Praxis Archives – Page 42 of 181

ICHEP’s online success

Originally set to take place in Prague, the International Conference of High Energy Physics (ICHEP) took place virtually from 28 July to 6 August. Running a major biennial meeting virtually was always going to be extremely difficult, but the local organisers rose to the challenge by embracing technologies such as Zoom and YouTube. To allow global participation, the conference was spread over eight days rather than the usual six, with presentations compressed into five-hour slots that were streamed twice: first as a live “premiere” and later as recorded “replay” sessions, for the benefit of participants in different time zones.

This was the first ICHEP meeting since the publication of the update of the European strategy for particle physics, which presented an ambitious vision for the future of CERN. Though VIP-guest Peter Gabriel – rock star and human rights advocate – may not have been aware of this when delivering his opening remarks, his urging that delegates speak up for science and engage with politicians resonated with the physicists virtually present.

Many scientific highlights were covered at ICHEP and it is only possible to scratch the surface here. The results from all four major LHC experiments were particularly impressive and the collective progress in understanding the properties of neutrinos shows no sign of slowing down.

Higgs physics
ATLAS and CMS presented the first evidence for the decay of the Higgs boson into a pair of muons. Combined, the results provide strong evidence for the coupling of the Higgs boson to the muon, with the strength of the coupling consistent with that predicted in the Standard Model. Prior to these new results, the Higgs had only been observed to couple to the much heavier third-generation fermions and the W and Z gauge bosons. The measurements also provide further evidence for the linearity of the Higgs coupling, now over four orders of magnitude (from the muon to top quark), indicating the universality of the Standard-Model Higgs boson as the mechanism through which all Standard Model particles acquire mass. These are highly non-trivial statements.

ATLAS also presented a combined measurement of the Higgs signal strength, which describes a common scaling of the expected Higgs-boson yields in all processes, of 1.06 ± 0.07. In this measurement, the experimental and theoretical uncertainties are now roughly equal, emphasising the ever-increasing importance of theoretical developments in keeping up with the experimental progress; a feature that will ultimately determine the precision that will be reached by the LHC and high-luminosity LHC (HL-LHC) Higgs physics programmes.

The range of Standard Model measurements presented at ICHEP 2020 by ATLAS and CMS was truly impressive

More generally, the precision we are seeing from the ATLAS and CMS Run 2 proton–proton data is truly impressive, and an exciting indication of what is to come as the integrated luminosity accumulated by the experiments ramps up, and then ramps up again in the HL-LHC era. One interesting new example was the first observation of WW production from photon–photon collisions, where the photons are radiated from the incoming proton beams. This is a neat measurement that demonstrates the breadth of physics accessible at the LHC.

Overall, the range of Standard Model measurements presented at ICHEP 2020 by ATLAS and CMS was truly impressive and we should not forget that it is still relatively early in the LHC programme. In parallel, direct searches for new phenomena, such as supersymmetry and the “unexpected”, continues apace. Results from direct searches at the energy frontier were covered in numerous parallel session presentations. The current status was summarised succinctly by Paris Sphicas (Athens) in his conference summary talk: “Looked for a lot of possible new things. Nothing has turned up yet. Still looking intensively.”

Flavour physics
Over the last few years, a number of deviations from theoretical predictions have been observed in B-meson decays to final states with leptons. Discrepancies have been observed in ratios of decays to different lepton species, and in the angular distribution of decay products. Taken alone, each of these discrepancies are not particularly significant, but collectively they may be telling us something new about nature. At ICHEP 2020, the LHCb experiment presented their recently published results on the angular analysis in B⁰ → K^*0 μ⁺μ^–. The overall picture remains unchanged. The full analysis of the LHCb Run-2 data set, including updated measurements of the relative rates of the muon and electron decay modes (R_K and R_K*), is eagerly awaited.

The search for rare kaon decays continues to attract interest

The search for rare kaon decays continues to attract interest. One of the most impressive results presented at ICHEP was the recent observation by NA62 of the extremely rare kaon decay, K⁺ → π⁺νν̄. Occurring only once in every 10 billion decays, this is an incredibly challenging measurement and the new NA62 result is the first statistically significant observation of this decay, based on just 17 events. Whilst the observed rate is consistent with the Standard Model expectation, its observation opens up a new future avenue for exploring the possible effects of new physics.

