New frontiers in gravitational-wave (GW) astronomy were discussed in the charming and culturally vibrant region of Oaxaca, Mexico from 14 to 19 November. Around 37 participants attended the hybrid Banff International Research Station for Mathematical Innovation and Discovery (BIRS) “Detection and Analysis of Gravitational Waves in the Era of Multi-Messenger Astronomy: From Mathematical Modelling to Machine Learning’’ workshop. Topics ranged from numerical relativity to observational astrophysics and computer science, including the latest applications of machine-learning algorithms for the analysis of GW data.
GW observations are a new way to explore the universe’s deepest mysteries. They allow researchers to test gravity in extreme conditions, to get important clues on the mathematical structure and possible extension of general relativity, and to understand the origin of matter and the evolution of the universe. As more GW observations with increased detector sensitivities spur astrophysical and theoretical investigations, the analysis and interpretation of GW data faces new challenges which require close collaboration with all GW researchers. The Oaxaca workshop focused on a topic that is currently receiving a lot of attention: the development of efficient machine-learning (ML) methods and numerical-analysis algorithms for the detection and analysis of GWs. The programme gave participants an overview of new-physics phenomena that could be probed by current or next-generation GW detectors, as well as data-analysis tools that are being developed to search for astrophysical signals in noisy data.
Since their first detections in 2015, the LIGO and Virgo detectors have reached an unprecedented GW sensitivity. They have observed signals from binary black-hole mergers and a handful of signals from binary neutron star and mixed black hole-neutron star systems. In discussing the role that numerical relativity plays in unveiling the GW sky, Pablo Laguna and Deirdre Shoemaker (U. Texas) showed how it can help in understanding the physical signatures of GW events, for example by distinguishing black hole-neutron star binaries from binary black-hole mergers. On the observational side, several talks focused on possible signatures of new physics in future detections. Adam Coogan (U. de Montréal and Mila) and Gianfranco Bertone (U. of Amsterdam, and chair of EuCAPT) discussed dark-matter halos around black holes. Distinctive GW signals could help to determine whether dark matter is made of a cold, collisionless particle via signatures of intermediate mass-ratio inspirals embedded in dark-matter halos. In addition, primordial black holes could be dark-matter candidates.
Bernard Mueller (U. Monash) and Pablo Cerdá-Durán (U. de Valencia) described GW emission from core-collapse supernovae. The range of current detectors is limited to the Milky Way, where the rate of supernovae is about one per century. However, if and when a galactic supernova happens, its GW signature will be within reach of existing detectors. Lorena Magaña Zertuche (U. of Mississippi) talked about the physics of black-hole ringdown – the process whereby gravitational waves are emitted in the aftermath of a binary black-hole merger – which is crucial for understanding astrophysical black holes and testing general relativity. Finally, Leïla Haegel (U. de Paris) described how the detection of GW dispersion would indicate the breaking of Lorentz symmetry: if a GW propagates according to a modified dispersion relation, its frequency modes will propagate at different speeds, changing the phase evolution of the signals with respect to general relativity.
Machine learning Applications of different flavours of ML algorithms to GW astronomy, ranging from the detection of GWs to their characterisation in detector simulations, were the focus of the rest of the workshop.
ML has seen a huge development in recent years and has been increasingly used in many fields of science. In GW astronomy, a variety of supervised, unsupervised, and reinforcement ML algorithms, such as deep learning, neural networks, genetic programming and support vector machines, have been developed. They have been used to successfully deal with noise in the detector, signal processing, data analysis for signal detections and for reducing the non-astrophysical background of GW searches. These algorithms must be able to deal with large data sets and demand a high accuracy to model theoretical waveforms and to perform searches at the limit of instrument sensitivities. The next step for a successful use of ML in GW science will be the integration of ML techniques with more traditional numerical-analysis methods that have been developed for the modelling, real-time detection, and analysis of signals.
The BIRS workshop provided a broad overview of the latest advances in this field, as well as open questions that need to be solved to apply robust ML techniques to a wide range of problems. These include reliable background estimation, modelling gravitational waveforms in regions of the parameter space not covered by full numerical relativity simulations, and determining populations of GW sources and their properties. Although ML for GW astronomy is in its infancy, there is no doubt that it will play an increasingly important role in the detection and characterization of GWs leading to new discoveries.
Ten years after the discovery of a Standard Model-like Higgs boson at the LHC, particle physicists face profound questions lying at the intersection of particle physics, cosmology and astrophysics. A visionary new research infrastructure at CERN, the proposed Future Circular Collider (FCC), would create opportunities to either answer them or refine our present understanding. The latest activities towards the ambitious FCC physics programme were the focus of the 5th FCC Physics Workshop, co-organised with the University of Liverpool as an online event from 7 to 11 February. It was the largest such workshop to date, with more than 650 registrants, and welcomed a wide community geographically and thematically, including members of other “Higgs factory” and future projects.
