Joachim Kupsch 1939–2018 • Bert Diddens 1928–2018 • Francis Farley 1920–2018

Joachim Kupsch 1939–2018

Joachim Kupsch

Eminent mathematical physicist Joachim Kupsch passed away in Heidelberg, Germany, on 19 June aged 78. He made wide-ranging contributions to scattering theory and elementary particle physics, quantum field theory and infinite-dimensional analysis, Fermionic integration and supersymmetry, not to mention open systems and decoherence. He also had many collaborators, most of them from Germany. His work, always characterised by mathematical rigour and scholarly exposition, includes three books. The last – Quantum Fields and Processes: A combinatorial approach (Cambridge University Press) came out in March 2018.

Joachim received his diploma in physics from the University of Köln in 1966 and embarked on a postdoc at the University of Bonn. He worked on analytic scattering theory during his tenure as a CERN fellow from 1968 to 1970, where he was influenced deeply by André Martin. After postdoctoral work and habilitation at the University of Heidelberg (1970–1973), Joachim secured a permanent position at the University of Kaiserslautern from 1973 to 2005 and then became an emeritus professor. During 1985–1986 he visited CERN many times, and until 2008 had guest-professor positions in China (Beijing and Shanghai), Portugal (Lisbon) and India (Mumbai, Chennai, Pune and Delhi).

One of the outstanding results of the analytic S-matrix theory is the Froissart–Martin bound, which sets an upper limit (equal to a constant times the square of the logarithm of energy) on the total cross section of a two-particle scattering process. It was first derived by Marcel Froissart in 1961 assuming Mandelstam representation with a finite number of subtractions; and was rigorously proved by Martin in 1966 using only unitarity and analyticity properties following from axiomatic field theory, in particular the analyticity of the absorptive part in the Lehmann–Martin ellipse. The question was whether it was possible to construct scattering amplitudes that saturate this bound and obey fundamental analyticity constraints?

In 1968, David Atkinson pioneered the theoretical construction of pion–pion scattering amplitudes obeying Mandelstam representation, crossing symmetry and elastic unitarity in the elastic region, and the inelastic unitarity inequalities in the inelastic region. Atkinson obtained an amplitude with a total cross section decreasing at high energies. Joachim joined this research with full vigour. After persevering for nearly 12 years, and after many intermediate results, he constructed a pion–pion amplitude saturating the Froissart–Martin bound, and obeying Mandelstam analyticity, crossing symmetry and inelastic unitarity in the inelastic region. The result is significant because the bound appears to be saturated at the LHC. An essential ingredient in his proof is the Auberson–Kinoshita–Martin theorem. Perhaps Joachim’s efforts in 1970 did not succeed because this theorem was not yet published. The main constraint not yet incorporated in Joachim’s 1982 construction is elastic unitarity in the elastic region.

Joachim died in the arms of Sigrid Kupsch-Losereit, his beloved wife of 45 years. His friends knew him to be a warm, soft spoken, affable and kind person; he will be sorely missed for both his academic and human qualities.

  • Shasanka Roy, Tata Institute of Fundamental Research, with input from André Martin and Sigrid Kupsch-Losereit.

Bert Diddens 1928–2018

Bert Diddens

On 28 August, following a short period of sickness, our friend and colleague Bert Diddens passed away at the respectable age of 90. He was one of the veterans in CERN’s proud history of particle physics and the first scientific director of the Dutch high-energy physics institute Nikhef.

Bert was born in the province of Groningen, in the north of the Netherlands. It is a region where people tend to be straightforward and down-to-earth, and Bert fitted that description very well, even up to his last days when telling his family that he didn’t want flowers at his funeral, as the money could be better spent on science. But behind this demeanour he was a gentle and sensitive person, loyal to his friends and colleagues. He remained interested in the sciences throughout his life, regularly visiting the Nikhef library to stay informed. This was illustrated by his always to-the-point comments when the jury consisting of him and all other former Nikhef directors deliberated on what was the best PhD thesis of the past year.

Bert studied physics at the University of Groningen, where he also received his PhD. The experimental work that led to it, however, was done in Leiden, where he studied gamma radiation from oriented cobalt and manganese nuclei using low-temperature techniques. After his PhD he joined the small group of physicists at the University of Liverpool in the UK, which served as a warm-up for CERN’s first experimental programme. He worked on proton–proton scattering at the university’s synchrotron, a topic that remained a thread throughout his early career.

In 1963 with Giuseppe Cocconi and Alan Wetherell, later joined by Jim Allaby, he formed a group to study proton–proton scattering at the Proton Synchrotron. The experiment revealed that the slope of the diffraction peak shrinks with increasing energy. A few years later, with Alan and Jim, he initiated an experiment at Serpukhov to study particle production and the total hadron–hadron cross section at the then-highest proton energy of 70 GeV. In 1970, with CERN’s Intersecting Storage Rings being constructed, Bert with his CERN colleagues joined Ugo Amaldi and Giorgio Matthiae of the Rome-ISS group to design an experiment to study small-angle proton–proton scattering, introducing a novel technique that later became known as “Roman Pots”. Just before he was asked in 1975 to become the first scientific director of the high-energy physics section of Nikhef, Bert turned to neutrino physics when his CERN team joined Klaus Winter in the CHARM (CERN–Heidelberg–Amsterdam–Rome–Moscow) experiment.

As a director at Nikhef he was responsible for shaping its first experimental programme, of which CHARM became a valuable part. As Nikhef did not yet have its own building, Bert had the responsibility to make sure that the design and construction of a new laboratory fitted the ambitions of the Dutch high-energy physics community. The success of today’s Nikhef is to a large extent determined by these first developments. When Nikhef had to decide which experiments to join at the Large Electron Positron collider (LEP), it was obvious that DELPHI would be one of them, extending into the LEP era the amicable bonds with his former CERN colleagues. He actively participated in the experiment after his directorship came to an end in 1983 and was the thesis supervisor for many PhD students of both DELPHI and CHARM.

We will all remember Bert Diddens with the greatest respect as a wonderful person, an excellent physicist and a key figure in establishing Nikhef as an important player in the international community of high-energy physics institutes.

  • His friends and colleagues.

Francis Farley 1920–2018

Francis Farley

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.

  • His friends and colleagues.