Arthur Bruce McDonald
active c. 1943, Sydney, Nova Scotia, Canada
Canadian physicist who directed SNO — the experiment proving solar neutrinos change flavor en route to Earth.
McDonald led the design of SNO: a tank of 1,000 tonnes of heavy water in a nickel mine 2 km under Ontario, able to measure electron neutrinos separately from all flavors. The 2001–2002 results showed solar neutrinos arrive at Earth mostly as other flavors — solving the 30-year-old 'solar neutrino problem'.
Nobel-winning work
McDonald's SNO measured three channels simultaneously (CC, ES, NC): electron neutrinos from the Sun were depleted while the total of all flavors matched the standard solar model. This proved neutrinos oscillate — hence have mass — combining with Kajita's Super-K result to establish that neutrinos are not massless.
Workplaces: Queen's University, Sudbury Neutrino Observatory (SNO)
Canada, United States