LEE, TSUNG-DAO

born Nov. 25, 1926, Shanghai, China Tsung-Dao Lee Chinese-born American physicist who, with Chen Ning Yang, received the Nobel Prize for Physics in 1957 for work in discovering violations of the principle of parity conservation (the quality of space reflection symmetry of subatomic particle interactions), thus bringing about major refinements in particle-physics theory. Lee immigrated to the United States in 1946, and, although he had no undergraduate degree, he entered the graduate school in physics at the University of Chicago, where he began his collaboration with Yang. After working briefly at the University of California at Berkeley, and for two years with Yang at the Institute for Advanced Study, Princeton, N.J., Lee was appointed assistant professor of physics at Columbia University in 1953. In 1956 Lee and Yang concluded that the theta-meson and tau-meson, previously thought to be different because they decay by modes of differing parity, are in fact the same particle (now called the K-meson). Because the law of parity conservation prohibits a single particle from having decay modes exhibiting opposite parity, the only possible conclusion was that for weak interactions, at least, parity is not conserved. They suggested experiments to test their hypothesis, and in 195657 Chien-Shiung Wu, working at Columbia University, experimentally confirmed their theoretical conclusions. (See also CP violation.) In 1960 Lee was appointed professor of physics at the Institute for Advanced Study, and three years later he returned to Columbia to assume the first Enrico Fermi professorship in physics. From 1964 he made important contributions to the explanation of the violations of time-reversal invariance, which occur during certain weak interactions.