Development of Muon Drift-Tube Detectors for High-Luminosity Upgrades of the Large Hadron Collider

B. Bittner, O.Kortner, H.Kroha, F.Legger, R.Richter, A.Engl, R.Hertenberger, F.Rauscher

Max-Planck-Institut fuer Physik, Munich

Ludwig-Maximilian University, Munich

The muon detectors of the experiments at the Large Hadron Collider (LHC) 
have to cope with unprecedentedly high neutron and gamma ray background rates.
In the very forward regions of the ATLAS muon spectrometer, for instance,
counting rates of 1 kHz per square centimeter are reached at the LHC design
luminosity. For high-luminosity upgrades of the LHC, up to 10 times higher
background rates are expected which require replacement of the muon chambers
in the critical detector regions. Tests at the CERN Gamma Irradiation Facility
showed that drift-tube detectors with 15 mm diameter aluminum tubes 
operated with Ar:CO2 (93:7) gas at 3 bar and a maximum drift time of about
200 ns provide efficient and high-resolution muon tracking up to the highest 
expected rates. For 15 mm tube diameter, space charge effects deteriorating
the spatial resolution of larger diameter tubes are strongly suppressed. 
The sense wires have to be positioned in the chamber with an accuracy
of better than 50 micron in order to achieve a chamber resolution of about 50 micron.
We report about the design, construction and test of a prototype
chamber which fulfills these requirements.