neutrinoless double beta decay

neutrinoless double beta decay
Name	Neutrinoless double beta decay

neutrinoless double beta decay is a hypothetical radioactive decay process in which an atomic nucleus emits two electrons without accompanying antineutrinos, violating lepton number conservation and implying that neutrinos are Majorana fermions. The process, if observed, would profoundly affect understanding in particle physics and cosmology, impacting theories associated with Enrico Fermi, Wolfgang Pauli, Bruno Pontecorvo, Peter Higgs, and institutions like CERN and Fermi National Accelerator Laboratory. Major experimental collaborations and observatories such as Super-Kamiokande, Sudbury Neutrino Observatory, KamLAND-Zen, GERDA, and EXO have driven searches and set limits.

Introduction

Neutrinoless double beta decay is framed within research programs led by groups at Lawrence Berkeley National Laboratory, Gran Sasso National Laboratory, SNOLAB, Oak Ridge National Laboratory, and Institut Laue-Langevin, and is motivated by foundational work from Marie Curie and Enrico Fermi on beta decay and nuclear transmutation. Interest is shared across projects like Majorana Demonstrator, CUORE, NEMO-3, SNO+, and collaborations involving Max Planck Society and Brookhaven National Laboratory. The search connects to theoretical proposals from Abdus Salam, Steven Weinberg, Sheldon Glashow, and Gerard 't Hooft and leverages detectors developed at Lawrence Livermore National Laboratory and Los Alamos National Laboratory.

Theoretical Background and Mechanisms

The mechanism revolves around whether neutrinos are Dirac or Majorana particles, a question debated in seminars at Institute for Advanced Study, Perimeter Institute, and departments at Harvard University, Princeton University, Oxford University, and University of Cambridge. The canonical light Majorana exchange mechanism was developed following ideas by Wolfgang Pauli and Bruno Pontecorvo, extended in frameworks by Tsung-Dao Lee, Chen-Ning Yang, Murray Gell-Mann, and formalized with operators used in work by Ettore Majorana. Alternative mechanisms invoke heavy sterile neutrinos as in models discussed at Fermi National Accelerator Laboratory and Institut de Physique Théorique (CEA), left-right symmetric models related to papers from Rudolf Haag and Mohapatra and Pati, and supersymmetric contributions explored in contexts linked to Stanford University and California Institute of Technology research groups. Nuclear matrix elements required for rate predictions are computed with methods associated with Oak Ridge National Laboratory's nuclear theory groups, relying on configurations studied at Paul Scherrer Institute and using many-body techniques advanced by researchers affiliated with Los Alamos National Laboratory.

Experimental Searches and Techniques

Search strategies exploit isotopes undergoing two-neutrino double beta decay such as Germanium-76 in GERDA and MAJORANA setups, Xenon-136 in EXO and KamLAND-Zen, Tellurium-130 in CUORE, and Molybdenum-100 in NEMO-3 and proposed AMoRE projects. Detector technologies include high-purity germanium detectors developed at Broadcom Inc. and Canberra Industries, time projection chambers used by collaborations associated with Lawrence Berkeley National Laboratory, bolometers realized at Gran Sasso National Laboratory, and liquid scintillator systems deployed by teams from Tohoku University and University of Tokyo. Background mitigation techniques are refined in facilities such as Sudbury Neutrino Observatory Laboratory and Laboratori Nazionali del Gran Sasso through shielding strategies inspired by work at SLAC National Accelerator Laboratory and Argonne National Laboratory, and underground siting choices informed by geology studies near Homestake Mine and Boulby Mine. Calibration and analysis pipelines draw on software and statistical methods used in experiments at CERN and in astrophysical observatories like IceCube.

Current Results and Limits

Current null results and half-life limits are reported by collaborations including GERDA, MAJORANA Demonstrator, CUORE, KamLAND-Zen, EXO-200, and NEMO-3, and are summarized in review articles from groups at Institute of High Energy Physics (China), KEK, and Institut de Physique Nucléaire d'Orsay. These experiments constrain the effective Majorana mass parameter with ranges interpreted in light of nuclear matrix element computations from TRIUMF, GSI Helmholtz Centre for Heavy Ion Research, and RIKEN. Claims of observation have been critically assessed with reference to analyses by researchers at University of Heidelberg and Max Planck Institute for Nuclear Physics, and experimental limits are regularly updated in conferences such as Neutrino Oscillation Workshop, International Conference on Neutrino Physics and Astrophysics, and meetings at European Physical Society events.

Implications for Particle Physics and Cosmology

Observation would confirm lepton number violation, influence baryogenesis scenarios like leptogenesis developed by Gianfranco Bertone-adjacent theorists and concepts from Kenneth G. Wilson-influenced field theory methods, and constrain mass models discussed at CERN Theory Department and Institute for Advanced Study. Cosmological consequences intersect with analyses from Planck (spacecraft), Wilkinson Microwave Anisotropy Probe, and structure formation studies by groups at Max Planck Institute for Astrophysics and Caltech. Connections extend to sterile neutrino hypotheses explored at Fermi National Accelerator Laboratory and to grand unified theories proposed at University of Chicago and MIT, affecting parameters relevant to experiments at Large Hadron Collider and precision measurements at National Institute of Standards and Technology.

Future Prospects and Proposed Experiments

Next-generation projects include ton-scale and multi-ton experiments proposed by collaborations tied to DUNE efforts at Fermilab, scale-up plans for nEXO connected to SNOLAB infrastructure, upgrade paths for LEGEND building on GERDA and MAJORANA techniques, and proposals such as CUPID and NEXT developed with teams from Gran Sasso National Laboratory, Lawrence Berkeley National Laboratory, and University of California, Berkeley. International coordination involves agencies like European Research Council, Japan Society for the Promotion of Science, US Department of Energy, and partnerships with Canadian Space Agency-partnered facilities. Sensitivity goals aim to probe effective Majorana masses in parameter space motivated by neutrino oscillation results from Super-Kamiokande, SNO, and Daya Bay, with anticipated physics reach discussed at workshops convened by International Atomic Energy Agency and institutes such as Perimeter Institute.

Category:Neutrino physics