Description
The Level-1 muon endcap trigger in the ATLAS experiment utilises signals from
the Thin Gap Chambers (TGCs) located in the outer muon stations. A significant
challenge for this system has been the high background rate caused by particles
not originating at the interaction point, which increased the Level-1 trigger
rate. To address this issue, the New Small Wheel (NSW) detectors, installed at
the inner muon stations during Long Shutdown 2, were integrated into the
Level-1 endcap muon trigger system for Run3 operations. In 2024, the full
integration of the NSW sectors into the Level-1 trigger decision was
successfully completed. By cross-checking the consistency between muon
candidates identified by TGC signals and those by the NSW, the system achieved
a significant improvement in the discrimination between muons and background
particles. This advancement reduced the Level-1 trigger rate by approximately
15 kHz, effectively decreasing the load on the Trigger and DAQ systems and
substantially enhancing the data-taking efficiency of the ATLAS experiment.
