  The hidden sector photon is a weakly interacting hypothetical particle with
sub-eV mass that kinetically mixes with the photon. We describe a microwave
frequency light shining through a wall experiment where a cryogenic resonant
microwave cavity is used to try and detect photons that have passed through an
impenetrable barrier, a process only possible via mixing with hidden sector
photons. For a hidden sector photon mass of 53 $\mu$eV we limit the hidden
photon kinetic mixing parameter $\chi < 1.7\times10^{-7}$, which is an order of
magnitude lower than previous bounds derived from cavity experiments in the
same mass range. In addition, we use the cryogenic detector cavity to place new
limits on the kinetic mixing parameter for hidden sector photons as a form of
cold dark matter.
