Estimating JUNO's Sensitivity to Solar Neutrino-to-antineutrino Conversion and Neutrino Magnetic Moments

Abstract

We investigated JUNO's sensitivity to a possible conversion of solar neutrinos into antineutrinos via the spin-flavor precession (SFP) mechanism, and assessed the implications for constraining the neutrino-magnetic moment (NMM). Using a sensitivity-based framework appropriate for counting experiments with no prior observations, we derive 90\% C.L.\ ensemble-average sensitivities on the solar antineutrino flux for 1.8--16.8 MeV and 8.0--16.8 MeV. For the entire energy window, the results do not improve the restrictions of other experiments; the relevance occurs in the highes-energy window. In this window, we report a flux of ${\varphi }_{\lim }\le 4.01\times 10^1\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$ and a probability of $P_{{\nu }_e\to {\bar{\nu }}_e}\le 2.07\times 10^{-5}$, the latter normalized to the ${}^8$B flux above threshold, ${\Phi }_{\mathrm{SSM}}(E>8\mathrm{MeV})$. Assuming transverse solar magnetic fields of $B_{\perp }=50$ and $100$~kG, the corresponding magnetic-moment sensitivities are ${\mu }_{\nu }\le 7.27\times 10^{-11}{\mu }_B$ and $3.64\times 10^{-11}{\mu }_B$ in the high-energy window. These results highlight that JUNO has the potential to achieve sensitivities comparable to the most stringent astrophysical limits; in particular, the high-energy selection (8.0--16.8~MeV) provides a sensitivity that is competitive with current results, while the full-energy window remains primarily limited by near-reactor backgrounds.

Accepted for publication in ApJ

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