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.
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.
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 KL → 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 B0d and B0s 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 B0s → φφ, new results on the determination of the angle γ of the unitarity triangle from B → DK and B0s → D±sK± decays – the former of which receives contributions from “tree” topologies only – and B0s → K+K– and B0d → 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 φs and decay-width difference ΔΓs were presented by CMS and LHCb in B0s → J/ψφ and B0s → J/ψππ decays. The latter is now the most precise φs result, with an uncertainty of 68 mrad, and the results are in agreement with the predictions of the Standard Model.
In the field of rare B-meson decays, there were reports on impressive theoretical progress for B0s → 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 B0d → 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 B0s 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.
In the field of elementary particle physics, the International Conference on High Energy Physics (ICHEP) is the largest meeting organized at a global level. Having started in 1950 at Rochester in New York, it was for several years known simply as the “Rochester Conference”. Organized by Section C11 (Particles and Fields) of the International Union for Pure and Applied Physics (IUPAP), the conferences have since taken place across the world, in recent years in Philadelphia (2008), Paris (2010) and Melbourne (2012), for example.
For its 37th edition, ICHEP went to Spain for the first time, where it took place at the Valencia Conference Centre on 2–9 July. The selection of Spain as host of the prestigious conference is recognition of the country’s progress in this field of fundamental knowledge. Its importance for Spain was clear from the presence at the inaugural session of Carmen Vela, secretary of state for research, development and innovation from the Ministry of Economy and Competitiveness, as well as several other academic and regional government representatives. ICHEP 2014 attracted a total of 967 scientists from 53 countries, with the largest delegation of 193 participants coming from Spain. The main international laboratories in the field were well represented, many at a high level: the directors of CERN, DESY, Fermilab, KEK and the Institute of High Energy Physics, Beijing, attended the conference, and participated actively in several sessions.
After the formidable impact in the media of the announcement of the discovery of the Brout–Englert–Higgs (BEH) boson at CERN on 4 July 2012, on the eve of the opening of the previous ICHEP in Melbourne (CERN Courier September 2012 p53), it was somehow unrealistic to hope that an announcement or confirmation of a result of similar outstanding scientific consequences would happen in Valencia. In this field of science, spectacular milestones alternate with less glamorous phases in which levels of knowledge are consolidated. In many cases, the construction of complete sets of precision measurements, and a deep understanding of them, reveal the way towards progress, and indicate the right roads of exploration to follow. In this respect, and given the large variety of data sets, analyses and interpretations of results presented, ICHEP 2014 did not disappoint.
Following what has become common practice in the ICHEP series, the programme in Valencia consisted of parallel and plenary sessions. In the 15 parallel sessions, 538 experimental and theoretical communications were presented, covering most of the areas in the field. A summary of the results discussed in these sessions was then given in 55 talks in the 42 plenary sessions that took place in the second half of the conference. The scientific programme was completed with 18 additional talks, as well as a display of more than 200 posters summarizing the work of young researchers.
The results of the experiments at CERN’s LHC and Fermilab’s Tevatron – studying proton–proton, proton–lead, lead–lead and proton–antiproton collisions at high energy – were presented in detail, those from the LHC being based on all of the data collected up to the start of the first long shutdown early in 2013. In particular, the dynamical features of the processes in these energy ranges (the QCD domain), the static and dynamical properties of the BEH boson, the properties of the top quark, the extremely rare decay modes and very small branching ratios of hadrons containing a b quark, and appropriate comparisons with the Standard Model figured in many of the presentations.
Although, the Standard Model explains most of the precise measurements collected up to now at a variety of experimental facilities, it is accepted widely that there are still plenty of questions to be answered – a situation that underlies the need to modify and extend the current paradigm to cure the detected weaknesses. Among the most notorious of these is the lack of understanding of the nature of dark matter – an intriguing form of matter that cannot be explained by the quarks and leptons of the Standard Model, and so points towards new physics. The capability of new models, such as supersymmetry, theories with extra dimensions, technicolour, etc, to overcome this and other conceptual and observational difficulties must be evaluated in the coming years, when the availability of new sets of data become a reality, in particular from the upgraded LHC.
