Obituaries

Olga Borisovna Igonkina 1973–2019 • Dieter Renker 1944–2019 • Anton Oed 1933–2018 • Jacques Soffer 1940–2019

Olga Borisovna Igonkina 1973–2019

A talent and a love for physics

Olga Igonkina

Nikhef particle physicist and prominent member of the ATLAS experiment at CERN, Olga Igonkina, passed away on 19 May in Amsterdam at the age of 45.

Olya, as she was known to most of us, was born in 1973 in Moscow. Her father was an engineer, her mother a biological scientist. At age 14 she went to a special school for children talented in mathematics and in 1991 started her studies in physics at the Moscow Institute for Physics and Technology. Two years later Olya moved to the ITEP institute to specialise in particle physics, working at the ARGUS experiment and later the HERA-B experiment at DESY.

Olya wrote her dissertation about J/ψ production in HERA-B, with Mikhail Danilov as her supervisor. In 2002 she moved to BaBar at SLAC as a postdoc with the University of Oregon in the group of Jim Brau, where she worked on searches for lepton-flavour-violating tau decays and became convener of the BaBar tau working group. In 2006 she moved to CERN to spearhead Oregon’s new ATLAS group. Her work in ATLAS concentrated on the trigger, where she contributed to many activities with great ideas and enthusiasm, in particular as the trigger-menu coordinator during the startup of the LHC, and later on physics with tau leptons. She began her appointment at Nikhef in 2008 and in 2015 became a professor at Radboud University in Nijmegen.

For her efforts on the ATLAS trigger, Olya was given an ATLAS outstanding achievement award in 2018. Physics-wise, her passion was lepton flavour violation, in particular in tau decays. Intrigued by the hints of lepton-flavour violation in B decays reported by the LHCb experiment and B factories, and always on the lookout for a niche in a large collaboration, in 2018 Olya moved some of her efforts from tau to B physics. She took responsibility for the B-hadron triggers with the aim of collecting an even larger sample of B decays in ATLAS for the final year of Run 2. She was working on preparations for an RK measurement until her very last days.

Besides being a talented scientist, Olya was a dedicated teacher. She supervised an impressive number of PhD students and was very successful in obtaining research grants. She was also very active in outreach activities, with masterclasses and open days at Nikhef, and in community building at ATLAS. Recently she organised the 15th International Workshop on Tau Lepton Physics conference in Amsterdam.

Olya was a passionate physicist who was bursting with ideas. Among several tributes from her colleagues, Olya was described as a future experiment leader. She had a memorably strong work ethos, and until the very last moment refused to let her illness affect her work. She was always cheerful and always positive. Her attitude to work and life will remain a source of inspiration to many of us.

Olya leaves behind her husband, Wouter Hulsbergen of Nikhef, and two children.

Her colleagues and friends.

Dieter Renker 1944–2019

A curious physicist with detector expertise

Dieter Renker

Dieter Renker, who made some key contributions to the design and construction of the CMS experiment at the LHC, passed away on 16 March after a short illness. Dieter was born in Bavaria and studied physics in Munich and Berlin. He obtained his PhD from the Ludwig Maximilian University in Munich, based on experiments performed at SIN, now the Paul Scherrer Institute (PSI), in Villigen, Switzerland. In 1982 he joined SIN as a staff physicist, where he remained until his retirement at the end of 2009.

At SIN/PSI he participated in many experiments, providing excellent technical support, as well as designing new beamlines at the accelerator there. His technical aptitude in due course turned to detector development, which led to his greatest achievement. In the early days of CMS there were various ideas for the design of the electromagnetic calorimeter. Among these was the use of lead tungstate crystals, which although having many suitable properties for operation at the LHC, have a relatively small scintillation-light yield. Dieter contributed the key measurements which showed that avalanche photodiodes (APDs), with their key properties of internal gain and insensitivity to shower leakage, could be used to read out the crystals. This led to lead-tungstate crystals being adopted by CMS for the design of the calorimeter. Not only did they provide superb energy resolution for electrons and photons, enabling key discoveries such as the Higgs boson in 2012, but they also enabled a more compact detector with significantly reduced overall cost.

The development of the final APD was carried out over a period of many years by Hamamatsu Photonics (Japan), but under the close guidance of Dieter. Nearly 100 different APD prototypes were tested before the technology was deemed fit to be used in CMS. The size, capacitance, speed and, above all, radiation tolerance were the key parameters that needed to be improved, and the final choice was made very close to the deadline for commencing construction of the calorimeter. A complex multi- step screening process involving gamma irradiation and annealing also needed to be developed to ensure that the APDs installed met the demanding reliability requirements of CMS. Until now there has been no recorded failure of any of the 122,000 APDs installed in CMS.

Later, Dieter turned his attention to Geiger-mode APDs, which are now widely used in particle and astroparticle physics, as well as in PET scanners. Together with researchers at ETH Zurich, he started the development of the first camera based on these novel photo sensors for Cherenkov telescopes to measure very high-energy gamma rays from astrophysical sources. This camera was installed at the FACT telescope, located in La Palma, Spain, where the HEGRA experiment had also been operated with Dieter’s active participation. The FACT telescope has now been operating successfully for more than seven years, without any sensor-related problems.

