Burton Richter 1931–2018 • Georges Dôme 1928–2018 • Hans Paar 1944–2018

Burton Richter 1931–2018

Burton Richter

Burton Richter, a major figure in particle physics who shared the Nobel Prize for the co-discovery of the J/ψ meson, passed away on 18 July in Palo Alto, California, at the age of 87.

Born in Brooklyn, New York, in 1931, Richter’s love of science began with the nightly blackouts during World War II, which revealed an unparalleled view of the night sky.

He studied physics at the Massachusetts Institute of Technology (MIT), where he was introduced to the electron–positron system by Martin Deutsch, who was conducting classical positronium experiments. He wrote his thesis on the quadratic Zeeman effect in hydrogen and completed his PhD in 1956 on the photoproduction of pi-mesons from hydrogen.

That year, Richter moved to Stanford University’s high-energy physics laboratory as a research associate. In 1960, he became an assistant professor of physics, then associate professor in 1963 and professor in 1967. During this time, Richter married his wife, Laurose, and had two children, Elizabeth and Matthew. By 1970, Richter’s talents in experimental particle physics and accelerator physics led to the Stanford Positron-Electron Asymmetric Ring (SPEAR) at the Stanford Linear Accelerator Center (SLAC). It included a groundbreaking type of general-purpose detector that has been used in particle colliders ever since, and it would eventually produce his biggest discovery.

After Richter secured funding for SPEAR in 1970, it took him just 27 months to build the accelerator, at a cost of $6 million. Experiments commenced in 1973 and, famously, in November 1974, SPEAR flushed out what the SLAC team dubbed the “psi” meson – a bound state of two charm quarks. Simultaneously, at Brookhaven National Laboratory on the other side of the continent, Sam Ting and his group had spotted the same resonance, which they christened the “J”. Just two years later, Richter and Ting shared the 1976 Nobel Prize in Physics for their pioneering discovery of the J/ψ, which proved the existence of a fourth type of quark (charm). It was a major step towards the establishment of the Standard Model of particle physics.

Before he received the Nobel Prize, in 1975 Richter began a sabbatical year at CERN, during which he pursued an experiment at CERN’s Intersecting Storage Rings (ISR) – the world’s first hadron collider. He was hosted by Pierre Darriulat and worked on adding a muon spectrometer arm to the R702 experiment. Richter also worked out the general energy-scaling laws for high-energy electron–positron colliding-beam storage rings, looking specifically at the parameters of a collider with a centre-of-mass energy in the range 100–200 GeV, arguing that such a machine would be required to better understand the relationship between the weak and electromagnetic interactions: “That study turned into the first-order design of the 27 km-circumference LEP project at CERN that was so brilliantly brought into being by the CERN staff in the 1980s,” he wrote in his Nobel biography.

His influential paper “Very High Energy Electron–Positron Colliding Beams for the Study of the Weak Interactions” (Nucl. Instrum. Methods 136 47) was followed by two detailed studies: one concerning the physics, published in November 1976 as CERN Yellow Report 76-18, of which Burt was a co-author, and an accelerator study headed by Kjell Johnsen. “Burt’s paper and his personal advocacy of high-energy electron–positron collision triggered interest at CERN, and had a powerful impact on the development of the Laboratory, also paving the way for the LHC and the discovery of the Higgs boson,” says CERN’s John Ellis.

In 1978, along with others at SLAC, Richter began to investigate the possibility of turning the 3.2 km linear accelerator at SLAC into a linear electron–positron collider. Construction of the SLAC Linear Collider (SLC) began in 1983, and Richter became director of SLAC the following year, until stepping down in 1999. During that time, he oversaw the construction of the SLC, the only linear electron–positron collider yet to be built, and led the way to other machines for photon science. While SLAC director, Richter also initiated interregional collaborations with DESY in Germany and KEK in Japan, and was a proponent of bringing into existence a high-energy linear collider as a global collaboration.

“Perhaps his greatest contribution as director was, in the 1990s, designing a future for SLAC that would look very different from the past,” said Stanford Provost Persis Drell, who served as SLAC director from 2007 to 2012. “He recognised that pursuing an X-ray free-electron laser at SLAC could be used to provide a revolutionary science opportunity to the photon science community, who use X-rays as their tool for discovery. This vision became the Linac Coherent Light Source. Burt recognised that outstanding science needed to drive the future of the institution, and he did not flinch from designing that future.”

When he stepped down as SLAC director, Richter focused on public policy issues in science and energy, for which he received the prestigious 2007 Philip Hauge Abelson Prize from the American Association for the Advancement of Science. In 2010, he published Beyond Smoke and Mirrors: Climate Change and Energy in the 21st Century, an apolitical layperson’s exploration of the facts of climate and energy. Among his many accolades, Richter received the US National Medal of Science, the nation’s highest scientific honour, in 2014; the Enrico Fermi Award in 2012; and the Ernest Orlando Lawrence Award in 1976.

“In my career I have met no one who has made more fundamental contributions in electron–positron and electron–electron colliders, in the precision instrumentation used in colliders and in experimental physics,” says Ting. “After we received the Nobel Prize together in 1976, I met him many times and we became good friends. My wife, Susan, and I are going to miss him deeply.”

  • His friends and colleagues at CERN, with additional input from Stanford News Service.

Georges Dôme 1928–2018

Georges Dôme

Georges Dôme, who had a long, productive and distinguished career at CERN dedicated to the study of accelerating radio-frequency (RF) structures and their interaction with particle beams, passed away on 27 June.

