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2d ago

NOvA and T2K Combine to Set Sub-2% Neutrino Mass-Splitting Benchmark

The Nature paper confirms compatibility, setting constraints that hinge on whichever mass ordering future studies reveal.

Scientists use a raft inside the Super-Kamiokande neutrino detector located about one km underground under Mount Ikeno near the city of Hida, Japan, in this undated handout image obtained by Reuters on October 22, 2025. Kamioka Observatory/ICRR (Institute for Cosmic Ray Research)/University of Tokyo/Handout via REUTERS
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Hyper-Kamiokande is open to the press as excavation of the cavity nears completion, Hida City, Gifu Prefecture, Japan, on June 28, 2025. The Hyper-Kamiokande project aims to elucidate the evolutionary history of the universe and a unified theory of elementary particles through the discovery of neutrino CP violation (differences in the properties of neutrinos and antineutrinos), the observation of supernova explosion neutrinos, and the discovery of proton decay, by using an ultra-large underground neutrino observatory consisting of a gigantic water tank and ultra-sensitive light sensors that surpasses the current Super-Kamiokande, and by improving the neutrino beam from the J-PARC accelerator. ( The Yomiuri Shimbun )
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Overview

  • Pooling nearly a decade of long-baseline data, the U.S. NOvA and Japan’s T2K collaborations published a joint oscillation analysis in Nature on Oct. 22.
  • The study measures the tiny mass gap between two neutrino states with less than 2% uncertainty, marking one of the field’s most precise results.
  • The combined dataset does not resolve whether the neutrino mass ordering is normal or inverted, showing no preference for either scenario.
  • The analysis implies that, if an inverted ordering is later established, the joint data would indicate a neutrino–antineutrino asymmetry relevant to explaining matter’s dominance.
  • Despite different energies, baselines and detector designs, the experiments’ results are compatible, with decisive tests expected from DUNE, Hyper-Kamiokande, JUNO and SNO+ later this decade.