The L1 Trigger

Abstract

The identification of the decays of a $\tau$ lepton to final state hadrons ($\tau _{{\text{ h }}}$) and a neutrino, representing about 65% of the total $\tau$ decays, is a challenging task at a hadron collider, especially for the hardware L1 trigger where a high optimization of the sequence of algorithm operations to be performed is required. The upgrade of the L1 trigger represents an opportunity to develop and implement a sophisticated $\tau$ algorithm as described in this chapter.The discussion is introduced by a general overview of the experimental challenges of $\tau _{{\text{ h }}}$ identification at the hardware level, followed by a short description of the algorithm used in the Run I and of its limitations. The algorithm used for the 2016 data taking is then described in detail. Finally, the commissioning of the algorithm with 2015 data is presented, and its performance measured with the data collected in 2016.