The Nobel Prize in Physics 2015
Born: 9 March 1959, Higashimatsuyama, Japan
Affiliation at the time of the award: University of Tokyo, Kashiwa, Japan
Prize motivation: "for the discovery of neutrino oscillations, which shows that neutrinos have mass."
Prize share: 1/2
Takaaki Kajita was born in Higashimatsuyama, Saitama, Japan. He studied at Saitama University and at the University of Tokyo where he received his doctorate in 1983. His doctoral advisor was the future Nobel Laureate Masatoshi Koshiba. Since 1988 he is affiliated with the Institute for Cosmic Radiation Research, University of Tokyo, and in 2015 he became its director. He is also a professor at the University of Tokyo. Takaaki Kajita is married to Michiko Kajita.
The Standard Model used by modern physics has three types of a very small and elusive particle called the neutrino. In the Super-Kamiokande detector, an experimental facility in a mine in Japan in 1998, Takaaki Kajita detected neutrinos created in reactions between cosmic rays and the Earth's atmosphere. Measurements showed deviations, which were explained by the neutrinos switching between the different types. This means that they must have mass. The Standard Model, however, is based on neutrinos lacking mass and the model must be revised.