Subject Grouping: Praxis

by Maurice Jacob, Editions Odile Jacob, ISBN 2738109802.

In this topical book, CERN theorist Maurice Jacob glibly traces the evolution of our understanding of the underlying structure of matter, from atoms to quarks – and its implications for cosmology. While the subject is not easy, the author manages to attain a remarkably deep level of insight without writing any equations. The many difficult concepts encountered en route are not glossed over or paraphrased (even though some of them could be). The presentation of the “Schrödinger’s cat” enigma is well done. A few explanations, like parity violation, would have benefited from an explanatory diagram. However, event displays from CERN’s LEP collider provide vivid examples of basic types of interaction.

An introduction manages to bring into the very first paragraph the enigma of quarks – unlike all other constituents of nature, quarks resist being isolated. The meat of the book goes on to trace in detail the mechanisms of the microworld, to climax on the one hand with the Standard Model and the state of particle physics today and on the other its implications for the Big Bang and the birth of the universe, which was initially just a big particle physics experiment.

Then comes a series of essays examining basic questions – the baffling concept of time, antimatter and the structure of the vacuum. Two more chapters look at the sociology of particle physics – how post-Second World War collaboration between scientists has catalysed new international understanding and helped overcome political barriers once perceived as insurmountable, and how this collaboration has attained a truly planetary level for the construction of the new LHC collider at CERN.

The final chapter examines the value of particle physics and its contributions to other branches of science – imaging for medicine and other applications, high-performance detectors, new techniques for data handling and parallel computing and underlines the value of research in education and training.

The book always uses CERN as its focus and reflects the vision of the organization’s spiritual fathers like Louis de Broglie who first saw the need for large-scale international scientific collaboration amid the ruins of post-war Europe.

by George Gamov and Russell Stannard, Cambridge University Press, ISBN 0521639921, pbk £10.95/$16.95.

Mr Tompkins is a dreamy, bemused character who blunders his way through the intricacies of modern physics.

Russell Stannard’s update of George Gamov’s famous portrayal appeared in 1999. At that time, Gamov’s 1965 “science fantasy” anthology was also reissued in paperback. Now the wheel has turned full circle with a paperback version of the new edition. Gamov’s original “Mr Tompkins in Wonderland” story appeared in 1940. Clearly there is still a lot of mileage left in Tompkins.

by Abraham Pais, Oxford University Press,
ISBN 0198506147, hbk £26.50.

The Genius of Science is the last of many books written by Abraham Pais, who died last year.

Pais was an eminent theoretical physicist who gradually became more and more interested in the history of science and produced the much acclaimed biographies of Einstein and Bohr. He was very interested in people and over the years accumulated a large number of friends, many of whom have made very important contributions to physics. Being an excellent speaker, Pais was often invited to address meetings organized in honour of his prestigious colleagues.

The extended versions of these talks make up most of the contents of this book, which Pais also calls A portrait gallery of twentieth-century physicists. Like all of Pais’s books, it is very readable and describes in more or less detail the work and characters of 17 physicists who have left their mark on the development of physics – Niels Bohr, Max Born, Paul Dirac, Albert Einstein, Mitchell Feigenbaum, Res Jost, Oskar Klein, Hendrik Kramers, Tsung Dao Lee and Chen Ning Yang, Wolfgang Pauli, Isidor Rabi, Robert Serber, John von Neumann, Viktor Weisskopf, Eugene Wigner and George Uhlenbeck.

The book is well researched and contains countless interesting anecdotes. One sees clearly that the best work is done by young researchers, and that theoretical physicists can be classified as either “golfers or tennis players” – the former do their creative work alone, while the latter are most creative when they can exchange ideas with others. Luckily, Pais was a tennis man who with this book shares with us his love of physics and his deep interest in people.

Elliot Leader, Cambridge University Press, ISBN 0521352819, hbk £90/$130.

Elliot Leader’s book – in the series of Cambridge Monographs on Particle Physics, Nuclear Physics and Cosmology – is a thorough introduction to the theory and experimental study of high-energy spin physics.

Both theoretically and experimentally, spin physics has always been a challenge. In recent years there has been considerable growth in research activities related to spin phenomena and their theoretical interpretation. There is an extensive list of review papers but few books devoted to the subject.

