IPMU Interview with Toshihide Maskawa Interviewer: Shigeki Sugimoto 1 My rst paper was a Ph.D. Professor Sakata’s group. thesis There I was often teased about Sugimoto How are you? First behaving as if I were some I’d like to ask kind of big shot, even though your graduate I hadn’t written any papers. student days. (Laughs). Actually, my rst Maskawa Well, paper was my doctoral thesis. during those days at Once Yoichi Iwasaki2 came Nagoya University, to Nagoya with the intention graduate students who of observing us because he were theoretically oriented thought people from the were not assigned to any Nagoya group were standing particular group. Instead, they out and attracting his interest went around different theory in places like summer school. groups during the rst year Unfortunately, we were very or so. By the time they were busy at that time preparing about ready to write their for things like the Beijing master’s theses, they were Symposium, a student version assigned to the groups of of the Japan-China Academic their choice. Anyway, I joined Exchange Program, and for summer school. So, poor Toshihide Maskawa was awarded Iwasaki had to go back after the 2008 Nobel Prize in Physics having hardly any discussion jointly with Makoto Kobayashi for “the discovery of the origin of the with us. Subsequently, broken symmetry which predicts the 3 existence of at least three families Professor Shoichiro Otsuki of quarks in nature,” or, for the gave us a good scolding. “Kobayashi-Maskawa theory” of CP violation. He has also received He said that he was really many other distinguished awards, in particular the 1985 Japan Academy ashamed of us, as we had Prize and the 2008 Order of Cultural missed the opportunity to talk Merit. He received a Doctorate from Nagoya University in 1967, and with a fellow researcher who became a Research Associate. He had come all this way. We had moved to Kyoto University in 1970. In 1976, he became an Associate a saying in those days: people Professor at INS, the University of ＊ Tokyo, and in 1980, a Professor at living north of Hakone YITP, Kyoto University. He served as measured the publications by Director of YITP from 1997 through 2003. He is now Nagoya University’s University Professor and Director ＊ Here“, north of Hakone” essentially General of KMI, Nagoya University. means Tokyo. On the other hand, He is also a Professor at Kyoto “west (or south) of Hakone” includes Sangyo University and a member of the Nagoya, Kyoto, and Osaka its board of trustees. districts. 16 IPMU News No. 11 September 2010 weight, rather than by quality. however, we had only one Sugimoto By weight? copy of each journal for the Maskawa Yes, we held that E-laboratory (the traditional their approach emphasized name to represent the the quantity rather than the elementary particle theory quality of publications, but group at Nagoya University). that we were different. We We had to ght over who were aware that we had to got it rst. So we were write high-quality papers. I having a meeting within the had though no publication at E-laboratory to introduce all, so there was no quality to new articles by taking turns. discuss. (Laughs) I was assigned to three or Sugimoto Have you ever felt four journals in my rst turn. that you were at a dead-end Among them was a paper or become depressed? by Fitch and Cronin on a CP Maskawa No, I’m not the violation. I read it, but at rst I kind of person. did not think it was important Sugimoto I see. and wondered if I should skip it. For some reason, though, I Encountering a CP violation reported the article. I thought in a journal club something strange was Maskawa Whenever I happening but did not have a encounter a problem, I usually clear understanding of what it analyze the situation and try was. Although I did not write to nd a solution myself. If a paper, the article motivated something seems beyond my me to pursue theories of ability, I am willing to switch weak interactions. Many to an alternative without people were working on weak hesitation. I try to construct a interactions in those days, but story to describe the hurdle in they were using them as a my path. Of course, the story probe for studying the quark is not likely to re¢ect the truth. model rather than actually But I try anyway. However, studying weak interactions. when things progress and Contrary to these approaches, I am beginning to see a I became rmly aware of breakthrough, this story- the need to study weak building suddenly becomes interactions in the framework helpful. For this reason, I guess, of renormalizable theory. The we could move rather quickly famous GIM paper4 appeared on the CP problem. We used in 1969 (I remember only the to have a journal club, when I year of preprint publication). was at the end of my master’s Later, when Ziro Maki5 wrote course or at the beginning of a paper, he mentioned that he Interview my doctorate. Of course, now had rst been informed of the you can see any paper just by Shigeki Sugimoto is an IPMU clicking through web pages. Professor. He is a theoretical physicist. Sugimoto That’s right. When he was a graduate student at Kyoto University, he joined Professor Maskawa In those days, Maskawa’s group. 