Jobs – Page 260 of 524

Basic Concepts of String Theory

By Ralph Blumenhagen, Dieter Lüst and Stefan Theisen
Springer
Hardback: £72 €84.35 $99
E-book: £56.99 €67.82 $69.95

This new textbook features an introduction to string theory, a fundamental line of research in theoretical physics during recent decades. String theory provides a framework for unifying particle physics and gravity in a coherent manner and, moreover, appears also to be consistent at the quantum level. This sets it apart from other attempts at that goal. More generally, string theory plays an important role as a generator of ideas and “toy” models in many areas of theoretical physics and mathematics; the spin-off includes the application of mathematical methods, originally motivated by and developed within string theory, to other areas. For example, string theory helps in the understanding of certain properties of gauge theories, black holes, the early universe and heavy-ion physics.

Thus any student and researcher of particle physics should have some knowledge of this important field. The book under discussion provides an excellent basis for that. It encompasses a range of essential and advanced topics, aiming at mid – to high-level students and researchers who really want to get into the subject and/or would like to look up some facts. For beginners, who just want to gain an impression of what string theory is all about, the book might be a little hefty and deterring. It really requires a serious effort to master it, and corresponds to at least a one-year course on string theory.

The book offers a refreshing mix of basic facts and up-to-date research, and avoids giving too much space to formal and relatively boring subjects such as the quantization of the bosonic string. Rather, the main focus is on the construction and properties of the various string theories in 10 dimensions and their compactifications to lower dimensions; it also includes thorough discussions of D-branes, fluxes and dualities. A particular emphasis is given to the two-dimensional world-sheet, or conformal field-theoretical point of view, which is more “stringy” than the popular supergravity approach. Filling this important gap is one of the strengths of this book, which sets it apart from other recent, similar books.

This is in line with the general focus of the book, namely the unification aspect of string theory, whose main aim is to explain, or at least describe, all known particles and interactions in one consistent framework. In recent years, additional aspects of string theory have been become increasingly popular and important lines of research, including the anti-de-Sitter/conformal-field-theory (AdS/CFT) correspondence and the quantum properties of black holes. The book barely touches on these subjects, which is wise because even the basic material would be more than would fit into the same book. For these subjects, a second volume may be in order.

All in all, this book is a perfect guide for someone with some moderate prior exposure to field and string theory, who likes to get into the principles and technical details of string model construction.

Lectures on Quantum Mechanics

By Steven Weinberg
Cambridge University Press
Hardback: £40 $75

This is a beautifully written book that is crafted with precision and is full of insight. However, this is for most people not the book from which to learn quantum mechanics for the first time. The cover notes acknowledge this and the book is advertised as being “ideally suited to a one-year graduate course” and “a useful reference for researchers”. That is not to say that it deals only with advanced material – the theory is built up from scratch and the logical structure is quite traditional.

The book starts with a careful exposition of the early history and the Schrödinger-equation analysis of the hydrogen atom and the harmonic oscillator, before moving on to cover the general principles, angular momentum and symmetries. The middle part of the book is concerned with approximate methods and develops the theory starting from time-independent perturbations and ending with the general theory of scattering. The final part deals mainly with the canonical formalism and the behaviour of a charged particle in an electromagnetic field, including the quantization of the field and the emergence of photons. The final chapter covers entanglement, the Bell inequalities and quantum computing, all in a mere 14 pages.

Perhaps what distinguishes this book from the competition is its logical coherence and depth, and the care with which it has been crafted. Hardly a word is misplaced and Weinberg’s deep understanding of the subject matter means that he leaves no stone unturned: we are asked to accept very little on faith. Examples include Pauli’s purely algebraic calculation of the hydrogen spectrum, the role of the Wigner-Eckhart theorem in a proper appreciation of the Zeeman effect and in atomic selection rules, as well as the emergence of geometrical phases. There is also a thoughtful section on the interpretations of quantum mechanics.

