June 18, 2001

SNO First Results

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BERKELEY, CA ó  After more than a yearís worth of data, the first results are in from the Sudbury Neutrino Observatory (SNO) and a mystery that has vexed scientists for more than 30 years has been solved. SNOís results indicate that solar neutrinos have a mass and will require an extension to the Standard Model of Particles and Fields which has successfully explained fundamental physics since the 1970's. SNOís first results when combined with the Super Kamiokandeís results definitively demonstrate that solar neutrinos are "oscillating" or transforming from one kind to another in transit from the core of the sun to the earth.

Sudbury Neutrino Observatory images

"When we combine the SNO results for electron-neutrinos with previous measurements, we can say with greater than 99-percent confidence that solar neutrinos are undergoing changes on their way to Earth," says Kevin Lesko, a physicist with the Lawrence Berkeley National Laboratory (Berkeley Lab) and a key member of the SNO research collaboration. "The measurements by SNO also provide a limit on the difference in mass between electron-neutrino and the other flavors of neutrino that are involved."

This mass difference, coupled with absolute neutrino mass measurements and the Kamiokandeís measurements, indicates that the combined mass of all the neutrinos in the universe is about equal to the combined mass of all the visible stars. That means neutrinos cannot account for all the "dark matter" known to make up most of the mass of the universe.

Lesko, leader of the Neutrino Astrophysics Group in Berkeley Labís Nuclear Sciences Division, has been a key member of the huge SNO collaboration since 1989. He oversaw the design and construction of the geodesic sphere and panel arrays which house SNO's elaborate web of ultrasensitive photomultiplier tubes (PMTs), working closely with Gary Koehler of Berkeley Labís Engineering Division who served as the SNO projectís senior designer, and Yoichi Kajiyama who was the projectís lead mechanical engineer.

Lesko can be reached for an interview at (510) 486-7731 or by e-mail at KTLesko@lbl.gov. For the official SNO press release, a copy of the science paper, images and a wealth of additional information on the project and its first results, follow the links below.

Additional information: