School of Physics - Theses
Permanent URI for this collection
Search Results
1 - 2 of 2
-
ItemSearching for Dark Matter( 2022)The nature of Dark Matter (DM) is one of the most prominent unanswered questions in particle physics. The Standard Model (SM) has been remarkably successful in describing subatomic phenomena, however not all observations can be explained using this model including DM. The existence of DM is supported by a number of independent astrophysical observations, which when taken together, indicate DM is an elementary particle or particles, however their nature remains largely unknown. The focus of this thesis is on work towards experimental searches for particle DM under the Weakly Interacting Massive Particle (WIMP) paradigm using alter- native but complementary methods to the astrophysical observations in order to test the particle nature of DM. The first approach used is collider searches which test for DM production from the incident SM particles in particle colliders. The second approach is Direct Detection (DD) which aims to observe DM scattering off a SM particle. Using the motion of the Earth and Sun, some more unique features of the expected DM signal may be used to enhance experimental sensitivity. The orbit of the Earth around the Sun results in a time dependent signal with period of a year. The large dataset collected by A Toroidal LHC ApparatuS (ATLAS) allows searches for DM in many areas of phase space. These searches are limited by the ability to identify and discriminate the hypothesised DM signals from back- ground. As such the reconstruction and proper identification of objects in the detector over the largest possible range of momenta plays a key role in what is experimentally accessible. The use of track-jets to allow the identification of low momentum b-hadrons as well as the extension of this identification to lower momentum ranges will be described. The pioneering use of these detector objects to search for DM in regions of phase space previously thought to be inaccessible or too difficult will be described. Many experiments have failed to find DM using direct detection but only one (DArk MAtter (DAMA)) still maintains they have found it, appearing as a time dependent signal. This result is somewhat at odds with other results, however due to experimental differences, it is not completely incompatible. To properly test this an independent experiment using the same experimental approach as DAMA is needed to verify the results. This is the aim of the Sodium-iodide with Active Background REjection (SABRE) experiment, the creation of data acquisition and management systems will be described as well as simulation results used to inform the design and understand detector backgrounds.
-
ItemExploring dark matter interactions( 2021)Understanding Dark Matter (DM) is one of the foremost goals of modern day particle physics. This thesis is focused on interactions between DM and visible matter. We examine the phenomenology that arises when existing frameworks are extended to make them theoretically consistent, and explore novel means of detection. The first chapter summarises current DM literature and experimental searches, as well as the motivation for pursuing a gauge invariant description of the interactions between the dark and visible sectors. The second chapter considers a gauge invariant portal between the dark and visible sectors, and how the phenomenology of a self consistent model described in a gauge invariant framework differs from the simplified models previously considered in the literature. We consider features of the direct detection signals characteristic of such a gauge invariant model, as well as constraints on these models arising from electroweak precision data, stability of the scalar potential, and DM relic density production. In chapter 3, we consider models in which the tree level contributions to nuclear recoil direct detection experiments are strongly suppressed. In this case, the leading order contributions arise at loop level. We investigate the size of these contributions for both the gauge invariant model presented in the previous chapter, as well as an inelastic DM model. In the fourth chapter we consider the capture of DM particles in the Sun, and their subsequent annihilation to other dark sector particles. The decay of these dark annihilation products, outside the Sun, leads to a flux of gamma rays that we compare with recent solar gamma ray measurements. We analyse this scenario in a model independent way, demonstrating excellent sensitivity to both spin-dependent and spin-independent scattering. We also determine constraints in the context of a self consistent model in which both the scattering and annihilation processes involve dark photons.