The Faculty of Physics and Astronomy mourns the loss of Prof. Helmut Koch, who passed away on April 8, 2024 in Bad Oeynhausen.
Obituary by Prof. Dr. Ulrich Wiedner
Helmut Koch began his physics studies at the Technical University of Aachen in 1960. The 1960s were also the time in which the quark model was developed and accelerators continued to deliver new, surprising results. It is not known whether this motivated Helmut Koch to devote himself to strong interaction, i.e. the physics of quarks and gluons, but he devoted the rest of his scientific life to this subject.
At CERN in Prof. Backenstoss' group, he therefore devoted himself to exotic atoms in which the electron was replaced by a pion, for example. His dissertation is entitled "Determination of the width of pionic 2p levels from intensity measurements on 2p-1s X-ray lines". Here, the strong interaction influences the orbits of the pions. After strange quarks became available, he investigated kaonic atoms and hypernuclei at the first low-energy kaon beam at CERN PS. The subsequent availability of antimatter in the form of antiprotons immediately began to fascinate him. He co-authored a publication on "Observation of Antiprotonic Atoms". Antiprotons were to stay with him ever since and the search for exotic forms of matter has determined his research ever since. He searched for baryonium states at CERN and very quickly recognized the potential of a new storage ring for antiprotons, the Low Energy Antiproton Ring (LEAR).
Prof. Dr. Helmut Koch (Image: private)
The presence of cooled, background-free antiprotons allowed the study of the strong interaction to be taken to a whole new level. The annihilation of quarks and antiquarks in the form of protons with antiprotons to gluons is a unique way to understand the strong interaction. A detector based on modern high-energy experiments, the Crystal Barrel Detector, was installed at LEAR under Helmut Koch's leadership. From then on, there was a new quality feature for the spectroscopic investigation of hadrons with light quarks. As a well-known particle physicist at CERN, Lucien Montanet, once remarked only half-jokingly, the quality criterion "4-star resonance" only existed if the particle had been observed accordingly by Crystal Barrel. Many high-quality publications resulted from the experiment during its 7-year run.
At the same time, Helmut Koch was planning for the time after Crystal Barrel. He was a member of a study group that wanted to build a European Hadron Facility, which like the SuperLEAR project went unrealized, as both were in financial competition with larger CERN expansions. However, Helmut Koch was able to continue the spectroscopic investigation of hadrons with the Babar experiment in Stanford, California, and at the ELSA accelerator in Bonn. When the opportunity arose to build another dedicated antiproton machine on European soil, Helmut Koch was fully committed to the project. It is thanks to his contribution that antiproton physics is part ofthe new FAIR facility in Darmstadt. The “A” in FAIR stands for antiprotons. Unfortunately, the PANDA experiment, which offers new and unique opportunities to study hadrons, is coming too late for him.
Finally, a word about the man and university professor Helmut Koch. He earned his Habilitation in Karlsruhe while working at CERN, and then became a C3 professor in Karlsruhe before accepting a C4 professorship in Bochum in 1990—something he never regretted because he felt verywelcome here. Above all, Helmut Koch was a true gentleman and humanist, always friendly and caring, someone who appreciated and supported his students and colleagues. He has always been willing to serve the hadron physics community, be it as a reviewer, conference organizer orDPG section chairman. Even in critical situations, he always remained level-headed and never a bad word came from him. His considerate and gracious demeanor also made him a popular companion on sailing trips, which were one of his favorite pastimes on vacation. Beautiful sailingtrips and gourmet dinners followed by a good glass of red wine are also among my personal unforgettable memories of a great person and mentor: Helmut Koch.