PNNL

Abstract

The MAJORANA DEMONSTRATOR was an ultra-low-background experiment designed for neutrinoless doublebeta decay (0?ßß) investigation in 76Ge. Located at the Sanford Underground Research Facility in Lead, South Dakota, the DEMONSTRATOR utilized modular high-purity Ge detector arrays within shielded vacuum cryostats, operating deep underground. The arrays, with a capacity of up to 40.4 kg (27.2 kg enriched to ~88% in 76Ge), have accumulated the full data set, totaling 64.5 kg yr of enriched active exposure and 27.4 kg yr of exposure for natural detectors. Our updated search improves previously explored three-nucleon decay modes in Ge isotopes, setting new partial lifetime limits of 1.83 × 1026 yr (90% confidence level) for 76Ge(ppp) ? 73Cu e+p+p+ and 76Ge(ppn) ? 73Zn e+p+. The partial lifetime limit for the fully inclusive triproton decay mode of 76Ge is found to be 2.1 × 1025 yr. Furthermore, we have updated limits for corresponding multinucleon decays.