Japanese physicist Takaaki Kajita was announced as a joint winner of the 2015 Nobel Prize in physics Tuesday for his groundbreaking work in experiments showing metamorphosis of the particle world.
Kajita, of the University of Tokyo, shared the prize with Arthur B. McDonald of Queen’s University in Canada.
In a boon for Japan’s science community, it came a day after microbiologist Satoshi Omura shared the Nobel Prize for medicine.
The Nobel committee said it honored the 56-year-old Kajita and McDonald, 72, “for the discovery of neutrino oscillations, which shows that neutrinos 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 body said.
The committee said that around the turn of the millennium, Kajita presented the discovery that neutrinos, known as nature’s most elusive particles, from the atmosphere switch between two identities on their way to the Super-Kamiokande detector in Hida, Gifu Prefecture.
At a news conference Tuesday evening at the University of Tokyo, Kajita expressed surprise at receiving the prize, saying, “My head turned totally blank.”
He praised his colleagues, saying they are the ones who deserve the honor. He also thanked his wife, Michiko, who lives in the city of Toyama, for her “years of patience with me, who was always doing research.”
Born in Higashimatsuyama, Saitama Prefecture, Kajita obtained a Ph.D. from the University of Tokyo in 1986. He is director of the Institute for Cosmic Ray Research and a professor at the University of Tokyo.
The University of Tokyo issued a congratulatory statement that pointed out Kajita was a student of 2002 Nobel physics winner Masatoshi Koshiba, who has also contributed to Japan’s neutrino research. Kajita, a disciple of Koshiba, phoned him soon after the Nobel Prize announcement, Koshiba told reporters.
The research group in Canada led by McDonald could demonstrate that neutrinos from the sun were not disappearing on their way to Earth, the Nobel committee said. Instead, they 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,” the Nobel body said.
It added that “the discovery led to the far-reaching conclusion that neutrinos, which for a long time were considered massless, must have some mass, however small. For particle physics this was a historic discovery.”
McDonald told a news conference in Stockholm by telephone that the eureka moment was when it became clear that his experiment had proven with great accuracy that neutrinos changed from one type to another in traveling from the sun to Earth.
Asked how he felt when he realized Tuesday that his work was suddenly going to receive the world’s focus, McDonald said, “It’s a very daunting experience, needless to say.”
McDonald said scientists still want to know what the actual mass of the neutrino is. And experiments are looking at whether there are other types of neutrinos beyond the three clearly observed.
The winners will split the 8 million Swedish kronor (about $960,000) prize money. Each winner will also get a diploma and a gold medal at the prize ceremony on Dec. 10.