Scientists spot elusive neutrinos in Sudbury

by Bruce Mason
Staff writer

UBC scientists are among the first to see the light created when neutrinos, the elusive but most common particles in the universe, interact in 1,000 tonnes of heavy water.

The breakthrough made at the Sudbury Neutrino Observatory (SNO) is the result of an international collaboration of nearly 100 scientists from 11 universities and laboratories including the University of British Columbia/TRIUMF group.

The results will help answer questions about the nature of matter on the smallest scale, as well as provide insights into the structure of the stars and the universe as a whole.

"Neutrinos are at least as common as the particles of light, but some of their basic properties, like their mass, aren't known for certain," says group member Chris Waltham, an associate professor of Physics. "This is because neutrinos are not at all easy to study as they interact rarely with other matter and so are very difficult to see."

UBC and TRIUMF personnel have been working on SNO since 1988, says TRIUMF research scientist Rich Helmer.

"To see neutrinos at last is a vindication of all these years of computer simulation and design, followed by detector construction and commissioning," he says.

Located 2,000 metres underground in a nickel mine in Sudbury, Ont., SNO is shielded from cosmic rays and other sources of unwanted "background."

It is designed to detect neutrinos from sources beyond the Earth, in particular from the sun, which bathes each square centimetre of the Earth's surface with billions of neutrinos a second.

SNO has been built to help resolve some of the mysteries that continue to surround neutrinos, in particular the puzzle of why previous experiments do not detect as many neutrinos from the sun as expected.

Among its first images are stunning examples of the pools of light formed by the interactions of neutrinos that began life in the sun or in the atmosphere on the opposite side of the Earth.

"This is tremendously exciting," says SNO director Prof. Art McDonald of Ontario's Queen's University. "It is 15 years since the start of the SNO project, and to see such clear examples of neutrino interactions within days of finally turning on the full detector was a real triumph for the entire SNO team."

To learn more about SNO, visit its official Web site at Assoc. Prof. Chris Waltham's site is at