  Small-diameter muon drift tube (sMDT) chambers with 15 mm tube diameter are a
cost-effective technology for high-precision muon tracking over large areas at
high background rates as expected at future high-energy hadron colliders
including HL-LHC. The chamber design and construction procedures have been
optimized for mass production and provide sense wire positioning accuracy of
better than 10 ?m. The rate capability of the sMDT chambers has been
extensively tested at the CERN Gamma Irradiation Facility. It exceeds the one
of the ATLAS muon drift tube (MDT) chambers, which are operated at
unprecedentedly high background rates of neutrons and gamma-rays, by an order
of magnitude, which is sufficient for almost the whole muon detector acceptance
at FCC-hh at maximum luminosity. sMDT operational and construction experience
exists from ATLAS muon spectrometer upgrades which are in progress or under
preparation for LHC Phase 1 and 2.