Celebrating CERN’s 60th anniversary
On the occasion of CERN’s 60th anniversary, the ICHEP 2014 organizing committee thought it appropriate to schedule a special session to highlight the contributions of this unique organization to the acquisition of scientific and technological knowledge in basic science, as well as the important role that CERN has played in fostering international collaboration, in the worlds of academia and education, in the training of researchers, engineers and technicians, and in activities dealing with knowledge and technology transfer to the industrial and business communities.
Speaking first, Rolf Heuer, CERN’s director-general, stressed the relevance of basic research in fostering technological development and innovation in a global and open worldwide environment, and sent encouraging key messages to the youngest sector of the audience. Lyn Evans, former head of the LHC Project, then gave a lively recollection of the technical developments and immense challenges involved in bringing the LHC construction project to a happy conclusion. He was followed by Sergio Bertolucci, director of research and computing technology, who reviewed CERN’s current activities and some of its past achievements, as well as the ongoing tasks related to future options following the road map defined by the European Strategy for Particle Physics approved by CERN Council in 2013. The many ongoing technical activities related to the LHC – which will start a new phase of operation at higher energy and luminosity in the spring of 2015 – were then presented by Miguel Jiménez, head of the technology department. Finally, Manuel Aguilar of CIEMAT summarised the successful evolution of high-energy particle physics in Spain, and the important role that CERN has played in this context (see “CERN and Spain”, below).
The presentation and discussion of new and relevant results in neutrino physics, obtained in a diverse set of experimental facilities, was another highlight of the conference, together with many topics in astroparticle physics and cosmology. The recent results obtained at the BICEP2 telescope at the South Pole – which might provide the first experimental evidence of cosmic inflation – and the current status of the analysis of the data collected by the European satellite Planck, together with the theoretical implications of these measurements, deserved particular attention. This special session on cosmology and particle physics, which was a major highlight of the conference, was closed beautifully with a splendid lecture by Alan Guth, one of the distinguished proponents of the theory of cosmic inflation.
The status of projects at different stages of design and prototyping for the construction of new large scientific installations (linear and circular colliders, neutrino beams and detectors, underground laboratories for the study of neutrinos and dark-matter candidates, detector arrays for high-energy cosmic rays, satellites and other space platforms, etc), and the regional strategies and road maps, are topics that were included in another interesting session, leading to ample discussions. The programme of the parallel sessions also included presentations dealing with the formidable effort that, at the global level, is carried out in R&D activities on detectors, accelerators, data acquisition and trigger issues, and computing technologies. Last but not least, the role and relevance of outreach and the relations between science, technology, industry and society were analysed and discussed.
The plenary sessions provided summaries of the contributions presented in the parallel sessions, as well as a concluding synthesis of the contents of the conference and on the future of the field. As emphasized in the closing talks by Young-Kee Kim of the University of Chicago and Antonio Pich of the University of Valencia, a wealth of new data has led to considerable advances in many areas since the previous ICHEP two years ago. However, it became equally clear that, in the years to come, there remains plenty of challenging work to be done to answer the many intricate and fundamental open questions that the field still faces. One subject that will trigger further attention in future is the possible connection between the scalar field responsible for electroweak-symmetry breaking (the BEH boson) and the scalar field that might be at the origin of cosmic inflation in the early stages of the universe (the inflaton). The solution to this and many other fascinating questions is awaiting new experimental data and revolutionary theoretical ideas. With all of these ingredients, this area of fundamental knowledge is clearly facing a challenging and exciting future.
In addition to the scientific programme, participants at the conference were able to appreciate an exhibition of posters concerning the situation of women studying physics in Palestine, while another exhibition showed the connection between art and scientific research. CERN’s travelling exhibition “Accelerating Science”, displayed at the Ciudad de las Artes y las Ciencias in Valencia’s town centre, received plenty of attention from the general public. The conference also had impressive media coverage in the press, the main broadcasting networks and in national and regional television channels. Around 15 journalists from the most relevant media in science communication attended sessions, reported on the main events and interviewed numerous participants.
