Improved rf cavity search for halo axions

The axion is a hypothetical elementary particle and cold dark matter candidate. In this rf cavity experiment, halo axions entering a resonant cavity immersed in a static magnetic field convert into microwave photons, with the resulting photons detected by a low-noise receiver. The ADMX Collaboration presents new limits on the axion-to-photon coupling and local axion dark matter halo mass density from a rf cavity axion search in the axion mass range $1.9–2.3\mu \mathrm{eV},$ broadening the search range to $1.9–3.3\mu \mathrm{eV}.$ In addition, we report first results from an improved analysis technique.