Queen’s University professor emeritus Arthur McDonald is the co-winner of the 2015 Nobel Prize in physics.

The announcement, made Tuesday morning by the Royal Swedish Academy of Sciences in Stockholm, said Dr. McDonald won the award, along with Takaaki Kajita of the University of Tokyo, “for their key contributions to the experiments which demonstrated that neutrinos change identities.”

The findings solved a puzzle that physicists had wrestled with for decades, the academy added in its announcement.

Dr. McDonald’s research took place at the Sudbury Neutrino Observatory (SNO) scientific collaboration, an advanced research facility located 2 km underground in an active nickel mine. The experiment demonstrated that neutrinos from the sun were not disappearing on their way to earth and were captured with a different identity when arriving at SNO.

Meanwhile, Dr. Kajita presented the discovery that neutrinos from the atmosphere switch between two identities on their way to the Super-Kamiokande detector in Japan.

This “metamorphosis” requires that neutrinos have mass.

“For particle physics this was a historic discovery,” the Nobel Committee said in its release. “Its Standard Model of the innermost workings of matter had been incredibly successful, having resisted all experimental challenges for more than 20 years. However, as it requires neutrinos to be massless, the new observations had clearly showed that the Standard Model cannot be the complete theory of the fundamental constituents of the universe.”

The discovery changed “our understanding of the innermost workings of matter and can prove crucial to our view of the universe,” added the committee.

Dr. McDonald arrived at Queen’s in 1989, was the inaugural Gordon and Patricia Gray Chair in Particle Astrophysics and served as the director of SNO, now known as SNOLAB.

The facility is operated by the SNOLAB Institute whose member institutions are Queen’s University, Carleton University, Laurentian University, University of Alberta and Université de Montréal. It is located two km below the surface in the Vale Creighton Mine near Sudbury, Ont.

He has been a professor emeritus since 2013. He earned his PhD in 1969 from the California Institute of Technology.

For his research, Dr. McDonald has received a number of awards and recognition including being elected a Fellow of the Royal Society of the UK and Commonwealth in 2009. In 2010 he received the Killam Prize in the Natural Sciences, in 2011 received the Henry Marshall Tory Medal from the Royal Society of Canada, its highest award for scientific achievement; and in 2013 he was awarded the European Physics Society HEP Division Giuseppe and Vanna Cocconi Prize for Particle Astrophysics.

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