Praxis Archives – Page 12 of 183

Steering the ship of member states

CERN turns 70 at the end of September. How would you sum up the contribution the laboratory has made to human culture over the past seven decades?

CERN’s experimental and theoretical research laid many of the building blocks of one of the most successful and impactful scientific theories in human history: the Standard Model of particle physics. Its contributions go beyond the best-known discoveries, such as of neutral currents and the seemingly fundamental W, Z and Higgs bosons, which have such far-reaching significance for our universe. I also wish to draw attention to the many dozens of new composite particles at the LHC and the incredibly high-precision agreement between theoretical calculation performed in quantum chromodynamics and the experimental results obtained at the LHC. These amazing discovering were made possible thanks to the many technological innovations made at CERN.

But knowledge creation and accumulation are only half the story. CERN’s human ecosystem is an oasis in which the words “collaboration among peoples for the good of humanity” can be uttered without grandstanding or hypocrisy.

What role does the CERN Council play?

CERN’s member states are each represented by two delegates to the CERN Council. Decisions are made democratically, with equal voting power for each national delegation. According to the convention approved in 1954, and last revised in 1971, Council determines scientific, technical and administrative policy, approves CERN’s programmes of activities, reviews its expenditures and approves the laboratory’s budget. The Director-General and her management team work closely with Council to develop the Organization’s policies, scientific activities and budget. Director-General Fabiola Gianotti and her management team are now collaborating with Council to forge CERN’s future scientific vision.

What’s your vision for CERN’s future?

As CERN Council president, I have a responsibility to be neutral and reflect the collective will of the member states. In early 2022, when I took up the presidency, Council delegates unanimously endorsed my evaluation of their vision: that CERN should continue to offer the world’s best experimental high-energy physics programme using the best technology possible. CERN now needs to successfully complete the High-Luminosity LHC (HL-LHC) project and agree on a future flagship project.

I strongly believe the format of the future flagship project needs to crystallise as soon as possible. As put to me recently in a letter from the ECFA early-career researchers panel: “While the HL-LHC constitutes a much-anticipated and necessary advance in the LHC programme, a clear path beyond it for our future in the field must be cemented with as little delay as possible.” It can be daunting for young people to speak out on strategy and the future of the field, given the career insecurities they face. I am very encouraged by their willingness to put out a statement calling for immediate action.

At its March 2024 session, Council agreed to ignite the process of selecting the next flagship project by going ahead with the fourth European Strategy for Particle Physics update. The strategy group are charged, among other things, with recommending what this flagship project should be to Council. As I laid down the gavel concluding the meeting I looked around and sensed genuine excitement in the Chambers – that of a passenger ship leaving port. Each passenger has their own vision for the future. Each is looking forward to seeing what the final destination will look like. Several big pieces had started falling into place, allowing us to turn on the engine.

What are these big pieces?

Acting upon the recommendation of the 2020 update of the European Strategy for Particle Physics, CERN in 2021 launched a technical and financial feasibility study for a Future Circular Collider (FCC) operating first as a Higgs, electroweak and top factory, with an eye to succeeding it with a high-energy proton–proton collider. The report will include the physics motivation, technological and geological feasibility, territorial implementation, financial aspects, and the environmental and sustainability challenges that are deeply important to CERN’s member states and the diverse communes of our host countries.

Fabiola Gianotti and Eliezer Rabinovici at CERN Council — **Charting the future** Director-General Fabiola Gianotti and her management team collaborate with Council to forge CERN’s future scientific vision. Credit: M Cavazza/CERN-PHOTO-202406-133-7

It is also important to add that CERN has also invested, and continues to invest, in R&D for alternatives to FCC such as CLIC and the muon collider. CLIC is a mature design, developed over decades, which has already precipitated numerous impactful societal applications in industry and medicine; and to the best of my knowledge, at present no laboratory has invested as much as CERN in muon-collider R&D.

A mid-term report of FCC’s feasibility study was submitted to subordinate bodies to the CERN management mid-2023, and their resulting reports were presented to CERN’s finance and scientific-policy committees. Council received the outcomes with great appreciation for the work involved during an extraordinary session on 2 February, and looks forward to the completion of the feasibility study in March 2025. Timing the European strategy update to follow hot on its heels and use it as an input was the natural next step.

At the June Council session, we started dealing with the nitty gritty of the process. A secretariat for the European Strategy Group was established under the chairmanship of Karl Jakobs, and committees are being appointed. By January 2026 the Council could have at its disposal a large part of the knowledge needed to chart the future of the CERN vision.

How would you encourage early-career researchers (ECRs) to engage with the strategy process?

