• Bjørn Jacobsen 1961–2017 • Guido Petrucci 1926–2017 • Peter Sonderegger 1935–2017

Bjørn Jacobsen 1961–2017

Norwegian delegate to the CERN Council and previous chair of the CERN Finance Committee, Bjørn Jacobsen, passed away on 13 June after a few months of illness.

Jacobsen studied physics at the University of Oslo, where he obtained his PhD in space physics in 1991. He spent the next 12 years in research in Norway and abroad, in particular two years at the European Space Research and Technology Centre (ESTEC) at Noordwijk in the Netherlands. In 2003 he joined the Research Council of Norway (RCN) where he worked until his death.

After joining the RCN he immediately connected with CERN, first as adviser to the Norwegian delegation and member of the Finance Committee. In 2008 he became Council delegate. He was chair of the Finance Committee 2011–2013 after having served as the committee’s vice chair 2009–2010. In his capacity as chair of the Finance Committee he also served as chair of the CERN Standing Advisory Committee of Audits (SACA) and, more recently, he was member of the external review committee set up in April 2016 to optimise CERN’s use of financial and human resources.

Jacobsen’s leadership of the Finance Committee was conducted with calmness and wisdom. He managed to balance firmness and flexibility, and was met with general acclaim and respect. Always attentive and consensus-oriented, he smoothly steered the committee through waters that sometimes got rough, remaining thoughtful and balanced. He was a modest and conscientious person who treated everybody with respect and friendliness.

Bjørn played an important role as a source of contact and inspiration for the small Norwegian community at CERN and the high-energy physics community at large in Norway. He was also instrumental in our successful programme to recruit Norwegian technical students to CERN. His assistance to the Norwegian research community was not limited to high-energy physics, though. Bjørn co-ordinated the support of all physics programmes of the Research Council of Norway. More recently he served as a special adviser of the Norwegian contribution to large international infrastructure programmes such as the European Spallation Source, the European Incoherent Scatter Scientific Association and the Nordic Optical Telescope.

Bjørn Jacobsen was a colleague, science policy adviser and friend that we could not afford to lose. We will miss him dearly, and his memory will stay with us.

• His colleagues and friends.

Guido Petrucci 1926–2017

Guido Petrucci, one of the engineers who contributed to the reputation of CERN as a centre of technological excellence, passed away on 9 July after a long illness.

Born in Trieste on 27 September 1926, Guido obtained a degree in electro-technical engineering from the University of Rome in 1951 and was awarded a prize for the best thesis of the year. After working for a private electronics company in Rome, in 1954, together with other Italian engineers and physicists, Guido was recruited to CERN by Edoardo Amaldi, then CERN Secretary-General, to provide scientific and technical staff to the newly created European laboratory. Guido joined CERN in April 1954 and was assigned to the PS magnet group. Shortly afterwards, he joined the CERN–Manchester group involved in cosmic-ray experiments using a cloud chamber in a magnetic field at the Jungfraujoch laboratory (there were no accelerators yet in operation at CERN in those years). In this environment he developed a keen interest for physics that shaped his career. He became one of the leading engineers in the CERN physics research divisions and he always worked in close contact with physicists.

One of Guido’s first contributions to the CERN research programme was the design of the magnet for the 2 m hydrogen bubble chamber, of which he supervised the construction and tests. At the same time, under the guidance of Simon van der Meer, he quickly learnt about beam optics and designed a large number of beam transport lines at the PS. Among his contributions, two are worth mentioning: a method to select particles in electrostatically separated beams using two small magnets, known as the Petrucci magnets; and the splitting of the slowly extracted proton beam to the PS East Area into three branches by means of a special magnet with two septa, providing a high degree of flexibility in the East Area beam layout.

In the second half of the 1960s Guido designed the storage ring for the third muon g-2 CERN experiment: a 7 m-radius ring consisting of 40 adjacent sector magnets excited by two all-around circular coils, with uniform magnetic field and focusing provided by a pulsed electrostatic quadrupole field. At the end of the experiment, in 1976, under Guido’s leadership, this ring was transformed into a strong-focusing synchrotron for the Initial Cooling Experiment (ICE). The ICE experiment demonstrated that stochastic cooling, and later electron cooling, can increase the phase space density of 3.5 GeV/c antiprotons produced by the PS by the required factor of around 108, marking a crucial step to the 1978 approval of SPS operation as a proton–antiproton collider.

