An assay-based background projection for the MAJORANA DEMONSTRATOR using Monte Carlo Uncertainty Propagation

Abstract

The background index is an important quantity which is used in projecting and calculating the half-life sensitivity of neutrinoless double-beta decay ($0\hat{I}½{\hat{I}}^2{\hat{I}}^2$) experiments. A novel analysis framework is presented to calculate the background index using the specific activities, masses and simulated efficiencies of an experiment's 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 background index distribution from the specific activity, mass and efficiency distributions. This analysis method is applied to the MAJORANA DEMONSTRATOR, which deployed arrays of high-purity Ge detectors enriched in ${}^{76}$Ge to search for $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$. The framework projects a mean background index of $\left[8.95\pm 0.36\right]\times 10^{-4}$cts/(keV kg yr) from ${}^{232}$Th and ${}^{238}$U in the DEMONSTRATOR's components.

9 pages, 3 figures