Neutrinoless double-beta decay search with the LEGEND experiment

TL;DR

The paper discusses the LEGEND experiment's efforts to detect neutrinoless double-beta decay using germanium-76, reporting initial data analysis, background levels, and sensitivity improvements over previous experiments.

Contribution

It introduces the LEGEND experiment's first results and its potential to significantly improve the sensitivity for neutrinoless double-beta decay detection.

Findings

LEGEND-200 analyzed 48.3 kg·yr of data with low background levels.

Combined data sets set a half-life sensitivity of over 2.8×10^{26} years.

The experiment aims to reach a background index of 2×10^{-4} counts/(keV·kg·yr).

Abstract

Neutrinoless double-beta decay is a nuclear decay, given as $(A,Z) \rightarrow (A, Z+2) +2e^{-}$, with deep consequences for the understanding of our universe. A strong experimental program is underway to search for this transition with many proposed experiments using different technologies. In this article the LEGEND experiment, which uses $^{76}$Ge as the isotope of interest, will be described. We will discuss both the first stage, LEGEND-200, which is now taking data at the Laboratori Nazionali del Gran Sasso of INFN in Italy, and the future stage, LEGEND-1000. LEGEND-200 has analyzed a first sample of data (48.3 kg$\cdot$yr) collected from March 2023 to February 2024 with a background index not far away from its goal of 2$\times$10$^{-4}$ cnts/(keV$\cdot$kg$\cdot$yr). Combining the LEGEND-200 data with those of \textsc{Gerda}\ and \textsc{Majorana Demonstrator}\ one obtains a sensitivity on the half-life of 0$\nu\beta\beta$ decay in $^{76}$Ge of $T_{1/2} > $ 2.8 $\times$ 10$^{26}$ yr at 90\% C.L. and a limit on $T_{1/2} > $ 1.9 $\times$ 10$^{26}$ yr at 90\% C.L.