Praxis Archives – Page 77 of 179

CP violation: past, present and future

Jim Cronin opened the meeting, 50 years after the famous paper was published.
Image credit: Honor-Clare Elliot.

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 K⁰_L 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 K⁰_L 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 K⁰_S 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”.

Nobel laureates Makoto Kobayashi, second from left, and Jim Cronin, with the organizers from QMUL, Adrian Bevan, right, and Marcella Bona.
Image credit: Honor-Clare Elliot.

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 K⁰_L 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.

Even BaBar came along to take part in the exhibition.
Image credit: Honor-Clare Elliot.

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 B_s oscillations and related observables gave valuable new constraints on the unitarity triangle, and again provided further detailed confirmation of the Standard Model.

Kobayshi speaks after accepting the book *Physics at the B Factories* at the conference dinner.
Image credit: Honor-Clare Elliot.

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.

• For more details on all of the speakers and presentations at the symposium, visit http://pprc.qmul.ac.uk/research/50-years-cp-violation.

Half a century of Bell’s theorem

John_Bell — John Bell. Credit: Renate Bertlmann.

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.

Physics With Trapped Charged Particles

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.

Strong Coupling Gauge Theories in the LHC Perspective (SCGT12)

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.

Proceedings of the Sixth Meeting on CPT and Lorentz Symmetry

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.

Engines of Discovery: A Century of Particle Accelerators. Revised and Expanded Edition

By Andrew Sessler and Edmund Wilson
World Scientific
Hardback: £58
Paperback: £32
E-book: £24
Also available at the CERN bookshop

The first edition of Engines of Discovery was published seven years ago to wide acclaim. Since then, particle physics has seen the dramatic start up of the LHC and the subsequent discovery of a Higgs boson – a long-awaited missing piece in the Standard Model of particles and their interactions. At the same time, the field of accelerators has seen further developments to push back frontiers in energy, intensity and brightness, together with growth in the use of accelerators in other areas of science, medicine and industry.

In the revised and expanded edition of their book, Sessler and Wilson have aimed to match this growth, in particular through a number of essentially new chapters. These naturally cover the work that is going into developing new machines for fundamental physics, from high-intensity super-beams and factories for neutrino physics, to future high-energy linear colliders, and back to the low energies of rare-isotope facilities and, lowest of all, the production of antihydrogen. However, most of the new chapters focus on applications beyond the confines of particle and nuclear physics, with dedicated chapters on the use of accelerators in isotope production and cancer therapy, industry, national security, energy and the environment. Here, for example, spallation neutron sources have been promoted to merit a chapter of their own.

Last, the authors have brought the future and the young more into focus by directing all of the final chapter, rather than only the last paragraph, “mainly to the young”. Sadly, Andrew Sessler – a visionary leader in the field of accelerator science – died earlier this year, but this book will stand as part of his legacy to future generations. It would have appealed greatly to me when I was young, and the hope is that it will inspire budding young scientists and engineers today, for they are the future of the field.

Dark Matter and Cosmic Web Story

By Jaan Einasto
World Scientific
Hardback: £82
E-book: £61

This book describes the contributions that led to a paradigm shift from the point of view of a scientist from behind the “Iron Curtain”. It describes the problems with the classical view, the attempts to solve them, the difficulties encountered by those solutions, and the conferences where the merits of the new concepts were debated. Amid the science, the story of scientific work in a small country – Estonia – occupied by the Soviet Union, and the tumultuous events that led to its break up, are detailed as well.

Innovative Applications and Developments of Micro-Pattern Gaseous Detectors

By Tom Francke and Vladimir Peskov
IGI Global
Hardback: $215
E-book: $215

Research in nuclear physics is inconceivable without the Geiger counter. This gas-filled instrument allows both the presence and the energy of ionizing particles and radiation to be measured. It is now 100 years since Hans Geiger designed the arrangement of its electrodes, but this construction is still used in most current gaseous detectors. In this arrangement, the electrons produced by collision and ionization of the gas atoms are multiplied in the electric field around a thin wire, and the resulting avalanche of electrons delivers an easily detectable signal.

