ADMX Run 2A: A Multi-Cavity QCD Axion Search*

The QCD axion is among the best motivated particle dark matter (DM) candidates. Cavity haloscopes like ADMX (Axion Dark Matter eXperiment) resonantly detect conversion of DM axions to photons under a strong magnetic field in a high-Q resonant cavity. Recent ADMX runs with a single cavity excluded most of the QCD axion parameter range between 2.7μeV and 4.2μeV and are set to cover the range until about 5.4μeV. However, at higher masses the wavelength of the generated photons shrinks, generally leading to a smaller cavity volume and reduced sensitivity. In this talk we present an array of four cavities, tuning in sync to scan a broad mass range from 5.4μeV to 7.6μeV with QCD axion sensitivity. We discuss experimental measurements of the quality factor and other important electromagnetic characteristics at room temperature and 4K. We show recent R&D and experimental improvements, and outline the path towards commissioning and run of the full axion search experiment.