ECRs have a central role to play. One of the biggest challenges when attempting to build a major novel research infrastructure such as the proposed FCC – which I sometimes think of as a frontier circular collider – is to maintain high-quality expertise, enthusiasm and optimism for long periods in the face of what seem like insurmountable hurdles. Historically, the physicists who brought a new machine to fruition knew that they would get a chance to work on the data it produced or at least have a claim for credit for their efforts. This is not the case now. Success rests on the enthusiasm of those who are at the beginning of their careers today just as much as senior researchers. I hope ECRs will rise to the challenge and find ways to participate in the coming European Strategy Group-sponsored deliberations and become future leaders of the field. One way to engage is to participate in ECR-only strategy sessions like those held at the yearly FCC weeks. I’d also encourage other countries to join the UK in organising nationwide ECR-only forums for debating the future of the field, such as I initiated in Birmingham in 2022.

What’s the outlook for collaboration and competition between CERN and other regions on the future collider programme?

Over decades, CERN has managed to place itself as the leading example of true international scientific collaboration. For example, by far the largest national contingent of CERN users hails from the US. Estonia has completed the process of joining CERN as a new member state and Brazil has just become the first American associate member state. There is a global agreement among scientists in China, Europe, Japan and the US that the next collider should be an electron–positron Higgs factory, able to study the properties of the Higgs boson with high precision. I hope that – patiently, and step by step – ever more global integration will form.

Do member states receive a strong return on their investment in CERN?

Research suggests that fundamental exploration actively stimulates the economy, and more than pays for itself. Member states and associate member states have steadfastly supported CERN to the tune of CHF 53 billion (unadjusted for inflation) since 1954. They do this because their citizens take pride that their nation stands with fellow member states at the forefront of scientific excellence in the fundamental exploration of our universe. They also do this because they know that scientific excellence stimulates their economies through industrial innovation and the waves of highly skilled engineers, entrepreneurs and scientists who return home trained, inspired and better connected after interacting with CERN.

A bipartisan US report from 2005 called “Rising above the gathering storm” offered particular clarity, in my opinion. It asserted that investments in science and technology benefit the world’s economy, and it noted both the abruptness with which a lead in science and technology can be lost and the difficulty of recovering such a lead. One should not be shy to say that when CERN was established in 1954, it was part of a rather crowded third place in the field of experimental particle physics, with the Soviet Union and the United States at the fore. In 2024, CERN is the leader of the field – and with leadership comes a heavy responsibility to chart a path beneficial to a large community across the whole planet. As CERN Council president, I thank member states for their steadfast support and I applaud them for their economic and scientific foresight over the past seven decades. I hope it will persist long into the 21st century.

Is there a role for private funding for fundamental research?

In Europe, substantial private-sector support for knowledge creation and creativity dates back at least to the Medici. Though it is arguably less emphasised in our times, it plays an important role today in the US, the UK and Israel. Academic freedom is a sine qua non for worthwhile research. Within this limit, I don’t believe there is any serious controversy in Council on this matter. My sense is that Council fully supports the clear division between recognising generosity and keeping full academic and governance freedom.

What challenges has Council faced during your tenure as president?

In February 2022, the Russian Federation, an observer state, invaded Ukraine, which has been an associate member state since 2016. This was a situation with no precedent for Council. The shape of our decisions evolved for well over a year. Council members decided to cover from their own budgets the share of Ukraine’s contribution to CERN. Council also tried to address as much as possible the human issues resulting from the situation. It decided to suspend the observer status in the Council of the Russian Federation and the Joint Institute for Nuclear Research. Council also decided to not extend its International Collaboration Agreements with the Republic of Belarus and the Russian Federation. CERN departments also undertook initiatives to support the Ukrainian scientific community at CERN and in Ukraine.

A second major challenge was to mitigate the financial pressures being experienced around the world, such as inflation and rising costs for energy and materials. A package deal was agreed upon in Council that included significant contributions from the member states, a contribution from the CERN staff, and substantial savings from across CERN’s activities. So far, these measures seem to have addressed the issue.

I thank member states for their steadfast support and I applaud them for their economic and scientific foresight over the past seven decades

While these key challenges were tackled, management worked relentlessly on preparing an exhaustive FCC feasibility study, to ensure that CERN stays on course in developing its scientific and technological vision for the field of experimental high-energy physics.

The supportive reaction of Council to these challenges demonstrated its ability to stay on course during rough seas and strong side winds. This cohesion is very encouraging for me. Time and again, Council faced difficult decisions in recent years. Though convergence seemed difficult at first, thanks to a united will and the help of all Council members, a way forward emerged and decisions were taken. It’s important to bear in mind that no matter which flagship project CERN embarks on, it will be a project of another order of magnitude. Some of the methods that made the LHC such a success can continue to accompany us, some will need to evolve significantly, and some new ones will need to be created.

