Pythia 6 is hosted by Hepforge, IPPP Durham

Effects of tunes and showers: the top mass

(By Skands, March 08, 2007)

This is just to note that we submitted a paper containing a discussion of the new Pythia tunes (PYTUNE) and a study of their effect on top mass precision to the archives at:

A previous study, comparing the old and new parton showers (including 'wimpy' and 'power' variants) on SUSY and top production can be found in:


ALPGEN + PYTHIA short tutorial

on: February 05, 2007, 09:21:50 AM by skands

Attached is a very brief, 1-page tutorial on how to download and run Alpgen, porduce unweighted events, and finally interface it to PYTHIA for showering and hadronization. For the list of processes implemented in Alpgen, see the Alpgen web page.

  • instructions3.pdf (32.23 KB - downloaded 16 times.)

New revamped PYTHIA homepage, at HepForge?

on: February 01, 2007, 06:19:32 AM by skands

As of today, the official homepage for PYTHIA has moved to the CEDAR/HepForge site at:

Please update any links you may have accordingly. The old site will remain functional in the near future, but will not be updated with developments beyond Jan 2007.

The new site has quite a few new features. For discussions about Pythia, as an experiment we are currently linking to this site. We hope this will help encourage people to start making use of it.

All the best, Peter

PYTHIA tunes for underlying event, showers, and min-bias (6.408+)

on: October 26, 2006, 03:59:21 PM by skands

The physics of 'underlying events' has recently come under more intense scrutiny, in part from a small (but merry) band of hardcore hadron collider QCD enthousiasts, but also due to increased requirements for minimizing theoretical and systematic uncertainties on precision measurements, both at the Tevatron and at LHC. However, hadron collisions in their full gore and glory are complicated beasts, and hence a variety of phenomenological models exist, with various degrees of sophistication. There are many uncertainties, however, and so a number of different 'tunes' are floating around. It is not always very easy or transparent for non-experts to evaluate the uncertainties. To make this at least slightly easier, we have now included in Pythia (since 6.408) a routine PYTUNE which can be called before PYINIT, and which gives access to a number of 'presets' for the underlying event, showers, and min-bias, such as Rick Field's Tune A, Tune DW, an ATLAS tune, and some preliminary tunes of the new interleaved framework for multiple interactions and showers. The available options are enumerated described in more detail the update notes, available on the Pythia homepage. If you have any questions about them, let me know.

Bug in versions 6.402 - 6.405 - underlying event too small

on: October 05, 2006, 12:15:28 PM by skands

A bug in PYTHIA versions 6.402 - 6.405, to do with the choice of infrared factorization scale for the underlying event, means that min-bias / underlying-event tunes, e.g. Rick Field's Tune A and friends, will not give the expected results with these versions, but instead slightly lower multiplicities. These versions are therefore not recommended for serious studies where the underlying event is an issue. The bug has been fixed in version 6.406 and onwards.

Last modified 11 years ago Last modified on Jul 12, 2007, 2:15:20 PM