PYTHIA 6.4 Physics and Manual
Torbjorn Sjostrand, Stephen Mrenna, Peter Skands
TL;DR
Pythia 6.4 presents a comprehensive framework for simulating high-energy collisions by combining perturbative QCD with nonperturbative hadronization, enabled through sophisticated Monte Carlo techniques. It details a modular architecture spanning hard subprocesses, parton showers, beam remnants, multiple interactions, and hadron decays, with extensive support for photon-induced processes, Higgs and beyond-Standard-Model physics, and SUSY/Technicolor scenarios. The manual emphasizes careful interpretation, cross-checks, and interfaces to external tools (LHA/SLHA), while providing practical guidance, examples, and a robust event-record system. Collectively, this work provides both the physics backbone and the practical toolbox needed for realistic event generation across a wide range of collider environments, including LEP, Tevatron, LHC, and future facilities. Its contributions enable detailed phenomenological studies, detector planning, and data interpretation by offering a flexible, interoperable, and extensively documented simulation ecosystem.
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, within and beyond the Standard Model, 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, underlying events and beam remnants, 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.