Weinberg has a characteristic style – his writing is full of respect for the reader and avoids sensational comments or attempts to over-emphasize key points. The price we pay is that the narrative is rather flat but in exchange we gain a great deal in elegance and content – it is for the reader to follow Weinberg in discovering the joys of quantum mechanics through a deeper level of understanding: I loved it!

Stochastic Cooling of Particle Beams

By Dieter Möhl
Springer
Paperback: £31.99 €36.87 $39.50
E-book: £24.99 €29.74 $49.95

Over the past decades, stochastic cooling of particle beams has grown, thrived and led to breathtaking results in physics from accelerator labs around the world. Now, great challenges lie ahead in the context of future projects, which strive for highly brilliant secondary-particle beams. For newcomers and researchers alike, there is no better place to learn about stochastic cooling than this book.

Dieter Möhl was one of the foremost experts in the field; ever since the beginning of the adventure in the 1970s, in the team of Simon van der Meer at CERN. Here he has surpassed himself to produce a personal book based not only on his masterful lectures over the years, but also covering, in the proper context and depth, additional subjects that have previously been dispersed across the specialized literature. He goes further by illustrating concepts with his recent personal studies on future projects (e.g. the accumulator ring RESR for the FAIR project) and is well placed to suggest innovations (e.g. alternative methods for stacking and momentum cooling, “split-function” lattices). Insightful remarks based on his experience, invaluable calculation recipes, realistic numerical examples, as well as an excellent bibliography go together to round up the whole book.

In this self-contained book, Möhl provides a superb pedagogical and concise treatment of the subject, from fundamental concepts up to advanced subjects. He describes the analytical formalism of stochastic cooling, stressing, whenever important, its interplay with the machine hardware and beam diagnostics.

The first six chapters introduce the ingredients of the state of the art of stochastic cooling. With deep insight, Möhl explains in chapter 2 all of the different techniques for betatron and/or momentum cooling. This is the most thorough yet compact overview that I know of, a great service to system designers and operators. In both the time-domain and frequency-domain pictures, the reader is guided step by step and with great clarity into delicate aspects of the subject (for instance, the mixing and power requirements) as well as rather complex calculations (such as for betatron cooling, the feedback via the beam and the cooling by nonlinear pickups and kickers). A great help to newcomers and a handy reference for the experts comes in the form of the comprehensive summary on the pickup and kicker impedances in chapter 3 as well as the discussion of the Schottky noise in chapter 4.

Chapter 7 deals with the Fokker-Planck equation and remarkably summarizes its most important application, namely in modelling the beam accumulation by stochastic cooling. The notoriously difficult bunched-beam cooling, which is of great interest for future colliders, is lucidly reviewed in chapter 8.

Dieter Möhl had practically finished the book when he unexpectedly passed away. Throughout this work of reference, his modesty and generosity emerge together with the quintessence of stochastic cooling, as part of his legacy.

Novel Superfluids: Volume 1

By Karl-Heinz Bennemann and John B Ketterson (eds.)
Oxford University Press
Hardback: £125 $210

This volume reports on the latest developments in the field of superfluidity. The phenomenon has had a tremendous impact on the fundamental sciences as well as a host of technologies. In addition to metals and the helium liquids, the phenomenon has now been observed for photons in cavities, excitons in semiconductors, magnons in certain materials and cold gasses trapped in high vacuum. It very likely exists for neutrons in a neutron star and, possibly, in a conjectured quark state at their centre. Even the universe itself can be regarded as being in a kind of superfluid state. All of these topics are discussed by experts in the respective subfields.

