On the morning of 11 November 1974, members of the programme selection committee at the Stanford Linear Accelerator Center in California were assembling for one of their regular meetings. Sam Ting, from Brookhaven National Laboratory, New York, met Burton Richter, a leading experimenter at SLAC and said: “Burt, I have some interesting physics to tell you.” Richter responded immediately: “Sam, I have some interesting physics to tell you!”
Neither realised they had discovered the same fundamental particle in two entirely different experiments, nearly 5,000km apart. Their breakthrough, which some regarded as the most important discovery in the history of particle physics, was so startling and far-reaching that Richter, who has died aged 87, and Ting shared the Nobel prize in 1976, making their award one of the most rapid in its history.
The particle, which Richter’s team named psi, proved to be the first example of “charmonium” – a short-lived pseudo-atomic system comprising a quark and antiquark each of which carries the property known as “charm”. Up to that moment the idea of charm had been pure hypothesis, invented by theorists to bring a pleasing symmetry to the fundamental varieties of matter.
So sudden and dramatic was the discovery, which within months led to a cascade of further breakthroughs in understanding of particles and forces, that the event became known in physics folklore as the “November Revolution”, recalling the October Revolution in Russia that changed 20th-century history.
For the psi exhibited behaviour utterly unlike that to which particle physicists were accustomed. For example, while the psi was short-lived on the scale of normal experience, nonetheless it survived hundreds of times longer than the conventional wisdom expected. A popular description at the time said: “It was as if an anthropologist had stumbled upon a hitherto unknown tribe of people who lived seven thousands of years rather than seven decades.”
This suspended animation was explained by the emerging theory of the strong force – quantum chromodynamics. Thus in addition to confirmation of the charm hypothesis, the November Revolution heralded the emergence of QCD in the physics lexicon.
Meanwhile, the discovery of further examples of charmonium – psi-like particles – followed by the production of particles with explicit charm brought a symmetry to the basic picture of matter.
The electron was known to be one of a family of four “leptons”, whereas the proton and neutron and related “strange” particles were built from three varieties of “quark” – whose existence had been confirmed by Richter’s colleagues at SLAC a few years earlier. The discovery of the charmed quark revealed that both quarks and leptons are linked in pairs (today we know of three such pairings or “generations”). The discovery of the psi was the dawn of this profound insight and the moment when the Standard Model of particles and forces began to be generally accepted.
Until that time, there had been a 2,000-year quest, begun in ancient Greece, to identify the basic seeds and structure of matter. After discovery of the psi, with its novel properties, attention moved to understanding how different varieties of matter emerged in the Big Bang, leading to the forms that comprise our present experience; particle physics increasingly moved towards experimental cosmology. Thus, from a modern perspective, the November Revolution was the experimental boundary between two epochs in the field of particle physics.
Burton was born in Brooklyn, New York, the son of Fanny (nee Pollack) and Abraham Richter, a textile worker. He attended Far Rockaway high school, which had already produced one Nobel laureate in physics – Richard Feynman; by coincidence the 1976 prize for Physiology or Medicine went to Baruch Blumberg, who had graduated from the school around the time that Richter matriculated.
Richter went to university at the Massachusetts Institute of Technology, graduating with a BSc in 1952 and PhD in 1956. His thesis work focused on the ability of high-energy gamma ray photons to liberate pi-mesons from atomic nuclei.
His interest in photons took him to a professorship at Stanford University, where he worked on experiments at the electron linear accelerator, Slac. In 1972 he exploited its ability to generate positrons – the antimatter analogues of electrons – and designed a scheme to feed them into a circular accelerator called Spear (Stanford Positron-Electron Asymmetric Ring), which was small enough to fit into what had previously been a parking lot adjacent to Slac.
The annihilation of electrons and positrons at Spear led to a raft of discoveries, of which the psi was just the beginning. Richter’s success with electrons and positrons at Spear helped inspire construction of LEP at Cern in Switzerland, from which the modern Large Hadron Collider has followed.
These were indirect by-products of Richter’s success in designing Spear. More immediate was his recognition that the wasteful X-rays unavoidably produced by the circulating particles in Spear could be put to use as probes of materials and biological samples. During his tenure as director of Slac from 1984 to 1999, he encouraged the evolution of Spear into the SSRL – Stanford Synchrotron Radiation Lightsource – the world’s first synchrotron radiation facility.
In later years his interests spread into nuclear power, climate change and energy technology. He was a president of the American Physical Society and the International Union of Pure and Applied Physics. A member of the US National Academy of Sciences, Richter also won the US’s highest scientific honour, the National Medal of Science, in 2014.
He is survived by his wife, Laurose (nee Becker), whom he married in 1960, their daughter, Elizabeth, son, Matthew, and two granddaughters.
• Burton Richter, physicist, born 22 March 1931; died 18 July 2018