Neutrino physics
Neutrino physics continues to be one of the most active areas of research in particle physics, so it was not surprising that the neutrino parallel sessions were the best attended of the conference. This is a particularly interesting time, with long-baseline neutrino oscillation experiments becoming sensitive to the neutrino mass ordering, and beginning to provide constraints on CP violation. Updates were presented by the NOvA experiment in the USA and the T2K experiment in Japan. Both experiments favour the normal-ordering hypothesis, although not definitively, and there is currently a slight tension between the CP violation results from the two experiments. It is worth noting that the combined interpretation of the two experiments is quite complex. The NOvA and T2K collaborations are working on a combined analysis to clarify the situation.

There were also a number of presentations on the next generation of long-baseline neutrino oscillation experiments, DUNE in the US and Hyper-Kamiokande in Japan, which aim to make the definitive discovery of CP violation in the neutrino sector. In the context of DUNE, the progress with liquid-argon time-projection- chamber (LArTPC) detector technology is impressive. It was particularly pleasing to see a number of physics results from MicroBooNE at Fermilab, and the single-phase DUNE detector prototype at CERN (ProtoDUNE-SP), that are based on the automatic reconstruction of LArTPC images – a longstanding challenge.

Virtual success
A vast range of high-qualify scientific research was covered in the 800 parallel session presentations and summarised in the 44 plenary talks at ICHEP 2020. The quality of the presentations was high, and speakers coped well with the challenge of pre-recording talks. The “replay” sessions worked extremely well too – an innovation that is likely to persist in the post-COVID world. About 3000 people registered for the meeting, which is more than double the previous two events. It was particularly pleasing to learn that almost 2500 connected to the parallel sessions.

Despite the many successes, we all missed the opportunity to meet colleagues in person; it is often the informal discussions over coffee or in restaurants and bars that generate new ideas and, importantly, lead to new collaborations. Whilst virtual conferences are likely to remain a feature in the post- COVID world, they will not replace in-person events.

Paul Murphy 1930–2020

Murphy was a long-time leader of particle physics at the University of Manchester. Credit: Murphy family

Leading member of the UK particle-physics community, Paul Murphy, passed away on 26 August. Paul was a keen and brilliant physicist who was head of the particle-physics group at the University of Manchester from 1965 until his retirement in 1990. He started his PhD as a Fulbright Scholar theoretician in Fermi’s group in Chicago, but later discovered that his real talent lay in experimentation. Styling himself as a “gas and glue” man, Paul was one of the few physicists at the time who could design and make spark chambers that worked.

He then went to Liverpool to work on the 400 MeV cyclotron before joining the Rutherford Laboratory and going to UC Berkeley to study hyperons at the 6 GeV Bevatron. On returning in the early 1960s, he and John Thresher carried out a series of experiments to determine the spin-parity of pion-nucleon resonances, for which they were awarded the Rutherford medal and prize by the UK Institute of Physics.

Aged only 34, Paul moved to Manchester to become a professor, heading up the newly formed high-energy physics group. As well as leading the group into two experiments at the new electron synchrotron, NINA, at the Daresbury Laboratory, he spearheaded the development of particle detectors at Manchester and built the group’s strong reputation in this area. First were the wire spark chambers with digital instead of photographic readout, a version of which was then used in the CERN, Holland, Lancaster, Manchester (CHLM) experiment that concentrated on proton–proton diffraction scattering at the CERN ISR facility. Paul then led the group developing (quieter) large-area drift chambers that were used to detect muons, first at the JADE experiment at DESY, which helped to discover the gluon, and then at LEP’s OPAL experiment at CERN. His sharp physics mind led him to be a pioneer at the start of each new accelerator facility, for instance realising the potential for NINA to produce a useable beam of neutral kaons.