An Introduction to Non-Perturbative Foundations of Quantum Field Theory

By Franco Strocchi
Oxford University Press
Hardback: £55 $98.50

Quantum Field Theory (QFT) has proved to be the most useful strategy for the description of elementary-particle interactions and as such is regarded as a fundamental part of modern theoretical physics. In most presentations, the emphasis is on the effectiveness of the theory in producing experimentally testable predictions, which at present essentially means perturbative QFT. However, after more than 50 years of QFT, there is still no single non-trivial (even non-realistic) model of QFT in 3+1 dimensions, allowing a non-perturbative control. This book provides general physical principles and a mathematically sound approach to QFT. It covers the general structure of gauge theories, presents the charge superselection rules, gives a non-perturbative treatment of the Higgs mechanism and covers chiral symmetry breaking in QCD without instantons

Industrial Accelerators and Their Applications

By Robert W Hamm and Marianne E Hamm (eds.)
World Scientific
Hardback: £100
E-book: £127

This new book provides a comprehensive review of the many current industrial applications of particle accelerators, written by experts in each of these fields. Readers will gain a broad understanding of the principles of these applications, the extent to which they are employed and the accelerator technology utilized. It also serves as a thorough introduction to these fields for non-experts and laymen alike. Owing to the growing number of industrial applications, there is an increased interest among accelerator physicists and many other scientists worldwide in understanding how accelerators are used in various applications. Many industries are also doing more research on how they can improve their products or processes using particle beams.

Imaging gaseous detectors and their applications

By Eugenio Nappi and Vladimir Peskov
Wiley-VCH
Hardback: €139
Paperback: €124.99

For those who belong to the Paleozoic era of R&D on gas detectors, this book evokes nostalgic memories of the hours spent in dark laboratories chasing sparks under black cloths, chasing leaks with screaming “pistols”, taming coronas with red paint and yellow tape and, if you belonged to the crazy ones of Building 28 at CERN, sharing a glass of wine and the incredible maggoty Corsican cheese with Georges Charpak. Subtitle it “The sorcerer’s Apprentice”, and an innocent student might think they have entered the laboratory of Merlin: creating electrons from each fluttering photon, making magical mixtures of liquids, exotic vapours, funny thin films and all of the strange concoctions that inhabited the era of pioneering R&D and led step-by-step to today’s devices.

The historical memory behind this book recalls all sorts of gaseous detectors that have been dreamt up by visionary scientists over the past 50 years: drift chambers, the ambitious time-projection chamber, resistive plate chambers, ring-imaging Cherenkov counters, parallel-plate avalanche counters, gas electron multipliers, Micromegas, exotic micro-pattern gaseous detectors (MPGDs) and more. All are included, both the ones that behaved and the ones that did not pay off – providing no excuse for anyone to re-make mistakes after reading the book. All of the basic processes that populate gas counters are reviewed and their functioning and limitations are explained in a simple and concise manner offering, to the attentive reader, key secrets and the solutions to obviate hidden traps. From the basic ionization processes to the trickiness of the streamer and breakdown mechanism, from the detection of a single photon to the problems of high rates – only lengthy, hands-on experience supported by a profound understanding of the physics of the detection processes could bring together the material that this book covers. Furthermore, it includes many notable explanations that are crystal clear yet also suitable for the theoretical part of a high-profile educational course.

Coming to more recent times, the use of microelectronics techniques in the manufacturing process of gas counters has paved the road to the new era of MPGDs. The authors follow this route, the detector designs and the most promising future directions and applications, critically but with great expectation, leaving the reader confident of many developments to come.

Each of us will find in this book some corner of our own memory, the significance of our own gaseous detector in recent and current experiments, together with a touch of the new in exploring the many possible applications of gas counters in medicine, biology or homeland security and – when closing the book – the compelling need to stay in the lab. Chapeau!

AMS measures antimatter excess in space

CCnew1_04_13 — Perched on the International Space Station around 400 km above the Earth, the Alpha Magnetic Spectrometer (AMS) collects data from primary cosmic rays before they can interact with the atmosphere.
Image credit: NASA.

The international team running the Alpha Magnetic Spectrometer (AMS) has announced the first results in its search for dark matter. They indicate the observation of an excess of positrons in the cosmic-ray flux. The results were presented by Samuel Ting, the spokesperson of AMS, in a seminar at CERN on 3 April, the date of publication in Physical Review Letters.

