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We observe that 85% of the matter in the universe is in the form of invisible "dark matter" -- but we still do not know what this dark matter is. My favorite dark matter candidate is an "axion" – a hypothetical particle suggested by the problem of explaining the fundamental symmetries of the nuclear forces. The axion has a very small mass compared to other suggested dark matter particles. In an experiment, it would behave more like a wave than a particle. So, to discover axions, we are using a method completely different from those of other dark matter searches. In the SLAC experiments ADMX and Dark Matter Radio, we are building ultra-low-noise radio receivers, immersed in high magnetic fields, to identify the axion as a new radio band coming in from the cosmos. If we discover the axion, any high school physics class will be able to tune in to the axion airwaves.

About the speaker:

Chelsea Bartram has been interested in radio for a long time.  As a kid, she tried to imagine radio waves bouncing off the ionosphere and into her yard in Ohio.  She earned a ham radio license, built a few antennas,  and realized that she could hear people talking in foreign countries!  But detecting radio waves created by people was not enough.  She built up her knowledge by earning a Ph.D. in nuclear physics at the University of North Carolina, Chapel Hill, in 2019, and then working as a postdoctoral fellow at the University of Washington.  In 2022, she joined SLAC as a Panofsky Fellow.  Her goal today is to discover the axion by combining the old technologies of radio reception with the latest ultra-low-temperature detectors and quantum sensors.