In memoriam Peter Truöl

Peter Truöl, Professor Emeritus for Elementary Particle Physics at the University of Zurich, died after a short serious illness on March 22^th at the age of 80 years.

From 1971 to 2006 Peter Truöl was Professor for Elementary Particle Physics at the Physik-Institut of the University of Zurich (UZH). From here, he strongly shaped the new field of experimental meson physics at PSI. Later he initiated the university's involvement in high-energy accelerator physics. With his research group he participated in various experiments at PSI, DESY, and CERN and also in Berkeley, Los Alamos, and Brookhaven.

After studying physics, mathematics and chemistry in Göttingen and Zurich, Peter Truöl received his PhD under the supervision of Prof. Verena Meyer at UZH in 1967 with a thesis on the properties of the ¹⁰B nucleus that he investigated through scattering α-particles on ⁶Li. A two-year research fellowship from ETH Zurich subsequently allowed him to work at the Bevatron and at the 184" cyclotron in Berkeley to experiment with pion beams. In 1969, at the age of only 30 years, he became assistant professor at the University of California, Los Angeles.

In 1971, Peter returned to UZH for his habilitation. He experimented with precise pion beams, first at CERN and starting in 1974 at the newly created Swiss Institute for Nuclear Research (now PSI-West). In collaboration with groups from the Universities of Lausanne and Munich he initiated important experiments to study nuclear resonances, to measure the neutron scattering length and other important reactions in what we now call low-energy particle physics. The large pair spectrometer that he helped to develop made a significant impact in the progress of this field. Some results of Peter's experiments later played a major role in the chiral perturbation theory of the strong interaction.

In 1979 Peter Truöl embarked in experiments at LEAR at CERN, where at that time antiprotons could be generated at large rates and very low momentum, allowing to stop antiprotons in a target. The ASTERIX spectrometer has been used to study the formation and the ground state of the proton-antiproton system and allowed to analyse exclusive final states of proton-antiproton annihilation at rest to a large variety of mesons. Under Peter‘s supervision, large multi-wire proportional chambers were built for this experiment at the Physik-Institut of the UZH for the first time.

In 1985 Peter joined the H1 collaboration and significantly contributed with his group to the detector, the trigger, the software and various analyses. Under the leadership of Peter a cylindrical multiwire chamber and a drift chamber were built in Zurich, and a trigger concept for the H1 experiment was developed and implemented. In addition Peter coordinated the construction of the superconducting compensation magnet for H1, a project performed in collaboration with PSI, ETH and the industry financed on his initiative by Kanton Zurich.

The next stage of his research work took Peter to Brookhaven. Here he took part in various measurements to study rare kaon decays, the most important result of which was to clarify the strength of the coupling of the strange quarks to the weak interaction. For this experiment too, he built large multi-wire proportional chambers at the Physik-Institut.

In his scientific work, Peter Truöl was equally interested in the experimental aspects, the theoretical understanding and last but not least the linguistic quality of the publications. To convey the latter was a particular concern of his when supervising his PhD students. Building huge precise detector systems at the university was a constant challenge for and stimulated the development of the infrastructure of the Physik-Institut, especially the mechanical workshop.

At UZH Peter Truöl introduced elementary particle physics to the curriculum of physics. He taught physics students in elementary particle physics for many years and gave the basic lectures for students of medicine and biology countless times. In doing so, he succeeded in conveying to his audience the fascination of research in fundamental physics questions and in making physics a basic subject for future scientists.

From 1993 to 2000 Peter Truöl chaired the Program Review Committee at the PSI, where his broad experience helped to identify many possible and even impossible experiments. Peter Truöl was Director of the Physik-Institut from 1999 to 2003 and served as Dean of the Faculty of Mathematics and Natural Sciences from 2003 to 2006. After his retirement, he remained closely associated with current research projects in physics and with the University of Zurich. From 2007 to 2012, he served on the Board of Science Alumni.

In Peter Truöl, the University of Zurich, his colleagues and former students are losing a person and a teacher to whom they owe a lot.

Katharina Müller, Ueli Straumann and Peter Robmann

[Published: June 2020]