First results from a microwave cavity axion search at 24 micro-eV

Abstract

We report on the first results from a new microwave cavity search for dark matter axions with masses above $20\hat{I}¼\text{eV}$. We exclude axion models with two-photon coupling $g_{a{\hat{I}}^3{\hat{I}}^3}\gtrsim 2\times 10^{-14}{\text{GeV}}^{-1}$ over the range $23.55\hat{I}¼\text{eV}<m_a<24.0\hat{I}¼\text{eV}$. These results represent two important achievements. First, we have reached cosmologically relevant sensitivity an order of magnitude higher in mass than any existing limits. Second, by incorporating a dilution refrigerator and Josephson parametric amplifier, we have demonstrated total noise approaching the standard quantum limit for the first time in an axion search.

5 pages, 3 figures, accepted for publication in PRL. v2: added changes made during the review process