Praxis Archives – Page 80 of 183

ICTP: theorists in the developing world

Fernando Quevedo, director of ICTP since 2009, came to CERN in September to take part in the colloquium “From physics to daily life”, organized for the launch of two books of the same name, to which he is one of the contributors. His participation in such an initiative is not just a fortunate coincidence, but testimony of his willingness to explain the prominent role that theoretical and fundamental physics have in human development. “Theory is the driving force behind the creation of a culture of science, and this is of paramount importance to developing societies,” he explains. “Abdus Salam founded the ICTP because he believed in this strong potential, which comes at a very low cost to the countries that cannot afford expensive experimental infrastructures.”

Unfortunately, theorists are not usually credited properly for their contributions to the development of society. “The reason is that a lot of time separates the theoretical advancement from the practical application,” says Quevedo. “People and policy makers at some point stop seeing the link, and do not see the primary origin of it anymore.” However, although these links are often lost in the complicated ripples of history, it is often the case that when people are asked to recall names of famous scientists, most likely they are theorists. Examples include Albert Einstein, Richard Feynmann, James Clerk Maxwell and, of course, Stephen Hawking. More importantly, theories such as quantum mechanics or relativity have changed not just the way that scientists understand the universe but also, years later, everyday life, with applications that range from lasers and global-positioning systems to quantum computation. For Quevedo, “The example I like best is Dirac’s story. He was a purist. He wanted to see the beauty in the mathematical equations. He predicted the existence of antimatter because it came out of his equations. Today, we use positrons – the first antimatter particle predicted by Dirac – in PET scanners, but people never go back to remember his contribution.”

Theorists often have an impact that is difficult to predict, even by their fellow colleagues. “When I was a student in Texas,” recalls Quevedo, “we were studying supersymmetry and string theory for high-energy physics, and we saw that some colleagues were working on even more theoretical subjects. At that time, we thought that they were not on the right track because they were trying to develop a new interpretation of quantum mechanics. Two decades later, some of those people had become the leaders of quantum-information theory and had given birth to quantum computing. Today, this field is booming!” Perhaps surprisingly, there is also an extremely practical “application” of string theory: the arXiv project. This online repository of electronic preprints of scientific papers was invented by string theorist Paul Ginsparg. Perhaps this will be the only practical application of string theory.

While Quevedo considers it important to credit the role of the theorists in the development of society and in creating the culture of science, at the same time, he recognizes an equivalent need for the theorists to open their research horizon and accept the challenge of the present time to tackle more applied topics. “Theorists are very versatile scientists,” he says. “They are trained to be problem solvers, and their skills can be applied to a variety of fields, not just physics.” This year, ICTP is launching a new Master’s course in high-performance computing, which will use a new cluster of computers. In line with Quevedo’s thinking, during the first year, the students will be trained in general matters related to computing techniques. Then, during the second year, they will have the opportunity to specialize not only in physics but also in other subjects, including climate change, astrophysics, renewable energy and mathematical modelling.

If you are from a poor country, why should you be limited to do agriculture, health, etc?

All of these arguments should not be seen as justifications for the need to support theoretical physics. Rather, wondering about the universe and its functioning should be a recognized right for anyone. “I come from Guatemala and have the same rights as Americans and Europeans to address the big questions,” confirms Quevedo. “If you are from a poor country, why should you be limited to do agriculture, health, etc? As human beings, we have the right to dream about becoming scientists and understanding the world around us. We have the right to be curious. After all, politicians decide where to put the money, but the person who is spending his/her life on scientific projects is the scientist.”

ICTP has the specific mandate to focus on supporting scientists from developing countries. Across its long history, the institute has proudly welcomed visitors from 188 countries – that is, almost the entire planet. While CERN’s activities are concentrated mainly in developed countries, the activity map of ICTP spreads across all continents more uniformly, including Africa and the whole of Latin America. “Some countries do not have the right level of development for science to get involved in CERN yet. ICTP can play the role of being an intermediate point to attract the participation of scientists from the least developed countries to then get involved with CERN’s projects,” Quevedo comments.

