Praxis Archives – Page 80 of 179

The strength of worldwide collaboration

The enthusiasm and motivation to explore particle physics at the high-energy frontier knows no borders between the nations and regions of the planet. It is shared between physicists of widely different cultures and origins. This is evident today when looking around the large but still overcrowded auditoria where the latest results from the LHC are presented, as with the announcements of the Higgs-boson discovery. Such results are, in turn, presented by speakers on behalf of LHC collaborations that span the globe, with physicists from all inhabited continents.

CCvie2_06_14 — Peter Jenni in the ATLAS cavern.
Image credit: Claudia Marcelloni.

Today we take this for granted, but it is worth remembering that it took about two decades to grow and consolidate these worldwide scientific and human projects into the peaceful, creative and efficient networks that are now exploring LHC physics. This process of collaboration building is of course not finished yet, and many challenges remain. CERN and its experiment collaborations at the LHC’s predecessors – the Large Electron–Positron collider and the Super Proton Synchrotron pp collider – have long been a fertile cradle for physicists teaming up from different regions, but with the LHC collaborations, globalization for the experiments has reached a new scale. Roughly speaking, about half of the participants in ATLAS and CMS are from non-member states of CERN.

I consider it a big privilege to have witnessed this evolution from inside CERN and actively from inside the ATLAS collaboration – and to have been able, humbly, to contribute to it a little. For me, the first contacts with far-away countries started with several visits as a junior member of CERN delegations in the late 1980s and early 1990s, presenting the LHC dream to colleagues and decision makers in places such as Russia (still the Soviet Union in the beginning), Eastern Europe and Japan, and later across the world. My “hat” changed quickly from predominantly CERN to ATLAS from the early 1990s, and the focus moved from generic LHC detectors and physics to a concrete experiment project.

A formidable evolution took place during the past 25 years, which was a pleasure to see. Presenting the LHC and ATLAS in the early years could be quite an adventure. There were places where electricity for the slides was not always guaranteed, many colleagues from potential new collaboration partners barely spoke any English, and the local custom could be that only the most senior professor would be expected to speak up. Today one may find, at the same places, the most modern conference installations and – even more enjoyable to see – confident, clever young students and postdocs expressing their curiosity and opinions.

What was also striking in the early times was the great motivation to be part of the experiment collaborations and to contribute – sometimes under difficult conditions – to the building up of the experiments. I often had the impression that colleagues in less privileged countries made extraordinary efforts, with many personal sacrifices, to fulfil their promises for the construction of the detectors. Those of us from richer countries should not forget that!

Of course an experiment like ATLAS could not have been built without the massive and leading contributions from CERN’s member states and other large, highly industrialized countries, and we experimentalists must be grateful for their support in the first place. They are the backbone that made it possible to be open to other countries that have great human talent but little in the way of material resources.

The years immediately following the ATLAS and CMS Letters of Intent in October 1992 were a time when the two collaborations grew most rapidly in terms of people and institutes. The spokespersons made many trips to far-flung, non-European countries to motivate and invite participation and contributions to the experiments, in parallel (and sometimes even in competition) with CERN’s effort to enlist non-member-state contributions to enable the timely construction of the accelerator. It was during this period that the current healthy mix of wealthy and less-wealthy countries was established in the two collaborations, placing value clearly not only on material contributions but also on intellectual ones.

The building up and consolidation of collaboration with continents in the Southern hemisphere is, in general, more recent, and has benefited, for example in the case of Latin America, from European Union exchange programmes, which in particular have brought many bright students to the experiments. Yet, there is a long way to go in Africa, with many talented people eager to join the great LHC adventure. Of course fundamental physics is our mission, but personally I am also convinced that attracting young people into science will help society in all regions, ultimately. So CERN with the LHC, which from the early dreams now spans half of the organization’s 60 years, can also be proud of contributing a seed to building up a peaceful global society. For me personally, besides the physics, the LHC has also brought many friends across the world.

Boundary Conformal Field Theory and the Worldsheet Approach to D-Branes

By Andreas Recknagel and Volker Schomerus
Cambridge University Press
Hardback: £65 $99
Also available as an e-book

Boundary conformal field theory is concerned with a class of 2D quantum field theories, which display a rich mathematical structure and have many applications, ranging from string theory to condensed-matter physics. This comprehensive introduction to the topic reaches from theoretical foundations to recent developments, with an emphasis on the algebraic treatment of string backgrounds.

Une introduction à L’aventure du grand collisionneur LHC: Du big bang au boson de Higgs

By Daniel Denegri, Claude Guyot, Andreas Hoecker and Lydia Roos
EDP Sciences
Paperback: €34
Also available at the CERN bookshop

The authors, leading figures in the CMS and ATLAS experiments, have succeeded in writing a remarkable book, which I enthusiastically recommend to anyone interested in learning about the recent progress, open questions and future perspectives of high-energy physics. Throughout its 300 pages, it offers a broad coverage of the present status of particle physics, adding a few chronological accounts to place things in an historical context.

