The Sudbury Neutrino Observatory, a Canadian physics research facility with substantial involvement by UW scientists, this month will complete more than seven years of neutrino measurements using a heavy water detector core.
During that time some 25,000 neutrino signals have been recorded, providing a very precise determination of the numbers and types of neutrinos from the sun, subatomic particles that constantly bombard the Earth.
Heavy water has the unique ability to detect all three types of neutrinos, and scientists working at Sudbury have been able to deduce the total number of solar neutrinos of all types reaching the Earth, as well as the number of electron neutrinos produced in the Sun’s core. The laboratory’s measurements showed that about two-thirds of solar neutrinos had changed from electron neutrinos to one of the other two types on the way to Earth, which resolved a 30-year discrepancy between theoretical predictions and actual observations.
Hamish Robertson, a UW physics professor and U.S. co-spokesman for the observatory, said the third phase of measurements, which started in 2004 and is now reaching its conclusion, has been productive.
“The installation and successful operation of new detectors in Sudbury’s heavy water core, led by groups from the University of Washington and Los Alamos National Laboratory, have enabled the laboratory’s most important neutrino reaction to be measured with maximum precision,” he said.
UW physicists John F. Wilkerson and Peter Doe and research engineer Tom Burritt also have played key roles in the international collaboration conducting the research at Sudbury, the world’s deepest underground laboratory, built in a nickel mine near Sudbury, Ontario. The team that built the observatory was awarded the Polanyi Prize this week by the Canadian government for its groundbreaking neutrino research.
Neutrinos are difficult to detect because they pass through most forms of matter very easily. Billions of the wispy particles pass through people’s bodies every second with no noticeable effect.