UC Santa Barbara

According to current estimates, the dark matter (DM) in our universe outweighs standard baryonic matter by a factor of five. Galaxies, including the Milky Way, are enveloped in dark halos responsible for their past formation and their present rotational dynamics. Despite the progress made by astrophysicists in identifying DM’s gravitational influence, its composition is unknown. Uncovering the particle nature of DM is therefore one of the main projects in fundamental physics. Experiments such as the Large Underground Xenon (LUX) seek to directly observe DM particles in the galactic halo as they collide with nuclei in target materials. LUX was operated at the Sanford Underground Research Facility (SURF) in Lead, South Dakota from April 2013 to May 2016. Though no evidence for DM events was found, the collected data allowed world-leading constraints to be placed on the interaction rate between DM particles and nucleons. Here we explore the WIMP (Weakly Interacting Massive Particle) hypothesis, and go through the signal models relevant to direct detection experiments like LUX. We describe the design and operation of the LUX detector, its calibration, as well as expected sources of background events and techniques employed to mitigate them. Data analysis and the implementation of models used in the profile likelihood ratio (PLR) procedure for setting frequentist confidence intervals are also discussed in detail. Finally, LUX limits on spin-dependent WIMP-nucleon scattering are given special attention.