Search for ultralight axion dark matter in a side-band analysis of a 199Hg free-spin precession signal

Ultra-low-mass axions are a viable dark matter candidate and may form a coherently oscillating classical field. Nuclear spins in experiments on Earth might couple to this oscillating axion dark-matter field, when propagating on Earth's trajectory through our Galaxy. This spin coupling resembles an oscillating pseudo-magnetic field which modu-lates the spin precession of nuclear spins. Here we report on the null result of a demon-stration experiment searching for a frequency modulation of the free spin-precession signal of 199Hg in a 1 ➭T magnetic field. Our search covers the axion mass range 10-16 eV & LE; ma & LE; 10-13 eV and achieves a peak sensitivity to the axion-nucleon coupling of gaNN & AP; 3.5 x 10-6 GeV-1.

Automated summary

Ultra-low-mass axions are considered a possible type of dark matter and could form a coherent oscillating classical field. Nuclear spins in experiments on Earth were tested for their coupling to this oscillating axion dark matter field as they travel along Earth's trajectory through our Galaxy. The experiment aimed to observe an oscillating pseudo-magnetic field modulating the spin precession of nuclear spins but found no frequency modulation signal. The search covered a range of axion masses from 10-16 eV ≤ ma ≤ 10-13 eV and achieved a peak sensitivity to the axion-nucleon coupling of gaNN ≈ 3.5 x 10-6 GeV-1.