Maria Fidecaro, an experimental physicist who joined CERN in 1957, passed away on 17 September. Maria was a familiar face to the CERN community until long into her retirement, often seen arm-in-arm with her husband Giuseppe as they made their way through the CERN corridors. She was also well-known to CERN visitors, featuring prominently in the Synchrocyclotron exhibition’s film.
Born in Rome in 1930, Maria completed her university studies at La Sapienza in 1951. There she met Giuseppe, and the pair studied cosmic rays at the Tête Grise laboratory located on the Matterhorn. In 1954 she obtained a fellowship from the International Federation of University Women and joined her future husband at the University of Liverpool developing techniques and experiments for the Synchrocyclotron, CERN’s first accelerator.
In summer 1956 the couple moved to Geneva, joining only a few hundred people at CERN, which had been established just two years earlier. Maria obtained a CERN fellowship in 1957 and began working in a team of three that was developing a novel method to provide polarised proton beams at the Synchrocyclotron – techniques that she would later adapt to carry out polarisation experiments at the Proton Synchrotron and the Super Proton Synchrotron (SPS). She remained at CERN for the rest of her career, where her early research interests included charge–exchange nucleon–nucleon scattering and proton–proton elastic scattering.
In the 1980s Maria participated in the WA78 experiment at the SPS, which was dedicated to the production of bb pairs. She then worked on detectors and analysis for the CPLEAR experiment, which was designed to enable precision measurements of CP, T and CPT violation in the neutral kaon system. She designed and led the construction of a high-granularity electromagnetic calorimeter, helping CPLEAR to achieve new levels of precision in the study of fundamental symmetries.
From 1991 to 1995 Maria was group leader of the CPL group in the Particle Physics Experiments division. She also took part in the NA48/2 experiment, searching for CP violation in the decay of charged kaons, and contributed to the early phases of NA62.
Maria celebrated her retirement in 1995, but continued her work at CERN as an honorary member of the personnel. She had a reserved attitude in all circumstances and a deep sense of duty to the community. As Maria explained in an interview in 2012, “every day or every week there is something new connected with our old work”.
Theoretical physicist Michel Gaudin, known for his influential works in the domain of integrable models, passed away on 4 August. Michel entered L’Ecole Polytechnique in 1951 and obtained his PhD in 1967 at the Université de Paris. In his PhD thesis he found a solution, given simultaneously in the famous paper by C N Yang, to the Fermi gas with delta-function interaction, introducing what was later called the nested or higher-level Bethe ansatz. Except for a year spent visiting Yang at Stony Brook in 1970, he spent all his scientific life at the fundamental research division of the Commissariat de l’Energie Atomique (CEA-Saclay).
Michel used only French as a scientific language and a significant part of his research remained unpublished. The publication of his book La fonction d’onde de Bethe in 1983 was thus a major event, remaining an inspiring and pedagogical source of a variety of original information that cannot be found anywhere else. Translated into Russian in 1987 and English in 2013, it is considered a classic in the field.
One of the most well-known of his findings is the so-called Gaudin determinant for the norm of the Bethe eigenstates, which now plays a fundamental role in the computation of correlation functions. In another essential work, following the method of C N Yang and C P Yang, Michel solved the thermodynamics of the Heisenberg–Ising ring, simultaneously with Takahashi. He also diagonalised a class of quadratic Hamiltonians in spin variables, now referred to as the Gaudin model, and considered various extensions, in particular a system comprising a single oscillator coupled to a collection of independent two-level atoms, which has become a classic in the cold-atom and Bardeen–Cooper–Schrieffer communities. In addition, his pioneering early works on random matrices with M L Mehta introduced elegant and powerful new methods that played a key role in many developments in random matrix theory, with applications ranging from nuclear physics to non-critical string theories.
An original and prolific personality, Michel was principally guided by a quest for elegance. Although he cared little for recognition, in 2019 he was awarded the prestigious Dannie Heineman Prize for Mathematical Physics.
Michel Gaudin was a man of high integrity and modesty whose life was completely devoted to science. He was known for his rigour and reclusive style of work, but when approached by his colleagues, he generously shared his knowledge and insights.
On 14 June, Roman Jackiw, one of the most brilliant and profound theorists of his generation, passed away at the age of 83.
