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Spin goes Chinese

Lecture hall at Peking University — The lecture hall at Peking University provided an attractive setting for many sessions.
Image credits: SPIN2014 organizers.

The biannual series of international symposia on spin physics plays a leading role at the interface of nuclear and particle physics on one hand, and the study of spin-dependent phenomena in experiment and theory on the other. The series grew from the merger of the five-yearly symposia on polarization phenomena in nuclear reactions, first held in Basel in 1960, and the symposia on high-energy spin, which started in 1974 and had reached the 13th edition by 1998. The joint meetings began as the 14th International Symposium on Spin Physics in 2000. The 21st International Symposium on Spin Physics (SPIN2014) is the first in the series that China has hosted – taking place on the 40th anniversary of the first high-energy spin meeting at Argonne National Laboratory in 1974.

The scientific programme of the symposium series today is based on physics with photons and leptons, spin phenomena in nuclei and nuclear reactions, and new physics beyond the Standard Model. It also includes new technologies related to accelerators, storage rings, polarized targets and polarized beams, and spin physics in medicine is also included. In addition, SPIN2014 extended the topics to incorporate spin in condensed matter, quantum communication and their related applications.

Hosted by Peking University, Beijing, and supported by many renowned research institutions and universities, both inside and outside of China, SPIN2014 took place on 20–24 October 2014. Nearly 300 participants attended from more than 20 countries. With 28 plenary talks and 177 parallel talks, the symposium provided a platform to communicate new results in the field of spin physics and to reinforce academic collaborations with colleagues. It was also an important platform to advertise the academic achievements of Chinese researchers, and to strengthen the importance of Chinese involvement in spin physics. The following gives an overview of the scientific programme.

Hadrons, nucleons and symmetries

A key highlight was the excellent opening plenary talk on the spin structure of the nucleon by Xiangdong Ji of Shanghai Jiao Tong University and the University of Maryland. The quest to determine the origin of nucleon spin challenges the understanding of QCD. There is a worldwide experimental programme underway using spin observables to gain insight into this fundamental question in hadronic physics. The conference also heard more than 50 reports from experiments carried out at Brookhaven, CERN, DESY, Jefferson Lab and KEK on measurements that included inclusive lepton scattering (quark and gluon contributions), proton–proton scattering (gluon contribution, quark flavour decomposition using W-boson production), semi-inclusive deep-inelastic scattering (quark flavour decomposition, transverse-momentum distributions), deeply virtual Compton scattering (quark orbital angular momentum) and fragmentation in electron–positron collisions. There were also discussions on future possible experiments, including polarized Drell–Yan scattering, at Fermilab, the Japan Proton Accelerator Research Complex, the Nuclotron-based Ion Collider fAcility (NICA) in Dubna, and Brookhaven’s Relativistic Heavy-Ion Collider (RHIC). Keh-Fei Liu of the University of Kentucky gave an overview of the exciting developments in lattice QCD in a plenary talk. This was followed by more than 20 presentations on theoretical research into the spin structure of hadrons.

Co-chair Haiyan Gao opening the conference.

The plenary programme on “Spin Physics in Nuclear Reactions and Nuclei” included a report by Andro Kacharava from the Forschungszentrum Jülich on results from the Cooler Synchrotron (COSY) on nucleon–nucleon scattering using polarization degrees of freedom to probe nuclear forces. Mohammad Ahmed of North Caroline Central University described the latest results on few-body reactions from the High Intensity Gamma-Ray Source Facility at the Triangle Universities Nuclear Laboratory, where both polarized beam and polarized targets were employed, as well as results on Compton scattering from ⁶Li and ¹⁶O. Fifteen talks in the parallel programme were related to spin physics in nuclear reactions and nuclei.

