Commissioning of the New sMDT Monitored Drift Tube Detectors for the Phase-1 Upgrade of the ATLAS Muon Spectrometer

The Muon Drift Tube (MDT) chambers provide very precise and reliable muon tracking momentum measurement in the ATLAS spectrometer. Already Run 2 of LHC they have to cope with high background counting rates up $$500$$ Hz/cm $${}^{2}$$ inner endcap layers. At High-Luminosity (HL-LHC), are expected increase by almost a factor 10. New small (15 mm)-diameter (so-called sMDT) detectors been developed for upgrades They an order magnitude higher rate capability allow installation additional new triplet thin-gap RPC trigger barrel layer detector HL-LHC. designed mass production at Max Planck Institute (MPI) Physics Munich achieve sense wire positioning accuracy 5 $$\mu$$ m. A pilot project upgrade is underway during 2019/2021 shutdown. Several sMDT already installed operated detector. detailed studies detection efficiency track resolution carried out after assembling MPI repeated CERN integration detectors. author will describe design, quality assurance certification path, as well present status commissioning, worth its preliminary results overview complete In experiment.