Roman Jackiw graduated from Cornell University in 1966 under the supervision of Ken Wilson, moving to Harvard as a junior fellow until 1969. Thereafter, he was a member of the Centre for Theoretical Physics at MIT. Having myself been a postdoc at MIT from 1968 to 1972, we got to know each other well and kept in touch since.
During the Harvard period, while visiting CERN, he wrote, together with John Bell, what is arguably his most famous paper. It became known as the Adler–Bell–Jackiw (ABJ) anomaly. Here “anomaly” stands for a symmetry that, while classically exact, is broken by quantum mechanical effects. This breaking makes it possible for the neutral pion to decay, as observed, into two photons. Another version of the ABJ anomaly, in the context of the strong interaction, provides a solution of the so-called U(1) problem: the absence of a ninth light pseudoscalar meson besides the π, K and η. Indeed, the relatively heavy η′ meson gets most of its mass through the ABJ anomaly and some topologically non-trivial gauge-field configurations.
Later, together with Claudio Rebbi of Boston University, Jackiw introduced the concept of theta-vacua in quantum chromodynamics by which the strong interaction, because of the above-mentioned non-trivial topology, depends on a somewhat hidden angular parameter, θ. Unless vanishing, the θ parameter introduces violations of time-reversal symmetry and, consequently, an electric dipole moment of the neutron for which very strong experimental upper bounds exist.
Interestingly, the combination of these two remarkable contributions by Jackiw imply what is perhaps the only serious theoretical tension facing the Standard Model today. Its resolution calls for the existence of a new particle, the axion, which turns out to also be an interesting candidate for explaining the dark-matter content of the universe.
Roman Jackiw made many other important contributions to the theory of fundamental interactions. One that gained lots of attention now goes under the name of Jackiw–
Teitelboim (JK) gravity, a two-dimensional version of general relativity that can be used as a simple theoretical laboratory for addressing several conceptual problems also occurring in the real world. Another pioneering contribution is the discovery (again with Claudio Rebbi) that fractional charges and spins are easily generated in field theories of interest to condensed-matter physics. Quasiparticles with such properties have indeed been “seen” experimentally.
Jackiw received much recognition for his work: among these the prestigious Dannie Heineman Prize for Mathematical Physics of the American Physical Society and the Dirac Medal of the International Center for Theoretical Physics in Italy.
Since the time of his work with John Bell, Jackiw was very attached to CERN and to the theoretical division/department. It was always a pleasure listening to his clear and inspiring talks while benefitting from his willingness to share – with scientific assurance but also much modesty – his deep ideas about quantum field theory. In one such occasion he told me: “you know, proving an exact result is like having a deposit in a bank: it keeps giving you interest forever”. He was certainly aware of the importance of his contributions to theoretical physics but never boasted too much about them.
I completed my PhD at the University of Tokyo (U-Tokyo) in 1995 on precise measurements of the orthopositronium decay rate, in which I solved the problem of the orthopositronium lifetime puzzle. The measurement ultimately confirmed second-order QED predictions with an accuracy of 100 ppm, and positronium’s hyperfine structure and Bose–Einstein condensation are ongoing projects in the Tokyo group. I remained at U-Tokyo as an assistant, associate and then full professor, and in 1995 I joined the OPAL experiment at LEP and then ATLAS at the LHC. At OPAL I took an initiative in electroweak gaugino searches and performed a new search for scalar top quarks. I continued to work on supersymmetry searches at ATLAS, and also made a contribution to the discovery of the Higgs boson. From 2017, I became director of the International Center for Elementary Particle Physics at U-Tokyo, and on 31 March 2024 I will leave the university after close to 40 years to take up my new role at KEK.
How does it feel to be taking over as KEK director general, and what will be your priorities in the coming years?
I am honoured and feel a sense of humility at the same time. We are at a critical time to determine future project(s), and strong international collaborations are crucial. I want to have fun and do my best! The successful accomplishment of ongoing programmes (SuperKEKB, J-PARC upgrade and Hyper-Kamiokande) is the top priority in the coming years. KEK also has photon factories, and upgrades to these are urgent. The International Linear Collider (ILC) is the top priority after SuperKEKB and the construction of Hyper-Kamiokande (Hyper-K).
Will you still play a role in ATLAS?
