Receiver Noise Characterization for ADMX Run 1C-Extended

The axion was originally proposed as a solution to the strong CP problem, however, it has been gaining popularity in recent years as a cold dark matter candidate. Many find the DFSZ axion model to be more compelling than its counterpart (KSVZ), due to its GUT compatibility. However, the DFSZ axion is significantly more weakly coupled to photons than the KSVZ axion, making it more difficult to detect. Notably, the Axion Dark Matter eXperiment (ADMX) was the first axion haloscope to reach sensitivity to the elusive DFSZ axion. ADMX was able to reach DFSZ sensitivity by using a dilution refrigerator to keep physical temperatures low, as well as employing low-noise quantum electronics to minimize receiver noise. To date, ADMX has excluded axion-photon couplings predicted by the KSVZ (DFSZ) model for the axion between 2.66-4.2 μeV (2.66-3.3 μeV & 3.9-4.1 μeV). Over the last year ADMX has been taking data designed to bridge the gap in DFSZ sensitivity for regions in the 3.3 to 3.9 μeV range. In this talk, I will be discussing the receiver noise calibration procedures used for this dataset. In particular, I will discuss the different types of measurements taken, as well as the noise models and analysis strategies used on said measurements.