The Upgrade and Performance of the ATLAS Tau Trigger towards Run 2

Tau triggers are used in a variety of highly anticipated ATLAS physics analyses, including the measurement of the Higgs boson coupling to fermions and searches for Higgs boson partners or heavy resonances decaying into pairs of tau leptons. As proton-proton collisions at the LHC reach instantaneous luminosities of over 10 34 cm −2 s −1 , the strategies for triggering have become more sophisticated than in Run 1. In these conditions single tau lepton triggers suffer from severe rate limitations, despite the advancements in algorithms used in the tau identification. Further fast algorithms and the design of topological selections are the main developments to allow a large program of physics analysis. In Run 2, topological criteria can be applied already at the first trigger level, due to the addition of the L1 topological processor. This makes it possible to use detailed information from sub-detectors in order to apply real-time event topology cuts. The evolution of the ATLAS tau trigger and its performance will be presented, including initial results from the early days of the LHC Run 2 operation.