A leader in the study of solar and atmospheric neutrinos, he was a scientist and director at Kamioka Observatory, Super-Kamiokande and the High Energy Physics Laboratory (KEK) in Japan.

[1] From 1972 to 1981 he also worked with the Double Arm Spectrometer (DASP) and JADE particle detector experiments at Deutsches Electron Synchrotron (DESY) in Hamburg, Germany.

[3] In 1981, Totsuka returned from Germany to Japan to work at the Kamioka Observatory, part of the Institute for Cosmic Ray Research (ICRR) at the University of Tokyo.

In 1988, after Masatoshi Koshiba retired, Totsuka took his place as organizer and spokesperson of a core group of researchers to promote an expanded Cherenkov detector, the Super-Kamiokande (Super-K) experiment.

[3][4][2] From 1995‐2002, Totsuka served as the director of the Kamioka Observatory, part of the Institute for Cosmic Ray Research (ICRR) at the University of Tokyo.

[7][8] Following an accident that destroyed over half of the Super-K photomultiplier tubes on 12 November 2001, Totsuka provided key leadership for reconstruction of the detector.

As a result, Kamioka was one of two locations on Earth to successfully measure the release of neutrinos from a cosmogenic source, when the supernova SN 1987A exploded in the Large Magellanic Cloud.

[10] The data from Kamiokande crucially confirmed the existence of the solar neutrino problem posed by the work of Davis and Bahcall.

Totsuka and his group published the first paper on the atmospheric neutrino anomaly in 1988, a result that would require “as-yet-unaccounted-for physics” to explain.

This was later confirmed through a collaboration between Super-Kamiokande and the Sudbury Neutrino Observatory (SNO) in Canada, reported in 2001, by comparing data collected by the two facilities.

[1][3][4][2] In addition, as the Director General at KEK, Totsuka successfully oversaw the K2K experiment and the Belle B-meson "factory", exploring differences between matter and antimatter.

In 2006, after cancer spread to his lung, he retired from his position at KEK, but served as a director of research at the Japan Society for the Promotion of Science.

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.