Has the ideal of Science for Peace been damaged?

Over the years CERN has developed the skills needed to construct bridges. CERN does not have much experience in dismantling bridges. This issue was very much on the mind of Council as it took its decisions.

Do you wish to make some unofficial personal remarks?

Thanks. Yes. I would like to mention several things I feel grateful for.

Nobody owes humanity a concise description of the laws of physics and the basic constituents of matter. I am grateful for being in an era where it seems possible, thanks to a large extent to the experiments performed at CERN. Scientists from innumerable countries, who can’t even form a consensus on the best 1970s rock band, have succeeded time and again to assemble the most sophisticated pieces of equipment, with each part built in a different country. And it works. I stand in awe in front of that.

The ecosystem of CERN, the experimental groups working at CERN and the CERN Council are how I dreamt as a child that the United Nations would work. The challenges facing humanity in the coming centuries are formidable. They require international collaboration among the best minds from all over the planet. CERN shows that this is possible. But it requires hard work to maintain this environment. Over the years serious challenges have presented themselves, and one should not take this situation for granted. We need to be vigilant to keep this precious space – the precious gift of CERN.

German community discusses future collider at CERN

German particle-physics community in Bonn — **Bonn workshop** The German particle-physics community gathered at Bonn to discuss the opportunities of a future collider at CERN. Credit: M Schott

More than 150 German particle physicists gathered at Bonn University for a community event on a future collider at CERN. More precisely, the focus set for this meeting was to discuss the opportunities that the FCC-ee would offer should this collider be built at CERN. The event was organised by the German committee for particle physics, KET, and took place from 22 to 24 May. Representatives from almost all German institutes and groups active in particle physics were present, an attendance that shows the large interest in the collider to be built at CERN after the successful completion of the HL-LHC programme.

The main workshop was preceded by a dedicated session with more than 80 early-career scientists, organised by the Young High Energy Physicists Association, yHEP, to bring the generation that will benefit most from a future collider at CERN up to speed on the workshop topics. It included a presentation by former ECFA chair Karl Jakobs (Freiburg University) “From Strategy Discussions to Decision-Taking for Large Projects”, explaining the mechanisms and bodies involved in setting a project like the FCC-ee on track.

The opening session of the main workshop featured a fresh view on “The physics case for an e⁺e^– collider at CERN” by Margarete Mühlleitner (KIT Karlsruhe), who spread excitement about the strong and comprehensive physics case from super-precise measurements of the properties of the Z boson, the W boson and the top quark to what most people associate with a future e⁺e^– collider: precision measurements of the Higgs boson and insights about its connection to many of the still open questions of particle physics like dark matter or the matter–antimatter asymmetry. Markus Klute (KIT Karlsruhe) gave an in-depth review of the FCC-ee project. The midterm results of the FCC feasibility study indicate that no showstoppers were found in all the aspects studied so far and that the integrated FCC programme offers unparalleled exploration potential through precision measurements and direct searches. The picture was rounded off by a presentation from Jenny List (DESY, Hamburg) who talked about alternative options to realise an e⁺e^– Higgs factory at CERN, and the perspective of the early-career researchers was highlighted by Michael Lupberger (Bonn University). While all these presentations concentrated on the science and technology of the FCC-ee or alternatives, Eckart Lilienthal, representing the German Ministry of Education and Research, BMBF, reminded the audience that a future collider project at CERN needs an affordable financial plan and that – given the large uncertainties at present – this requires the community to prepare for different scenarios including one without the FCC-ee. Lilienthal confirmed that the future of CERN remains of the highest priority to BMBF.

The event was an important step in building consensus in the German community for a future collider project at CERN

The workshop went on to review many aspects of the FCC-ee and possible alternatives in more detail: accelerator R&D, detector concepts and technologies, computing and software, theory challenges as well as sustainability. The workshop witnessed the first meetings of the newly established German detector R&D consortia on silicon detectors, gaseous detectors and calorimetry. They will receive BMBF funding for the next three years and will allow German groups to strongly participate in the recently formed international DRD consortia in the context of the ECFA detector roadmap.

The path ahead

The workshop concluded with discussion sessions on the future collider scenarios for CERN, the engagement of the German community and a path to prepare the German input to the update of the European Strategy for Particle Physics. A series of three additional community workshops will be held in Germany before this input is due in March 2025.