Paul was a firm believer in making the most of wherever he found himself. He played a major role in national and international particle physics, chairing and contributing to many strategic decision-making bodies. He was also an engaging educator at all levels, often livening up his lectures with many anecdotes.

Paul was a passionate humanitarian and loved people; he wanted to show everyone he met that he valued them, for example, by learning how to welcome them in their own language. His insight into people and physics alike was extraordinary, and his penchant for making a little friendly mischief never far from the surface.

Terascale summer school goes global

In a joint venture by physicists at DESY, the first Terascale Summer School took place online from 23 July to 12 August, providing more than 160 undergraduate students from over 30 countries with an engaging introduction to the world of particle and astroparticle physics. Following a wide-ranging three weeks of teaching, an impromptu fortnight-long online tutorial, which only concluded yesterday, focused on strong interactions and Monte Carlo techniques, allowing students to deepen their knowledge through practical exercises.

Terascale chat — Terascale’s online format encouraged students to ask questions. Credit: I Melzer-Pellmann

As the school had been forced online due the ongoing pandemic, the organisers settled upon a reduced programme with just one or two 45 minutes lectures per day. Active moderation was key, with students typing questions in the chat box, and the moderator interrupting the lecturer when appropriate, to give the participants a chance to speak up. This format conferred upon less brash participants a more comfortable way to ask questions, several students noted. When one brave pioneer had broken the ice, queries flowed every few minutes – a resonance effect characterised by a lively, stimulating and relaxed atmosphere which boosted concentration levels.

With its global reach and breathing space for students to explore concepts independently, Terascale 2020’s compact online format may merit consideration during less extraordinary times too.

An intuitive approach to teaching

This elementary textbook, suitable for either advanced undergraduate or introductory postgraduate courses, is a gem. Its author, Andrew Larkoski, is a phenomenologist with expertise in QCD, and a visiting professor at Reed College. It is worth mentioning that Reed College is also home to David J. Griffiths, who is the author of several successful textbooks, including his well-known “Introduction to Elementary Particles” (Wiley, 2nd edition, 2008). Larkoski’s book has a similar scope to Griffiths’ and certainly lives up to its legacy.

Larkoski begins with an introduction to special relativity and the standard preliminaries to particle physics, such as the Dirac equation, Fermi’s Golden rule and a very accessible introduction to group theory. The book also features a superb 30-page chapter on experimental concepts and statistics — an excellent resource for any student starting a particle-physics project for the first time. The main menu follows: matrix element and cross-sections calculations for QED, QCD and weak interactions. The book includes a nice introduction to electroweak unification, the basics of flavour physics, neutrino oscillations, and an accessible discussion on parton evolution and jets. The latter will be particularly useful for students of LHC physics. The book closes with an insightful chapter on open problems in particle physics.

A very nice collection of unsolved exercises will serve as an invaluable resource for lecturers. Many refer to processes currently being studied at the LHC and other projects. The book’s modernity is also evident through mentions throughout the text on the latest results in dark matter and neutrino physics, and a discussion on how the Higgs boson discovery was made.

Analogies are drawn between Feynman diagrams and electrical circuits

A particularly attractive feature of Larkoski’s writing is his use of intuitive and conceptual discussions: dimensional analysis is used often in calculations to get an idea of what we expect; analogies are drawn between Feynman diagrams and electrical circuits; connections between space curvature and quantum chromodynamics are pointed out, just to mention some of the very many examples you can find in the book.

One point that the lecturers should be aware of is that Larkoski employs the Weyl basis of Dirac γ-matrices, whereas Griffiths, Thomson (Modern Particle Physics, Cambridge, 2013), Halzen & Martin (Quarks and Leptons, Wiley, 1984), and other popular textbooks which currently form the backbone of many university courses, use the Dirac basis. As a result, both equations and Feynman rules look different, and care will be required when multiple textbooks are used in the same course. In general, Larkoski is closer to Thomson and Griffiths, as it does not include the wide range of calculations of Halzen & Martin, which is slightly more advanced.

Larkoski’s new book will certainly find its way among the most popular particle physics textbooks. Its clear and intuitive presentation will doubtlessly deepen the understanding of students who read it, and inspire lecturers to a more conceptual approach to teaching.

