  The dark photon is a promising candidate for the dark matter which comprises
most of the matter in our visible Universe. Via kinetic mixing with the
Standard Model it can also be resonantly converted to photons in an
electromagnetic cavity, offering novel experimental possibilities for the
discovery and study of dark matter. We report the results of a pathfinder dark
photon dark matter cavity search experiment performed at Hunan Normal
University and the Institute of Physics, Chinese Academy of Sciences,
representing the first stage of the APEX (Axion and dark Photon EXperiment)
program. Finding no statistically significant excess, we place an upper limit
on the kinetic mixing parameter $|\chi|<3.7\times 10^{-13}$ around $m_A\simeq
29.5$ $\mu$eV at 90% confidence level. This result exceeds other constraints on
dark photon dark matter in this frequency range by roughly an order of
magnitude.
