Direct limits on the interaction of antiprotons with axion-like dark matter

TL;DR

This paper presents direct experimental constraints on the interaction between antiprotons and axion-like dark matter particles, significantly improving previous bounds and exploring potential links to matter-antimatter asymmetry.

Contribution

It provides the first direct laboratory limits on axion-antiproton interactions using spin resonance data, advancing understanding of dark matter's microscopic properties.

Findings

Constraints on axion-antiproton coupling parameter $f_a/C_{\overline{p}}$ from 0.1 to 0.6 GeV.

Improved bounds over astrophysical limits by up to five orders of magnitude.

Limits on Lorentz- and CPT-violating terms in the Standard Model Extension.

Abstract

Astrophysical observations indicate that there is roughly five times more dark matter in the Universe than ordinary baryonic matter, with an even larger amount of the Universe's energy content due to dark energy. So far, the microscopic properties of these dark components have remained shrouded in mystery. In addition, even the five percent of ordinary matter in our Universe has yet to be understood, since the Standard Model of particle physics lacks any consistent explanation for the predominance of matter over antimatter. Inspired by these central problems of modern physics, we present here a direct search for interactions of antimatter with dark matter, and place direct constraints on the interaction of ultra-light axion-like particles $-$ one of the dark-matter candidates $-$ and antiprotons. If antiprotons exhibit a stronger coupling to these dark-matter particles than protons, such a CPT-odd coupling could provide a link between dark matter and the baryon asymmetry in the Universe. We analyse spin-flip resonance data acquired with a single antiproton in a Penning trap [Smorra et al., Nature 550, 371 (2017)] in the frequency domain to search for spin-precession effects from ultra-light axions with a characteristic frequency governed by the mass of the underlying particle. Our analysis constrains the axion-antiproton interaction parameter $f_a/C_{\overline{p}}$ to values greater than $0.1$ to $0.6$ GeV in the mass range from $2 \times 10^{-23}$ to $4 \times 10^{-17}\,$eV/$c^2$, improving over astrophysical antiproton bounds by up to five orders of magnitude. In addition, we derive limits on six combinations of previously unconstrained Lorentz-violating and CPT-violating terms of the non-minimal Standard Model Extension.