The overall FCC programme – comprising an electron-positron Higgs and electroweak factory (FCC-ee) as a first stage followed by a high-energy proton-proton collider (FCC-hh) – combines the two key strategies of high-energy physics. FCC-ee offers a unique set of precision measurements to be confronted with testable predictions and opens the possibility for exploration at the intensity frontier, while FCC-hh would enable further precision and the continuation of open exploration at the energy frontier. The February workshop saw advances in our understanding of the physics potential of FCC-ee, and discussions of the possibilities provided at FCC-hh and at a possible FCC-eh facility.
The overall FCC programme combines the two key strategies of high-energy physics: precision measurements at the intensity frontier and the open exploration at the energy frontier
The proposed R&D efforts for the FCC align with the requests of the 2020 update of the European strategy for particle physics and the recently published accelerator and detector R&D roadmaps established by the Laboratory Directors Group and ECFA. Key activities of the FCC feasibility study, including the development of a regional implementation scenario in collaboration with the CERN host states, were presented.
Over the past several months, a new baseline scenario for a 91 km-circumference layout has been established, balancing the optimisation of the machine performance, physics output and territorial constraints. In addition, work is ongoing to develop a sustainable operational model for FCC taking into account human and financial resources and striving to minimise its environmental impact. Ongoing testing and prototyping work on key FCC-ee technologies will demonstrate the technical feasibility of this machine, while parallel R&D developments on high-field magnets pave the way to FCC-hh.
Physics programme A central element of the overall FCC physics programme is the precise study of the Higgs sector. FCC-ee would provide model-independent measurements of the Higgs width and its coupling to Standard Model particles, in many cases with sub-percent precision and qualitatively different to the measurements possible at the LHC and HL-LHC. The FCC-hh stage has unique capabilities for measuring the Higgs-boson self-interactions, profiting from previous measurements at FCC-ee. The full FCC programme thus allows the reconstruction of the Higgs potential, which could give unique insights into some of the most fundamental puzzles in modern cosmology, including the breaking of electroweak symmetry and the evolution of the universe in the first picoseconds after the Big Bang.
Presentations and discussions throughout the week showed the impressive breadth of the FCC programme, extending far beyond the Higgs factory alone. The large integrated luminosity to be accumulated by FCC-ee at the Z-pole enables high-precision electroweak measurements and an ambitious flavour-physics programme. While the latter is still in the early phase of development, it is clear that the number of B mesons and tau-lepton pairs produced at FCC-ee significantly surpasses those at Belle II, making FCC-ee the flavour factory of the 2040s. Ongoing studies are also revealing its potential for studying interactions and decays of heavy-flavour hadrons and tau leptons, which may provide access to new phenomena including lepton-flavour universality-violating processes. Similarly, the capabilities of FCC-ee to study beyond-the-Standard Model signatures such as heavy neutral leptons have come into further focus. Interleaved presentations on FCC-ee, FCC-hh and FCC-eh physics also further intensified the connections between the lepton- and hadron-collider communities.
The impressive potential of the full FCC programme is also inspiring theoretical work. This ranges from overarching studies on our understanding of naturalness, to concrete strategies to improve the precision of calculations to match the precision of the experimental programme.
The physics thrusts of the FCC-ee programme inform an evaluation of the run plan, which will be influenced by technical considerations on the accelerator side as well as by physics needs and the overall attractiveness and timeliness of the different energy stages (ranging from the Z pole at 91 GeV to the tt threshold at 365 GeV). In particular, the possibility for a direct measurement of the electron Yukawa coupling by extensive operation at the Higgs pole (125 GeV) raises unrivaled challenges, which will be further explored within the FCC feasibility study. The main challenge here is to reduce the spread in the centre-of-mass energy by a factor of around ten while maintaining the high luminosity, requiring a monochromatisation scheme long theorised but never applied in practice.
Detectors status and plan Designing detectors to meet the physics requirements of FCC-ee physics calls for a strong R&D programme. Concrete detector concepts for FCC-ee were discussed, helping to establish a coherent set of requirements to fully benefit from the statistics and the broad variety of physics channels available.
The primary experimental challenge at FCC-ee is how to deal with the extremely high instantaneous luminosities. Conditions are the most demanding at the Z pole, with the luminosity surpassing 1036 cm-2s-1 and the rate of physics events exceeding 100 kHz. Since collisions are continuous, it is not possible to employ “power pulsing” of the front-end electronics as has been developed for detector concepts at linear colliders. Instead, there is a focus on the development of fast, low-power detector components and electronics, and on efficient and lightweight solutions for powering and cooling. With the enormous data samples expected at FCC-ee, statistical uncertainties will in general be tiny (about a factor of 500 smaller than at LEP). The experimental challenge will be to minimise systematic effects towards the same level.
The mind-boggling integrated luminosities delivered by FCC-ee would allow Standard Model particles – in particular the W, Z and Higgs bosons and the top quark, but also the b and c quarks and the tau lepton – to be studied with unprecedented precision. The expected number of Z bosons produced (5×1012) is more than five orders of magnitude larger than the number collected at LEP, and more than three orders of magnitude larger than that envisioned at a linear collider. The high-precision measurements and the observation of rare processes made possible by these large data samples will open opportunities for new-physics discoveries, including the direct observation of very weakly-coupled particles such as heavy-neutral leptons, which are promising candidates to explain the baryon asymmetry of the universe.
