英国の科学者、第四のニュートリノ存在を否定—新しい物理学の手がかりに (UK scientists rule out fourth neutrino in search for new physics)

2025-12-03 英国研究イノベーション機構（UKRI）

＜関連情報＞

• https://www.ukri.org/news/uk-scientists-rule-out-fourth-neutrino-in-search-for-new-physics/
• https://www.nature.com/articles/s41586-025-09757-7

MicroBooNEで2本のニュートリノビームによる軽いステライルニュートリノの探索 Search for light sterile neutrinos with two neutrino beams at MicroBooNE

The MicroBooNE Collaboration
Nature  Published:03 December 2025
DOI:https://doi.org/10.1038/s41586-025-09757-7

Abstract

The existence of three distinct neutrino flavours, ν_e, ν_μ and ν_τ, is a central tenet of the Standard Model of particle physics^1,2. Quantum-mechanical interference can allow a neutrino of one initial flavour to be detected sometime later as a different flavour, a process called neutrino oscillation. Several anomalous observations inconsistent with this three-flavour picture have motivated the hypothesis that an additional neutrino state exists, which does not interact directly with matter, termed as ‘sterile’ neutrino, ν_s (refs. ^{3,4,5,6,7,8,9}). This includes anomalous observations from the Liquid Scintillator Neutrino Detector (LSND)³ experiment and Mini-Booster Neutrino Experiment (MiniBooNE)^4,5, consistent with ν_μ → ν_e transitions at a distance inconsistent with the three-neutrino picture. Here we use data obtained from the MicroBooNE liquid-argon time projection chamber¹⁰ in two accelerator neutrino beams to exclude the single light sterile neutrino interpretation of the LSND and MiniBooNE anomalies at the 95% confidence level (CL). Moreover, we rule out a notable portion of the parameter space that could explain the gallium anomaly^6,7,8. This is one of the first measurements to use two accelerator neutrino beams to break a degeneracy between ν_e appearance and disappearance, which would otherwise weaken the sensitivity to the sterile neutrino hypothesis. We find no evidence for either ν_μ → ν_e flavour transitions or ν_e disappearance that would indicate non-standard flavour oscillations. Our results indicate that previous anomalous observations consistent with ν_μ → ν_e transitions cannot be explained by introducing a single sterile neutrino state.