Speaker
Description
With the start of the Long Shutdown 3 (LS3) of the LHC in July 2026, lasting nearly four years, ATLAS will enter the implementation phase of the major detector upgrades required for High-Luminosity LHC operation. The Muon Spectrometer will undergo a substantial transformation to meet the stringent operational demands imposed by the increased luminosity, trigger rates, and radiation levels foreseen at the HL-LHC. A comprehensive replacement of the front-end and readout electronics for the Monitored Drift Tube (MDT), Resistive Plate Chamber (RPC), and Thin Gap Chamber (TGC) systems is planned to ensure compatibility with the higher trigger rates and extended latencies of the new level-0 trigger. A key element of the upgrade concerns the RPC system. New RPC chambers featuring 1 mm gas gaps will be installed in the inner barrel layer, significantly improving trigger acceptance, rate capability, and robustness under high background conditions. These upgrades play a central role in maintaining efficient and selective muon triggering at HL-LHC luminosities. In parallel, MDT chambers will be integrated into the level-0 trigger to sharpen the transverse momentum threshold, and selected inner barrel MDTs will be replaced by small-diameter MDT chambers to optimize performance in high-occupancy regions. In the barrel–endcap transition region, new TGC triplet chambers will replace the existing doublets to reduce the high trigger rates caused by random coincidences. In addition, the power distribution systems and associated electronics for the RPC, TGC, and MDT detectors will be upgradeded to address component obsolescence, ageing, and radiation tolerance requirements. This contribution will present an overview of the upgrade strategy and challenges. Results from prototype and production studies, as well as the current project status, will be reported, together with a discussion on the expected performance improvements and their impact on muon triggering, reconstruction, and physics results at the High-Luminosity LHC.
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