Praxis Archives – Page 16 of 179

Looking forward at the LHC

Proposed Forward Physics Facility — **New territory** 3D rendering of the proposed Forward Physics Facility and its experiments. Credit: A Navascues Cornago

The Forward Physics Facility (FPF) is a proposed new facility to operate concurrently with the High-Luminosity LHC, housing several new experiments on the ATLAS collision axis. The FPF offers a broad, far-reaching physics programme ranging from neutrino, QCD and hadron-structure studies to beyond-the-Standard Model (BSM) searches. The project, which is being studied within the Physics Beyond Colliders initiative, would exploit the pre-existing HL-LHC beams and thus have minimal energy-consumption requirements.

On 8 and 9 June, the 6th workshop on the Forward Physics Facility was held at CERN and online. Attracting about 160 participants, the workshop was organised in sessions focusing on the facility design, the proposed experiments and physics studies, leaving plenty of time for discussion about the next steps.

Groundbreaking

Regarding the facility itself, CERN civil-engineering experts presented its overall design: a 65 m-long, 10 m-high/wide cavern connected to the surface via an 88 m-deep shaft. The facility is located 600 m from the ATLAS collision point, in the SM18 area of CERN. A workshop highlight was the first results from a site investigation study, whereby a 20 cm-diameter core was taken at the proposed location of the FPF shaft to a depth of 100 m. The initial analysis of the core showed that the geological conditions are positive for work in this area. Other encouraging studies towards confirming the FPF feasibility were FLUKA simulations of the expected muon flux in the cavern (the main background for the experiments), the expected radiation level (shown to allow people to enter the cavern during LHC operations with various restrictions), and the possible effect on beam operations of the excavation works. One area where more work is required concerns the possible need to install a sweeper magnet in the LHC tunnel between ATLAS and the FPF to reduce the muon backgrounds.

Currently there are five proposed experiments to be installed in the FPF: FASER2 (to search for decaying long-lived particles); FASERν2 and AdvSND (dedicated neutrino detectors covering complementary rapidity regions); FLArE (a liquid-argon time projection chamber for neutrino physics and light dark-matter searches); and FORMOSA (a scintillator-based detector to search for milli-charged particles). The three neutrino detectors offer complementary designs to exploit the huge number of TeV energy neutrinos of all flavours that would be produced in such a forward-physics configuration. Four of these have smaller pathfinder detectors, FASER(ν), SND@LHC and milliQan that are already operating during LHC Run 3. First results from these pathfinder experiments were presented at the CERN workshop, including the first ever direct observation of collider neutrinos by FASER and SND@LHC, which provide a key proof of principle for the FPF. The latest conceptual design and expected performance of the FPF experiments were presented. Furthermore, first ideas on models to fund these experiments are in place and were discussed at the workshop.

In the past year, much progress has been made in quantifying the physics case of the FPF. It effectively extends the LHC with a “neutrino–ion collider’’ with complementary reach to the Electron–Ion Collider under construction in the US. The large number of high-energy neutrino interactions that will be observed at the FPF allows detailed studies of deep inelastic scattering to constrain proton and nuclear parton distribution functions (PDFs). Dedicated projections of the FPF reveal that uncertainties in light-quark PDFs could be reduced by up to a factor of two or even more compared to current models, leading to improved HL-LHC predictions for key measurements such as the W-boson mass.

In the past year, much progress has been made in quantifying the physics case of the FPF

High-energy electrons and tau neutrinos at the FPF predominantly arise from forward charm production. This is initiated by gluon–gluon scattering involving very low and high momentum fractions, with the former reaching down to Bjorken-x values of 10^–7 – beyond the range of any other experiment. The same FPF measurements of forward charm production are relevant for testing different models of QCD at small-x, which would be instrumental for Higgs production at the proposed Future Circular Collider (FCC-hh). This improved modeling of forward charm production is also essential for understanding the backgrounds to diffuse astrophysics neutrinos at telescopes such as IceCube and KM3NeT. In addition, measurements of the ratio of electron-to-muon neutrinos at the FPF probe forward kaon-to-pion production ratios that could explain the so-called muon puzzle (a deficit in muons in simulations compared to measurements), affecting cosmic-ray experiments.

The FPF experiments would also be able to probe a host of BSM scenarios in uncharted regions of parameter space, such as dark-matter portals, dark Higgs bosons and heavy neutral leptons. Furthermore, experiments at the FPF will be sensitive to the scattering of light dark-matter particles produced in LHC collisions, and the large centre-of-mass energy enables probes of models, such as quirks (long-lived particles that are charged under a hidden-sector gauge interaction), and some inelastic dark-matter candidates, which are inaccessible at fixed-target experiments. On top of that, the FPF experiments will significantly improve the sensitivity of the LHC to probe millicharged particles.

The June workshop confirmed both the unique physics motivation for the FPF and the excellent progress in technical and feasibility studies towards realising it. Motivated by these exciting prospects, the FPF community is now working on a Letter of Intent to submit to the LHC experiments committee as the next step.