Quevedo’s relationship with CERN goes beyond his role as ICTP’s director. CERN was his first employer when he was a young postdoc, coming from the University of Texas. He still comes to CERN every year, and thinks of it not only as a model but, more importantly, as a “home away from home” for any scientist. Like two friends, CERN and ICTP have a variety of projects that they are developing together. “CERN’s director-general, Rolf Heuer, and myself recently signed a new memorandum of understanding,” he explains. “ICTP scientists collaborate directly in the ATLAS computing working groups. With CERN we are also involved in the EPLANET project (CERN Courier June 2014 p58), and in the organization of the African School of Physics (CERN Courier November 2014 p37). More recently, we are developing new collaborations in teacher training and the field of medical physics.”

Does Quevedo have a dream about the future of CERN? “Yes, I would like to see more Africans, Asians and Latin Americans here,” he says. “Imagine a more coloured cafeteria, with people really coming from all corners of the planet. This could be the CERN of the future.”

ICTP’s 50th anniversary

In June 1960, the Department of Physics at the University of Trieste organized a seminar on elementary particle physics in the Castelletto in Miramare Park. The notion of creating an institute of theoretical physics open to scientists from around the world was discussed at that meeting. That proposal became a reality in Trieste in 1964. Pakistani-born physicist Abdus Salam, who spearheaded the drive for the creation of ICTP by working through the International Atomic Energy Agency, became the centre’s director, and Paolo Budinich, who worked tirelessly to bring the centre to Trieste, became ICTP’s deputy director.

From 6 to 9 October this year, ICTP celebrated its 50 years of success in international scientific co-operation, and the promotion of scientific excellence in the developing world. More than 250 distinguished scientists, ministers and others attended the anniversary celebration. In parallel, the programme included exhibitions, lectures and special initiatives for schools and the general public.

• For the whole programme of events with photos and videos, visit www.ictp.it/ictp-50th-anniversary.aspx.

Cosmic particles meet the LHC at ISVHECRI

ISVHECRI 2014 attracted more than 120 physicists from around the world. (Image credit: Michael Hoch/CMS.)

In August this year, CERN hosted the International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI), the 18th meeting in the series that started in 1980 in Nakhodka, Russia, and is supported by the International Union for Pure and Applied Physics. In the early years, the symposia focused mainly on studying hadronic interactions of cosmic rays in the atmosphere and in emulsion chambers, which were the main cosmic-ray detectors at the time. The scope of the series has since widened, and it has become a frontier for scientists from both the cosmic-ray and high-energy physics communities to discuss hadronic interactions as a common research subject of the two fields.

At this year’s symposium, which was organized jointly by high-energy and cosmic-ray physicists – Albert de Roeck, Michelangelo Mangano and Bryan Pattison, of CERN, and David Berge of NIKHEF – the participants focused on the latest data on hadron production from CERN’s LHC, and the implications for interpreting cosmic-ray measurements. The LHC is the first collider to provide data at an equivalent proton–nucleon energy that exceeds that of the so-called “knee” – the observed change in cosmic-ray flux at 3 × 10¹⁵ eV, which is still to be explained. A series of review talks provided a comprehensive, cross-experiment overview of the latest LHC data, ranging from dedicated measurements of hadron production in the forward direction to a multitude of minimum-bias measurements in proton–proton and heavy-ion collisions. In addition, presentations showed how the forward measurements made at the HERA electron–proton collider at DESY have proved to be very useful for cosmic-ray studies. These reviews were complemented by an evening lecture on Higgs physics by John Ellis of Kings College London.

**Fig**. 1. The mean depth of shower maximum, X_max, and the relative average logarithmic muon content lnR_μ in air showers (R being the muon number relative to 1.45 × 10⁷), as measured at the Pierre Auger Observatory, compared with predictions calculated with different hadronic-interaction models.
Image credit: Aab *et al*. 2014.

Tanguy Pierog of Karlsruhe Institute of Technology (KIT) and CERN’s Peter Skands reviewed the different approaches chosen for developing hadronic-interaction models for applications in cosmic-ray and high-energy physics. Even though the predictions of such models that were developed for cosmic-ray interactions turned out to cover the first LHC data rather well, some retuning was necessary, both to improve the description of the measurements at the LHC and to obtain more reliable high-energy extrapolations. The predictions of the models show an increasing convergence after such tuning, and lead to a more consistent description of air-shower data.