The Bonn event was an important step in building consensus in the German community for a future collider project at CERN. The FCC-ee project generated a lot of interest and many groups plan to embark more strongly on this project. Contributions concerning the physics case, theory challenges, detector design and development, software, computing, and accelerator development were discussed. Alternative options for a future collider project at CERN need to be kept open to address the unanswered fundamental questions of particle physics in case the FCC-ee is not built at CERN. This event was clear evidence that a bright future for CERN remains of highest priority for the German particle-physics community and funding agency.

Become a Particle Physicist in Eight Simple Moves

Simone Ragoni is passionate about outreach. His Instagram page, quarktastic, has more than 10 thousand followers, and is one of the very few that successfully makes particle physics and academia relatable. He wrote Become a Particle Physicist in Eight Simple Moves while completing his PhD on the ALICE experiment. The first move is to sip his favourite beverage: coffee.

As a social-media manager and communicator, I’ve been following Ragoni for years. His main tool is humour. And I’m proof it works. I will always remember the basic structure of a proton, because life is indeed full of “ups” and “downs”.

Did I say gentle humour? Nah. Ragoni goes all the way. But he confesses that his humour can only be understood by a handful of people. Particle physics is esoteric – and readers will want to join the club. His book invites you into the world of a young particle physicist. Being a nerd is the new cool.

A highlight is when Ragoni describes how to keep those distributions fit. If you know, you know. There is a pun here and the author explains it very well. He next turns to the tedious work that goes into publishing a paper. “Monte Carlo simulations are our real playground,” he writes, “where we unleash all our fantasy, the perfect world where everything is nice.” But particle physicists are cautious. Five sigma is needed to claim a discovery – a one in 3.5 million chance of being wrong. The author concludes with encouragement to make your own measurements using CERN’s open data.

Ragoni’s book is a delightful gift for anyone whom you want to inspire to become a particle physicist of tomorrow or simply to convey the excitement of what you do, with a quirky bonus of being presented bilingually in English and Italian, should you be keen on improving your physics vocab in one of those languages. It is a gateway to the captivating world of particle physics, skilfully blending humour with profound insights, and inspiring readers to explore further and consider joining the ranks of future particle physicists.

I built a physics museum in my classroom

Teaching modern physics to high-school students presents many challenges: overpacked curricula focusing on classical physics; the depth of knowledge needed by students (and teachers) to understand these topics; and students being over-focused on grades and university admissions. By exposing my students to the work being done at major research laboratories around the world, I have managed to find a way to overcome many of those obstacles.

Some time ago, British Columbia removed provincial examinations, giving teachers a bit more freedom to make additions to their curricula. I chose to insert small one- or two-day units throughout the year, which give my students multiple exposure to modern physics topics. These short introductions over a two-year period mean that physics students don’t need to know all the fine details, which decreases their stress and concerns.

Knowledge sharing

Physics teachers are lucky to have access to high-quality professional development via workshops run by CERN, LIGO, the Perimeter Institute (which produces excellent resources for use in physics classes) and others. These often-week-long events give teachers an overview of how a given research facility works, in the hope that they will bring that knowledge back to their students. Along the way, the teachers attend lectures from leading researchers and see first-hand careers in the field that they can bring back to share with their class.

I have been fortunate enough to attend workshops at these facilities. I have also taken part in a research experience at SNOLAB, brought students on tours of TRIUMF and mentored my students as they conducted research at the Canadian Light Source. All these experiences have given me the knowledge and confidence to introduce the facilities and the work done at them to my students in a way that hopefully piques their curiosity.

The pieces provide a starting point for conversations around what these decommissioned parts were used for and the kind of science they supported

While at CERN for the 2019 international teacher programme, I had the opportunity to visit both the CMS and ALICE detectors and to attend lectures from renowned particle physicists. We spent time in S’Cool LAB and visited many of the behind-the-scenes parts of CERN. While all of these experiences left an imprint on my teaching, it was during quiet visits to what was then called the Microcosm garden – which hosts decommissioned pieces of accelerators and detectors as a form of art – that helped transform the physical space in my classroom.

In 2022 my school in British Columbia renovated a large, old classroom to become our new physics lab. Knowing that I had more space to work with than before, I was inspired to start building my own version of the Microcosm garden on my classroom walls. I soon connected with the outreach team at TRIUMF who were excited to help get my project started with a photomultiplier tube, a control panel from a xenon-gas handling system, a paddle scintillator and a light guide. Since then, I have added a Lucas cell from SNOLAB, a piece of the electron gun from the Canadian Light Source and, most recently, a small-strip half-gap prototype from the New Small Wheel upgrade of the ATLAS detector. The pieces provide a starting point for conversations with students around what these decommissioned parts were used for, and the kind of science they supported.

