CERN Accelerating science

ATLAS Note
Report number	ATL-DAQ-PROC-2025-019
Title	Enhancing the ATLAS Level-1 endcap muon trigger with New Small Wheel integration in Run3
Author(s)	Sue, Yuki (KEK High Energy Accelerator Research Organization (JP))
Corporate Author(s)	The ATLAS collaboration
Collaboration	ATLAS Collaboration
Publication	2025
Imprint	30 Oct 2025
Number of pages	5
In:	The 32nd International Symposium on Lepton Photon Interactions at High Energies (Lepton Photon 2025), Madison, Wisconsin, Us, 25 - 29 Aug 2025
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Free keywords	Leve-1 Trigger ; Muon Endcap Trigger ; TGC ; NSW
Abstract	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.
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