Collaborative Research: Combating Cosmogenic Argon Isotopes in LEGEND

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Neutrinos are electrically neutral and have non-zero mass, although their mass is very small. These properties raise the possibility that neutrinos are their own antiparticles (i.e. Majorana particles). If a neutrino is, indeed, its own anti-particle then this would shed light on the reason why matter dominates over antimatter in our universe and would point to new physics at energies far beyond those of our largest collider-accelerators. If neutrinos are Majorana particles, then double-beta decay without the simultaneous emission of neutrinos, or zero-neutrino double-beta decay (0νββ), becomes possible. The PI will search for 0νββ in an upcoming experiment. The ultra-rare nature of the decay, and the extreme sensitivity sought by the experiment, require backgrounds to be strictly controlled. For example, the experiment must be constructed with ultra-pure materials, be deployed underground, and make use of advanced techniques to discriminate signal from background.The LEGEND experiment will use germanium detectors enriched in the isotope Ge-76 to conduct a search for 0νββ. LEGEND hopes to achieve 10 ton-years of exposure with backgrounds reduced by over an order-of-magnitude compared to what has been previously demonstrated. This project aims to address the leading background contribution to the LEGEND experiment. For example, the presence of trace amounts of radioactive Ar-42 in the liquid argon bath in which LEGEND’s Ge detectors will operate will interfere with the counting of real 0νββ events. The PI will perform measurements in liquid argon in order to develop tools to accurately estimate the impact of this source of background and also develop analysis tools to remove it from the data. The PI also aims to develop a robust and validated background model that can be integrated into the LEGEND data processing framework. The goal is to produce reliable energy spectra which can be used for background estimation and fitting, and accurately model pulse shape discrimination techniques which can be used to suppress backgrounds arising from Ar-42.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.