[Cuga] Jefferson Lab mourns Ingo Sick - a message from Rolf Ent

Lorelei Carlson lorelei at jlab.org
Mon May 31 18:37:14 EDT 2021

Ingo Sick, an eminent and well-known nuclear physicist retired from the University of Basel in Switzerland, passed away this Sunday, two days after his 82nd birthday. He had been suffering from stomach cancer for a few months. Ingo was at the root of much of the electron scattering science for which the Continuous Electron Beam Accelerator Facility was built, and largely contributed to the education of how to become a successful experimental nuclear physicists to many well-known present Jefferson Lab staff and users.

Ingo was together with Bernhard Frois the 1987 Bonner Prize recipient, with as citation: "For their elegant studies of nuclei using high-energy electron scattering. In particular, their precision measurements of nuclear charge and current densities have offered novel perspectives on ground states and valence orbitals. Their studies of few-nucleon systems have demonstrated the need for sub-nucleon degrees of freedom in a complete description of the nucleus. This body of work has provided firm benchmarks against which to test our understanding of the nuclear many-body problems."

>From this citation the strong relation with, and in fact the foundation of, the nuclear physics program pursued at Jefferson Lab from its start to present days jumps out. The University of Virginia and University of Basel groups developed, in collaboration with Jefferson Lab, the “UVA-Basel-JLab” dynamically polarized nuclear target systems that were used for the spin structure function measurements at SLAC in the 1990s in order to shed light on the topical “proton spin puzzle”. The target was conceived and used for measurements of the elusive neutron charge form factor at Jefferson Lab, a key science highlight of early Jefferson Lab operations to learn about the charge density distribution in the net-neutral charge neutron. It was then used for many, many other Jefferson Lab experiments, up to today! The Basel group also built and delivered the Hall C Moller Polarimeter, that was used for the first precise measurements of the Jefferson Lab electron beam polarization.

Of note is also Ingo’s involvement in experiments using the light few-body nuclei, including determination of the proton, deuteron, helium-3, and hydrogen-3 elastic form factors, the latter via a well-known experiment using a tritium target at Saclay, and the determination of the electromagnetic structure of the helium-isotopes at SLAC. These measurements still set a standard in the field today.

Ingo and his group also led a quasi-elastic (e,e’p) scattering experiment off the carbon-12 (12-C) nucleus (and other heavier nuclei) at Jefferson Lab that measured the so-called spectral function and uniquely showed where the “missing strength” of the valence proton orbitals in 12-C went: the strength was shifted to larger excitation energies and higher proton momenta due to correlations in nucleon-nucleon pairs. This remains a current topic of interest at Jefferson Lab, with many science highlights.

Ingo and his group were active and highly appreciated scientists at many well-known (electron) scattering facilities worldwide, at Saclay (France), at NIKHEF (Netherlands) where Ingo had been granted an honorary doctorate from the University of Utrecht for his contribution to accelerator and nuclear physics, at MAMI-Mainz (Germany), at SLAC (US), at the Paul Scherrer Institute (Switzerland) and at our Jefferson Lab.

Ingo had an instinct for the scientific issues and the ultimate goals of nuclear physics experiments, and how to do them right. He also worked well together with nuclear theorists, leading to a wealth of high-cited papers.

Furthermore, Ingo also was always in for dinners (but no fish), skiing trips, and other activities. And he loved good wine which he stored in big amounts in the air-raid shelter of his house!

Ingo will be sorely missed at Jefferson Lab, both by many collaborators who received part of their science insights from him, be it directly from their education at Basel or indirectly benefitting from his presence and knowledge of experiments, and for his truly unique view on nuclear physics.

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