Constraints on Galactic Dark Photons from a DALI Prototype

An analysis of 36 hours of data from a DALI haloscope reveals no statistically significant excess attributable to dark-photon dark matter. We therefore set new constraints in the 6.88691–6.91792 GHz band, reaching a dark-photon-to-photon kinetic mixing strength of $\chi \lesssim 6.8\times {10}^{-14}$ at $28.54\mu \mathrm{e}\mathrm{V}$. To our knowledge, this result established the strongest laboratory-based exclusion limit in this frequency range.