21st Patras Workshop on Axions, WIMPs and WISPs

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

Not scheduled

20m

University of Western Australia

Oral Presentation

Speaker

Raj Aryan Singh (Swinburne University of Technology)

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 $\mu$eV range, remains comparatively under explored because it requires large volume, high quality factor resonators with experimentally viable coupling, mode control, and low noise readout performance.
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 $\mu$eV. 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 based on a resonant cavity architecture optimized for low frequency operation, with detailed characterization of the relevant electromagnetic mode structure, loaded quality factor, coupling, receiver response, and system noise.
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 previously experimentally unexplored mass range. The analysis demonstrates that low-frequency haloscope searches can be made 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 substantially 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 toward probing currently inaccessible regions of low-mass axion dark matter parameter space.