string fragmentation machinery in version 8.170
   occasionally could derail and lead to an effective tilting of the
   fragmenting system, thereby giving rise to unphysical extra jets.

* Bug fix in machinery with two hard processes, where the maximal
   default pT scale for showers was set by an analysis of the whole
   outgoing state rather than individually for each of the two.

* A number of minor bug fixes and documentation improvements.

For a more extensive listing, see the "Update History" in the
online html/php manual.

As always, we look forward to constructive feedback. (Although our
limited manpower means that not all suggestions/requests can be met.)

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