Obituary: Professor Max Klein

The University is saddened to learn of the passing of Professor Max Klein.

Professors Monica D'Onofrio and Tim Veal, from the Department of Physics, pay tribute:

It is with immense sadness that we share the news of the passing of our dear and esteemed colleague and friend Max Klein, who left us on August 23.

The many of us who were fortunate enough to have worked alongside Max over the years know how profound his knowledge of physics was and how dedicated he was to experimental particle physics. We admired his ability to mentor and support students, postdocs and early career researchers, as well as his wise and calm approach to solving problems. Throughout his long and exceptional career, Max worked with passion on theory, detectors, accelerators, and data analysis.

Born in Berlin, Max earned his Diploma in Physics in 1973 from Humboldt University of Berlin (HUB, East-Germany, GDR), with a thesis on low energy heavy ion physics. He received his PhD in 1977 from the Institute for High Energy Physics (IHEP) of the Academy of Sciences of the GDR in Zeuthen (now part of DESY) on the subject of multiparticle production, and his habilitation degree in 1984 from HUB.

From 1973 to 1991 he conducted research at IHEP Zeuthen, spending several years from 1977 at the Joint Institute for Nuclear Research (JINR) in Dubna, and from the 1980s at DESY and CERN. For his role in determining the asymmetry of the interaction of polarized positive and negative muons with the NA4 muon spectrometer at CERN's SPS M2 muon beam, he was awarded the Max von Laue Medal by the Academy of Sciences of the GDR in 1985.

Max worked as Scientist at DESY from 1992 to 2006. As a member of the H1 experiment at the lepton-proton collider HERA since 1985, his research focused on investigating the internal structure of protons using deep inelastic scattering. He served as spokesperson of the H1 collaboration from 2002 to 2006 for two mandates. Under his leadership the Zeuthen group constructed and operated several sub detectors of H1, and the collaboration flourished with new groups joining.

Max became a Professor in the Department of Physics at the University of Liverpool in 2006, making many contributions to research and teaching. He joined the ATLAS collaboration in 2007, bringing his knowledge and experience to the experiment during the preparation of the LHC startup. He was elected chair of the Publication Committee in 2008-2009 (deputy chair in 2007-2008) and, during the following years, made key contributions to data analysis, notably on PDF and on the high-precision 7 TeV inclusive W and Z boson production cross sections and associated properties.

In 2017, Max was elected (deputy) chair of the ATLAS Collaboration Board (CB), serving two years (2018-2019) as chair and making invaluable contributions to the experiment and its collaborative life. He fostered communication between the CB and ATLAS management, always attentive to the voices of the CB members. Max's teaching in the department included mathematics for physicists, thermodynamics and statistical physics for undergraduates and high energy physics for postgraduates.

Feedback from students frequently mentioned Max being kind and helpful and his neat hand-written derivations and summaries were particularly appreciated. Max was also a highly valued academic advisor, final year project and PhD supervisor.

Max coordinated Welcome Week activities for incoming undergraduate students for several years and made regular contributions to open days especially with his engaging explanations of particle physics at the cloud chamber.

Max led the Liverpool ATLAS team from 2009 to 2017. Under his guidance, the 30-strong group contributed to the maintenance of the semiconductor tracker detector, as well as to ATLAS data preparation, precision SM measurements, Higgs physics studies, and new physics searches. The group also developed hybrids, mechanics, and software to the new ITk Pixel and Strip detectors.

In recent years, Max's scientific contributions extended well beyond ATLAS. He was a strong advocate for the development of an electron beam upgrade of the LHC, the LHeC, and collaborated closely with the CERN accelerator group and international teams on R&D of energy-recovery linacs (ERL). Among many other roles and activities, Max was spokesperson of the PERLE (powerful energy-recovery linac for experiments) collaboration at Orsay, coordinator of new accelerator studies for LHeC and FCC-eh, and coordinator of the Energy Recovery Accelerator Roadmap.

In 2013, Max was awarded the Max-Born-Prize by the Deutsche Physikalische Gesellschaft (DPG) and the Institute of Physics (IOP) for his fundamental experimental contributions to the elucidation of the proton structure using deep-inelastic scattering. The prize citation stands as a testament to his scientific stature: "In the last 40 years, Max Klein has dedicated himself to the study of the innermost structure of the proton. In the 90s he was a leading figure in the discovery that gluons form a surprisingly large component of proton structure. These gluons play an important role in the production of Higgs bosons in proton-proton collisions for which experiments at CERN have recently found promising candidates."

In 2022, a colloquium for Max's50 years in particle physics was held in Liverpool, celebrating his long-standing contributions to the community with many colleagues from Liverpool, the UK and from around the world, and with his family. The presentations can be found here.

Besides being a distinguished scientist, Max was a man of unwavering principles grounded in his selfless interactions with others and his deep sense of humanity. His visions were rooted in realism. Drawing from his experience as a bridge between East and West, he was a strong advocate for international scientific collaboration and the responsibility of scientists toward their societies.

Max's passing is a profound loss for our department and for the high energy physics community, but his legacy will endure. Our deepest condolences go to his family, especially to his beloved wife and our close colleague Uta.

Monica D'Onofrio and Tim Veal

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