It is only recently that other electrode arrangements for gas counters have been proposed and tested. Besides offering improved properties such as higher counting rates, a certain number of prior conceptions of the electron amplification process had to be revised. These new counters are called “micro-pattern gaseous detectors” because the same lithographic technique is used for their production as is employed in the semiconductor industry.

In their book, Francke and Peskov describe the complete historical development of these counters and discuss the properties and special features of each type. Smaller detectors with a sensitive window of up to 30 × 30 cm² can be built using the lithographic technique exclusively. These are mainly detectors in a hermetically sealed housing filled with high-pressure gas. Detectors of this type are very stable for many years. For example, the detector of the two-axis diffractometer D20 at the Institut Laue–Langevin has been operating for 14 years. Detectors with larger sized windows work at normal gas pressure and with constant gas current. Their electrodes still have to be assembled precisely by hand.

This handbook should allow every research scientist to choose and produce the best detector possible for a specific application. Numerous pictures with descriptions and many diagrams assist in making a good choice, while the detailed bibliography is particularly helpful.

Portrait of Gunnar Källén: A Physics Shooting Star and Poet of Early Quantum Field Theory

By Cecilia Jarlskog (ed.)
Springer
Hardback: £62.99 €74.89
E-book: £49.99 €59.49

This book is extremely interesting. Mainly a collection of testimonies, it helps in understanding the special personality of Gunnar Källén – his kindness and aggressiveness. Cecilia Jarlskog is named as “editor”, but she is more than an editor in having written an informative biography.

Källén worked in the “Group of Theoretical Studies” – one of three groups that were set up as part of the “provisional CERN” in 1952 – which was based in Copenhagen until it was officially closed in 1957. He later became professor at Lund University, and tragically died in 1968 when his plane crashed while he was flying it from Malmö to CERN.

I was impressed by Steve Weinberg’s admiration for Källén – he considers himself a student of Källén, although he was Sam Treiman’s student – as well as by that of James Bjorken and Wolfgang Pauli, who wanted Källén as professor at ETH Zurich. I cannot comment on the fact that it was finally Res Jost who was appointed, because I have the highest esteem for him also.

It is interesting that Pauli disapproved of Källén’s work on the n-point function. It was only long after Pauli’s death that Källén quit this subject, and took a 90° turn with the writing of his book on elementary particles. It is true that Källén failed, while being critical of Jacques Bros, Henri Epstein and Vladimir Glaser because they were not using invariants. However, Bros–Epstein–Glaser succeeded and proved crossing symmetry, allowing proof of the Froissart bound without dispersion relations, and providing a starting point for the Pomeranchuk theorem.

Because the book is based on testimonies, there is a certain redundancy, in particular about the accident, but this is unavoidable. Overall, Cecilia Jarlskog has done an excellent job. The plane crash was a tragedy, and if he had lived, Källén would certainly have made further important contributions. (His two passengers – his wife Gunnel and Matti von Dardel – survived the crash. Matti has told me that her husband Guy von Dardel and Källén were planning a collaboration between a theoretician and an experimentalist. The accident put an end to that.)

CERN: a bridge between cultures and nations

CERN is a unique institution, born from the ashes of war as a beacon of science and peace. Ben Lockspeiser, the first president of CERN Council, encapsulated the spirit of CERN succinctly when he said: “Scientific research lives and flourishes in an atmosphere of freedom – freedom to doubt, freedom to enquire and freedom to discover. These are the conditions under which this new laboratory has been established.”

Today, CERN has 21 member states and collaboration agreements with around 40 other countries. More than 10,000 people from around the world, representing nearly 100 nationalities, come to the laboratory on the Franco-Swiss border to carry out their research. At CERN, you find collaborations between people from countries more often associated with conflict than with reconciliation, which is the way it has always been at CERN.

The following short articles, written mainly from personal experience, highlight what CERN has meant to people in various regions of the world, from the Europe of the 1960s through to later decades, and the laboratory’s wider engagement with countries in other regions, such as Asia, Australasia and South America.

