Abstract
Based on the notion that the local dark-matter field of axions or axionlike particles (ALPs) in our Galaxy induces oscillating couplings to the spins of nucleons and nuclei (via the electric dipole moment of the latter and/or the paramagnetic axion-wind effect), we establish the feasibility of a new method to search for ALPs in storage rings. Based on previous work that allows us to maintain the in-plane polarization of a stored deuteron beam for a few hundred seconds, we perform a first proof-of-principle experiment at the Cooler Synchrotron (COSY) to scan momenta near . This entails a scan of the spin-precession frequency. At resonance between the spin-precession frequency of deuterons and the ALP-induced electric dipole moment (EDM) oscillation frequency, there is an accumulation of the polarization component out of the ring plane. Since the axion frequency is unknown, the momentum of the beam and, consequently, the spin-precession frequency are ramped to search for a vertical polarization change that occurs when the resonance is crossed. At COSY, four beam bunches with different polarization directions are used to make sure that no resonance is missed because of the unknown relative phase between the polarization precession and the axion or ALP field. A frequency window of 1.5 kHz width around the spin-precession frequency of 121 kHz is scanned. We describe the experimental procedure and a test of the methodology with the help of a radio-frequency Wien filter located on the COSY ring. No ALP resonance is observed. As a consequence, an upper limit of the oscillating EDM component of the deuteron as well as its axion coupling constants are provided.
- Received 16 August 2022
- Revised 6 December 2022
- Accepted 19 April 2023
DOI:https://doi.org/10.1103/PhysRevX.13.031004
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Axions are hypothetical particles that have been proposed as candidates for dark matter. But so far, no experiment has detected axions or a broader family of axionlike particles (ALPs). One way to search for ALPs is with a particle accelerator, looking for changes in the polarization direction of a beam of charged particles circulating within it. Here, we report on the first demonstration of such a search. While we do not detect any ALPs, we provide upper limits on various coupling strengths between ALPs and deuterons, which could in turn inform future searches.
This search strategy assumes that ALPs can cause small vibrations in the spin of nucleons or light nuclei with a frequency related to their mass. If true, then sufficiently light ALPs would show a coherent vibrational pattern lasting many seconds and covering a volume of space much larger than that of particle accelerators. This makes it feasible to look for such vibrations by measuring the properties of the particle beam itself.
Using the Cooler Synchrotron COSY in Jülich, Germany, we circulate a beam of deuterons with their nuclear spins aligned. The spins precess in the magnets used to maintain the beam orbit. If this precession frequency matches the frequency of ALP waves, then a resonance would rotate the polarization out of the ring plane, resulting in a vertical polarization change. While changing the spin precession frequency constantly, we search for a polarization change that would mark when the resonance is crossed. We observed no such change.
The next priority is to search for axionlike particles in light mass ranges where other techniques have potential issues. It may prove useful to join forces with a static electric dipole search that is under development, sharing access to the storage ring as the technology of these two experiments is nearly identical. The search must be supported over the many months required to cover a significant range of frequencies at a useful sensitivity.