With overlapping requirements, designs for FCC-ee can follow the example of detectors proposed for linear colliders.
The detectors that will be located at two (possibly four) FCC-ee interaction points must be designed to fully profit from the extraordinary statistics. Detector concepts under study feature: a 2 T solenoidal magnetic field (limited in strength to avoid blow-up of the low-emittance beams crossing at 30 mrad); a small-pitch, thin-layers vertex detector providing an excellent impact-parameter resolution for lifetime measurements; a highly transparent tracking system providing a superior momentum resolution; a finely segmented calorimeter system with excellent energy resolution for electrons and photons, isolated hadrons and jets; and a muon system. To fully exploit the heavy-flavour possibilities, at least one of the detector systems will need efficient particle-identification capabilities allowing π/K separation over a wide momentum range, for which there are ongoing R&D efforts on compact, light RICH detectors.
With overlapping requirements, designs for FCC-ee can follow the example of detectors proposed for linear colliders. The CLIC-inspired CLD concept – featuring a silicon-pixel vertex detector and a silicon tracker followed by a 3D-imaging, highly granular calorimeter system (a silicon-tungsten ECAL and a scintillator-steel HCAL) surrounded by a superconducting solenoid and muon chambers interleaved with a steel return yoke – is being adapted to the FCC-ee experimental environment. Further engineering effort is needed to make it compatible with the continuous-beam operation at FCC-ee. Detector optimisation studies are being facilitated by the robust existing software framework which has been recently integrated into the FCC study.
The IDEA (International Detector for Electron-positron Accelerator) concept, specifically developed for a circular electron-positron collider, brings in alternative technological solutions. It includes a five-layer vertex detector surrounded by a drift chamber, enclosed in a single-layer silicon “wrapper”. The distinctive element of the He-based drift chamber is its high transparency. Indeed, the material budget of the full tracking system, including the vertex detector and the wrapper, amounts to only about 5% (10%) of a radiation length in the barrel (forward) direction. The drift chamber promises superior particle-identification capabilities via the use of a cluster-counting technique that is currently under test-beam study. In the baseline design, a thin low-mass solenoid is placed inside a monolithic, 2 m-deep, dual-readout fibre calorimeter. An alternative (more expensive) design also features a finely segmented crystal ECAL placed immediately inside the solenoid, providing an excellent energy resolution for electrons and photons.
Recently, work has started on a third FCC-ee detector concept comprising: a silicon vertex detector; a light tracker (drift chamber or full-silicon device); a thin, low-mass solenoid; a highly-granular noble liquid-based ECAL; a scintillator-iron HCAL; and a muon system. The current baseline ECAL design is based on lead/steel absorbers and active liquid-argon, but a more compact option based on tungsten and liquid-krypton is an interesting option. The concept design is currently being implemented inside the FCC software framework.
All detector concepts are under evolution and there is ample room for further innovative concepts and ideas.
Closing remarks Circular colliders reach higher luminosities than linear machines because the same particle bunches are used over many turns, while detectors can be installed at several interaction points. The FCC-ee programme greatly benefits from the possibility of having four interaction points to allow the collection of more data, systematic robustness and better physics coverage — especially for very rare processes that could offer hints as to where new physics could lie. In addition, the same tunnel can be used for an energy-frontier hadron collider at a later stage.
The FCC feasibility study will be submitted by 2025, informing the next update of the European strategy for particle physics. Such a machine could start operation at CERN within a few years after the full exploitation of the HL-LHC in around 2040. CERN, together with its international partners, therefore has the opportunity to lead the way for a post-LHC research infrastructure that will provide a multi-decade research programme exploring some of the most fundamental questions in physics. The geographical distribution of participants in the 5th FCC physics workshop testifies to the global attractiveness of the project. In addition, the ongoing physics and engineering efforts, the cooperation with the host states, the support from the European physics community and the global cooperation to tackle the open challenges of this endeavour, are reassuring for the next steps of the FCC feasibility study.
In the 1970s, the study of low-energy (few GeV) hadron–hadron collisions in bubble chambers was all the rage. It seemed that we understood very little. We had the SU(3) of flavour, Regge theory and the S-matrix to describe hadronic processes, but no overarching theory. Of course, theorists were already working on perturbative QCD and this started to gain traction when experimental results from the Big European Bubble Chamber at CERN showed signs of the scaling violations and made an early measurement of the QCD scale, ΛQCD. We have been living with the predictions of perturbative QCD ever since, at increasingly higher orders. But there have always been non-perturbative inputs, such as the parton distribution functions.
Hadron Form Factors: From Basic Phenomenology to QCD Sum Rules takes us back to low-energy hadron physics and shows us how much more we know about it today. In particular, it explores the formalism for heavy-flavour decays, which is particularly relevant at a time when it seems that the only anomalies we observe with respect to the Standard Model appear in various B-meson decays. It also explores the connections between space-like and time-like processes in terms of QCD sum rules connecting perturbative and non-perturbative behaviour.
