This year’s Nobel Prize in Physics has been awarded to Takaaki Kajita and Arthur B. McDonald for their discovery of neutrino oscillations, which show that the subatomic particles have mass.
“The discovery has changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe,” the Royal Swedish Academy of Sciences, which award the prize, said in a statement.
Kajita, of the University of Tokyo, presented the discovery that neutrinos—the second-most-abundant particles in the cosmos after photons—from the atmosphere switch between two identities on their way to the Super-Kamiokande detector in Japan. McDonald’s group, at Queen’s University, Kingston, Canada, meanwhile showed neutrinos from the Sun weren’t disappearing on their way to Earth, but instead were captured with a different identity when arriving at the Sudbury Neutrino Observatory.
A neutrino puzzle that physicists had wrestled with for decades had been resolved. Compared to theoretical calculations of the number of neutrinos, up to two thirds of the neutrinos were missing in measurements performed on Earth. Now, the two experiments discovered that the neutrinos had changed identities.
The discovery led to the far-reaching conclusion that neutrinos, which for a long time were considered massless, must have some mass, however small.
The discovery prompted a rethink of the Standard Model of particle physics, which required neutrinos to be massless.
Kajita said he was checking his emails when he received the phone call informing him of the honor. It’s “kind of unbelievable,” he said.
You can listen to his interview upon receiving the prize here:
McDonald was awoken with news of the Nobel Prize. “As it turns out,” he said, “I did not mind.” Here’s McDonald’s interview: