LEGEND-200

LEGEND-200
Name	LEGEND-200
Location	Gran Sasso National Laboratory
Start date	2019
Type	Neutrinoless double beta decay search
Participants	LEGEND Collaboration

LEGEND-200 LEGEND-200 is a physics experiment searching for neutrinoless double beta decay using enriched germanium detectors deployed at the Laboratori Nazionali del Gran Sasso site. The project follows on techniques developed by the GERDA and MAJORANA Demonstrator experiments and aims to probe the Majorana fermion nature of the neutrino and the violation of lepton number. The collaboration brings together institutions from across Europe, North America, and Asia to pursue high-sensitivity measurements in a deep-underground environment.

Overview

LEGEND-200 operates within the infrastructure of the Laboratori Nazionali del Gran Sasso and builds directly on predecessor programs such as GERDA Phase II and the MAJORANA Demonstrator. The scientific goals relate to fundamental questions addressed in programs like the Neutrino Platform and by experiments including KamLAND-Zen, CUORE, EXO-200, and SNO+. The collaboration interfaces with funding agencies and oversight bodies such as the European Research Council, the National Science Foundation, and national laboratories like Lawrence Berkeley National Laboratory and Brookhaven National Laboratory.

Experimental Design and Setup

The experimental design centers on arrays of high-purity germanium-76 detectors operated as ionization detectors in a cryogenic environment, following design principles employed by GERDA and the MAJORANA Demonstrator. The setup places detectors in a low-background cryostat immersed in liquid argon at the Gran Sasso National Laboratory underground site to exploit shielding from cosmic-ray muons analogous to locations used by Super-Kamiokande and Sudbury Neutrino Observatory. The layout integrates systems developed at institutions such as Max Planck Institute for Nuclear Physics, Lawrence Livermore National Laboratory, and University of Washington to manage cryogenics, cabling, and low-radioactivity materials.

Detector Technology

Detectors are p-type point contact (PPC) and inverted coaxial high-purity germanium units enriched in germanium-76 to increase sensitivity to neutrinoless double beta decay, leveraging technologies refined by MAJORANA and GERDA. Each detector incorporates low-mass, low-radioactivity mounts and signal readout chains developed with expertise from groups at Pacific Northwest National Laboratory and Oak Ridge National Laboratory. Signal processing uses digital electronics patterned after systems at CERN and institutions like Fermi National Accelerator Laboratory, with pulse-shape discrimination techniques similar to those used in COHERENT and XENON1T to reject multi-site events and surface backgrounds.

Data Collection and Analysis

Data acquisition follows protocols used by large-scale projects including ATLAS, CMS, and neutrino observatories such as IceCube to ensure robust triggers, slow-control integration, and calibration campaigns. Calibration uses gamma-ray sources and deployment systems comparable to those developed at Institut für Kernphysik, Center for Underground Physics, and Enrico Fermi Institute. Analysis pipelines implement background modeling and statistical inference techniques in common with efforts at European Organization for Nuclear Research and universities such as Massachusetts Institute of Technology and University of Oxford, applying likelihood fits, Bayesian inference, and blind-analysis methods similar to those in Planck and LIGO Scientific Collaboration publications.

Backgrounds and Shielding

The experiment mitigates backgrounds from radon progeny, cosmogenic activation, and radioactive impurities drawing on material-screening programs associated with SNOLAB, Boulby Underground Laboratory, and Canfranc Underground Laboratory. Passive shielding includes layers inspired by designs used at Borexino and Daya Bay, while active veto systems employ liquid argon scintillation detection with wavelength-shifting and photodetectors comparable to components developed for DEAP-3600 and Double Chooz. Muon veto and overburden considerations mirror practices at Gran Sasso and deep sites such as Sudbury to suppress cosmic-ray induced backgrounds.

Results and Sensitivity

LEGEND-200 targets a half-life sensitivity for neutrinoless double beta decay in germanium-76 competitive with, and intended to improve upon, limits set by GERDA and MAJORANA Demonstrator. Projected effective Majorana neutrino mass reach is compared with implied ranges from neutrino oscillation results reported by Super-Kamiokande, NOvA, T2K, and global fits such as those from the Particle Data Group. Interim results and background indices are benchmarked against achievements from KamLAND-Zen, CUORE, and EXO-200, with discovery potential contingent on achieved background reduction and exposure accumulated by collaboration sites including groups at University of Manchester and University of Milano-Bicocca.

Collaboration and Funding

The collaboration includes institutions and research groups from countries represented in projects like European Research Council-funded consortia and national programs supported by agencies such as the Deutsche Forschungsgemeinschaft, Natural Sciences and Engineering Research Council, and Japan Society for the Promotion of Science. Management and technical coordination draw on the governance models used by collaborations at CERN, SLAC National Accelerator Laboratory, and multinational experiments like ALICE and Belle II. Industrial partners supply purification, cryogenic, and detector fabrication services used by laboratories including Pirelli, Borealis AG, and specialized vendors collaborating with INFN and other institutes.

Category:Neutrino experiments Category:Particle physics experiments Category:Underground laboratories