Speaker
Description
The MAJORANA DEMONSTRATOR is a neutrinoless double beta decay (0νββ) experiment consisting of ~30 kg of germanium detectors enriched to 88% in $^{76}$Ge and ~14 kg of natural germanium detectors. The detectors are divided between two cryostats and surrounded by a graded passive shield. The DEMONSTRATOR concluded in March 2021 and set a 0νββ half-life limit of $T_{1/2} > 8.3 \times 10^{25}$ yrs based on its full exposure. The experiment achieved one of the lowest background rates in the region of the 0νββ Q-value, 15.7 cnts/(FWHM t y). This background rate, however, was higher than the rate of 2.9 cnts/(FWHM t y) projected by material assays and simulations. This discrepancy arises from an excess of events from the $^{232}$Th decay chain. Background model fits aim to understand the observed $^{232}$Th excess and other deviations from assay-based projections, as well as allow a precision measurement of the 2νββ half-life. Comparisons of the data with simulations indicate the $^{232}$Th excess cannot arise from near-detector components. This is an important finding related to the design and implementation of the LEGEND-200 experiment. The final results of the DEMONSTRATOR are presented along with its latest background model.
*This material is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, the Particle Astrophysics and Nuclear Physics Programs of the National Science Foundation, and the Sanford Underground Research Facility.
| Submitted on behalf of a Collaboration? | Yes |
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