Yoji Totsuka, a particle physicist known for his groundbreaking discovery about neutrinos, died Thursday of multiple organ failure caused by cancer, his family said. He was 66.
Totsuka, who held the title of special professor emeritus at his alma mater, the University of Tokyo, was considered a hopeful for a Nobel Prize in physics for his finding that neutrinos, elementary particles, have mass.
He was a colleague of Masatoshi Koshiba, a cowinner of the 2002 Nobel Prize in physics for the detection of cosmic neutrinos, and did neutrino research at Kamiokande, an advanced observatory built 1,000 meters below ground in Gifu Prefecture. After Kamiokande was succeeded by Super Kamiokande in 1996, Totsuka led the research at the facility. There he found that neutrinos, which are created when cosmic rays hit Earth's atmosphere, mutate in their flight in a phenomenon called neutrino oscillation. The finding led him to conclude that neutrinos have mass, a result that called for a revision of the conventional theory of particle physics.
Among major awards he received, Totsuka was honored with Japan's prestigious Order of Culture and won a Benjamin Franklin Medal.
After completing his doctorate at the University of Tokyo in 1972, he taught there and became a professor in 1987. He was later posted as professor at the High Energy Accelerator Research Organization in 2002 and served as its chief between 2003 and 2006.