hep-ph/0108264
LU TP 01-21
(second edition)
April 2002

PYTHIA  6.2

Physics and Manual


Torbjörn Sjöstrand,$^1$ Leif Lönnblad,$^1$
Stephen Mrenna,$^2$ Peter Skands$^1$

$^1$Department of Theoretical Physics,
Lund University, Sölvegatan 14A,
S-223 62 LUND, SWEDEN

$^2$Computing Division, Simulations Group,
Fermi National Accelerator Laboratory
MS 234, Batavia, IL 60510, USA

Abstract

The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, with emphasis on those where strong interactions play a rôle, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, beam remnants and underlying events, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

The code and further information may be found on the PYTHIA web page:
http://www.thep.lu.se/$\sim$torbjorn/Pythia.html .

The information in this edition of the manual refers to PYTHIA version 6.206, of 10 April 2002.

The official reference to the latest published version is
T. Sjöstrand, P. Edén, C. Friberg, L. Lönnblad, G. Miu, S. Mrenna and E. Norrbin, Computer Physics Commun. 135 (2001) 238.

Dedicated to

the Memory of


Bo Andersson


1937 - 2002

originator, inspirator