• Ludwig Faddeev 1934–2017 • Victor Kryshkin 1939–2017 • Heinrich Leutz 1928–2017

Ludwig Faddeev 1934–2017

Ludwig Dmitrievich Faddeev was an outstanding scientist who made exceptional contributions to modern theoretical and mathematical physics. He was born in 1934 in what is now St Petersburg, Russia, and attended Leningrad University. His name is well known in theoretical physics in connection with the quantum three-body system, and he made decisive contributions to the quantisation of the Yang–Mills theory and gravitational fields. The Faddeev–Popov covariant prescription for quantisation of non-Abelian gauge theories (“Faddeev–Popov ghosts”, discovered in 1966–1967) laid some of the foundations for the Standard Model of strong, weak and electromagnetic interactions.

Faddeev is one of the creators of modern mathematical physics, and he believed that mathematical beauty is the most important guiding principle in physics. As predecessors of this point of view, he cited Dirac, Weyl and Fock – the latter having been one of his teachers at Leningrad. In the 1970s, Faddeev was one of the first to recognise the importance of the newly discovered solutions of nonlinear partial differential equations – solitons, and he believed that they would reduce the number of fields in Lagrangians. His work stimulated the widespread application of solitons in relativistic quantum field theory.

Work by Faddeev and his group on the so-called quantum method of inverse scattering is now the basis of a flourishing branch of mathematics and mathematical physics involving quantum groups and their representations. In 1980, Faddeev also clarified the group-theoretical origin of anomalies in the context of “cocycles”, after which he continued his work on multidimensional solitons and Yang–Mills theory in the 1990s until his retirement.

Faddeev created a very special atmosphere at the Leningrad Steklov Mathematics Institute in the 1970s and 1980s, during which he supervised several currently world-renowned mathematicians and theoretical physicists. He visited the theory department at CERN for the first time in 1973 and made several further visits.

The importance of Faddeev’s work has been recognised with awards for both physics and mathematics, including the 1975 Dannie Heineman Prize for Mathematical Physics of the American Physical Society; the 1990 ICTP Dirac Medal; the 2002 Pomeranchuk Prize; the 1996 Max Planck Medal; the 1995 and 2004 Russian Federation State Prizes; the 2006 Henri Poincaré Prize; and the 2008 Shaw Prize. Faddeev was a member of the Russian Academy of Sciences from 1976, as well as a number of foreign academies including the US National Academy of Sciences and the French Academy of Sciences. From 1976 to 2000 he was deputy director of the Steklov Mathemetical Institute and was the founding director of the Euler International Mathemetical Institute, which he led until his death.

Ludwig Faddeev was a man of great honesty who was always ready to discuss new ideas. We will miss him very much.

• Irina Aref’eva and Andrey Slavnov, Steklov Mathematics Institute.

Victor Kryshkin 1939–2017

Victor Kryshkin of the Institute for High Energy Physics (IHEP) in Protvino passed away on 16 January after a long illness. He was a long-standing member of the CMS collaboration and made several important contributions to the CMS detector.

After graduation from Voronezh University, Kryshkin started work as an experimental physicist in Tomsk Institute for Nuclear Physics. There he carried out his first experiment: measuring the lifetime of the neutral π meson, which was included in the Review of Particle Physics. Since 1973 he worked at IHEP in Protvino, and was one of the key people who proposed and then established the two-arm magnetic spectrometer, with the main aim to study hadron production with high-momentum transfer in proton–proton and proton–nuclear interactions. Many important scientific results revealing the structure of elementary particles were obtained using this apparatus. The most important result of these studies was the observation of a kink in the dependence of the cross-section for the production of meson pairs on the sum of transverse momenta in proton–proton interactions at an energy of 70 GeV.

In 1991 Kryshkin became professor of physics at IHEP, and since 1992 he was an active participant in the CMS experiment at CERN’s Large Hadron Collider. He was a technical co-ordinator of the CMS hadron-endcap calorimeter and made major contributions to the design of the detector. Under his leadership, the Protvino group assembled all of the active elements of the hadron-endcap calorimeters. More recently, Kryshkin performed several original studies on gas-discharge detectors, which he was planning to use in calorimetry. The novelty of his research has been confirmed by 21 registered patents.

Victor Kryshkin was not only a prominent scientist, he was also a very interesting companion, possessing an encyclopedic knowledge in many fields. His main hobby was studying astrophysics and space science and he was also interested in history and art. He read a lot, particularly Russian and English literature, and liked to tell jokes and anecdotes. Living in Leningrad after the Second World War, Kryshkin learnt how to paint, and never missed an opportunity to visit an art gallery or museum. He could not imagine his life without music, especially jazz. He loved his family very much and leaves behind his wife Galina, a son and three granddaughters.

On behalf of the CMS collaboration, we offer our condolences to his family and colleagues.

• His friends and colleagues.

Heinrich Leutz 1928–2017

Heinrich Leutz, who joined CERN in 1966 as leader of the BEBC physics aspects group,

passed away on 26 February, aged 89, following several years of serious health problems. During his long and active career in experimental physics he took part in three main research fields: nuclear spectroscopy; high-energy physics with bubble chambers; and detector technologies for hadron colliders. In each of these areas, Leutz was responsible for original inventions that led to improved physics results.

During his first active research period in the 1950s and 1960s, based at the University of Heidelberg, Leutz led a research group studying colour centres in crystals, nuclear beta decay, electron capture, polarisation and photon spectroscopy. One of his remarkable contributions during this period concerned the idea to grow scintillation crystals doped with radioactive isotopes, which allowed precise spectroscopy to be performed while avoiding source-thickness and scattering-correction effects. Important publications from this period demonstrate excellent research results in nuclear physics during the 1950s and 1960s.

His move to high-energy physics started in the 1970s when he joined the French–German–CERN programme to design and construct the Big European Bubble Chamber (BEBC) at CERN as the SPS started up. Responsible for the physics aspect of the BEBC project, Leutz soon became well known in the bubble-chamber community around the world. His team developed a track-sensitive liquid-hydrogen-filled, optically transparent target box to observe primary particle interactions, surrounded by a heavy-liquid neon-hydrogen mixture to provide improved photon conversion. His bold proposal was no less than to operate a “bubble chamber inside a bubble chamber” by finding a temperature and pressure regime such that the pressure cycle was transmitted from the heavy liquid to the hydrogen volume for primary interactions, allowing interactions and tracks in both media to be visualised on the same photo. A further step was the construction of a high-resolution fast-cycling bubble chamber (LEBC activity) that was used for charm physics and allowed one of the first definitive studies of charm production at a proton facility.

After the closure of bubble chambers around 1984, Leutz concentrated on promoting detector technologies for high-energy colliders within the CERN LAA (Lepton Asymmetry Analyser) programme. In particular, he dedicated his efforts to the development of plastic scintillating fibres and new photodetectors called hybrid photon detectors for particle tracking in LHC-like environments and for non-high-energy physics applications. In this last phase of his professional career, he particularly enjoyed being surrounded by motivated and motivating young people: a new generation that he endeavoured to shape and which had the great opportunity to be mentored by him. Books and publications testify to his outstanding contributions to experimental physics, even beyond his retirement from CERN in 1993.

Throughout his professional life, Leutz developed his exceptional talents to promote original ideas, establish collaborations with physics teams worldwide, motivate high-level technical support in his own team and – last but not least – make friends to whom he always offered great hospitality at his home, together with his wife Ingrid. Whenever they meet at CERN, friends and former colleagues recall the great times they spent with Heinrich Leutz.

• His friends and colleagues.