Low energy electron recoil searches with the LUX-ZEPLIN experiment for beyond the Standard Model physics

Abstract

One of the biggest open questions in physics is confirming the fundamental nature of dark matter, an elusive type of matter that is measured to contain up to 84% of the calculable mass in the universe. There is currently no known way to observe dark matter directly; consequently, all current evidence for dark matter and its contributions to the total measured mass comes from indirect observations, which look for the gravitational impact of dark matter’s presence throughout the universe. Through the construction of detectors in recent years, experiments aim to observe dark matter directly on Earth instead of searching the cosmos.

The LUX-ZEPLIN (LZ) experiment is the foremost of these direct searches for dark matter. It is based at the Sanford Underground Research Facility (SURF) in South Dakota. Using a dual-phase time projection chamber detector that contains 7 tonnes of xenon for dark matter searches, LZ has set worldleading results for Weakly Interacting Massive Particle (WIMP) interactions with nucleons. LZ’s signal-discrimination ability from extensive calibration campaigns makes it sensitive to additional signals and processes beyond traditional WIMP interactions that are not just dark-matter candidates, allowing for expanded physics searches to be carried out. One of these searches looks for low-energy electron recoil signals, which are a potential method of interaction for Beyond Standard Model (BSM) particles within LZ.

This thesis will discuss the work done by the author for low-energy electron recoil searches in LZ and present the results from these searches using LZ’s first and third science runs. One of the low-energy electron recoil models, solar-axions, will be investigated more closely with a study on expanding the solar axion model to include additional production methods and interactions. This thesis will also discuss the development of cuts aimed at tagging and removing events that correspond to periods of excess noise within the time projection chamber and outer detector of LZ.