Rebuilding East–West relations

Adolf Mukhin, far right, and Vladimir Nikitin, far left, during their visit to CERN in 1961.
Image credit: CERN.

In July 1946, at the invitation of the Physical Society of London, physicists met at the Cavendish Laboratory in Cambridge for the International Conference on Fundamental Particles and Low Temperatures. This was the first such meeting in Europe since the conference on New Theories in Physics, which had been organized in part under the auspices of the International Institute for Intellectual Cooperation, a branch of the League of Nations, in Warsaw eight years earlier. As nobody from the so-called Eastern block was present in Cambridge, it seems that new clouds were already forming over the world – and over science.

Ten years later, in July 1956, CERN organized the Symposium on High-Energy Accelerators and Pion Physics, less than two years after its official foundation. Held at the Institut de Physique in Geneva, it attracted more than 300 participants from 22 countries, including some 50 scientists from the US and about the same number from the USSR, all of whom had been invited by CERN and were able, for the first time, to exchange information freely and compare ideas. Highly interesting papers dealing, in particular, with new principles for the acceleration of particles and with pion physics, were presented and discussed. According to CERN’s Annual Report for 1956, the conference was a landmark in the history of the organization.

It followed an opening in the West–East relationship around 1955. In August that year, the International Conference on the Peaceful Uses of Atomic Energy – “Atoms for Peace” – took place in Geneva, attended by a delegation from the USSR that included a number of scientists, among them Vladimir Veksler. A year later, the Joint Institute of Nuclear Research (JINR) was established with a charter very similar to the CERN convention, and with Dmitri Blokhintsev as the first director. It was based on scientific institutions that had grown up after the Second World War in a town on the Volga that eventually was named Dubna – city of sciences. At the same time, Soviet scientific work previously recorded in internal reports was declassified and published in scientific journals. English translations were published, mainly in the US, and learning Russian became popular among physicists.

It was the first time that a large delegation of Soviet scientists working in particle physics took part in a scientific conference in the West

The symposium organized by CERN in July 1956 offered the opportunity for many people to make personal contacts, and especially during an excellent reception held by the Soviet delegation at the Hotel Metropole, where they were all lodged for security reasons. Vodka ran abundantly. Many of the Soviet physicists subsequently became directors of the different laboratories of JINR and/or were to have important roles in Soviet physics. It was the first time that a large delegation of Soviet scientists working in particle physics took part in a scientific conference in the West.

The scientific sessions included reports from the Soviet delegation on the work done during the years 1950–1955 at the synchrocyclotron of the Institute of Nuclear Problems, which in 1956 became the Laboratory of Nuclear Problems, JINR. This was when the whole world learnt that the USSR had what was then the largest synchrocyclotron ever built – with a diameter of 6 m. At the same time, the world learnt that Bruno Pontecorvo had an active part in the scientific work with that machine. Although he was not present in Geneva, he had contributed to a paper on the synchrocyclotron’s beams and their use.

Adolf Mukhin presented results on π⁺p scattering at energies in the 176–310 MeV range. These results, together with those on pion production from other experiments, created some embarrassment in the physics community interested in performing similar experiments at the CERN Synchrocyclotron (SC). In 1956 the SC was still being constructed, and pion beams for users were foreseen only for early in 1958. Fortunately nature was kind, because weak interactions were soon to come to the fore, and experiments at the SC were able to make an important impact. Later, in 1961, Mukhin was one of the first two experimental physicists from the USSR to visit CERN for a long period – the other was Vladimir Nikitin – during which he joined an experiment on muon nuclear capture at the SC.

• With the kind help of Maria Fidecaro, CERN.

CERN is knowledge, understanding and peace

Stan Majewski, at the back with glasses, with Georges Charpak, centre at the table, and colleagues, at a typical banquet in Georges’s lab.
Image credit: I Giomataris.

