LEGEND Collaboration

LEGEND Collaboration
Name	LEGEND Collaboration
Type	Scientific collaboration
Purpose	Neutrinoless double-beta decay search

LEGEND Collaboration

The LEGEND Collaboration is an international scientific consortium focused on searching for neutrinoless double beta decay using high-purity germanium detectors enriched in germanium-76. Founded by groups with prior roles in GERDA and MAJORANA Demonstrator, the Collaboration brings together institutions and national laboratories from Europe and North America to pursue a breakthrough in understanding the Majorana fermion nature of neutrinos, its implications for the matter–antimatter asymmetry, and connections to physics beyond the Standard Model.

Overview

LEGEND consolidates expertise from experiments such as GERDA and MAJORANA Demonstrator to implement a staged program of increasingly sensitive searches for neutrinoless double-beta decay in germanium-76. The project is situated at underground laboratories including Laboratori Nazionali del Gran Sasso, Sanford Underground Research Facility, and has collaborations with institutes such as Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, and CERN. The Collaboration leverages techniques developed in low-background physics and radiopurity screening pioneered by groups involved with XMASS, EXO-200, CUORE, and KamLAND-Zen.

Scientific Goals

LEGEND aims primarily to determine whether neutrinos are their own antiparticles (Majorana particles), which would demonstrate lepton number violation and provide insight into mechanisms like the seesaw mechanism that generate neutrino mass. A confirmed observation of neutrinoless double-beta decay would constrain the effective Majorana neutrino mass and inform models associated with leptogenesis, grand unified theories studied at CERN and in proposals from laboratories including Fermilab and SLAC National Accelerator Laboratory. Secondary goals include precision measurements of two-neutrino double-beta decay spectra, contributions to nuclear matrix element determinations used by theorists connected to Institute for Nuclear Theory and Lawrence Livermore National Laboratory, and development of detector technologies transferrable to projects such as DARWIN (experiment) and DUNE.

Experimental Design and Detectors

LEGEND uses arrays of high-purity germanium detectors enriched to ~88–90% in germanium-76, operated in liquid argon cryostats with active veto systems derived from techniques used by GERDA and shielding approaches similar to MAJORANA Demonstrator. The staged program begins with LEGEND-200—deploying ≈200 kg of enriched detectors in the Laboratori Nazionali del Gran Sasso—and plans for LEGEND-1000 with ≈1000 kg hosted at facilities such as Sanford Underground Research Facility. Detector types include inverted coaxial and point-contact geometries developed with contributions from PNNL, MPIK, Max Planck Society, and university groups such as University of North Carolina at Chapel Hill and University of Washington. Background reduction strategies exploit materials screening by teams at SNOLAB, Pacific Northwest National Laboratory, and radiopurity facilities associated with Gran Sasso National Laboratory and Colorado State University. Signal identification employs pulse-shape discrimination, liquid argon scintillation readout technologies advanced at LNGS and instrumentation expertise from DESY and KIT.

Collaboration and Organization

LEGEND is organized as a multinational collaboration with institutional members from national laboratories and universities across United States Department of Energy-funded laboratories, European research centers, and Canadian institutes. The governance structure includes an executive board, technical boards for detector, cryogenics, and low-background activities, and working groups for data analysis and simulation, aligned with best practices from consortia such as ATLAS, CMS, and LIGO Scientific Collaboration. Key institutional participants include Lawrence Berkeley National Laboratory, Los Alamos National Laboratory, Oak Ridge National Laboratory, TRIUMF, and European partners like INFN, Helmholtz Association, and CNRS. Collaboration meetings are held at venues including Gran Sasso, CERN, and partner universities; publication and data policies draw on precedents from Double Chooz and SNO+.

Research Program and Timeline

The research program is staged: commissioning and operation of LEGEND-200, data-taking to reach a half-life sensitivity beyond 10^27 years, followed by design and deployment of LEGEND-1000 targeting sensitivity beyond 10^28 years for neutrinoless double-beta decay of germanium-76. Milestones include detector production schedules involving isotope enrichment providers with links to facilities used by MAJORANA Demonstrator, cryostat construction with contractors experienced by GERDA, and coordinated simulation efforts using codes from groups at CERN and Brookhaven National Laboratory. Timelines interface with grant cycles from agencies such as U.S. Department of Energy, European Research Council, and national funding bodies in Italy, Germany, and Canada.

Results and Publications

LEGEND builds on null-result constraints reported by GERDA and MAJORANA Demonstrator on the neutrinoless double-beta decay half-life of germanium-76, and on precision two-neutrino decay measurements feeding into nuclear matrix element analyses performed by theorists at Oak Ridge National Laboratory and Institut de Physique Nucléaire d'Orsay. Collaboration publications appear in journals commonly used by similar projects, with technical papers detailing detector performance, background models, and radiopurity assays authored by researchers affiliated with University of Oxford, Imperial College London, Technical University of Munich, and others. Conference presentations take place at meetings such as Neutrino Physics Conference, International Conference on High Energy Physics, and workshops hosted by Institute for Nuclear Theory.

Funding and Support

Funding and logistical support for LEGEND come from a mixture of national science agencies and laboratories, including agencies analogous to U.S. Department of Energy, National Science Foundation-supported programs, European Commission framework grants, and national research councils such as INFN, DFG, and NSERC. In-kind contributions include isotope enrichment services, cryostat fabrication from industrial partners used by prior experiments, and underground laboratory space provided by Laboratori Nazionali del Gran Sasso and Sanford Underground Research Facility. Collaborative resource sharing mirrors practices established by multinational projects such as CERN experiments and large-scale neutrino initiatives like DUNE.

Category:Neutrino experiments