A highlight of the social programme was the marvellous concert on the theme of “Science and music working for peace”, given by the Orchestra and Chamber Choir of the Professional Conservatoire of Music of Valencia. This was accompanied by the projection of images – many unpublished – relating to the history of CERN and the development of particle physics in Spain. Finally, the conference banquet at the wonderful Huerto de Santa María provided a brilliant ending for the social programme.
• The Spanish institution in charge of organization was the Instituto de Física Corpuscular (IFIC), Joint Centre University of Valencia – CSIC (Council for Scientific Research). There was also ample sponsorship from several domestic and international institutions.
CERN and Spain
This year has seen celebrations of the 30th anniversary of the return of Spain to CERN in November 1983, after a long period of absence that began in 1969. Many generations of Spanish researchers, engineers and technicians have been educated and trained in the international, highly competitive and technological CERN environment, At the same time, numerous companies and industrial firms in Spain have become acquainted with a diverse range of techniques, procedures and innovations, many of them at the forefront of technology and with remarkable potential. It is appropriate to recognize not only the nurturing effect that CERN has had in the positive evolution of science in Spain – particularly the experimental and technological components – but also the importance for CERN of having Spain among its member states. Today, Spain contributes approximately 8.5% to the CERN budget and, beyond this substantial support, brings a well-trained and motivated community that is eager to take part in the CERN adventure.
The ceremony was attended by official delegations from 35 countries, while other events attracted people from CERN and in the surrounding area to listen to talks, hear music, and see science in the streets. At the same time, webcasts took many of the activities to a much wider “internet” audience, who could also participate in the celebrations via social media.
Celebrations will continue in many different places during the rest of the year. To find out more, visit http://cern60.web.cern.ch/.
The official CERN60 ceremony on 29 September featured the European Union Youth Orchestra, directed by Maestro Vladimir Ashkenazy, with 42 musicians covering all of CERN member and observer states.
An address by the president of the CERN Council, Agnieszka Zalewska, marked the culmination of speeches that had been given by official delegates from the UK, France, Switzerland, Italy, Germany and Portugal.
On 29 September, the German federal minister of education and research, Johanna Wanka, was one of the 35 official delegations to sign the guestbook, with Sigurd Lettow, CERN’s director for administration and general infrastructure.
On 19 September, during a week of CERN Council meetings, a symposium celebrated the 60th anniversary of the first Council session, held in October 1954, just one week after the CERN Convention entered into force. Speakers included CERN’s librarian, Jens Vigen, who presented highlights of Council’s history, here with a view of the Council chamber at CERN.
Croatian students of Gymnasium “Fran Galović” Koprivnica were just some of many who sent in images via social media, with the hashtag #MyCERN60, to wish CERN a happy 60th birthday. Through drawings, cakes, parties and more, people around the world contributed in beautiful and heart-warming ways.
On 17 September, a symposium on “60 years of CERN – 60 years of Science for Peace” took place in the Globe of Science and Innovation. It focussed on the human achievements throughout CERN’s history, and the role that the organization has played in promoting international co-operation. Talks included “SESAME: a parallel universe in the Middle East?” by Eliezer Rabinovici, of the Hebrew University in Jerusalem.
The United Nations Orchestra performed a concert at CERN on 19 September to celebrate the 60th anniversary. Under the baton of conductor and artistic director Antoine Marguier, the orchestra accompanied soloist Matteo Fedeli, who, under the patronage of the Permanent Mission of Italy to the United Nations, performed on a Stradivarius violin.
CERN took part in the annual European Researchers’ Night on 26 September with “Pop Science”, in which CERN researchers showcased their work at multiple venues in Geneva and neighbouring France. The event mixed arts, poetry, theatre, music and science, and included shows with liquid nitrogen, CERNLand games for young people and numerous talks and discussions.
The second TEDxCERN event took place on 24 September, with the theme “Forward: Charting the future with science”. Of the many inspirational talks, Jamie Edwards, now 14, received a standing ovation after he spoke about attempting to achieve nuclear fusion in his school lab by colliding the nuclei of hydrogen atoms via inertial electrostatic confinement.
