Improved Receiver Noise Calibration for ADMX Axion Search: 4.54 to 5.41 $\mu$eV

TL;DR

This paper develops a detailed noise model for the ADMX axion search receiver, presents new calibration measurements, and offers insights to reduce system noise, enhancing the sensitivity of axion detection efforts.

Contribution

It introduces a comprehensive noise model for axion haloscope receivers, including calibration techniques and analysis of cavity-JPA interactions, to improve noise temperature understanding.

Findings

Identified a previously unknown cavity-JPA interaction.

Provided calibration data at 1280 MHz during ADMX's recent run.

Suggested methods for lowering system noise temperature.

Abstract

Axions are a well-motivated candidate for dark matter. The preeminent method to search for axion dark matter is known as the axion haloscope, which makes use of the conversion of axions to photons in a large magnetic field. Due to the weak coupling of axions to photons however, the expected signal strength is exceptionally small. To increase signal strength, many haloscopes make use of resonant enhancement and high gain amplifiers, while also taking measures to keep receiver noise as low as possible such as the use of dilution refrigerators and ultra low-noise electronics. In this paper we derive the theoretical noise model based on the sources of noise found within a typical axion haloscope receiver chain, using the Axion Dark Matter eXperiment (ADMX) as a case study. We present examples of different noise calibration measurements at 1280~MHz taken during ADMX's most recent data-taking run. These new results shed light on a previously unidentified interaction between the cavity and JPA, as well as provide a better understanding of the systematic uncertainty on the system noise temperature used in the axion search analysis for this data-taking run. Finally, the consistency between the measurements and the detailed model provide suggestions for future improvements within ADMX and other axion haloscopes to reach a lower noise temperature.