The Phase-1 Upgrade of the ATLAS Level-1 Endcap Muon Trigger

The Level-1 muon trigger for the ATLAS experiment identifies muons with high transverse momentum. Under the high luminosity condition in LHC Run 3, more powerful trigger system is needed to reject the backgrounds. New trigger processor board for Run 3 has been produced to achieve the required performance, by combining information from five different detectors. The performance of the new board and the readout system has been confirmed by a beam test. The new algorithms to make use of the new detectors have been developed, and are tested by MC simulation. With the new algorithms, the trigger rate is estimated to become lower than the required rate in Run 3.