Spin physics plays an important role in studies of fundamental symmetries

Spin physics plays an important role in studies of fundamental symmetries and searches for new physics beyond the Standard Model of particle physics. Plenary talks included reports on the latest result on the weak charge of the proton from parity-violating electron scattering by Dave Mack of Jefferson Lab. Mike Snow of Indiana University presented recent results on hadronic parity-violating experiments such as np → dγ, while Brad Filippone of Caltech provided an overview of the worldwide effort on searches for particle electric-dipole moments (EMDs). Frank Maas described the latest results on dark-photon searches from the University of Mainz and elsewhere. From China, Wei-Tou Ni of National Tsinghua University discussed the role of spin experiments in probing the structure and origin of gravity. Thirteen talks relating to fundamental symmetries were presented in the associated parallel sessions.

Current tools and future facilities

The methods to study spin-dependent effects are fundamental for the spin-physics community. At SPIN2014, the two main areas of interest were acceleration, storage and polarimetry of polarized beams, and sources of polarized ion and lepton beams and polarized targets. Nearly all of these disciplines formed part of the exciting plenary of Annika Vauth of DESY, who discussed the status of beam polarization and the International Linear Collider that could be built in Japan. Nearly 20 parallel talks were devoted to accelerator aspects, among them studies in the US and in China on electron–ion colliders (EICs), at JINR on the use of NICA as a polarized-ion collider, on storage rings for searches for ion EDMs, and on the new tools to be developed to meet these challenges. The operation of existing rings with polarized beams and the steady improvement of their operational parameters were also covered, with RHIC and its amazing performance as the only double-polarized ion collider built so far, and with COSY, which is famous for its stored polarized beams in the medium-energy range and the variety of internal targets.

More than a dozen parallel talks on sources and targets were presented, introduced by Dmitriy Toporkov of the Budker Institute of Nuclear Physics in his plenary on experiments with polarized targets in storage rings, in which he showed the potential of this technique. The review on polarized sources by Anatoli Zelenski of Brookhaven and other parallel talks covered a wide span of polarized beams, from high-intensity electrons for an EIC, to protons, as in H^– ions for RHIC, to deuterons for COSY and ³He ions for eRHIC. Chris Keith of Jefferson Lab and other speakers in the parallel sessions covered solid targets polarized by dynamic nuclear polarization or by the brute-force method in several lepton-scattering experiments. Gas targets for H, D and ³He atoms were also discussed.

The poster session presented new research results.

The conference heard reports on major upgrades of spin capabilities at existing facilities. The status and plans for Jefferson Lab’s 12 GeV upgrade were presented in a plenary talk by associate director Rolf Ent, and Wolfgang Lorenzon of the University of Michigan described the possibility of polarizing the Fermilab proton beam and mounting a programme of polarized Drell–Yan measurements. In Europe, the Mainz Energy-Recovering Superconducting Accelerator provides a high-intensity low-energy polarized electron facility, while COSY has embarked on a major development of new polarized proton- and deuteron-beam capabilities, motivated by experiments to look for nonzero EDMs in light nuclei.

In the US, the QCD community is pursuing a high-luminosity polarized EIC

Alexander Nagaytsev of JINR described the new accelerator NICA under construction in Dubna, together with the planned spin-physics programme, including measurements of polarized Drell–Yan and J/ψ production. In the US, the QCD community is pursuing a high-luminosity polarized EIC. This could be implemented at Brookhaven or Jefferson Lab. The concept has driven R&D in both high-intensity polarized electron guns and a polarized ³He source. In the European Physical Journal A plenary lecture, Zein-Eddine Mezziani of Temple University gave a compelling presentation on the spin science that motivates this new machine. Physicists in China have recently become interested in a similar facility.

Further features

As a novelty, SPIN2014 included a significant programme on spintronics – low-dimensional solid-spin systems exhibiting different quantum effects that can be employed, for example, in quantum computers, metrology, information technology and more. This ambitious field of research and technology is being pursued actively at Tsinghua and Peking Universities, and many other Chinese institutes, and was presented in a public lecture (see below) as well as in parallel sessions that included 20 talks. Apart from spintronics themes, medical applications such as imaging were discussed, a highlight being the beautiful talk by Warren Warren of Duke University on “Imaging with Highly Spin-Polarized Molecules”. There were also two talks on the application of polarized fuel for fusion reactors.

