The Phase-II Upgrade of the ATLAS Muon Spectrometer

ATLAS will upgrade its muon spectrometer for high-luminosity LHC runs. The coverage of fast trigger chambers in the inner station will be increased in both barrel (by adding a new layer of Resistive Plate Chamber - RPC) and endcap (by upgrading the EIL4 Thin Gap Chambers - TGC) regions. To create space for the additional layer of RPC in small sectors, the present Monitored Drift Tube (MDT) chambers need to be replaced by small-diameter MDT chambers. A TGC tracking trigger will be implemented using segmentsfound by TGC chambers in the endcap middle station and by the Phase-I upgraded New Small Wheel (NSW) detector in the endcap inner station. MDT data will be used for the first time at the first trigger level to improve the trigger muon momentum resolution. In addition, most electronics will be replaced to handle higher data rates and longer latency expected at high-luminosity LHC runs. We are on track for all upgrade activities for an installation starting at the beginning of 2024.