Despite being published in a collection that targets the general public, the book delves into several topics to a deep level and will be useful reading for many professional physicists. To accommodate different audiences, the authors have organized the book nicely in two “layers”, the standard flow of chapters being complemented by extra boxes giving “further reading”. Still, the reader is often told that some sections might be left aside in a first reading. It seems to me that this is a well-balanced solution for such a book, although I wonder if most readers from the “general public” would agree with the claim that the text is written in a “simple and pedagogical form”. The first chapter, describing the Standard Model, is particularly demanding and long, but these 40 pages should not deter: the rest of the book provides easier reading.

I was impressed particularly by the care with which the authors prepared many figures, which in some cases include details that I have not seen in previous works of this kind – for example, the presence of gluon lines and quark–antiquark loops inside the cartoon representing the pion, besides the standard valence quarks. Such representations are common for the proton, especially when discussing deep-inelastic scattering measurements, but it is rare to point out that any hadron – including the π or the Υ – should equally be characterized by “parton distribution functions”. The profusion of high-quality figures and photographs contributes significantly to making this book well worth reading.

A few things could be improved in a future edition. For instance, the number of footnotes is excessive. While meant as asides not worth including in the main body of the text, they end up disrupting the fluidity of the reading, especially when placed in the middle of a sentence. Most footnotes should be integrated in the text, deleted, or moved to the end of the book, so that the reader can ignore them if preferred. While understanding that this book is addressed to a French audience, I would nevertheless recommend “smoothing out” some French-specific choices. For instance, I was pleased to read that Pierre Fayet, in Paris, had an important role in the development of the MSSM extension to the Standard Model, but I was puzzled to see no other name mentioned in the pages devoted to supersymmetry.

Being one of the “LHC adventurers” myself, I read with particular curiosity the chapters devoted to the construction of the LHC accelerator and experiments, which include many interesting details about sociological aspects. I would have liked this part to have been further expanded, especially knowing by personal experience how fascinating it is to listen to Daniel Denegri, when he tells all sorts of anecdotes about physics and physicists.

All in all, this is a highly recommendable book, which provides an interesting guided tour through present-day high-energy physics while, at the same time, offering opportunities for non-French people to learn some French expressions, such as “se faire coiffer au poteau“. Note, however, that the enjoyable reading comes mixed with harder sections, which require extra effort from the reader: this book, like the LHC data, provides “du pain sur la planche“.

The Physics of Quantum Mechanics

By James Binney and David Skinner
Oxford University Press
Hardback: £49.99
Paperback: £24.99
Also available as an e-book

The aim of this book is to give students a good understanding of how quantum mechanics describes the material world. It shows that the theory follows naturally from the use of probability amplitudes to derive probabilities. It emphasizes that stationary states are unphysical mathematical abstractions that enable solution of the theory’s governing equation – the time-dependent Schrödinger equation. Every opportunity is taken to illustrate the emergence of the familiar classical, dynamical world through the quantum interference of stationary states.

Introduction to Modern Physics: Solutions to Problems

By Paolo Amore and John Dirk Walecka
World Scientific
Paperback: £32

John Dirk Walecka’s Introduction to Modern Physics: Theoretical Foundations, published in 2009 aimed at covering a range of topics in modern physics in sufficient depth that things would “make sense” to students, so that they could achieve an elementary working knowledge of the subjects. To this end, the book contained more than 175 problems. Now, Introduction to Modern Physics: Theoretical Foundations provides solutions to these problems.

An Introduction to Birth, Evolution and Death of Stars

By James Lequeux, translated from the original Naissance, évolution et mort des étoiles, published by EDP Sciences
World Scientific
Paperback: £17

How stars form from interstellar matter, how they evolve and die, was understood only relatively recently. All of these aspects are covered in this book by Lequeux, who directed the Marseilles observatory from 1983 to 1988 and served for 15 years as chief editor of the European journal Astronomy & Astrophysics. The text is accompanied by many images, while the theory is explained as simply as possible, but without avoiding mathematical or physical developments when they are necessary for a good understanding of what happens in stars.

Differential Manifolds: A Basic Approach for Experimental Physicists

By Paul Baillon
World Scientific
Hardback: £57
Also available at the CERN bookshop

The theory of differential manifolds is a common substratum of much of our current theoretical descriptions of physical phenomena. It has proved to be well adapted to many branches of classical physics –mechanics, electromagnetism, gravitation – for which it has provided a framework for a precise formulation of fundamental laws. Its use in quantum physics has led to spectacular discoveries associated with the unification of electromagnetic, weak and strong interactions. In this connection, manifolds appear not only in the description of the substratum of these phenomena but also in the description of the phenomena themselves, in terms of the so-called gauge theories.

