Anselm Citron (1923 - 2014)

Anselm Citron, one of CERN’s pioneers, an enthusiastic scholar and internationally renowned researcher, passed away on 8 December at the age of 91.

Anselm Citron, front, looks at a quadrupole for the muon beam at the SC with, left to right, Bengt Hedin, Marinus van Gulik and Pierre Lapostolle.

Born in Germany, Citron went to high school in the Netherlands, where he had been sent to escape the persecution of people with Jewish roots. After abitur and a short period at a technical high school, he took part in the last stages of the Second World War before returning to Freiburg in 1945. There, he studied physics under Wolfgang Gentner, and obtained his PhD.

Citron then joined the Cavendish Laboratory, Cambridge, in 1952, to take part in research on accelerator physics. A year later, he came to the newly founded CERN as one of its first 12 staff physicists and contributed to the construction of the Proton Synchrotron, for which he was responsible for the high-frequency power system and beam shielding. It was then that the decision was taken to construct the hill known as Mont Citron at the end of the PS experimental hall (now the site of Linac 4). After this, he moved to work on CERN's Synchrocyclotron, for which he constructed the first muon channel with strong focusing.

In 1964, Citron was sent to Brookhaven National Laboratory to work in the machine division. Several offers of professorships ensued, and he decided to go to Karlsruhe University in 1965, joining and expanding the Institut für Experimentelle Kernphysik (IEKP) founded by Herwig Schopper.

At Karlsruhe, Citron’s research projects included the development of high-frequency superconducting cavities, which are still being used in contemporary accelerators, as well as the development of electron cooling at the Low Energy Antiproton Ring (LEAR) at CERN. In parallel, he initiated research efforts at CERN and PSI, with noteworthy highlights including: precise measurements with muonic, pionic and antiprotonic atoms; pion-induced reactions with light nuclei at CERN and PSI; meson spectroscopy with antiprotons with the Crystal Barrel experiment at LEAR; and the observation of the f₀(1500), a glueball candidate.

We remember Anselm Citron dearly, as a highly esteemed colleague who was greatly appreciated and respected. He was an internationally renowned scientist who paved the way in modern particle-physics research. He also acted as an example for many of his colleagues, particularly in his enduring engagement on behalf of the persecuted.

Helmut Koch, Thomas Müller, Herwig Schopper, IEKP

For a longer version see the CERN Courier, March 2015 edition, page 41.