The AMS results are based on an analysis of some 2.5 × 10¹⁰ events, recorded over a year and a half. Cuts to reject protons, as well as electrons and positrons produced in the interactions of cosmic rays in the Earth’s atmosphere, reduce this to around 6.8 × 10⁶ positron and electron events, including 400,000 positrons with energies between 0.5 GeV and 350 GeV. This represents the largest collection of antimatter particles detected in space.

The data reveal that the fraction of positrons increases from 10 GeV to 250 GeV, with the slope of the increase reducing by an order of magnitude over the range 20–250 GeV. The data also show no significant variation over time, or any preferred incoming direction. These results are consistent with the positrons’ origin in the annihilation of dark-matter particles in space but they are not yet sufficiently conclusive to rule out other explanations.

The AMS detector is operated by a large international collaboration led by Nobel laureate Samuel Ting. The collaboration involves some 600 researchers from China, Denmark, Finland, France, Germany, Italy, Korea, Mexico, the Netherlands, Portugal, Spain, Switzerland, Taiwan and the US. The detector was assembled at CERN, tested at ESA’s ESTEC centre in the Netherlands and launched into space on 16 May 2011 on board NASA’s Space Shuttle Endeavour. Designed to study cosmic rays before they interact with the Earth’s atmosphere, the experiment is installed on the International Space Station. It tracks incoming charged particles such as protons and electrons, as well as antimatter particles such as positrons, mapping the flux of cosmic rays with unprecedented precision.

An excess of antimatter within the cosmic-ray flux was first observed around two decades ago in experiments flown on high-altitude balloons and has since been seen by the PAMELA detector in space and the Large Area Telescope on the Fermi Gamma-ray Space Telescope. The origin of the excess, however, remains unexplained.

One possibility, predicted by theories involving supersymmetry, is that positrons could be produced when two particles of dark matter collide and annihilate. Assuming an isotropic distribution of dark-matter particles, these theories predict the observations made by AMS. However, the measurement by AMS does not yet rule out the alternative explanation that the positrons originate from pulsars distributed around the galactic plane. Moreover, supersymmetry theories also predict a cut-off at higher energies above the mass range of dark-matter particles and this has not yet been observed.

AMS is the first experiment to measure to 1% accuracy in space – a level of precision that should allow it to discover whether the positron observation has an origin in dark matter or in pulsars. The experiment will further refine the measurement’s precision over the coming years and clarify the behaviour of the positron fraction at energies above 250 GeV.

ATRAP makes world’s most precise measurement of antiproton magnetic moment

CCnew2_04_13 — Stephan Ettenauer with the Penning trap apparatus that allows measurements of single antiprotons in the ATRAP experiment.

The Antihydrogen TRAP (ATRAP) experiment at CERN’s Antiproton Decelerator has reported a new measurement of the antiproton’s magnetic moment made with an unprecedented uncertainty of 4.4 parts per million (ppm) – a result that is 680 times more precise than previous measurements. The unusual increase in precision results from the experiment’s ability to trap individual protons and antiprotons, as well as from using a large magnetic gradient to gain sensitivity to the tiny magnetic moment.

By applying its single particle approach to the study of antiprotons, the ATRAP experiment has been able make precise measurements of the charge, mass and magnetic moment of the antiproton. Using a Penning trap, the antiproton is suspended at the centre of an iron ring-electrode that is sandwiched between copper electrodes. Thermal contact with liquid helium keeps the electrodes at 4.2 K, providing a nearly perfect vacuum that eliminates the stray matter atoms that could otherwise annihilate the antiproton. Static and oscillating voltages applied to the electrodes allow the antiproton to be manipulated and its properties to be measured.

The result is part of an attempt to understand the matter–antimatter imbalance of the universe. In particular, a comparison of the antiproton’s magnetic moment with that of the proton, tests the Standard Model and its CPT theorem at high precision. The ATRAP team found that the magnetic moments of the antiproton and proton are “exactly opposite”: equal in strength but opposite in direction with respect to the particle spins and consistent with the prediction of the Standard Model and the CPT theorem to 5 parts per million.

