Obituary of Wu-Ki Tung

Wu-Ki Tung, a Fellow of the APS and among the most influential theoretical high-energy physicists of his generation, died on March 30th, 2009 at the age of 69. He had retired from the Michigan State University Department of Physics and Astronomy in 2007, and moved to Seattle where he continued his work as an Affiliated Professor of Physics at the University of Washington. His wife Beatrice, their sons, Lei and Bruce, their grandchildren, and his mother survive him.

Wu-Ki Tung was born in Yunan, China and educated at National Taiwan University. In 1961 he came to the United States to pursue graduate study at Yale University, where he received his Ph.D. in 1966 under the guidance of Loyal Durand and Charles Somerfield. After research appointments at the Institute for Theoretical Physics at SUNY Stony Brook, and at the Institute for Advanced Study in Princeton, he served on the faculties of University of Chicago, Illinois Institute of Technology (where he also served as chair of the Department of Physics), and Michigan State University.

Wu-Ki Tung contributed to many areas of theoretical physics. His early career focused on formal physics of the day, from Regge Theory and dispersion relations, to current algebra and early precursors to scaling violation. Wu-Ki is best known, however, for his contributions to elucidating the consequences of QCD for all high-energy processes in the framework of the Parton Model. Wu-Ki pioneered a multi-decade, global analysis of the momentum densities of partons in nucleons through the inclusion of all relevant experimental results in order to extract an accurate, formally correct, set of parton distribution functions which could be used to interpret subsequent experiments. From an early fit to data from deep-inelastic scattering and lepton-pair production (done in collaboration with Jorge Morfin), the tools that he created were expanded to include the difficult effects of heavy quark flavors and the first rigorous treatment of experimental and theoretical uncertainties. He continued to work on physics until his final week, during which he completed an invited Scholarpedia article on Bjorken Scaling.

One can identify two consistent themes in almost all of Wu-Ki Tung’s work. First, the use of group theory, which he applied in his early work on relativistic field equations for arbitrary spin, and continued through the application of symmetry techniques to kinematical analyses of high energy scattering and beyond. A tangible legacy of this passion was his beautiful text, Group Theory in Physics, used around the world since 1982. Second, begun in three papers completed in collaboration with Stephen Adler, the identification and application of what came to be known as “scaling violation”, ultimately leading to his most influential work on nucleon distribution functions. Wu-Ki also took particular pride in lucid writing, achieving a narrative-like clarity in his exposition of technically difficult material.

His natural inclination to scientific collaboration led to the founding of the Coordinated Theoretical-Experimental Project on QCD, known throughout the High Energy Physics Community as CTEQ. This unique collaboration of theorists and experimentalists has been active since 1992, and currently consists of 32 physicists from 18 universities. CTEQ embodied Wu-Ki’s dual view of scientific research as both an intensely personal, skilled activity, and one involving an intimate community of colleagues. His love of pedagogy led him to create the annual CTEQ summer schools held in the U.S., Europe, and Mexico and heavily attended since their inception in 1992. His natural interactivity led him to embrace both collaboration and open communication with competing approaches, often including representatives of alternative approaches in CTEQ meetings and as summer school guests. His innate drive for completeness led to the “QCD Handbook” prepared for Reviews of Modern Physics. Finally, his insistence on the importance of give-and-take led him to create CTEQ to be broadly representative of both the theoretical and the experimental communities. CTEQ was very much a collaboration of friends for Wu-Ki and he delighted in bringing people together. Both because it changed the way in which measurements are made, and because it brought him many close friends, CTEQ is perhaps his most treasured physics legacy.

Wu-Ki loved his work, thoroughly enjoyed his friends, was immensely proud of his family, and treasured his participation in academia. The application of his characteristically passionate, yet thoughtful, approach was not limited to scientific matters. He was a strong leader, an attentive mentor, and a loyal friend. All of us who were fortunate enough to know Wu-Ki have been touched and enriched by his involvement in our lives. We will miss him.