PYTHIA 6.2 Physics and Manual
Torbjörn Sjöstrand, Leif Lönnblad, Stephen Mrenna
TL;DR
PYTHIA 6.2 Physics and Manual presents a comprehensive, Fortran-based framework for simulating high-energy particle collisions by integrating hard subprocess matrix elements, parton showers, and nonperturbative hadronization via the Lund string model. It articulates a detailed structure for event records, random-number generation, and Monte Carlo techniques, and it documents extensive physics content from QCD jets to Higgs, SUSY, and beyond, including photon- and lepton-induced processes. The manual emphasizes modularity, cross-checks, and the interplay between different modeling approaches, while providing robust facilities for user-defined external processes via the Les Houches interface. This work underpins widespread collider phenomenology by offering a versatile, customizable tool suite with broad applicability to current and future experiments. Its design enables detailed exploration of detector performance, acceptance corrections, and physics interpretations across a wide spectrum of high-energy processes.
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 role, 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 information in this edition of the manual refers to PYTHIA version 6.200, of 31 August 2001. 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.