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Abstract

The fundamental nature of dark matter remains one of the most profound mysteries in modern physics. Liquid xenon (LXe) time projection chambers (TPCs) are at the frontier of sensitivity to search for weakly interacting massive particle (WIMP) candidates. This thesis presents contributions to both current dark matter searches with the XENONnT experiment and foundational studies of infrared (IR) scintillation in xenon with the potential to enhance the sensitivity of next-generation detectors like XLZD. The combined analysis of XENONnT's first two science runs, with a total exposure of 3.1 tonne-years, found no evidence for dark matter. Consequently, it placed competitive upper limits on the WIMP-nucleon cross section as low as 1.7 × 10⁻⁴⁷ cm² for a WIMP mass of 30 GeV/c². Through a dedicated analysis optimized to achieve an even lower energy threshold, XENONnT achieved the first measurement of ⁸B solar neutrinos in a ton-scale detector via coherent elastic neutrino-nucleus scattering (CEνNS), observing 10.6 excess events above background with 2.73 σ significance. The statistical methods, sensitivity studies, and robustness assessments developed in this thesis were central to these results. Furthermore, this thesis investigates IR scintillation in xenon, showing promising results for future detector applications. Systematic measurements in gaseous xenon revealed a substantial IR light yield of approximately 6000 photons/MeV, which is similar in magnitude to ultraviolet (UV) scintillation commonly used in current detectors. The time response was characterized for the first time, finding a dominant microsecond-scale component that challenges previous understanding of xenon de-excitation pathways. Additionally, a dual-phase xenon TPC was operated with broad wavelength sensitivity spanning UV to IR, observing signals consistent with IR scintillation in both liquid and gaseous phases.