Germanium-Based Neutrinoless Double-Beta Decay Searches

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Neutrinos are subatomic particles which are both abundant in the Universe and elusive at the same time. They are electrically neutral and barely interact with matter. In addition, neutrinos have tiny masses and the reason for this is unknown and could be related to whether neutrinos are their own antiparticles. The particle-antiparticle nature of neutrinos can be investigated by searching for an extremely rare form of radioactive decay, namely neutrinoless double beta decay. One of the most common forms of radioactivity is (normal) beta decay, where one electron is emitted from a nucleus along with an antineutrino. Two-neutrino double beta occurs when two electrons and two antineutrinos are emitted by a neucleus. Finally, a more exotic decay process has been hypothesized called neutrinoless double beta decay; in this process two electrons and no antineutrinos are emitted, and this is only possible if neutrinos are their own antiparticles. The search for this hypothetical decay is a priority for nuclear science, and a positive observation would shed light on the compelling mystery of why there is more matter than antimatter in the Universe. This project facilitates ongoing and future experimental searches for neutrinoless double beta decay in Germanium-76. This project will advance experimental nuclear physics, yield new scientific knowledge, and help early-career scientists develop their technical skills. The major research activities of this project focus on the MAJORANA DEMONSTRATOR (MJD) experiment in South Dakota and the multi-phased Large Enriched Germanium Experiment for Neutrinoless double beta Decay (LEGEND). This project supports MAJORANA’s continued operation as well as its data analysis of the full physics dataset, particularly by contributing to energy calibration and statistical analysis, so that the final double beta decay sensitivity of the DEMONSTRATOR can be realized. New scientific knowledge on (alpha, neutron) reactions in the MAJORANA calibration data will come from the proposed measurement of deexcitation gamma rays. The LEGEND project aims to measure a double beta decay half-life beyond 10e28 yr. The initial LEGEND-200 phase is under construction and the later LEGEND-1000 phase is under design. Research activities at USD for LEGEND include 1) contributing to the extensive simulation efforts of the LEGEND-200 phase, 2) expanding existing efforts on LEGEND-1000 background prediction and modeling by investigating cosmogenic and radiogenic backgrounds for both the evolving baseline design and promising alternative designs, and 3) developing analysis routines that will significantly suppress LEGEND backgrounds.The project will serve to train undergraduate, graduate and postdoctoral students in the techniques of precision nuclear physics and in the analysis of large and complex data sets. The PI will also engage in physics education and outreach through his participation in "Neutrino Day" at the Sanford Underground Research Facility (SURF) in Lead, South Dakota.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.