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

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 ${\phi }_{\mathrm{l}\mathrm{i}\mathrm{m}}\le 4.01\times {10}^1\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$ 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, ${\mathrm{\Phi }}_{\mathrm{S}\mathrm{S}\mathrm{M}}(E>8\mathrm{M}\mathrm{e}\mathrm{V})$. 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.