UNC-CH Physics and Astronomy Master’s Presentation

David Alberto Hervas

“An Assay-based Background Model for the MAJORANA DEMOSTRATOR”

The MAJORANA collaboration is searching for neutrinoless double-beta decay (0νββ) in 76Ge using modular arrays of enriched, high-purity Ge detectors. The MAJORANA DEMONSTRATOR consists of an array of 44 kg of high-purity Ge detectors (30 kg enriched to 88% 76Ge) with a p-type point contact geometry located in the Sanford Underground Research Facility in Lead, South Dakota. The ultra-low background and record energy resolution achieved by the MAJORANA DEMONSTRATOR enable a sensitive 0νββ search, as well as additional searches for physics beyond the Standard Model. The discrepancy between the measured background index of the MAJORANA DEMONSTRATOR, 11.9 ± 2.0 counts/(FWHM ton yr), and that predicted by the preliminary background model, < 2.2 counts/(FWHM ton yr), motivated the development of an updated assay-based background model. This “as-built” background model reflects the DEMONSTRATOR’s operational geometry and detector configuration. Building on the simulation of the as-built geometry and on-going assay campaigns, Monte Carlo uncertainty propagation is used to produce an updated assay-based background index for the MAJORANA DEMONSTRATOR.