The book takes us back to low-energy hadron physics and shows us how much more we know about it today
The general introduction reminds us of the formalism of form factors in the atomic case. This is generalised to mesons and baryons in chapters 2 and 3, after the introduction of QCD in chapter 1, with an emphasis on quark and gluon electroweak currents and their generalisation to effective currents. Hadron spectroscopy is reviewed from a modern perspective and heavy-quark effective theory is introduced. In chapter 2, the formalism for the pion form factor, which is related to the pion decay constant, is introduced via e-π scattering. Due emphasis is placed on how one may measure these quantities. I also appreciated the explanation of how a pseudoscalar particle such as the pion can decay via the axial vector current – a question
often raised by smart undergraduates. (Clue: the axial vector current is not conserved). Next, the πe3 decay is considered and generalised to K-, D- and B-meson semileptonic decays. Chapter 3 covers the baryon form factors and their decay constants, and chapter 4 considers hadronic radiative transitions. Chapter 5 relates the pion form factor in the space-like region to its counterpart in the time-like region in e+e– → π+π–, where one has to consider resonances and widths. Relationships are developed, whereby one can see that by measuring pion and kaon form factors in e+e– scattering one can predict the widths of decays such as τ → ππν and τ → KKν. In chapter 6, non-local hadronic matrix elements are introduced to extend the formalism to deal with decays such as π → γγ and B → Kμμ.
The book shifts gears in chapters 7–10. Here, QCD is used to calculate hadronic matrix elements. Chapter 7 covers the calculation of the form factors in the infinite momentum frame, whereby the asymptotic form factor can be expressed in terms of the pion decay constant and a pion distribution amplitude describing the momentum distribution between two valence partons in the pion. In chapter 8, the QCD sum rules are introduced. The two-point correlation of quark current operators can be calculated in perturbative QCD at large space-like momenta, and the result is expressed in terms of perturbative contributions and the QCD vacuum condensates. This can then be related through the sum rule to the hadronic degrees of freedom in the time-like region. Such sum rules are used to gain information on both condensate densities or quark masses from accurate hadronic data and hadronic decay constants and masses from QCD calculations. The connection is made to parton–hadron duality and to the operator product expansion. Some illustrative examples of the technique, such as the calculation of the strange-quark mass and the pion decay constant, are also given. Chapter 9 concerns the light-cone expansion and light-cone dominance, which is then used to explain the role of light-cone sum rules in chapter 10. The use of these sum rules in calculating hadron form factors is illustrated with the pion form factor and also with the heavy-to-light form factors necessary for B → π, B → K, D → π, D → K and B → D decays.
Overall, this book is not an easy read, but there are many useful insights. This is essentially a textbook, and a valuable reference work that belongs in the libraries of particle-physics institutes around the world.
Billed as a bizarre adventure filled with brain-tickling facts about particles and science wonders, Your Adventures at CERN invites young audiences to experience a visit to CERN in different guises.
The reader can choose one of three characters, each with a different story: a tourist, a student and a researcher. The stories are intertwined, and the choice of the reader’s actions through the book changes their journey, rather than following a linear chronology. The stories are filled with puzzles, mazes, quizzes and many other games that challenge the reader. Engaging physics references and explanations, as well as the solutions to the quizzes, are given at the back of the book.
Author Letizia Diamante, a biochemist turned science communicator who previously worked in the CERN press office, portrays the CERN experience in an engaging and understandable way. The adventures are illustrated with funny jokes and charismatic characters, such as “Schrödy”, a hungry cat that guides the reader through the adventures in exchange for food. Detailed hand-drawn illustrations by Claudia Flandoli are included, together with photographs of CERN facilities that take the reader directly into the heart of the lab. Moreover, the book includes several historical facts about particle physics and other topics, such as the city of Geneva and the extinct dinosaurs from the Jurassic era, which is named after the nearby Jura mountains on the border between France and Switzerland. A particle-physics glossary and extra information, such as fun cooking recipes, are also included at the end.
Although targeted mainly at children, this book is also suitable for teenagers and adults looking for a soft introduction to high-energy physics and CERN, offering a refreshing addition to the more mainstream popular particle-physics literature.
Stephon Alexander is a professor of theoretical physics at Brown University, specialising in cosmology, particle physics and quantum gravity. He is also a self-professed outsider, as the subtitle of his latest book Fear of a Black Universe suggests. His first book, The Jazz of Physics, was published in 2016. Fear of a Black Universe is a rallying cry for anyone who feels like a misfit because their identity or outside-the-box thinking doesn’t mesh with cultural norms. By interweaving historical anecdotes and personal experiences, Alexander shows how outsiders drive innovation by making connections and asking questions insiders might dismiss as trivial.
Alexander is Black and internalised his outsider sense early in his career. As a postdoc in the early 2000s, he found that his attempts to engage with other postdocs in his group were rebuffed. He eventually learned from his friend Brian Keating, who is white, the reason why: “They feel that they had to work so hard to get to the top and you got in easily, through affirmative action”. Instead of finding his peers’ rejection limiting, Alexander reinterpreted their dismissal as liberating: “I’ve come to realise that when you fit in, you might have to worry about maintaining your place in the proverbial club… so I eventually became comfortable being the outsider. And since I was never an insider, I didn’t have to worry that colleagues might laugh at me for my unlikely approach.”
