Optimisation of large-radius jet reconstruction for the ATLAS detector in 13 TeV proton-proton collisions

Jet substructure has provided new opportunities for searches and measurements at the LHC. Since the first ATLAS studies in Run 1 of the LHC, jet substructure reconstruction has seen continuous development. A range of new input objects, pileup mitigation techniques and jet grooming algorithms motivate a thorough reoptimisation of the large-R jet reconstruction algorithms used in ATLAS. In this paper, this reoptimisation procedure is presented, and the performance of a wide range of large-radius jet definitions is compared. The relative performance of these jet definitions is assessed using metrics such as their pileup stability and ability to identify hadronically-decaying W bosons and top quarks with large transverse momenta. A new type of jet input object, called a ‘unified flow object’ is introduced which combines calorimeter- and inner-detector-based signals in order to achieve optimal performance across a wide kinematic range. Large-radius jet definitions are identified which significantly improve on the current ATLAS baseline definition.