Aligning future colliders at SLAC

The 2023 International Workshop on Future Linear Colliders (LCWS2023) took place at SLAC from 15 to 20 May, continuing the series devoted to the study of high-energy linear electron–positron colliders that started in 1992. A linear collider is appealing because it could operate as a Higgs factory during its initial stage, while maintaining a clear path for future energy upgrades. Proposed linear-collider Higgs factories are designed for greater compactness, energy efficiency and sustainability, with lowered construction and operation costs compared to circular machines.

With a wide programme of plenary and parallel sessions, the workshop was a great opportunity for the community to discuss current and future R&D directions, with a focus on sustainability, and was testament to the eagerness of physicists from all over the world to join forces to build the next Higgs factory. More than 200 scientists participated, about 30% of which were early-career researchers and industry partners.

Energy frontiers

As set out by the 2020 update of the European strategy for particle physics and the Energy Frontier report from Snowmass 2021, particle physicists agreed that precision Higgs-boson measurements are the best path toward further progress and to provide insights into potential new-physics interactions. The Higgs boson is central for understanding fundamental particles and interactions beyond the Standard Model. Examples include the nature of dark matter and matter–antimatter asymmetry, which led to the prevalence of matter in our universe.

Ideally, data-taking at a future e⁺e^–Higgs factory should follow the HL-LHC directly, requiring construction to start by 2030, in parallel with HL-LHC data-taking. Any significant delay will put at risk the availability of essential and unique expertise, and human resources, and endanger the future of the field.

Among the e⁺e^– colliders being evaluated by the community, the International Linear Collider (ILC), based on superconducting RF technology, has the most advanced design. It is currently under consideration for construction in Japan. However, for a long time now, Japan has not initiated a process to host this collider. One alternative approach is to construct a large circular collider – a strategy now being pursued by CERN with the FCC-ee, and by China with the CEPC. Both colliders would require tunnels of about 100 km circumference to limit synchrotron radiation. The FCC-ee machine is foreseen to operate in 2048, seven years after the end of the HL-LHC programme, with a substantial cost in time and resources for the large tunnel. An alternative is to construct a compact linear e⁺e^– collider based on high-gradient acceleration. CERN has a longstanding R&D effort along these lines, CLIC, that would operate at a collision energy of 380 GeV.

New technologies proposed for higher-energy stages will require decades of R&D

Given the global uncertainties around each proposal, it is prudent to investigate alternative plans based on technologies that could enable compact designs and possibly provide a roadmap to extend the energy reach of future colliders. As also highlighted in the Snowmass Energy Frontier report, consideration should be given to the timely realisation of a Higgs factory in the US as an international effort. For instance, the Cool Copper Collider (C³) is a new and even more compact proposal for a Higgs-producing linear collider. It was developed during Snowmass 2021 and made its debut at LCWS with more than 15 talks and five posters. This proposal would use normal-conducting RF cavities to achieve a collision energy of 500 GeV with an 8 km-long collider, making it significantly smaller and likely more cost-effective than other proposed Higgs factories.

There are many advantages of the linear approach. Among them, linear colliders are able to access energies of 500 GeV and beyond, while for circular e⁺e^– colliders the expected luminosity drops off above centre-of-mass energies of 350–400 GeV. This would allow precision measurements that are crucial for indirect searches for new physics, including measurements of the top-quark mass and electroweak couplings, the top-Higgs coupling, and the cross section for double-Higgs production.

At LCWS 2023, the community showed progress on R&D for both accelerator and detector technologies and outlined how further advances in ILC technology, as well as alternative technologies such as C³ and CLIC, promise lower costs and/or extended energy reach for later stages of this programme. Discoveries at a Higgs factory may point to specific goals for higher energy machines, with quark and lepton collisions at least 10 times the energies of the LHC. New technologies proposed for such higher-energy stages – using pp, muon and e⁺e^– colliders – will require decades of R&D. Construction and operation of a linear Higgs factory would be a key contribution towards this programme by developing an accelerator workforce and providing challenges to train young scientists.

In this regard, a key outcome of the SLAC workshop was a statement supporting the timely realisation of a Higgs factory based on a linear collider to access energies beyond 500 GeV and enable the measurements vital for new physics to the P5 committee, which is currently evaluating priorities in US high-energy physics for the next two decades.

Theoretical astroparticle physicists gather at CERN

The European Consortium for Astroparticle Theory (EuCAPT) was founded in 2019 to bring together the European community of theoretical astroparticle physicists and cosmologists. The goals of EuCAPT include the exchange of ideas and knowledge, coordinating scientific and training activities, helping scientists attract adequate resources for their projects, and promoting a stimulating, fair and open environment in which young scientists can thrive. With these main goals in mind, the annual EuCAPT symposium serves to bring the community together and stimulate discussions on recent developments. After three years with largely online events, EuCAPT gathered for the first time in person for its annual symposium at CERN, the hub of the European initiative.

