Search for QCD axion dark matter around 24.5 μeV using an 8-cell microwave resonant cavity haloscope 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. As part of the efforts within the Center for Axion and Precision Physics Research of the Institute for Basic Science, we are searching for axion dark matter using the haloscope method sensitive to masses around $24.5~\mathrm{eV}$ 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 $40~\mathrm{mK}$ within a magnetic field of $8~\mathrm{T}$. The expected axion signal resonating with the $\mathrm{TM}_{010}$-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 $20~\mathrm{dB}$ gain as the first stage of amplification, the system noise temperature was estimated to be $450~\mathrm{mK}$, corresponding to 1.6 photons. In this paper, we present results from data taken between December 2021 and June 2022, covering approximately $100~\mathrm{MHz}$.