# Search for axionlike dark matter with a liquid-state nuclear spin comagnetometer

## TL;DR

This study used liquid-state NMR with comagnetometry to search for axionlike dark matter, setting new constraints on its coupling to nucleons and improving previous laboratory and astrophysical limits across a range of particle masses.

## Contribution

The paper demonstrates a novel liquid-state NMR comagnetometry approach to search for axionlike dark matter, providing the most stringent laboratory constraints to date for certain mass ranges.

## Key findings

- No axionlike dark matter signal was detected.
- The experiment constrains the coupling parameter to be less than 6×10⁻⁵ GeV⁻¹ for specific masses.
- Results improve previous limits by orders of magnitude for certain mass ranges.

## Abstract

We report the results of a search for axionlike dark matter using nuclear magnetic resonance (NMR) techniques. This search is part of the multi-faceted Cosmic Axion Spin Precession Experiment (CASPEr) program. In order to distinguish axionlike dark matter from magnetic fields, we employ a comagnetometry scheme measuring ultralow-field NMR signals involving two different nuclei ($^{13}$C and $^{1}$H) in a liquid-state sample of acetonitrile-2-$^{13}$C ($^{13}$CH$_{3}$CN). No axionlike dark matter signal was detected above background. This result constrains the parameter space describing the coupling of the gradient of the axionlike dark matter field to nucleons to be $g_{aNN}<6\times 10^{-5}$ GeV$^{-1}$ (95$\%$ confidence level) for particle masses ranging from $10^{-22}$ eV to $1.3\times10^{-17}$ eV, improving over previous laboratory limits for masses below $10^{-21}$ eV. The result also constrains the coupling of nuclear spins to the gradient of the square of the axionlike dark matter field, improving over astrophysical limits by orders of magnitude over the entire range of particle masses probed.