Neutrinoless Double-Beta Decay with Germanium Detectors: Majorana Demonstrator and LEGEND

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The non-zero masses and neutral electric charge of neutrinos allows for the possibility that neutrinos are their own antiparticles (i.e. Majorana particles), in which case an ultra-rare form of nuclear decay known as neutrinoless double-beta decay (NLDBD) may occur. If neutrinos are shown to be Majorana particles, it would provide an explanation for the very small masses of neutrinos; point to new physics at energies beyond the reach of our most powerful colliders; and motivate an explanation for the prevalence of matter over anti-matter in the Universe. This award supports software and instrumentation research on an experiment to test the Majorana characteristics of neutrinos and the next phase experiment, called LEGEND. Both experiments use ultra-pure germanium detectors and are at the cutting edge of science. The PI will train graduate students in novel techniques that will allow them to compete in high-technology based careers. Additionally, the PI has an innovative program in outreach to the public. The LEGEND Experiment will use the ultra-pure materials developed by the MAJORANA Collaboration and the liquid cryogen active shielding developed by the GERDA Collaboration in the construction of a phased-deployment ton-scale experiment with discovery potential for NLDBD at half-lives beyond 10e28 years. This project will extend LEGEND's sensitivity to NLDBD and dark matter by building on a full understanding of the backgrounds in the MAJORANA DEMONSTRATOR and reducing backgrounds associated with cosmogenic Argon isotopes in a liquid cryogen compton veto. Specifically, the PI and his group aim to: construct a comprehensive background model of the MAJORANA DEMONSTRATOR NLDBD experiment using Monte Carlo simulations and experimental data; investigate the feasibility of germanium detector array deployment in a liquid neon environment to extend the physics reach of LEGEND; and develop preliminary designs and background models for the LEGEND-200 (200-kg) and LEGEND-1000 (1000-kg) phases of the LEGEND experiment.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.