Author ORCID Identifier

Document Type


Date of Award


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Wenqin Xu


Neutrinoless double-beta decay (0νββ) is a hypothetical nuclear decay mode. 0νββ searches are a high priority in nuclear physics. Discovery would ascertain the nature of the neutrino as the first known fundamental Majorana particle, and have far-reaching implications for physics beyond the Standard Model, including a lower bound on the effective neutrino mass scale, first direct evidence of a lepton number violating process, and insight into the matter-antimatter asymmetry in the universe. The next-generation LEGEND (Large Enriched Germanium Experiment for Neutrinoless ββ Decay) project will search for neutrinoless double-beta decay of 76Ge. LEGEND builds on infrastructure and technical expertise of current 0νββ in Ge experiments, developing new material components and techniques. LEGEND aims to operate in a quasi-background free configuration. Backgrounds must be aggressively reduced to reach this ambitious goal. The signals generated by the passage of cosmogenically-induced muons and their secondary particles, especially free neutrons, are a source of background. For at least one of the candidate host sites for LEGEND, cosmogenics are expected to be one of the most significant sources of background, and must be addressed with detailed characterization and novel suppression techniques. Characterization of cosmogenically-induced background in sensitive experiments is an active area of research, but results are dependent on the location and large-scale design of the experiment. A particle simulation and analysis module has been developed to investigate this topic for LEGEND. Early simulations estimate background from cosmogenics in the LEGEND-1000 baseline design, demonstrating the need for baseline design modifications for shallower host sites. Background suppression techniques are developed and tested using the simulation module, and strategies for addressing the cosmogenics issue and reducing project risk for LEGEND-1000 are highlighted. A post-design background mitigation with methane doping is proposed and studied for the first time. Experimental data of the requisite sensitivity from current experiments is limited, so uncertainties are also probed via direct comparisons of simulation frameworks. Methods are proposed to use LEGEND-200 data to characterize cosmogenic activity expected in LEGEND-1000 using new interaction channel combinations. This would reduce uncertainties and add to existing data for deep underground cosmogenic activation.

Subject Categories

Nuclear | Physics


Cosmogenic radiation, Neutron physics, Simulations

Number of Pages



University of South Dakota

Included in

Nuclear Commons



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