With Toshihide Maskawa Interviewer: Shigeki Sugimoto

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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. Iwasaki was familiar graduates from Nagoya’s because they had to explain was found. It was difcult to with our work since he E-laboratory, went to a beer- everything with only protons determine if it was really a was working at YITP, Kyoto garden on the roof of a and electrons. Many problems charm or not. In those days, it University. He later moved department store in Shinjuku. with nuclear structure quickly was not at all clear. to Tsukuba University. He They congratulated me with went away after the discovery Sugimoto I guess people informed Sugawara (he was two liters of beer. of the neutron. This landmark tended to believe it in Nagoya, at KEK) about our paper. Sugimoto Did you experience in¢uenced him didn’t they? Sugawara had many friends have a great sense of a great deal. The 1950s was Maskawa Yes, they did, in the United States. He told accomplishment? a very confusing era, when relatively speaking. I don’t them about our work. He Maskawa Yes. Professor particles after particles were

18 IPMU News No. 11 September 2010 being discovered. He wanted Kobayashi, he moved that gA/gV ratio does not agree, you take six instead of four?” to settle it once and for all by part to the last place for some because the sign comes out It was merely a matter of introducing a new concept like reason. wrong.” So we threw that playing with numbers. Heisenberg had done. Also, Sugimoto Do you mean the idea away. And we went on to Sugimoto I see. for him, that new concept order had been changed? struggle within the framework Maskawa We started our had to be a real particle like Maskawa Yes, that part of the four-quark model. In discussion the next day Heisenberg’s neutron. So appeared last. desperation to get away from from ten o’clock, the time he proposed the model of Sugimoto I see. For you, was it, we needed something that Kobayashi would usually show proton, neutron, and lambda. the most attractive part of the could push us to abandon up. I suggested we write a Because of this landmark paper the prediction of the the four-quark scheme. It paper with the idea that the experience, Professor Sakata existence of six quarks? could have been either of six-quark scheme will work, as could not think of introducing Maskawa Yes, that was us who rst felt that way. I I had thought the day before. hypothetical quarks. Professor the most interesting part. happened to give up rst. Kobayashi thought for a brief Ohnuki told me that he However, I have not asked Perhaps I did not have enough moment and agreed. It was as himself was conned to a Kobayashi why he changed persistence. (Laughs) A place simple as that. similar direction under this the order. like a bathtub where you are Sugimoto Were you very environment. So I tried to alone is a relatively good place excited when you came up have a different mindset. Coming up with the six- to relax and review an overall with that idea? Once I nd a breakthrough, quark model in the bathtub scenario, rather than working Maskawa No, I was not. It or even half a breakthrough, I Sugimoto I see. By the way, on specics. In the bathtub, may sound ironic, but I felt should go back to the starting it is by now well known that I was about to give up the relieved because at last I could point once more, rather than you came up with the six- whole thing because every nish it. I did not have a sense sticking to it. quark model in the bathtub. direction we had tried had of great accomplishment. Sugimoto I see. You explore Maskawa In mathematics failed to lead to any successful Rather, it was Yoichi Iwasaki, other possibilities. we can introduce 100 quarks idea. So I was about to decide Hirotaka Sugawara, and Maskawa I call this approach and develop a general to write a paper dealing with Hidezumi Terazawa,20 all “abstraction.” When we scheme. Since particle physics our failure, even though doing living north of Hakone,＊ who abstract an approach even if is a natural science, we cannot so would put us to shame. recognized the importance it is half successful, we will talk about something that I thought I did not want to of the paper! The only thing see various other possibilities. does not exist, even if it is continue any longer. (Laughs) I felt was that I had come up At the beginning, when we interesting. In those days, three Then, as I was getting out of with a solution to the problem don’t know anything, we quarks were known. Also, we the bathtub, an idea came to of CP violation that had have to be specic. Otherwise knew that four quarks would me“, Wait a minute. We don’t been bothering me. In Kyoto, we cannot identify in which make an interesting model. So need to do it that way – we however, I used to be teased, direction we need to go. But, we had a strong inclination to can write a paper to show with people saying things like once you have identied the stick to four quarks. But our that the 6-quark model will “Hey, Dr. Maskawa! Do six direction, you don’t need to discussion did not lead to any work.” The reason why I came quarks really exist?” stick to the Yoshida-route (for viable model. At any rate, I up with the idea of six was…. Sugimoto Is that so? climbing Mount Fuji). You can thought I could reproduce the Sugimoto You pretty much Subsequently, however, all of also reach the top using the CP violation if I introduced, knew that the six-quark them were found one after Gotenba-route. So we wrote in today’s language, right- scheme would work, didn’t the other in experiments. down every possibility that we handed currents. I showed you? How did you feel when that could think of at that time. it to Kobayashi. Probably he Maskawa Yes, even when happened? Interview Here is a mystery that I still do knew right away it wouldn’t we were unaware of the Maskawa Well, let me see not understand. In our paper I work. But as he was cautious, difculty of the problem, we … Some people continue to put the six-quark model in the he only said“ Let me check at could probably answer it right work on the same subject as rst place. But when I handed home.” The next day he said away if someone asked the if it were their life’s work, like over my Japanese draft to “No, it wouldn’t work. The question“ What happens if “I have nished this, the next

