Exploring Anomaly-Free Dark Photon Models Through Solar Neutrino-Electron Scattering in Ton-Scale Dark Matter Detectors

We study the phenomenological implications of anomaly-free dark photon models using low-energy solar neutrino-electron elastic scattering data from the ton-scale PandaX-4T and XENONnT experiments. Focusing on $U(1{)}_X$ gauge extensions that incorporate both kinetic and mass mixing, we derive novel exclusion limits across the parameter spaces of six benchmark models. Our analysis demonstrates that the stringency of these limits is directly correlated with the theoretical leptonic charge assignments of the respective models. Additionally, we provide model-independent limits by isolating the pure kinetic and pure mass mixing scenarios. In the sub-MeV mediator mass regime, our results meaningfully improve upon existing limits from previous neutrino-electron scattering experiments, such as CHARM-II, TEXONO, and GEMMA. Ultimately, these findings yield improved limits on low-mass dark photon models, demonstrating their complementarity with other ventures in the global search for dark portals.