Novel Limits on Dark Photon Mixing from Radiation Safety

I propose a novel laboratory search for dark photons based on radiation-safety monitoring at synchrotron radiation facilities, including NanoTerasu, SPring-8, the KEK Photon Factory, and the European Synchrotron Radiation Facility. Dark photons can be produced parasitically in undulators or via photon-mirror interactions and subsequently traverse optical systems and shielding. Taking into account quantum effects and the internal structure of undulators, mirrors, and detectors, I show that even a simple Geiger-Müller counter routinely used for radiation-safety monitoring can detect such dark photons outside the shielding and set the strongest purely laboratory limits on the kinetic mixing parameter, χ ≲ 5 × 10 − 6 , in the mass range 1–50 eV. Since radiation safety is strictly regulated, the resulting limits provide robust and realistic constraints.