Speakers
Description
The ${\rm M{\scriptsize AJORANA}~D{\scriptsize EMONSTRATOR}}$ is a neutrinoless double beta decay ($0\nu\beta\beta$) experiment consisting of ~30 kg of germanium detectors enriched to 88% in $^{76}\rm{Ge}$ and ~14 kg of natural germanium detectors. The detectors are divided between two cryostats and surrounded by a graded passive shield. The ${\rm{D\scriptsize EMONSTRATOR}}$ achieved one of the lowest background rates in the region of the $0\nu\beta\beta$ Q-value, 11.9 $\pm$ 2.0 cts/(FWHM t y) from the low-background configuration of the initial 26 kg-yr exposure. Nevertheless this background rate is a factor of four higher than the projected background rate based on component assays. This discrepancy arises from an excess of events from the $^{232}\rm{Th}$ decay chain. Background model fits using two different statistical approaches aim to understand this deviation from assay-based projections, potentially determine the source(s) of observed backgrounds, and allow a precision measurement of the two-neutrino double-beta decay half-life. These fits, combined with supplemental analyses, indicate the origin of the $^{232}\rm{Th}$ excess is not from a near-detector component, which has informed design decisions for the next-generation LEGEND experiment. Recent findings have narrowed the suspected locations for the excess activity, motivating the ongoing simulation and assay campaign.