Equipped with some knowledge of what modern research in the field looks like, I have successfully built a system where I am able to inspire students to want to study physics. Since attending my first major workshop in 2018, I have seen an increase in the number of students entering physics majors. Some of them have already gone on to internships at CERN and TRIUMF, after getting their first exposure to these organisations in my classes. My hope is that by having pieces of the facilities I talk about displayed on my classroom walls, this will further inspire more of my students to want to learn about them, possibly setting them on paths to careers in physics.

A new generation, a new vision

The 2024 Aspen Winter Conference, The Future of High Energy Physics: A New Generation, A New Vision, attracted 50 early-career researchers (ECRs) from across the world to the Aspen Center for Physics, 8000 feet above sea level in the Colorado Rockies, from 24 to 29 March. The conference built on the many new ideas that arose from the recent Snowmass process of the US particle physics community (CERN Courier January/February 2024 p7). The conference sought to highlight the role of ECRs in realising bold long-term visions for the field, covering theoretical questions, the experimental vision for the next 50 years and the technologies required to make it a reality. Students, postdocs and junior faculty are often the drivers of new ideas in science. Helping them transition new ideas to the mainstream requires enthusiasm, community support and time.

Crossing frontiers

85% of the matter in the universe at most minimally interacts with the electromagnetic force but provided the gravitational seed for large-scale structure formation in the early universe. Hugh Lippincott (University of California, Santa Barbara) summarised cross-frontier searches. Pursuing all possible scenarios via direct detection will require scaling up existing technology and developing new technologies such as quantum sensors to probe lighter dark-matter candidates. On the one hand, the 60 to 80 tonne “XLZD” liquid xenon detector will merge the expertise of the XENONnT, LUX-ZEPLIN and DARWIN collaborations; on the low-mass side, Reina Maruyama (Yale) discussed the ALPHA and HAYSTAC haloscopes, which seek to convert axions into photons in highly tuned resonant cavities. Indirect detection and collider experiments will also play an important role in closing in on minimal dark-matter models.

Delegates expressed a sense of urgency to probe higher energies. Cari Cesarotti (MIT) advocated R&D towards a future muon collider, arguing that muons offer a clean and power-efficient route to the 10 TeV scale and above. Recently, experts have estimated that challenges due to the finite muon lifetime could be overcome on a 20-year technically limited timeline. Both CERN and China have proposed building 100 km-circumference tunnels, initially hosting an electron–positron collider followed by a 100 TeV hadron machine, however, the timeline suggests that almost all of the conference attendees would be retired before hadron collisions come online. Elliot Lipeles (Pennsylvania) proposed skipping the electron-positron stage and immediately pursuing an intermediate-energy hadron collider: existing magnets in a 100 km tunnel could produce 37 TeV collisions, advancing measurements of the Higgs self-coupling and electroweak phase transition, dark matter and its mediators, and naturalness.

The energy, intensity and cosmic frontiers of particle physics target deeply connected questions

Neutrinos were discussed at length. Georgia Karagiorgi (Columbia University) argued that three short-baseline anomalies remain, potentially hinting at additional sterile neutrinos or dark-sector portals. Julieta Gruszko (North Carolina at Chapel Hill) presented an exciting future for experiments that seek to discern the fundamental nature of neutrinos. A new tonne-scale generation of detectors comprising LEGEND1000, nEXO and CUPID may succeed in confirming the Majorana nature of the neutrino if they observe neutrinoless double beta decay.

Talks on the importance of science communication and education provoked a great deal of discussion. Ethan Siegal, host of popular podcast “Starts with a Bang” spoke on public outreach, Kevin Pedro (Fermilab) on advocacy with policymakers in Washington, DC, and Roger Freedman (University of California Santa Barbara) on educating the next generation of physicists. In public programming, Nausheen Shah (Wayne State) was the guest speaker at a screening of Hidden Figures, the inspiring true story of the black women who helped the US win the space race, and Philip Chang (University of California San Diego) lectured on “An Invitation to Imagine Something from Nothing”.

The energy, intensity and cosmic frontiers of particle physics target deeply connected questions. Dark matter, dark energy, cosmic inflation and baryogenesis have remained unexplained for decades, and the structure of the Standard Model itself provokes questions, not least in relation to the Higgs boson and neutrinos. Innovative and complementary experiments are needed across all areas of particle physics. Judging from the 2024 Aspen Winter Conference, the future of the field is in good hands.

Wonderstruck wanderings

**Head-scratcher** An illustration of a flea from Robert Hooke’s Micrographia, which was the first text to include what were awe-inspiring microscopic images. Credit: National Library of Wales

The wonder and awe that we sense when we look at the starry skies is a major motivation to do science. Both Plato (Theaetetus 155d) and Aristotle (Metaphysics 982b12) wrote that philosophy starts in wonder. Plato went even further to declare that the eye’s primary purpose is none other than to see and study the stars (Timaeus 47c). But wonder and awe also play a wider role beyond science, and are fundamental to other endeavours of human civilisation, such as religion. In Wonderstruck: How Wonder and Awe Shape the Way We Think, Helen De Cruz (Saint Louis University) traces the relationship between wonder and awe and philosophy, religion, magic and science, and the development of these concepts throughout history.

