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Nathan Isgur (May 25, 1947 – July 24, 2001) was atheoretical physicist from theU.S. andCanada.[1]
Isgur was born inSouth Houston, Texas and finished high school atSouth Houston High School. He was a scholarship student atCaltech. where his initial interest was in biology, but he moved toward physics and graduated with aB.Sc degree in 1968. Isgur began work on his doctorate at theUniversity of California, Berkeley, but received his draft notice during his first year there. Denied a draft deferment to continue his education at Berkeley he went toToronto in order to pursue his graduate studies and to avoid serving in a war he disagreed with on moral and political grounds. Isgur received a letter of introduction from Nobel LaureateOwen Chamberlain at Berkeley, toR.E. Pugh, at theUniversity of Toronto, who took him on as a graduate student. Isgur received aPh.D. degree inparticle theory from Toronto in 1974.
Isgur eventually became a Canadian citizen due to his inability to travel, having been unable to renew his U.S. passport due to his draft status, and because of his position as awar resister. This situation continued to inhibit his ability to travel to the United States until PresidentJimmy Carter issued a blanket amnesty for alldraft resisters.
After completion of his doctorate, Isgur was granted aNatural Sciences and Engineering Research Council Fellowship, which allowed him to stay at Toronto as a post-doctoral candidate. He was hired as an assistant professor in the department of physics in 1976 in recognition of his outstanding merit by department head Robin Armstrong, even though he had not been able to travel to gain experience outside the Department owing to passport difficulties. In 1975 Isgur published on the mixing angle of pseudo-scalarmesons due to annihilation intogluons.[2] He embarked on a long collaboration withGabriel Karl from theUniversity of Guelph, involving the study of excitedbaryons inquark models. The principal physical idea of the model was taken fromquantum chromodynamics: the forces between quarks areflavour-independent. This idea gave rise to their "QCD-improved" quark model.[3]
Isgur had a large group of graduate students, usually 5-6 at a given time. During his 14 years at the University of Toronto, he mentored 13 Ph.D.s: Simon Capstick, Kevin Dooley, Paul Geiger, Stephen Godfrey, Gregory Grondin, Richard Kokoski, Roman Koniuk, David Kotchan,Kim Maltman, Colin Morningstar, Catherine Reader, Eric Swanson, and John Weinstein.
Two conferences he organized included theBaryon Conference (1980) in Toronto and theAdvanced Study Institute on Quark Interactions at Whitehorse, Yukon (1984) useful in the development of light and heavyquark spectroscopy.
Isgur was one of the leaders of theCHEER project, this envisaged an electron ring to be built atFermilab by a Canadian group to study electron-proton collisions. CHEER was not funded, in favor of theTevatron proton–antiproton collider, but led to a strong Canadian involvement in theZEUS experiment at theHERA electron-proton collider inHamburg,Germany.
He returned to the USA to the newly built accelerator at Newport News (CEBAF), which eventually becameJefferson Lab, to build an entirely new Theory Group and influence the experimental research of the Laboratory. Isgur become the head of the Theory Group at Jefferson Lab in 1990 and eventually became the chief scientist in 1996. He joined the faculty at theCollege of William & Mary at Williamsburg.
Isgur andMark Wise studied the semileptonic decays of mesons with a charm and bottom quark and they discovered what is now known as the heavy quark symmetry of QCD.[4]This symmetry, which becomes exact for infinitely heavy quarks, leads to important simplifications of form-factors in such decays.
He was also involved later on in severalNatural Sciences and Engineering Research Council grant selection committees, becoming the chair of the Subatomic Physics GSC in the early 1990s. Isgur 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. He took a strong interest inTRIUMF, Canada's premiere particle and nuclear physics facility.
He was diagnosed withmultiple myeloma in 1996, and died five years later at the age 54.
The work with Wise led to them receiving theSakurai Prize of theAmerican Physical Society (APS) in 2001, jointly with M. Voloshin. He was awarded the prize with the following citation:
For the construction of theheavy quark mass expansion and the discovery of the heavy quark symmetry in quantum chromodynamics, which led to a quantitative theory of the decays of c and b flavored hadrons.[5]
Isgur was also a recipient of theHerzberg Prize (CAP), the Steacie Fellowship (NSERC), theSteacie Prize, and theRutherford Memorial Medal in Physics (RSC) (1989). He was a Fellow of theRoyal Society of Canada and of the American Physical Society.[6]
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