Guido then worked on the design and construction of the magnet for the UA1 experiment, a dipole with a horizontal field of 0.7 T perpendicular to the beam axis over a volume of 3.5 × 3.5 × 7 m3. The UA1 magnet had a second life during the 1990s as the magnetic spectrometer of the CERN NOMAD neutrino experiment, and it is now used in Japan as part of the near neutrino detector in the T2K experiment at J-PARC. After designing the UA1 magnet, Guido went on to design the magnetic structures of the ALEPH and DELPHI solenoidal spectrometers at LEP.

Guido retired from CERN in 1991, but he continued to work on a number of projects. These include: the ELETTRA synchrotron light source in Trieste, for which he contributed to the magnet design and construction; the hadron therapy project of the TERA foundation; the mechanical design of the tracking system for the KLOE experiment at the electron–positron collider DAFNE in Frascati; and the PVLAS experiment at the Legnaro INFN laboratory to measure the birefringence of vacuum induced by a strong magnetic field, for which he contributed to the design of a system to rotate at a frequency of 0.3 Hz a 5 T superconducting dipole disconnected from its power supply.

Guido was an exceptionally bright engineer, always able to find simple and elegant solutions to difficult technical problems, and always willing to provide advice to his colleagues.

However, his personality was not only confined to his professional talents: he loved beauty in all its forms and had deep and broad cultural interests, covering all aspects of the arts, such as music (he held a piano diploma from the Rome conservatory), architecture and painting. He had many interests and was always willing to learn new subjects: a discussion with Guido was always an enriching experience, and he will be sorely missed by all those who had the privilege of being among his collaborators and friends.

• His colleagues and friends.

Peter Sonderegger 1935–2017

Peter Sonderegger, an outstanding all-round physicist, left us on 9 August at the age of 82. Peter mastered theory as brightly as he did instrumentation, a domain in which he drove much innovation. His intellectual power and knowledge were amazing, allowing him to go boldly off the beaten track on several topics, and he also had linguistic and musical talents.

After graduating from ETH Zürich, he started at Saclay in around 1960 before coming to CERN and obtaining a permanent position in 1971. In the 1960s, a period dominated by Regge poles and duality, Peter’s activities concerned two-body hadronic reactions, notably charge exchange and polarisation measurements. Responsible for physics at the Omega Spectrometer, he pursued them, mostly on backward and large transverse momentum scattering, including the search, until 1999, for narrow objects, as the elusive baryonium states. He also performed original searches and a systematic study of soft photons which, according to first principles, must appear in hadronic reactions. His rigour prevented him from drawing premature conclusions. In the 1976 Ω charm search, motivated by the J/ψ discovery, a presumed signal was reported that caused turmoil, threatening to disrupt the CERN programme, but Peter’s clairvoyance (he was convinced that the signal was fake) and courage avoided that.

Drell–Yan dilepton production was one of his interests. The Omega Beam Dump, proposed in 1976, gave the first publication of the SPS era, measuring J/ψ production by various incident hadrons on hydrogen at 39.5 GeV/c. Peter’s suggestion of an innovative centrality calorimeter allowed NA38 to pursue such studies with ions.

Peter devoted much work to HEP instrumentation, especially calorimetry, but also pixel detectors (such as NA60). He inspired a seminal 1983 NIM paper on fibre calorimetry, which led to lead scintillating fibre calorimetry and culminated with the “spaghetti” hadron calorimeter proposal of 1987. Highly active in the relevant R&D programmes (LAA, RD34), motivating and helping many young physicists, Peter was naturally involved in the genesis of the ATLAS tile calorimeter.

Peter developed an early interest and activity in heavy-ion physics, and was a major actor in a series of experiments from NA38 to NA60. He initiated the original and masterly performed NA51 experiment and is co-author of the ALICE LOI (1993) and of the 2003 LHC safety study group report, addressing supposedly dangerous events in LHC collisions. He played a major role in initiating the popularisation of particle physics, as in Aix Pop 1973, and, with José Gago, in the development of science in Portugal, including the field of astroparticle physics. NA38 was the first experiment with official Portuguese participation.

Besides being a great physicist, he was always asking what science could bring to society and was a courageous “alert launcher” about certain aspects of the nuclear industry. However, the greatest memory of Peter will be his extraordinary humanity – his moral rectitude, lack of personal ambition concerning career and honours, and great solicitude and generosity for others. It was a privilege and a pleasure to know Peter Sonderegger.

• His friends.