Identifying Hadronic Tau Decays Using Calorimeter Topological Clusters at ATLAS

New tau identification variables based on calorimeter topological clusters are investigated. These are shown to possess additional discriminating power against QCD jets not provided by the existing calorimeter-based variables. These new variables are close to the physics of tau hadronic decays, easily understood, and reveal characteristics of tau hadronic decays in the ATLAS calorimeter. They are also used to estimate how much separation can be obtained given an ideal calorimeter and thus how much the limitations of the hardware and the reconstruction software limit tau identification at ATLAS. Some of these new variables are also shown to be robust against underlying event and in-time pileup, two effects which negatively impact tau identification.