First Results from a Microwave Cavity Axion Search at 24 μeV

Abstract

We report on the first results from a new microwave cavity search for dark matter axions with masses above $20\mu \mathrm{eV}$. We exclude axion models with two-photon coupling $g_{a\gamma \gamma }\gtrsim 2\times {10}^{-14}{\mathrm{GeV}}^{-1}$ over the range $23.55<m_a<24.0\mu \mathrm{eV}$. 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.