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Richard Dalitz (1925–2006)

by Frank Close

Professor Richard Dalitz, whose name became a byword in high-energy physics, has died, aged 80.

Dalitz, an Australian who took British nationality, spent a decade in the US and held a chair at Oxford University. He was born at Dimboola, in Victoria’s west, but his mother was keen that her children should go to school in the city, so the family moved when Dick, as he was widely known, was two.

After gaining degrees in mathematics and physics at Melbourne University, he moved to Britain in 1946 to do his PhD.

He was known for the Dalitz plot, Dalitz pairs and Castillejo-Dalitz-Dyson poles. The first of these, the geometrically based form of diagram he invented, has already led to at least five Nobel prizes and within a few years may lead to the discovery of the elusive elementary particle known as the Higgs boson.

Yet Dalitz never received this ultimate scientific recognition himself, though he came within a step of sharing a Nobel Prize for the discovery that, in particle terms, parity (or mirror symmetry) is not a property of nature.

Within two years at Cambridge University, he ran out of money. Taking wife VaIda and their young child, he took a one-year post at Bristol University and became enthralled with discoveries in the field of cosmic radiation, such as the pion (the carrier of the force that binds atomic nuclei) and “strange” particles.

It was after joining the group of famous physicist Rudolf Peierls at Birmingham University in 1949 and completing his thesis that, in 1951, he made his first seminal contribution, demonstrating that the electrically neutral pion could decay into a photon (a light particle), an electrically charged electron, and a positron (the anti-particle of the electron). The electron – positron pair became known as the Dalitz pair.

During the subsequent 50 years, Dalitz plots led to the discovery of about 100 ephemeral elementary particles, many surviving no longer than the time taken by a light beam to cross an atomic nucleus.

From 1953 Dalitz was in the US, first at Cornell University in upstate New York and, from 1956 as a professor at the Enrico Fermi Institute in Chicago.

At the end of the 1950s, Dalitz plots were made of the tracks of elementary particles coming from bubble chambers in the new high-energy particle accelerators.

Dalitz returned to Britain in 1963 (a time when Peter Higgs, at Edinburgh, was working on the ideas that would lead to the prediction of his boson particle the following year), but Dalitz retained a connection with Chicago until 1966.

Rudolf Peierls, meanwhile, had become a professor at Oxford and succeeded in getting Dalitz to join him as a Royal Society research professor at the university, a post he held for 27 years.

About this time, particle physics was revolutionised with the discovery that many particles are made up of even more fundamental particles, the quarks. In 1965, Dalitz showed how the idea explained properties of protons and neutrons.

In addition to his international stature, in Britain he was instrumental in starting an annual meeting of theoretical particle physicists at the Rutherford Laboratory, which continues today at Durham University.

After retirement in 1990, Dalitz remained an inspiration to students new and old, and was visiting the department of theoretical physics earlier this month, as ever, discussing the subject of particle physics with undiminished enthusiasm.

With Dalitz’s death, physics has lost one of its greatest unsung scientists. He is survived by his wife, three daughters and a son.

Copyright Guardian Newspapers Limited 2006
Re-printed in The Age, 8 February 2006