With deep sadness we learned of Meinhard Regler having passed away, after steadily detoriating health, on 22 September 2024 at the age of 83.

He was born in Vienna and spent his early childhood in Freiberg (Saxony, Germany) where his father – a pioneer of early X-ray technology – was professor at the Bergakademie. Having barely survived the end of WW II, the family returned to Vienna in 1947, where Meinhard attended primary school, Lycée français and Akademisches Gymnasium.

From 1960 he studied physics at TU Wien (TUW), in his master thesis studying the acceleration of deuterons in a proton linac at CERN. In 1966, Meinhard joined the newly founded Institute of High Energy Physics (HEPHY) of the Austrian Academy of Sciences. He settled in Geneva to participate in an experiment to measure ∆S/∆Q in Ke3 decays at the PS, and in 1970 obtained his PhD with distinction from TUW.

In 1970 Meinhard became staff member at CERN’s Data Handling Division. He joined the split field magnet (SFM) experiment, then the biggest electronic detector, at the very first pp collider, the Intersecting Storage Rings (ISR). As coordinator of SFM, he understood the revolutionary potential of George Charpak’s invention, the multiwire proportional chamber (MWPC), for precise tracking. Together with HEPHY, he contributed special MWPC designs for SFM. Since the magnet’s configuration was a nightmare for track reconstruction (zero field yet maximal gradient at the beam crossing), he realized the importance of rigorous statistical methods for track and vertex fitting – at that time only used for bubble chambers – at the emerging big tracking facilities, resulting in several seminal papers.

In 1975 Meinhard decided not to pursue a career offered by CERN. Instead, he returned to Vienna as leader of HEPHY’s experimental division. From 1993 until his retirement end 2006 he was deputy director and member of the institute’s 3-men coordination board, responsible for the detector development and software analysis groups.

The motivation behind Meinhard’s decision was to firmly establish experimental particle physics expertise, beyond bubble chamber know-how, in his native Austria. At TUW, where he gained the venia legendi and in 1989 became associate professor, he founded a series of specialized lectures and practical courses, which shaped a generation of particle physicists. In 1978 Meinhard, together with George Charpak, founded the world’s first international instrumentation conference – the Wire Chamber Conference, later known as the Vienna Conference on Instrumentation (VCI) – which successfully evolved into a regular tri-annual series in Vienna, with its 17th issue to come in Februay 2025.

Meinhard continued active participation in experiments at CERN, e.g. WA1 at SPS (p scattering off a polarized target), UA1 at the proton-antiproton collider (calibration of the PM readout of the “gondola” ecal), and the European Hybrid Spectrometer (EHS) at SPS (construction of a hadron calorimeter, together with University of Strasbourg).

In 1984 Meinhard joined the DELPHI experiment at LEP, where HEPHY was responsible for the forward drift chambers. He soon realized the emerging potential of semiconductor tracking devices, and in a huge effort established that technology at HEPHY, with particular emphasis on silicon strips, readout electronics, and radiation hardness. HEPHY contributed to DELPHI’s upgrade by a new Very Forward Tracker (VFT). This detector hardware expertise, initiated by Meinhard, was and is successfully continued with esteemed contributions to the CMS tracker at LHC, the Belle vertex detector at KEKB, and many more.

The LEP detectors, and in particular DELPHI (with TPC’s original “géometrie de fleur” and VFT), constituted a new generation of complex modular facilities, posing a challenge to detector-oriented data analysis. Remembering his experience at SFM, Meinhard revisited his studies of that time. Together with his group and participation by CdF Paris, new efficient methods were developed for track and vertex reconstruction, which in retrospect turned out of being known by statisticians as Kalman filter. Seminal papers were published from 1985 on, and these methods are now standard at most collider experiments.

Thus, Meinhard established what may be called the “Vienna School of data analysis”. Further studies in his group introduced a lot of novel analysis methods, in particular robustification and neural networks – essential for the high luminosities at LHC.

Meinhard had always been a fierce advocate of considering data analysis as an integral part of detector design from the very beginning. In the context of the ECFA Workshops for Physics and Detectors at a future electron-positron linear collider, he contributed to the optimization of the ILD, SiD and CLIC detector concepts by developing, together with a student, a fast simulation & reconstruction tool (LiC Toy) based on MatLab. Another important contribution consisted in extending the analytical Gluckstern formulae.

Meinhard Regler is co-author of the standard textbook “Data Analysis Techniques for High-Energy Physics” by C.U.P. (editor of the 1st edition 1990, translated to Russian; co-editor with R.F. of the 2nd edition 2000, in 2010 translated to Chinese). He also is author of about a dozen monographies and co-author of several hundred scientific papers.