From 31 May to 2 June, 180 participants came together in the CERN main auditorium (with a further 100 online) to exchange on topics including dark matter, particle astrophysics, cosmology of the early and late universe, and gravitational waves. The programme alternated between invited overview talks from leading scientists and lightning talks by early-career researchers. No fewer than 50 posters reflected the rich diversity of EuCAPT science, with prizes for the best poster and best lightning talks awarded at the end of the conference.

A highlight of the symposium was an interactive session with the members of the different EuCAPT task forces, ranging from outreach, training and community building to funding and many more, which allowed participants to learn more about the work done within the consortium and to join these activities. EuCAPT founding director Gianfranco Bertone (University of Amsterdam), who gave a well-attended public evening talk at CERN and who is due to step down in January 2024, said: “Leading EuCAPT has been an incredible experience. In four years we have grown into a vibrant and diverse community of more than 1600 scientists, based at 130 institutions across Europe. With a solid organisational structure in place, and many ongoing scientific activities, we are now ready to take the next steps.”

With further EuCAPT activities, such as the first EuCAPT school in Valencia this autumn, ongoing throughout the year, the EuCAPT community will continue to grow such that at the next EuCAPT symposium there will be ample new scientific developments and progress to discuss.

Towards a century of trailblazing physics

Approval timeline — **Real time** Taking into account past experience with building colliders at CERN, the approval timeline, and assuming that the HL-LHC will run until 2041, FCC could begin operations in 2045–2048. From the perspective of the technical schedule alone, operation of FCC-ee could start in 2040 or earlier. Credit: E Bentall

The Future Circular Collider (FCC) offers a multi-stage facility – beginning with an e⁺e^– Higgs and electroweak factory (FCC-ee), followed by an energy-frontier hadron collider (FCC-hh) in the same 91 km tunnel – that would operate until at least the end of the century. Following the recommendation of the 2020 update of the European strategy for particle physics, CERN together with its international partners have launched a feasibility study that is due to be completed in 2025. FCC Week 2023, which took place in London from 5 to 9 June, and attracted about 500 people, offered an excellent opportunity to strengthen the collaboration, discuss the technological and scientific opportunities, and plan the submission of the mid-term review of the FCC feasibility study to the CERN Council later this year.

The FCC study, along with the support of the European Union FCCIS project, aims to build an ecosystem of science and technology involving fundamental research, computing, engineering and skills for the next generation. It was therefore encouraging that around 40% of FCC Week participants were aged under 40.

Working together

In his welcome speech, Mark Thomson (UK STFC executive chair) stressed the importance of a Higgs factory as the next tool in exploring the universe at a fundamental level. Indeed, one of the no-lose theorems of the FCC programme, pointed out by Gavin Salam (University of Oxford), is that it will shed light on the Higgs’ self-interaction, which governs the shape of the Brout–Englert–Higgs potential. In her plenary address, Fabiola Gianotti (CERN Director-General) confirmed that the current schedule for the completion of the FCC feasibility study is on track, and stressed that the FCC is the only facility commensurate with the present size of CERN’s community, providing up to four experimental points, concluding “we need to work together to make it happen”.

Designing a new accelerator infrastructure poses a number of challenges, from civil engineering and geodesy to the development of accelerator technologies and detector concepts to meet the physics goals. One of the major achievements of the feasibility study so far is the development of a new FCC layout and placement scenario, thanks to close collaboration with CERN’s host states and external consultants. As Johannes Gutleber (CERN) reported, the baseline scenario has been communicated with the affected communes in the surrounding area and work has begun to analyse environmental aspects at the surface-site locations. Synergies with the local communities will be strengthened during the next two years, while an authorisation process has been launched to start geophysical investigations next year.

Essential for constructing the FCC tunnel is a robust 3D geological model, for which further input from subsurface investigations into areas of geological uncertainty is needed. On the civil-engineering side, two further challenges include alignment and geodesy for the new tunnel. Results from these investigations will be collected and fed into the civil-engineering cost and schedule update of the project. Efforts are also focusing on optimising cavern sizes, tunnel widenings and shaft diameters based on more refined requirements from users.

Transfer lines have been optimised such that existing tunnels can be reused as much as possible and to ensure compatibility between the lepton and hadron FCC phases. Taking CERN’s full experimental programme into account, the option of using the SPS as pre-booster for FCC-ee will be consolidated and compared with the cost with a high-energy linac option.

A new generation of young researchers will need to take the reins to ensure FCC gets delivered and exploit the physics opportunities offered by this visionary research infrastructure

At the heart of the FCC study are sustainability and environmental impact. Profiting from an R&D programme on high-efficiency klystrons initially launched for the proposed Compact Linear Collider, the goal is to increase the FCC-ee klystron efficiency from 57% (as demonstrated in the first prototypes) to 80% – resulting in an energy saving of 300 GWh per year without considering the impact that this development could have beyond particle physics. Other accelerator components where work is ongoing to minimise energy consumption include low-loss magnets, SRF cavities and high-efficiency cryogenic compressors.

The FCC collaboration is also exploring ways in which to reuse large volumes of excavated materials, including the potential for carbon capture. This effort, which builds on the results of the EU-funded “Mining the Future” competition launched in 2020, aims to re-use the excavated material locally for agriculture and reforestation while minimising global nuisances such as transport. Other discussions during FCC Week focused on the development of a renewable energy supply for FCC-ee.

