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Search for proton decay via

p \to e^{+} η

and

p \to μ^{+} η

with a 0.37 Mton-year exposure of Super-Kamiokande

https://doi.org/10.1103/PhysRevD.110.112011

Taniuchi, N; Abe, K; Abe, S; Asaoka, Y; Bronner, C; Harada, M; Hayato, Y; Hiraide, K; Hosokawa, K; Ieki, K; et al (December 2024, Physical Review D)

A search for proton decay into

e^{+} / μ^{+}

and a

η

meson has been performed using data from a

0.373 Mton \cdot year

exposure (6050.3 live days) of Super-Kamiokande. Compared to previous searches this work introduces an improved model of the intranuclear

η

interaction cross section, resulting in a factor of 2 reduction in uncertainties from this source and

\sim 10 %

increase in signal efficiency. No significant data excess was found above the expected number of atmospheric neutrino background events resulting in no indication of proton decay into either mode. Lower limits on the proton partial lifetime of

1.4 \times 10^{34} years

for

p \to e^{+} η

and

7.3 \times 10^{33} years

for

p \to μ^{+} η

at the 90% CL were set. These limits are around 1.5 times longer than our previous study and are the most stringent to date. Published by the American Physical Society2024

Free, publicly-accessible full text available December 1, 2025

The Super-Kamiokande and T2K Collaborations present a joint measurement of neutrino oscillation parameters from their atmospheric and beam neutrino data. It uses a common interaction model for events overlapping in neutrino energy and correlated detector systematic uncertainties between the two datasets, which are found to be compatible. Using 3244.4 days of atmospheric data and a beam exposure of

19.7 (16.3) \times 10^{20}

protons on target in (anti)neutrino mode, the analysis finds a

1.9 σ

exclusion of

C P

conservation (defined as

J_{C P} = 0

) and a

1.2 σ

exclusion of the inverted mass ordering. Published by the American Physical Society2025

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