Extended Axion Dark Matter Search Using the CAPP18T Haloscope

TL;DR

This paper reports an extended search for axion dark matter using the CAPP18T haloscope with advanced superconducting magnet technology, setting new upper bounds on axion-photon coupling in a specific mass range.

Contribution

The study introduces technological improvements and system reconstruction in the CAPP18T experiment, enabling more reliable high-mass axion searches beyond benchmark models.

Findings

No axion signal detected within the scanned frequency range.

Established the most stringent upper bounds on axion-photon coupling in the 19.883-19.926 μeV mass range.

Demonstrated the effectiveness of advanced superconducting magnet and microwave technologies in axion searches.

Abstract

We report an extended search for the axion dark matter using the CAPP18T haloscope. The CAPP18T experiment adopts innovative technologies of a high-temperature superconducting magnet and a Josephson parametric converter. The CAPP18T detector was reconstructed after an unexpected incident of the high-temperature superconducting magnet quenching. The system reconstruction includes rebuilding the magnet, improving the impedance matching in the microwave chain, and mechanically readjusting the tuning rod to the cavity for improved thermal contact. The total system noise temperature is $\sim$0.6\,K. The coupling between the cavity and the strong antenna is maintained at $\beta \simeq 2$ to enhance the axion search scanning speed. The scan frequency range is from 4.8077 to 4.8181 GHz. No significant indication of the axion dark matter signature is observed. The results set the best upper bound of the axion-photon-photon coupling ($g_{a\gamma\gamma}$) in the mass ranges of 19.883 to 19.926\,$\mu$eV at $\sim$0.7$\times|g_{a\gamma\gamma}^{\text{KSVZ}}|$ or $\sim$1.9$\times|g_{a\gamma\gamma}^{\text{DFSZ}}|$ with 90\,\% confidence level. The results demonstrate that a reliable search of the high-mass dark matter axions can be achieved beyond the benchmark models using the technology adopted in CAPP18T.