Mitsuyoshi Tanaka Dissertation Award Talk: First results from the HAYSTAC axion search*

Hypothetical particles called axions are among the leading candidates for the mysterious cold dark matter (CDM) that binds galaxies together and constitutes more than 80% of the matter in the universe. CDM axions may be detected via their resonant conversion into photons in a "haloscope" detector: a tunable, high-$Q$ microwave cavity maintained at cryogenic temperature, immersed a strong magnetic field, and coupled to a low-noise receiver. At the limits of current technology, the conversion power in such a detector is $\lesssim 10^{-22}\mathrm{ W}$ for $\mu\mathrm{eV}$-mass axions, and drops rapidly with increasing axion mass, because higher frequency cavities with smaller resonant volumes are required. In this talk I will introduce the essential physics of CDM axion detection, and review the main results of my doctoral research with HAYSTAC (the Haloscope at Yale Sensitive to Axion CDM), for which I received the 2019 Tanaka award. HAYSTAC is the first detector to achieve sensitivity to viable axion models in the $10\mathrm{ }\mu\mathrm{eV}$ mass decade, and the first to demonstrate noise performance limited by the laws of quantum mechanics. I will end the talk with a brief preview of next steps for HAYSTAC specifically and a broader outlook for the field of light dark matter detection.