Besides the communication of recent results at the physics frontier, SPIN2014 also organized a lecture on popular science by Qi-Kun Xue from Tsinghua University on “Quantum Anomalous Hall Effect and Information Technology”, attended by more than 100 people from Peking University, Tsinghua University, Beijing University of Posts and Telecommunications, Beihang University and others. A memorial session devoted to the memory of CERN’s Michel Borghini was organized by Alan Krisch of Michigan and Akira Massike of Kyoto, highlighting Borghini’s contributions to the development of solid polarized targets.

A poster session for presenting new research results included Outstanding Poster Awards, sponsored by the Hanscom endowment from Duke University. From 14 posters, three young researchers from the China Institute of Atomic Energy, Tsinghua University and the Institute of Modern Physics of the Chinese Academy of Sciences received awards. The hope is that the poster session and awards will inspire young researchers to work with passion in the area of spin physics. A reception and banquet, and a visit to the nearby Summer Palace, served to bring all of the participants together, enhancing close discussions. They will surely remember SPIN2014 as a stimulating meeting that demonstrated the beauty and vitality of the field – and look forward to the next in the series, which will take place on 26–30 September 2016 at the University of Illinois Urbana-Champaign.

• For more about the organizers and sponsors of SPIN2014, and details of the full programme, visit www.phy.pku.edu.cn/spin2014/.

Seeing is believing

Lucio Rossi, CERN, is leader of the High-Luminosity LHC project.
Image credit: CERN-HI-0806018-05.

Seeing has always been a trigger for curiosity – the desire to know reality – and light is a means for bridging reality with our minds. It is not the only means, but probably the most important. Sight conveys the most information, the most detail about the world around us. Think, for example, of the richness of detail in today’s high-definition (HD) or 3D images. Now, to remind us of light’s importance and how useful it is in our lives, the UN has declared 2015 as the International Year of Light.

From Euclid, who first put down the principles of geometric optics in 300 BC, to Alhazen, whose first real theory of light and sight around 1000 AD was so influential in Europe, to Francesco Maurolico who in the 16th century developed a modern theory of sight and the functioning of the eyes – light and sight have long fascinated scientists. Indeed, light is fundamentally linked to the birth of modern science. In 1609–1610, Galileo Galilei was able to perfect the lens and telescope, making the first modern scientific instrument. The “canone occhiale” or “spectacles cannon” – the words at the root of the Italian for telescope – allowed him to see “things never seen beforehand”, as he wrote in his “instant book” Sidereus Nuncius. Thanks to an instrument based on light, he was able to discover the moons of Jupiter and make the Empyrean Heaven a place where change happens, and therefore worthy of investigation by physicists.

Later in the 17th century, Francesco Grimaldi first observed diffraction – soon formalized by Christiaan Huygens in a complete physics theory – and in 1873 Ernst Abbe showed that this limits the detail of what we can see. The resolution of our vision depends on the wavelength of the light or any other wave used for detection, such as sound waves, as in bats, or electromagnetic waves of different wavelengths. So, if we use millimetre-range infrared waves, the image is inevitably less well resolved than with submicrometre visible light. That is why our vision is so good and we can appreciate the splendour of HD images.

For more than a century, physicists have been able to see with finer wavelength “light” – for example, X-rays with wavelengths 100–1000 times shorter – and today, being able to “see” atoms at the nanometre scale, daily life is invaded by “nanotechnology”. Nevertheless, we can peer down to much smaller scales. Just 90 years ago, Louis de Broglie put forward the unimaginable idea that a particle can behave like a wave, with a wavelength inversely proportional to its momentum. This completed the particle–wave duality initiated by Albert Einstein in his annus mirabilis, when he realized that waves behave like particles and introduced the concept of light quanta, the photons.

