RESEARCH ARTICLE


Constraints on the Active and Sterile Neutrino Masses from Beta-Ray Spectra: Past, Present and Future1



Otokar Dragoun*, Drahoslav Vénos*
Nuclear Physics Institute of the ASCR, CZ-25068 Řež, Czech Republic


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© Dragoun and Venos; Licensee Bentham Open

open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution-Non-Commercial 4.0 International Public License (CC BY-NC 4.0) (https://creativecommons.org/licenses/by-nc/4.0/legalcode), which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

* Address correspondence to these authors at the Nuclear Physics Institute of the ASCR, CZ-25068 Řež, Czech Republic; Tel: 420-212-241-677; E-mail: dragoun@ujf.cas.cz, venos@ujf.cas.cz


Abstract

Although neutrinos are probably the most abundant fermions of the universe their mass is not yet known. Oscillation experiments have proven that at least one of the neutrino mass states has mi > 0.05 eV while various interpretations of cosmological observations yielded an upper limit for the sum of neutrino masses ∑mi < (0.14 ‒ 1.7) eV. The searches for the yet unobserved 0νββ decay result in an effective neutrino mass mββ < (0.2 ‒ 0.7) eV. The analyses of measured tritium β-spectra provide an upper limit for the effective electron neutrino mass m(ve) < 2 eV. In this review, we summarize the experience of two generations of β-ray spectroscopists who improved the upper limit of m(ve) by three orders of magnitude. We describe important steps in the development of radioactive sources and electron spectrometers, and recapitulate the lessons from now-disproved claims for the neutrino mass of 30 eV and the 17 keV neutrino with an admixture larger than 0.03%. We also pay attention to new experimental approaches and searches for hypothetical sterile neutrinos.

Keywords: Active neutrino, Beta-ray spectrum, Beta-spectrometer, Neutrino, Neutrino mass, Sterile neutrino.