After 40 years at CERN, what have I Iearnt? From a Russian: the meaning of 8 March, how communication can be achieved with few words, and friendship, even if interrupted abruptly, can remain for life. From a Chinese: is the insurmountable really insurmountable? From an Iranian: what is important is not appearance but that you are respected. This is a short list – in reality, I was always learning something from the people I met at CERN. If nothing else, new recipes, what to see in their countries, or new cultural insights.

When I arrived at CERN in 1969, I thought I was a rare being – not only an academic woman but also a biologist. However, time showed that the biggest rarity was the place where I had come to work. During the first month, I was invited for dinner to the home of my boss, Johan Baarli, a Norwegian physicist who was head of the Health Physics Group. Travelling there on the bus, I met a Polish radiation-dosimetry physicist, Mieczyslaw Zielczyn´ski, who was also invited. At that time it was a great rarity to encounter someone from behind the “Iron Curtain”, and although we could not talk much because of our different languages, we became lifelong friends. A still bigger surprise came in April 1971, when the International Congress on Protection against Accelerator and Space Radiation was held at CERN, and Russian, American and European physicists and engineers could speak freely with each other.

As a collaborator on studies towards the possible applications of high-energy particle beams for cancer therapy, a Russian biologist, Valentina Kurnaeva, was working with me, whose husband was with the Serpukhov collaboration at the Proton Synchrotron. I still have many memories of good work and warm hospitality – invited for lunch, I arrived at noon, but the meal did not start until 2:00 p.m., and at 10:00 p.m. we were still there, singing, talking, eating and drinking. Sadly, it ended abruptly when one of the Russians disappeared mysteriously. My friends had to leave within a week, and we cried knowing that there was not much hope that we would see each other again.

By the end of the 1970s, Chinese physicists were appearing at CERN, with three in the Radiation Protection Group. They were friendly and eager to know everything. The Chinese philosophy on life helped me a great deal, not only because they were hard workers, no matter what time of day or night, but also because of their kindness and politeness. When I organized the farewell party after the decision was taken to end radiobiological activity at CERN in 1981, one of them did me a drawing. Even now, when I feel down, I look at it and it cheers me up. It is true that there is always light somewhere, one just has to pass over the mountain.

Later, when I was doing the safety courses for the physicists who had to work underground at the Large Electron–Positron (LEP) collider, I needed translations of a safety note and a sticker to call the fire brigade, in as many languages as possible. It was simple to find help with Chinese, Russian and many other languages, but the adventure was to find someone to help with Arabic and Turkish. Finally, I found assistance with the Turkish version by asking a worker who drove a truck in the Transport Group to help me. He was so proud that he introduced me to all of his family on a CERN open day, and I regularly met him thereafter and discussed safety issues.

What a big family CERN is and, I hope, will remain. It has opened my eyes and my mind to the world

During the LEP era in the 1990s, I would meet and lunch with an Iranian engineer. At that time Iran was closed to the West and pictures showed completely veiled women. She wore blue jeans and had studied in the US and UK, so I decided to ask her, how was it when she went home? Was it hard to switch from a typical western mode to the other? I was astonished by her answer. At home she felt free, respected for her knowledge and capabilities and not at all devalued as a woman – just the opposite of what I thought from reading the press.

During my last period of time at CERN, a rose left on my table on 8 March by Dmitry Rogulin, a Russian computer scientist working on a technology-transfer project, brought back sweet memories. It took me back to when I was first told by Valentina of what the date means, some time before International Women’s Day became recognized in the West.

What a big family CERN is and, I hope, will remain. It has opened my eyes and my mind to the world. For anyone working there, CERN truly is knowledge, understanding and peace.

• Marilena Streit-Bianchi worked at CERN for 41 years, first in radiobiological research, then later in safety training and finally technology transfer. She is also responsible for CERN’s Oral History Project.

From physics in Poland to medicine in America – via CERN

My formative years as a young Polish experimental high-energy physicist were spent at CERN, starting in 1974 and lasting, with breaks, until 1984, when I emigrated from Europe to the US. Today, I am a research faculty member in the radiology department in a medical centre – quite a transformation for a person with PhD training in experimental high-energy physics, who specialized initially in the development of gaseous particle detectors.

