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The Path to the Nobel Prize

The Prize

The 2015 Nobel Prize in Physics was awarded jointly to Dr. Arthur B. McDonald and Dr. Takaaki Kajita “for the discovery of neutrino oscillations, which shows that neutrinos have mass.” This revolutionary work redefined the basic laws of particle physics, and confirmed the detailed understanding of how the sun burns.

The Nobel Prize was established in 1901. Dr. McDonald is the fourth Canadian, and first faculty member of Queen’s University, to receive the Nobel Prize in Physics. In December 2015, Dr. McDonald travelled to Sweden to receive the Nobel Prize medal from the Royal Swedish Academy of Sciences.

The medal depicts Alfred Nobel (1833-1896), who bequeathed the bulk of his fortune to honour outstanding contributions to humanity.

The inscription on the reverse of the medal for physics, taken from Virgil’s Aeneid, reads, “Inventas vitam iuvat excoluisse per artes,” which, loosely translated, says, “And they who bettered life on earth by their newly found mastery.”

Solving the Solar Neutrino Problem

Outstanding scientific contributions to measurements of basic neutrino properties and solar models have moved us closer to understanding our universe and its evolution.

Painstaking efforts by an international scientific collaboration, under Dr. McDonald’s leadership as Director of the Sudbury Neutrino Observatory (SNO) experiment, led to the creation of the ultimate low-radioactivity instrument. This instrument ultimately solved the Solar Neutrino Problem, which was a major discrepancy between the measurement of the number of neutrinos reaching the earth and the theoretical models of the number generated in the solar interior. The original Directors of the SNO scientific collaboration in 1964 were Queen’s Dr. George Ewan and Dr. Herb Chen of the University of California, Irvine, and many members of the physics and other departments at Queen’s and other institutions provided expertise throughout the project.

The SNO experiment was carried out in a unique low-radioactivity laboratory near Sudbury, Ontario, two kilometres underground, to eliminate radioactivity from cosmic rays. SNO separately observed electron neutrinos from all active neutrino types, providing clear evidence that the electron neutrinos from the core of the sun were changing their type, a process arising from neutrinos of finite mass undergoing oscillations. The results from SNO, coupled with results for atmospheric neutrinos from the Super-Kamiokande experiment in Japan, required modifications to the Standard Model of Elementary Particles to include massive neutrinos. SNO results also provided a very accurate confirmation of current models of the sun and its energy-generation processes.

After years of study by the scientific community, answering these questions was a major accomplishment, and provided increased insight into the evolution of our universe and neutrinos – fundamental building blocks of nature. To this day, results from SNO are motivating new experiments at SNOLAB, an expanded underground laboratory, as well as internationally. All of these experiments are aimed at further understanding neutrino properties and their effects in the early universe.

For his leadership and scientific scholarship, Dr. McDonald has received dozens of national and international honours, most notably the 2015 Nobel Prize in Physics and the 2016 Breakthrough Prize. In 2018, the Arthur B. McDonald Canadian Astroparticle Physics Research Centre, based at Queen’s, was launched thanks to support from the Canada First Research Excellence Fund. These accolades brought worldwide attention to Canadian research excellence and its inspirational potential. In 2022, Dr. McDonald was an inaugural recipient alongside Nobel Laureate Donna Strickland of the Canadian Association of Physicists Fellowship, a career honour recognizing contributions to physics research and education, leadership within the Canadian physics community and inspiring the next generation of physics graduates.

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A Nobel Prize in Physics for Dr. Arthur B. McDonald

An interest in mechanics led Dr. McDonald, the 2015 co-winner of the Nobel Prize in Physics, to study the universe on a fundamental level, through physics.

The Neutrino Breakthrough

Science journalist Ivan Semeniuk retraces the history of Canada’s Nobel Prize-winning physics experiment, and explains the discoveries.