Instead of finding his peers’ rejection limiting, Alexander reinterpreted their dismissal as liberating
Alexander argues that true breakthroughs come from “deviants”. He draws parallels between outsiders in physics and graffiti artists, who were considered vandals until the art world recognised their talent and contributions. Alexander recounts his own “deviance” in a humorous and sometimes self-deprecating manner. He recalls a talk he gave at a conference about his first independent paper, which involved reinterpreting the universe as a three-dimensional membrane orbiting a five-dimensional black hole. During the talk he was often interrupted, eventually prompting a well-respected Indian physicist to stand up and shout “Let him finish! No one ever died from theorising.”
Alexander took these words to heart, and asks his readers to do the same during the speculative discussions in the second part of his book. Here, Alexander intersperses mainstream physics with some of his self-described “strange” ideas, acknowledging that some readers might write him off as an “oddball crank”. He explores the intersection of physics with philosophy, biology, consciousness, and searches for extraterrestrial life. Some sections – such as the chapter on alien quantum computers generating the effect of dark energy – feel more like science fiction than science. But Alexander reassures readers that, while many of his ideas are strange, so are many experimentally verified tenants of physics. “In fact, the likelihood that any one of us will create a new paradigm because we have violated the norms… is very slim” he observes.
Science wise, this book is not for the faint-hearted. While many other public-facing physics books slowly wade readers into early-20th-century physics and touch on more abstract concepts only in the final chapters, part I of Fear of a Black Universe dives directly into relativity, quantum mechanics and emergence. Part II then launches into a much deeper discussion about supersymmetry, baryogenesis, quantum gravity and quantum computing. But the strength of Alexander’s new work isn’t in its retellings of Einstein’s thought experiments or even its deconstruction of today’s cosmological enigma. More than anything, this book makes a case for cultivating diversity in science that goes beyond “gesticulations of identity politics”.
Fear of a Black Universe is both mind-bending and refreshing. It approaches physics with a childlike curiosity and allows the reader to playfully contemplate questions many have but few discuss for fear of sounding like a crank. This book will be enjoyable for scientists and science enthusiasts who can set cultural norms aside and just enjoy the ride.
What attracted you to the position of DESY director of particle physics?
DESY is one of the largest and most important particle-physics laboratories in the world. I was born and grew up in Hamburg and took my first career steps at DESY during my university studies. I received my PhD there in 1999 and returned as a scientist in 2016, so I know the lab very well. It is a great lab and department, with many opportunities and so many excellent people. I am sure it will be fun to work with all of them and to develop a strategy for the future.
What previous management roles do you think will serve you best at DESY?
Being ATLAS deputy spokesperson from 2013 to 2017 was one of the best roles I’ve had in my career, and I benefitted hugely from the experience. I was fortunate to have an excellent spokesperson in Dave Charlton and I learned a lot from him, as well as from many others I worked with. I try to understand enough details to make educated decisions but not to micromanage. I also think motivating people, listening to them and promoting their talents is key to achieving common goals.
What are the current and upcoming experiments at DESY?
The biggest on-going experimental activities in particle physics are the ATLAS and CMS experiments. We have large groups in both, and for each we are building a tracker end-cap based on silicon-strip detectors at our detector assembly facility, primarily together with German universities. This is a huge undertaking that is currently ongoing for the HL-LHC. Another important activity is to build a vertex detector to be installed in 2023 at the Belle II experiment running at KEK in Japan. We also have a significant programme of local experiments covering axion searches. One of the big projects next summer will be the start of the ALPS II experiment, which will look for axion-like particles by shining an intense laser on a “wall” and seeing if any laser photons appear on the other side, having been transformed into axions by a large magnetic field. We have two other axion experiments planned: BabyIAXO, which looks for axion-like particles coming from the Sun, for which construction is now starting; and MadMax, which looks for axions in the dark-matter halo. Axions were postulated by Peccei and Quinn to solve the strong-CP problem but are also a good candidate for dark matter if they exist. A further experiment, which DESY theorist Andreas Ringwald and I proposed, LUXE, would deliver the European XFEL 16.5 GeV electron beam into a high-intensity laser so that the beam electrons experience a very strong electromagnetic field within their rest frame. LUXE would reach the so-called Schwinger limit, and allow us to see what happens when QED becomes strong and transitions from the perturbative to the non-perturbative regime.
There are many accelerators at DESY, such as PETRA, where the gluon was discovered in the 1970s. Today, PETRA is one of the best synchrotron-radiation facilities in the world and is used for a wide range of science, for example imaging of small structures such as viruses. It is an application of accelerators where the impact on society is more direct and obvious than it is in particle physics.
How can we increase the visibility of particle physics to society?
This is a very important point. The knowledge we get from particle physics today is clear, but it is less clear how we can transfer this knowledge to help solve pressing problems in society, such as climate change or a pandemic. Humankind desires to increase its knowledge, and it is important that we continue with fundamental research purely to increase our knowledge. We have already come so far in the past 5000 years. And, many technical innovations were made for that purpose alone but then resulted in transformative changes. Take the idea of the accelerator. It was developed at Berkeley during the 1930s with no particular application in mind, but today is used routinely around the world to prolong life by irradiating tumours. Or the transistor, without which there would not be any computers, which was developed in the 1920s based on the then-emerging understanding of atoms. It is important to promote both targeted research that directly addresses problems as well as fundamental research, which every now and again will result in groundbreaking changes. When thinking about our projects and experiments we need to keep in mind if and how any of our technical developments can be made in a way that addresses big societal problems.
