Abstract:

Recent measurements solidified the case for abundant cold dark matter in our universe. These same measurements elevated the axion, a hypothetical elementary particle, to the premier cold dark matter candidate. Dark matter axions have almost no interactions with normal matter and radiation, but in a RF cavity threaded by a large static magnetic field, a handful per second would convert into microwave photons. These photons can be detected by an exquisitely sensitive microwave receiver. This detector is fully operational and continues to search for axions in our Milky Way halo. We are beginning a high-sensitivity upgrade that exploits advances in SQUID microwave amplifier technology. The final stage of this upgraded experiment will be definitive, sensitive to the entire range of plausible dark matter axion masses and couplings.