Theorist Tord Riemann, who made key contributions to e+e– collider phenomenology, left us on 2 April.
Tord was born in 1951 in East Berlin, educated at the Heinrich-Hertz-Gymnasium specialist mathematics school in Berlin and studied physics at Humboldt University in Berlin from 1970. He graduated in 1977 with a doctorate devoted to studies of the lattice approach to quantum field theory. He obtained a research position in the theory group of the Institute of High Energy Physics of the Academy of Sciences of the GDR in Zeuthen (later DESY Zeuthen), and in 1983–1987 worked at JINR, then in the Soviet Union, in the group of Dmitry Bardin.
In 1989/1990 Tord visited the L3 experiment at CERN, starting a fruitful collaboration on the application of the ZFITTER project at the Large Electron–Positron (LEP) collider. In 1991–1992 he was a research associate in the CERN theory division, working out the so-called S-matrix approach to the Z resonance. This was a profound contribution to the field, and a breakthrough for the interpretation of LEP data. Tord was one of the first to realise the great potential of a new e+e– “Tera-Z” factory at the proposed Future Circular Collider, FCC-ee, and led the charge reviving precision calculations for it.
Tord’s scientific fields of interest were broad
Tord’s scientific fields of interest were broad, and aimed at predicting observables measured at accelerators. His research topics included linear-collider physics; Higgs, WW, ZZ, 2f and 4f production in e+e– scattering; physics at LEP and FCC-ee; methods in the calculation of multi-loop massive Feynman integrals; NNLO Bhabha scattering in QED; higher-order corrections in the electroweak Standard Model and some extensions; and electroweak corrections for deep inelastic scattering at HERA. Apart from ZFITTER, he co-authored several programmes, including topfit, GENTLE/4fan, HECTOR, SMATASY, TERAD91, DISEPNC, DISEPCC, DIZET, polHeCTOR and AMBRE.
While being an active research scientist throughout his career, Tord will also be warmly remembered as a great mentor to many of us. He was a thesis advisor for two diploma and seven PhD students, and was actively engaged in supporting many postdoctoral researchers. He was co-founder and organiser of the bi-annual workshop series Loops and Legs in Quantum Field Theory and of the biannual DESY school Computer Algebra and Particle Physics.
In 2000, Tord and the ZFITTER collaboration were awarded the First Prize of JINR, and in 2014 the article “The ZFITTER Project” was awarded the JINR prize for the best publication of the year in Physics of Elementary Particles and Nuclei. In 2015 Tord was awarded an Alexander von Humboldt Polish Honorary Research Fellowship.
Tord Riemann cared about high standards in scientific research, including ethical issues. He was a true professional of the field. Despite illness, he continued working until his last day.
Tord was an outstanding scientist, a just person of great honesty, a reliable friend, colleague and family man. We feel a great loss, personally and as a scientific community, and remain thankful for his insights, dedication and all the precious moments we have shared.