If approved, a new generation of young researchers will need to take the reins to ensure FCC gets delivered and exploit the physics opportunities offered by this visionary research infrastructure. A dedicated early-career researcher session at FCC Week gave participants the chance to discuss their hopes, fears and experiences so far with the FCC project. A well-attended public event “Giant Experiments, Cosmic Questions” held at the Royal Society and hosted by the BBC’s Robin Ince also reflected the enthusiasm of non-physicists for fundamental exploration.

The highly positive atmosphere of FCC Week 2023 projected a strong sense of momentum within the community. The coming months will keep the FCC team extremely busy, with several new institutes expected to join the collaboration and with the scheduled submission of the feasibility-study mid-term review advancing fast ahead of its completion in 2025.

EPP-2024: progress and promise

Maria Spiropulu and Michael Turner — **Co-chairs** Maria Spiropulu (Caltech) and Michael Turner (University of Chicago and UCLA) are co-chairs of EPP-2024, which aims to help federal agencies, policymakers and academic leaders understand the future prospects for and societal benefits of particle-physics research. Credit: D Overbye

What is the origin and purpose of EPP-2024?

Michael Turner (MT): In June 2022, the US Department of Energy (DOE) and National Science Foundation (NSF) asked the US National Academy of Sciences to convene a committee to provide a long-term (30 years or more) vision for elementary particle physics in the US and to deliver its report in mid 2024. EPP-2024 follows three previous National Academy studies, the last one in 2006 being notable for its composition (more than half of the members were “outsiders”) and the fact that it both set a vision and priorities. EPP-2024 is an 18-member committee, co-chaired by Maria and myself, and comprises mostly particle physicists from across the breadth of the field. It includes two Nobel Prize winners, eight National Academy members and CERN Director-General Fabiola Gianotti. It will recommend a long-term vision, but will not set priorities.

How does EPP-2024 relate to the current “P5” prioritisation process in the US?

MT: The field is in the process of the third P5 (Particle Physics Project Prioritization Panel) exercise, following previous cycles in 2008 and 2014. The DOE and the NSF asked the 30-member P5 committee (chaired by Hitoshi Murayama of UC Berkeley) to provide a prioritised, 10-year budget plan in the context of a 20-year globally-aware strategy by October 2023. By way of contrast, EPP-2024 will assess where the field is today, describe its ambitions and the tools and workforce necessary to achieve those ambitions, all without discussing budgets, specific projects or priorities.

Both P5 and EPP-2024 have benefitted from the community-based activity, Snowmass 2021, sponsored by the American Physical Society, which brought together more than 1000 particle physicists to set their priorities and vision for the future in a report published in January 2023. Together, EPP-2024 and P5 will provide both a long-term vision and a shorter-term detailed plan for particle physics in the US that will maintain a vibrant US programme within the larger context of a field that is very international.

What took EPP-2024 to CERN earlier this year?

Maria Spiropulu (MS): CERN, from its inception, has been structured as an international organisation; pan-European surely, but structurally internationally ready. In 2018 I was in the Indian Treaty room of the White House when the then CERN Director-General Rolf Heuer proclaimed CERN as the biggest US laboratory not on US soil. Indeed, in the past decade the ties between US particle physics and CERN have become stronger – in particular via the LHC and HL-LHC and also the neutrino programme – and ever more critical for the future of the field at large, so it was only natural to visit CERN and to discuss with the community in our EPP Town Hall, the early-career contingent and others. It was a very productive visit and we were impressed with what we saw and learned. The early-career scientists were fully engaged and there was a long and lively discussion focused both on the long-term science goals of the field, the planning process in Europe and in the US, the role of the US at CERN and CERN’s role in the US, as well as the involvement of early-career researchers in the process. As the field evolves and innovative approaches from other domains are employed to address persistent science questions and challenges, we see our workforce as a major output of the field both feeding back to our research programme and the society writ large.

The questions we are asking now are big questions that require tenacity, resources, innovation and collaboration. Every technology advance and invention we can use to push the frontiers of knowledge we do. Of course, we need to investigate whether we can break these questions into shorter-timescale undertakings, perhaps less demanding in scale and resources, and with even higher levels of innovation, and then put the pieces together. Ultimately it is the will and determination of those who engage in the field that will draft the path forward.

How would you define particle physics today?

MT: There is broad agreement that the mission of particle physics is the quest for a fundamental understanding of matter, energy, space and time. That ambitious mission not only involves identifying the building blocks of matter and energy, and the interactions between them, but also understanding how space, time and the universe originated. As evidenced by the diversity of participants at Snowmass – astronomers and physicists of all kinds – the enterprise encompasses a broad range of activities. Those being prioritised by P5 range from experiments at particle accelerators and underground laboratories to telescopes of all kinds and a host of table-top experiments.

