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Yoji Totsuka Edit Profile

戸塚 洋二

physicist , university professor

Yoji Totsuka, Japanese physics educator. Recipient Nishina Memorial prize Nishina Foundation, 1987, Asahi prize 1988, 1999, Rossi prize American Astronomical Society, 1989, Inoue prize, 1990, Special prize, European Physical Society, 1995; co-recipient Benjamin Franklin medal in Physics, Franklin Institute, 2007.


Totsuka, Yoji was born on March 6, 1942 in Fuji, Japan. Son of Kazuo and Mitsuko (Ono) Totsuka.


Bachelor of Science in Physics, University Tokyo, 1965. Master of Science, University Tokyo, 1967. Doctor of Science, University Tokyo, 1972.


Totsuka died on July 10, 2008 from colorectal cancer. Totsuka became a Associate at the University of Tokyo in 1972, followed by seven years at Deutsches Electron Synchrotron (DESY) in Germany, where he investigated electron–positron collisions. Subsequently, he became an Associate Professor of the University of Tokyo from 1979 to 1987.

In 1987, he was promoted to full Professor at the University of Tokyo. He later became the Director of the Kamioka Observatory, part of the Institute for Cosmic Ray (ICRR) at the University of Tokyo in 1995 and then Director of the Institute for Cosmic Ray in 1997. In 2003, Totsuka became the Director General of the High Energy Accelerator Organization (KEK).

The experiment, though designed to detect proton decay, actually ended up successfully measuring the first and so far only neutrinos from a cosmogenic source on Earth, from SN 1987A, along with the Irvine–Michigan–Brookhaven (IMB) detector in the US. The success of Kamiokande, through Totsuka's leadership, led to the funding of a substantially larger water Cherenkov detector in 1991, the storied Super-Kamiokande (Super-K) detector, which is still an active international collaboration. It was at Super-K that the first definitive evidence for neutrino oscillations was measured, via a high-statistics, high-precision measurement of the atmospheric neutrino flux. Super-K also confirmed, along with the Sudbury Neutrino Observatory (SNO), the solution to the solar neutrino problem.

The measurement of neutrino oscillations at such a high level of precision was a critical chapter in the history of particle physics. Neutrino oscillations, and thus the existence of neutrino mass, are not a prediction made by the Standard Model of particle physics. Indeed, the Standard Model requires that neutrinos are massless.

Totsuka's experiment provided incontrovertible evidence that there is still much about particle physics yet to be understood. For the remainder of his time as a physicist, as the Director General at KEK, he oversaw successful the K2K experiment and the Belle B-meson "factory". When he left physics, towards the end of his life, Totsuka turned his attention to communicating with the Japanese public about his illness, science, and culture.

He maintained a blog, The Fourth Three-Months, where he candidly discussed the extent, progress, and treatment of his cancer. Totsuka also revealed an interest in gardening, particularly the flowers in the area where he spent much of his career, in Mozumi, the village where Super-K is located.


  • Asahi Prize, 1987\r\nNishina Memorial Prize, 1988\r\nBruno Rossi Prize, (American Astronomical Society),1989\r\nInoue Prize for Science, 1990\r\nEPS Special Prize, European Physical Society, 1995\r\nOrder of Culture, 2004\r\nBenjamin Franklin Medal in Physics, 2007.


Member Japan Physical Society, Japan Astronomical Society, American Physical Society(Wolfgang Kurt Hermann Panofsky prize in Experimental Particle Physics, 2002).


Married Hiroko Miyata, January 2, 1944. Children: Hirofumi, Yumi.

Kazuo Totsuka

Mitsuko (Ono) Totsuka

Hiroko Miyata

Yumi Totsuka

Hirofumi Totsuka