Personally, I will leave the ATLAS experiment. I thank all ATLAS collaborators with whom I have had a wonderful and exciting time for more than 20 years. Japan has contributed to the HL-LHC projects and the associated ATLAS upgrades, as it did for the first phase of LHC/ATLAS. Now we begin an additional contribution to HL-LHC concerning the power supply for the quench heater and radio-frequency generators for the crab cavities. The Japanese high-energy physics community and MEXT (Ministry of Education, Culture, Sports, Science and Technology) would like to continue their large contributions to CERN, the LHC and ATLAS.
How is data collection progressing at SuperKEKB, and what are the current luminosity targets?
SuperKEKB represents a new generation of electron–positron colliders based on nanobeam technology. The highest instantaneous luminosity achieved so far (5 × 1034 cm–2 s–1, a record for an e+e– machine) was obtained with only half the beam current of its predecessor KEKB. Now, SuperKEKB is emerging from a long shutdown and will restart in December. The first target is to reach higher than 1035 cm–2 s–1 with the nominal beam current, after which the beam will be squeezed further to reach a final target that is a factor of 10 higher. SuperKEKB opens up opportunities for the discovery of a new CP phase and phenomena beyond the Standard Model. Many new baryon and meson states will be discovered, and a deep understanding of QCD at low energy will be obtained.
What is the current situation with the ILC, and do you expect any advances in the near future regarding Japan’s hosting of the facility?
The Japanese community considers the ILC as the top-priority project after SuperKEKB and the neutrino CP-violation programme at Hyper-K. We would like to realise the ILC as a “global project” built up through a worldwide collaborative effort in which all decisions (such as the construction decision itself, cost sharing, the construction location, risk management and organisation scheme) are taken collectively by all partners from the beginning. This is a new approach in particle physics. We are setting up the ILC technology network and a global discussion framework in collaboration with the IDT (the International Development Team established by the International Committee for Future Accelerators).
Moving to neutrinos, how are things going with the T2K upgrade and Hyper-K projects, and how strongly do these relate to LBNF/DUNE in the US?
A megawatt power-upgrade of the drive accelerator at J-PARC and the construction of the Hyper-K detector are ongoing without any serious problems. We expect to start the neutrino programme with Hyper-K in 2027, with the main goal of establishing the CP phase in the neutrino sector. We have much experience with T2K and water Cherenkov detectors, which are an advantage for this programme. We can also share our experience of the target of the high-power proton beam with LBNF. DUNE and Hyper-K are quite different detectors, so we can cover each other.
What are KEK’s major collaborations in the broader region, for example JUNO and the Super Charm-Tau factory?
These are very interesting programmes. The Japanese high-energy physics community has contributed to many ongoing programmes overseas, and we also have many important projects in Japan. Human resources are limited and focussing on these ongoing programmes is the priority.
The SuperKEKB and neutrino programmes, in addition to the muon programmes in Japan, always open a window for the world. New collaborators are always welcome to these programmes. As for involvement in other proposed future-collider projects, for example FCC and CEPC, it depends on the realisation of the ILC and the collaboration frameworks that will be proposed.
How do you view the current global picture of high-energy physics?
My happy time as a scientist in OPAL and with ATLAS, and the enormous success of LEP and the LHC prove that international collaboration is very successful in our field. I am afraid that our next major project has become too large and will cost more than one country can afford, which is why we need the ILC to be a global project. I understand that this approach will not be easy, but we have fantastic experience to build on. Now we face problems in international relations generally, such as war, pandemics and budget tensions in many counties. We can overcome them, I hope.
The European Physical Society Conference on High Energy Physics (EPS-HEP), which took place in Hamburg from 21 to 25 August, attracted around 900 physicists in-person and online to discuss a plethora of topics and results. An intense programme underlined both the vibrancy and diversity of the field, including the first evidence for a stochastic gravitational-wave background as well as the latest measurement of the anomalous magnetic moment of the muon – the latter sparking many discussions that continued during the breaks.
The participants were treated to many LHC Run 2 legacy results, as well as brand-new ones using freshly analysed Run 3 data. A large chunk of these results comprised precision measurements of the Higgs boson in view of gaining a deeper understanding of the origin of electroweak symmetry breaking. As the Higgs boson is deeply connected to many open questions potentially linked to physics beyond the Standard Model (SM), such as the origin of particle masses and flavour, studying it in the context of effective field theory is a particularly hot topic. A rich potential programme of “simplified” models for Higgs physics that can better quantify the reach of the LHC and offer new observables is also under development.