19 22 step is this.” I am not that Memories of Professor But the same Professor Sakata community. Ziro Koba, when type. Once I let it go, I don’t Sakata presented impressive lectures he was YITP professor, used feel it to be my work. So, Sugimoto I forgot to ask on different occasions. His to say“ I didn’t teach you when I was congratulated on you this earlier. What kind of summary at the“ Models and anything” whenever people the Nobel Prize, I was happy, person was Shoichi Sakata? Structures” workshop that he called him Koba-sensei, and he of course, but it was not like What memories do you have organized at YITP was very would give no further answer I was jumping for joy. To me, about him? impressive. I was tempted to them. Professor Sakata was it was more like“ Oh, that Maskawa In those days, to say“ Why can’t you give worried, I think, that young particular work somehow he was alternating between us such a nice talk in the people might not have the deserved the prize.” (Laughs) his ofce in Nagoya and the E-laboratory?” (Laughs) We all courage to say“ no” even if Sugimoto I see. Science Council of Japan listened intensely to his talks he said something wrong. Maskawa Of course different in Tokyo weekly. The time whenever they were given at He probably thought that people feel differently. he spent in his ofce of the YITP. Probably he was thinking the organization must have Sugimoto Let me ask you E-laboratory was when he of many different ways to a ¢at structure to promote about the Nobel Prize. May I could relax. So I recall that manage the research group; discussion as equals. I could ask you for your impression nearly everything he said was for example, what functions sense that, through talking now that things have more or amusing. were needed for the group to with senior members, though I less settled down? Sugimoto Really? develop into a good research had never heard that directly. Maskawa Well, I think Maskawa In the seminar organization. He had a famous Sugimoto I see. You had that the whole thing is overly room, he used to listen to saying in those days, which tradition. Let me ask an odd exaggerated in Japan. It is the lecture at rst, but after a was that“ The best philosophy question. You were calling him probably not such a big deal while he used to start reading and best organization are Sakata-sensei,＊＊＊ weren’t you? in the United States. the newspaper. When that enough for good research. Maskawa Yes, because he Sugimoto I agree. was done, he used to begin I am just Tadano Bonji.” It was really my sensei. Maskawa I think it should preparing tea. Probably he came from a pre-war comic. A Sugimoto (Laughing) But I be enough to say just was sending a signal to stop. character in the comic named was not allowed to call you “Congratulations,” if you (Laughs) One day we had Tadano Bonji (Mr. Ordinary) Maskawa-sensei. know a Nobel laureate. a power failure during the resembled Professor Sakata. So Maskawa I could not Sugimoto Indeed. Did it seminar. When that happened, he got that nickname, which just call him Sakata-san. To change your life in any way? Professor Sakata happened to even Professor Shin’ichiro me, Yukawa-san23 was just Maskawa Yes, I am receiving see the front wall where an Tomonaga21 referred to in one Yukawa-san. more requests for lectures electric clock was still running. of his essays. Professor Sakata Sugimoto Really? and interviews. It is partly my Someone said“ Power failure!” did not mind it, and told us, Maskawa Their relationship fault. My personality makes He then said“ No, the clock is “You young people can do was rather interesting. When it difcult to refuse those running.” good research here because I was a graduate student at requests. Sugimoto It must have been we have a good philosophy Nagoya, I used to visit YITP. Sugimoto You must have a battery-type. and good organization.” I ＊＊“ Power failure” is written as become busy! Maskawa Right. He fell for that hook, line, and 停電 in Japanese. 停 means“ stop” Maskawa Yes, in that immediately noticed that. He sinker, and worked very hard. and 電 means “ electric.” Usually, 電 is combined with other Chinese sense. One more thing is I then said“, A power failure (Laughs) character(s) to form a specic word became popular through my means the electromagnetic Sugimoto I don t remember having a meaning related to electric ’ or electronic phenomenon/effect. So, appearance on TV, probably interaction switches off.＊＊ We if you told me this directly, Professor Sakata offered this strained interpretation of 停電 as“ stopping because I come across a bit should say that what we have but I was told not to call you electromagnetic interaction.” like a comedian. here is simply a termination of Maskawa-sensei＊＊＊ when I ＊＊＊“ Sensei (先生)” is a Japanese Sugimoto (Laughs) the transportation of power.” rst joined your group as a word meaning“ teachers,” “professors,” and other professionals Maskawa I am frequently Sugimoto (Laughs) graduate student. of authority. For Professor Maskawa, asked to shake hands and give Maskawa Many of his Maskawa That was “Sakata-sensei” means not merely “Professor Sakata,” but demonstrates autographs. comments were of this sort. common in the particle theory his respect for him as a teacher.