It is important that we inspire the general public, in particular the young, about science. Educational programmes are key, such as Beamline for Schools, which is one of CERN’s flagship schemes. This was hosted by DESY during Long Shutdown 2 and a team at DESY will continue the collaboration.
CERN recently launched its Quantum Technology Initiative. Does DESY have plans in this area?
DESY received funding from the state of Brandenburg to build a centre for quantum computing, the CTQA, which is located at DESY’s Zeuthen site. Karl Jansen, one of our scientists there, has spent most of his life working on lattice QCD calculations and is leading this effort. I myself am involved in research using quantum computing for particle tracking at the LUXE experiment. The layout of the tracker for this experiment is simpler compared to the LHC experiments, which is why we want to do it here first. We have to understand how to use quantum computers in conjunction with classical computers to solve actual problems efficiently. There is no doubt that quantum computing solves questions that are otherwise not possible, and we also think they will be able to solve problems more efficiently by using less resources compared to classical machines. That could also contribute to reducing the impact of computing on climate change.
What was your participation in the 2020 update of the European strategy for particle physics (ESPPU) and how have things progressed since?
It was exciting to be part of the ESPPU drafting process. I was very impressed by the sincerity and devotion of the people in the hall in Bad Honnef when the process concluded. There was a lot of respect and understanding of the different views on how to balance the scientific ambitions with the realities of funding, R&D needs and other factors.
The ESPPU recommended first and foremost to complete the HL-LHC upgrade. This is a big undertaking and demands our focus. For the future, an electron-positron Higgs factory is the highest priority, in addition to ramping up accelerator R&D. Last year an accelerator R&D roadmap was prepared following the ESPPU recommendation. Very different directions are laid out, and now the task is to understand how to prioritise and streamline the different directions, and to ensure the relevant aspects are progressing significantly by the next update (probably in 2026). For instance CERN’s main focus is R&D on the next generation of magnets for a new hadron machine, while DESY has a strong progamme in plasma-wakefield accelerators for electron machines. But both DESY and CERN are also contributing to other aspects and there are other labs and universities in Europe which make important contributions. At DESY we also try to exploit synergies between developing new accelerators for photon science and high-energy physics.
What is the best machine to follow the LHC?
The next machine needs to be a collider that can measure the Higgs properties at the per-cent and even in some cases the per-mille level – a Higgs factory. In addition to the excellent scientific potential, factors to consider are timescale and cost, but also making it a “green” accelerator and considering its innovation potential. Finding a good balance there is not easy, and there are several proposals that were studied as part of the ESPPU.
What are your three most interesting open questions in particle physics?
Mine are related to the Higgs boson. One is the matter–antimatter asymmetry, because the exact form of the electroweak phase transition is closely related to the Higgs field. If it was a smooth transition, it cannot explain the matter–antimatter asymmetry; if it was violent, it could potentially be able to explain it. We should be able to learn something about this with the HL-LHC, but to know for sure we need a future collider. The second question is why is there a muon? Flavour physics fascinates me, and the Higgs-boson is the only particle that distinguishes between the electron, the muon and the tau, which is why I would like to study it extensively. The third question is what is dark matter? One intriguing possibility is that the Higgs boson decays to dark-matter particles, and with a Higgs factory we could measure this, even if it only happens for 0.3% of all Higgs bosons. The Higgs boson is so important for understanding our universe, that’s why we need a Higgs factory, although we will already learn a lot from the LHC and HL-LHC.
Today, women make up more than 30% of the scientists at DESY, whereas in 2005 it was less than 10%
Is the community doing a good job in communicating beyond the field?
It is crucial that scientists communicate scientific facts, especially now when there are “post-truth” tendencies in society. We have a duty as people who are publicly funded to communicate our work to the public. Many people are excited about the origin of the universe and the fundamental laws of physics we are studying. Activities such as the CERN and DESY open days attract many visitors. We also see really good turnouts at public lectures as well as during our “science on tap” activity in Hamburg. I gave a talk about the first minutes of the universe, and the bar was packed and people had many questions during one of these events. We should all spend some of our time communicating science. Of course, we have to mostly do the actual research, otherwise we do not have anything to communicate.
You are the first female director in DESY’s 60-year history. What do you think about the situation for women in physics, for instance the “25 by ‘25” initiative?
The 25 by ‘25 initiative is good. We have been fortunate at DESY that there was a strong drive from the German government. Research funding has increased a lot during the past 10–15 years and there was dedicated funding available to attract women to large research centres. Today, women make up more than 30% of the scientists at DESY, whereas in 2005 it was less than 10%. Having special programmes unfortunately appears to be necessary as change happens too slowly by itself otherwise. Having women in visible roles in science is important. I myself was inspired by several women in particle physics, such as Beate Naroska, the only female professor at the physics department when I was a student, Young-Kee Kim, who was spokesperson of the CDF experiment when I was a postdoc and later deputy-director of Fermilab, and last but not least Fabiola Gianotti, who was spokesperson of ATLAS when I joined and is now the Director-General of CERN.