New frontiers
The ATLAS and CMS collaborations presented no fewer than 37 and 27 new preliminary results, respectively. Besides Higgs-sector physics, the experiments revealed their latest results of searches for physics beyond the SM, including new limits on the existence of supersymmetric and dark-matter particles. At the intensity frontier, the latest search for the ultra-rare decay K+→ π+e+e–e+e– from the NA62 experiment placed upper limits on dark-boson candidate masses, underlining the powerful complementarity between CERN’s fixed-target and LHC programmes. The Belle II collaboration presented first evidence of the decay B+→ K+νν, as well as the result of their R(X) = Br(B → Xτντ)/Br(B → Xℓνℓ) measurement – the first at a B factory. The LHCb collaboration also presented an update of its recent R(D*) = Br(B → D*τντ)/Br(B → D*ℓνℓ) measurement. Another highlight was LHCb’s observation of the hypernuclei antihypertriton and hypertriton.
Intense discussions took place on novel and potentially game-changing accelerator concepts
The state of the art in neutrino physics was presented, covering the vast landscape of experiments seeking to shed light on the three-flavour paradigm as well as the origin of the neutrino masses and mixings. So far, analyses by T2K and NOvA show a weak preference for a normal mass ordering, while the inverted mass ordering is not yet ruled out. With a joint analysis between T2K and NOvA in progress, updates are expected next year. At CERN the FASER experiment, which made the first observation of muon neutrinos at a collider earlier this year, presented the first observation of collider electron neutrinos. Looking outwards, a long-awaited discovery of galactic neutrinos was presented by IceCube.
The current FCC feasibility status was presented, along with that of other proposed colliders that could serve as Higgs factories. The overarching need to join forces between the circular- and linear-collider communities and to use all the gained knowledge for getting at least one accelerator approved was reflected during the discussions and many talks, as were the sustainability and energy consumption of detector and accelerator concepts. Intense discussions took place on novel and potentially game-changing accelerator concepts, such as energy recovery technologies or plasma acceleration. While not yet ready to be used on a large scale, they promise to have a big impact on the way accelerators are built in the future. Beyond colliders, the community also looked ahead to the DUNE and Hyper-Kamiokande experiments, and to proposed experiments such as the Einstein Telescope and those searching for axions.
A rich social programme included a public lecture by Andreas Hoecker (CERN) about particle physics at the highest energies, a concert with an introduction to the physics of the organ by Wolfgang Hillert (University of Hamburg), as well as an art exhibition called “High Energy” and a Ukrainian photo exhibition depicting science during times of war.
The next EPS-HEP conference will take place in 2025 in Marseille.
The cold was biting the morning of 17 July, when Wurundjeri Elder Uncle Tony Garvey welcomed 219 particle physicists to the unceded lands of the Wurundjeri, Bunurong and Wadawurrung peoples for the 31st International Conference on Lepton Photon Interactions, hosted in Melbourne, Australia. Although the distance to Melbourne is considerable, a broad range of nationalities were represented, and about a third of participants were students.
Over five days of pronouncements, presentations and posters, topics included current and future prospects in detector technologies, advances in theoretical calculations (with a particular focus on effective field theories), and improving diversity and outreach in physics. Results from a large number of experiments were presented, many of which are building excitement for the next generation of measurements that seek to provide even more rigorous tests of the Standard Model (SM) and improved searches for physics beyond it (BSM).
The results presented were too numerous to review comprehensively. However, they tended to skew towards flavour physics, with a particular emphasis on searches for CP- and lepton flavour-violation and tests of lepton-flavour universality (LFU). Overall, tensions between the SM and experimental measurements of LFU remain. In particular, Kazuki Kojima (Nagoya University) presented a measurement of R(D*), which is a test of LFU performed with B-meson decays, finding the ratio R(D*) = 0.267+0.041–0.039 (stat.)+0.028–0.033 (syst.). While compatible with the SM, it increases the tension with theory from 3.2σ to 3.3σ when all measurements of R(D) and R(D*) are combined.