However, even the latest generation of interaction models does not solve the discrepancies found for the production of muons in extensive air showers at very high energy. A discrepancy in the number of muons at giga-electron-volt energies is seen, for example, in the data from the Pierre Auger Observatory on inclined showers whose electromagnetic component is absorbed in the atmosphere before reaching the detectors at the Earth’s surface (figure 1). Furthermore, data from the KASCADE-Grande experiment presented by Juan Carlos Arteaga of Universidad Michoacana, Morelia, indicate a much weaker attenuation of the muonic-shower component than expected from simulations. KIT’s Ralf Ulrich pointed out that, in contrast to the electromagnetic-shower profile, which depends on neutral-pion production in high-energy interactions only, both high- and low-energy interactions are important for understanding the production of muons in air showers. Therefore, measurements from fixed-target experiments such as NA61/SHINE at CERN and the Main Injector Particle Production experiment at Fermilab, which Boris Popov of JINR reviewed, are also important for obtaining a better understanding of muon production in air showers. Alternative scenarios for enhancing this muon production, involving extensions of the Standard Model, were discussed by Glennys Farrar of New York University.

**Fig**. 2. Zenith-angle distribution of high-energy neutrinos detected by IceCube. The northern sky (upgoing neutrinos) is dominated by atmospheric neutrinos, the prediction of which matches the observations well. The astrophysical signal is seen mainly in neutrinos from the southern sky (downgoing).
Image credit: Aartson *et al*. 2014.

Many talks at the symposium illustrated the importance of multimessenger observations in astroparticle physics, for understanding not only the sources and the mass composition of cosmic rays but also a plethora of astrophysical phenomena. Examples are the review by Eli Waxman of the Weizmann Institute on different cosmic-particle accelerators and discussion of the propagation of ultra-high-energy cosmic rays by Andrew Taylor of the Dublin Institute for Advances Studies.

One highlight of the meeting was the discussion of high-energy neutrinos from astrophysical sources recently detected by IceCube (figure 2). Kota Murase of the Institute for Advanced Study, Princeton, reviewed different theoretical scenarios for the production of neutrinos in the tera- to peta-electron-volt energy range (10¹² – 10¹⁵ eV). Tom Gaisser of the University of Delaware summarized the knowledge on neutrinos produced in interactions of cosmic rays in the atmosphere, which constitute the dominant background of non-astrophysical origin in the IceCube data. At peta-electron-volt and higher neutrino energies, the atmospheric lepton flux is dominated by the decay of charm particles, and LHC measurements on the production of heavy flavours are the only experimental data that reach the equivalent relevant energies. Given the limited acceptance in the forward direction at the LHC, QCD calculations and models are still of central importance for understanding high-energy neutrino production, as Victor Gonzalez of Universidade Federal de Pelotas and others discussed. Similarly, as Ina Sarcevic of the University of Arizona pointed out, calculating the interaction cross-section of neutrinos of energies up to 10¹⁹ eV is a challenge in perturbative QCD because of the need for parton densities at very low x. Anna Stasto of Penn State presented different theoretical approaches to understand low-x QCD phenomena, concluding that there is no multipurpose framework of general applicability.

The remaining uncertainties in predicting hadron production in high-energy interactions were one of the central questions discussed at the meeting, and highlighted by Paolo Lipari of INFN/Roma in his concluding remarks. There was general agreement that, in addition to ongoing theoretical and experimental efforts, the measurement of particle production in LHC collisions of protons with light nuclei, for example oxygen, would be the next step needed to reduce the uncertainties further.

CERN: a forward look

On 1 July, the cycle of events celebrating CERN’s 60th anniversary opened in Paris with an event commemorating the anniversary of the CERN Convention, which was signed at the UNESCO headquarters in 1953 by representatives of the founding members. These 12 signatures are indeed worth commemorating. For more than half a century, the convention has stood the test of time as a masterpiece of simple and minimalistic legal language that focuses wisely on the essential cornerstones of CERN’s institutional basis and governance. At the same time, it provides for the leeway that is necessary to adapt the organization to a changing political environment, and to new scientific and technological challenges. The convention is a testimony to the wisdom and foresight of CERN’s founding fathers, on a par with their vision of rebuilding peace in Europe by establishing a unique focal point that would foster scientific collaboration on an unprecedented scale, between nations that had fought a war against each other only a few years earlier. On the basis of this convention, CERN has served as a model for other successful European science organizations, and most recently for the SESAME synchrotron light source in the Middle East.