Mike Lamont and National Academy of Sciences representatives — **Down under** CERN director of accelerators and technology Mike Lamont guiding US representatives of the National Academy of Sciences around the LHC during the EPP-2024 visit in February. Credit: CERN-PHOTO-202302-047-8

Long ago when I was an undergraduate at Caltech working with experimentalist Barry Barish (now a gravitational-wave astronomer), particle physics comprised experimenters who worked at accelerators and theorists who sought to explain and understand their results. While these two activities remain the core of the field, there is a “cloud” of activities that are also very important to the mission of particle physics. And for good reason: almost all the evidence for physics beyond the Standard Model involves the universe at large: dark matter, dark energy, baryogenesis and inflation. Neutrino masses were discovered in experiments that involved astrophysical sources (e.g. the Sun and cosmic-ray produced atmospheric neutrinos), and many of the big ideas in theoretical particle physics involve connecting quarks and the cosmos. Although some of the researchers involved in such cloud activities are particle physicists who have moved out of the core, the primary research of most isn’t directly associated with the mission of particle physics.

We stand on the tall shoulders of the Standard Model of particle physics – and general relativity – with a programme in place that includes the LHC, neutrino experiments, dark-matter and dark-energy experiments, CMB-polarisation measurements, precision tests and searches for rare processes and powerful theoretical ideas – not to mention all the ideas for future facilities. I believe that we are on the cusp of a major transformation in our understanding of the fundamentals of the physical world at least as exciting as the November 1974 revolution that brought us the Standard Model.

How can particle physics maintain its societal relevance next to more applied domains?

MS: To be sure, the edifice of science is ever more relevant to human civilisation and most of society’s functions. Particle physics and associated fields capture human imagination and curiosity in terms of questions that they grapple with – questions that no one else would take up, at least not experimentally. All science domains, technology-needs and products are important to our 21st-century workings. Particle physics is not more or less important, in fact it consumes and optimises and adapts the advances of most other domains toward very ambitious objectives of building an understanding of our universe. I would also argue that because we are the melting pot of so much input and tools from other seemingly unrelated science and technology domains, the field offers a very fertile and attractive ground for training a workforce able to tackle intellectually and technologically ambitious puzzles. It can be seen as overly demanding – and this is where mentorship, guidance and clarity of opportunities play a crucial role.

How does EPP-2024 take into account international aspects of the field?

MS: This is exemplified by a committee membership that includes the CERN Director-General, and also by the multiple testimonies and panels focusing on international collaboration, including the framework, the optimisation of science and societal outcomes, and the training of an outstanding workforce. We have collected information from distinguished panels and experts in Europe, Asia and the US that have traditionally led the field, and we study how smaller economies and nations participate and contribute successfully and to the benefit of their nations and the international discovery science goals at large. We also interrogate the role of our science in diplomacy and in scientific exchanges that may overcome geopolitical tensions. International big projects are not a walk in the park; in our field they have proven to be necessary, so we put in deliberate emphasis to make them work towards achieving ambitious goals that are otherwise intractable.

What has the EPP-2024 committee learned so far – any surprises?

MT: For me, a relative outsider to particle physics, several things have stood out. First, the breadth of the enterprise today: cosmology has become fully integrated into particle physics, and new connections have been made to AMO physics (quantum sensors, trapped atoms and molecules, atomic interferometry), gravitational physics (gravitational waves and precision tests of gravity theory), and nuclear physics (neutrino masses and properties). Not only have dark-matter searches for WIMPs and axions become “big science”, but there is exploration of a host of new candidates that has spurred the invention of novel detection schemes.

I believe that we are on the cusp of a major transformation in our understanding at least as exciting as the November 1974 revolution

In the US, particle physics has become a big tent that encompasses tabletop experiments to look for a small electric dipole moment of the electron, large galaxy surveys, cosmic microwave background experiments, long-baseline neutrino experiments, and of course collider experiments to explore the energy frontier. It is difficult to draw a box around a field called elementary particle physics.

On the science side, much has changed since the last National Academy report in 2006, which noted discovering the Higgs boson and exploring the soon-to-be-discovered world of supersymmetry as its big vision. The aspirations of the field are much loftier today, from understanding the emergence of space and time to the deep connections between gravity and quantum mechanics. At the same time, however, the path forward is less clear than it was in 2006.

Record attendance at IPAC23

The 14^th International Particle Accelerator Conference (IPAC23) took place from 7 to 12 May in Venice, Italy. The fully in-person event had record attendance with 1660 registered participants (including 273 students) from 37 countries, illustrating the need for real-life interactions in the global accelerator landscape after the COVID-19 pandemic. IPAC is not only a scientific meeting but also a global marketplace for accelerators, as demonstrated by the 311 participants from 121 companies present.

Following inspiring opening speeches by Antonio Zoccoli (INFN president) and Alfonso Franciosi (Elettra president) about the important role of particle accelerators in Italy, the scientific programme got under way. It included 87 talks and over 1500 posters covering all particles (electrons, positrons, protons, ions, muons, neutrons, …), all types of accelerators (storage rings, linacs, cyclotrons, plasma accelerators, …), all use-cases (particle physics, photon science, neutron science, medical and industrial applications, material physics, biological and chemical, …) and institutes involved across the world. The extensive programme offered such a wide perspective of excellence and ambition that it is only possible to highlight a short subset of what was presented.