Not to be outdone, the LHC experiments presented a range of precision measurements of SM parameters, further reducing the available parameter space for BSM physics. In particular, Linda Finco (INFN Torino) from ATLAS presented the most precise measurement of the Higgs-boson mass: 125.11 ± 0.09 (stat.) ± 0.06 (syst.) GeV, using the full Run 1 and Run 2 datasets for both the H → ZZ → 4ℓ and H →γγ channels. This is one of the most precisely determined masses of any SM particle, a real achievement of precision physics.
Now that the available parameter space for BSM models is shrinking, more innovative approaches to particle physics are needed. One such approach, presented by Ling Sun (Australian National University), is to use the phenomenon of superradiance to search for ultralight bosons around rapidly rotating black holes. The boson clouds extract angular momentum from the black hole when the superradiance condition is met, producing gravitational radiation that could be measured by current and future gravitational-wave detectors. Such a method provides an avenue to measure particles that interact only through gravity, opening a novel avenue for exploring particles beyond the SM.
On the penultimate evening, Alan Duffy (Swinburne University) and Suzie Sheehy (University of Oxford and University of Melbourne) delivered a public lecture “How to discover a universe” to a mix of conference participants, high-school students and the interested public, stressing that science is cultural as well as technological. The best poster was awarded to Emily Filmer (University of Adelaide) for “Searches for BSM physics using challenging long-lived signatures with the ATLAS detector”, while the “people’s choice” was awarded to Eliot Walton (Monash University) for her poster “The Queer History of Physics”. Australia’s small but growing particle-physics community was extremely well represented, and the exposure of the global community to us made Lepton Photon 2023 a resounding success.
On its silver jubilee, the Planck 2023 conference took place at the University of Warsaw from 22 to 26 May, attracting around 180 participants. Initiated by a meeting in a small town near Warsaw, Kazimierz Dolny, in 1998 and hosted each year by theory groups across Europe, the series has become one of the key conferences on beyond-the-Standard Model physics. Plenary talks covering the latest topics in theory and phenomenology as well as many parallel talks given by young researchers are the core of the conference programme, following the evolving trends in particle physics and cosmology from the Planck to the electroweak scales.
This year’s conference focused on “Hot topics in particle physics and cosmology: theory facing experimental prospects”. The first day’s plenaries were mainly devoted to machine-learning techniques and to collider physics. Enthusiastic speakers on the former met with some reservation in parts of the audience, which stressed the need for a good balance between new techniques and new physics ideas, while the collider talks emphasised the importance of precision Higgs physics and its prospects at the LHC and HL-LHC for a full understanding of the Brout–Englert–Higgs mechanism. On the theory side, the approach of effective field theory was strongly advocated. A separate session was devoted to flavour physics, in which new ideas on the origin of flavour were presented. A review of rare decays as precision tests of the Standard Model (SM) and as probes of new physics complemented the experimental summary.
The conference was dominated by topics at the interface between particle physics and cosmology. Covered in the many talks were axion couplings and search strategies, axions in rare decays, models of CP violation with nucleon and atomic electric dipole moments with or without the QCD axion, searches for very light and weakly interacting axion-like particles as a complementarity to heavy new particle searches in colliders, and much more.
The conference was very successful in connecting new theoretical ideas with planned experimental programmes
Another issue vividly under consideration was dark matter. Among important theoretical questions is the role of gravity in the production of dark matter. Avoiding overabundance of gravitationally produced dark matter is an important constraint on effective quantum gravity. Similar logic concerns right-handed neutrinos as a dark-matter candidate in simple extensions of the SM. Both were analysed in a number of presentations. Anticipating the results from the Nanograv experiment (CERN Courier September/October 2023 p7), various concrete sources of such signals were reviewed, such as primordial black-hole production, domain walls, cosmic strings and phase transitions in the early universe. Selected theoretical aspects of dark-matter models (such as accidental dark matter with its several realisations) and the analysis of their experimental signatures through new theoretical developments in computing high-energy photon signals from heavy classic WIMPs were presented.
