Abstract
In the global landscape of neutrinoless double beta (0νββ) decay search, the use of semiconductor germanium detectors provides many advantages. The excellent energy resolution, the negligible intrinsic radioactive contamination, the possibility of enriching the crystals up to 88% in the 76Ge isotope as well as the high detection efficiency, are all key ingredients for highly sensitive 0νββ decay search. The Majorana and Gerda experiments successfully implemented the use of germanium (Ge) semiconductor detectors, reaching an energy resolution of 2.53 ± 0.08 keV at the Qββ and an unprecedented low background level of 5.2×10−4 cts/(keV·kg·yr), respectively. In this paper, we will review the path of 0νββ decay search with Ge detectors from the original idea of E. Fiorini et al. in 1967, to the final recent results of the Gerda experiment setting a limit on the half-life of 76Ge 0νββ decay at T1/2>1.8×1026 yr (90% C.L.). We will then present the LEGEND project designed to reach a sensitivity to the half-life up to 1028 yr and beyond, opening the way to the exploration of the normal ordering region.
Highlights
The evidence for non-zero neutrino masses as a consequence of the neutrino oscillation discovery [1,2,3,4] provides, among others, a hint of physics beyond the Standard Model (SM)
The detector itself is the source of 0νββ-decay, and different technologies can be implemented: a single phase Time Projection Chamber (TPC) using Liquid Xenon (LXe), such as EXO-200 [29], a high-pressure TPC with Gaseous Xenon (GXe), such as [30], or a Xe-loaded liquid scintillator, such as KamLAND-Zen [31]
We reviewed the successful story of the experiments employing germanium semiconductor detectors in the search for the 0νββ transition of 76 Ge
Summary
The evidence for non-zero neutrino masses as a consequence of the neutrino oscillation discovery [1,2,3,4] provides, among others, a hint of physics beyond the Standard Model (SM). Despite many experimental efforts carried out about neutrino physics since the first pioneering experiment by Reines ad Cowan in 1956 [5], there are still open points to be clarified such as the neutrino nature, the mass ordering and the absolute mass scale. We will review the story of the 0νββ decay search of 76 Ge with germanium semiconductor detectors. A review of the main aspects of the 0νββ theory will be presented. In the fifth and sixth section, we will summarize the main characteristics, performance and results of the contemporary G ERDA and M AJORANA experiments currently leading the field with the best sensitivity, the lowest background level and the best resolution among all the other 0νββ decay experiments. In the seventh section, we will present the LEGEND project conceived to extend the sensitivity up to 1028 yr to fully cover the inverted hierarchy region
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