(A) sensitive search for dark matter axions around 24.5 µeV using a multi-cell microwave cavity and a flux-driven Josephson parametric amplifier

Abstract

Axion, a hypothetical particle originally emerging from a proposed solution to the strong CP problem of particle physics, is one of the favored candidates addressing the dark matter puzzle. This work explains the design and operation of a axion haloscope sensitive to masses around 24.5 µeV at Kim-Shifman-Vainshtein-Zakharov (KSVZ) sensitivity. A unique 8-cell cavity, used for the first time in search of KSVZ axions, is cooled down to 40 mK within a magnetic field of 8 T. The expected axion signal resonating with the TM010-like mode of the cavity is picked up using an antenna and transferred to the readout chain. Implementing a flux-pumped Josephson parametric amplifier with 20 dB gain as the first stage of amplification, the system noise temperature was estimated to be 450 mK, corresponding to 1.6 photons. This work resulted in the exclusion of dark matter axion masses from 2.4111 µeV to 2.4565 µeV for axion two-photon couplings gaγγ > 1.3 GeV$^{−1}$ using data taken between December 2021 and September 2022. This is the largest region covered at such high sensitivities by a single haloscope experiment operating above 1 GHz to date.