Oct 7 2015
Arthur B. McDonald, one of the two recipients of the 2015 Nobel Prize in Physics, was a professor of physics at Princeton University from 1982 to 1989 when he began developing the experiment for which he received worldwide recognition Oct. 6.
McDonald, now a professor emeritus of physics at Queen's University in Canada, was recognized by the Royal Swedish Academy of Sciences for showing that neutrinos — which mostly emanate from the sun and are the second most numerous particle in the universe after photons — have mass.
Specifically, McDonald led a large experiment known as the Sudbury Neutrino Observatory (SNO) that revealed in 2001 that neutrinos oscillate, or change types known as "flavors," as they travel through space. This finding prompted a modification of the Standard Model of elementary particles, which is the theoretical diagram of how subatomic particles interact, and resolved a 30-year-old mystery known as the solar neutrino problem.
McDonald came to Princeton from Atomic Energy Canada Limited to study nuclear reactions using Princeton's cyclotron, a low-energy particle accelerator that was shut down in the 1990s. While at the University, he shifted his research focus to neutrinos and developing the SNO project. That work included designing the project, bringing on collaborators, and securing funding and resources, including the eventual home of the SNO particle detector located 6,800 feet underground in the Creighton nickel mine in Sudbury, Ontario. In 1989, McDonald left Princeton for Queen's University so that he could directly oversee the SNO experiment. He was soon joined at Queen's by Princeton assistant professors Mark Chen, now a professor of physics at Queen's, and Aksel Hallin, a professor of astroparticle physics at the University of Alberta who received his doctorate in physics from Princeton in 1983.
Neutrinos travel close to the speed of light and pass through ordinary matter almost undisturbed, which makes them nearly impossible to detect. In the late 1960s, scientists found that the number of neutrinos arriving from the sun was between one-third and one-half the number predicted by theoretical models. This discrepancy became known as the solar neutrino problem. McDonald and his SNO team found that because neutrinos produced in the sun morph into different flavors, past experiments could not have detected them.
A notable and ultimately successful feature of the project was the use of "heavy water," which largely consists of deuterium, an isotope of hydrogen that includes a neutron and is thus atomically heavier. The idea that heavy water would make a detector more sensitive to neutrino reactions was first proposed by the late Herbert Chen, a professor of physics at the University of California-Irvine who received his Ph.D. in theoretical physics from Princeton in 1968.
For his work, McDonald has won many awards, including being a co-winner of the 2007 Benjamin Franklin Medal for Physics, named an Officer of the Order of Canada in 2006, and receiving the Order of Ontario in 2012.
Source: http://www.princeton.edu/