A physicist and mathematician, Dôme arrived at CERN in the early 1960s from the École Royale Militaire, Brussels, via the SLAC National Accelerator Laboratory in the US, where for 18 months he attacked the problems that would be his lifelong interest. His initial work at CERN concerned the theoretical studies of accelerating RF structures for the 300 GeV linac project, in the process contributing to the development of numerical computations of magnetic-field distributions.

With the advent of the Super Proton Synchrotron (SPS) project, he joined the team of Clemens Zettler, who was responsible for building the accelerating systems of the new machine. Georges derived the formulae to describe and use the accelerating structures, which are still the workhorse of the SPS machine today. He was in charge of the detailed measurements of the structures, specified the precision machining of the many drift tubes to fix the central operating frequency of the structures, and also identified and measured the higher-order frequency modes whose impedance can destroy the particle beams. Different antennas and probes were then designed to render these modes harmless.

Georges also designed the structure of the SPS higher-harmonic cavity, another component necessary in the struggle to stabilise the beams of ever increasing intensity. His work has been essential in ensuring that the high-intensity beams for the LHC and the SPS fixed-target experimental programme are available and that the future LHC Injectors Upgrade (LIU) project is possible.

The SPS is a very versatile machine and its RF group has had to study and solve many varied problems to follow the different requirements. Georges made important contributions on many occasions, for example to the studies of particle diffusion due to RF noise, which was critical for beam lifetime in the proton–antiproton collider.

In the 1990s, Georges was asked by Vittorio Vaccaro from the University of Naples in Italy to review a paper on the coupling impedance of a circular iris, a subject that had long interested Georges. This triggered 20 pages of Georges’ closely spaced, small-character calculations and a fruitful collaboration on wakefields and impedance with members of the University of Naples.

Georges studied a subject in depth and was a precise and meticulous mathematician with a strong love for Bessel functions. He was always willing to go over a piece of work for his colleagues, but this could be a daunting prospect. It would come back annotated in blue pencil, every inherent inaccuracy revealed by his rigorous, uncompromising approach. This, of course, was splendid – you knew it was now perfect – and his unfailing good humour and willingness to help made this process very easy.

Georges was a fine mentor, looking after his students and both his younger, and older, colleagues. His body of work, supplemented by the excellent RF lectures he gave at the CERN accelerator schools, is a reference for accelerator physicists, and he continued this work for many years after his retirement. He was also a lifelong friend of and supporter of the CERN library.

Georges was in every way a gentleman, quiet and courteous, always interesting to talk to – a good person to find at a gathering. We will miss him.

  • His friends and colleagues.

Hans Paar 1944–2018

Hans Paar

Hans Paar, emeritus professor of physics at the University of California, San Diego (UCSD), passed away on 17 June after a short illness. Paar was initially trained at Delft University of Technology in his native country of the Netherlands. This engineering background served him well throughout his career, allowing him to take on important tasks in the design, construction and testing of equipment in all the particle-physics experiments he participated in.

Paar started his particle-physics career at Columbia University in the US, where he worked with Leon Lederman on one of the first experiments at Fermilab (E70). After completing his PhD thesis on this project, he relocated to Europe to work as a CERN fellow with another Nobel Laureate, Jack Steinberger, on WA1, the first experiment with the high-energy neutrino beam of the newly commissioned Super Proton Synchrotron (SPS).

In 1978, Paar joined a team at NIKHEF, the Dutch National Institute for Subatomic Physics, that worked on the TPC/2γ experiment at the SLAC National Accelerator Laboratory in the US, and he quickly became one of the leaders of the collaboration that carried out this experiment. His visibility at SLAC led to an offer from the UCSD, which he then joined as a faculty member in 1986 and where he remained for the rest of his career.

Paar was an internationally recognised physicist. He studied the properties of the bottom quark at electron–positron colliders since the early 1990s, first as a member of the CLEO collaboration (Cornell) and later the BaBar collaboration (SLAC). He also made essential contributions to the design and construction of novel types of calorimeters, in the context of the SPACAL and DREAM projects at CERN.

Later in Paar’s career, his research interests included observational cosmology. Paar and his colleagues set out to detect the B-mode polarisation of the cosmic microwave background radiation to address one of the most fundamental problems in astrophysics – the inflation of the early universe. Paar made crucial contributions to the realisation of this project, named POLARBEAR, which is carried out at high altitude in the Atacama Desert in Chile. Not only did he provide expert leadership, design and analysis skills, he also secured a $600,000 private donation, which helped enable the fabrication of the telescope.

Paar cared deeply about education and creating a nurturing, motivating environment for students. He was instrumental in modernising the UCSD’s curriculum on quantum mechanics at all levels and authored the textbook An Introduction to Advanced Quantum Physics. As part of the UCSD Research Experience for Undergraduates programme, he gave a “Physics of Sailing” course consisting of lectures on the physics of the sport, followed by a full day of sailing on San Diego Bay.

Hans had many interests outside of physics. He was also a devoted husband, (step)father and a very good friend to many. He was a gifted piano player and a serious model-train enthusiast. He helped to create an atmosphere of creative thought and friendliness within every group he was part of. Our thoughts go to his wife Kim, his daughter Suzanne and his stepsons Eric and Alain. We all owe Hans for many happy memories.

  • His friends and colleagues.