The High-Luminosity LHC project is already on the starting blocks to be ready 10 years from now

In this way, particle accelerators can generate the finest “light”. The cyclotrons and synchrotrons of the 1950s and 1960s were capable of illuminating entities such as protons, but were limited by diffraction in the femtometre range. Each new, more powerful accelerator joined the race for the finest light, allowing the best resolving power. Most recently, with the LHC, the simple relation λ = h/p tells us that at 1 TeV (the average collision energy of a quark–quark interaction) we can resolve the attometre, or 10^–18 m, scale. However, thanks to higher energy in some collisions and to sophisticated experimental techniques, the LHC has shown that quarks are point-like at the level of 5 × 10^–20 m, or 50 zeptometres.

But light is only a means, a bridge between reality and our minds, where the image is formed and vision occurs. Indeed the light generated by the LHC would be useless without “eyes” – the LHC detectors that collect the collision events to record the detail illuminated by the light. As with the eyes, the collected information is then transmitted to the mind for image formation. At the LHC, the computers, the physics theory, the brains of the experimentalists and theoretical physicists – all of these form the “mind” where the wonderful images of, for example, the Higgs boson, are formed and, finally, known. Exactly as with sight, some signals (most of them, in fact) are first treated “unconsciously” (by the trigger) and only a selected part is treated consciously on a longer time scale.

Now the LHC is restarting and we will be able to generate light almost as twice as fine, thanks to the 13 TeV collision energy. Moreover, the High-Luminosity LHC project is already on the starting blocks to be ready 10 years from now (see A Luminous future for the LHC). Why high luminosity? Just as in a room where we might ask for more light to investigate finer details and measure the properties of objects more precisely, with the LHC we are planning to increase luminosity by a factor of five (instantaneous) or 10 (integrated) to make more precise measurements and so extend our sight, i.e., the physics reach of the collider and the detectors.

With our accelerators, detectors, computing facilities, physics analysis and theory, we really do reproduce the act of sight, generating the finest light and therefore perceiving a reality that is unimaginable to our normal senses: the frontier of the infinitely small.

Symmetries in Nature: The Scientific Heritage of Louis Michel

By Thibault Damour, Ivan Todorov and Boris Zhilinskii (eds)
World Scientific
Hardback: £83

Reflecting the oeuvre of “a man of two cultures: the culture of pure mathematics and the culture of theoretical physics”, this volume is centred around the notion of symmetry and its breaking. Starting with particle physics, the content proceeds to symmetries of matter, defects and crystals. The mathematics of group extensions, non-linear group action, critical orbits and phase transitions is developed along the way. The symmetry principles and general mathematical tools provide unity in the treatment of different topics. The papers and lecture notes are preceded by a lively biography of Louis Michel, and a commentary that relates his selected works both to the physics of his time and to contemporary trends.

The Bethe Wavefunction

By Michel Gaudin (translated by Jean-Sébastien Caux)
Cambridge University Press
Hardback: £70 $110
E-book: $88

Available in English for the first time, this translation of Michel Gaudin’s book La fonction d’onde de Bethe brings this classic work on exactly solvable models of quantum mechanics and statistical physics to a new generation of graduate students and researchers in physics. The book begins with the Heisenberg spin chain, starting from the co-ordinate Bethe ansatz and culminating in a discussion of its thermodynamic properties. Delta-interacting bosons (the Lieb–Liniger model) are then explored, and extended to exactly solvable models associated to a reflection group. After discussing the continuum limit of spin chains, the book covers six- and eight-vertex models in extensive detail, while later chapters examine advanced topics such as multi-component delta-interacting systems and Gaudin magnets.