Fifty years after the seminal discovery of CP violation by James Christenson, James Cronin, Val Fitch and René Turlay, Queen Mary University of London held a meeting on 10–11 July to celebrate the anniversary. This stimulating retrospective was attended by around 80 participants, many of whom had been involved in the numerous experimental and theoretical developments in CP-violation physics during the intervening half-century. The primary focus was to review the experimental and phenomenological aspects of CP violation during the past 50 years, but the meeting also included talks on the future of CP-violation experiments with heavy flavours as well as with neutrinos.
The meeting got off to a barnstorming start with talks by Nobel prize laureates Jim Cronin (1980) and Makoto Kobayashi (2008). Cronin explained that since René Turlay had sadly passed away in 2002, while Val Fitch was no longer able to travel and contact with Jim Christenson appeared to have been lost, he alone of the original team was available to attend such meetings. He carefully outlined the historical context in neutral-kaon physics surrounding the discovery of CP violation at Brookhaven in 1964, giving significant credit to Robert Adair, whose earlier experiment had discovered “anomalous regeneration of K0L mesons” in 1963. This in turn had stimulated Fitch to suggest to Cronin that the latter’s existing apparatus might be used to repeat and improve upon that measurement with 10 times the sensitivity. A search for CP violation in K0 decays to two charged pions would be an additional test that could be made as a by-product of the new experiment.
The proposal was made in 1963 and the experiment commenced within three weeks. Illustrating his talk with photographs of the original laboratory notebooks kept by the team, Cronin explained that it was Turlay alone who performed the analysis for the CP-violation signal, and found a signal corresponding to 40 two-pion K0L decays by Christmas 1963. This result implied that CP violation was manifest in the neutral-kaon system, corresponding, for example, to an admixture of the CP = +1 component in the long-lived K0 at the level of 2.3 × 10–3 – a result later confirmed by other experiments.
Cronin continued by reviewing the later experimental work in CP-violation physics with neutral kaons, confirming and building upon the original discovery, and culminating in the unequivocal demonstration, almost 40 years later, of direct CP violation in the kaon system. His talk stimulated several questions. One participant commented that the time from submission of the seminal paper to publication was very short. Another asked if there had been any expectation or indication of a CP-violation signal before the experiment. Cronin responded in the negative: “We did not even think CP violation was the most important thing – we really wanted to measure K0S regeneration.” A former student of Cronin commented that at the time he was “having lectures from these guys”, and that he “could tell that something exciting was going on behind the scenes”.
Towards a theory
The second talk was by Kobayashi, who together with Toshihide Maskawa had shown in 1973 how to accommodate CP violation into the gauge theory of electroweak interactions, albeit necessitating their bold suggestion of a third family of quarks – insight for which they were to receive the Nobel prize in 2008. Kobayashi carefully outlined the context in which his decisive work with Maskawa on CP violation was performed. He had entered graduate school in 1970 at Nagoya, where the theoretical physics group was led by Shoichi Sakata, and where Maskawa had completed his PhD in 1967. Kobayashi explained how their theoretical ideas had been influenced deeply by Sakata’s work, especially by his 1956 model of hadrons. This was a forerunner to the quark model that, in particular, stimulated the study of the SU(3) group in the context of particle physics. Moreover, a paper by Sakata together with Ziro Maki and Masami Nakagawa in 1962 had included a theory describing mixing in the lepton sector using a 2 × 2 matrix with a single mixing angle.
Maskawa had moved to Kyoto in 1970 and Kobayashi followed him there in 1972, at which point they started to work together on trying to incorporate CP violation into the recently formulated gauge theory of electroweak interactions. They quickly realized that it would not be possible to achieve this goal with only four quarks, and concluded that extra particles would be needed. Their paper enumerated several possibilities, including the six-quark model with their 3 × 3 mixing matrix, which would turn out to be correct. This work, as Kobayshi pointed out, “only took a couple of months”.
