Tracking Performance of Micromegas chambers for the ATLAS New Small Wheel project

For the upcoming data taking period, the innermost end-caps of the ATLAS Muon Spectrometer will be upgraded with the New Small Wheels (NSWs), deploying Micro-Mesh Gaseous Detectors (Micromegas) and small-strip Thin Gap Chambers for improved tracking and trigger capabilities at increased collision rates introduced by the High-Luminosity LHC upgrade. This dissertation focuses on the reconstruction of inclined tracks with the Micromegas detectors, as they will be present in the NSW. The first of two parts of the thesis covers a dedicated test beam campaign, where the position reconstruction performance of one of the first Micromegas modules from the series production was investigated. Focus was laid on the reconstruction of clusters from inclined tracks, employing two different reconstrution algorithms, the micro Time Projection Chamber (μTPC) and the Cluster Time Projection (CTP) methods. While the performace of the μTPC method, especially in terms of the reconstruction efficiency, suffered from the exceptionally high noise levels observed temporarily in the test beam, the CTP method was able to reconstruct clusters with a precision of 212 μm at efficiencies of 90 % and above. In the second part of this thesis, the simulation of the Micromegas detectors inside the ATLAS offline software, athena, has been significantly improved and several parameters have been optimized in order to better mimic the response of the actual detector. Furthermore the reconstruction algorithms for inclined tracks have been integrated into athena, and their performance was studied for different physics scenarios obtained from the detector simulation. The CTP method showed the most promising results and will therefore be used for the precise reconstruction of muon tracks in ATLAS, which is of key importance for the physics program of the collaboration.