All that would suffice for a lifetime achievement, but not so for Meinhard. In January 1990, shortly after the fall of the “iron curtain”, he had a vision: using the opportunity of open borders with Austria’s eastern neighbours to create an international center of excellence for applied science in the Vienna region – project AUSTRON. In 1993-96 a planning office led by Meinhard (partly on leave from HEPHY) compiled the Feasibility Study for a high-flux pulsed spallation neutron source (SNS), then recommended by the European Science Foundation (ESF). Ultimately, the costs prevented its realization, but parts of the study became valuable input later for the European Spallation Source (ESS) project at Lund.

Far from being discouraged, Meinhard shifted his idea towards a facility for cancer therapy by proton and carbon-ion beams – MedAustron. This innovative technique permits more precise treatment of tumors with less damage of surrounding tissue than conventional X-rays.

At that time no such light ion facility existed in Europe. Its key component, a rapid-cycling synchrotron (RCS), had already been studied in the context of the SNS. With incredible personal effort, Meinhard Regler, together with top experts for accelerator technology and radio-oncology, pushed that idea from a vision to its successful realization [1].

Supported in particular by the governments of the province of Lower Austria and the city of Wiener Neustadt (designated host), in 1996 a non-profit society was founded by Meinhard to run a planning office situated near the future site. Crucial support was provided by CERN (Kurt Hübner) with the “Proton Ion Medical Machine Study” (PIMMS) in collaboration with the TERA Foundation (Ugo Amaldi) and MedAustron. The study group, led by Phil Bryant, issued a Feasibility Study in 1998 (for which Meinhard contributed e.g. the design of a “riesenrad gantry”), followed in 2004 by a detailed Design Study. In 2007, the stakeholding authorities founded a company (EBG) for the construction and running of MedAustron. An agreement was signed between EBG and CERN to host construction of the RCS (by a team of young Austrian engineers led by Michael Benedikt (CERN), a former student of Meinhard), thereafter to be moved to the Wiener Neustadt site, and for further cooperation.

After the groundbreaking ceremony in 2011, MedAustron was commissioned 4 years later. Clinical treatment started end of 2016 with protons and mid 2019 with C ions. So far, about 2500 patients have been treated. Additionally, a special beam line for non-clinical research is available for external institutions, e.g. used by HEPHY for detector tests.

Not surprisingly, Meinhard was invited as lecturer to many international conferences and post-graduate schools worldwide. Besides chairing, until his retirement, the VCI series in Vienna, he was local chairman of the European Particle Accelerator Conference (EPAC) 2000 in Vienna, organizer of the CERN Accelerator Schools 1994 and 2004 in Baden near Vienna,

co-organizer (together with W.M.) of the ECFA Linear Collider Workshop 2005 in Vienna, and member of the scientific advisory committees of many more conferences. Meinhard Regler was Austria’s member at the Advisory Committee of CERN Users (ACCU) 1978-81, chairman of the Section for Nuclear and Particle Physics (FAKT) of the Austrian Physical Society (1980-82), Austria’s member at the Restricted European Committee for Future Accelerators (RECFA) 1992-97, and member of the Elected Board of the European Physical Society’s International Group on Accelerators (EPS-IGA) 1996-2002.

Honours received include the Kuschenitz Prize for Scientific Achievements of the Austrian Academy of Sciences (1986), Honorary Membership of the Austrian Society for Radio-oncology, Radiobiology and Medical Radiation Physics (ÖGRO) (2001), the Acknowledgement Prize for Science of the Province of Lower Austria (2006), and the highest scientific decoration of Austria – the Honorary Cross for Science and Arts of First Class (2006). At MedAustron’s groundbreaking ceremony in March 2011, Meinhard was publicly honoured by the Governor of Lower Austria and by the Federal Minister for Science and Research “for having significantly contributed to the origination of project MedAustron in Wiener Neustadt”.

Besides his scientific activities, Meinhard was socially engaged as co-founder and long-term president of Lebenshilfe Wien – a non-profit organization in support of mentally handicapped people – highlighted by building and running of a new residential home.

Meinhard enjoyed life and loved sports: basket ball, sailing and wind surfing (he held a trainer licence), bicycle cruising, hiking and mountain climbing – often together with friends and colleagues at weekends and holidays in Austria or elsewhere in the Alps.

Meinhard’s philosophy was able to encompass both scientific truth and religious belief (albeit often against official church doctrine), which helped him to always keep a firm moral stance in life. His character was absolutely incorruptible, strictly committed to truth, and responsive to honest loyalty, independent thinking and constructive criticism.

Meinhard Regler was an outstanding person. We have lost a worldwide respected scientist, visionary innovator, talented organizer, gifted teacher, great humanist, honest man and good friend. We are missing him, but his legacy will forever stay with us.

Winfried Mitaroff and Rudolf Frühwirth, HEPHY Vienna

[1] For a comprehensive report of MedAustron’s history, see e.g. M. Benedikt and Ph. Bryant: CERN Courier, vol. 51 no. 8 (Oct. 2011), pp. 33-35, https://cds.cern.ch/record/1734709/files/vol51-issue8-p033-e.pdf, opens an external URL in a new window