More exotic problems at the interface between particle physics and cosmology were also touched upon. One example is how annihilating dark matter can affect late stellar evolution and the spectrum of black holes, which can be tested with gravitational-wave observations. Another is how the apparent anomaly in the primordial abundance of 4He can be linked to a neutrino–antineutrino asymmetry in the early universe that impacts Big Bang nucleosynthesis. Gravitational waves as a probe of beyond-the-SM physics were discussed at length, also including possible new-physics signals from pulsar timing arrays.
The conference was very successful in connecting new theoretical ideas with planned experimental programmes. The next Planck meeting will be held in Lisbon.
Exactly three decades ago, the first conference in the Les Rencontres du Vietnam series was held in Hanoi, initiated by Jean Trân Thanh Vân, who is also the architect of the Rencontres de Moriond series held each March in La Thuile, Italy. 2023 also marks the 10th anniversary of the International Centre for Interdisciplinary Science and Education (ICISE) in Quy Nhon, host of the Vietnam event.
An official partner of UNESCO, Rencontres du Vietnam’s scientific conferences and schools promote collaboration between Vietnamese or Asia-Pacific scientists and colleagues from other parts of the world. ICISE’s ambitious goal is to focus on the development of science and education, helping young Asian students and scientists to grow their knowledge by attending lectures and exchanging ideas with high-level overseas counterparts.
The 2023 event, entitled “Windows on the Universe”, took place from 6 to 12 August and consisted of two joint conferences, one reporting on the progress and developments in particle physics and the other discussing recent developments in astrophysics. The conference featured joint sessions between both communities, as well as separate plenary and parallel sessions for each discipline. The event attracted some 150 participants, including theorist and 1999 Nobel Laureate Gerard ’t Hooft.
In the tradition of ICISE-based conferences, a significant proportion of participants came from Asia, in particular from Vietnam, where the fundamental-research community has grown considerably since the start of ICISE activities. For example, Vietnam is now a member of the T2K experiment. Son Cao (IFIRSE) gave the plenary review on the results from this and other long-baseline neutrino experiments. Many others, including young scientists, presented their latest work during the parallel sessions.
During an extended opening session, some of the very first “Rencontres” participants shared entertaining memories of how it all began. The scientific part of the meeting followed, with keynote talks from a select group of excellent speakers covering most of the activities in particle physics and astrophysics. A highlight was the final day, when different views on future directions in particle physics were discussed, and the latest Fermilab muon g−2 measurement experiment – released just hours beforehand (see Muon g-2 update sets up showdown with theory) – was presented.
Throughout the week, ICISE confirmed its reputation as an excellent venue for conferences in Southeast Asia. At the end of the meeting, a group of some 40 scientists accepted an invitation to spend a day in Hanoi for an audience with Vietnam’s president, Võ Văn Thưởng, who, together with his staff, discussed science and education in the country. This was the final highlight of a very successful celebratory edition of the Rencontres du Vietnam in 2023.
The book Unifying Physics of Accelerators, Lasers and Plasma, by Andrei Seryi and Elena Seraia, provides a comprehensive overview of the fundamental principles and physics of three distinct areas: accelerators, lasers and plasma, bridging them via inventive principles that offer readers a unified perspective. The strength of the book lies in its accessibility and clarity.
Originally published in 2016, the first edition was picked up by CERN’s “eBooks for all!” programme to be converted to open access. The second edition, released in April 2023, has been updated throughout to cover new and essential areas in accelerator science. The material for the book originated from lectures and courses with the aim to teach undergraduate and graduate students several physics disciplines in a coherent way, while at the same time ensuring that this training would develop and stimulate innovativeness. It is written with a fine balance between technical rigour and a conversational tone, avoiding heavy mathematics and using back-of-the-envelope-type derivations and estimations wherever possible. This makes the book inspiring for both experts seeking in-depth knowledge and curious minds looking for an introduction to the field.
With the authors’ systematic approach, readers can easily follow the logical progression of ideas, facilitating comprehension and aiding future reference. They introduce the reader to the basics of accelerators and the art of inventiveness, and provide a solid foundation for understanding the key concepts of accelerators, lasers and plasma, and how they can be integrated and used together to advance scientific research.