Max Zolotorev: 1941-2020

Max Samuilovich Zolotorev, a pioneer of experimental studies of atomic parity violation, passed away on 1 April in his home in Oregon, US.

Max was born in Petrovsk, a small town not far from the Russian city of Saratov, where his mother found herself evacuated from the advancing German army. Upon graduating from secondary school, despite showing unusual talent and ability from an early age, he was not admitted to an institute or even a vocational school because he was Jewish. After eventually securing a position with the Novosibirsk Electro Technical Institute in Siberia, where he demonstrated outstanding academic performance, he was able to transfer to the newly founded Novosibirsk State University. He graduated in 1966, before obtaining his first and second doctoral degrees in 1974 and 1979 at the Institute of Nuclear Physics in Novosibirsk Academgorodok.

Max started out by working on measurements of the hyperon magnetic moments. However, in the early 1970s he was drawn into studying fundamental physics using the methods of atomic, molecular and optical physics. Together with his mentor and colleague Lev Barkov, he was the first to discover parity violation in atoms by observing optical rotation of the plane of polarisation of light propagating through a bismuth vapour.

The 1978 measurement came at a crucial time in the development of the Standard Model. While observations of high-energy neutrino scattering on nuclei at CERN in 1973 provided evidence of neutral weak currents, there was no evidence that the neutral weak current violated parity as predicted by the Glashow–Weinberg–Salam (GWS) model. Furthermore, earlier atomic parity violation experiments had produced null results, in contradiction with theoretical predictions. The observation of parity violation in bismuth, followed later by measurements of parity violating electron scattering at SLAC, was crucial evidence that the GWS model was indeed the correct description of the weak interaction.

Max Zolotorev was an inspiring mentor and teacher who always set the highest expectations for his students

Max and his colleagues also established the foundation for some of today’s most sensitive magnetometers with their measurements in the late 1980s of nonlinear Faraday rotation, clearly identifying the crucial role of quantum coherences. In 1989 Max emigrated to the US and took up a research position at SLAC, later moving to Lawrence Berkeley National Laboratory, where he worked until his retirement in 2018. At SLAC, Max and colleagues proposed using lasers to cool hadrons in colliders as a variation on van der Meer’s stochastic cooling method. The “optical stochastic cooling” concept will soon be tested at Fermilab by a group led by a former student of Max’s. Another of his co-inventions is the so-called “slicing method” to produce ultrashort pulses of X-rays essential for time-resolved studies of the properties of condensed matter.

Max Zolotorev was an inspiring mentor and teacher who always set the highest expectations for his students. His ability to find “weak spots” in one’s scientific logic was legendary. One of Max’s great insights was that, as physicists, we should never design our experiments around what was sitting in our labs or in our heads. Instead, we should choose deep and important problems, think hard about them and develop the cleverest way to approach them that we can, learn new subjects, build new apparatus, and push our boundaries and limits. Max’s work exemplified the curiosity, creativity and rigour of physics at its best.

Ulrich Becker 1938–2020

Ulrich J Becker, professor emeritus at MIT, passed away on 10 March at the age of 81. He was a major contributor to the L3 experiment, the Alpha Magnetic Spectrometer and the advancement of international collaborations in high-energy physics.

Becker was born in Dortmund, Germany, on 17 December 1938 – the day that nuclear fission was discovered in Berlin. As a young man, he was adept as an electrician, coal miner, and even in steel smelting, but he was more drawn to physics. He studied at the University of Marburg and obtained his PhD in Hamburg, focusing on the photo-production and leptonic decays of vector mesons.

In late 1965 Becker met Sam Ting, who admitted him to his group at DESY using the 6 GeV synchrotron to measure the size of the electron. It was a complementary match: Becker was a dogged researcher with detector and hardware acumen, and Ting was a master in scientific organization and politics. They presented their results at the XIIIth International Conference on High Energy Physics at Berkeley in 1966, showing that electrons have no measurable size, which contradicted earlier results.

