Calibrating the ATLAS Muon Spectrometer for a Search for Charged Stable Massive Particles

Many theories extending the Standard Model predict charged stable massive particles in reach of the LHC. In the last years, ATLAS conducted multiple searches for those particles as they offer signatures distinct from that of every Standard Model particle: Due to their high mass, stable massive particles are expected to exhibit velocities significantly below the speed of light, providing a model-independent approach to observe New Physics. As low particle velocities result in large times of flight, in particular in the outer parts of the detector, timing measurements in the ATLAS muon spectrometer provide a valuable handle for those searches. Meaningful timing and velocity measurements are impossible without an in-depth calibration of the muon spectrometer systems, which was therefore carried out for the previous ATLAS searches. A complete revision of the ATLAS reconstruction algorithm for charged stable massive particles in the last few years requires a renewed approach to the muon spectrometer calibration. This thesis presents studies on the changes coming with the new reconstruction algorithm and provides a novel understanding of the algorithm’s output. In addition, a calibration procedure for timing measurements with the ATLAS muon spectrometer is described that seizes upon the previous calibration and extends it, involving corrections of charge drift times and propagation times of signals, and deriving calibration constants for more than 735,000 detector elements. Thereby, it takes advantage of the new reconstruction algorithm for charged stable massive particles and the enlarged dataset of 128.3/fb of proton–proton collisions taken with the ATLAS particle detector at √s = 13 TeV in 2015–2018.