20 IPMU News No. 11 September 2010 A student like me was also institute (Kobayashi-Maskawa proceed as far as collaboration Sugimoto Such as having asked to join Yukawa at the Institute for the Origin of among different disciplines is drinks together. lunch table. He noticed a short Particles and the Universe, concerned? Maskawa Not necessarily, man with an unfamiliar face, KMI). What direction are you Maskawa I think the rst but something like that. and asked me“ Whose student aiming to take? thing is human relations. (Laughs) are you?” I answered that I Maskawa Basically, the People just communicate daily, Sugimoto Thank you very came from Professor Sakata’s universe is its own subject. like having a chat after a meal. much for your time. group. We then discussed a Koichi Yamawaki24 made the In doing so, both sides might few topics. I must have praised effort to establish KMI. His discover interesting problems. 1 Shoichi Sakata (1911-1970). Professor Sakata at points in standpoint is that elementary Once that happens, there 2 Later he served as President, the conversation. He gradually particles have a hierarchical are many ways to proceed Tsukuba Univ. 3 Professor Emeritus, Kyushu Univ. became sullen. structure. He thinks quarks further. People should not 4 S.L. Glashow, J. Iliopoulos, and L. Maiani, Physical Review D2 (1970) Sugimoto I see. (Laughs) also have structure. He will conne themselves to their 1285. Maskawa Even at that age, take the lead and steer the territories. Each person has 5 Ziro Maki (1929-2005) later served as Director of YITP, Kyoto they were competing with group. worked hard in a specic eld Univ. each other. Sugimoto Are you aiming and accumulated skills and 6 G. ’t Hooft, Nuclear Physics B33 (1971) 173 and B35 (1971) 167; G. Sugimoto Was it rivalry? at a new direction that could knowledge. If each person ’t Hooft and M. Veltman, Nuclear Physics B44 (1972) 189. ’t Hooft Maskawa Yes, they were lead to a Nobel Prize? draws on those individual and Veltman received 1999 Nobel rivals. On the other hand, Maskawa No, we are strengths, working together Prize in Physics. 7 He later served as Director of when Professor Yukawa made not directly aiming in that with people who have YITP. Now, Professor, YITP, Kyoto Univ. a one-day visit to Nagoya, direction. Some people different skills and strengths, 8 2008 Nobel Laureate in Physics. Professor Sakata was carrying might deserve a Nobel I believe they can do great 9 An unusual event found in a cosmic-ray experiment in 1971 Yukawa’s bag and making Prize as a result of their ne things. by Kiyoshi Niu, now Professor Emeritus, Nagoya Univ. way for him at the doors. accomplishments. I don’t Sugimoto I am now working 10 1979 Nobel Laureate in Physics. Sakata was following a strict believe we should go for it at IPMU, which has people 11 Later he served as Director General, KEK. sensei-student relationship. just by shouting a slogan. working on pure mathematics. 12 Professor, Univ. of Hawaii. When I was talking with But, we should always keep Collaborative work with 13 19th International Conference on High Energy Physics. Professor Sakata, I used to in mind that we must try to them is a major issue. In that 14 2008 Nobel Laureate in Physics. 15 At that time, he was working at walk slightly behind him. come up with fundamental sense, IPMU has a similarity INS, the Univ. of Tokyo. So I did not bother to make solutions. As we have to with KMI. Do you think there 16 A composite model of elementary particles proposed by Shoichi way for him at the doors. He produce results, sometimes we is any possibility for the two Sakata. He postulated that hadrons comprised three opened the doors. choose subjects that lead to institutions to collaborate? fundamental particles: proton (p), Sugimoto (Laughs) publication without too much Maskawa We should start neutron (n), and lambda (Λ), and their antiparticles. Maskawa I did not notice it difculty. I am not against with a simple exchange of 17 Murray Gell-Mann proposed classifying hadrons into octets. at all. I realized it after I went these approaches. They have people, such as inviting people Later he proposed the quark through the door. (Laughs) In some importance. But at the to seminars. People may model with fractionally charged quarks as elementary building a sense, Professor Sakata had same time we should have, nd some interesting work. blocks. In 1969 he received the different ways of behaving, in the corner of our mind, an We can then try to invite Nobel Prize in Physics. 18 Professor Emeritus, Nagoya Univ. one for his superiors and attitude of wanting to answer people for longer periods, of 19 Werner Heisenberg (1901-1976). 1932 Nobel Laureate in Physics. one for younger people. fundamental questions. six months or a year. Once 20 A theorist, formerly at INS, the He denitely had different Sugimoto KMI has people this exchange is established Univ. of Tokyo. 21 Shin’ichiro Tomonaga (1906-1979). standards̶a sort of double from the mathematics and our understanding of 1965 Nobel Laureate in Physics. 22 Ziro Koba (1915-1973) died in Interview standard. department working on each other is deeper, we can Kopenhagen when he was subjects close to physics. They think of a scheme for more a Professor at the Niels Bohr Institute. KMI and IPMU: How to start may move into directions ongoing joint work. I do think 23 Hideki Yukawa (1907-1981). collaboration Japan’s rst Nobel Laureate. In that are slightly different we should start personal 1949 he received the Nobel Prize Sugimoto Finally, let me ask from describing the real exchanges, including very in Physics. 24 Deputy Director of KMI and a question about your new world. How do you plan to simple ones. (Laughs) Professor Emeritus, Nagoya Univ.