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arXiv · 2605.16721

Towards Measuring the CP-Violating Phase with Atmospheric Neutrinos

John F. Beacom·Nicole F. Bell·Matthew J. Dolan·Stephan A. Meighen-Berger·Ho Man Yim
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Abstract

We propose a new approach to measuring the CP-violating phase in neutrino mixing using atmospheric neutrinos, differing significantly from prior work. We develop an up-down flux ratio for sub-GeV atmospheric neutrinos that incorporates realistic detection effects and reduces systematic uncertainties. For the example of Hyper-Kamiokande -- the first experiment with sufficient atmospheric-neutrino statistics in this energy range -- our approach can surpass the sensitivity of the Tokai to Hyper-Kamiokande (T2HK) long-baseline experiment near $\mathit{\delta_\mathrm{CP} = 90^\circ}$ and $\mathit{270^\circ}$. Realizing this potential will require additional, but realistic, work to reduce theoretical uncertainties. Success will provide an important, complementary probe to multi-\$1B accelerator-based experiments.

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John F. Beacom, Nicole F. Bell, Matthew J. Dolan, Stephan A. Meighen-Berger, Ho Man Yim. 2026-05-16. Towards Measuring the CP-Violating Phase with Atmospheric Neutrinos. https://arxiv.org/abs/2605.16721

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