• David Jackson 1925–2016 • Edward J Lofgren 1914–2016 • Peter Weilhammer 1938–2016 • Wolfhart Zimmermann 1928–2016

David Jackson 1925–2016

The life of John David Jackson bridged the era of tabletop nuclear-physics experiments and the modern age of large, complex accelerators. Jackson’s first professional appointment was in 1949 as assistant professor of mathematics at McGill University in Montreal, Canada, where, half a century earlier, Ernest Rutherford first showed that radioactive matter emits three distinct types of radiation. Shortly after moving to Manchester, UK, Rutherford performed the famous alpha-particle scattering experiment, which demonstrated the existence of the nucleus. When Jackson arrived at McGill, much of Canadian physics was still under the spell of Rutherford: theoretical physicists were often only found in mathematics departments, and quantum mechanics was not even taught. Jackson played a significant role in changing this character of physics in Canada.

Jackson was born in London, Ontario, and obtained his undergraduate education at the University of Western Ontario. In 1946 he was admitted to MIT, where he obtained his doctorate under Victor Weisskopf. His thesis on neutron–proton scattering, published in a widely known paper with John Blatt, led to an offer of a postdoc position from Hans Bethe at Cornell at a time when Feynman was doing his famous work there. Although Cornell was among the hottest destinations in theoretical physics at the time, Jackson felt an obligation to return to Canada. He later wrote that “the foolishness and chauvinism of youth is evident in my acceptance of the [McGill] offer.” But it was at McGill that Jackson first displayed his remarkable talents as a teacher of theoretical physics and developed the first draft of what was to become the first (1962) edition of his famous textbook, Classical Electrodynamics.

In 1956, Jackson spent a year at Princeton. In that year he produced a brilliant study of the muon-catalysed fusion of protons and deuterons into He3, and participated actively in the stream of developments unleashed by the discovery of parity violation. In the summer of 1957, Jackson accepted a professorship at the University of Illinois at Urbana, where his research focus began to turn to particle and high-energy physics, and in 1963–1964 he undertook a sabbatical at CERN. In 1967, he accepted a professorship at the University of California in Berkeley, where he remained for the rest of his life. The “November Revolution” of 1974 gave Jackson the opportunity to display his mastery of “simple” nuclear physics and quantum mechanics in his overnight analysis of the amazingly narrow J/ψ resonance discovered in electron–positron collisions at SPEAR. At first his calculation of the J/ψ width was controversial, but before long he was shown to be correct.

Owing to his outstanding personality and superb technical ability, Dave (as he was often known) was in great demand for public service. In addition to membership of the National Academy of Sciences and many important committees, he was acting head of the Fermilab theory department (1972–1973), editor of Annual Reviews of Particle and Nuclear Physics (1977–1993), chair of the Berkeley physics department (1978–1981) and deputy director of the central design group for the Superconducting Super Collider (1984–1987). Jackson was also a strong proponent of increasing the participation of women in physics.

David Jackson inspired many because of the character traits he displayed to his colleagues, in his lectures, his publications and even in his infamous homework problems: intellectual rigour, tenacity and self-discipline in the pursuit of demanding goals, strict honesty, and a total absence of vanity.

• Kurt Gottfried and Maury Tigner, Cornell University.

Edward J Lofgren 1914–2016

One of the few remaining physicists who worked on the Manhattan Project, Ed Lofgren passed away peacefully on 6 September at the age of 102. He was a key figure in the development of the Bevatron at Lawrence Berkeley National Laboratory and was its first director during the early days of large-scale particle physics.

Lofgren was born in Chicago as the youngest of seven in a family of Swedish immigrants, and attended Los Angeles Junior College in 1931. He was accepted by Caltech but could not find a job that paid enough to be able to afford it. Later, he transferred to the University of California at Berkeley and received his undergraduate degree in 1938. In 1941, Lofgren interrupted his graduate studies at Berkeley to contribute to the war effort, in which he developed uranium-hexafluoride sources used in the Calutron “farm” at Oak Ridge for uranium enrichment (which would later become the topic of this PhD thesis). In 1944 he moved to Los Alamos and manned a radiation-monitoring site located 9 km from Ground Zero, where the first nuclear test was carried out.

After the war, Lofgren worked on an experimental verification of the McMillan–Veksler “phase-stability” principle by converting the 37 Cyclotron into the world’s first synchro-cyclotron. This led to the redesign of the 184 Cyclotron, offering a substantially higher accelerating efficiency and a maximum energy almost 10 times higher than the initial design. Following a brief stint at the University of Minnesota investigating cosmic rays with high-altitude balloons, Lofgren returned to the “Rad Lab” at Berkeley in 1948 and served as director of the Bevatron from 1954. He continued his stewardship of this accelerator until his retirement as a laboratory associate director in 1979.

