The Search for Lightly Ionizing Particles in the Large Underground Xenon Detector

Abstract

Observations as early as the 1930s indicated significant disagreements between anticipated gravitational galactic rotations based upon solar luminous intensity and the observed rotations of galaxies. The cause of the observed increased rotational velocity in galaxies was ascribed to a large invisible mass termed dark matter. Various indirect observations affirmed the notion of dark matter and also suggested that the dark matter consists of non-baryonic material. Dark matter currently stands as one of the great mysteries in modern physics.

A leading candidate for dark matter is known as the Weakly Interacting Massive Particle (WIMP) which nicely fits dark matter projections. The Large Underground Xenon (LUX) experiment, located in the Homestake Mine of the Sanford Underground Research Facility (SURF), was a xenon-based direct detection experiment designed and built for the detection of WIMPs. LUX had a dual-phase Time Projection Chamber (TPC) which allowed for precise energy and position reconstruction of events. Reanalyzing the LUX data, it becomes possible to search for more exotic theoretical dark matter forms and new physics.

The Lightly Ionizing Particle (LIP), a theoretical particle with a charge of ∫ ∙ ⅇ with ∫ < 1 and ⅇ the electron charge, arises in a variety of dark matter conceptions associated with additional dark sectors as well as other physical constructs such as monopoles and quantized charges. This work seeks to use data from the first underground run of LUX Run03, and reanalyze it to search for tracks in the detector as a result of LIP interactions. Throughout the reanalysis new techniques in simulation, data analysis, and data processing are developed, including pulse chopping to separate merged signals. The LIP search, making use of traditional cut methods as well as machine learning for event classification, places new limits on LIP flux in the charge range 0.01ⅇ to 0.3ⅇ as low as 10⁻¹⁰ cm⁻² s⁻¹ sr⁻¹.