26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

ORGAN-Low : Pathfinder Search for Sub-μeV Axion Dark Matter with the Re-entrant Haloscope Design

Not scheduled

1h 30m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral AIP | Astroparticle Physics (GAP) Parallel sessions

Description

The QCD axion remains one of the most compelling dark matter candidates, offering a simultaneous solution to the Strong CP problem and the nature of dark matter. Axion haloscopes search for this particle through its resonant conversion into microwave photons in a strong magnetic field, but most mature experimental sensitivity has so far been concentrated at GHz frequencies. The lower-frequency region around a few hundred MHz, corresponding to axion masses in the sub-to-few μeV range, remains comparatively under-explored because it requires large volume, high quality factor resonators with experimentally viable coupling, mode control, and low noise readout.
In this work, we report the design, construction, commissioning, and first pathfinder search using a prototype low-frequency axion haloscope operating in the 450-460 MHz range, corresponding to axion masses of approximately 1.86-1.90 μeV. The prototype is a one-fifth linear-scale version of our planned full-scale detector, developed as a pathfinding platform to validate the detector design, readout chain, data acquisition strategy, and analysis framework before scaling to the final experiment. The detector is basically a re-entrant cavity optimized for low-frequency operation, with full electromagnetic and readout characterization.
Using data collected with the prototype detector, we perform a pathfinding axion search across the 450-460 MHz band and derive experimental sensitivity limits in this experimentally unexplored mass range. The analysis demonstrates that low-frequency haloscope searches can be experimentally feasible with a compact prototype platform while achieving meaningful sensitivity to axion dark matter. These results provide an experimentally validated foundation for the next stage of the program: a full-scale detector with enhanced sensitivity and broader frequency coverage, targeting the 100-500 MHz range. By demonstrating both the performance of the prototype and the scalability of the detector concept, this work establishes a practical route towards probing inaccessible regions of low-mass axion dark matter parameter space.