Two talks followed on the experimental search for CP-violating phenomena with neutral kaons – past and future – by Marco Sozzi of the University of Pisa and Taku Yamanaka of Osaka University. The search for direct CP violation had needed measurements of K0L decaying to two π0s. This was dubbed the “decay where nothing goes in and nothing comes out”, but successive experiments succeeded in studying it with staged experimental innovations. Between the first observation of CP violation and the eventual demonstration of direct CP violation in neutral kaons, the number of K0 decays observed increased by 5–6 orders of magnitude as a result of technological innovations. Much was made of the long drawn-out history of measurements of Re(ε’/ε) – the observable manifestation of direct CP violation in neutral kaons – with apparent fluctuations (albeit within experimental uncertainties) in its value throughout two generations of experiments on both sides of the Atlantic, before it settled down eventually to its current value of (1.65±0.26) × 10–3. One participant asked what value of η – Wolfenstein’s CP-violating imaginary parameter in the Cabibbo–Kobayashi–Maskawa (CKM) matrix – does the measured value of ε’ correspond to? Sozzi responded that the cancellations in the calculation of ε’ in terms of η are so complete that it is not possible to make such a one-to-one correspondence.
In considering the legacy of the neutral-kaon experiments, Cronin commented that although a great deal of work had been done during the years to measure the values of the elements of the CKM matrix, it was still a great mystery as to why their values are what they are, and he asked whether theory had left the field “in trouble” over this. However, Yamanaka could “only share his frustration”. The baton for CP-violation experiments with kaons now passes to the K0TO (K0 to Tokai) experiment at the Japan Proton Accelerator Research Complex (J-PARC), and the NA62 experiment at CERN.
The meeting moved on next to the B factories, with two historical talks by Jonathan Dorfan, now of the Okinawa Institute of Science and Technology, and Masanori Yamauchi of KEK, respectively, on the PEP-II storage rings at SLAC and the KEK-B collider. The large mixing among neutral B mesons and their relatively long lifetimes offered the possibility to observe large CP violation in their decays, but it was necessary to produce them in motion to allow their decay times to be resolved. The large cross-section in the region of the Υ(4S) made it the ideal production environment, but symmetric collisions would have implied near-stationary B mesons. Pier Oddone, together with Ikaros Bigi and Tony Sanda, proposed a solution in 1987 by suggesting the production of boosted neutral B mesons using asymmetric pairs of e+ and e− beams tuned to the Υ(4S) resonance. This approach has been vindicated by the success of the B factories in comparison with competing ideas, such as fixed-target production by a hadronic beam, for example, at the HERA-B project.
These talks thoroughly reviewed many interesting details of the beam designs. PEP-II and KEK-B pioneered true “factory running” of colliders, with continuous injection used for the first time in these projects. In the end, PEP-II produced a total integrated luminosity of 557 fb–1 between 1999 and 2008, and KEK-B produced 1000 fb–1 by its shutdown in 2010. PEP-II was built by an innovative collaboration between the Lawrence Berkeley Laboratory, the Lawrence Livermore National Laboratory, and SLAC. Asked if this was a model for the future, Dorfan replied: “The time was right. The [US Department of Energy] let us manage ourselves. There was no messing with our budget by Congress, which was a great advantage. Physicists were very involved. It couldn’t be done now!”
BaBar and Belle
Next came talks on the experiments at the B factories, BaBar and Belle, in which their histories were given a thorough airing. The BaBar collaboration had asked Laurent de Brunhoff for permission to use the name and image of his father’s famous fictional elephant, which was duly given with certain conditions attached. (For example, the elephant can be shown holding something only if he is using his trunk, not his hands or feet.) The collaboration went on to pioneer the technique of blind analysis – not as the first experiment to exploit it, but the first to make it standard throughout its analyses. As David Hitlin of the California Institute of Technology, the first spokesperson of BaBar, recalled in his talk, one collaborator had insisted early on that “we don’t need a blind analysis because we know the answer already,” which had convinced Hitlin of the need for it.
The presentations gave a virtual tour of BaBar’s and Belle’s CP-violating and T-violating measurements with B mesons, probes of new physics, tests of penguin amplitudes, neutral-meson mixing with charm, and tests of CP violation in tau decays. Both experiments proved spectacularly that the CKM description of CP violation in the Standard Model is correct. In question time, one collaboration member reported a conversation with a journalist at a conference in Tokyo in 2000. “What’s it like to do a blind analysis? – It’s the scariest thing I’ve ever done in my life,” had been the candid response. The meeting then turned its attention to the Tevatron at Fermilab, where precise measurements of Bs oscillations and related observables gave valuable new constraints on the unitarity triangle, and again provided further detailed confirmation of the Standard Model.