Essential emotion

De Cruz’s book is rich in content, drawing from psychology, anthropology and literature. Aptly for particle physicists, she points out that it is not only the very largest scales that fill us with awe, but also the very smallest, as for example in Robert Hooke’s Micrographia, the first book to include illustrations of insects and plants as seen through a microscope. Everyday things may be sources of wonder, according to philosopher and rabbi Abraham J Heschel, who has written on religion as a response to the awe that we feel when we look at the cosmos. Even hard-nosed economists recognise the fundamental role of wonder, she observes: Adam Smith, the famous economist who wrote The Wealth of Nations, believed that wonder is an essential emotion that underlies the pursuit of science, as it prompts people to explore the unknown and seek knowledge about the world. Although particle physics is not mentioned explicitly in the book – the closest instance is a quote from Feynman’s Lectures on Physics – the implications are clear. And while the sources quoted are mostly Western, other traditions are not ignored, with references to Chinese and Japanese culture present, among others.

Wonderstruck — Credit: Princeton University Press

The book also motivates questions that it does not address, some of which are especially interesting for fundamental physics. For example, modern human beings who live and work in cities spend most of their lives in an environment that alienates them from nature, and nature-induced awe must compete with technology-driven amazement. One can maybe glimpse that in outreach, where curiosity about technology sometimes, though not always, eclipses interest about the fundamental questions of science. While the book discusses this topic in the context of climate change – a reality that reminds us that we cannot ignore nature – there is more one can do with respect to the effects of such an attitude in motivating fundamental science.

At a time when large scientific projects, such as CERN’s proposed Future Circular Collider, are being considered, generating a lot of discussions about cost and benefit, this book reminds us that the major motivation of a new telescope or collider is to push into the frontiers of the unknown – a process that starts and finishes with wonder and awe. As such, the book is very useful reading for scientists doing fundamental research, especially those who engage with the public.

Ilario Boscolo 1940–2024

Ilario Boscolo, who was one of the proponents of the AEgIS experiment at CERN, passed away on 16 April 2024 at the age of 84.

Ilario Boscolo was born in Codevigo, Italy in 1940 and graduated from the nearby University of Padua. In 1968 he joined the University of Lecce, where he initiated research in accelerator physics, high-intensity electron beams and free electron lasers (FELs), and far-infrared and CO₂ lasers. Among his important scientific contributions at that time were the development of a prototype electrostatic accelerator, investigations on far-infrared lasers optically pumped in a cavity, and a much-cited theoretical proposal for a two-stage FEL for coherent harmonic amplification (an optical klystron). Ilario spent long periods of study in international research institutes, including the ENEA fusion energy centre in Frascati and the University of California Santa Barbara, where he collaborated with world-leading FEL researchers Luis Elias and William Colson.

In 1987 Ilario was called to the University of Milan, where he became full professor, to participate in the INFN project ELFA (electron laser facility for acceleration) and was responsible for the photocathode emission. His interest then turned to other topics, including efficient electron sources based on field emission from carbon nanotubes or ferroelectric ceramics and, within CERN, pulsed laser phase coding systems for new acceleration facilities. Within the INFN SPARC–SPARX initiative, started in 2003 and based in Frascati, he focused on laser applications for the development of pulsed, high-brightness UV and X-ray FEL sources. In particular, he showed that the high beam quality of the electron sources depends on suitable shaping of comb laser pulses, the study of which was realised in a dedicated laser laboratory at Milan founded by Ilario.

In 2007 Ilario was one of the proponents of the AEgIS experiment at the CERN Antiproton Decelerator, which aimed to investigate the properties of antimatter, in particular its gravitational interactions. This required the production of a low-energy beam of antihydrogen atoms, obtained by a charge-exchange process with positronium atoms laser-excited at Rydberg levels. Led by Ilario, the Milan laser laboratory was responsible for the laser system that was required to make this pairing possible. AEgIS demonstrated the first pulsed-production of antihydrogen atoms in 2018, enabling a series of antimatter studies that are ongoing.

In all his activities, Ilario showed great passion and enthusiasm for both science and its applications. This positive attitude was also widely displayed through his didactical activity in various courses at the University of Milan. He was responsible for a new physics laboratory for the biology programme and for the laser laboratory for the physics programme. In addition, his greatest success was the complete reconstruction of the general physics laboratory for first-year students. By encouraging students to practice and elaborate on their own, with only little guidance from the teacher, this laboratory left an indelible mark on their training as physicists.

