Abstract
This Letter reports on the first results from the Taiwan Axion Search Experiment with a Haloscope, a search for axions using a microwave cavity at frequencies between 4.707 50 and 4.798 15 GHz. Apart from the nonaxion signals, no candidates with a significance of more than 3.355 were found. The experiment excludes models with the axion-two-photon coupling vertical bar g(a gamma gamma)vertical bar greater than or similar to 8.1 x 10(-14) GeV-1, a factor of eleven above the benchmark Kim-Shifman-Vainshtein-Zakharov model, in the mass range 19.4687 < m(a) < 19.8436 mu eV. It is also the first time that a haloscope experiment places constraints on g(a gamma gamma) in the mass region of 19.4687 < m(a) < 19.7639 mu eV, reaching a sensitivity 3 orders of magnitude better than the limits obtained by nonhaloscope experiments.