In 1970 Becker joined the MIT faculty, where he found mentors including Victor Weisskopf and Martin Deutsch. He was promoted to associate professor in 1973, and the following year he began designing a precision spectrometer for Brookhaven National Laboratory. He joined a group led by Ting which used the spectrometer to search for heavy particles produced when protons were smashed into a fixed target of beryllium. Instead, the team recorded an unexpected bump in the data corresponding to the production of a heavy particle with a lifetime that was about a thousand times longer than predicted.

Meanwhile, MIT alumnus Burton Richter was reviewing data from Stanford Linear Accelerator Laboratory when he too found what looked like a long-lived heavy resonance. Ting flew to Stanford in November and he and Richter quickly organized a lab seminar. They presented their discovery of the J/Ψ particle, a bound state of a charm quark and antiquark, on 11 November 1974, sparking rapid changes in high-energy physics. One of Becker’s favorite stories was when he went to Munich in 1975 to share their finding, and Werner Heisenberg interrupted to comment: “Whenever they don’t know what it is, they invent a new quark.” To which Becker replied: “Look, Professor Heisenberg, I’m not arguing whether this is charm or not charm. I’m telling you it’s a particle which doesn’t go away.” A deadly silence followed before Heisenberg replied: “Accepted”. Ting and Richter shared the 1976 Nobel Prize in Physics for the J/Ψ discovery. If only one of the groups, MIT, had discovered it, it is likely that Becker would also have shared in the prize.

He enjoyed reviving broken and abandoned mechanical items.

Becker, who was made a full professor at MIT in 1977, developed several other major instruments which were the catalyst for discoveries. His large-area drift chamber would provide large acceptance coverage for experiments, and his drift tube enabled physicists to measure particles near the interaction point. Those developments led Becker to design and build the huge muon detectors for the MARK-J experiment at DESY, which resulted in the discovery of the three-jet pattern from gluon production. Becker then led hundreds of colleagues in designing the muon detector for the L3 experiment at LEP. He also made important contributions to advancing international collaboration in high-energy physics, for example involving China.

In 1993, Becker started to work with MIT’s team on building an Alpha Magnetic Spectrometer (AMS) — another Ting project which was born when he and Becker were on a coffee break while working on L3. The first AMS detector flew in the Space Shuttle in June 1998 and gathered about 100 hours of cosmic-ray data. Becker then went on to help design the transition radiation detector for AMS-02, which has so far collected more than 150 billion cosmic-ray events from its position on the International Space Station.

He enjoyed reviving broken and abandoned mechanical items. One of his biggest renovations was MIT’s cyclotron, which he converted into one of the biggest functioning magnets in the country, with a strength of up to 1 T. He used it to develop particle detectors for the International Linear Collider, and to characterise gas mixtures for the design of drift and other gas detectors in different magnetic and electric fields.

Becker was a mentor to many great physicists, and invested much to ensure his students received an excellent education. In 2013 he transitioned to emeritus status, but still he came in every day to mentor students. At the age of 81, he even picked up Python to continue his craft. His friendly approach and deep understanding of physics made him a superb teacher, even if his style was highly individual.

Our community has lost an excellent researcher and teacher, and a wonderful colleague and human being. Ulrich Becker is survived by his wife Gerda, his three children and two grandchildren.

Eugène Cremmer: 1942-2019

Eugene Cremmer — Cremmer had an important role in 11D supergravity. Credit: ENS

Theorist Eugène Cremmer, who passed away in October 2019, left his mark in superstring and supergravity theory. He will be remembered across the world as a brilliant colleague, as original as he was likeable.

Born in Paris in 1942, his parents ran a bookstore. The neighbourhood children were firmly oriented towards vocational schools and Eugène was trained in woodworking. He was eventually spotted by a mathematics teacher, obtained a technical Baccalauréat degree and then pursued mathematics at École Normale Supérieure (ENS) in Paris in 1962. In 1968–1969, following a triggering of research into dual models by Daniele Amati and Martinus Veltman, Eugène began to compute higher loop diagrams in a remarkable series of technically impressive papers. The first one was written with André Neveu, and others with Joël Scherk in 1971–1972 while a postdoc at CERN. At that time, CERN was an important cradle of string theory, with groups from different countries forming a critical mass.

