New Limit on Dark Photon Kinetic Mixing in the 0. 2-1. 2 eV Mass Range From the Dark E-Field Radio Experiment

We report new limits on the kinetic mixing strength of the dark photon spanning the mass range 0. 21 -- 1. 24 eV corresponding to a frequency span of 50 -- 300 MHz. The Dark E-Field Radio experiment is a wide-band search for dark photon dark matter. In this paper we detail changes in calibration and upgrades since our proof-of-concept pilot run. Our detector employs a wide bandwidth E-field antenna moved to multiple positions in a shielded room, a low noise amplifier, wideband ADC, followed by a 2^24-point FFT. An optimal filter searches for signals with Q 10⁶. In nine days of integration, this system is capable of detecting dark photon signals corresponding to several orders of magnitude lower than previous limits. We find a 95% exclusion limit on over this mass range between 6 10^-15 and 6 10^-13, tracking the complex resonant mode structure in the shielded room.