arXiv · 2607.25466
Distinguishing the Axion-Wind and Oscillating-EDM Couplings in Storage-Ring Searches for Axion Dark Matter
Abstract
Resonant spin-precession experiments in storage rings are sensitive to two distinct axion and axion-like particle dark-matter couplings: an oscillating electric dipole moment (EDM) primarily driven by the axion-gluon interaction, and the axion-wind (derivative) coupling acting as an effective pseudomagnetic field on the spin. Both effects produce a vertical polarization buildup at the same resonance frequency and are therefore degenerate in this standard observable. It is shown that the two couplings enter the vertical build-up and the spin-precession phase walk as the difference and sum of their resonance strengths, respectively. Measuring both observables simultaneously at fixed energy in a multi-bunch configuration allows the individual coupling strengths to be extracted up to a two-fold sign ambiguity. As a complementary approach, the ratio of electric to magnetic bending fields in a combined storage ring can be varied while keeping the resonance frequency fixed. This leaves the axion-wind contribution unchanged while modifying the EDM contribution in a calculable way, enabling a clean separation of the two effects. Both approaches can be used in future storage-ring facilities dedicated to EDM measurements.
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V. Hejny, J. Pretz. 2026-07-28. Distinguishing the Axion-Wind and Oscillating-EDM Couplings in Storage-Ring Searches for Axion Dark Matter. https://arxiv.org/abs/2607.25466
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