Japanese physicist Takaaki Kajita was announced as a joint winner of the 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.

It 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 Gifu Prefecture.

Meanwhile, a research group in Canada led by McDonald could demonstrate that neutrinos from the sun were not disappearing on their way to Earth, it 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.”

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.