Date of Award

Spring 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Advisor

Maruyama, Reina

Abstract

Overwhelming evidence has been observed for the existence of dark matter; however, it has yet to be directly detected. Since 1997, the DAMA/LIBRA experiment has claimed to detect a dark matter signal, taking the form of an annual modulation consistent for over 20 yearly cycles. Though DAMA/LIBRA reports a 13.7 sigma significance, experiments utilizing different detector technologies have excluded their result by several orders of magnitude. To definitively test the validity of the claim, COSINE-100 and ANAIS-112 have mounted experiments with the same detector medium, NaI(Tl). Both experiments have reported results consistent with no modulation and are on the cusp of concluding the DAMA/LIBRA debate. The results of the search for the annual modulation of dark matter by direct combination of the COSINE-100 and ANAIS-112 experiments and the validation of the consistency of results between them are presented in this dissertation. Combining experimental data achieves an exposure of 485 kg*yr for the 3-year combined datasets and 984 kg*yr for the 6-year combined datasets, resulting in modulation values of -0.0002 +/- 0.0026 (0.0021 +/- 0.0028) cpd/kg/keV in the 1--6 (2--6) keV energy regions for the 3-year datasets and values of 0.0005 +/- 0.0019 (0.0027 +/- 0.0019) cpd/kg/keV in the 1--6 (2--6) keV energy regions for the 6-year datasets. Finally, a modulation of 0.0005 +/- 0.0017 cpd/kg/keV is found for the nuclear-recoil equivalent energy region 6.7--20 keV_nr which accounts for the difference in quenching factors. Also presented are the investigation of modulation arising from analysis artifacts in the dark matter search as well as efforts for optimizing radiopurity in next generation NaI(Tl) detectors by measuring their cosmogenic activation rates with artificially activated NaI(Tl) crystals and through simulation of backgrounds in varying detector geometries.

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