Starting proceedings was a report by Malika Meddahi (CERN) on the successful LHC Injectors Upgrade (LIU) project. This project, with its predominantly female leadership team, was executed on budget and on schedule. It provides the LHC with beams of increased brightness as required by the ongoing luminosity upgrade, as later reported by CERN’s Oliver Brüning. The focus then shifted to advanced X-ray light sources. Emanuel Karantzoulis (Elettra) presented Elettra 2.0 – a new ultra-low emittance light source in construction in Trieste. Axel Brachmann (SLAC) updated participants on the status of LCLS-II, the world´s first CW X-ray free-electron laser (XFEL). While beam commissioning is somewhat delayed, the superconducting RF accelerator structures perform beyond the performance specification and the facility is in excellent condition. The week´s programme included an impressive overview by Dong Wang (Shanghai Advanced Research Institute) on the future of XFELs for which user demand has led to an enormous investment aiming in particular at “high average power”, which will be used to serve many more experiments including those for highly non-linear QED. Gianluca Geloni (European XFEL) showed that user operation for the world`s presently most powerful XFEL has been successfully enhanced with self-seeding. Massimo Ferrario (INFN) described the promise of a novel, high-tech plasma-based FEL being explored by the European EuPRAXIA project.

IPAC23_poster — The poster sessions with more than 400 posters per day are the core of IPAC23. Credit: IPAC23

Jörg Blaurock (FAIR/GSI) presented the status of the €3.3 billion FAIR project. Major obstacles have been overcome and the completed tunnel and many accelerator components are now being prepared for installation, starting in 2024. The European Spallation Source in Sweden is advancing well and the proton linac is approaching full beam commissioning, as presented by Ryoichi Miyamoto (ESS) and Andrea Pisent (INFN). Yuan He from China (IMP, CAS) presented opportunities in accelerator-driven nuclear power, both in safety and in reusing nuclear fuels, and impressed participants with the news on a Chinese facility that is progressing well in terms of up-time and reliability. This theme was also addressed by Ulrich Dorda (Belgian Nuclear Research Centre) who presented the status of the Multi-purpose Hybrid Research Reactor for High-tech Applications (MYRRHA) project. Another impressive moment of the programme was Andrey Zelinsky’s (NSC in Ukraine) presentation on the Ukraine Neutron Source facility at the National Science Center “Kharkov Institute of Physics & Technology” (NSC KIPT). Construction, system checks and integration tests for this new facility have been completed and beam commissioning is being prepared under extremely difficult circumstances, as a result of Russia’s invasion.

Technological highlights included a report by Claire Antoine (CEA) on R&D into thin-film superconducting RF cavities and their potential game-changing role in sustainability. Sustainability was a major discussion topic throughout IPAC23, and several speakers presented the role of accelerators for the development of fusion reactors. The final talk of the conference by Beate Heinemann (DESY) showed that without accelerators, much knowledge in particle physics would still be missing and she argued for new accelerator facilities at the energy frontier to allow further discoveries.

The prize session saw Xingchen Xu (Fermilab), Mikhail Krasilnikov (DESY/Zeuthen) and Katsunobu Oide (KEK) receive the 2023 EPS-AG accelerator prizes. In addition, the Bruno Touschek prize was awarded to Matthew Signorelli (Cornell University), while two student poster prizes went to Sunar Ezgi (Goethe Universität Frankfurt) and Jonathan Christie (University of Liverpool).

IPAC23 included for the first time in Europe an equal opportunity session, which featured talks from Maria Masullo (INFN) and Louise Carvalho (CERN) on gender and STEM, pointing to the need to change the narrative and to move “from talk to targets”. The 300 participants in the session learnt about ways to improve gender balance but also about such important topics as neurodiversity. The very well attended industrial session of IPAC23 brought together projects and industry in a mixed presentation and round-table format.

For the organizers, IPAC23 has been a remarkable and truly rewarding effort, seeing the many delegates, industry colleagues and students from all over the world coming together for a lively, peaceful and collaborative conference. The many outstanding posters and talks promise a bright future for the field of particle accelerators.

Iraq to join SESAME as associate member

On 25 July, during its 42nd meeting, the Council of SESAME unanimously approved Iraq’s request to become an associate member. Iraq will now become a prospective member of SESAME as a stepping stone to full membership.

“My visit to SESAME on 8 June 2023 has convinced me that Iraq will stand to greatly benefit from membership, and that this would be the right moment for it to become a member,” stated Naeem Alaboodi, minister of higher education and scientific research and head of the Iraqi Atomic Energy Commission, in his letter to Rolf Heuer, president of the SESAME Council. “However, before doing so it would like to better familiarise itself with the governance, procedures and activity of this centre, and feels that the best way of doing this would be by first taking on associate membership.”

