Upgrades of the ATLAS Muon Spectrometer with sMDT Chambers 

H.Kroha

Max-Planck-Institut fuer Physik, Munich

for the ATLAS Muon Collaboration


The Monitored Drift Tube (MDT) chambers of the ATLAS muon spectrometer demonstrated that
they provide very precise and robust tracking over large areas. Goals of ATLAS muon detector upgrades 
are to increase the acceptance for precision muon momentum measurement and triggering and to improve 
the rate capability of the muon chambers in the high-background regions when the LHC luminosity increases.
Small-diameter Muon Drift Tube (sMDT) chambers have been developed for these purposes. With half the 
drift-tube diameter of the MDT chambers and otherwise unchanged operating parameters, sMDT chambers share 
the advantages with the MDTs, but have more than ten times higher rate capability and can be installed in 
detector regions where MDT chambers do not fit in. The chamber assembly methods have been optimized for 
mass production, reducing cost and construction time considerably and improving the the sense wire 
positioning accuracy to better than ten microns. Two sMDT chambers have been installed in 2014 to improve 
the momentum resolution in the barrel part of the spectrometer. The construction of twelve chambers for the 
feet regions of the ATLAS detector has started. A just recently approved project foresees the replacement 
of the MDT chambers at the ends of the inner barrel detector layer with sMDTs making space for additional 
RPC trigger chambers and improving the rate performance. Design, construction and installation of the new 
sMDT chambers for ATLAS will be discussed as well as tests of their performance.