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

TL;DR

This paper reviews the progress and challenges in constraining active and sterile neutrino masses through beta-ray spectra, highlighting experimental advancements, disproof of past claims, and future search directions.

Contribution

It provides a comprehensive overview of experimental techniques, historical claims, and new approaches in measuring neutrino masses via beta-ray spectroscopy, including sterile neutrino searches.

Findings

Upper limit for electron neutrino mass improved by three orders of magnitude.

Disproved previous claims of 30 eV and 17 keV neutrino masses.

Discussed future experimental approaches for sterile neutrino detection.

Abstract

Although neutrinos are probably the most abundant particles of the universe their mass is not yet known. Oscillation experiments have proven that at least one of the neutrino mass states has m_{i}>0.05 eV while various interpretations of cosmological observations yielded an upper limit for the sum of neutrino masses \sum m_{i}<(0.14-1.7) eV. The searches for the yet unobserved 0\nu\beta\beta decay result in an effective neutrino mass m_{\beta\beta}<(0.2-0.7) eV. The analyses of measured tritium \beta-spectra provide an upper limit for the effective electron neutrino mass m(\nu_e)<2 eV. In this review, we summarize the experience of two generations of \beta-ray spectroscopists who improved the upper limit of m(\nu_e) 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.