[Paper Review] LEGEND-1000 Preconceptual Design Report

LEGEND Collaboration|arXiv (Cornell University)|Jul 23, 2021

Color Science and Applications3 references52 citations

TL;DR

LEGEND-1000 aims to build a ton-scale, 76Ge-based neutrinoless double-beta decay experiment with an active liquid argon shield to reach discovery sensitivity beyond 10^28 years half-life and probe neutrino masses in the inverted ordering region.

ABSTRACT

Parallel talk presented at the XXI International Workshop on Neutrino Telescopes - Padova 29 September - 3 October 2025 (https://agenda.infn.it/event/44606/) On behalf of the LEGEND Collaboration Abstract: The LEGEND experiment searches for the neutrinoless double-beta (0νββ) decay of Ge-76 using isotopically-enriched high-purity germanium (HPGe) detectors with the ultimate discovery sensitivity beyond a half-life of 10^28 years. The project is conducted in stages. The first one, LEGEND-200, was steadily accumulating physics data at LNGS (Laboratori Nazionali del Gran Sasso, Italy) for more than one year with 140 kg of HPGe detectors. In 2024 the Collaboration unblinded the first data to check the sensitivity of the experiment and study the composition of the LEGEND-200 background, which was slightly higher than predicted based on screening measurements of the components. The detector array was subsequently disassembled to investigate the source of the elevated background, with nearby components undergoing re-cleaning and/or replacement as necessary. LEGEND-200 is scheduled to resume data taking in 2025. In this talk we will present the performance of the ongoing experiment and give an update on the status of its second phase: LEGEND-1000. Funds: This work is supported by the U.S. DOE and the NSF, the LANL, ORNL and LBNL LDRD programs; the European ERC and Horizon programs; the German DFG, BMBF, and MPG; the Italian INFN; the Polish NCN and MNiSW; the Czech MEYS; the Slovak RDA; the Swiss SNF; the UK STFC; the Canadian NSERC and CFI; the LNGS and SURF facilities.

Motivation & Objective

• Motivate and justify a ton-scale search for neutrinoless double-beta decay (0νββ) using enriched 76Ge Detectors.
• Define a baseline LEGEND-1000 design leveraging prior Gerda and Majorana Demonstrator innovations.
• quantify discovery potential and background goals to cover the inverted neutrino mass ordering region.
• Outline the modular LEGEND-1000 approach, including detector, shielding, and underground-laboratory requirements.

Proposed method

• Utilize 1000 kg of Ge detectors enriched to >90% in 76Ge arranged in four 250-kg modules with ~400 ICPC crystals.
• Immerse Ge detectors in radiopure underground liquid argon (UGLAr) as an active shield and use LAr scintillation light for background rejection.
• Achieve superb energy resolution with FWHM ~0.12% at Qββ and apply pulse-shape discrimination to separate bulk 0νββ events from backgrounds.
• Employ multivariate event topology discrimination leveraging detector granularity and LAr veto to suppress backgrounds to <1×10^-5 cts/(keV kg yr).
• Phase in with LEGEND-200 experience using inverted-coaxial point-contact detectors to scale mass and maintain resolution.

Experimental results

Research questions

• RQ1 What is the discovery potential of LEGEND-1000 for 0νββ decay in 76Ge given projected backgrounds and energy resolution?
• RQ2 Can a 1000 kg 76Ge ensemble reach a 0νββ half-life sensitivity beyond 10^28 years and probe mββ in the 9–21 meV range over ~10 years?
• RQ3 How do detector design, active LAr shielding, and underground location influence background suppression and signal extraction?
• RQ4 What are the required facilities, materials, and data-analysis approaches to achieve quasi-background-free operation?
• RQ5 What is the feasibility and timeline for deploying a four-module, 400-detector array with phased commissioning?

Key findings

• LEGEND-1000 targets a discovery sensitivity at 99.7% CL with a 50% chance of observing a 3σ signal for 0νββ beyond 10^28 years half-life.
• Projected mββ sensitivity is in the range 9–21 meV over 10 years of live time in inverted ordering.
• Background goal is less than 1×10^-5 counts/(keV kg yr) through multiple mitigation strategies (ICPC detectors, LAr veto, UG LAr, and ultra-clean materials).
• The design builds on LEGEND-200 developments, achieving >2× mass per crystal and excellent energy resolution, enabling a quasi-background-free search.
• The experimental setup emphasizes a fully contained single-site energy deposition at Qββ with no concurrent detector signals as a 0νββ signature.