Michael Hasinoff

Despite the long-standing success of the Standard Model, we know it to be an incomplete description of our universe as it does not describe dark matter: a sector of matter discovered through cosmological observations of its large-scale gravitational interactions. The particle scale interactions of dark matter remain unknown. A dominant open question in particle physics is how dark matter interacts with itself and how (if at all) dark matter interacts with Standard Model particles. DarkLight seeks to address this question through the search for a dark boson: a postulated particle that would mediate interactions between the Standard Model and dark matter. DarkLight will attempt to produce the dark boson using the TRIUMF superconducting electron linear accelerator, and identify the dark boson through the reconstruction of its mass using its Standard Model decay products.Parent particle mass reconstruction relies on the correct identification of particles as originating from the same decay. This manifests as particles arriving at the detector system at the same time. To make this identification, a trigger system is used to make precise measurements of the arrival times of particles and prompt data readout when a coincidence is observed between each particle type’s detector system. A thorough understanding of the capabilities and limitations of the trigger system is necessary to ensure this identification is correct and to maintain data quality. This thesis presents the characterization of the DarkLight trigger system. The time resolution of the system is found to exceed the minimum standard for confident decay pair matching, and the trigger system is determined to be able to resolve the position of impact of an incoming particle, which is an important feature in background suppression. A discussion of the accuracy of time measurements made using the trigger system is presented. The efficiency of the trigger detectors is maintained across their central region, but further investigations into the peak efficiency are required. The system was found to be minimally affected by scintillator crazing. While poor light guide connections have a significant negative impact on data quality, they can be identified for replacement from the analysis of pulse width data.

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The existence of a CP violating θ term in the QCD Lagrangian and the smallness of that term (θ 10⁻¹⁰) is known as the Strong CP problem and is an unresolved problem in particle physics. The most favoured solution to the strong CP problem is the Peccei-Quinn mechanism which introduces an additional U(1) symmetry. When this symmetry is spontaneously broken a pseudo-goldstone boson called the axion is produced. Cosmological studies of the axion have shown that it may be produced in abundances through the oscillation of the axion field in the early universe (called the misalignment mechanism) and so can be a source of dark matter. This led to the development of axion haloscopes to search for these axions. Standard axion searches rely on resonant cavities in a strong magnetic field. These axions are thought to be virialized and non-relativistic, this leads to them having a frequency with a small linewidth (on the order of kHz). To detect these axions the cavities must be tuned in discrete steps. In this thesis we will discuss a different method to search for axions based on broadband search ideas. Specifically we will focus on relativistic axions which can be produced under a variety of models. This means that line width of axions from relativistic models will be large (∼ 1 GHz) and this will require a new detection strategy. We will discuss new methods for detecting broadband axions including a search for daily modulations which, up until now, have been ignored in the literature. The idea is to collect the signal over an entire season during a specific hour and fit the resulting power excess as a function of time (measured in hours) during a twenty-four hour period. We will discuss how a genuine signal can be discriminated from a spurious signal and background noise by considering B=0 data and by studying the phase drift of the daily modulations. Finally we will comment on how these broadband searches may be applied to current axion cavity experiments.

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