Overview of the LEGEND-1000 experiment

The discovery of Neutrinoless double beta decay (0νββ) would have profound implications for neutrino physics and cosmology. It would provide unambiguous evidence for the Majorana nature of neutrinos, lepton number non-conservation and the absolute neutrino mass scale. The Large Enriched Germanium Experiment for Neutrinoless ββ decay (LEGEND) searches for 0νββ in the ⁷⁶Ge isotope. The proposed LEGEND-1000 phase will consist of 1000 kg of Ge detectors enriched to more than 90% in ⁷⁶Ge isotope, designed to achieve a discovery potential going beyond the inverted-ordering neutrino mass region. For 10 years of live time, LEGEND-1000 will probe 0νββ decay with 99.7% CL discovery sensitivity (a 50% chance of measuring a signal of at least 3σ significance for T_1/2^0ν of 1.3 × 10²⁸ of years) corresponding to a m_ββ upper limit in the range of 9–21 meV. The LEGEND-1000 will employ high-purity p-type, Inverted Coaxial Point Contact (ICPC) detectors with excellent energy resolution immersed in underground-sourced liquid argon (reduced in the ⁴²Ar isotope), allowing the rejection of backgrounds external to the Ge detector. The pulse shape analysis distinguishes bulk 0νββ events from multi-site events and surface backgrounds. By combining the lowest background and best energy resolution, LEGEND-1000 will perform a quasi-background-free search and can make an unambiguous discovery of 0νββ decay with just a handful of counts at Q_ββ - the decay Q value.