Another strong passion of Ilario was civil commitment, reflected in his constant engagement with university governance and studies of politics and economics, to which he dedicated himself with his usual inexhaustible enthusiasm, particularly after his retirement.

Ilario is remembered by his collaborators and students as a person of great culture, of brilliant insights, of a willingness to discuss physics and politics with anyone, and as an exquisite friend. He was a true scientist, leaving a deep mark on physics and a bright memory for everyone who had the honour of knowing him.

Alec Geoffrey Hester 1928–2024

Alec Hester, a former editor of CERN Courier and later physics subject specialist at the CERN library for nearly 30 years, passed away in Geneva on 9 March at the age of 96.

Born in Hatfield, to the north of London, in 1928, Alec graduated in physics from Imperial College London in 1949. He continued there for his PhD, building a Van de Graaff accelerator to study (p, alpha) reactions in light nuclei. Yes, in those days postgraduate students built their own accelerators! One of his older fellow students was Don Perkins, who passed away in 2022.

In 1952 Alec interrupted his studies to take a job in the publicity department of General Electric at its site in Kent, England. Nine years later he came to CERN to take over the editorship of CERN Courier from Roger Anthoine. The Courier was then just two years old, and it was during Alec’s period as editor that it began to move beyond its initial role as the house journal for CERN staff to one that communicated the work of CERN and other laboratories to a wider scientific and technical readership. Marking the end of Alec’s editorship in the December 1965 issue, Anthoine wrote: “The editing and production of our periodical, with limited means, requires not only very definite intellectual qualities, for collecting and processing information from all over the Laboratory, but also considerable physical and moral toughness to cope with the many dictates of production, which are the lot of every editor… It is mainly thanks to [Alec’s] drive that CERN Courier, which now has a circulation of 6000 copies (French and English versions combined), has risen from the rank of ‘internal information journal’ to that of ‘world spokesman for European sub-nuclear physics’.”

In 1966 Alec moved to the CERN scientific information service as the physics subject specialist, remaining there until his retirement in February 1993. His accurate and painstaking work developing the library’s bibliographic databases provided the nucleus for those searchable on the CERN Document Server today.

Alec leaves behind Annemarie, his wife for over 70 years, his daughters Barbara and Dagmar, and his four grandchildren.

Rudolf Bock 1927–2024

Renowned experimental physicist and co-initiator of relativistic heavy-ion physics, Rudolf Bock, passed away on 9 April 2024 aged 96.

Rudolf Bock was born in Mannheim, Germany in May 1927 and obtained his diploma in physics from the University of Heidelberg in 1954. He conducted his doctoral thesis on deuteron-induced nuclear reactions at the cyclotron of the Max Planck Institute for Medical Research in Heidelberg and received his doctorate from Heidelberg University in 1958. He then investigated nuclear reactions at the newly founded MPI for Nuclear Physics (MPIK) at the tandem accelerators there, initially with light ions and from 1963 with heavier ions.

In 1967 he was appointed full professor at the University of Marburg and was involved in the development of a joint accelerator project for heavy-ion research, ultimately leading to the UNILAC accelerator project. On 17 December 1969, the research centre GSI (Gesellschaft für Schwerionenforschung) was founded in Darmstadt–Wixhausen. As one of its founding fathers and subsequently as a long-standing member of the GSI board of directors, Rudolf Bock played a decisive role in the development of nuclear physics with heavy ions. At the same time, he maintained his contacts with Heidelberg as an honorary professor and as an external scientific member of the MPIK. In 2000 he was awarded an honorary doctorate from Goethe University Frankfurt.

Research with relativistic heavy-ion beams soon led to great successes. From 1974 Rudolf Bock established a working group at GSI under the leadership of Hans Gutbrod and Reinhard Stock, who set up and successfully carried out two major experiments at the Berkeley Bevalac accelerator. These resulted in the discovery of compressed, hot nuclear matter with hydrodynamic flow behaviour and thus formed the basis for his later experiments on quark–gluon plasma at CERN.

From the mid-1980s, the heavy-ion synchrotron SIS18 was set up at GSI under the leadership of director Paul Kienle. Thanks to Rudolf Bock’s guidance and in cooperation with surrounding universities, three new experiments (FOPI, KAOS and TAPS) were created, which focused on the formation of compressed nuclear matter as well as on hadron production and in particular the formation of light atomic nuclei. Around the same time, he was working on plans for experiments at much higher energies, which could ultimately only be realised at the CERN
SPS accelerator, with decisive contributions from GSI and LBL Berkeley. This led to the development of today’s global programme in ultra-relativistic nuclear–nuclear collisions, which has been pursued since the 1990s at the AGS and SPS, from 2000 with four experiments at RHIC and, since 2010, has been led by ALICE at the LHC at the highest energies.

