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Bug reports and physics questions

• Users often combine PYTHIA with a set of other libraries in their studies, and then problems originally attributed to PYTHIA usually turn out to be located somewhere else. Therefore first of all check that the problem remains if no other libraries are being used. If you want to file a report that involves other libraries you have to have a very convincing case that the problem is in PYTHIA to be taken seriously.
• Make sure you use a clean copy of PYTHIA, not one that has been subject to "local modifications" by parties unknown. Also make sure it is a recent one - you may have encountered a true bug, but one already solved in the current version. If uncertain, pick up a new copy directly from the PYTHIA webpage, and create a new cleanly compiled PYTHIA library code.
• Write a simple standalone main program mymainNN.cc, with NN between 00 and 99, that demonstrates the claimed bug. Feel free to use some of the existing sample main programs share/Pythia8/examples/mainNN.cc as templates.
• Put the mymainNN.cc program in the share/Pythia8/examples subdirectory and run it from there (make mymainNN followed by ./mymainNN).
• Now systematically peel away all irrelevant code in the main program, so that only code really needed to reproduce and document the bug remains. Where explanations in the code would be helpful, do add comments in English.
• Send the main program, with a description what is the problem and whatever guesses you may have about a probable cause.

If you don't know whom to send the bug report to, then use the generic address pythia8@projects.hepforge.org.

For special topics it may be faster to contact the PYTHIA person(s) most directly involved in this field. Here is a brief list of specialities

Name	E-mail	Topics
Christian Bierlich	christian.bierlich@thep.lu.se	rope hadronization and string shoving; heavy-ion collisions; ALICE matters
Nishita Desai	desai@theory.tifr.res.in	SUSY, SLHA, BSM
Leif Gellersen	leif.gellersen@thep.lu.se	scale uncertainties; matching and merging
Ilkka Helenius	ilkka.m.helenius@jyu.fi	photoproduction, gamma-gamma; diffraction
Philip Ilten	philten@cern.ch	taus, onia, configure and Makefile; LHCb matters
Leif Lönnblad	leif.lonnblad@thep.lu.se	heavy-ion collisions (pA and AA)
Stephen Mrenna	mrenna@fnal.gov	SUSY, BSM, matching and merging; CMS matters
Stefan Prestel	stefan.prestel@thep.lu.se	matching and merging, also to NLO; DIRE parton shower; ATLAS matters
Torbjörn Sjöstrand	torbjorn@thep.lu.se	SM processes, parton showers, MPIs, colour reconnection, hadronization, core structure and utilities
Peter Skands	peter.skands@monash.edu	SLHA, parton showers, MPIs, colour reconnection, hadronization, tuning; VINCIA
Marius Utheim	marius.utheim@thep.lu.se	hadronic rescattering

Note: write one email putting all relevant authors in cc, or use the pythia8@projects.hepforge.org list mentioned above. Never contact several persons independently on the same topic, thereby potentially leading to doublework. Abuse will have consequences.

Do note that the major collaborations, such as ATLAS and CMS, have their own Monte Carlo support groups, with a lot of experience in solving typical issues, many of which are related to the setups and interfaces created inside the collaborations. If you are a member of a major collaboration you should always turn to these groups in the first place, and only turn to us when it has been confirmed as a true problem going beyond the local installation.

You may also direct PYTHIA-related questions to us, following the same pattern as above, but note that manpower is limited, so focus on topics that do require our expertise. We cannot act as teachers of particle physics in a broader sense, however. If you are a PhD student it is the task of your supervisor to see to it that you are offered the particle physics courses you need, and to answer all general questions you may have. Summer schools can offer a most useful complement to the basic courses at you local university. In particular we would like to mention the MCnet annual Monte Carlo school for general information on the physics and usage of event generators, and the CTEQ annual summer school on QCD analysis and phenomenology.

Code contributions

To be successful, a contribution must not only introduce useful new functionality but also be written in a form that fits nicely into the existing PYTHIA framework. The CODINGSTYLE file in the PYTHIA distribution explains how to achieve clean and uniform style.

Feel free to consult beforehand whether a specific contribution would be welcome, so you don't waste time on something that e.g. may already be under way, or that may not fit so well. This in particular is the case if linking to external libraries are involved, since fitting a new library into the PYTHIA build procedure can be a rather delicate process, not always worth the bother.

For PhD students specifically, we offer MCnet-funded studentships of 3 - 6 months, during which you may come to Lund (or some other MCnet node) to work on a short project involving Monte Carlo event generators. This could be the implementation of a new feature into PYTHIA, the use of PYTHIA in a new context, or something else. You must have an idea yourself what you would like to work on, that preferably also would be beneficial for your PhD studies, and have the support of your thesis supervisor. See montecarlonet.org for more information how to apply!