CERN had a special ambiance and offered tremendous opportunities to any young particle physicist, not only those from Poland. However, the Polish contingent at CERN was always disproportionally large compared with the size of the country in the Soviet block. We always had much more freedom to travel than others from the block, and I benefited 200% from that opportunity. I owe much gratitude to all who were supportive. Luckily for my family and me, we left Poland before martial law was imposed in December 1981.

At CERN I worked in several groups, but I owe the most to Georges Charpak and Fabio Sauli, and to the “Nucleus Heidelberg” group. Whatever I learned later after emigrating to the US was a natural continuation and expansion of that initial training – not just in a technical sense, but mostly in a cultural sense, with the mindset that everything is possible. This was the message from Georges, at least to young people like us. It was Georges who got me interested in imaging in nuclear medicine, and throughout my life I have repeated to all who would listen that I would not have been able to invent the breast-specific gamma imaging (BSGI) camera followed by other medical imagers, were it not for Georges. I was lucky to be able to tell him this in person – he did not believe me – in Paris, about six months before his death. On that trip I also stopped by the Hôtel Dieu hospital in Paris where I could see one of the BSGI cameras that I invented in operation. What satisfaction! And it all started at CERN.

I am still a proud member of the international particle-physics community, all these years after I left CERN and then Fermilab. What is exciting is that I still communicate with many of my colleagues and friends from the CERN-related community who are now working in medical imaging, including David Townsend, Paul Lecoq, Stefaan Tavernier, José Maria Benlloch, Franco Garibaldi, Alberto Del Guerra and João Varela. I cannot imagine my career without CERN.

• Stan Majewski is a faculty member at Radiology Research, Department of Radiology, University of Virginia.

Two generations of Chinese collaboration with CERN

In China in 1975. At the front are Wu Lein-Fu, centre, vice-chairman of the National Peoples Congress, between Vicki Weisskopf, left, and Willibald Jentschke, with Sanqiang Qian far left. At the back are Léon Van Hove, centre left, and Georges Charpak, centre right, with Zehui He second from right.
Image credit: CERN-PHOTO-7510436-1.

The first official approach from CERN to China was in January 1966, when Bernard Gregory, then director-general, sent a letter to the director of the Institute of Atomic Energy (IAE) at the Chinese Academy of Sciences (CAS), expressing the wish to establish a scientific exchange programme between CERN and China. The IAE director at that time happened to be my father, Sanqiang Qian. Unfortunately, the letter arrived on the eve of the disastrous so-called “Cultural Revolution” in China (1966–1976), and my father never saw this letter because he was among the first people to be wrongly criticized, even before the “Cultural Revolution” started. Together with my mother, Zehui He – one of the deputy directors of the IAE (CERN Courier December 2011 p29) – my father was banished in 1969 to the remote countryside to work in agriculture, until he was allowed to return to Beijing for medical treatment in 1972 and then returned gradually to work at the IAE and CAS.

Meanwhile, part of the IAE was separated out to establish a new independent institute of CAS – the Institute of High Energy Physics (IHEP) – at the start of 1973, and my mother was appointed one of the IHEP deputy directors until 1984. The first director of IHEP was Wenyu Chang, who had some private contact with high-energy physicists in the US prior to 1972, and then exchanged official letters with CERN during 1972 and into 1973. He led the first delegation from China to visit CERN in June and July 1973. This was followed by the milestone visit to China in September 1975 by Victor Weisskopf, Willibald Jentschke and Léon Van Hove – respectively, CERN’s former, then current, and elect director-generals – together with Georges Charpak. During the visit, the CERN delegation had extensive discussions with their Chinese counterparts led by Sanqiang Qian who, as vice-president of CAS, visited CERN in June 1978.

Since then, CERN–Chinese collaboration has grown steadily from the visits of a few theorists and accelerator experts from a couple of Chinese institutes in the 1970s and 1980s, through larger groups on the L3 and ALEPH experiments at the Large Electron–Positron collider, to groups on all of the four major LHC experiments, with contributions from more than 10 Chinese universities and research institutes and more than 100 physicists and students.