Some of the most intriguing aspects of the CERN Convention are in the provisions for membership in the organization. Whereas Article II stipulates that “the Organization shall provide for collaboration among European States in nuclear research of a pure scientific and fundamental character…”, nowhere is it stated explicitly that membership in CERN is restricted to European states. This ambiguity is by no means fortuitous. It reflects the fact that already in the early 1950s, a possible enlargement of membership beyond Europe was a hotly debated issue on which the provisional council could not reach agreement. It agreed, however, on a carefully crafted compromise that left a door open to shaping the membership policy of CERN at a later stage, and to adapting it to an evolving scientific and political landscape.

Indeed, Council has debated a widening of membership on several occasions, and confirmed repeatedly a restrictive interpretation of Article II, whereby membership remained reserved for European countries. Only in 2010 did Council approve the most radical shift of paradigm of CERN’s membership policy to date, embedded in a policy of “geographical enlargement” and opening full membership to non-European states, irrespective of their geographical location. At the same time, Council introduced the new instrument of associate membership to facilitate the accession of new members, including emerging countries outside Europe, which might not command sufficient resources to sustain full membership in the foreseeable future.

CERN’s new membership policy follows a twofold rationale. It reflects the globalization of particle physics, which in turn has become a prominent paradigm for the globalization of science at large, and it prepares CERN for its long-term future. Since 2004, the community of CERN “users” has grown from just above 6000 to almost 11,000 scientists and engineers. This dramatic growth has been driven by non-member states more than by the member states. Whereas the numbers are dominated by North America, in recent years the most important growth rates have been observed in communities from Asia and Latin America, where new players emerge on the field of international science. Particle physics has a strong tradition of defying political and geographical boundaries. CERN’s new membership policy underpins, in part, the global migration of the particle-physics community, which reflects the scientific attractiveness and success of the LHC.

More important, geographical enlargement is a first step in preparing CERN’s membership and governance for the post-LHC future. Whereas the LHC experiments today are truly global operations, the LHC machine was built as a predominantly European project, with a technically and politically important contribution of about 10% from outside Europe, mostly provided in kind. This model is not likely to work for a large next-generation facility in Europe. With the CLIC and FCC studies, CERN is exploring two different, challenging avenues to prepare its future, and the future of the field, after the LHC. No cost estimate exists yet for the various options, but it seems inconceivable that any of them could be approved and built within the same membership, governance and funding structures that worked 20 years ago – successfully, but under great labour pains – for the LHC.

With 10 applications for membership or associate membership received from countries of varying size, and from inside and outside Europe (Brazil, Croatia, Cyprus, Israel, Pakistan, Russia, Serbia, Slovenia, Turkey and Ukraine), during the past four years, the enlargement process has made a promising start. Some of the accession procedures have been completed (Israel has become CERN’s 21st member state), Serbia is an associate member in the pre-stage to membership, and other accession procedures are expected to conclude in the near future. (Romania, which applied for membership before the introduction of the new policy in 2010, has been integrated a posteriori in the same accession procedure as the other, more recent applicant states.) Other countries that would seem natural candidates acknowledge the promise and potential of a continued scientific and technological partnership, but have remained absent so far, or are hesitant on political or financial grounds.

More work, stamina, and patience will be needed to enlarge the membership of CERN to a size that is commensurate with its future ambitions in quantity and quality. Moreover, not all states that are obvious candidates for a closer scientific and technical partnership might share today the values of a governance that is excellence driven and consensus oriented, and that has prevailed most of the time in CERN’s 60-year history. In the long term, broadening the institutional base without sacrificing the traditional values of European co-operation that have been a key ingredient in CERN’s past successes is likely to emerge as the true challenge of the enlargement process.

Accelerator Physics at the Tevatron Collider

By Valery Lebedev and Vladimir Shiltsev (eds)
Springer
Hardback: £99 €116.04 $149
E-book: £79 €91.62 $119

This fascinating book, compiled and edited by two of the leaders of Tevatron’s Run II, describes the achievements and lessons from Fermilab’s famous machine, which shut down for the last time at the end of September 2011. The authors and editors take us on a mesmerizing tour through the components and history of this remarkable accelerator, and provide a lively account of how, across the years, numerous obstacles were overcome, and how novel technologies contributed to the astonishing success of “one of the most complex research instruments ever to reach the operation stage”. Not only was the Tevatron the highest-energy particle collider for about a quarter of a century, it was also a pioneering accelerator in almost every regard.

