Constraints on axionlike dark matter with masses down to 10^-23 eV/c²

We analyzed a 6.7-year span of data from a rotating torsion-pendulum containing ≈ 10²³ polarized electrons to search for the “wind” arising from ultralight, axionlike dark matter particles with masses between 10^-23 and 10^-18 eV/c². Over most of this range we obtain a 95% confidence limit F_a/C_e ≥ 1 × 10¹⁵ eV on the axionlike decay constant.