My own work at CERN started in 1988, following my PhD from Illinois Institute of Technology in 1985 and work as a postdoc at Fermilab. The first five years of my work were with the INFN/Frascati group (based at CERN) on the ZEUS experiment at DESY. I was fortunate to work with top experts so that I could learn new techniques and skills more efficiently and make contributions, in particular in developing track-reconstruction algorithms by the Kalman filtering method. I’m pleased to see that this algorithm is used today by almost all experiments in high-energy physics, including the major LHC experiments.

Since 1994 I have worked on the CMS experiment, helping Peking University (PKU) to join the CMS collaboration in 1996, and proposing that PKU participate in the resistive-plate-chamber (RPC) system for forward muon detection. With strong support from the Chinese funding agencies, and with many colleagues from PKU and other countries, I was able to contribute to the entire RPC process, from prototyping and co-ordinating the chamber construction, through testing and installation, to commissioning and monitoring during Run I of the LHC. Muon triggering and reconstruction were to be crucial to the Higgs-boson discovery.

I felt extremely fortunate and excited when ATLAS and CMS announced the discovery of a Higgs boson in 2012, and when the award of the Nobel Prize in Physics to François Englert and Peter Higgs was announced in 2013. These achievements were the consequence of the tremendous hard work and close collaboration among thousands of physicists from more than 30 countries for about 20 years, which is nearly two-thirds of my physics career!

• Sijin Qian is a professor at Peking University (PKU) and deputy team leader of the PKU group in CMS. He represented China and 18 other non-member states of CERN on the CMS Management Board from 2008 to 2010. Chinese involvement in CMS is supported by NSFC, MoST and CAS.

Forging links between CERN and Argentina

Mario Benedetti, left, shakes hands with Cristina Fernández de Kirchner, the president of Argentina, when she visited CERN in 2009, together with the science minister, Lino Barañao, far right, and CERN’s director-general, Rolf Heuer.
Image credit: CERN-HI-0906085-19.

In Argentina, the situation in 1975 was already becoming desperate. Then on 24 March 1976, a military junta was installed. Some of my friends in the faculty had disappeared, and I with my beard – something that made me look suspicious at the time – was saved by chance.

Knowing about CERN, and wishing as a young engineer to specialize, I applied for a job. Being from a non-member state, it was not easy to be selected, but chance, tenacity and probably the type of expertise helped. In September, I obtained authorization for leave from the National University of La Plata, where I was working as a researcher, and moved to the extraordinary international scientific research centre that CERN had already become. When I arrived, I was immediately taken by the spirit of universality that reigned there. This was surely the experience that changed my life and my way of thinking and looking at things forever. Few places in the world were so open in spirit. Science was above any political, social, religious or racial difference. It was the common objective that was important. Ask, and there was always someone ready to help or teach you, and it has remained so throughout the 38 years I have been collaborating with CERN.

When I went back to Argentina in 1978 at the end of the first military government, I tried without success to get an agreement signed between the government and CERN. After much toing and froing, and following my second stay at CERN in 1988 and 1989, a first agreement was set up finally. This was not a particularly fruitful agreement, but it led to the act of intent signed in 2006 by Lino Barañao – currently the minister of science in Argentina – who at the time was president of the National Agency for Science and Technology (ANPCyT). In turn, this was followed in 2007 by a framework agreement concerning both physics and technological collaboration between Argentina and CERN. Then, in 2009, the first protocol for collaboration between CERN and the Laboratory of Instrumentation and Control (LIC) of the National University of Mar del Plata, was signed.

About 30 students and researchers from the laboratory that I have been working for and leading have collaborated, either from Argentina or by being at CERN, and this has been beneficial to both partners. The developments carried out for CERN accelerators for many years – including most recently work for Linac4 – have undoubtedly contributed to improving the technology and the academic level of our research. Moreover, not only scientific achievements but also human relationships have been part of these wonderful 38 years of fruitful collaboration, for which I am grateful and proud.

