Neutrino electromagnetic properties after the first $pp$ solar neutrino observation at XENONnT

Abstract

The XENONnT Collaboration has recently reported the first measurement of low-energy solar neutrinos through elastic neutrino-electron scattering in a dark matter detector, opening a new window on Standard Model predictions and on neutrino electromagnetic properties. We analyze these data to extract the $pp$ neutrino flux normalization and the weak mixing angle at low momentum transfer ($\sim 0.1$ MeV). We also derive bounds on the neutrino charge radii, magnetic moments, and millicharges, as well as on the sterile-neutrino dipole portal. Since the $pp$-flux determination displays a mild excess, we further investigate the role of the $^{14}$C background in the fit and assess how it affects the extracted parameters. Our results show that dark matter detectors now offer a probe of neutrino physics that is complementary to dedicated precision experiments.