A new method with minimized systematic error sources to detect axion dark matter in storage rings using an rf Wien filter

Abstract

Axion, a hypothetical pseudo-scalar particle, is a direct consequence of the Peccei-Quinn mechanism, which was proposed to solve the strong CP problem in 1977. It is also a plausible candidate for dark matter. The axion feebly interacts with the Standard Model (SM) particles, which makes it extremely challenging to detect a sign of its existence. Nevertheless, there have been many efforts to search for the axion-SM interaction, the prevailing method among which is a cavity haloscope seeking for the axion-photon interaction, more suited for axion-frequencies above 100 MHz. On the other hand, there is another branch of interaction, namely a coupling between the axion and the nuclear electric dipole moment (EDM), which induces an oscillating EDM at the axion Compton frequency. A storage ring EDM experiment provides a powerful method sensitive to a proton EDM as small as $10^{-29}$ $e\cdot$cm. We extend the storage ring EDM concept to measure an oscillating EDM with a comparable sensitivity by exploiting a new spin resonance scheme using an rf Wien filter. The new method does away with the severe spin resonance systematic error sources by a careful combination of frequencies used. We introduce this new method from a basic working principle to a projected sensitivity on the axion-EDM coupling constant.