• Mario Benedetti, director of LIC at the University of Mar del Plata (1983–2012), has worked at CERN’s Proton Synchrotron and most recently for the LHC upgrade.

From ‘down under’ to CERN

The announcement at CERN in July 2012 of the discovery of a Higgs boson was timed to coincide with the International Conference on High-Energy Physics, in Melbourne.
Image credit: ATLAS-PHO-COLLAB-2012-014-2.

In 1943, Mark Oliphant, an Australian physicist who had been working at Birmingham in the UK, took up a post as Ernest Lawrence’s deputy at Oak Ridge. In his spare time, Oliphant proposed a new method of accelerating particles – the synchrotron. Upon his return to England, he completed in 1953 the construction of the Birmingham 1 GeV proton synchrotron, one of the world’s first high-energy particle accelerators. Another Australian, Colin Ramm, joined Oliphant at Birmingham to work on the synchrotron. Ramm’s exceptional talents in instrumentation led to an invitation to join CERN soon after the organization’s foundation – initially to work on the design and construction of the magnet system of CERN’s Proton Synchrotron and later as leader of the Nuclear Physics Apparatus Division. This division built the famous heavy-liquid bubble chamber that made the first observations of high-energy neutrino interactions. In 1972, Ramm joined Melbourne University, where he continued analysing neutrino data from CERN.

In the mid-1960s, David Caro and Geoff Opat founded the Melbourne High Energy Physics Group, Australia’s first experimental particle-physics group. Its initial research programme, carried out at Brookhaven, searched for excited sub-nuclear species by observing interactions of antiprotons with deuterons in a bubble chamber. The 250,000 frames of 70-mm film were analysed at Melbourne.

A key appointment at Melbourne was that of Stuart Tovey, recruited in 1975 from CERN as an experienced experimentalist. Tovey was to become a pioneer of Australian involvement at CERN (CERN Courier March 2011 p46). He was prominent in the 1960s and 1970s in the study of hyperons and kaons, and later participated in the discovery of the W and Z bosons in the UA2 experiment.

The foundations for strengthening the involvement of Australia at CERN were laid towards the end of the 1980s, with the return to Australia of Geoffrey Taylor to work alongside Tovey at Melbourne. In 1991, Australia and CERN signed an International Co-operation Agreement. The group led by Lawrence Peak at Sydney University, which had a strong programme in cosmic rays, neutrino physics and fixed-target accelerator experiments at Fermilab, evolved towards accelerator-based experiments at CERN. The groups at ANSTO, Melbourne and Sydney participated in NOMAD in the mid-1990s – an important milestone because the Australian groups participated for the first time as equals in all stages of a major CERN experiment. Melbourne and Sydney have also participated in the Belle experiment at KEK since 1997.

A major highlight is Australia’s involvement in ATLAS. The international engagement and solid personal and professional ties with CERN of both Taylor and Tovey ensured strong participation of the Melbourne and Sydney groups from the early 1990s. They contributed to the construction of silicon modules for the end-cap wheels of the semiconductor tracker, through Australian industry delivered large precision-machined alloy plugs serving as ATLAS radiation shields, and set up a Tier-2 centre of the Worldwide LHC Computing Grid. Australian physicists have subsequently made significant contributions to the ATLAS Higgs analysis. An experimental particle-physics group led by Paul Jackson at Adelaide University also joined ATLAS in 2012.

The successful Centre of Excellence for Particle Physics at the Terascale, which incorporates Adelaide, Melbourne, Monash and Sydney Universities under the exceptional leadership of Taylor, will no doubt continue to build on these achievements in the years to come. The future looks bright and the only way for “down under” is up.

It was a great privilege and honour to have been part of the stimulating intellectual environment at Melbourne in the 1980s, and to be mentored and introduced by the likes of Opat, Peak, Ramm, Taylor and Tovey to the magical world of particles and fields.

• Emmanuel Tsesmelis is CERN’s deputy head of international relations. He has worked on UA2, NOMAD and CMS, and has led the LHC experimental areas group.

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