Current status of LEGEND: Searching for Neutrinoless Double-Beta Decay in $^{76}$Ge: Part I

TL;DR

This paper reviews the current status of LEGEND, a large-scale experiment using enriched germanium detectors to search for neutrinoless double-beta decay in $^{76}$Ge, aiming to explore the inverted neutrino mass hierarchy.

Contribution

It provides an overview of previous experiments and details the plan and initial status of the LEGEND project to achieve higher sensitivity in detecting neutrinoless double-beta decay.

Findings

GERDA and Majorana Demonstrator achieved low background rates.

LEGEND aims to build a ton-scale detector within a decade.

The first stage, LEGEND-200, is underway.

Abstract

Neutrinoless double-beta decay($0\nu\beta\beta$) decay is a hypothetical process that violates lepton number, and whose observation would unambiguously indicate that neutrinos are Majorana fermions. In the standard inverted-ordering neutrino mass scenario, the minimum possible value of m$_{\beta\beta}$ corresponds to a half-life around 10$^{28}$ yr for $0\nu\beta\beta$ decay in $^{76}$Ge, which is the target of the next generation of experiments. The current limits of GERDA and \textsc{Majorana Demonstrator} indicate a half-life higher than 10$^{26}$ yr. These experiments use high-purity germanium (HPGe) detectors that are highly-enriched in $^{76}$Ge. They have achieved the best intrinsic energy resolution and the lowest background rate in the signal search region among all $0\nu\beta\beta$ experiments. Taking advantage of these successes, a new international collaboration - the Large Enriched Germanium Experiment for Neutrinoless $\beta\beta$ Decay (LEGEND) - has been formed to build a ton-scale experiment with discovery potential covering the inverse-ordering neutrino mass range in a decade, following a phased approach. This first part of LEGEND proceedings describes GERDA and \textsc{Majorana Demonstrator} capabilities and the general plan of LEGEND to reach the goal, while the second part is focused in the status of the first stage of LEGEND, LEGEND-200.