In late 1974 Eugène returned to ENS with a small group of pilgrims from the theoretical-physics group at Orsay. He worked with Jean-Loup Gervais on string field theory and later collaborated with Scherk, the author, and several visitors on supersymmetry, supergravity and applications to string theory. His revolutionary 1976 paper with Scherk introduced the linking number of a cyclic dimension by a closed string. This would turn out to be crucial for heterotic string models, T duality and mirror symmetry, for the so-called Scherk– Schwarz compactification, and was soon applied to branes. The 1977 proposal with Scherk of spontaneous compactification of the six extra dimensions of space remains central in modern string theory. In 1978–1979 his pioneering papers on 11D super-gravity and 4D N = 8 supergravity made the 11th dimension unescapable and exhibited exceptional (now widely used) duality symmetries. For these works, Eugène received the CNRS silver medal in 1983. Some 15 years later, duality symmetries were extended to higher degree forms.

The successes of Eugène’s work led to many invitations abroad. Though he chose to remain in France, he maintained collaborations and activities at a high level. He was director of the ENS theoretical-physics laboratory in 2002–2005. Eugène was as regular as clockwork, arriving and leaving the lab at the same time every day – the only exception I witnessed was due to Peter van Nieuwenhuizen’s work addiction, which he enjoyably inflicted upon us for a while. At 12:18 p.m. Eugène would always gather all available colleagues to go to lunch, and this led Guido Altarelli to observe “Were Eugène to disappear the whole lab would starve to death!” Eugène kept his papers in an encrypted pre-computer order, and nobody could understand how he was able to extract any needed reference in no time, always remembering most of the content. He cultivated his inner energy by walking quickly while absorbed in thought. We have lost a role model and a modest, full-time physicist.

A price worth paying

The LHC — **Deep impact** Projects such as the LHC deliver global visibility and impact. Credit: CERN-PHOTO-201906-179-2

Science, from the immutable logic of its mathematical underpinnings to the more fluid realms of the social sciences, has carried us from our humble origins to an understanding of such esoteric notions as gravitation and quantum mechanics. This knowledge has been applied to develop devices such as GPS trackers and smartphones – a story repeated in countless domains for a century or more – and it has delivered new tools for basic research along the way in a virtuous circle.

While it is undeniable that science has led us to a better world than that inhabited by our ancestors, and that it will continue to deliver intellectual, utilitarian and economic progress, advancement is not always linear. Research has led us up blind alleys, and taken wrong turnings, yet its strength is its ability to process data, to self-correct and to form choices based on the best available evidence. The current coronavirus pandemic could prove to be a great educator in the methods of science, demonstrating how the right course of action evolves as the evidence accumulates. We’ve seen all too clearly how badly things can go wrong when individuals and governments fail to grasp the importance of evidence-based decision making.

Fundamental science has to make its case not only on the basis of cultural wealth, but also in terms of socioeconomic benefit. In particle physics, we also have no shortage of examples. These go well beyond the web, although an economic impact assessment of that particular invention is one that I would be very interested in seeing. As of 2014, there were some 42,200 particle accelerators worldwide, 64% of which were used in industry, a third for medical purposes and just 3% in research – not bad for a technology invented for fundamental exploration. It’s a similar story for techniques developed for particle detection, which have found their way into numerous applications, especially in medicine and biology.

The benefits of Big Science for economic prosperity become more pertinent if we consider the cumulative contributions to the 21st-century knowledge economy, which relies heavily on research and innovation. In 2018, more than 40% of the CERN budget was returned to industry in its member-state countries through the procurement of supplies and services, generating corollary benefits such as opening new markets. Increasing efforts, for example by the European Commission, to require research infrastructures to estimate their socioeconomic impact are a welcome opportunity to quantify and demonstrate our impact.

