[Paper Review] Constraining Ultralight Dark Matter through an Accelerated Resonant Search

Zitong Xu, Xiaolin Ma+10 more|arXiv (Cornell University)|Sep 28, 2023

Dark Matter and Cosmic PhenomenaPhysics and Astronomy68 references3 citations

TL;DR

This study presents an accelerated resonant search for ultralight axion dark matter using a 21Ne spin-based magnetometer in nuclear magnetic resonance (NMR) mode, achieving 0.73 fT/Hz¹² sensitivity. By employing large-frequency steps (up to 0.25 Hz) while maintaining high sensitivity, the method improves scanning efficiency by ~30-fold and sets stringent new constraints on axion-like particles (ALPs) in the 4.5–15.5 Hz range, surpassing astrophysical limits in key bands.

ABSTRACT

Experiments aimed at detecting ultralight dark matter typically rely on resonant effects, which are sensitive to the dark matter mass that matches the resonance frequency. In this study, we investigate the nucleon couplings of ultralight axion dark matter using a magnetometer operating in a nuclear magnetic resonance (NMR) mode. Our approach involves the use of a $^{21}$Ne spin-based sensor, which features the lowest nuclear magnetic moment among noble-gas spins. This configuration allows us to achieve an ultrahigh sensitivity of 0.73 fT/Hz$^{1/2}$ at around 5 Hz, corresponding to energy resolution of approximately 1.5$ imes 10^{-23}\, m{eV/Hz^{1/2}}$. Our analysis reveals that under certain conditions it is beneficial to scan the frequency with steps significantly larger than the resonance width. The analytical results are in agreement with experimental data and the scan strategy is potentially applicable to other resonant searches. Further, our study establishes stringent constraints on axion-like particles (ALP) in the 4.5--15.5 Hz Compton-frequency range coupling to neutrons and protons, improving on prior work by several-fold. Within a band around 4.6--6.6 Hz and around 7.5 Hz, our laboratory findings surpass astrophysical limits derived from neutron-star cooling. Hence, we demonstrate an accelerated resonance search for ultralight dark matter, achieving an approximately 30-fold increase in scanning step while maintaining competitive sensitivity.

Motivation & Objective

• To develop a faster, more efficient resonant search strategy for ultralight dark matter, particularly axion-like particles (ALPs), by overcoming the time-consuming nature of traditional frequency scanning.
• To improve sensitivity in resonant searches by leveraging high amplification factors to extend usable bandwidth beyond conventional resonance widths.
• To establish tighter experimental constraints on ALP couplings to nucleons by exploiting a low-nuclear-magnetic-moment 21Ne sensor with ultrahigh sensitivity.
• To validate a novel scan strategy with large steps (0.25 Hz) that maintains competitive sensitivity, enabling faster coverage of the target frequency band.

Proposed method

• Utilized a 21Ne spin-based magnetometer operating in NMR mode to detect resonant couplings between ultralight dark matter and nucleons.
• Achieved an ultrahigh sensitivity of 0.73 fT/Hz¹² at ~5 Hz, corresponding to an energy resolution of ~1.5 × 10⁻²³ eV/Hz¹².
• Implemented a frequency scan with steps of 0.25 Hz—significantly larger than the typical resonance width—while maintaining sensitivity through high amplification.
• Applied analytical models to explain the transition between flat and peaked power spectral density (PSD) regimes, identifying conditions where large steps remain effective.
• Used a cumulative measurement time of 1440 hours across 49 individual scans, with each run optimized near the ALP coherent time ($T \approx \tau_a$).
• Applied statistical analysis with look-elsewhere effect correction using $N_F$-corrected $q_{\rm global}$ to assess significance, with $q_{\rm global}$ thresholds of [41.33, 47.36] for 5\sigma detection.

Experimental results

Research questions

• RQ1 Can large-frequency steps (>> resonance width) be used in resonant dark matter searches without sacrificing sensitivity?
• RQ2 How does high amplification factor enable effective bandwidth extension in resonant NMR-based dark matter detection?
• RQ3 What are the resulting constraints on axion-like particle couplings to protons and neutrons in the 4.5–15.5 Hz Compton-frequency range?
• RQ4 Can laboratory-based constraints surpass astrophysical limits derived from neutron-star cooling in specific frequency bands?
• RQ5 Are transient peaks in the power spectral density indicative of dark matter signals or background fluctuations?

Key findings

• The experiment achieved a sensitivity of 0.73 fT/Hz¹² at ~5 Hz, corresponding to an energy resolution of approximately 1.5 × 10⁻²³ eV/Hz¹².
• The scan strategy with 0.25 Hz steps enabled a ~30-fold increase in scanning speed while maintaining competitive sensitivity.
• In the frequency bands 4.6–6.6 Hz and ~7.5 Hz, the laboratory constraints surpassed existing astrophysical limits from neutron-star cooling.
• No significant ALP signal was found after accounting for the look-elsewhere effect; candidate peaks at 5\sigma were transient and attributed to background fluctuations.
• Theoretical analysis confirmed that large steps are viable when the system is in the magnetic-dominated regime, with bandwidth expansion explained by high amplification factors.
• The study provides a generalizable framework applicable to other resonant dark matter experiments, including cavity and NMR-based searches.