Timing at the ATLAS detector: Challenges and Possibilities of Track-Time Association

In the coming years the Large Hadron Collider (LHC) will be upgraded to run at an instantaneous luminosity of $5 \times 10^{34}\,\, \mathrm{cm^{-2}s^{-1}}$ compared to current Run 3's $2 \times 10^{34}\,\, \mathrm{cm^{-2}s^{-1}}$. In order to adapt to this change the ATLAS detector will undergo a number of transformations, among which is the addition of a timing detector in the forward region. The High Granularity Timing Detector (HGTD) is still in development, but once installed it will be the first timing detector at ATLAS. The HGTD will provide timing at design resolution of $30$ ps before irradiation for tracks in the $2.4 < |\eta| < 4.0$ range. This thesis presents a study of the performance of current methods for assigning tracks time with HGTD hits based on simulated high-transverse momentum muon samples. These methods are based on spatial Inner Tracker (ITk) to HGTD track extrapolation and work well for muons, but for pileup tracks and tracks from secondary particles this extrapolation is significantly less effective. Furthermore, this thesis explores the possibilities of using track-time to improve pileup filtering for muon isolation. It is shown that time-cuts can have significant impart on muon isolation efficiency.