RAT is a simulation and analysis package built with GEANT4, ROOT, and C++, originally developed by S. Seibert for the Braidwood Collaboration. Versions of RAT are now being used and developed by several particle physics experiments.

RAT combines simulation and analysis into a single framework, which allows analysis code to trivially access the same detector geometry and physics parameters used in the detailed simulation.

RAT follows the "AMARA" principle: As Microphysical as Reasonably Achievable. Each and every photon is tracked through an arbitrarily detailed detector geometry, using standard GEANT4 or custom physics processes. PMTs are fully modeled, and detected photons may be propagated to a simulation of front-end electronics and DAQ.

This generic version is intended as a starting point for collaborations looking for an easy-to-learn, extensible detector simulation and analysis package that works out of the box. Once acquainted with RAT, it is easy to customize the geometry elements, physics details, data structure, analysis tools, etc., to suit your experiment's needs.