Richard Henry Dalitz. 28 February 1925 — 13 January 2006

Richard (Dick) Henry Dalitz was a theoretical physicist whose principal contributions were intimately connected to some of the major breakthroughs of the twentieth century in particle and nuclear physics. His formulation of the ‘τ–θ’ puzzle led to the discovery that parity is not a symmetry of nature—the first of the assumed space-time symmetries to fail. He pioneered the theoretical study of hypernuclei, of strange baryon resonances, and of baryon spectroscopy in the quark model (at a time when many considered it ‘naive’), to all of which he made lasting contributions. The ‘Dalitz plot’ and ‘Dalitz pairs’ are part of the vocabulary of particle physics. Throughout his career he remained in close touch with many experimentalists, and he had an encyclopaedic knowledge of the data. Many of his papers were stimulated by experimental results and were concerned with their analysis and interpretation, work that often required the forging of new phenomenological tools; many also indicated what new experiments needed to be done. As a consequence, he was a theorist exceptionally valued by experimentalists. He created and ran a strong particle theory group at Oxford, which attracted many talented students and researchers, and which has continued to thrive.