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The 2017 Benjamin Lee Memorial
Nakwoo Kim
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The 2017 Benjamin Lee Memorial

NAKWOO KIM
KYUNG HEE UNIVERSITY, SEOULY



Timeline Wall; Chronology of Benjamin W. Lee

Benjamin W. Lee () was one of leading particle physicists of his generation and the head of the theoretical physics department at Fermi National Accelerator Laboratory, when he tragically died in a car accident in 1977. To the general public in South Korea, he posthumously achieved celebrity status and became a household name during the 1990s, when a fictional novel, which sold millions of copies, described a patriotic physicist who was clearly modeled after Benjamin Lee.

To theoretical physicists, Benjamin Lee is still most famous for his numerous contributions to the development of renormalization in gauge theory and the legendary lecture note "Gauge Theories", written together with E.S. Abers and published in Phys. Rep. in 1973. As 2017 marked 40 years since Benjamin Lee's death, the Asia Pacific Center for Theoretical Physics (APCTP) and the particle physics division of the Korean Physical Society (KPS) decided to have a special session during the regular KPS meeting, which was held in Gyeongju during 25-27th of October 2017.



At APCTP we have been running the "Benjamin Lee Professorship" program since 2012, in honor of the celebrated achievements of Benjamin Lee. In 2017 we invited Prof. G. 't Hooft, a Nobel laureate of physics in 1999, and also Prof. V. Mukhanov as the recipients of this program. Along with these two distinguished guests, several local particle physicists were also invited to discuss the legacy of Benjamin Lee. Here in this article I would like to briefly summarize what was presented at the special session.

The title of 't Hooft's talk last year was "The early days of the Standard Model - remembering Benjamin Lee". The most well-known achievement of Prof. 't Hooft is his proof of renormalizability of the Yang-Mills theory in 1971. It paved the way for gauge theories to be accepted as the mathematical framework responsible for fundamental interactions, summarized in the Standard Model.

In the lecture note on gauge theories, Abers and Lee digested the proof of 't Hooft and retold it elegantly to make it accessible for most of the theoretical physicists of the time. It was only after this work that gauge theory was accepted as 'the' theory of elementary particles. Let us first recall that Ben Lee was 11 years older than 't Hooft. Around 1970, when 't Hooft was still a graduate student, he attended a summer school at Cargese. For him, the most interesting lectures were by Ben Lee and by K. Symanzik, and they both talked about the topic of renormalization. When 't Hooft asked them about his idea of applying renormalization to gauge theory, they both encouraged him and said it was a good idea. Lee and Symanzik also added that 't Hooft's own supervisor, Markus Veltman, was the best person for learning and working together on that topic. In 1971, after 't Hooft proved renormalizability of gauge theory, Veltman organized a conference at Utrecht University, and among the attendees were Steven Weinberg, Sheldon Glashow, and Abdus Salam, the trio that would be awarded Nobel Prize in 1979 for electroweak theory.



Prof. K. Fujikawa told us about his collaboration with Ben Lee. Together with A.I. Sanda, they studied how the renormalization process should be done more systematically for spontaneously broken gauge theory. At that time B. Lee and Sanda were at Fermilab, and Fujikawa was a postdoc at the Enrico Fermi Institute of the University of Chicago, where Prof. Nambu was a central figure in the particle physics group. But Fujikawa found it more comfortable to talk with Ben Lee, since they were closer in age. He also stressed that it was Ben Lee who was responsible for the name the "Higgs particle", which is well known to be central in the generation of mass in particle physics. The title of Fujikawa's talk was "A hard working genius", and he described an episode where he received a phone call from Ben Lee on a Monday night, as Lee was excited about what he found after some calculation and wanted to discuss it with Fujikawa. Even though Ben Lee at that time was already a full professor, he was frequently working after midnight.

Prof. Jewan Kim, emeritus of Seoul National University, showed us many photos and told us about Ben Lee's role in the progress of particle physics activities of South Korea. It is well-known that Ben Lee was in the committee for the AID (Agency for International Development) loan and visited South Korea. With other Korean physicists he started organizing a summer school in Korea, but before the summer school materialized, Ben Lee died in a car accident. Sadly, the summer school became a memorial symposium, and it was held in 1978. At the conference there were many renowned physicists, including T. Kinoshita, L. Lederman, A. Salam, and C. Quigg. At that time it would have been difficult to invite scientists with such a high profile to Korea, were it not for Ben Lee's memorial. In that regard, Ben Lee gave a gift to Korean particle physicists as he passed away.

Prof. Jihn E. Kim started his talk by telling us that he and Ben Lee went to the same high school and also were in the same department (chemical engineering) at the same university (Seoul National), and then even changed their major to exactly the same topic. In that regard they had quite a special relationship. Although he first heard about Ben Lee as an undergraduate, and exchanged correspondence afterwards on research issues, they met for the first time only in 1977; Kim's later research was, in fact, based on a development made by Ben Lee: the strong CP problem.

Prof. Seong Youl Choi of Chonbuk National University reviewed a well-known paper of Ben Lee, C. Quigg, and H. B. Thacker, "Weak interactions at very high energies: The role of the Higgs-boson mass", published in Physical Review D. 1977. This paper was published posthumously, soon after Ben Lee's death. In this paper, the authors studied how the mass of the Higgs boson affects the renormalization of weak interactions. The point is that, in order to satisfy unitarity, the Higgs boson mass is bounded by 700 GeV. The upshot of this paper was that there should be either the discovery of the Higgs boson or a new physics at least at 1TeV. Of course, we now know the Higgs mass is 125 GeV, and the folklore of a "new physics at TeV scale" was first and elegantly presented in this paper.

The last speaker of this session was Prof. Youngjoon Kwon from Yonsei University. He emphasized the contribution Ben Lee made to flavor physics and the discovery of new particles (e.g. charm and top). He reminded us how Ben Lee's contribution was appreciated by the experts in the field, by showing us the front page of a paper by J. Ellis et. al, which was published just one month after Ben Lee's death. These authors dedicated the paper 'to our friend Benjamin W. Lee who cannot share with us the joys of new discoveries'. What was discussed in that paper was the discovery of the upsilon particle, which turned out to be the first particle containing a bottom quark. A seminal paper in that regard was Ben Lee's work with M. K. Gaillard, "Rare decay modes of the K mesons in gauge theories", Phys. Rev. D (1974). In that paper, Gaillard and Lee adopted GIM, or the Glashow-Iliopoulis-Maiani mechanism to predict the mass of 'extra' quarks, and they wrote it 'should be less than, say, a few GeV'. Indeed, the charm quark mass was found to be 1.3GeV. This work became a beacon for the coming generation in heavy flavor physics. It remains a source of inspiration both today and for future projects, as seen, for example, in the Belle experiment at the High Energy Accelerator Research Organisation (KEK).

Let us mention another important paper of Ben Lee, which is relevant to cosmology. In 1977, Ben Lee and S. Weinberg wrote a paper on heavy neutrinos and argued that in order to be consistent with cosmology its mass should be larger than 2 GeV. Particle physicists working on cosmological issues became commonplace after this paper, and in this regard Ben Lee was again a forerunner.

 

Nakwoo Kim is a professor at Kyung Hee University and is currently one of the academic coordinators for the Asia Pacific Center for Theoretical Physics (APCTP). He did his undergraduate study and also received his PhD at Seoul National University. He had research fellow positions at Queen Mary University of London and at the Max Planck Institute for Gravitational Physics in Potsdam. He works on string theory and supersymmetric quantum field theories.