However, Leader’s book provides a comprehensive introduction, with a pedagogical approach to high-energy spin physics. The novelty of the book is also in the rather detailed description of experimental techniques and apparatus, as well as the standard theoretical part. A large number of appendices with technical details and formalism are valuable for the pedagogical treatment of spin problems and make for quick reference.

A significant part of the monograph deals with the problem of nucleon spin structure – the topic widely discussed since 1988 when the results of the European Muon Collaboration showed that the spin of the proton is not the sum of the spins of its individual quarks.

The small-x behaviour of the polarized structure function is one of the unsolved problems en route to a final resolution of the overall nucleon spin puzzle and is discussed from different points of view. The gluon anomaly and a general perturbative QCD approach to the nucleon spin problem are discussed in detail, including the evolution, scheme-dependence and phenomenology of the polarized parton distributions.

Alongside these topics, an introduction to the parton model, the Standard Model, QCD and the general formalism of polarized deep-inelastic scattering is presented. The helicity structure of QCD interactions is considered thoroughly and fermion spin structure is analysed for the case of massive and massless spinors. Possibilities of testing Standard Model and perturbative QCD predictions in the two-spin and parity-violating single-spin asymmetries measured at large angles are listed. Such experiments are useful tools for the detection of gluon polarization, which is a possible solution of the nucleon spin problem.

Another outstanding problem of spin physics is the observation of significant single-spin transverse asymmetry. In the framework of perturbative QCD, the polarization of an individual quark in a hard subprocess should vanish because of the vector type of the QCD interaction, which leads to chirality conservation. However, experimentally there is a mass of data showing large asymmetries or large polarizations, in both elastic and semi-inclusive reactions.

The different mechanisms for producing non-zero, single-spin transverse asymmetries, including final-state interactions, are considered. All such explanations are in fact beyond the standard QCD parton model. The most prominent single-spin asymmetry was observed in inclusive hyperon production, where over two decades ago it was discovered that highly polarized , L hyperons are produced in the collision of unpolarized protons. Most dramatic is that despite the large hyperon polarization, it has no tendency to decrease with the transverse momentum of the produced hyperon, as could be expected from perturbative QCD mechanisms. This whole area of high-energy physics is a challenge for the theory of strong interactions. Only phenomenological models have had any success in the quantitative description of hyperon polarization data.

One chapter is devoted to spin effects in elastic scattering at high energy, which is a most fundamental type of reaction and where a lot of experimental data exist at low and medium energies. There are also high-energy data that demonstrate a rising dependence of analysing power in proton-proton scattering with transferred momentum. A conclusion made in the book clearly indicates that QCD demands the opposite behaviour of the analysing power in elastic proton-proton scattering, but there are no specific predictions for analysing power based on QCD and it does not provide an estimate for where the decreasing behaviour begins. The experimental study of this process is an indispensable source of knowledge on the nucleon wavefunction and a clear and unambiguous way to check perturbative QCD as well as the models based on the non-perturbative approaches to hadron dynamics.

Significant attention is devoted to technical problems, in particular the mechanisms of polarized hadron and electron production and acceleration. In particular, polarized proton sources, polarized targets, difficulties in the acceleration of polarized particles (including “Siberian snakes”) and polarization at LEP, HERA and SLC are described. This increases the potential reader audience. Besides these problems, the book treats in detail the polarimetry issues that are essential for modern experimental high-energy spin physics, especially for the experimental programme with polarized protons at RHIC.

The first five chapters of the book consider the basic formalism and definitions of spin, helicity, spin-density matrix, transition amplitudes and observables of a reaction. The properties of helicity states and wavefunctions under Lorentz and discrete transformations are described in a clear, pedagogical manner. For example, an intelligible derivation of the famous Thomas precession is presented.

In conclusion, it should be stressed that in the light of ongoing major experimental studies (for example, COMPASS at CERN, RHIC-SPIN at Brookhaven and SPIN@U70 at IHEP), this book is useful and timely, describing the state of the field and providing reference points for the interpretation of forthcoming experimental data in high-energy spin physics – a subject that underwent rapid growth during the last decades of the past century. The book is suitable for students at graduate level and will be of interest to the broad high-energy physics community.