SESAME (Synchrotron-light for Experimental Science and Applications in the Middle East), based in Allan, Jordan, was founded on the CERN model and established under the umbrella of UNESCO. It opened its doors to users in 2017, offering third-generation X-ray beamlines for a range of disciplines, with the aim to be the first international Middle-Eastern research institution enabling scientists to collaborate peacefully for the generation of knowledge (CERN Courier January/February 2023 p28). SESAME has eight full members (Cyprus, Egypt, Iran, Israel, Jordan, Pakistan, Palestine and Turkey) and 17 observers, including CERN. One of SESAME’s main focuses is archaeological heritage. This will be the topic of the first Iraqi user study, which involves two Iraqi institutes collaborating in a project of the Natural History Museum in the UK.

Iraq has been following progress at SESAME for some time. As an associate member Iraq will enjoy access to SESAME’s facilities for its national priority projects and more opportunities for international collaboration.“Iraq’s formal association with SESAME will be very useful for Iraqi scientists to gain the required scientific knowledge in many different areas of science and applications using synchrotron radiation,” said Hua Liu, deputy director-general of the International Atomic Energy Agency, which has been actively encouraging its member states located in the region to seek membership of SESAME.

“The Council and all the members of SESAME are delighted by Iraq’s decision,” added Heuer. “We look forward to further countries of the region joining the SESAME family. With more beamlines available in the future, we hope that user groups from different countries will be working together on projects and we will see more transnational collaboration.”

A frog among birds

“Well, Doc, You’re In”: Freeman Dyson’s Journey through the Universe is a biographical account of an epochal theoretical physicist with a mind that was, by any measure, delightful and diverse. It portrays Dyson, a self-described frog among birds, as a one-off synthesis of blitz-spirit Britishness with American space-age can-do. Of the elite cadre of theoretical physicists who ushered in the era of quantum field theory, which dominates theoretical physics to this day, who else would have devoted so much time and sincere scientific energy to the development of a gargantuan spacecraft, powered by nuclear bombs periodically dropped beneath it, that would take human civilisation beyond our solar system!

Written by colleagues, friends, family members and selected experts, each chapter is more of a self-contained monograph, a link in a chain, than it is a portion of the continuous thread that one would find for a more traditional single-author biography. What is lost as a result of this format, such as an occasional repetition of key life moments, is more than sufficiently compensated by richness of perspective and a certain ease of pick-up put-down that comes from the narrational independence of the various chapters. If it has been a while since the reader last had a moment to pick it up, not much will be lost when one delves back in.

The early years of Dyson-caliber 20th-century theoretical physicists and mathematicians of his cohort are often interwoven with events surrounding the development of nuclear weapons or codebreaking. Dyson’s story as told in “Well, Doc, You’re In” stands apart in this respect, as he spent the war years working in Bomber Command for the Royal Air Force in England. His reflections on aspects of his own experience mirror, in some ways, the sentiments of future colleagues involved in the Manhattan project, noting: “Through science and technology, evil is organised bureaucratically so that no individual is responsible for what happens.”

“Well, Doc, You’re In”: Freeman Dyson’s Journey through the Universe — Credit: MIT Press

The following years spent wrestling with quantum electrodynamics (QED) at Cornell make for lighter reading. The scattered remarks from eminent theorists such as Bethe and Oppenheimer on Dyson and his work, as well as from Dyson on his eminent colleagues, bring a sense of reality to the unfolding developments that would ultimately become a momentous leap forward in the understanding of quantum field theory.

“The preservation and fostering of diversity is the great goal that I would like to see embodied in our ethical principles and in our political actions,” said Dyson. Following his deep contributions to QED, Dyson embraced this spirit of diversity and jumped from scientific pond to pond in search of progress, be it the stability of matter or the properties of random matrices. It is interesting to learn, with hindsight, of the questions that gripped Dyson’s imagination at a time when particle physics was entering a golden era. As a reader one almost feels the contrarian spirit, or rebellion, in these choices as they are laid out against this backdrop.

Although scientifically Dyson may have been a frog, jumping from pond to pond, professionally he was anything but. Aged 29 he moved to the Institute for Advanced Study at Princeton and he stayed there to the end. In around 1960 Dyson joined the JASON defence advisory group, a group of scientists advising the US government on scientific matters. He remained a member until his passing in 2020. This consistent backdrop makes for a biographical story, which is essentially free from the distractions of the professional manoeuvring that typically punctuates biographies of great scientists. A positive consequence is that the various authors, and the reader, may focus that bit more keenly on the workings of Dyson’s mind.

For as long as graduate students learn quantum field theory, they will encounter Dyson. Sci-fi fans will recognise the Dyson Sphere (a structure surrounding a star to allow advanced civilisations to harvest more energy) featured in Star Trek, or note the name of the Orion III Spaceplane in 2001: A Space Odyssey. Dyson’s legacy is as vast and diverse as the world his mind explored and “Well, Doc, You’re In” is a fascinating glimpse within.