CERN has been subject to economic impact assessments since the 1970s, with one recent cost–benefit analysis of the LHC, conducted by economists at the University of Milan, concluding with 92% probability that benefits exceed costs, even when attaching the very conservative figure of zero to the value of the organisation’s scientific discoveries. More recent studies (CERN Courier September 2018 p51) by the Milan group, focusing on the High-Luminosity LHC, revealed a quantifiable return to society well in excess of the project’s costs, again, not including its scientific output. Extrapolating these results, the authors show that future colliders at CERN would bring similar societal benefits on an even bigger scale.

Across physics more broadly, a 2019 report commissioned by the European Physical Society found that physics-based industries generate more than 16% of total turnover and 12% of overall employment in Europe – representing a net annual contribution of at least €1.45 trillion, and topping contributions from the financial services and retail sectors (CERN Courier January/February 2020 p9).

Of course, there are some who feel that limited resources for science should be deployed in areas such as addressing climate change, rather than blue-sky research. These views can be persuasive, but are misleading. Fundamental research is every bit as important as directed research, and through the virtuous circle of science, they are mutually dependent. The open questions and mind-bending concepts explored by particle physics and astronomy also serve to draw bright young minds into science, even if individuals go on to work in other areas. Surveys of the career paths taken by PhD students working on CERN experiments fully bear this out (CERN Courier April 2019 p55).

In April 2020, as a curtain-raiser to the update of the European Strategy for Particle Physics, Nature Physics published a series of articles about potential future directions for CERN. An editorial pointed out the strong scientific and utilitarian case for future colliders, concluding that: “Even if the associated price tag may seem high – roughly as high as that of the Tokyo Olympic Games – it is one worth paying.” This is precisely the kind of argument that we as a community should be prepared to make if we are to ensure continuing exploration of fundamental physics in the 21st century and beyond.

Pierre Lazeyras 1931–2020

Pierre Lazeyras, who played leading roles in the ALEPH experiment, neutrino beams and silicon detectors during a 35-year-long career at CERN, passed away on 4 April aged 88.

Pierre graduated from the École supérieure de physique et chimie industrielle (ESPCI) in Paris in 1954 and, after working in Anatole Abragam’s group at CEA Saclay, he joined CERN as a staff member in October 1961. He was one of the early collaborators in the Track Chamber (TC) division, which built the two-metre bubble chamber and the Big European Bubble Chamber (BEBC). In parallel, he headed the team that developed one of the first superconducting bending magnets for BEBC’s “beam s3”.

Pierre directed the TC SPS neutrino beam group from 1972, which included the construction of the horns, the 185 m-long iron muon shielding and the beam monitoring, for which silicon-diode particle detectors were employed. After some initial teething troubles, the SPS neutrino beams operated for nearly 20 years without major problems. The silicon monitors were found to be more precise than the early gas-filled ion chambers, and this was the beginning of the era of silicon micro-strip detectors. Pierre encouraged the microelectronics developments for this new technology and its integrated readout circuits. These advances also came just in time for the UA2 experiment at the SPS and for wider applications in the LEP experiments.

Pierre was instrumental in the formation and success of ALEPH. From the conception of the experiment in 1982 right through to the LEP2 phase in 1996, he was ALEPH technical coordinator – a role that was quite new to those of us coming from smaller experiments. Pierre made sure we were realistic in our ambitions and our estimates of the difficulties and planning constraints, and we owe it mainly to him that the various parts of ALEPH were assembled without major problems. He was always available for advice even if, in his careful and reserved style, he did not try to direct or micro-manage everything.

In addition to being responsible for general safety in the experiment (which had no major incidents during its 11 years of operation), Pierre ensured that the construction of ALEPH was completed within budget. He also played an essential role at a crucial moment for the experiment in the early 1990s: the problem with the superconducting magnet cryostat. Under Pierre’s supervision, a vacuum leak was located, close to the edge of the magnet, and the cryostat then underwent “surgery” using a milling machine suspended from a crane. It was a wonderful exercise in imagination and, to the relief of all, a complete success. Pierre had always insisted that such a huge superconducting magnet and cryostat inherently constituted a fragile device, and had objected to the idea of warming up the magnet during annual shutdowns, citing the mechanical stress resulting from this procedure. He was absolutely right.

