A Search for Neutrinoless Double-Beta Decay in ${}^{76}$Ge with 26 kg-yr of Exposure from the MAJORANA DEMONSTRATOR

Abstract

The MAJORANA Collaboration is operating an array of high purity Ge detectors to search for the neutrinoless double-beta decay of ${}^{76}$Ge. The MAJORANA DEMONSTRATOR consists of 44.1 kg of Ge detectors (29.7 kg enriched to 88% in ${}^{76}$Ge) split between two modules constructed from ultra-clean 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-beta decay in ${}^{76}$Ge with $26.0\pm 0.5$ kg-yr of enriched exposure. With the DEMONSTRATOR's unprecedented energy resolution of 2.53 keV FWHM at $Q_{{\hat{I}}^2{\hat{I}}^2}$, 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 ${}^{76}$Ge neutrinoless double-beta decay half-life of $2.7\times 10^{25}$ yr (90% CL) with a median sensitivity of $4.8\times 10^{25}$ 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 low-background configurations is $11.9\pm 2.0$ counts/(FWHM t yr).

11 pages, 11 figures