Stanley Wojcicki 1937–2023

Stanley G Wojcicki, a long-time leader in experimental particle physics, died on 31 May at the age of 86. Stan made a number of seminal contributions to the field, beginning with the discovery of many short-lived particles as a graduate student at Berkeley. He quickly rose to prominence, becoming an expert on K-meson physics, where he made a series of investigations and discoveries that played an important role in understanding the structure of the Standard Model.

Stan hardly had a typical childhood. Born in Warsaw, Poland, his youth was dominated by World War II, which caused great hardships, including the separation of his family for several years, followed by a difficult life under the communist regime. Finally, his mother, brother and he managed to escape to Sweden. There, they were refugees for eight months, before they were finally able to move to the US. Stan’s father remained in Poland, where he was jailed for five years, and never received a visa to rejoin his family.

From a very young age, Stan was an exceptional student who loved and excelled at mathematics. He continued to stand out in school in his new country and gained admission to Harvard University as an undergraduate, majoring in physics. He went on to Berkeley as a graduate student in physics, which is where he and I met and became lifelong friends, colleagues and sometimes collaborators.

Upon receiving his PhD in 1962, Stan spent a year at CERN and Collège de France, Paris (1964–1965). He returned frequently to CERN, including for a period supported through a John Simon Guggenheim Fellowship in 1973–1974. During that year, Stan continued his research on the excited states of hadrons made from combinations of quarks. He continued his close association with CERN, once again as a scientific associate in 1980–1981, and for shorter periods throughout his career.

Stan was appointed assistant professor in the physics department at Stanford in 1966, advanced to full professor in 1974, served as chair from 1982–1985 and stayed on the faculty until his retirement in 2015. He characteristically became interested in the newest and most exciting areas in the field, and was quick to join the design effort for the Superconducting Super Collider (SSC). He served as deputy director of the SSC central design group in Berkeley and was deeply involved in proposing and obtaining approval for the construction of the SSC in Texas. He continued to be active in many aspects of the SSC until it was cancelled by Congress in 1993, and wrote an insightful two-volume history of the project.

After the SSC disappointment, Stan characteristically bounced back to take on a new emerging area of particle physics: neutrino masses and oscillations. He proposed and led the MINOS experiment, a key element of a long-baseline neutrino experiment that sent a beam of neutrinos through a near detector at Fermilab and to a second detector, 735 km away, in a deep mine in Minnesota. MINOS was very important in providing evidence confirming the observations of atmospheric neutrino oscillations from Super-Kamiokande in Japan.

Stan received many honours, including the Pontecorvo Prize in 2011 and the APS Panofsky Prize in 2015 for his neutrino work. He met his wife, Esther, while he was a PhD student at Berkeley. They married in 1961 and had three daughters of whom he was very proud, Susan (CEO of YouTube), Janet (professor of paediatrics at UCSF Medical School) and Anne (founder and CEO of 23andMe). He will be very much missed by his many long-time friends and colleagues.

Milos Lokajicek 1952–2023

Milos Lokajicek, a long-time employee of the division of elementary particle physics of the Institute of Physics of the Czech Academy of Sciences, passed away in June at the age of 70. Milos was involved in almost all the key experiments in which the Czech particle-physics community participated, especially in the collection and processing of experimental data.

Milos began his career in the 1980s on an experiment at the Serpukhov accelerator in the former USSR, investigating proton–antiproton and later deuteron–antideuteron collisions in the Ludmila hydrogen bubble chamber. After obtaining his PhD in 1984, while still at JINR Dubna, he was also involved in the DELPHI experiment at LEP, which played a key role in the Czech Republic’s entry into CERN in 1993.

After returning to the Institute of Physics, he was at the origin of the participation of Czech physicists in the ATLAS experiment at the LHC, the construction of which was approved in 1994. Together with other staff of the Institute of Physics and colleagues from Charles University, he initiated the construction of the ATLAS TileCal hadron calorimeter and built a laboratory for the assembly and testing of the calorimeter submodules in the former garage of the Institute of Physics.

Since his participation in the Ludmila and DELPHI experiments, Milos focused on data processing. Already in the mid-1990s, he had built a computer farm for data processing and modelling at the Institute of Physics, which today serves several large experiments.

In 1997, together with colleagues from Charles University and the Czech Technical University, he initiated the group’s participation in the D0 experiment at the Tevatron, Fermilab. Participation in this experiment was important for the training of young physicists in ATLAS, the construction of which was beginning at that time. After the Tevatron was decommissioned in 2011, Milos obtained funding for the Fermilab–CZ research infrastructure in 2016 with a gradual transition to the neutrino-physics programme. He worked on the NOvA experiment and also used his experience and contacts at CERN for the future DUNE experiment.

The reach of Milos’s work extends far beyond his home institute. Within the Czech Republic, it was the coordination of the activities of Czech institutions in Fermilab and the development of data processing. He was also a long-standing member of the Committee for Cooperation of the Czech Republic with CERN. His international reputation is documented by numerous memberships in steering committees of experiments and projects, and a number of conferences he co-organised. Among the most important are ACAT 2014, CHEP2009, DØ Week 2008 and ATLAS Week 2003.

Milos’s collegiality and friendship will be missed by all of us.

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