Proceedings of the Conference in Honour of the 90th Birthday of Freeman Dyson

By K K Phua, L C Kwek, N P Chang and A H Chan (eds)
World Scientific
Hardback: £56
Paperback: £29
E-book: £22

As a tribute to Freeman Dyson on the occasion of his 90th birthday, and to celebrate his lifelong contributions in physics, mathematics, astronomy, nuclear engineering and global warming, a conference covering a range of topics was held in Singapore in August 2013. This memorial volume brings together an interesting lecture by Professor Dyson, “Is a Graviton Detectable?”, contributions by speakers at the conference, as well as guest contributions by colleagues who celebrated Dyson’s birthday at Rutgers University and the Institute for Advanced Study in Princeton.

Astroparticle, Particle, Space Physics and Detectors for Physics Applications: Proceedings of the 14th ICATPP Conference

By S Giani, C Leroy, L Price, P-G Rancoita and R Ruchti (eds)
World Scientific
Hardback: £117
E-book: £88

Exploration of the subnuclear world is done through increasingly complex experiments covering a range of energy in diverse environments, from particle accelerators and underground detectors to satellites in space. These research programmes call for new techniques, materials and instrumentation to be used in detectors, often of large scale. The reports from this conference review topics that range from cosmic-ray observations through high-energy physics experiments to advanced detector techniques.

What We Would Like LHC to Give Us

By Antonino Zichichi (ed.)
World Scientific
Hardback: £104
E-book: £78

This book is the proceedings of the International School of Subnuclear Physics, ISSP 2012, 50th Course, held in Erice on 23 June–2 July 2012. The course was devoted to celebrations of the 50th anniversary of the subnuclear-physics school, started in 1961 by Antonino Zichichi with John Bell at CERN, and formally established in 1962 by Bell, Blackett, Weisskopf, Rabi and Zichichi in Geneva (at CERN). The lectures cover the latest, most significant achievements in theoretical and experimental subnuclear physics.

Next Generation Experiments to Measure the Neutron Lifetime: Proceedings of the 2012 Workshop

By Susan J Seestrom (ed.)
World Scientific
Hardback: £63
E-book: £47

The neutron lifetime is an important fundamental quantity, as well as a parameter influencing important processes such as nucleosynthesis and the rate of energy production in the Sun, so there is great interest in improving the limits of its value to a precision level of 0.1 s. This workshop, held in November 2012, aimed to create a road map of R&D for a next-generation neutron-lifetime experiment that can be endorsed by the North American neutron community. The focus was on experiments using traps with ultracold neutrons and confinement by a combination of magnetic and/or gravitational interaction to avoid systematic uncertainties introduced by neutron interactions with material walls.

Gravity: Newtonian, Post-Newtonian, Relativistic

By Eric Poisson and Clifford M Will
Cambridge University Press
Hardback: £50 $85
E-book: $68
Also available at the CERN bookshop

I heard good things about this book before I got my hands on it, and turning the pages I recognized a classic. Several random reads of its 788 large, dense pages offered a deeper insight into a novel domain, far away from my daily life where I work with the microscopic and cosmological worlds. On deeper inspection, it was nearly all that I hoped for, with only a couple of areas where I was disappointed.

The forward points out clearly that the reader should not expect any mention of cosmology. Yet the topic of the book has a clear interface with the expanding universe via its connection to our solar system, the so-called vacuole Einstein–Straus solution. Another topic that comes in too short for my taste is that of Eddington’s isotropic (Cartesian) co-ordinates. They appear on pages 268–269, and resurface in a minor mention on page 704 before the authors’ parametrized post-Newtonian approach is discussed. While this is in line with the treatment in the earlier book by one of the authors (Theory and Experiment in Gravitational Physics by C M Will, CUP 1993), it seems to me that this area has grown in significance in recent years.

The book is not about special relativity, but it is a topic that must of course appear. However, it is odd that Box 4.1 on pages 191–192 on “Tests of Special Relativity” relies on publications from 1977, 1966, 1941 and 1938. I can feel the pain of colleagues – including friends in particle and nuclear physics – who have worked hard during recent decades to improve limits by many orders of magnitude. And on page 190, I see a dead point in the history of special relativity – authors, please note. Lorentz failed to write down the transformation named after him by Poincaré, who guessed the solution to the invariance of Maxwell’s equations, a guess that escaped Lorentz. However, Einstein was first to publish his own brilliant derivation.

