Takaaki Kajita, 56, director of the University of Tokyo's Institute for Cosmic Ray Research (ICRR), was awarded the Nobel Prize in Physics together with Arthur McDonald of Queen's University, Canada, the Royal Swedish Academy of Sciences announced Tuesday.
The award honors Kajita for his discovery "of neutrino oscillations, which shows that neutrinos have mass."
Kajita is the eleventh Japanese Nobel Prize winner in Physics, following the most recent winners: Isamu Akasaki, Hiroshi Amano and Shuji Nakamura, who shared the prize in 2014.
The prize money of 8 million Swedish kronor (about ¥115 million) is divided equally between winners in physics. The award ceremony will be held in Stockholm on Dec. 10.
According to the academy, the discovery led to the far-reaching conclusion that neutrinos, which for a long time were considered massless, must have some mass, however small.
"Around the turn of the millennium, Takaaki Kajita presented the discovery that neutrinos from the atmosphere switch between two identities on their way to the Super-Kamiokande detector in Japan," the academy's press release said.
In 1988, Kajita announced the probability that neutrinos have mass, based on the data of "atmospheric neutrinos," which emerge when cosmic rays from space collide with the Earth's atmosphere.
Born in 1959 in Higashi-Matsuyama, Saitama Prefecture, Kajita graduated from Saitama University's faculty of science, majoring in physics.
After entering graduate school at the University of Tokyo, he joined the laboratory of Masatoshi Koshiba, professor emeritus at the university. Koshiba won the 2002 Nobel Prize in Physics for the first detection of neutrinos using a neutrino detector he had designed.
Kajita obtained his PhD in science in 1986 and became a professor at the ICRR in 1999 after working as an assistant and associate professor. He has served as the director of the ICRR since 2008. He has also served as the chief at the Research Center for Cosmic Neutrinos, an affiliate of the ICRR, since 1999.
The research group in Canada led by McDonald could demonstrate that the neutrinos from the sun were not disappearing on their way to Earth. Instead, they were captured with a different identity when arriving to the Sudbury Neutrino Observatory.