This mathematical theory constitutes an important body of contemporary mathematics. Baillon’s book, which aims at making the subject accessible to a readership that is rich in a completely different culture, adopts an unconventional expository style. Instead of appealing to intuition based on mathematically non-rigorous images and analogies – a common practice – it insists on providing complete proofs of most of the elementary mathematical facts on which the theory is grounded.

A substantial part of the book is devoted to a detailed description of the necessary mathematical equipment. Applications culminate in an introduction to some delicacies of the electroweak theory, as well as of general relativity.

Modern Particle Physics

By Mark Thomson
Cambridge University Press
Hardback: £40 $75
Also available as an e-book, and at the CERN bookshop

Mark Thomson has written a wonderful new introductory textbook on particle physics. As the title suggests, it is modern and up-to-date. It contains several chapters on the latest developments in neutrino physics, B-meson physics, on the LHC and of course also on the Higgs boson. All the same, as new data pour in, the latter part on the Higgs boson will have to be updated in future editions, of which I expect there to be many.

The book is aimed at students who are already familiar with quantum mechanics and special relativity, but not quantum field theory. Interestingly, although written by an experimentalist, I would say that this book, in level, is most closely comparable to the well-known textbook by Francis Halzen and Alan Martin, both theorists. However, it is an improvement in many ways.

It starts out with an extensive discussion on what can be measured by detectors, as well as the basics of scattering theory, and the Klein–Gordon and Dirac equations. Thomson then guides the reader carefully through pedagogical steps to the computation of matrix elements and cross-sections for scattering processes at fixed-target experiments and colliders. He uses the helicity-eigenstate basis, which helps to make the underlying physics in the reactions more evident. As a theorist, I might have enjoyed an emphasis on two-component fermions, but this might not be so readily digestible for experimentalists.

I found the chapter on flavour SU(3) well written and elucidating. The chapter on neutrino physics discusses the implications of the measurements of θ₁₃ nicely, and presents the MINOS and Sudbury Neutrino Observatory experiments and their relevance to the determination of the neutrino parameters. Regarding neutrino oscillations, Thomson points out rightly the necessity of the wave-packet treatment, but unfortunately gives no reference to a more detailed discussion, such as the paper by Boris Kayser. The gauge principle and spontaneous symmetry breaking are explained in great detail. The emphasis throughout is always on explicit and concrete computations.

The book is well written – it is easy to read, with clear pedagogical lines of reasoning, and the layout is pleasing. There are numerous homework problems at the end of each chapter. My only criticism would be that since Thomson is an experimentalist, I expected a modern version of Don Perkins’ book, with many details on experimental techniques – that is, a different book. However, as I am teaching an introduction to theory this autumn, I will definitely be using this book.

Jim Yeck: a life in big infrastructures

Jim Yeck – a man who delights in seeing things built.
Image credit: ESS.

To paraphrase lines from the title song of a well-known film: “If there’s something big in your neighbourhood, who ya gonna call?” If the neighbourhood is particle physics, then it could well be Jim Yeck, who delights in seeing things built. This enthusiasm has underpinned his leadership of a number of successful big scientific infrastructure projects in the US, including the important US hardware contribution to the LHC and the ATLAS and CMS experiments.

Yeck’s first exposure to big science projects was as a graduate engineer in the late 1980s at the Princeton Plasma Physics Laboratory, where there was a proposal to build the $300 million Compact Ignition Tokomak. However, in 1989 the project was cancelled, because plasma ignition could not be guaranteed and the international ITER initiative was on the horizon. “It was a formative experience,” says Yeck, and instead of nuclear fusion, he found himself working on risk assessment for large science projects, which was to prove valuable for his future career.

In the autumn of 1990, he was asked by the US Department of Energy (DOE) to become the project manager for the construction of the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory. Like its ancestor – the Intersecting Storage Rings at CERN – RHIC was built with two interlaced rings, but broke new ground by incorporating 1740 superconducting magnets, most of which were made in industry. Looking back, Yeck points out that the project was approved in a different era, “when you knew you had issues that you would have to work out later”. Basically underfunded, it was built against a background of tight budget constraints. “Such a project needs strong leadership, which we had in Nick Samios, the lab director, Satoshi Ozaki, the project director, and others,” he says.

