Abstract
Neutrinoless double-beta decay of ^{76}Ge is searched for with germanium detectors where source and detector of the decay are identical. For the success of future experiments it is important to increase the mass of the detectors. We report here on the characterization and testing of five prototype detectors manufactured in inverted coaxial (IC) geometry from material enriched to 88% in ^{76}Ge. IC detectors combine the large mass of the traditional semi-coaxial Ge detectors with the superior resolution and pulse shape discrimination power of point contact detectors which exhibited so far much lower mass. Their performance has been found to be satisfactory both when operated in vacuum cryostat and bare in liquid argon within the Gerda setup. The measured resolutions at the Q-value for double-beta decay of ^{76}Ge (Q_{beta beta } = 2039 keV) are about 2.1 keV full width at half maximum in vacuum cryostat. After 18 months of operation within the ultra-low background environment of the GERmanium Detector Array (Gerda) experiment and an accumulated exposure of 8.5 kgcdot year, the background index after analysis cuts is measured to be 4.9^{+7.3}_{-3.4}times 10^{-4} text {counts}/(text {keV} cdot text {kg} cdot text {year}) around Q_{beta beta }. This work confirms the feasibility of IC detectors for the next-generation experiment Legend.
Highlights
As of the hypothetical neutrinoless double beta (0νββ) decay eluded detection in any of the candidate isotopes (e.g. 76Ge [1,2], 130Te [3], 136Xe [4,5])
Among the many challenges inherent to these experiments, one is to scale up the isotope mass by one order of magnitude while lowering the background, which requires a change of germanium detector design
Previous studies have demonstrated the excellent performance of inverted coaxial (IC) point contact Ge detectors [7,8]
Summary
As of the hypothetical neutrinoless double beta (0νββ) decay eluded detection in any of the candidate isotopes (e.g. 76Ge [1,2], 130Te [3], 136Xe [4,5]). Latest 76Ge-based experiments, GERmanium Detector Array (Gerda) and Majorana Demonstrator, benefited from the high background rejection capability of point contact Ge detectors. They feature an excellent energy resolution at the 76Ge double-β decay Q-value (2039 keV), referred to as Qββ hereafter, as compared to other detector types. Previous studies have demonstrated the excellent performance of inverted coaxial (IC) point contact Ge detectors [7,8] Their new design allows to increase the detector mass of Broad Energy Ge (BEGe) [9] and P-type, point contact (PPC) [10] detectors from 0.7–1.0 kg up to 2.0–3.0 kg. The amount of surrounding radioactive components like cables and mechanical supports are lowered per detector mass as well as the surface-to-volume ratio. Final results within the Gerda LAr cryostat after 18 months of operation are shown in the last section
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