Departmental Oral Examination (Thesis Title: "Search for New High-Mass Phenomena in Events with Two Muons using the ATLAS Detector at the Large Hadron Collider")
Physics and Astronomy
Although elementary particles and their interactions are extremely well modeled by the Standard Model of particle physics, some experimental measurements cannot be explained entirely by this theory. Many extensions of the Standard Model predict the existence of new phenomena at high energies. In particular, new resonance models and contact interaction models leading to dimuon final states are numerous.
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 background prediction. Interpretations both in the context of resonant and non-resonant new physics models are carried out. In particular, lower limits on the mass of hypothetical Z' bosons are set between 4.0 TeV for the Z'SSM model and 3.3 TeV for the Z'ψ model, and lower limits on the contact interaction energy scale Λ 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 scale factors for high-pΤ 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). Work carried out with the sTGC collaboration, which aims to characterize and integrate the NSW into the ATLAS detector in the coming years, is described. Particularly, results of various test beam campaigns carried out at Fermilab and at CERN are presented. Position resolution measurements of less than 50μm are obtained. Measurements using the latest electronics readout chain of the sTGC detectors under realistic conditions are also presented.