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 $\phi_{\mathrm{lim}}\le 4.01\times10^{1}\ \mathrm{cm^{-2}\,s^{-1}}$ and a probability of $P_{\nu_e\rightarrow\bar{\nu}_e}\le 2.07\times10^{-5}$, the latter normalized to the ${}^8$B flux above threshold, $\Phi_{\rm SSM}(E>8~\mathrm{MeV})$. Assuming transverse solar magnetic fields of $B_\perp=50$ and $100$~kG, the corresponding magnetic-moment sensitivities are $\mu_\nu\le 7.27\times10^{-11}\,\mu_B$ and $3.64\times10^{-11}\,\mu_B$ 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.