Francis Farley, who played a pivotal role in experiments to measure the anomalous magnetic moment of the muon, passed away on 16 July at his home in the south of France at the age of 97.
The son of a British Army engineering officer, Francis was born in India and educated in England. Before he could complete his education, he transferred to military research and worked on radar, developing his knowledge of electronics and demonstrating his abilities in innovation. Following a secondment to Chalk River Laboratories in Ontario, Canada, he resumed his formal education with a PhD in 1950 from the University of Cambridge, before starting his academic career at Auckland University in New Zealand. During his time at Auckland, he studied cosmic rays; represented New Zealand at a United Nations conference on atomic energy for peaceful purposes; measured neutron yields from plutonium fission (whilst on secondment to Harwell, UK); and wrote his first book Elements of Pulse Circuits.
In 1957 Francis joined CERN, where he started his long and remarkable journey on experiments to measure the anomalous magnetic moment of the muon (muon g-2). This endeavour would span nearly five decades and four major experiments, three at CERN and one at Brookhaven National Laboratory (BNL) in the US. The initial result from the first experiment had an accuracy of just 2%, whereas the final result from the last experiment reached 0.5 parts per million. Each experiment was at the time seen as a tour de force, and the measurement added an important restraint on the imaginations of theorists. It was also striking that each new measurement was within the error limits of the previous ones.
Many other people, including various highly renowned physicists, contributed to this long effort, but Francis is the sole common author, making seminal contributions to all of the experiments. The first experiment was performed on the initiative of Leon Lederman, a CERN visitor at the time, at CERN’s first accelerator, the 600 MeV Synchrocyclotron. The other members of the noteworthy team on this experiment were Georges Charpak, Richard Garwin, Theo Muller, Hans Sens and Antonino Zichichi. By the time of the second experiment, CERN’s Proton Synchrotron was operating and the second and third experiments were performed there – taking advantage of the higher-energy muons that the accelerator provided. Francis alone continued onto these experiments, but among others joining the experiments was Emilio Picasso. Later Francis, again alone, continued as a member of the most recently completed g-2 experiment at BNL. In the spirit of always looking for major improvements, it is noteworthy that in his review paper “The 47 years of muon g-2”, written with Yannis Semertzidis, a totally new structure for a muon storage ring is suggested, should greater accuracy be justified for a future experiment.
The first experiment showed that the muon was a “heavy electron”, the second validated electron loops in the photon propagator, and the third showed the contribution from virtual hadron loops. Each measurement has spurred theoretical physicists to include more and more effects in their calculations of the muon magnetic moment: higher-order corrections in quantum electrodynamics, first-order and then higher-order hadronic and electroweak contributions. These advances in the theoretical prediction in turn justified the next generation of experiment, to give an even more stringent test of theory. The muon storage rings also allowed tests of relativistic time dilation, with the third experiment achieving an accuracy of 0.1% for a “muon clock” moving at a speed of 0.9994c and the most accurate test of the “twin paradox”.
During the 1970s, when he was again based in the UK and Dean of The Royal Military College of Science, Francis also started to do research in wave energy. This work continued through his retirement, in parallel to the work on g-2. In this area too, he established a formidable reputation, with many papers written and patents produced over a period of 40 years. Indeed, his most recent paper on wave energy was published just a few days after his death.
Early in his retirement, he designed the beam transport system for a proton-therapy system at a cancer hospital, which was still being used more than 20 years later. He also published a special-relativistic single-parameter analysis of data on redshifts of type 1A supernovae that showed no evidence for acceleration or deceleration effects. Even more recently, he worked on other tests of relativity based on analysis of data from the muon g-2 experiments.
He received many honours, including election to a fellow of the Royal Society and the Hughes Medal for his work at CERN on g-2.
Outside of work, Francis had a passion for flying gliders, was a keen skier and windsurfer, a regular swimmer, and liked large American cars. All of these befitted a hardworking but somewhat playboy image, that years later formed much of the basis of his novel Catalysed Fusion.
Francis was a wonderful source of new ideas and insights, with a prodigious output. He was always enthusiastic, and he could be charming but forceful, and a stickler for precision.
He will be much missed.