PYTHIA 6.3 Physics and Manual
Torbjörn Sjöstrand, Leif Lönnblad, Stephen Mrenna, Peter Skands
TL;DR
Pythia 6.3: Physics and Manual documents a comprehensive, modular Monte Carlo event generator for high-energy physics, detailing how hard scattering, parton showers, hadronization, and decays are integrated into full collision events. It emphasizes factorization of complex processes into manageable components, using a blend of first-principles matrix elements and robust phenomenological models, with extensive support for QCD, electroweak, Higgs, SUSY, extra dimensions, and beyond-the-Standard-Model scenarios. The manual presents practical guidance on installation, initialization, event generation, and analysis, along with a thorough description of data structures (the PYJETS/HEPEVT event record), random-number generation, and numerical techniques essential for reliable simulations. Together, it offers a versatile toolkit for simulating a wide spectrum of collider environments (e+e−, ep, and hadron–hadron), including photoproduction, diffractive events, and complex BSM frameworks, and provides interfaces to external PDFs and SUSY spectrum calculators for flexible, state-of-the-art phenomenology. The work underpins a foundational resource for detector design, data analysis validation, and theoretical studies in particle physics, supporting detailed, first-principles-inspired event generation across a broad energy frontier.
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.