IN MEMORIAM

Nathan Isgur, 1947-2001

Dr. Nathan Isgur

Nathan Isgur, one of Canada’s leading theoretical physicists, died on July 24th 2001 at Williamsburg,VA. Nathan lost his struggle with multiple myeloma, a rare Cancer of the bone marrow.

Nathan was born on May 25, 1947 in South Houston, TX and finished in high school there. He studied next at Caltech, where he graduated with a B.S.c degree in 1968. This was the period of the Vietnam War and Nathan chose to come to Toronto for his graduate studies to avoid the draft; he had a letter of introduction from Owen Chamberlain (at Berkeley) to R.E.Pugh, at the University of Toronto, who took him on as a graduate student. Nathan received a Ph.D. degree in particle theory from Toronto in 1974. Meanwhile, Nathan’s passport had expired and he couldn’t travel outside Canada until 1977 when President Carter issued a pardon to Americans who evaded the draft.

With an NSERC Fellowship, Nathan was allowed to stay at Toronto as a post-doc. By 1976 the Physics Department, under the leadership of Robin Armstrong, recognized Nathan’s outstanding merit and hired him as an assistant professor, even though Nathan had no experience outside the Department. Nathan had started to publish immediately after his doctorate, and his first remarkable publication was in 1975 on the mixing angle of pseudo-scalar mesons due to annihilation into gluons (his explanation is standard now). Shortly thereafter, Nathan and one of us (GK) embarked on a long collaboration, involving the study of excited baryons in quark models. This was a good time to work on the subject, and although Nathan had no prior experience in the subject, his physical intuition, hard work and sheer determination made the project very successful. The principal physical idea of the model was taken from QCD: the forces between quarks are flavour-independent. This “QCD-improved” quark model for baryons still remains the benchmark for theoretical and experimental work. Nathan was an ideal collaborator, working out everything with tremendous enthusiasm, and being equally good at generating brilliant ideas and doing laborious calculations.

He had a large group of graduate students, usually 5-6 at a given time. During Nathan’s stay on the faculty at Toronto (14 years), he mentored 13 Ph.D.’s, most of whom are now doing research at Canadian and U.S. campuses. These are: S. Capstick, K. Dooley, P. Geiger, S. Godfrey, G. Grondin, R. Kokoski, R. Koniuk, D. Kotchan, K. Maltman, C. Morningstar, C. Reader, E. Swanson and J. Weinstein.

The most important research conducted later by Nathan was in collaboration with Mark Wise, who had been an under-graduate student in Nathan’s classes at Toronto. Mark was by now on the Faculty at Caltech. Isgur and Wise studied the semileptonic decays of mesons with a charm or beauty quark and they discovered what is now known as the heavy quark symmetry of QCD. This symmetry, which becomes exact for infinitely heavy quarks, leads to important simplifications of form-factors in such decays. This work was strongly acclaimed and led to Isgur and Wise receiving the Sakurai prize of the APS in the year 2001, jointly with M. Voloshin.

During this very productive period at Toronto, Nathan was also teaching undergraduate and graduate courses, running seminars, and organizing canoe trips. Nathan was a superb teacher at all levels: One of us (PS) still remembers vividly Nathan’s infectious enthusiasm and laconic style when lecturing to first-year undergraduates. He would stand up in front of the class and devote most of his time to explaining and discussing the physics of a particular problem, waving his finger up and down to mimic an accelerating electric charge or dashing across the lecture room when illustrating the effects of special relativity. He hosted annual picnics and Raclette parties at Toronto’s Centre Island, to which he invited what seemed to be the entire particle physics group at Toronto. For many students, Nathan became the inspiration for why one should study physics, and the role model for how one could contribute.

Among the activities at Toronto, two Conferences organized in part by Nathan are memorable. One was the Baryon Conference (1980) in Toronto and the other was the Advanced Study Institute on Quark Interactions at Whitehorse, Yukon (1984). The latter was especially great fun for the participants. These meetings brought together many influential researchers in “quark physics” and were useful in the development of light and heavy quark spectroscopy.

Nathan interacted a great deal with experimentalists. Nathan was one of the leaders of the CHEER project – this envisaged an electron ring to be built at Fermilab by a Canadian group to study electron-proton collisions. Although CHEER was not funded – in favor of the Tevatron proton antiproton collider – the project led to a strong Canadian involvement in the ZEUS experiment at the HERA electron-proton collider in Hamburg, Germany. Canada contributed significantly to the construction of both the HERA collider and the ZEUS detector, in large measure because of the intellectual excitement that Nathan generated in pursuit of CHEER.

Nathan was also involved later on in several Natural Sciences and Engineering Research Council grant selection committees (GSC), eventually becoming the Chair of the Subatomic Physics GSC in the early 1990’s. He was influential in changing the manner in which nuclear and particle physics was funded in Canada, helping to bring in an “envelope” system of funding for subatomic physics. Nathan also took a strong interest in TRIUMF, now Canada’s premiere particle and nuclear physics. Nathan became one of the clear leaders in Canadian physics, eventually adopting this country by taking out Canadian citizenship.

Nevertheless, Nathan was lured back to the USA by the newly built accelerator at Newport News (CEBAF), which eventually became Jefferson Lab (JLab). The attraction was the opportunity to build an entirely new Theory Group and influence the experimental research of the Laboratory. Nathan accepted the offer to become the head of Theory at JLab in 1990 and eventually became the JLab’s Chief Scientist in 1996. Nathan took with him those Toronto graduate students who had not quite finished their projects, and they all finished their degrees at Newport News. With his move to JLab, Nathan ceased to do undergraduate and graduate teaching, although he joined the Faculty at William and Mary College at Williamsburg.

At JLab, in addition to being Head of the Theory Group, Nathan was involved in the direction of the experimental program and also was directing the liaison with southeastern universities in the USA. This work led to 62 appointments to the Physics Faculties in this area, through joint and bridged positions. Nathan also encouraged Canadian work at JLab, and groups from the University of Regina and University of Manitoba now play key roles on various JLab experiments.

Nathan was devoted to his family. While in Canada, he married Karin Bergsagel, with whom he had two sons, Bram and Ben. By chance, his father in-law, an oncologist at Princess Margaret’s Hospital in Toronto, is a world expert on multiple myeloma, the illness Nathan was diagnosed with in 1996.

During his last four years Nathan published extensively, mainly as a single author, trying to record his thoughts on hadron physics. This was in addition to his duties at the Lab, and the rigors of his medical treatment. Nathan continued to be the intellectual centre of the Jefferson Lab until shortly before his death. His determination was heroic.

Nathan’s achievements in physics have been recognized through large number of honours both in Canada and the United States. Nathan was a recipient of the Herzberg Prize (CAP), the Steacie Fellowship and Prize (NSERC), the Rutherford Medal in Physics (RSC), and the Sakurai Prize (APS). Nathan was a Fellow of the Royal Society of Canada and a Fellow of the American Physical Society. The Southern Universities Research Association held a special ceremony of recognition for Nathan in December 1999. Nathan was an invited speaker at numerous conferences and universities throughout the world.

Canada has lost one of its great physicists and teachers.

Gabriel Karl (Guelph) and Pekka Sinervo (Toronto)