The ORGAN Experiment: Phase1a Status and Results*

Precise cosmological measurements provide strong evidence for the existence of dark matter, and estimate that it accounts for 85% of all the matter in our Universe. Axions are hypothetical, massive, spin-0 particles that were first postulated as an elegant solution to the strong CP problem in quantum chromodynamics. The weakly interacting nature of axions simultaneously make them a popular dark matter candidate which can be searched for in experiments known as “haloscopes”, which exploit a putative axion-photon coupling. We present experimental details and initial results for Phase 1a of the Oscillating Resonant Group AxioN (ORGAN) experiment, a microwave cavity axion haloscope exploring the highly motivated ~ 60 - 200 μeV region of axion mass parameter space, corresponding to 15 - 50 GHz photons. Phase 1a scans for axion masses in the 15-16 GHz region of axion-photon coupling parameter space using a tunable TM₀₁₀ conducting-rod resonator. This initial phase of ORGAN is set to be the most sensitive experiment in this region, achieving ALP-cogenesis sensitivity. Subsequent stages of ORGAN will utilise the Phase 1a infrastructure as a test bed for various technologies and techniques, such as GHz single photon counting, and novel cavity designs to explore the full 15-50 GHz range.