Pierre was also involved in the design of the large stabilised superconductors for the LHC-experiment magnets and served as a member of the magnet advisory group of the LHC into his retirement, his wisdom being highly appreciated. He was also an active member of the CERN Staff Association. Following his retirement in 1996, he joined the Groupement des Anciens and was a representative on the CERN health insurance supervisory committee, where his advice and opinions were always wise and measured.

Pierre was not only highly talented and used his experience most effectively, he was also a warm person, someone on whom one could always rely. He would always tell you straight how things were and then suggest how any problems could be tackled. A typical remark by Pierre would be: “Ask me to approve or reject your ideas, do not ask me what work I have for you.” We will remember him as a very dear friend and colleague.

Aldo Michelini 1930–2020

Aldo Michelini, who led OPAL and other important experiments at CERN, passed away at Easter at the age of 89. He was known as much for his kindness and care for his colleagues, particularly those embarking on their careers, as for the physics at which he excelled.

Aldo first came to CERN in 1960, bringing experience from several tracking-chamber experiments, including a stint with Jack Steinberger at Columbia University, and he lost no time in making an impact. One of his earliest contributions was to equip CERN’s Wilson chamber magnet with spark chambers, which he then used as part of a CERN/ETH/Imperial College/Saclay collaboration to measure properties of the K⁰₂ meson and pp and K^–p charge-exchange interactions using a polarised target.

As the 1960s advanced, Aldo formed a partnership and life-long friendship with his compatriot, Mario Morpurgo, who was an early pioneer of superconducting magnet technology. The two were part of the small team spearheading the development of the Omega spectrometer, a general-purpose device built around a large superconducting magnet that could be arranged and configured according to the physics to be studied. Omega was initially equipped with spark chambers and installed on a PS beamline, receiving its first beam in 1972, and moved to the SPS in 1976 where it became the backbone of the fixed-target programme there for 20 years.

In 1973, Aldo headed a similar project to build a general-purpose spectrometer for the North Area. This became NA3, which was the first experiment to receive beam in the new SPS hadron hall, EHN1, in May 1978. NA3 embarked on a programme of high-mass dimuon production with π⁺, π^–, K⁺, K^–, p and p beams, enabling the first observation of upsilon production by pions. It also probed the structure of the incoming particles via the Drell–Yan process. The spectrometer carried out a string of valuable experiments under Aldo’s guidance until 1981, when he became spokesperson of the OPAL experiment being planned for LEP. Aldo remained at the helm of OPAL right up to his retirement in 1995.

OPAL was built around tried and tested technology, including a paradoxical novelty for Morpurgo: a warm magnet. Huge for its time, with a collaboration of some 300 people, OPAL was nevertheless the smallest of the four LEP experiments. It was a scale that lent itself well to Aldo’s unique style of management – leading through example and consensus. Colleagues remember him smiling and looking very worried, or more often than not, the other way around. This was strangely motivational, with team members striving to make him smile more and worry less. His personality shaped the unique OPAL team spirit. Despite his gentle nature, Aldo was more than capable of making tough choices, and winning over those who might initially have disagreed with him.

When OPAL detected the first Z boson at LEP on 13 August 1989, Aldo was heard to remark that the young people had taken over. The average age of those in the control room that day was well under 30, and that youthfulness was no accident. Aldo actively supported the young members of the collaboration, making sure that they were visible at collaboration meetings and conferences. He also imbued them and the whole collaboration with a culture of never publishing even preliminary results before being absolutely certain of them. As a result, OPAL’s scientists built a strong reputation, with many conference conversations including the words, “let’s wait and see what OPAL has to say”. Aldo’s faith in the younger generation was rewarded by some 300 successful PhD theses from OPAL, while more than 100 CERN fellows passed through the collaboration over its lifetime.

Aldo was a great leader, commanding respect and affection in equal measure. That the collaboration was still able to gather more than 100 members in 2019 to celebrate the 30th anniversary of that first Z decay is testimony to the kind of person Aldo was, and to the spirit that he engendered. Although he was unable to attend that gathering, he sent a message, and was loudly cheered. He will be sorely missed.

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