Search for dark-matter axions beyond the quantum limit: the Cosmological Axion Sarov Haloscope (CASH) proposal

Abstract: Firmly established in astrophysical observations, dark matter evades direct detection in experiments. Axions and axion-like particles are among the leading dark-matter candidates, and numerous attempts to detect them in laboratories have been performed. Here, we propose to advance these efforts substantially, extending the sensitivity for dark-matter axions in the mass range $(38-54)~\mu$eV down to the axion-photon couplings $g_{a\gamma\gamma}\lesssim \left(10^{-14}-10^{-15}\right)$ GeV$^{-1}$, motivated by generic models of Quantum Chromodynamics axion. Single-photon detectors operating at ultra-low temperatures are key elements of the experiment. The projected sensitivity will be reached in one year of data taking with magnetic field of $(1-10)$ T, making Cosmological Axion Sarov Haloscope (CASH) the most sensitive haloscope in this mass range.