Electric fields and their implications in the LUX-ZEPLIN time projection chamber

Thesis

Dark matter, though traced by its gravitational and cosmological imprints, continues to evade direct detection. The LUX–ZEPLIN (LZ) experiment, a dual-phase xenon time projection chamber, stands at the forefront of this pursuit. This thesis interrogates the microscopic and macroscopic roles of electric fields in LZ and their consequences for charge transport, event reconstruction, and low-energy sensitivity through enhanced signal–background discrimination and targeted background mitigation. Measurements of drift velocity and longitudinal diffusion in liquid xenon yield a self-consistent transport model that anchors field reconstruction and exhibits quantitative concordance with the Cohen–Lekner formulation of electron transport. A data-driven and simulation-informed programme then maps time-evolving and azimuthally asymmetric fields and introduces a novel surface-charge modelling framework that reveals charge redistribution on PTFE walls. These methods refine field mapping and, in turn, the description of charge drift, reducing biases and uncertainties in position reconstruction while clarifying diffusion-induced broad- ening. They also inform a low-energy ionisation-only analysis that demonstrates operation below the scintillation threshold. The advances reported here strengthen LZ’s forthcoming WIMP searches as sensitivities approach the neutrino fog, building on world-leading performance for mχ ≳ 9 GeV/c², and they support a wide suite of physics analyses, including 0νββ, by tightening charge-transport and field systematics. Taken together, these studies furnish field-motivated design guidance for the next-generation XLZD detector and underscore the role of electric fields as a central, quantitative lever among the determinants of performance, calibration, and physics reach.

Authors: Dey, S

• DOI: 10.5287/ora-y0ndjk2dg
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: dark matter; xenon microphysics; direct detection; liquid noble time projection chambers; dual phase tpcs
• Subjects: Particle Physics; Dark Matter