[Paper Review] First Search for Axion-Like Particles in a Storage Ring Using a Polarized Deuteron Beam

S. Karanth, E. J. Stephenson+61 more|arXiv (Cornell University)|Aug 15, 2022

Dark Matter and Cosmic Phenomena4 citations

TL;DR

This paper presents the first search for axion-like particles (ALPs) using a polarized deuteron beam in a storage ring, leveraging spin dynamics and polarization jumps induced by ALP coupling to measure the effective electron EDM. The method achieves a sensitivity limit of $ d_{\text{AC}} \sim 10^{-22} \, \text{e} \cdot \text{cm} $, setting a new constraint on ALP couplings via beam polarization measurements in the COSY ring at Forschungszentrum Jülich.

ABSTRACT

Based on the notion that the local dark-matter field of axions or axion-like 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 performed a first proof-of-principle experiment at the Cooler Synchrotron COSY to scan momenta near 970 MeV/c. This entailed a scan of the spin precession frequency. At resonance between the spin precession frequency of deuterons and the ALP-induced EDM oscillation frequency there will be 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 were ramped to search for a vertical polarization change that would occur when the resonance is crossed. At COSY, four beam bunches with different polarization directions were used to make sure that no resonance was missed because of the unknown relative phase between the polarization precession and the axion/ALP field. A frequency window of 1.5-kHz width around the spin precession frequency of 121 kHz was scanned. We describe the experimental procedure and a test of the methodology with the help of a radiofrequency Wien filter located on the COSY ring. No ALP resonance was observed. As a consequence an upper limit of the oscillating EDM component of the deuteron as well as its axion coupling constants are provided.

Motivation & Objective

• To search for axion-like particles (ALPs) via their coupling to the deuteron's spin in a storage ring environment.
• To develop a calibration method for detecting ALP-induced polarization jumps in a rotating beam.
• To set a new experimental limit on the effective electron EDM induced by ALP interactions.
• To validate the sensitivity of the storage ring setup using numerical simulations of spin dynamics under varying scan rates.
• To calibrate the relationship between axion-induced spin oscillation and measurable polarization jumps in the COSY ring.

Proposed method

• Utilizes a polarized deuteron beam in the COSY storage ring with controlled ramping of revolution frequency to induce spin precession.
• Employs numerical simulations of the 3x3 density matrix evolution over 15 steps per turn to model spin dynamics with high precision (0.1% convergence).
• Calibrates the polarization jump response using two orthogonal axion phase inputs ($\phi_a = 0$ and $\pi/2$) and combines results in quadrature to determine maximum jump size.
• Derives the effective electron EDM using the relation $ d_{\text{AC}} = \frac{1}{2\pi} \frac{\hbar}{B\rho} \frac{w}{0.958} \left| \frac{\psi_{\text{AC}}}{\Delta p_y} \right|_{\text{calib.}} A $, where $ A $ is the observed jump amplitude.
• Applies corrections for ramp rate ($ w $) and ring geometry (0.958 factor) to scale calibration results to actual experimental conditions.
• Validated the method against the axion-wind effect and confirmed consistency with radial spin rotation models.

Experimental results

Research questions

• RQ1 Can axion-like particles be detected via their coupling to the spin of polarized deuterons in a storage ring?
• RQ2 What is the sensitivity of the COSY storage ring setup to ALP-induced effective electron EDMs?
• RQ3 How does the polarization jump scale with the axion-induced spin oscillation amplitude and scan rate?
• RQ4 To what extent can numerical simulations of spin dynamics accurately predict measurable polarization jumps?
• RQ5 What is the maximum detectable effective electron EDM using this method, and how does it compare to existing limits?

Key findings

• The calibration method achieves a sensitivity of $ 9.35 \times 10^{-7} $ rad/turn for fast scans and $ 8.48 \times 10^{-7} $ rad/turn for slow scans, relating axion-induced spin oscillation to measurable polarization jumps.
• The effective electron EDM is estimated to be below $ 10^{-22} \, \text{e} \cdot \text{cm} $ for typical observed jump amplitudes.
• The polarization jump scales approximately linearly with the axion-induced spin oscillation amplitude in the relevant range, enabling reliable calibration.
• The method accounts for ring geometry and scan rate via correction factors $ w $ and 0.958, improving accuracy in sensitivity estimation.
• Numerical simulations with 15 steps per turn converge to within 0.1% precision, validating the reliability of the jump prediction model.
• The calibration results are consistent across different scan rates and phase configurations, confirming robustness of the method.