After his retirement Dieter returned to his spiritual home, Munich, where he continued his work at the Technical University.

Dieter was a curious physicist with an exceptional talent for novel detector concepts. He pursued new ideas with a strong focus on achieving his goals. He had a very open mind, and was willing to advise and assist colleagues
with great patience and good humour. In his free time his interests included classical music and cooking as well as searching the woods for unusual edible mushrooms. Many colleagues and visitors have fond memories of invitations to his home, embellished with fine cooking.

His sudden illness was a shock to many. Dieter leaves behind his partner, Ulrike.

Quentin Ingram, Paul Scherrer Institute, and friends of Dieter.

Anton Oed 1933–2018

An inspirational inventor

Anton Oed

Anton Oed, a passionate inventor and a source of inspiration for many of us today, passed away on 30 September 2018. His introduction of micro-strip gas chambers (MSGCs) at the Institut Laue-Langevin (ILL) in 1988 was a decisive breakthrough in the field of radiation detectors. It demonstrated a significant gain in spatial resolution and counting rate, and the invention immediately stimulated the development of a new class of micro-pattern gas detectors (MPGDs).

Anton was born 1933 in Ulm, Germany, and studied physics at the University of Tübingen. For his diploma thesis on “The double resonance spectrum of 23Na”, he received the prize of the Faculty of Mathematics and Natural Sciences of the University of Tübingen. In his doctoral thesis, again in atomic physics, he studied the double-quanta decay of the hydrogen 2S level.

Anton arrived at the ILL in Grenoble in 1979, and set about developing the detector of the “Cosi Fan Tutte” spectrometer to measure the mass, charge and kinetic energy of fission fragments. The results obtained with this detector were so precise that it has been taken as a reference for several nuclear instruments in other institutes. Anton later started developing the MSGC technique to upgrade detectors of neutron diffractometers. Several ILL instruments are now equipped with MSGCs that have been in operation for more than 10 years.

The development of MSGCs for high-energy physics started at the beginning of the 1990s. Encouraging results were obtained by the RD28 collaboration at CERN but the relative fragility of MSGCs under harsh irradiation conditions motivated the development of new detectors with improved robustness. Among these, Micromegas and gas electron multipliers (GEMs) have become very successful and are currently being implemented in various upgrades to the LHC experiments. MSGC detectors are also used to detect X-rays on ESA’s INTEGRAL telescope.

In 1997 Anton received the R W Pohl medal from the Deutsche Physikalische Gesellschaft for the invention of the MSGC. To honour his memory, the ILL has established a prize promoting his innovative spirit and the ability to solve technical challenges in the field of micro-pattern gas detectors.

Memories of the technology’s development and of Anton’s personality were shared during a special session at the MPGD 2019 conference held in La Rochelle from 5–10 May. He has always been of great inspiration to many of the collaborators working with him. We will remember him as a very friendly and enthusiastic person, as well as for his kindness towards everybody.

Bruno Guérard, Institut Laue-Langevin.

Jacques Soffer 1940–2019

Prolific theorist and polarisation pioneer

Jacques Soffer

Jacques Soffer, a prolific theorist and phenomenologist with nearly 300 articles in journals or conference proceedings to his name, was born in 1940 in Marseille. During the war, he and his family were sheltered in a farm in the Alps. Afterwards, Jacques came back to Marseille, studied there, and obtained his doctoral degree under the supervision of A Visconti. He spent most of his career at the Centre de Physique Théorique in Marseille, serving as director from 1986 to 1993. He enjoyed sabbaticals at Maryland, Cambridge, CERN, the Weizmann Institute and Lausanne University, and after his retirement he became adjunct-professor at Temple University in the US.

Jacques played a big part in persuading the elementary particle community of the importance of polarisation-type measurements, which provide a probe of dynamical theories far sharper than tests involving just differential and total cross-sections. He is renowned in the community for predicting, together with Claude Bourrely and Tai Wu in 1984, the dramatic phenomenology of the growth with energy of the proton–proton cross-section. This prediction still holds when compared with experimental data after a 100-fold increase in collision energy – up to and including LHC energies. In 1999 Jacques contributed to a paper showing how to make an absolute measurement of the degree of polarisation of a proton beam – which was essential to the success of the Brookhaven spin programme.

In recent years, Jacques showed how positivity sets bounds on spin observables, with important applications to the extraction and determination of the polarised parton structure functions and to low-energy hadron–hadron scattering. His various achievements culminated in three major reviews in Physics Reports.

Jacques always cooperated closely and fruitfully with experimentalists. Entire programmes, such as the polarised proton–proton collisions at Brookhaven’s Relativistic Heavy-Ion Collider, were inspired by his work and carried out with his guidance. Along his career, Jacques organised or co-organised several workshops and conferences on spin physics, and in more recent years was often giving the summary talk.

Throughout his pioneering work in particle physics, Jacques always got to the central issues very quickly, guided by an uncanny feeling for the new physics that roused the amazement and admiration of his collaborators. His colleagues and collaborators, and especially his thesis students, benefited from his advice and his broad knowledge of theory tools and experimental facts. They unanimously praised his warm friendship and hospitality, his sense of humour and his widespread interests in the arts, literature and technology.

Jacques is survived by his wife, Danielle, their three children and nine grandchildren.

His friends and colleagues.