Gilad Perez of the Weizmann Institute then gave a theoretical talk outlining how the physics of the top quark could offer new insights into the flavour problem in the future, especially at the LHC, with unique opportunities for flavour-tagging in top decays. The extremely large mass of the top quark makes it the only quark to decay before it forms hadrons, and this gives unique access in hadron physics to a decaying quark’s spin, charge and flavour. Another important effect of the top’s large mass is its importance for fine tuning the weak vacuum – had its mass been a mere 3% greater, the weak vacuum would have been unstable and there would have been no weak interaction in the form observed. The ATLAS and CMS experiments at the LHC have already collected more than five million tt- pairs, with many more to come. Semi-leptonic decays of t quarks provide a strong flavour-tagging of the resulting b quarks, making such decays akin to a new type of B factory, barely explored so far.
In an historical overview of the LHCb experiment’s genesis, the first spokesperson, Tatsuya Nakada, now of the École polytechnique fédérale de Lausanne, described how it was born out of the “shotgun marriage” of the three earlier proposals for B physics at the LHC: COBEX – a collider-mode forward-spectrometer concept to exploit the large bb cross-section in high-energy proton–proton collisions; LHB – using a bent crystal for extraction of the beam halo for a fixed-target B experiment; and GAJET – using the gas-jet target concept. The LHC Committee had reviewed the three ideas, and in its wisdom stipulated that there should be a collider-mode experiment, but redesigned under new management to allow the three proto-collaborations to merge into a single entity, which became LHCb. “The first time I think a committee was really clever,” Nakada commented. Approval was not trivial, but the impressive results to date have already vindicated the approach taken. A second talk on LHCb by Steve Playfer of Edinburgh University gave a detailed review of its physics output, where the cleanliness of the signatures has surprised even the participants. CP violation in B-baryon decays is a promise for the future.
There were also presentations on the contributions to CP-violation physics from ATLAS and CMS at the LHC. These experiments cannot measure CP violation in purely hadronic B decays because they do not have the required particle identification to reconstruct the exclusive final states. However, with the huge cross-sections available at these energies and the experiments’ good lepton-identification capabilities, they are well placed to surpass the B factories in sensitivity to CP violation in final states in which J/ψ particles decay to leptons.
The discovery of CP violation in neutrinos would be the crowning achievement of neutrino-oscillation studies
Further talks reviewed the theoretical and experimental status of CP violation in charm and the prospects for its discovery, as well as future prospects at the planned upgrades to both Belle and LHCb, and also at neutrino facilities. The discovery of CP violation in neutrinos would be the crowning achievement of neutrino-oscillation studies. There were also two detailed reviews of the history of T violation, first in kaon physics and then in B decays.
A final talk by Marco Ciuchini of INFN/Roma Tre University reviewed the theoretical implications and future perspectives on CP violation. Again, Cronin wondered why the community is not yet in a position to understand the spectra of fermion masses and mixings, including CP violation. The speaker responded that “this is the hardest problem”. One questioner asked if a deviation from the Standard Model were to be observed with the upgraded LHCb or Belle II, thereby indicating some new physics in virtual-loop processes, what energy machine would be needed to observe such physics directly? The answer, said Ciuchini, would depend on the details of the new physics.
The conference dinner took place at the Law Society in the City of London, in grand surroundings appropriate for a 50th anniversary. During the past six years, BaBar and Belle have been collaborating on a grand review of Physics at the B Factories, and the occasion was used to announce the completion of this monumental tome. It was also a fitting opportunity to present complimentary copies to Cronin and Kobayashi, in honour of their personal contributions to the current understanding of CP violation.
This year sees the 50th anniversary not only of the proposal of quarks, but also of what is arguably one of the most groundbreaking theoretical findings in physics: Bell’s theorem (Bell 1964).
