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| NEMO-3 | |
|---|---|
| Name | NEMO-3 |
| Mission | Double beta decay search |
| Site | Modane Underground Laboratory |
| Duration | 2003–2011 |
| Status | Completed |
NEMO-3 NEMO-3 was a particle physics experiment that operated at the Modane Underground Laboratory searching for rare processes associated with double beta decay and neutrino mass measurements. The project involved collaborations among institutions such as the CEA, CNRS, IN2P3, University of Manchester, and IEAP Prague, and contributed to global efforts alongside experiments like GERDA, EXO-200, KamLAND-Zen, and CUORE. The detector combined tracking and calorimetry techniques developed in the traditions of Nuclear emulsion and Time Projection Chamber experiments to study isotopes including ^100Mo, ^82Se, ^48Ca, and ^150Nd.
NEMO-3 was designed to detect both two-neutrino double beta decay and neutrinoless double beta decay to probe Majorana fermion properties and lepton-number violation relevant to theories such as seesaw mechanism and leptogenesis. The collaboration aimed to set limits on the effective Majorana neutrino mass and to measure half-lives of isotopes used by nuclear-structure models like the Quasiparticle Random Phase Approximation and shell-model calculations developed by groups including those at University of Tübingen and Los Alamos National Laboratory. The experiment's hybrid design provided topological and calorimetric event reconstruction to distinguish signal from backgrounds studied by contemporaneous projects including SNO+ and SuperNEMO.
The detector comprised a cylindrical arrangement of source foils, a tracking chamber with drift cells, and a calorimeter made of plastic scintillators coupled to photomultiplier tubes, drawing on technologies pioneered at CERN and LAL-Orsay. Source isotopes such as ^100Mo and ^82Se were prepared by teams at IN2P3 and ITEP, mounted in thin foils to minimize scattering and energy loss, while a wire chamber provided vertex and track curvature information used in combination with magnetic fields similar to those applied in the OPERA and Borexino experiments. The calorimeter measured electron energies with timing resolution informed by developments at SLAC and NERSC, and the whole assembly sat inside a passive shielding array of lead and iron with radon suppression measures inspired by Gran Sasso National Laboratory practices.
Installed in Hall A of the Modane Underground Laboratory beneath the Alps, the experiment benefited from overburden provided by the Frejus Road Tunnel to reduce cosmic ray muon flux, paralleling site choices made by MACRO and Frejus experiment collaborations. NEMO-3 began data taking in 2003 and ran through 2011, with operations managed by institutes including CEA Saclay and University of Manchester; maintenance periods and calibrations referenced standards from National Physical Laboratory and used radioactive sources such as ^207Bi and ^90Sr for energy-scale calibration. Environmental monitoring and slow-control systems echoed practices from IceCube and Kamioka Observatory.
Event selection combined topological track reconstruction and calorimetric energy sums to isolate two-electron final states, employing pattern-recognition algorithms and reconstruction codes influenced by software frameworks from ROOT and analysis techniques developed at DESY. Monte Carlo simulations used packages and cross-section libraries curated by GEANT4 and benchmarked against measurements from CERN NA48 and JINR Dubna experiments; statistical treatments applied maximum-likelihood fits, Feldman–Cousins intervals, and Bayesian limits similar to those used by LUX and XENON100. Background model validation relied on external assay data from ORNL and NIST, and blind-analysis procedures mirrored practices at BaBar and Belle.
Primary goals included precision measurement of two-neutrino double beta decay half-lives and setting competitive limits on neutrinoless decay modes to constrain effective Majorana mass and mechanisms such as heavy-particle exchange studied in Left–right symmetric model frameworks. NEMO-3 published half-life results for ^100Mo, ^82Se, ^48Ca, and ^150Nd which informed nuclear matrix element calculations by groups at University of Jyväskylä and CEA. Limits on neutrinoless double beta decay were reported that complemented constraints from KamLAND-Zen and GERDA, influencing global fits of neutrino mass parameters performed by collaborations including Particle Data Group and model studies from Perimeter Institute.
Background control addressed internal contamination from isotopes like ^214Bi and ^208Tl originating in source foils and detector materials, with screening campaigns employing gamma spectroscopy at facilities such as LSC and Gran Sasso assay labs. External backgrounds from radon progeny and cosmic-induced neutrons were mitigated using radon suppression and shielding methods similar to Borexino purification campaigns and muon veto strategies employed by Super-Kamiokande. Systematic uncertainties included energy calibration, reconstruction efficiencies, and nuclear matrix element model dependence discussed in literature from Argonne National Laboratory and GSI Helmholtz Centre.
NEMO-3 left a technical and scientific legacy, motivating the design of the SuperNEMO demonstrator and shaping detector concepts for next-generation projects such as LEGEND and nEXO. Its event topology approach influenced hybrid tracking–calorimetry proposals considered at CERN and in proposals at SNOLAB and informed radiopurity protocols adopted by CUORE and SNO+. Data and techniques from NEMO-3 continue to be referenced by collaborations at IPHC Strasbourg and theory groups at Universität Dortmund and University of Sussex in ongoing efforts to resolve the Majorana nature of neutrinos.
Category:Particle physics experiments Category:Neutrino experiments Category:Underground laboratories