In the first of nine chapters, Steve Holmes, former Fermilab accelerator director, John Peoples, former Fermilab director, together with Ronald Moore and Vladimir Shiltsev, recall the history of Fermilab and the “Energy Saver/Doubler”, which was later to become known as the Tevatron. Across almost three decades, the peak luminosity of this collider was increased by four orders of magnitude. The second chapter, in which Alexander Valishev joins the two editors as author, surveys the Tevatron’s linear and nonlinear beam-optics control. I particularly enjoyed the review of the intricate and spectacular nonlinear dynamics experiments performed in the late 1980s and early 1990s, which had been conceived to unveil the origin of dynamic aperture (e.g., the famous “E778 experiment”) and the effect of tune modulation.

The third chapter, by Jerry Annala and co-workers, brings us to the heart of the accelerator. As the first superconducting hadron storage ring, the Tevatron designers and operators had many issues to tackle. These included the effects of large intrinsic nonlinear field errors; the dynamic chromaticity drifts owing to the decay of persistent-current field errors, whose successful automatic compensation depended on many details of the preceding magnet cycles, such as the length of the flat top, the ramp rate, etc; and, last but not least, the “snapback” – i.e. the sudden re-induction of the persistent currents in the superconducting cable at the start of the energy ramp. From my student days, I vividly remember how much the Tevatron experience guided the development of the later superconducting machines, such as HERA at DESY. This chapter also presents the Recycler, the first large-scale all-permanent-magnet storage ring, operating at 8 GeV.

In the following chapter, Chandra Bhat, Kiyomi Seiya and Shiltsev present two of the most fascinating techniques of longitudinal beam manipulation – slip stacking, which has doubled the proton intensity in the Main Injector, and radiofrequency barrier buckets, used for the accumulation and processing of antiprotons. Next, Alexey Burov, Lebedev and their colleagues discuss the Tevatron’s impedance and collective effects. There are noteworthy handy formulae for the transverse and longitudinal impedance of laminated vacuum chambers developed for the Tevatron, which I have used myself often.

Chapter six, by Richard Carrigan and several co-authors, treats mechanisms of emittance growth and beam loss, including important mitigation measures such as collimation, beam removal from the abort gap using the “Tevatron electron lens” as a pulsed exciter, tests of halo deflection with bent crystals, and the Tevatron luminosity model. Lebedev, Ralph Pasquinelli and others then delve into antiproton production, stochastic cooling and the first relativistic electron cooler, based on a 4.3 MV pelletron, which many of my colleagues had thought to be unfeasible. The antiproton source technology, which had begun at CERN, was brought to maturity at the Tevatron complex, where from 1994 to 2010 the antiproton intensity was raised by another factor of 10, making this the most powerful antiproton source constructed, by far. In chapter eight, Shiltsev and Valishev discuss beam–beam effects, including the famous “scallop”-shaped pattern of emittance growth along the antiproton bunch trains, which I witnessed myself fill after fill around the year 2002, while visiting the Tevatron control room. Finally, advanced beam instrumentation, including Schottky monitors and proton synchrotron-light diagnostics, are summarized in chapter nine.

At the end of the book I found a list of about 30 PhD theses, completed on accelerator-physics topics at the Tevatron across a span of about 25 years. I smiled when I realized that many of these earlier PhD students have become today’s leaders in the accelerator field. This illustrates the exceptional training experience from participating in a demanding and inspiring collider programme such as the Tevatron’s.

Undoubtedly, this book will serve as a wonderful and unique reference for many decades to come. The authors and editors are to be congratulated for their effort to compile and preserve the accelerator knowledge of the Tevatron, accumulated during 25 years of successful struggle and permanent innovation. The Tevatron’s lessons and achievements would be all too easily forgotten without such a written record. In conclusion, I recommend this book highly to accelerator professionals around the world. Reading it should be all but compulsory for anyone wishing to improve the performance of an existing frontier machine, or design the next generation of highest-energy colliders.