The COVID-19 pandemic has cost more than five million lives and disrupted countless more. Without the results of decades of curiosity-driven research, however, the situation would have been much worse. The pandemic therefore serves as a stark and brutal reminder of the links between basic science and the balanced, sustainable and inclusive development of our planet.
The International Year of Basic Sciences for Sustainable Development (IYBSSD), proclaimed by the United Nations (UN) general assembly on 2 December 2021, is a key moment of mobilisation to convince economic and political leaders, as well as the public, of the critical links between basic research and the 2030 Agenda for Sustainable Development adopted by all UN member states in 2015. Due to their evidence-based nature, universality and openness, basic sciences not only contribute to expanding knowledge and improving societal welfare, but also help to reduce societal inequality, improve inclusion and foster intercultural dialogue and peace. They are thus central in achieving the UN Agenda’s 17 Sustainable Development Goals.
Virtuous circle
Many examples of basic sciences’ transformative contribution to society are so widespread that they are taken for granted. The web was born at CERN from the needs of global particle physics; general relativity underpins the global positioning system; search engines and artificial intelligence rely on brilliant mathematics and statistical methods; mobile phones derive from the discovery of transistors; and Wi-Fi from developments in astronomy. The discovery of DNA, positron emission tomography, magnetic resonance imaging and radiotherapy have transformed medical diagnostics and treatments, while advances in basic physics, chemistry and materials science are reducing pollution and revolutionising the generation and storage of renewable energy.
Basic science, together with applied scientific research and technological applications, is thus one of the key elements of the virtuous circle that allows the sustainable development of society. Yet, basic sciences are often not as prominent as they should be in discussions concerning societal, environmental and economic development. The aims of the IYBSSD are to focus global attention on the enabling role of basic science and to improve the collaboration between basic sciences and policy-making.
Particle physics has a major role to play in making the IYBSSD a success
The IYBSSD, led by the International Union of Pure and Applied Physics – which will celebrate its centenary in 2022 – has received strong support from around 30 international science unions and organisations active in physics, mathematics, chemistry, life science and social science, along with 70 national and international academies of sciences, and 30 Nobel laureates and Fields medallists. A series of specific activities coordinated at local, national and international levels will aim to promote inclusive collaboration (with special attention paid to gender balance), enhance basic-science training and education, and encourage the full implementation of open-access publishing and open data in the basic sciences.
The IYBSSD inauguration ceremony will take place at UNESCO on 8 July, and a closing ceremony is planned to take place at CERN in 2023, hopefully timed with the completion of the Science Gateway building. Events of all sorts proposed by countries, territories, scientific unions, organisations and academies endorsed by the steering committee will occur throughout the year.
The role of particle physics
As one of the most basic sciences of all, particle physics has a major role in making the IYBSSD a success. The high-energy physics community should use all the available opportunities in 2022 and 2023, be it through conferences, workshops, collaboration meetings or other activities, to place our field under the auspices of the IYBSSD. We need to show how this community advances science for the benefit of society, how much it re-enchants our world and therefore makes it worth sustaining, how much it contributes in its practice to openness, equity, diversity and inclusion, and to multicultural dialogue and peace. The CERN model is emblematic of these contributions. Many of the programmes of the CERN & Society foundation also promote these values in line with the IYBSSD objectives.
The need for humanity to maintain and develop high levels of interest and participation in basic sciences makes awareness-raising initiatives such as the IYBSSD critical. Following the recent international years of physics, chemistry, mathematics and astronomy, it is now time for us to get behind this unprecedented, global interdisciplinary initiative
Italian theoretical physicist Luciano Girardello passed away in January, aged 84. He made important contributions to quantum field theory, supersymmetry and supergravity, and will always be remembered by friends and colleagues for his irony, vision and great humanity.
Born on 10 September 1937, Luciano graduated at the University of Milano. After a first postdoctoral fellowship at Boulder, Colorado, he worked at many institutions across the world, including Harvard University, the École normale supérieure in Paris and CERN. Upon his return to Italy, he became professor at the University of Milano, where he spent several years, and in 2000 he moved to the new University of Milano-Bicocca, contributing to the creation of its physics department, where he remained for the rest of his career.
Luciano was one of the first to study the mechanisms of supersymmetry breaking, rooting the theory in reality
Luciano was interested in all aspects of fundamental physics, from quantum field theory to gravity, and made seminal contributions to the foundations of supersymmetry and supergravity in their early days. In a fruitful collaboration with other pioneers of the subjects, including Eugène Cremmer, Sergio Ferrara and Antoine Van Proeyen, he investigated the coupling of matter in supergravity, which is fundamental for the experimental search for supersymmetry, the modern theory of gravitation and the effective theories of string compactifications. Luciano was one of the first to study the mechanisms of supersymmetry breaking, rooting the theory in reality. In the final part of his career, he applied the AdS/CFT correspondence, or gauge/gravity duality, to the understanding of fundamental problems in quantum field theory. He was not interested in theoretical speculations or mathematical tricks but rather in understanding the nature of things and in the cross-fertilisation of fields and ideas. Many of his contributions to physics were born in the corridors of the CERN theory division, in long days and endless nights spent with friends and collaborators.
