Searching for invisible axion dark matter

—by Aaron Quiskamp

EQUS researchers at UWA, as part of the ADMX Collaboration, are working to narrow the parameter space for finding the axion—a candidate dark-matter particle.

The Axion Dark Matter eXperiment (ADMX), based in Washington State, Seattle, is the most mature and sensitive axion dark-matter experiment in the world.  It consists of a strong magnetic field, which converts dark-matter axions into microwave-frequency photons, to be detected using highly sensitive, low-noise quantum readout circuits.  

The latest results from the collaboration, based on the third phase of the experiment (Run1c), exclude axions at frequencies of 800–1,020 MHz with very low axion–photon couplings (so-called invisible dark matter).  The new results build on previous work by the collaboration to exclude the allowable parameter space for axions, bringing us one step closer to completely excluding the parameter space or finding the axion!

The UWA team—Aaron Quiskamp, Catriona Thomson, Ben McAllister, Maxim Goryachev and Mike Tobar—contributes to the collaboration by modelling cavity designs for the current experiment and for future experiments.  We also contribute to the ‘Hi-Res’ branch of the analysis team: we analyse the data to look for very narrow axion signals, which are predicted to result from late inflows of non-thermalised axion dark matter into the Galactic halo.

The next step for the project involves building new cavities and cavity arrays to push higher and higher into the axion mass–coupling parameter space, thereby ruling out axions or discovering them.  The experiment is also relocating and upgrading to a larger magnet.

This work and the expertise gained by being a part of the collaboration helps us with one of EQUS’ flagship projects, ORGAN, an axion experiment based at UWA searching for axions at higher masses.  Keep an eye out for more on ORGAN soon!