Identifying hadronic tau decays using calorimeter topological clusters at ATLAS

The ATLAS experiment collects data on the world's highest energy proton-proton collisions. Its primary goals are to search for direct evidence of physics beyond the Standard Model of particle physics, and to provide a final verdict on the existence of the Standard Model Higgs boson. A robust tau identification procedure is an important ingredient in the search for Standard Model and supersymmetric Higgs bosons. In this study, new tau identification variables based on calorimeter topological clusters are investigated. These variables complement existing calorimeter-based variables by bringing additional discriminating power against hadronic jets. They have a straightforward physics interpretation which allows them to be calculated at particle-level. Some of these new variables are shown to be robust against background noise from the underlying event and in-time pileup, two effects which negatively impact tau identification. Several of these new variables are now part of the official tau reconstruction software at ATLAS.