The book includes a wide range of relevant topics such as beam dynamics, cavities, synchrotron radiation, laser and plasma physics and their role in accelerators. It then delves into advanced accelerator concepts such as radiation generation, wakefield acceleration and laser-plasma accelerators, free-electron lasers and plasma-based light sources. The authors also weave in the historical development of accelerator, laser and plasma technologies, highlighting milestones that have shaped the scientific landscape. They also extensively explore the next generation of accelerators, cutting-edge technologies and state-of-the-art facilities employed in these fields. New chapters added to the second edition, which are crucial in the accelerator area and relevant for future projects, include topics such as superconducting technology, beam cooling, final focusing, polarisation, beam stability, energy recovery, advanced technologies and no fewer than 40 inventive principles.
Also remarkable are the more than 380 illustrative diagrams that allow the reader to visualise the content for a better understanding. In the eBook most of the pictures have been changed to even more attractive colour versions.
The authors commit to scientific integrity, reinforcing their authority in the field. In addition, their pedagogical strength and clear aim to help the reader develop a deeper understanding of the material is emphasised with numerous end-of-chapter exercises. In the second edition, the guide to the solutions has been added directly into the book.
This book is the first of its kind where the three disciplines of accelerators, lasers and plasmas are connected towards building more compact accelerators. One of the highlights is the authors’ emphasis on the potential synergistic effects that can arise from integrating these three areas. With its accessible explanations, cutting-edge research coverage, and compelling arguments for interdisciplinary collaboration, this is an indispensable resource for physicists, researchers and students alike.
At the end of two pedagogical seminars that Pietro Faccioli gave in April 2013 at CERN and HEPHY, Vienna, on the topic “Angular momentum and decay distributions in high energy physics: an introduction and use cases for the LHC”, several people, including myself, encouraged him to turn his slides into a textbook on particle polarisation. Ten years later I received a copy of Particle Polarization in High Energy Physics: An Introduction and Case Studies on Vector Particle Production at the LHC from Carlos Lourenço, co-author and Pietro’s long-term colleague. During this decade, much has been learned about particle polarisation and related topics, in particular thanks to measurements made at the LHC. As someone who had a front-row seat to observe this progress in the context of polarisation measurements in the CMS experiment, I can attest to the importance and timeliness of this book.
Throughout the first four chapters, the authors guide the reader through a mosaic of relatively easy paths that introduce important concepts, including among others: helicity conservation, parity properties, polarisation frames and their transformations, frame-independent polarisation, and the Lam–Tung relation. Throughout the narrative, they often present real or simulated examples of caveats that can induce irreversible distortions in the measured distributions, potentially biasing the experimental results or their interpretation. The second half of the book (running to another 150 pages) targets a more expert audience, interested, for example, in acquiring the background knowledge needed to study cascade decays to vector particles or smearing effects of higher-order QCD (“non-planar”) processes. Appendix B, in particular, with page-long equations and no figures, must have been prepared “on demand” for people studying rare Z and W radiative decays with LHC data.
The pedagogical style of the text and the quality of the figures have clearly benefitted from the multiple interactions that the authors had with many people through physics schools, university seminars and workshops. The reader can also easily appreciate that the authors contributed to the field of particle polarisation with several original ideas, both regarding the development of robust data-analysis methods and their phenomenological interpretations. It is particularly eye-opening to see how easy it is to obtain biased experimental results if the analysis methods follow simplified approaches, ignoring the intrinsic multidimensionality of polarisation measurements. While thetext is very well written, the aspect that most distinguishes this book from others on similar topics is the presence of several beautiful figures, providing a welcome visual presentation of non-trivial concepts.
The authors contributed to the field of particle polarisation with several original ideas
Thanks to the CERN-supported open-access publication, the book can be directly downloaded by anyone who is interested. Although many readers will prefer a paper copy, the PDF file has the advantage that the reader can very easily navigate within the book by clicking on the many links connecting the text to figures, equations, cited references, and even to words in the very useful index. It is particularly practical to be one click away from an equation shown, sometimes, a hundred pages earlier.
Given the steady increase in the size of data samples being collected by the LHC experiments and the role that the polarisation aspects play in precision measurements of Standard Model processes, as well as in improving the efficiency of searches for new particles, the authors may soon be tempted to write a sequel. In such a future edition, it would be good to include a list of exercises for the interested reader, based on the authors’ behind-the-scenes knowledge and including realistic “traps” that readers should avoid. This would strengthen even further the role of the book as a guide for students and researchers involved in analysis of experimental data or in the interpretation of results.