Yeck remained with RHIC until the autumn of 1997, when the US was in the final stages of signing an agreement to contribute to building hardware for the LHC and the ATLAS and CMS experiments, and to become an Observer State of CERN. The DOE and the National Science Foundation (NSF) appointed him project director for this $531 million contribution, which comprised $200 million from the DOE for the LHC accelerator, and $331 million from the DOE and the NSF for ATLAS and CMS. At the time more than 550 US scientists from nearly 60 universities and six of the DOE’s national laboratories were involved.

“This was on the heels of the cancellation of the SSC [the Superconducting Super Collider] and the community recognized that it was imperative that the LHC should work and that the US should be part of it,” Yeck recalls. “People rallied together – it was beautiful.” There were to be many difficult issues to resolve and compromises to be made, but with a background in engineering rather than particle physics, Yeck had the advantage of being a clearly defined “enabler”, with no bias.

In late 2003, with the LHC’s progress on firm ground, Yeck moved on again, to become director of a rather different astroparticle-physics project. The IceCube Neutrino Observatory at the South Pole is not only at an exotic location with an international collaboration, it is run principally by the University of Wisconsin, and Yeck says that it interested him to show that a university can take on leadership of a large infrastructure project. IceCube was funded to the tune of $280 million, in this case mostly by the NSF, who had less experience of big projects than the DOE. There was also the interesting logistical challenge of constructing and operating the huge 1 km³ detector at the South Pole.

The old model of a country going it alone doesn’t work for such projects
Jim Yeck

During the long construction phase linked to summers at the South Pole, Yeck agreed to help launch construction of the National Synchrotron Light Source II back at Brookhaven, and served as deputy project director in the years 2006–2008. Then, 10 years after taking on IceCube, he made his latest change – to another kind of facility, another continent, and a different user community. In March 2013 he became chief executive officer (CEO) of the European Spallation Source (ESS), taking over from the first CEO, Colin Carlile.

The ESS will serve a research community dispersed across many fields of science, with potential users numbering in the thousands. “The old model of a country going it alone doesn’t work for such projects,” says Yeck. Instead, the ESS is furthering the approach of bringing many nations to work together, and with 17 partner countries it is approaching CERN in terms of the number of members. Using an analogy that should appeal to physicists, Yeck says: “CERN is an existence proof, and others have drawn on this. But the initial conditions have to be right.” When setting up rules for the governance of the new facility, ESS based many of the principles on those established 60 years ago for CERN.

Yeck’s experience has taught him what is important in making a success of such a project: “The facility has to be a priority for the scientific community”, he says. “If you don’t have that foundation, it’s a problem. Then you need commitments and a strong role from the facility host. And the leadership has to see itself as enabling the success of others.” A particular challenge of the ESS is that it is new in more ways than one – a new organization on a green-field site, much like CERN was in 1954. “Such an organization needs experienced people who can catalyse the successful efforts of many,” says Yeck. “We also have to establish realistic goals – it’s a case of putting experience over hope.”

The ESS management has been working hard during the past year on a realistic plan, which was reviewed in November by a committee of 33 members from a broad community, chaired by CERN’s Mario Nessi. Yeck learnt to appreciate the value of such reviews during his time in the US. “If you have problems, you can also seek collective ownership of solutions,” he explains. “And there will be problems. To pretend that you are not going to have them is a big mistake.” However, Yeck is a man who delights in seeing things built and the ESS is no exception. “It’s fantastically challenging, with contributions from many people,” he says, “but that’s what’s captivating.”

Snapshots from the early days

1952: The first meeting of the provisional CERN Council on 15 February 1952, with key people including Sir Ben Lockspeiser, Edoardo Amaldi, Felix Bloch, Lew Kowarski, Cornelis Bakker and Niels Bohr (at the back).

The letter to Isidor Rabi, dated the same day, tells him of the signing of an agreement to create CERN.

1953: The convention establishing the organization was signed, subject to ratification, by the representatives of 12 future member states, at the sixth session of the CERN Council in Paris on 29 June–1 July.

Image credit: CERN-PHOTO-195401-001 – 1.

Could this be the first photo taken of the CERN site? Recently found in the archives, this montage shows the road from Meyrin as it crosses the border into France – now close to the location of the main entrance into CERN.

1953: The edition of 30 October of the newspaper La Suisse shows Albert Picot from the State of Geneva and members of CERN Council visiting the site of the future laboratory the day before. Geneva was selected as the site for CERN at the third Council session in Amsterdam in October 1952, and the choice was approved by a referendum in the Canton of Geneva in June 1953, by 16,539 votes to 7332.

1954: The Villa de Cointrin at the airport in Geneva was the first seat for CERN’s management and administrative offices. It is still visible through fences today.

1954: By November, the foundations of the machine hall and experimental halls for the Synchrocylcotron, CERN’s first accelerator, were taking the shape of a rigid “raft”.

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