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

TL;DR

This experiment searched for ultralight axion dark matter by detecting frequency modulations in nuclear spin precession signals, setting new limits on axion-nucleon coupling within a specific mass range.

Contribution

First to perform a side-band analysis of extsuperscript{199}Hg spin precession to search for axion dark matter in the specified mass range.

Findings

No axion signal detected within the sensitivity limits.

Set new upper bounds on axion-nucleon coupling strength.

Demonstrated the effectiveness of side-band analysis in such searches.

Abstract

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 modulates the spin precession of nuclear spins. Here we report on the null result of a demonstration experiment searching for a frequency modulation of the free spin-precession signal of \magHg in a \SI{1}{\micro\tesla} magnetic field. Our search covers the axion mass range $10^{-16}~\textrm{eV} \lesssim m_a \lesssim 10^{-13}~\textrm{eV}$ and achieves a peak sensitivity to the axion-nucleon coupling of $g_{aNN} \approx 3.5 \times 10^{-6}~\textrm{GeV}^{-1}$.