Reviews of Accelerator Science and Technology: Volume 6 – Accelerators for High Intensity Beams

By Alexander W Chao and Weiren Chou (eds)
World Scientific
Hardback: £98
E-book: £74
Also available at the CERN bookshop

As particle accelerators strive for ever-increasing performance, high-intensity particle beams are becoming one of the critical demands from a majority of users – whether for proton, electron or ion beams – and for most applications. The accelerator community has therefore put a great deal of effort into the pursuit of high-intensity accelerator performance, on a number of fronts. Recognizing the topic’s importance, the editors have dedicated this volume of Reviews of Accelerator Science and Technology to accelerators for high-intensity beams. As well as reviews of applications at the intensity frontier in particle and nuclear physics, this volume also looks at applications, for example, in radiography and the production of radiopharmaceuticals, as well as in accelerator-driven systems and the inertial production of fusion energy. Other chapters deal with different types of accelerator, such as superconducting hadron linacs and rapid-cycling synchrotrons, and accumulator rings for high-intensity hadron beams. Key accelerator subsystems that allow high-intensity operation are also covered, with chapters on ion injectors, ion charge-strippers, targets and secondary beams, neutron-beam lines and beam-material interactions. The final chapter follows the journal’s tradition of looking at people who have shaped the field. This time, Giorgio Brianti and David Plane contribute their personal recollections about John Adams, who made so many pioneering contributions to CERN’s unrivalled accelerator complex. In particular, it outlines Adams’s abilities as an international collaboration leader.

Path Integrals and Hamiltonians: Principles and Methods

By Belal E Baaquie
Cambridge University Press
Hardback: £75 $120
E-book: £96

Providing a pedagogical introduction to the essential principles of path integrals and Hamiltonians, this book describes cutting-edge quantum-mathematical techniques applicable to a vast range of fields, from quantum mechanics, solid-state physics, statistical mechanics, quantum field theory and superstring theory to financial modelling, polymers, biology, chemistry and quantum finance. The powerful and flexible combination of Hamiltonian operators and path integrals is used to study a range of different quantum and classical random systems. With a practical emphasis on the methodological and mathematical aspects of each derivation, this introduction to these mathematical methods is suitable for researchers and graduate students in physics and engineering.

Nambu: A Foreteller of Modern Physics

By T Eguchi and M Y Han (eds)
World Scientific
Hardback: £45
E-book: £23

Seeds for many developments in contemporary particle physics were sown by Yoichiro Nambu in his lectures and papers in the 1960s and 1970s – in particular, his work on the mechanism of spontaneous broken symmetry, for which he was to receive the Nobel prize. Tackling first the problem of maintaining gauge invariance in a field theory of superconductivity, he went on to develop these ideas in field theories for elementary particles, in particular inspiring the important work that led to the Brout–Englert–Higgs (BEH) mechanism for generating mass through spontaneous symmetry breaking in the Standard Model. These developments culminated at CERN in July 2012 (not 2011, World Scientific please note) with the discovery of an appropriate scalar particle – a Higgs boson. This book collects together the important papers related to this story and much more, some never published before in book form. The text is not only of historical value, but also provides a window into the mind of a man that many refer to as “Nambu the seer”. It is a valuable resource for researchers in elementary particle theory, and for those who are interested in the history of modern physics.

Principles of Discrete Time Mechanics

By George Jaroszkiewicz
Cambridge University Press
Hardback: £85 $130
E-book: $104

Could time be discrete on some unimaginably small scale? Exploring the idea in depth, this book systematically builds the theory up from scratch, beginning with the historical, physical and mathematical background to the chronon hypothesis. Covering classical and quantum discrete-time mechanics, the author presents all of the tools needed to formulate and develop applications of discrete-time mechanics in a number of areas, including classical and quantum mechanics and field theories.

Beam Dynamics in High Energy Particle Accelerators

By Andrzej Wolski
World Scientific
Hardback: £98
E-book: £74

This book by Andrzej Wolski is not a general textbook but, rather, a theoretical monograph on some of the basic physics of particle accelerators, with a strong emphasis on what can be treated analytically. It is decidedly not an introduction to accelerators. Indeed it contains no description, photo or diagram of what a particle accelerator looks like, no list of numerical parameters, nor any indication of what purposes such a device might serve. I could find no mention of the name, or energy, of any past or present accelerator. The unit of MeV first appears in relation to the spacing of spin resonances. I wonder whether the author consciously sought to imbue his work with a whiff of Whittaker’s treatise? No criticism intended – I rather admire his temerity – just make sure that you have some background before tackling this 590-page opus.

The first two words of the title are key to its coverage: beam dynamics is treated as an application of classical Hamiltonian mechanics and electrodynamics. These are the explicit prerequisites. Among existing books, those of S Y Lee (a little shorter and denser) and H Wiedemann (almost twice as long), are pitched at a similar level, but structured as textbooks with exercises and more applications.

