Searching for dark matter with a 1000 km baseline interferometer

TL;DR

This study conducts a broadband search for axion-like particle dark matter using a 1000 km baseline interferometer with atomic comagnetometers, setting new constraints on ALP couplings across a wide mass range.

Contribution

It introduces a novel large-baseline interferometric method with atomic comagnetometers to search for ALP dark matter over nine orders of magnitude in mass.

Findings

No significant ALP signal detected.

Set new upper limits on ALP-neutron, ALP-proton, and ALP-electron couplings.

Improved laboratory constraints for neutron and proton couplings by up to three orders of magnitude.

Abstract

Axion-like particles (ALPs) arise from well-motivated extensions to the Standard Model and could account for dark matter. ALP dark matter would manifest as a field oscillating at an (as of yet) unknown frequency. The frequency depends linearly on the ALP mass and plausibly ranges from $10^{-22}$ to $10$ eV/$c^2$. This motivates broadband search approaches. We report on a direct search for ALP dark matter with an interferometer composed of two atomic K-Rb-$^3$He comagnetometers, one situated in Mainz, Germany, and the other in Krak\'ow, Poland. We leverage the anticipated spatio-temporal coherence properties of the ALP field and probe all ALP-gradient-spin interactions covering a mass range of nine orders of magnitude. No significant evidence of an ALP signal is found. We thus place new upper limits on the ALP-neutron, ALP-proton and ALP-electron couplings reaching below $g_{aNN}<10^{-9}$ GeV$^{-1}$, $g_{aPP}<10^{-7}$ GeV$^{-1}$ and $g_{aee}<10^{-6}$ GeV$^{-1}$, respectively. These limits improve upon previous laboratory constraints for neutron and proton couplings by up to three orders of magnitude.