Colorado State University Physicist a Participant in International Experiment on Neutrinos

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Colorado State University Professor Bill Fairbank spent a good part of May about a half-mile underground in New Mexico, studying the physical mass of the tiniest particles that make up matter – particles known as neutrinos.

Fairbank is one scientist in a team of about 80 international collaborators participating in the Enriched Xenon Observatory 200, or EXO-200, experiment hosted by the SLAC National Accelerator Laboratory, which is operated by Stanford University for the U.S. Department of Energy.

They’re studying a mysterious mechanism called “neutrinoless double-beta decay” in which two neutrinos – acting as particle and antiparticle – do not emerge from the nucleus. SLAC recently announced that the group found, with the highest degree of sensitivity yet, that these mysterious particles behave like other elementary particles at the quantum level.

The results shed light on the mass and other properties of the neutrino and prove the effectiveness of a new instrument that will yield even greater discoveries in this area, SLAC officials said.

The research has been conducted at a New Mexico salt bed buried 2,150 feet deep at the DOE’s Waste Isolation Pilot Plant. Fairbank and five of his students have been working part time at the site for the past five years.

“One of the remarkable things about nature is we don’t know the mass of neutrinos, and that’s what we’re trying to discover,” Fairbank said. “They have at least a million times less mass than electrons. In New Mexico, we have a tank that contains 400 pounds of an isotope of xenon in a liquid. That’s a lot of atoms. We look for a decay of one of those atoms or a few of those atoms in a year, and the only place where we can study that decay without interference is underground.

“Our additional role at CSU is to develop new ideas for an even better experiment in the future,” he said.

EXO is a collaboration that involves scientists from SLAC, Stanford, the University of Alabama, Universität Bern, Caltech, Carleton University, University of Illinois Urbana-Champaign, Indiana University, UC Irvine, ITEP (Moscow), Laurentian University, the University of Maryland, the University of Massachusetts-Amherst, the University of Seoul and the Technische Universität München. This research was supported by DOE and NSF in the United States, NSERC in Canada, SNF in Switzerland and RFBR in Russia.