Exploring and enabling the science potential of DarkSide-20k and other current and future liquid argon dark matter search experiments

Abstract

One of the best hints we currently have of physics beyond the standard model is the existence of dark matter. Astrophysical and cosmological evidence suggests dark matter makes up approximately 85% of the total mass in the Universe. There are numerous experiments currently attempting to make an observation of dark matter and an abundance of proposed candidates. Yet still, to date, we do not know what constitutes dark matter or how it interacts. Direct detection experiments aim to measure interactions of dark matter from our galaxy's dark matter halo with a target material. DarkSide-20k is a dual-phase liquid argon experiment aiming to probe the dark matter-nucleon interaction cross-section for GeV - TeV scale dark matter candidate masses. In order to carry out these experiments, detector technologies and methods have been developed to enable searches with low thresholds and low background rates. In this thesis, work is described on the design, assembly and testing of state of the art low radioactivity silicon photosensors with single photon capabilities which will be used to instrument the DarkSide-20k detector. This includes work carried out to characterise sensors in cryogenic conditions to determine important parameters and the stability of the sensors. Additionally, a key theme of this work is to understand and explore the sensitivity of DarkSide-20k and other LAr and LXe experiments to a broad range of possible dark matter interactions and dark matter masses. A non-relativistic effective field theory approach is used to extend beyond the simplest spin-independent interaction. Exclusion limits and projected sensitivities of various isospin-violating dark matter models are evaluated to explore target complementary at specific Xe- and Ar-favoured parameter points. The Migdal effect is considered as a method of extending the sensitivity in the parameter space of each of the non-standard interactions to much lower dark matter candidate masses than would otherwise be possible. This means that DarkSide-20k will be able to probe dark matter parameter space down to tens of MeV, using a search only considering the ionisation signal. Results are presented for current and future experimental setups, and the loss of sensitivity at high cross-section due to interactions of dark matter within the Earth before reaching underground detectors is taken into account.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Darren Price (Supervisor) & Justin Evans (Supervisor)