Yoji Totsuka - Research

Research

Totsuka's career in neutrino physics began following his time at DESY, when he began working as part of the Kamiokande experiment with Nobel prize winner Masatoshi Koshiba. 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".