August 20, 2014
UW project becomes a focal point in hunt for dark matter
Three major experiments aimed at detecting elusive dark matter particles believed to make up most of the matter in the universe have gotten a financial shot in the arm. Two of the projects are at large national laboratories; the other is at the University of Washington.
The selection will bring greater intensity to the UW research, with more equipment and scientists involved in the work.
University of Washington physicists Leslie Rosenberg (left) and Gray Rybka examine the Axion Dark Matter Experiment detector package before it is lowered into the bore of a superconducting magnet in late 2013. The experiment is being conducted at the UW’s Center for Experimental Nuclear Physics and Astrophysics.Mary Levin / UW
“We’re kind of transitioning from an experiment into a facility. We haven’t quite figured out what the implications of this are,” said Leslie Rosenberg, a UW physics professor and a leader of the Axion Dark Matter Experiment.
Dark matter is believed to make up about one-quarter of the mass of the universe, and as much as 85 percent of all matter. However, it apparently does not interact with light or matter and so has never been directly observed. Scientists search for it through gravitational and other interactions.
The Axion Dark Matter Experiment is searching for a theorized-but-never-seen elementary particle called the axion. A very sensitive detector at the UW’s Center for Experimental Nuclear Physics and Astrophysics is hunting for cold dark matter axions in the halo of the Milky Way galaxy by detecting their conversion into microwave photons.
For nearly a century, scientists have theorized that there must be an unseen substance that prevents galaxies from spinning apart. Axions are one candidate for cold dark matter that would act as that gravitational glue.
Two federal agencies, the Department of Energy’s Office of High Energy Physics and the National Science Foundation Physics Division, in July approved more than $5 million in funding spanning several years for the second generation of the axion search.
The other dark matter experiments selected for funding are the Super Cryogenic Dark Matter Search at SnoLab, located in a nickel mine near Sudbury, Ontario, and the LZ Dark Matter Search Experiment at the Sanford Underground Research Facility, located in a former gold mine near Lead, South Dakota. Both of those experiments are searching for a different dark-matter candidate called a weakly interactive massive particle.
Those projects and the axion experiment were chosen for additional funding from among nearly two dozen proposals.
“Axions are becoming a more and more compelling candidate for dark matter and this is essentially authorization for us to recruit good scientists for the search,” said Gray Rybka, a UW research assistant professor of physics working on the axion project.
The existing detector uses a powerful magnet surrounding a sensitive microwave receiver that is supercooled to less than 4.2 kelvins, or about minus-452 F or minus-269 C. The apparatus is enclosed in a borehole in the floor of the UW’s North Physics Laboratory. Supercooling greatly increases the sensitivity of the detector.
The new federal authorization will bring total funding for the axion search effort to around $20 million since 2011, Rosenberg said. Already there are potential users from other institutions who could plug into the UW-based experiment as soon as October. They would use instruments tuned to frequencies different from the one already in place.
“Certainly we’re going to have a big ramp-up for our project,” Rosenberg said. “We envision more magnet bores, more cryogenic capability.”
With the added capacity, he believes that in as little as three years scientists might have confirmed the axion as cold dark matter or eliminated it from further consideration. Either way, it would be a major step in dark matter research.
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