PyJet

pyjet is a Python interface that exposes the jet clustering functionality of the FastJet C++ library to Python programs. It is used in high-energy physics for organizing lists of four-momentum vectors (particles or detector signals) into jets according to standard infrared-safe algorithms. The library provides Python bindings to core FastJet concepts such as jet definitions, clustering sequences, and jet collections, enabling analysis pipelines entirely in Python.

Key features include support for common jet algorithms (anti-kt, kt, Cambridge/Aachen), configuration of the jet radius parameter R, access to jet properties and constituents, and the ability to retrieve inclusive or exclusive jet lists. PyJet typically represents particles as PseudoJet objects and uses a JetDefinition to specify the algorithm and parameters. ClusterSequence objects perform the clustering and provide methods to access jets and their properties, such as momentum components and constituent lists. Some workflows also allow calculation of jet areas and background estimation depending on the underlying FastJet features.

Installation is usually via Python package managers; the package on PyPI is named pyjet and may require a system C++ compiler and the FastJet library (or include a bundled version). Prebuilt wheels are sometimes available for popular platforms.

Example usage involves creating PseudoJet inputs, constructing a JetDefinition, running a clustering sequence, and extracting the jets that meet a pt threshold.

pyjet is complementary to other HEP software stacks and is referenced alongside FastJet and related jet-physics tools.