Jan Nassalski

With great sadness we have learned of the sudden and unexpected passing of Jan Nassalski. Jan was a long-standing and faithful friend of CERN, a prominent figure in the deep inelastic scattering community and more recently a diligent CERN Council delegate. But first and foremost he was an ingenuous physicist and dedicated teacher.

Jan Nassalski graduated from the Physics Department of Warsaw University in 1966. He started his scientific career at the Warsaw University of Technology and in 1971 joined the Institute of Nuclear Research (now the Soltan Institute for Nuclear Studies), which he finally headed as Scientific Director.

He has collaborated with the Laboratory of High Energy Physics in the Joint Institute of Nuclear Studies in Dubna, the Rutherford Laboratory in Didcot, and the Fermi Laboratory in Batavia, but from the late 70’s his activity was concentrated at CERN.

His continuous participation in experiments on one of CERN’s longest running experimental facilities, the muon beam, started by joining the European Muon Collaboration. In the early 80’s he set up a group studying the nucleon structure in deep inelastic muon scattering. He participated in the ground-breaking discovery that the quark spins contribute little to the nucleon spin (1988) and was a key contributor to the structure function studies in NMC, leading to the measurement showing violation of the Gottfried sum rule. In the 90’s Jan focused on high precision experiments of the polarised structure of the nucleon. Under his leadership the Warsaw group contributed to the first test of the Bjorken sum rule (SMC) and was essential in studying the gluon polarisation in the nucleon (COMPASS), an important step in understanding the quark/gluon structure of the matter around us. For his colleagues Jan Nassalski was reference point for all aspects of physics in the domain of deep inelastic scattering.

Jan’s group from the Soltan Institute for Nuclear Studies also successfully contributed to the NA48 experiment, with electronic elements required for read-out of the Liquid Krypton Calorimeter. Jan’s group was very active in physics analysis, leading some rare kaon decay studies and precise measurements of fundamental properties of neutral mesons. In particular, Jan was one of the main authors of the precision-measurement of the eta meson mass. He was a rigorous physicist, a great motivator and a crystal clear communicator.

In his home country of Poland, he was tireless in his outreach activities, publishing widely in the Polish media. Whenever CERN launched a new outreach initiative, the uptake in Poland was phenomenal, and Jan’s hand could be seen behind that success. For example, a CERN educational CD was distributed free with a popular science magazine, and more recently, Jan has played a vital role in making CERN’s high school teacher programme a great success in Poland. Jan was particularly proud of this work, and justifiably so.

As a Council delegate, Jan represented his country’s interests powerfully and with great conviction. Although softly spoken, he knew how to carry an argument. Yet even in the most heated of debates, he was a model of politeness and courtesy. Jan’s colleagues at CERN and in the CERN Council agree that he will be strongly missed. Particle physics has lost not only an excellent physicist, but also a true gentleman.

Thanks to his natural kindness and sense of humor, his infinite patience and above all his extreme rigour and great integrity, exchanges with Jan were of high standard and rewarding. The quality and accuracy of his judgments always made them an irreplaceable reference. Jan was to all of us more than a colleague, we will greatly miss his perceptiveness and sensitivity as well as his advice. We will all remember him as a precious friend.

His colleagues and friends