Resolution and Efficiency of Monitored Drift-Tube Chambers with Final Read-out Electronics at High Background Rates

The performance of a monitored drift-tube chamber for ATLAS with the final read-out electronics was tested at the Gamma Irradiation facility at CERN under varyin photon irradiation rates of up to 990~Hz\,cm$^{-2}$ which corresponds to 10 times the highest background rate expected in ATLAS. The signal pulse-height measurement of the final read-out electronics was used to perform time-slewing corrections. The corrections improve the average single-tube resolution from 106~$\mu$m to 89~$\mu$m at the nominal discriminator threshold of 44~mV without irradiation, and from 114~$\mu$m to 89~$\mu$m at the maximum nominal irradiation rate in ATLAS of 100~Hz\,cm$^{-2}$. The reduction of the threshold from 44~mV to 34~mV and the time-slewing corrections lead to an average single-tube resolution of 82~$\mu$m without photon background and of 89~$\mu$m at 100~Hz\,cm$^{-2}$. The measured muon detection efficiency agrees with the expectation for the final read-out electronics.