Abstract
The Majorana Collaboration is operating an array of high-purity Ge detectors to search for the neutrinoless double- decay of . The Majorana Demonstrator consists of 44.1 kg of Ge detectors (29.7 kg enriched to 88% in ) split between two modules constructed from ultraclean materials. Both modules are contained in a low-background shield at the Sanford Underground Research Facility in Lead, South Dakota. We present updated results on the search for neutrinoless double- decay in with kg yr of enriched exposure. With the Demonstrator's energy resolution of 2.53 keV FWHM at , which is the best among all neutrinoless double- decay experiments, we observe one event in the region of interest with 0.65 events expected from the estimated background, resulting in a lower limit on the neutrinoless double- decay half-life of yr [90% confidence level (CL)] with a median sensitivity of yr (90% CL). Depending on the matrix elements used, a 90% CL upper limit on the effective Majorana neutrino mass in the range of 200–433 meV is obtained. The measured background in the configurations with full shielding and optimized grounding is counts/(FWHM t yr).
4 More- Received 7 February 2019
DOI:https://doi.org/10.1103/PhysRevC.100.025501
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