New Constraint on Low-Mass Dark Photon Dark Matter with the Dark E-Field Radio Experiment

We report new limits on the kinetic mixing strength of dark photon dark matter spanning the mass range 0.21−1.24 μ⁢eV, corresponding to a frequency span of 50–300 MHz. The Dark E-field Radio experiment is a wideband, direct detection search for dark photon dark matter, located at the University of California, Davis. Our detector employs a wide-bandwidth E-field antenna moved to multiple positions in an RF-shielded room, a low noise amplifier, wideband analog-to-digital converter, followed by a 2^24-point fast Fourier transform. A signal-matched filter searches for signals with Q≈10^6. In nine days of integration, this system is capable of detecting dark photon signals corresponding to a kinetic mixing strength 𝜀 several orders of magnitude lower than previous limits. We find a 95% exclusion limit on 𝜀 over this mass range between 6 ×10^−15 and 6 ×10^−13, tracking the complex resonant mode structure in the shielded room. Future runs are discussed that will extend this search into hundreds of µeV and incorporate a mode-stirring apparatus currently undergoing testing.