We report a follow-up axion haloscope search near 1.036 GHz that completes and extends our previous work [Phys. Rev. X 14, 031023 (2024)], in which a portion of the HEMT-based data could not be analyzed due to unrecorded experimental information. While recovering this dataset, we identified an excess near 1.036 GHz that satisfied our candidate-selection criteria, motivating dedicated validation studies, including independent cross-checks and re-examination with the original apparatus. The excess did not persist under these investigations and was not confirmed as an axion dark-matter signal. We subsequently extended the search over a 20-MHz band surrounding the candidate using a quantum-noise-limited amplifier, achieving sensitivity close to the Dine-Fischler-Srednicki-Zhitnitsky benchmark. In the absence of a confirmed signal, we set improved 90% confidence-level upper limits on the axion-photon coupling over the frequency range 1.026-1.045 GHz. This work highlights the importance of robust candidate-validation strategies as haloscope searches approach discovery-level sensitivity.
@article{arxiv.2602.05388,
title = {Extended Haloscope Search and Candidate Validation near 1.036G Hz},
author = {Saebyeok Ahn and Boris I. Ivanov and Ohjoon Kwon and HeeSu Byun and Arjan F. van Loo and SeongTae Park and JinMyeong Kim and Junu Jeong and Soohyung Lee and Jinsu Kim and Caglar Kutlu and Andrew K. Yi and Yasunobu Nakamura and Seonjeong Oh and Danho Ahn and SungJae Bae and Hyoungsoon Choi and Jihoon Choi and Yonuk Chong and Woohyun Chung and Violeta Gkika and Jihn E. Kim and Younggeun Kim and Byeong Rok Ko and Lino Miceli and Doyu Lee and Jiwon Lee and Ki Woong Lee and MyeongJae Lee and Andrei Matlashov and Pallavi Parashar and Taehyeon Seong and Yun Chang Shin and Sergey V. Uchaikin and Yannis K. Semertzidis and SungWoo Youn},
journal= {arXiv preprint arXiv:2602.05388},
year = {2026}
}