Assay-based background projection for the Majorana Demonstrator using Monte Carlo uncertainty propagation

experiments. An analysis framework is presented to calculate the BI using the specific activities, masses, and simulated efficiencies of an experiments components as distributions. This Bayesian framework includes a unified approach to combine specific activities from assay. Monte Carlo uncertainty propagation is used to build a BI distribution from the specific activity, mass, and efficiency distributions. This method is applied to the Majorana Demonstrator, which deployed arrays of high-purity Ge detectors enriched in

{}^{76}{Ge}

to search for

0 ν β β

. The original assay-based projection is requantified in the new framework, using the as-built geometry of the Demonstrator and additional assay information. While 47% higher than the original projection, the resulting BI of

[8.95 \pm 0.36] \times 10^{- 4} cts/(keV kg yr)

from the

{}^{232}{Th}

and

{}^{238}U

decay chains does not account for the higher-than-expected BI observed by the Demonstrator. This method enables us to demonstrate the statistical incompatibility between the Demonstrator's observed background and the assay results.

Note:

9 pages, 3 figures

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