Luciano’s wide and original lectures on different topics at the universities of Milano and Milano-Bicocca inspired students for more than 30 years. His deep thoughts, vision and culture also informed and educated many generations of talented young physicists who are now active in the international arena. Greatly admired as a physicist, he will be remembered by those who had the good fortune to know him well as a great human being, a cultivated and refined person, and an old-time gentleman.
Patricia McBride, distinguished scientist at Fermilab, has been elected as the next spokesperson of the CMS collaboration. She will take over from current spokesperson Luca Malgeri in the autumn, becoming the first woman to lead the 3000-strong collaboration.
McBride graduated in physics at Carnegie Mellon University, and completed a PhD at Yale analysing charm decays at Fermilab’s E630 experiment. After a postdoc at Harvard working on the Crystal Ball experiment at DESY and the L3 experiment at CERN, she joined Fermilab in 1994, later becoming head of its scientific computing programmes and head of the Particle Physics Division. Since joining CMS in 2005, she has served as deputy head of CMS Computing, head of the CMS Center at Fermilab and as US CMS Operations programme manager. She was deputy CMS spokesperson from 2018 to 2020.
It will be a challenging, but exciting time for the collaboration
Patricia McBride
Among other appointments, McBride was chair of the American Physical Society (APS) Division of Particles and Fields, the US Liaison Committee of the International Union of Pure and Applied Physics (IUPAP) and the IUPAP Commission for Particles and Fields. In 2009 she was elected as an APS fellow for her original contributions to flavour physics at LEP and the Tevatron, and for the development of major new initiatives in B physics and collider physics.
McBride’slove for particle physics started at the end of middle school when her mother gave her a book about particle accelerators. She will take up the leadership of CMS soon after LHC Run 3 gets under way, and is therefore looking forward to exciting times ahead: “CMS is looking forward to the Run-3 physics programme and at the same time will be pushing to keep the detector upgrades for the HL-LHC on track,” she says. “It will be a challenging, but exciting time for the collaboration.”
Experimental particle physicist David Saxon passed away on 23 January. A native of Stockport, south of Manchester, where his father was a parish minister, he attended the University of Oxford and obtained his doctorate measuring pion–nucleon scattering at the Rutherford Laboratory, followed by a short postdoc there. His doctoral research took him to Paris and Berkeley, where in both cases he reported that his arrival was marked by the onset of student riots.
After a period at Columbia University, he moved to Illinois to work in Leon Ledermann’s group at the newly built Fermilab. Here he helped to develop electron and muon identification techniques, which would prove fruitful in future electroweak experiments. The group did not discover the W and Z, but did find a signal that was later associated with charm mesons. Returning to Rutherford, soon to be Rutherford Appleton Laboratory (RAL), in 1974 David was quickly promoted to senior researcher. Realising that the future lay in “counter” physics, rather than bubble chambers, he worked on hadron–proton scattering in the resonance region. With the PETRA collider at DESY announced soon afterwards, David helped to form the UK contribution to the TASSO experiment, which made important measurements of electron–positron scattering. The PETRA experiments would go on to discover the gluon, enabling the Standard Model to be constructed with confidence.
After PETRA came HERA, which remains the world’s only high-energy electron–proton collider. David first led the RAL team working on the central tracking detector for the ZEUS experiment, but it was not long before he was invited to the newly reinstituted Kelvin professorship at the University of Glasgow, where he arrived in 1990 and spent the remainder of his academic career. He built the group significantly, its present healthy state founded on what he achieved. In addition to taking Glasgow into ZEUS, he nurtured many other activities – in particular involvement in the ALEPH experiment at LEP – and was instrumental in the design of central tracking systems for projects that eventually combined to become ATLAS.
David was instrumental in the design of central tracking systems for projects that eventually combined to become ATLAS
He was hardly installed in Glasgow before being appointed for several years as chair to the UK’s former Particle Physics Committee. There was no more important position to hold at the time, and David’s good sense, insight and intelligence helped to enable the subject to survive and prosper during a time when funding was tight and the UK funding system was being reorganised. Undaunted, he convinced the group in Glasgow that now was an excellent opportunity to host the 1994 edition of ICHEP.
David was one of the most sociable of people, always a good team player and invariably provocative and stimulating in conversation. Inevitably, the call came to move higher up in the university, first as a highly regarded head of department and later as dean of the science faculty – a post he occupied until shortly before his retirement. Meanwhile, he served on numerous local, national and international committees, including the UK CERN delegation and CERN policy committees, where his perceptiveness was always in demand. The UK recognised his distinguished and important contributions to science with the award of an OBE.
It was a sadness that his final years were marked by Parkinson’s disease, but he still participated in CERN Council meetings. He was at all times supported by his wife Margaret, with whom he had a son and a daughter, and found strength and comfort in his church membership. Those who were fortunate enough to know and work with David will never forget his positive and energetic character, always fair-minded, competitive without being aggressive, and caring. He will be much missed, and inspirational memories will remain.
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