• Vinod Chohan 1949–2017 • Satoshi Ozaki 1929–2017 • Yassen Stanislavov Stanev 1962–2017

Vinod Chohan 1949–2017

Vinod “Nick” Chohan came to CERN in 1975 as a fellow, then went to SIN (today PSI) near Zürich. In 1980 he returned to CERN as a machine-supervisor in the PS division. At that time, the construction of the Antiproton Accumulator (AA, the world’s first machine to produce, accumulate and store antiprotons) was just finished and the team was busy running it in. The purpose of the AA was to supply antiprotons to the SPS to allow it to function as a proton–antiproton collider, and Nick became a prominent member of the AA operations team that made this possible. His speciality was the controls aspects of the highly complicated processes within the AA and for the transfer of the antiprotons to the SPS. Simon van der Meer, inventor of stochastic cooling, on which the AA was based, had written practically all of the software himself, in his own highly sophisticated style. Nick became the only one to fully understand it, and later extend it to the Antiproton Collector (AC) and convert it for integration into the PS controls system.

When, in 1991, the PS Beam Diagnostics (BD) Group was founded, Nick was the natural choice to become the section leader for systems integration with the PS controls.

In 1996, when the high-energy collider part of CERN’s antiproton programme was terminated, Nick took on the additional responsibility of PS divisional safety officer. Then, in 2002, he became heavily involved in the LHC project. Nick moved to the Accelerator Technology (AT) Division, where he led a team that first tested an LHC prototype-sector and then all of the 1706 superconducting bending magnets. CERN manpower was insufficient, but a collaboration with India, managed by Nick, made it possible.

Once the LHC became operational, Nick returned to his old affinity with antiprotons, now at the low-energy end of the programme, as editor of the ELENA design report. In 2014, the 65 year bell rang in his retirement. But for Nick, that was not a reason to stop work at CERN. He joined the CERN scientific information service and provided highly welcome help on accelerator physics literature, photographic documentation and articles for Wikipedia.

Throughout his years at CERN, we all knew Nick as friendly and easy-going, always helpful and dedicated in his typical competent manner. We are deeply moved by his sudden disappearance and shall hold on to the memory of the many good moments and years of collaboration and friendship that we shared with him.

• His friends and colleagues.

Satoshi Ozaki 1929–2017

World-renowned physicist Satoshi Ozaki, who helped design and build accelerators for scientific research across two continents including two of the flagship facilities at Brookhaven National Laboratory (BNL), died on 22 July aged 88. He was a senior scientist emeritus at BNL and a key driver of international collaborations in high-energy and nuclear physics.

Ozaki joined Brookhaven Lab in 1959 with a master’s degree in physics from Osaka University, Japan, and a PhD in physics from the Massachusetts Institute of Technology. He worked in a group he eventually co-led with Samuel Lindenbaum on experiments at Brookhaven’s Alternating Gradient Synchrotron (AGS), developing state-of-the-art electronic detectors and an online data facility for monitoring detector performance by reconstructing subsets of data in real time. This was the first system of its kind and is now a routine component of data-acquisition systems for complex electronic detectors. The Ozaki–Lindenbaum group also developed a multiparticle spectrometer at the AGS that served many experimental groups at Brookhaven and collaborating universities. In addition, Ozaki led the development of detectors for ISABELLE, the first design for a dual-ring superconducting collider at Brookhaven.

Ozakiʼs work in large-scale detector development led to an invitation in 1981 from KEK to direct the construction of TRISTAN, the first major high-energy particle collider in Japan. Under Ozaki, this $500 million project was completed on time and within budget to start operations in 1987, accelerating and storing beams of electrons and positrons at 30 GeV – the highest energy in the world at the time. In 1989, Ozaki returned to Brookhaven to head the Relativistic Heavy Ion Collider (RHIC) project, which achieved first collisions in 2000 and is now the highest energy collider in the US, with many important discoveries about the quark–gluon plasma under its belt. Ozaki was also essential in securing Japanese support for RHIC-related projects.

In 2005, Ozaki joined the National Synchrotron Light Source II (NSLS-II) project. As the initial head of the NSLS-II accelerator division, Ozaki built up the group and remained with the project as a senior advisor even after formally retiring at the end of 2012. He took on the major task of procuring the storage-ring magnets, and attended the formal dedication of the completed facility in February 2015. Ozaki was also involved in the Facility for Rare Isotope Beams (FRIB) currently under construction at Michigan State University.

Ozakiʼs accomplishments have been recognised with numerous prestigious awards, including the 2007 IEEE Nuclear and Plasma Sciences Society Accelerator Science and Technology Award and the 2009 Robert R Wilson Prize of the American Physical Society, and in 2013 he was recognised with Japanʼs prestigious Order of the Sacred Treasure.

Ozaki was predeceased by his wife, Yoko, and is survived by their two children, Keiko Simon and Tsuyoshi Ozaki, their spouses, and four grandchildren.

• Brookhaven National Laboratory.

Yassen Stanislavov Stanev 1962–2017

Yassen Stanev of the Bulgarian school of theoretical physics and INFN at the University of Rome “Tor Vergata”, passed away on 9 June after a short illness. He was born in Sofia, Bulgaria, on 4 July 1962. After graduating in physics at the University of Sofia, he worked in its theoretical-physics department before joining the Institute for Nuclear Research and Nuclear Energy of the Bulgarian Academy of Sciences in 1992. Stanev defended his PhD thesis on conformally invariant quantum-field theory models in 1994 under the guidance of Ivan Todorov, who has long been a distinguished Bulgarian visitor of the CERN theory department. Since 2004, he had been working at the University of Rome.

Stanev had a wide range of scientific interests, including super-conformal field theories (CFTs), quantum groups, string theory and gauge theories. His work on the structure of the conformally invariant three-point correlation of the stress-energy tensor, published while he was a PhD student in his 20s, is still influential today. His pioneering work in the mid 1990s with his Italian colleagues unveiled the general completeness relations for 2D CFT’s in the presence of boundaries and cross-caps, and his related results on open strings (which include the first chiral type-I superstring model in four dimensions) are well known among string theorists. After the advent of the AdS/CFT correspondence, he worked extensively on N = 4 SYM and its conformal deformations. His last research, on two-point correlators in N = 2 gauge theories, involved an international team of colleagues and appeared a month before his premature death.

Stanev was also a gifted teacher and, during the last few years, he was a member of the INFN theoretical-physics committee. We will miss his wit, humour, critical views and his friendship.

• His friends and colleagues.