I was born in Nagoya, Japan on April 7, 1944. As it was in the middle of the Second World War, I was evacuated to Kawagoe Village in Mie Prefecture the following year to escape the aerial bombardment over Nagoya. Soon after the war ended, my father passed away. As I was only two years old at the time, I have no memory of him. My father, Hisashi, was a physician. At the end of his career, he served as the director of the central public health centre in Nagoya.
After my father’s death, we moved back to Nagoya to find our house rendered to ashes by the bombing. So we stayed at my mother’s family house. My mother, Ai, came from a family surnamed Kaifu. At that time, my mother’s parents and their elder son’s family were living in the house. The latter’s elder son, Toshiki Kaifu, who is my cousin, later became Japan’s prime minister. I don’t have any siblings. I have another cousin named Norio Kaifu, who is an astronomer. He served as the director of the National Astronomical Observatory of Japan.
In 1975, I married Sachiko Enomoto. My son, Junichiro, was born in 1977. Sachiko died of cancer at age 39. Junichiro majored and obtained a master’s degree in urban planning. He currently works at a private consultant firm. In 1990, I remarried. My wife Emiko Nakayama’s father, Tadasi, was a mathematician known for his research on Frobenius algebras. As he had passed away when Emiko was a child, I never had a chance to meet him. Emiko gave birth to our daughter Yuka.
I went to elementary and middle school in regular public schools. Nothing particularly unique happened during those school years. In high school, I played tennis every day. Though I never really got that good at it, I continued to enjoy playing tennis in my adult years. At around that time, I read The Evolution of Physics by Albert Einstein and Leopold Infeld. I don’t remember to what extent I actually understood it, but the book sparked my interest in physics.
I entered the Physics Department of Nagoya University. Besides it being my local university, what also attracted me to Nagoya University was the presence of Shoichi Sakata on its faculty. The model of elementary particles bearing his name was famous, so even high school students knew about it.
As a graduate student, I began my research in particle physics as a member of Prof. Sakata’s lab. A free atmosphere abounded in the lab; treated impartially, the graduate students were allowed to participate in discussions among the researchers. I believe that I learned a lot from that experience.
Regrettably, Prof. Sakata passed away while I was still a graduate student. During my graduate student days, I engaged in many discussions with Prof. Yoshio Ohnuki. I also met Toshihide Maskawa at Nagoya University. As I recall, our first contact was when I was an undergraduate student: As a graduate student he was helping us with our studies. I began conducting joint research with Maskawa after entering graduate school. Our research theme at that time was on chiral symmetry. We were trying to approach the subject from a quark-model perspective.
In March 1972, I received my doctoral degree in physics from Nagoya University. At that time, it was not easy for post-doctoral researchers to find positions. Fortunately, however, I was hired as a research associate in the Physics Department of Kyoto University. I moved to Kyoto in April. I resumed joint research with Maskawa, who had transferred to Kyoto University a little before me. We worked on CP violation, the research for which we later received the Nobel Prize. Engaging each other in discussion, we advanced our research quickly, completing it in a relatively short period of time. By the end of August, we had finished writing our paper.
With the discovery of the J/ψ-particle in 1974, there was, as in other countries, quite a commotion in Japan. Many theories were ventured as to the character of the J/ψ-particle; ultimately, however, it was determined to be a charmonium, which is a bound state of the c quark and its anti-particle. Before that, the hint of a fourth quark was obtained by Kiyoshi Niu in his experiment exposing emulsion chambers to cosmic rays. In this connection, a few Japanese groups, including mine, were investigating a four-quark model but were not able to predict the long lifetime of the charmonium state.
In 1975, the tau lepton was discovered. Since this indicated the existence of third-generation quarks, the six-quark model we proposed began to attract attention.
Although I did not contribute directly to the development of the six-quark model, I did write a paper with Katsuhiko Sato that was somewhat related. We tried to elucidate the limitations on the mass and lifetime of neutrinos in using cosmological arguments when similar flavour mixing exists within a leptonic sector.
During that period, KEK (the National Laboratory for High Energy Physics, now the High Energy Accelerator Research Organisation) had started operating its proton synchrotron accelerator, and discussions were underway on planning the following TRISTAN project. My first relationship with KEK was participation in these discussions. I was then hired as an associate professor in KEK’s Theory Division and moved to Tsukuba in 1979. At that time, the Theory Division was headed by Hirotaka Sugawara. Motohiko Yoshimura came to the Division about the same time I did. That year, I received the Nishina Memorial Prize.
Upon arriving at KEK, I became engaged in drafting the proposal for the TRISTAN project. It was originally intended to be an electron-positron-proton collider. However, the one approved for construction in 1981 was an electron-positron collider. Operation started in 1987. With our dream to discover the top quark unfulfilled, TRISTAN was shut down in 1995.
During that period, I spent three months at CERN (the European Organisation for Nuclear Research) from November 1982. While I was there, the W particle was discovered. It was a very exciting experience for me. However, just before my arrival at CERN, J.J. Sakurai died while working there as a visiting researcher. In 1985, I was awarded the J.J. Sakurai Prize, instituted in that year by the American Physical Society. The same year I received the Japan Academy Prize.
In 1989, I was appointed head of KEK’s Physics Division II, where I assumed responsibility for an experimental research group. We set about in earnest to prepare plans for a post-TRISTAN accelerator: It would be the B-factory accelerator constructed inside the TRISTAN tunnel and operated with an aim to proving CP violation in a B-meson system. Construction was approved and started in 1994. Experiments using the B-factory started in 1999, and the initial results were obtained in 2000.
In 2003, I was appointed director of KEK’s Institute of Particle and Nuclear Studies, in which position I was directly responsible for the Institute’s experimental research activities including those conducted using the B-factory accelerator. At the time, Yoji Totsuka was appointed as KEK’s director general. Later, I came to work together with Totsuka again at the Japan Society for the Promotion of Science (JSPS), but he regrettably passed away in July 2008.
During my tenure as director of the Institute, KEK was converted from a government organisation to an independent research corporation. I became very busy in carrying out this reorganisation. Fortunately, we are able to steadily improve the performance of the B-factory accelerator during that period. Its experimental results showed our 6-quark theory to be virtually accurate.
I retired from KEK when my tenure as the Institute’s director ended in 2006. For a while, I was able to enjoy a life of relative freedom. In the meantime, I was invited to become an IIAS (International Institute for Advanced Studies) Fellow. In that capacity, I travel on occasion to the Kansai district to hold discussions and write papers with Taichiro Kugo, with whom I have conducted joint research in the past.
In October 2007, I became an executive director of JSPS, where I enjoy many opportunities to meet researchers from a wide spectrum of fields.
In recent years, I received the Person of Cultural Merit award in 2001 and the Order of Culture award in 2008, both from the Japanese government, and the High Energy Particle Physics Prize in 2007 from the European Physical Society.
This autobiography/biography was written at the time of the award and later published in the book series Les Prix Nobel/ Nobel Lectures/The Nobel Prizes. The information is sometimes updated with an addendum submitted by the Laureate.