The cooperation between GSI and LBL Berkeley was not only the beginning of relativistic heavy-ion physics. Supported by Hermann Grunder, then head of the LBL accelerator department, Rudolf Bock started the inertial confinement fusion programme in Germany. He also laid an important foundation for ion-beam therapy by supporting the secondment of Gerhard Kraft from GSI to the cancer-therapy programme at LBL. After his retirement in December 1995, Rudolf Bock maintained his scientific activities at GSI, his primary interest being the development of experiments on plasma physics and inertial-confinement fusion with high-intensity ion and laser beams.

Throughout the course of his scientific career, Rudolf Bock established numerous new research collaborations with institutes in Germany and abroad. As he himself had taken part in the Second World War and had spent several years as a prisoner of war in Russia, the idea of international understanding and peacekeeping was an important concern for him. As early as 1969 he invited many Russian scientists to the nuclear-physics conference at MPIK, and from the 1970s he promoted many collaborations between GSI and Russian institutes. He also pushed for Russia to become the largest member state in the GSI/FAIR project. The Russian invasion of Ukraine in February 2022 was therefore a great disappointment for him and for all of us.

Rudolf Bock was regularly present at GSI until his last days and continued to take an interest in current research and developments on campus. His advice and foresight will be sorely missed.

Werner Rühl 1937–2023

Theoretical physicist Werner Rühl died on 31 December 2023 in Füssen, Germany at the age of 86.

He was born in 1937, at a time when theoretical physics in Germany was being destroyed by the Nazis. After the Second World War, the ongoing study of cosmic rays and the availability of higher energies from accelerators made particle physics the most interesting field for budding researchers like him. Part of the way ahead was obvious: learn from the US and profit from the new spirit of European unity embodied by the creation of CERN.

Rühl followed this path in the straightest possible way. He obtained his PhD in 1962 in Cologne and became a research associate at CERN in 1964. Two years later he took up a postdoc at Rockefeller University, New York, before returning to CERN as a staff member in 1967, and obtained a chair in 1970 at the newly founded University of Kaiserslautern.

A more difficult decision concerned mathematics, for which many experimentalists had little regard. Initially, Einstein had shared this attitude, but then he worked hard on Riemannian geometry to understand gravity. Heisenberg’s successes were based on deep mathematics, too, but he tried his best to limit its scope. SU(2) and the analogy between spin and isospin were fundamental, and the representation theory of SU(2) had been fully explored in the context of atomic physics. Dirac’s understanding of spinors and his introduction of the delta distribution opened the way for a thorough investigation of non-compact groups like SL(2,C). This allowed us to break the wall between maths and physics, which happened initially in the Soviet Union. Rühl was very aware of this fact and was deeply impressed by the work of Israel Moiseevich Gelfand. In winter 1967/1968 he gave a series of lectures on this topic for the academic training programme at CERN, which in 1970 became the core of his book The Lorentz group and harmonic analysis. A mathematical fruit was his elementary proof of the Plancherel theorem for classical groups, published in 1969.

Rühl’s appointment to a chair at Kaiserslautern was a happy choice for both sides. Internationally recognised professors like Rühl had adequate resources for students, visitors and conferences, and four theory colleagues were hired between 1970 and 1973. In 1983–1985 Rühl was chairman of the physics department and member of the university senate. He published good papers with his PhD students and supported the global development of science, in particular through his work with postdocs from Oran University. For many years he also worked as a mentor for gifted students from all faculties for the prestigious Studienstiftung des deutschen Volkes scholarship foundation.

Despite his dominating affinity for mathematics, Rühl maintained an interest in experimental physics and occasionally published related work. His understanding of Russia facilitated successful collaborations with outstanding colleagues who had moved to the West, with some of his most important contributions stemming from his collaborations with colleagues from Yerevan. After his retirement in 2004 he continued to publish as before. Eleven years later he moved to Füssen near the Alps. For five years he could enjoy his passion for skiing, before an accident impaired his health.

Werner Rühl always had an open mind for new developments. He had studied the large-N behaviour of theories with symmetries like O(N) and did respected work on lattice theories. From the 1980s, his citation rate increased more and more – a tendency that lasted way beyond his retirement. The original take on AdS/CFT duality in the context of O(N) sigma models and high-spin theories stands out the most. At the end of his life it must have been a great satisfaction for Werner Rühl to watch the ripening of these late fruits.

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