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We investigate how recent updates to neutrino oscillation parameters and the sum of neutrino masses influence the sensitivity of neutrinoless double-beta ( $0\nu \beta \beta$) decay experiments. Incorporating the latest cosmological constraints on the sum of neutrino masses and laboratory measurements on oscillations, we determine the sum of neutrino masses for both the normal hierarchy (NH) and the inverted hierarchy (IH). Our analysis reveals a narrow range for the sum of neutrino masses, approximately $0.06\mathrm{eV}/{\mathrm{c}}^2$for NH and $0.102\mathrm{eV}/{\mathrm{c}}^2$for IH. Utilizing these constraints, we calculate the effective Majorana masses for both NH and IH scenarios, establishing the corresponding allowed regions. Importantly, we find that the minimum neutrino mass is nonzero, as constrained by the current oscillation parameters. Additionally, we estimate the half-life of $0\nu \beta \beta$decay using these effective Majorana masses for both NH and IH. Our results suggest that upcoming ton-scale experiments will comprehensively explore the IH scenario, while 100-ton-scale experiments will effectively probe the parameter space for the NH scenario, provided the background index can achieve 1 event/kton-year in the region of interest. Published by the American Physical Society2024 

This paper focuses on the research and development of high-purity germanium (HPGe) crystals for detector fabrication, specifically targeting applications in rare-event physics searches. The primary objective was to produce large-scale germanium crystals weighing >1 kg with a controlled diameter of ∼10 cm and an impurity range of approximately 1010/cm 3. Ensuring structural integrity and excellent crystalline quality requires a thorough assessment of dislocation density, a critical aspect of the crystal development process. Dislocation density measurements play a crucial role in maximizing the sensitivity of HPGe detectors, and our findings confirmed that the dislocation density fell within acceptable ranges for detector fabrication. Additionally, this paper examines the segregation coefficient of various contaminants during the crystal development process. Comprehensive analysis of impurity segregation is essential for reducing contaminant quantities in the crystal lattice and customizing purification processes. This, in turn, minimizes undesired background noise, enhancing signal-to-noise ratios for rare-event physics searches and overall detector performance. The investigation included the segregation coefficients of three major acceptors and one donor in crystals grown at the University of South Dakota, providing valuable insights for optimizing crystal purity and detector efficiency. 

Charge trapping degrades the energy resolution of germanium (Ge) detectors, which require to have increased experimental sensitivity in searching for dark matter and neutrinoless double-beta decay. We investigate the charge trapping processes utilizing nine planar detectors fabricated from USD-grown crystals with well-known net impurity levels. The charge collection efficiency as a function of charge trapping length is derived from the Shockley-Ramo theorem. Furthermore, we develop a model that correlates the energy resolution with the charge collection efficiency. This model is then applied to the experimental data. As a result, charge collection efficiency and charge trapping length are determined accordingly. Utilizing the Lax model (further developed by CDMS collaborators), the absolute impurity levels are determined for nine detectors. The knowledge of these parameters when combined with other traits such as the Fano factor serve as a reliable indicator of the intrinsic nature of charge trapping within the crystals. We demonstrate that electron trapping is more severe than hole trapping in a p-type detector and the charge collection efficiency depends on the absolute impurity level of the Ge crystal when an adequate bias voltage is applied to the detector. Negligible charge trapping is found when the absolute impurity level is less than 1.0$$\times$$10$^11/^3$ for collecting electrons and 2.0$$\times$$10$^11/^3$ for collecting holes.