We know that no book is perfect and complete, entirely without errors and omissions. So the question to be asked is, how useful is this book to you? To find the answer, I’d recommend reading the highly articulate preface available, for example, under “Front Matter” on the publisher’s website. I quote a few words because I could not say it better: “This book is about approximations to Einstein’s theory of general relativity, and their applications to planetary motion around the Sun, to the timing of binary pulsars, to gravitational waves emitted by binary black holes and to many real-life, astrophysical systems…this book is therefore the physics of weak gravitational fields.”

Personally, I found in the book what I was looking for: the technical detail of the physics of large objects such as planets and stars, which can be as many times larger than the proton as they are smaller than the universe. I could not put the book down, despite its weight (1.88 kg). Some might prefer the Kindle edition, but I would hope for a shrunk-silk volume. Whichever you choose or is available, in dollars per page this book is a bargain. It is a great read that will enrich any personal library.

Data Analysis in High Energy Physics: A Practical Guide to Statistical Methods

By Olaf Behnke, Kevin Kröninger, Grégory Schott and Thomas Schörner-Sadenius (eds)
Wiley
Paperback: £60 €72
E-book: £48.99 €61.99
Also available at the CERN bookshop

This book is actually 11 books in one, with 16 authors, four of whom are also editors. All are high-energy physicists, including one theorist, and all are experts in their assigned areas of data analysis, so the general level of the book is excellent. In addition, the editors have done a good job putting the 11 chapters together so that they work as a single book, and they have even given it a global index. Still, each chapter has its own author(s) and its own style, and I will comment on the individual contributions that I found most interesting.

Roger Barlow (“Fundamental Concepts”) gives a good introduction to the foundations, but surprisingly he has some trouble with frequentist probability, which is the one that physicists understand best because it is the probability of quantum mechanics. Instead of taking an example from physics, where experiments are repeatable and frequentist probability is applicable, he uses life insurance and finds problems. But his example for Bayes’s theorem works fine with frequentist probabilities, even if they are not from physics.

Olaf Behnke and Lorenzo Moneta (“Parameter Estimation”) have produced a useful practical guide for their chapter. The treatment is remarkably complete and concise. I especially liked figure 2.9, which illustrates the fit of a typical histogram to a single peak, showing the value of chi-square as a function of peak position across the whole range of the abscissa, with a local minimum at every fluctuation in the data.

Luc Demortier (“Interval Estimation”) displays an impressive knowledge of both frequentist and Bayesian methodologies, and is careful to list the good and bad features of both in a level of detail that I have seen nowhere else, and did not expect to find in a “practical guide”. He succeeds in presenting a balanced view overall, even though his personal prior shows through in the first sentence, where the point estimate is intuitively defined as “in some sense the most likely value”, instead of the more tangible “in some sense the value closest to the true value”.

The most remarkable aspect of this book is found in the chapters devoted to topics that are not usually covered in books on statistics. Therefore “Classification” (by Helge Voss) is treated separately from “Hypothesis Testing” (by Grégory Schott), describing techniques that are common in data analysis but not used in traditional statistics. In “Unfolding”, Volker Blobel reminds us that statistics is really an inverse problem, although it is not usually treated as such. There are two separate chapters on “Theory Uncertainties” and other “Systematic Uncertainties”, a chapter on “Constrained Fits” and two chapters on “Applications”, some of which duplicate subjects treated elsewhere, but of course from a different point of view. In the concluding chapter, Harrison Prosper, in his inimitable style, takes the reader on “a journey to the field of astronomy”.

In summary, this ambitious project has produced a useful book where experimental physicists will find expert knowledge about a range of topics that are indispensable to their work of data analysis.

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Hadrons, nucleons and symmetries

Current tools and future facilities

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