ATLAS Level-0 Endcap Muon Trigger for HL-LHC

The status of the development of the Level-0 endcap muon trigger system for the ATLAS experiment at the HL-LHC is presented. The upgraded system reconstructs muon candidates with an improved pT resolution by combining data from various subdetectors. This is realized by exploiting the evolution of the data transmission technologies, to send all hit data of TGCs and the data of other subdetectors to the backend counting room. Primitive muon candidates are reconstructed using track segments reconstructed from hit data of TGCs. An intial implementation of the TGC track segment reconstrution with a firmware for a FPGA is tested, and it is verified to succesfully reconstruct muon candidates for ideal cases. The trigger efficiency is estimated with a software algorithm and using a Monte Carlo simulation. The efficiency is estimated to be higher than 90% for the threshold pT>20 GeV and for the endcap region. The trigger rate is estimated with a software algorithm and using pp collision data, which are overlaid to emulate the high pileup condition at the HL-LHC. The rate is estimated to be lower than 25 kHz for the threshold pT>20 GeV and for the endcap region. This evaluation does not include the precise determination of pT using MDT hits, and the trigger rate is expected to decrease with its inclusion.