I liked chapter one, a useful description of the electromagnetic fields in magnets and RF cavities that goes into more depth than most, and is careful to explain some key practical concepts that are sometimes taken for granted. On the other hand, there is no mention of how strong you can make those fields. Subsequent chapters cover thoroughly the well-trodden ground of linear single-particle dynamics and optics in the two transverse degrees of freedom, taking a Hamiltonian approach ab initio. I was a little disappointed in the perpetuation of an unfortunate choice of the canonical variables for longitudinal motion, first made in a well-known computer program in the 1980s. Perhaps it is as well to follow the crowd now, but subsequent Hamiltonians become messier than necessary, and there is some unnatural fudging around the dispersion function.

Unusually, but logically, longitudinal motion is treated in the context of a chapter on coupling, before the introduction of a formalism for full linear coupling. There is a standard discussion of synchrotron radiation (omitting the quantum lifetime) and low-emittance lattice modules for light sources. Nonlinear dynamics gets a great deal of attention, with discussions of the traditional topics of Lie transformations, canonical perturbation theory, symplectic integrators, nonlinear resonances, dynamic aperture and frequency map analysis. Practical results on linear perturbations are also worked in.

Like Lee and Wiedemann, Wolski says surprisingly little about colliders. There is no mention of low-beta collision optics, dispersion suppressors or separation schemes. A brief discussion of the head-on beam–beam effect and a passing mention of luminosity are appended to a more comprehensive discussion of single-beam space charge. Perhaps this reminds us that most accelerators are not colliders. There is a good derivation of the Touschek lifetime, but the standard results on intra-beam scattering (Piwinski, Bjorken–Mtingwa) are only quoted.

The final chapters cover wake-fields and impedances, and the collective instabilities they drive. The formal approach works well here, imposing order and clarity on what can be a confusing array of concepts and definitions. Several important beam- instability mechanisms are treated in detail.

The book seems relatively free of misprints (although there is a glaring one after equation 2.17). Overall, this is a recommendable addition to the literature, covering its topics clearly and thoroughly.

Edinburgh takes on the flavour of beauty

Beauty 2014 participants line up for the traditional conference photo.
Image credit: Greig Cowan

The magnificent Playfair Library in the historic centre of Edinburgh provided a spectacular setting for the scientific presentations of the 15th International Conference on B-Physics at Frontier Machines (Beauty 2014). The purpose of this conference series is to review the state of the art in the field of heavy-flavour physics, and to address the physics potential of existing and future B-physics experiments. This line of research aims to explore the Standard Model at the high-precision frontier, the goal being to reveal footprints of “new physics” originating from physics beyond the Standard Model in observables that can be predicted reliably. Hosted by the University of Edinburgh on 14–18 July, Beauty 2014 attracted around 90 physicists, including leading experts on flavour physics from across the world, to present and discuss the latest results in the field.

The key topics in flavour physics are strongly suppressed rare decays and decay-rate asymmetries that probe the phenomenon of CP violation. The non-invariance of weak interactions under combined charge-conjugation (C) and parity (P) transformations was discovered 50 years ago through the observation of K_L → π⁺π^– decays (CERN Courier July/August 2014 p21). The Cabibbo–Kobayashi–Maskawa (CKM) mechanism, postulated 10 years later, allows CP violation to arise in the Standard Model, in particular in the decays of B mesons (CERN Courier December 2012 p15). These particles are hadronic bound states of a b antiquark and a u, d, s or c quark. In the case of the neutral B⁰_d and B⁰_s mesons, quantum-mechanical particle–antiparticle oscillations give rise to interference effects, which can induce manifestations of CP violation. Flavour-changing neutral currents are forbidden at the tree level in the Standard Model, and are therefore sensitive to new particles that might reveal themselves indirectly through their contributions to loop processes. These features are at the basis of the search for new physics at the high-precision frontier.

The exploration of B physics is dominated currently by the dedicated LHCb experiment, as well as the general-purpose ATLAS and CMS experiments at the LHC. The completion of the upgrade of the KEKB collider and the Belle detector in Japan in the coming years will see KEK re-join the B-physics programme, when the Belle II experiment starts up at SuperKEKB (CERN Courier January/February 2012 p21).

At Beauty 2014, the programme of 13 topical sessions included 61 invited talks. The majority covered a variety of new analyses and experimental results, complemented by a series of review talks on theoretical aspects. In addition, seven early-career researchers (PhD students and postdocs) presented posters in a dedicated session.

