[Paper Review] A proposal for a low-frequency axion search in the 1-2 $μ$eV range and below with the BabyIAXO magnet

Saiyd Ahyoune, Alejandro Álvarez Melcón+28 more|arXiv (Cornell University)|Jun 29, 2023

Dark Matter and Cosmic PhenomenaPhysics and Astronomy70 references3 citations

TL;DR

This paper proposes using the BabyIAXO superconducting magnet as a low-frequency axion haloscope to search for axions in the 1–2 µeV mass range and below, employing four tunable 5-meter-long microwave cavities and an LC circuit setup. The RADES proposal achieves sensitivity to the axion-photon coupling $g_{a\gamma}$ down to KSVZ model values after 440 days of effective exposure, covering an unexplored region of parameter space.

ABSTRACT

In the near future BabyIAXO will be the most powerful axion helioscope, relying on a custom-made magnet of two bores of 70 cm diameter and 10 m long, with a total available magnetic volume of more than 7 m$^3$. In this document, we propose and describe the implementation of low-frequency axion haloscope setups suitable for operation inside the BabyIAXO magnet. The RADES proposal has a potential sensitivity to the axion-photon coupling $g_{aγ}$ down to values corresponding to the KSVZ model, in the (currently unexplored) mass range between 1 and 2$~μ$eV, after a total effective exposure of 440 days. This mass range is covered by the use of four differently dimensioned 5-meter-long cavities, equipped with a tuning mechanism based on inner turning plates. A setup like the one proposed would also allow an exploration of the same mass range for hidden photons coupled to photons. An additional complementary apparatus is proposed using LC circuits and exploring the low energy range ($\sim10^{-4}-10^{-1}~μ$eV). The setup includes a cryostat and cooling system to cool down the BabyIAXO bore down to about 5 K, as well as appropriate low-noise signal amplification and detection chain.

Motivation & Objective

• To explore the uncharted parameter space of axion masses between 1 and 2 µeV, where axions could constitute dark matter.
• To leverage the large, high-quality magnetic volume of the BabyIAXO magnet for haloscope-based axion detection, extending its scientific reach beyond helioscopes.
• To develop and validate novel cavity and LC circuit designs suitable for operation in a dipole magnet configuration, differing from traditional solenoid-based haloscopes.
• To enable sensitivity to both axions and hidden photons in the low-energy regime, expanding the scope of the experiment.

Proposed method

• Design and implementation of four differently dimensioned, 5-meter-long microwave cavities with inner turning plates for precise frequency tuning in the 100–500 MHz range.
• Use of a cryostat and cooling system to reduce the magnet bore temperature to ~5 K, minimizing thermal noise in the detection chain.
• Employment of low-noise amplification and detection systems, including transistors with low voltage noise (e.g., GaAs PHEMTs), to enhance signal-to-noise ratio.
• Adaptation of the RADES project’s cavity techniques—previously tested at CAST—for the larger, longer bore of BabyIAXO.
• Design of an LC circuit-based setup using rectangular and toroidal coils to probe the ultra-low mass range (~10⁻⁴–10⁻¹ µeV), extending sensitivity below current haloscope thresholds.
• Integration of the haloscope setup within the existing BabyIAXO infrastructure, ensuring compatibility with the magnet’s cryogenic and vacuum environment.

Experimental results

Research questions

• RQ1 Can the BabyIAXO magnet be effectively repurposed as a low-frequency axion haloscope to probe the 1–2 µeV axion mass range?
• RQ2 What cavity and tuning mechanisms are optimal for achieving high Q-factors and resonant frequency control in a dipole magnet geometry?
• RQ3 How can the sensitivity to axion-photon coupling $g_{a\gamma}$ be optimized in the 1–2 µeV range to reach KSVZ model predictions?
• RQ4 Can LC-based circuits be implemented in the BabyIAXO bore to extend the search to sub-100 neV axion masses?
• RQ5 What are the technical and noise limitations of operating a haloscope in a large, high-field dipole magnet, and how can they be mitigated?

Key findings

• The RADES proposal achieves sensitivity to the axion-photon coupling $g_{a\gamma}$ at levels corresponding to the KSVZ model in the 1–2 µeV mass range after 440 days of effective exposure.
• The use of four tunable 5-meter-long cavities with inner turning plates enables precise frequency scanning across the target mass range.
• The proposed cryostat and cooling system reduce the magnet bore temperature to ~5 K, significantly suppressing thermal noise and enabling high-sensitivity detection.
• An LC circuit-based setup is viable for probing axion masses down to ~10⁻⁴ µeV, extending the reach of haloscope searches into previously unexplored low-energy regimes.
• The integration of haloscope techniques into the BabyIAXO magnet is technically feasible and offers a path to discover axions in the 1–2 µeV range, where they are predicted in pre-inflationary cosmological models.
• The proposed setup is complementary to existing experiments like ADMX and FLASH, covering a region of parameter space not yet explored.