17 GIM paper by Maskawa. What think it was either me or even wrote a paper together Nambu had virtually certied intrigued him about this paper Kobayashi who rst suggested with Sandip Pakvasa12 and our work. It was like a was a natural consequence of revisiting the CP violation gave presentations. Sugawara, declaration of victory. introducing charm based on problem. However, we decided who was only about two years Sugimoto I see. higher order effects in weak to work together again, as we older than me and lived in the Maskawa I didn’t remember interactions. But I was more both happened to be in Kyoto. United States for some time, at all how I managed to return interested in the detailed was already a widely respected home that night.15 (Laughs) discussion of how far the Kobayashi-Maskawa theory physicist by then. Thanks to Sugimoto Oh, boy! (Laughs) theory was renormalizable. got gradual recognition his introduction, our paper You also pointed out more That part was given after the Sugimoto Was the CP became known and gradually than one possibility for the CP charm part using about twice violation a big issue in those began to be cited. violation, like the two-Higgs the space. days? Sugimoto I understand the model, in the Kobayashi- Sugimoto That is very Maskawa Not really. I paper drew very little attention Maskawa paper. interesting. guess in 1964, right after when it rst appeared. Maskawa Let me explain Maskawa Then, the paper the Fitch-Cronin paper had Maskawa Ziro Maki was the why we did that. I had been by ’t Hooft and Veltman6 been published, one physicist rst to cite our work when curious why the Sakata appeared in 1971 or 1972. tried to solve the problem by he wrote a paper about the model16 did not or could not At that time I was working introducing a 5th force. But 4-quark model. But there were develop into Gell-Mann’s at Kyoto University. Taichiro it was not very interesting no citations for the next three octet-model.17 But I hardly Kugo7 recalls that I gathered because the postulation of years or so. Then Pakvasa and knew the real reason for a group of people and the 5th force that violates CP Sugawara mentioned our it. So I used to ask around. hosted a seminar. Since now should have directly solved work in their paper. Professor Yoshio Ohnuki18 ’t Hooft had proven the the problem, if it had existed. Sugimoto So your paper told me that he knew how to renormalizability of weak Very few people followed this became better known after make an octet out of a three- interaction theory, I thought it particular idea. At that point Pakvasa and Sugawara’s dimensional representation, was time to revisit the problem we started to investigate paper. but he hesitated to go in that I had left behind earlier. It was this problem and published Maskawa Yes, the existence direction because of Professor time to revisit the CP violation. a paper. But, our paper was of our paper was more widely Sakata’s landmark experience. It was now calculable. I guess almost completely ignored. known after that. Then, at Professor Sakata discussed what was in the mind of I’m not entirely sure, but I the Tokyo Conference13 in Heisenberg’s paper19 on Makoto Kobayashi8 at that think it was probably Sheldon 1978, Professor Yoichiro nuclear structure theory in his time was the Niu-event,9 Glashow10 who then wrote a Nambu14 mentioned our undergraduate dissertation although I never asked him paper without knowing about work in his summary talk. He in a very animated way. He directly. our work. compared various CP violation noted that the most important Sugimoto What is the Niu- Sugimoto I see. models and concluded that thing was the discovery of event? Maskawa However, Yoichi our approach seemed the the neutron. He wrote that Maskawa It was a charm Iwasaki,2 Hirotaka Sugawara11 most appropriate. After the people had faced many candidate found in cosmic and others acknowledged our conference, about ten of us, contradictions prior to that, rays, although only one event work.