Walter Oelert, founding spokesperson of COSY-11 and an experimentalist of rare foresight in the study of antimatter, passed away on 25 November 2024.
Walter was born in Dortmund on 14 July 1942. He studied physics in Hamburg and Heidelberg, achieving his diploma on solid-state detectors in 1969 and his doctoral thesis on transfer reactions on samarium isotopes in 1973. He spent the years from 1973 to 1975 working on transfer reactions of rare-earth elements as a postdoc in Pittsburgh under Bernie Cohen, after which he continued his nuclear-physics experiments at the Jülich cyclotron.
With the decision to build the “Cooler Synchrotron” (COSY) at Forschungszentrum Jülich (FZJ), he terminated his work on transfer reactions, summarised it in a review article, and switched to the field of medium-energy physics. At the end of 1985 he conducted a research stay at CERN, contributing to the PS185 and the JETSET (PS202) experiments at the antiproton storage ring LEAR, while also collaborating with Swedish partners at the CELSIUS synchrotron in Uppsala. In 1986 he habilitated at Ruhr University Bochum, where he was granted an APL professorship in 1996.
With the experience gained at CERN, Oelert proposed the construction of the international COSY-11 experiment as spokesperson, leading the way on studies of threshold production with full acceptance for the reaction products. From first data in 1996, COSY-11 operated successfully for 11 years, producing important results in several meson-production channels.
At CERN, Walter proposed the production of antihydrogen in the interaction of the antiproton beam with a xenon cluster target – the last experiment before the shutdown of LEAR. The experiment was performed in 1995, resulting in the production of nine antihydrogen atoms. This result was an important factor in the decision by CERN management to build the antiproton–decelerator (AD). In order to continue antihydrogen studies, he received substantial support from Jülich for a partnership in the new ATRAP experiment aiming for CPT violation studies in antihydrogen spectroscopy.
Walter retired in 2008, but kept active in antiproton activities at the AD for more than 10 years, during which time he was affiliated with the Johannes Gutenberg University of Mainz. He was one of the main driving forces on the way to the extra-low-energy antiproton ring (ELENA), which was finally built within time and financial constraints, and drastically improved the performance of the antimatter experiments. He also received a number of honours, notably the Merentibus Medal of the Jagiellonian University of Kraków, and was elected as an external member of the Polish Academy of Arts and Sciences.
Walter’s personality – driven, competent, visionary, inspiring, open minded and caring – was the type of glue that made proactive, successful and happy collaborations.
