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17h ago

Joint NOvA–T2K Analysis Strengthens Hint Neutrinos Behave Differently From Antineutrinos

The merged datasets improved precision on oscillation parameters relevant to the matter–antimatter puzzle.

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The world’s first neutrino observation in a hydrogen bubble chamber. It was found November 13, 1970, on this photograph from the Zero Gradient Synchrotron’s 12-foot bubble chamber. The invisible neutrino strikes a proton where three particle tracks originate (lower right). The neutrino turns into a mu-meson, the long center track (extending up and left). The short track is the proton. The third track (extending down and left) is a pi-meson created by the collision. Image credit: Argonne National Laboratory.
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Overview

  • The first-of-its-kind combined study by the NOvA and T2K collaborations, published in Nature, integrates long-baseline accelerator data in a single analysis.
  • NOvA sends neutrinos 810 kilometers from Fermilab to a 14,000-ton detector in Ash River, Minnesota, while T2K fires a beam 295 kilometers from J-PARC to Super-Kamiokande in Japan.
  • The joint result reports a developing asymmetry between neutrino and antineutrino oscillations, consistent with CP-symmetry violation, yet still short of a definitive claim.
  • Researchers estimate such oscillation behavior could have increased the early-universe matter-to-antimatter ratio by roughly one part per billion.
  • Detecting these rare events remains arduous, with heavy background rates and roughly one accelerator-born neutrino recorded per day in NOvA’s far detector.