Search for invisible axion dark matter of mass m${}_a=43\mu$eV with the QUAX--$a\gamma$ experiment

A haloscope of the QUAX–$a\gamma$ experiment composed of an oxygen-free high thermal conductivity-Cu cavity inside an 8.1 T magnet and cooled to $\sim 200$ mK is put in operation for the search of galactic axion with mass $m_a\simeq 43\mu \text{eV}$. The power emitted by the resonant cavity is amplified with a Josephson parametric amplifier whose noise fluctuations are at the standard quantum limit. With the data collected in about 1 h at the cavity frequency ${\nu }_c=10.40176$ GHz, the experiment reaches the sensitivity necessary for the detection of galactic QCD-axion, setting the $90\mathrm{\%}$ confidence level limit to the axion-photon coupling $g_{a\gamma \gamma }<0.639\times {10}^{-13}$ GeV${}^{-1}$.