Developing optical calibration systems and background models for the Pacific Ocean neutrino experiment

Over the last two decades, the field of neutrino astronomy has been rapidly expanding as experimental observations demonstrate the significant potential of neutrinos as probes for studying the cosmos. The Pacific Ocean Neutrino Experiment (P-ONE) is a next generation cubic-kilometre scale neutrino telescope designed to observe high-energy TeV to PeV neutrinos. P-ONE will be deployed on an abyssal plain at a depth of 2.6 km in the Pacific Ocean off Canada's West Coast. The detector consists of an array of kilometre tall mooring lines instrumented with optical sensors that detect Cherenkov light induced as a result of neutrino interactions. In order to accurately reconstruct the properties of the incident neutrino from the light signature, the detector needs to be well calibrated. In particular, the optical properties of the seawater, the position of every optical sensor, and the anticipated detector backgrounds must be well understood. The deep sea is a dynamic environment where conditions can change quickly, so a real-time calibration system is essential for the successful operation of P-ONE. This thesis will summarize the development of a dedicated calibration module, designed to emit fast, isotropic light pulses, allowing for in-situ optical calibration of the detector. Module performance is characterized in both air and water, and is presented along with an accompanying optical simulation, that guided the design. Characterizing the ambient light of the deep sea is critical for developing methods to discriminate between signal and ambient backgrounds. Site characterization has demonstrated that the environmental background is dominated by bioluminescence and decays of radioactive potassium 40K in sea salt. This thesis documents the modelling of the radioactive background, providing first estimates of the anticipated 40K background in P-ONE. The work concludes with an outline of a novel algorithm implemented into the P-ONE analysis framework that efficiently reproduces this signal, eliminating the overhead of time-intensive simulation. Lastly, this thesis highlights the design of a camera system for monitoring bioluminescence, opening the door for interdisciplinary studies of deep sea organisms.