Validation of Monte Carlo event generators in the ATLAS Collaboration for LHC Run 2

This note reviews the main steps followed by the ATLAS Collaboration to validate the properties of particle-level simulated events from Monte Carlo event generators in order to ensure the correctness of all event generator configurations and production samples used in physics analyses. A central validation procedure is adopted which permits the continual validation of the functionality and the performance of the ATLAS event simulation infrastructure. Revisions and updates of the Monte Carlo event generators are also monitored. The methodology behind the validation and tools developed for that purpose, as well as various usage cases, are presented. The strategy has proven to play an essential role in identifying possible problems or unwanted features within a restricted timescale, verifying their origin and pointing to possible bug fixes before full-scale processing is initiated.