To celebrate the theorem and the work of the Irish physicist John Stewart Bell, who was on leave from CERN when he wrote his seminal paper, the university of Vienna held the conference Quantum [Un] Speakables II on 19–22 June. Distinguished invited specialists in the question of non-locality brought up by Bell’s theorem discussed the impacts of the theorem and the future of scientific investigations, together with 400 participants.
John Clauser, who was the first to investigate Bell’s theorem experimentally, mentioned the difficulties he had in acquiring money for his experiments. The breakthrough did not come until the 1980s, when Alain Aspect measured a clear violation of Bell’s proposed inequalities. The philosophical debate between Niels Bohr and Albert Einstein on whether quantum mechanics is complete or not thus seemed also to be settled experimentally – in favour of Bohr. In his talk, Aspect stressed Bell’s ingenious idea to discover the practical implications of what had until then been merely a philosophical debate.
An important further development of Bell’s theorem was the Greenberger– Horne–Zeilinger experiment, in which the entanglement of three instead of only two particles was considered. Another important contribution was achieved with the Kochen–Specker Theorem – next to Bell’s theorem, this is the second important “no-go” theorem for hidden variables in quantum mechanics. In their talks, Daniel Greenberger, Michael Horne and Simon Kochen focused on current questions in their research. Anton Zeilinger, who was co-chair of the conference with Reinhold Bertlmann, stressed the huge impact of Bell’s theorem for technical applications: quantum computing, quantum teleportation and quantum cryptography, which are based on the concept of non-locality as outlined by Bell.
More personal remarks came from Bertlmann, who had worked with Bell as a postdoc at CERN and is the protagonist of his famous paper “Bertlmann’s socks and the nature of reality”, and from Bell’s widow Mary Bell, an accelerator physicist.
The conference title refers to a paper that Bell wrote in 1984, in which he identified what he called “unspeakables”. These are notions that he wanted to eliminate from the vocabulary of physics, because for him they did not qualify as well defined – among them measurement, apparatus and information. However, the title also allowed for another meaning. After 50 years, many important implications of Bell’s theorem have been found, but there is much that follows from the theorem that no one talks or even thinks about yet, and so is still to discover.
By Martina Knoop, Niels Madsen and Richard C Thompson (eds) World Scientific
Hardback: £78
Paperback: £36
E-book: £27
This is a collection of articles on physics with trapped charged particles, by speakers at the Les Houches Winter School in January 2012. They cover all types of physics with charged particles, and are aimed at introducing the basic issues as well as the latest developments in the field. Topics range from detection and cooling techniques for trapped ions to antihydrogen formation and quantum information processing with trapped ions. The level is appropriate for PhD students and early career researchers, or interested parties new to the subject.
By Yasumichi Aoki, Toshihide Maskawa and Koichi Yamawaki (eds) World Scientific
Hardback: £109
E-book: £82
The proceedings of the KMI-GCOE Workshop held in Nagoya in December 2012 contain contributions that are focused mainly on strong coupling gauge theories and the search for theories beyond the Standard Model, as well as new aspects in hot and dense QCD. These include many of the latest, important reports on walking technicolour and related subjects in the general context of conformality, discussions of phenomenological implications with the LHC, as well as theoretical implications of lattice studies.
By V Alan Kostelecký (ed.) World Scientific
Hardback: £76
E-book: £57
The Sixth Meeting on CPT and Lorentz Symmetry held in 2013 focused on tests of these fundamental symmetries and on related theoretical issues, including scenarios for possible violations. Topics covered at the meeting include searches for CPT and Lorentz violations in a range of experiments from atomic, nuclear, and particle decays to high-energy astrophysical observations. Theoretical discussions included physical effects at the level of the Standard Model, general relativity, and beyond, as well as the possible origins and mechanisms for Lorentz and CPT violations.
To provide the best experiences, we use technologies like cookies to store and/or access device information. Consenting to these technologies will allow us to process data such as browsing behavior or unique IDs on this site. Not consenting or withdrawing consent, may adversely affect certain features and functions.
Functional
Always active
The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network.
Preferences
The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user.
Statistics
The technical storage or access that is used exclusively for statistical purposes.The technical storage or access that is used exclusively for anonymous statistical purposes. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you.
Marketing
The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes.