Starting from its first operations in 1954, when the Bevatron was the world’s highest-energy machine, seminal experiments contributed to the foundations for particle physics. The antiproton was discovered in 1955, swiftly followed by the antineutron in 1956 and multiple resonances thereafter. The Bevatron era also saw the first industrial-scale physics collaborations, where large groups would systematically analyse millions of photos taken at bubble chambers. The dozens of meson and baryon resonances that were discovered provided the impetus for the introduction of the quark model.

Later, in 1965, Lofgren led the “200 BeV” design study at Berkeley, but after the decision was made to build Fermilab in Illinois he did not take part in the project. By 1970, when the Bevatron’s 6 GeV beams had fallen far behind other accelerators, Lofgren and Herman Grunder gave it a new lease of life by converting it into a heavy-ion accelerator: the Bevalac. The Bevalac pioneered the fields of relativistic heavy-ion physics, high-energy calibration of satellite cosmic-ray instrumentation, and medical treatments with heavy-ion beams. Many hundreds of cancer patients were treated with neon and other beams at the facility, laying the foundations for today’s hadron-therapy programmes.

His three daughters remember him as a caring father always willing to describe the natural wonders around him to anybody who would listen. Even in his last weeks of life, he was seen explaining the famous San Francisco fog to fellow residents at his Oakland retirement centre. He will be greatly missed.

• Jose Alonso, Lawrence Berkeley National Laboratory.

Peter Weilhammer 1938–2016

Peter Weilhammer passed away on 27 May. He was born in 1938 in Munich and obtained his PhD in physics at the Ludwig Maximilian University in 1969, after which he became a research staff member of the Max Planck Institute and worked with Werner Heisenberg. In 1971 he came to CERN, where his achievements covered the whole spectra of work from particle-physics analysis, detector technology and steering the future of CERN.

Peter’s managerial capabilities were recognised very early, and his record is impressive. In the early 1970s he was an official CERN observer at Brookhaven National Laboratory and a member of its scientific council. In the period 1972–1976, he was a physics programme co-ordinator at CERN, a secretary of the nuclear-physics research board and an adviser to the then Director-General. In the periods 1974–1981 and 1984–1989 he was spokesperson of the ACCMOR collaboration; led the WA3 and NA32 experiments; and, later, led the DELPHI micro-vertex team. From 1986–1999 he was head of CERN’s solid-state detector group, and also headed two international collaborations on radiation-hard silicon and diamond detectors. Following this, he was chairman of BELLE’s silicon-vertex-detector review committee, a member of the CERN technical advisory board to the Director-General and elected spokesman of the CIMA collaboration for the development of novel SPECT and PET instrumentation.

Peter made outstanding contributions to high-precision semiconductor detectors, entering this domain at the beginning of the 1980s with the NA11 experiment. He was one of the main proponents and constructors of high-precision vertex detectors for the NA11, NA32, DELPHI and ATLAS experiments, showing continuous initiative in developing new devices and pursuing systematic studies in heavy-radiation environments and for different applications.

Peter was full of initiative, very energetic and not afraid of taking risks. He worked closely with people from all over the world, helping them as much as he could. In addition to all of this, Peter was a professional ski instructor and a climber, and many of us have enjoyed trips with him in the mountains. He inspired many of us both in our professional and private lives. Our thoughts go to his family and many friends.

• His friends and colleagues.

Wolfhart Zimmermann 1928–2016

Wolfhart Zimmermann, who passed away on 18 September, was one of the outstanding German theoretical physicists of the second part of the 20th century. He made influential discoveries and in 1991 he received the Max Planck medal for contributions to quantum field theory and renormalisation theory.

Zimmermann studied physics and mathematics in Freiburg and Göttingen, completing his thesis in cohomology in 1950. He spent several years in the US, at the Institute for Advanced Study, the Courant Institute of Mathematical Science and the University of Chicago. He then returned to Europe, becoming a fellow at the Max Planck Institute for Physics and Astrophysics in Munich, followed by director in 1991.

His scientific work concerned perturbative-renormalisation theory, and the development of a general theory of quantised fields. Guided by the experience from renormalised-perturbation theory, Lehmann, Simanzyk and Zimmermann based their “LSZ” theory on a weak-convergence asymptotic condition for the field operators by asymptotic free fields, thus establishing a connection between the physical interpretation in terms of particles and the collision cross-section. The LSZ approach was the starting point of the proof of the experimentally verified dispersion relations and also led to experimentally verifiable predictions that can be extended to cover situations with composite particles.

Zimmermann was closely involved in the physics and physicists of CERN and particularly with Henri Epstein, Yurko Glaser, André Martin and Raymond Stora.

• Philippe Blanchard, Bielefeld University.