However, the potential for much greater measurement precision puts ATRAP in position to test the Standard Model prediction much more stringently. Combining the single particle methods with new quantum methods that make it possible to observe individual antiproton spin flips should make it feasible to compare an antiproton and a proton to 1 part per billion or better.

Precision measurements of B⁰_s mesons put the squeeze on new physics

The “winter” conferences earlier this year saw the LHCb collaboration present three important results from its increasingly precise search for new physics.

One fascinating area of study is the quantum-mechanical process in which neutral mesons such as the D⁰, B⁰ and B⁰_s can oscillate between their particle and antiparticle states. The B⁰_s mesons oscillate with by far the highest frequency of about 3 × 10¹² times per second, on average about nine times during their lifetime. In an updated study, the collaboration looked at the decays of B⁰_s mesons into D^–_sπ⁺ with D^–_s decays reconstructed in five different channels. While the B⁰_s oscillation frequency Δm_s has been measured before, the oscillations themselves had been previously seen only by folding the decay-time distribution onto itself at the period of the measured oscillation. In this updated analysis the oscillation pattern is spectacularly visible over the full decay-time distribution, as figure 1 shows. The measured value of the oscillation frequency is Δm_s = 17.768 ± 0.023 ± 0.006 ps^–1, which is the most precise in the world (LHCb collaboration 2013a).

CCnew3_04_13 — Fig. 1. The decay-time distribution measured for B⁰_s oscillations.

CP violation can occur in the B⁰_s sector – in the interference between the oscillation and decay of the meson – but it is expected to be a small effect in the Standard Model. Knowledge of such CP-violating parameters is important because they set the scale of the difference between properties of matter and antimatter; they may also reveal effects of physics beyond the Standard Model. LHCb has previously reported on a study of B⁰_s decays into J/ψ φ and J/ψ π⁺π^– final states, but now the analysis has been finalized. One important improvement is in the flavour tagging, which determines whether the initial state was produced as a B⁰_s or anti-B⁰_s meson. This decision was previously based on “opposite-side” tagging, i.e. from measuring the particle/antiparticle nature of the other b-quark produced in conjunction with the B⁰_s. The collaboration has now achieved improved sensitivity by including “same-side” tagging, from the charge of a kaon produced close to the B⁰_s, as a result of the anti-s-quark produced in conjunction with the B⁰_s. This increases the statistical power of the tagging by about 40%. The values of the CP-violating parameter φ_s, together with the difference in width of the heavy and light B⁰_s mass states, ΔΓ_s, are shown in figure 2, which also indicates the small allowed region for these two parameters, corresponding to φ_s = 0.01 ± 0.07 ± 0.01 rad and ΔΓ_s = 0.106 ± 0.011 ± 0.007 ps^–1 (LHCb collaboration 2013b)

CCnew5_04_13 — Two-dimensional profile likelihood in the (ΔΓ_s, φ_s) plane showing the small allowed region for the two parameters.

Last, the collaboration has opened a door for important future measurements with a first study of the time-dependent CP-violating asymmetry in hadronic B⁰_s meson decays into a φφ pair, a process that is mediated by a so-called penguin diagram in the Standard Model. Both φ mesons decay in turn into a K⁺K^– pair. The invariant mass spectrum of the four-kaon final state shows a clean signal of about 880 B⁰_s → φφ decays. A first measurement of the CP-violating phase φ_s for this decay indicates that it lies in the interval of (–2.46, –0.76) rad at 68% confidence level. This is consistent with the small value predicted in the Standard Model, at the level of 16% probability. Although the current precision is limited, this will become a very interesting measurement with the increased statistics from further data taking (LHCb collaboration 2013c)

These results represent the most precise measurements to date, based on data corresponding to the 1 fb^–1 of integrated luminosity that LHCb collected in 2011. They are in agreement with the Standard Model predictions and significantly reduces the parameter region in which the signs of new physics can still hide.

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