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Abstract

Drift tube detectors are excellent candidates for precision muon tracking systems in experiments at future colliders like the HL-LHC and FCC-hh, which require unprecedentedly high rate capability. The small-diameter Muon Drift Tube (sMDT) chambers with 15 mm tube diameter have demonstrated sufficient rate capability and are currently under construction for the upgrade of the inner barrel layer of the ATLAS muon spectrometer at the HL-LHC. The rate capability of sMDT chambers in terms of muon detection efficiency and spatial resolution is limited by the performance of the readout electronics. A new (s)MDT ASD (Amplifier-Shaper-Discriminator) readout chip with a faster peaking time compared to the legacy ATLAS MDT chip for use at the HL-LHC has been developed. With reduced jitter in the discriminator threshold crossing time, the time- and spatial resolution are improved independent of the $\gamma$-background irradiation. Additionally, a method compensating for the gas gain drop due to space charge at high $\gamma$-background flux by adjusting the sMDT operating voltage has been developed. Simulation shows, that the addition of active baseline restoration circuits in the front-end electronics in order to suppress signal-pile-up effects at high background counting rates allows for further improvement of efficiency and resolution at high rates. In this thesis, the new ASD readout chip has been tested on sMDT chambers with and without background irradiation. A cosmic ray experimental setup housing three test chambers has been designed, constructed, and installed at the CERN Gamma Irradiation Facility (GIF++), where extensive tests have been conducted. The test chambers were equipped with old and new readout chips and with discrete readout circuits with baseline restoration functionality. In absence of a muon beam at CERN in 2020, cosmic muon tracks have been studied at varying background irradiation from the $^{137}$Cs $\gamma$-source. The results show the reach in rate capability of the sMDT detectors with optimized readout electronics.