Search for invisible axion dark matter of mass ma=43 μeV with the QUAX– aγ experiment

An haloscope of the QUAX--$a\gamma$ experiment composed of an OFHC-Cu cavity inside an 8.1 T magnet and cooled to $\sim200$ mK was put in operation for the search of galactic axion with mass $m_a\simeq43~\mu\text{eV}$. The power emitted by the resonant cavity was amplified with a Josephson Parametric Amplifier whose noise fluctuations are at the Standard Quantum Limit (SQL). With the data collected in about 1 h at the cavity frequency $\nu_c=10.40176$ GHz the experiment reached the sensitivity necessary for the detection of galactic QCD-axion setting the $90\%$ confidence level (CL) limit to the axion-photon coupling $g_{a\gamma\gamma}<0.639\cdot10^{-13}$ GeV$^{-1}$.