Highlights of the conference included a measurement of CP violation in the decay B⁰_s → φφ, new results on the determination of the angle γ of the unitarity triangle from B → DK and B⁰_s → D^±_sK^± decays – the former of which receives contributions from “tree” topologies only – and B⁰_s → K⁺K^– and B⁰_d → π⁺π^– decays, which also receive “penguin” contributions where new particles might enter in the loops. The results for γ are consistent among one another within the uncertainties and the information on the unitarity triangle coming from global fits of various observables. The error on direct γ measurements is now approximately 9°, with significant contributions from the latest results from LHCb, which will continue to improve this precision. Impressive new measurements of the weak phase φ_s and decay-width difference ΔΓ_s were presented by CMS and LHCb in B⁰_s → J/ψφ and B⁰_s → J/ψππ decays. The latter is now the most precise φ_s result, with an uncertainty of 68 mrad, and the results are in agreement with the predictions of the Standard Model.

Coffee-break discussions in the Playfair Library.
Image credit: Stephan Eisenhardt

In the field of rare B-meson decays, there were reports on impressive theoretical progress for B⁰_s → μ⁺μ^– decays. This is one of the rarest decays that nature has to offer, and is therefore a very sensitive probe of new physics. Theoretical improvements relate to the calculation of higher-order electroweak and QCD corrections, which resulted in a higher precision on the predicted theoretical Standard Model branching ratio for this channel. The experimental evidence for this decay was reported by the CMS and LHCb collaborations in the summer of 2013, and is one of the highlights of Run 1 of the LHC. New combined results have recently been made public by the two collaborations.

Measurements of the angular distribution of the rare B⁰_d → K*⁰μ⁺μ^– decay and comparison with respect to calculations within the Standard Model was another hot topic. A discrepancy is observed in a single bin in the distribution of the so-called P₅´ observable. The key question is whether strong-interaction processes or new physics effects are causing this discrepancy. The possibilities led to interesting discussions during the session, which continued during the coffee breaks. Improved statistics on this and related channels from Run 2 at the LHC are awaited eagerly.

The opening talk of the conference was given by John Ellis of King’s College London and CERN, who presented his perspective and vision for the search for new physics

In the ratio of the rates of B⁺ → K⁺μ⁺μ^– and B⁺ → K⁺e⁺e^– decays, which test lepton-flavour universality, LHCb reported a new 2.6σ deviation from the Standard Model, which has to be explored in more detail. Moreover, first results on measurements of the photon polarization in b → sγ by the B factories and LHCb were presented, and this will be studied in a more powerful way by Belle II and the upgraded LHCb.

Many other interesting measurements and developments were discussed at the conference. One of these concerned the first observation of a heavy-flavoured spin-3 particle, the D*_s(2860)^– meson, observed by LHCb in the decay of a B⁰_s meson (CERN Courier September 2014 p8). Another was the confirmation of an exotic resonance Z(4430) composed of four quarks, also by LHCb (CERN Courier June 2014 p12). In addition, many more results were presented on heavy-flavour production and spectroscopy at the B factories, at Fermilab’s Tevatron and at the ALICE, ATLAS, CMS and LHCb experiments.

On the theory frontier, there was an excellent review of the spectroscopy of B hadrons and bottomonium. Impressive progress reported in the calculation of non-perturbative parameters with lattice QCD has already had an important impact on various analyses. Other topics included the status of lepton-flavour violation and models of physics beyond the Standard Model, searches for exotic new physics such as Majorana neutrinos, charm physics and rare kaon decays.

The opening talk of the conference was given by John Ellis of King’s College London and CERN, who presented his perspective and vision for the search for new physics – in particular supersymmetry – at the LHC and beyond. A whole session was devoted to prospects for the future B-physics programme, addressing the upgrades of LHCb, ATLAS, CMS and Belle II. An exciting summary and outlook talk by Hassan Jawahery of the University of Maryland concluded the conference.

The University of Edinburgh provided an impressive social programme. No visit to Scotland is complete without whisky tasting, and participants were treated to the option of 25 different samples. A walking tour of the historic Edinburgh Castle was complemented by a bus tour and a boat ride under the famous Forth Bridge. The conference dinner, held at the Dynamic Earth museum, included another Scottish speciality – haggis.

In conclusion, the 15th Beauty conference was a great success, with presentations of exciting new results. Now it is time to look forward to the next edition, to be held in the spring of 2016.

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