Precision drift-tube chambers for the ATLAS muon spectrometer at super-LHC

The precise measurement of muon momenta up to 1 TeV/c is one of the most challenging aspects of the ATLAS experiment at the Large Hadron Collider (LHC) at CERN. The ATLAS muon spectrometer is equipped with three layers of Monitored Drift Tube (MDT) chambers in a magnetic field generated by a superconducting air-core magnet system which are designed to cope with neutron background counting rates of up to 500 cm⁻²s⁻¹. However, 10 times higher background rates are to be expected at Super-LHC, the high-luminosity upgrade of the LHC. We investigate the possibility of increasing the rate capability of the drift tube detectors by reducing the tubes diameter from the current value of 30 mm to 15 mm. Cosmic ray test results of a prototype detector with 15 mm diameter drift tubes in the presence of γ ray fluxes of up to 2000 cm⁻²s⁻¹ are discussed.