First results from a microwave cavity axion search at 24 micro-eV
  We report on the first results from a new microwave cavity search for dark
matter axions with masses above $20~\mu\text{eV}$. We exclude axion models with
two-photon coupling $g_{a\gamma\gamma} \gtrsim 2\times10^{-14}~\text{GeV}^{-1}$
over the range $23.55~\mu\text{eV} < m_a < 24.0~\mu\text{eV}$. 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.
