Search for New High-Mass Phenomena in Events with Two Muons using the ATLAS Detector at the Large Hadron Collider

Elementary particles and their interactions are extremely well modeled by the Standard Model of particle physics. However, experimental observations such as indirect detection of dark matter and theoretical problems such as the hierarchy of energy scales cannot be explained entirely by this theory. Many extensions of the Standard Model which solve these shortcomings predict the existence of new phenomena at high energies. In particular, there are numerous new resonance models, such as Grand Unified Theories, and contact interaction models leading to dimuon final states. This dissertation presents a search for new high-mass phenomena in events with two muons using the ATLAS detector at the Large Hadron Collider. The search results are found to be consistent with the Standard Model prediction. Interpretations are carried out in the context of both resonant and non-resonant new physics models. In particular, lower limits on the mass of hypothetical $Z'$ bosons are set between 4.0 TeV for the $Z'_\text{SSM}$ model and 3.3 TeV for the $Z'_\psi$ model, and lower limits on the contact interaction energy scale $\Lambda$ are set between 18 TeV and 30 TeV, depending on the chiral structure of the contact interaction. In addition to data analysis at the energy frontier, the performance of muon reconstruction and identification within the ATLAS experiment is detailed. More precisely, calculations of muon trigger efficiencies for high-momentum muons using events containing a leptonically decaying $W$ boson and jets are presented. A new muon identification working point is also investigated. Finally, as the ATLAS experiment enters its second long shutdown, the first layer of the endcap regions of the muon spectrometer will be replaced with the New Small Wheels (NSWs), in order to improve both the triggering and tracking capabilities of the ATLAS detector. One of the two main technologies used in the NSW is small-strip Thin Gap Chambers (sTGCs). Results of various test beam campaigns carried out at Fermilab and at CERN, aimed at characterizing sTGCs, are presented. Position resolution measurements of less than 50 $\mu$m are obtained. Measurements using the latest electronics readout chain of the sTGC detectors under realistic conditions are also presented.