19 April 2018

The Standard Model in a Nutshell • Technology Meets Research: 60 Years of CERN Technology, Selected Highlights • A Primer on String Theory • A Student’s Guide to Dimensional Analysis

The Standard Model in a Nutshell
By Dave Goldberg
Princeton University Press

The Standard Model in a Nutshell

This book is an excellent source for those interested in learning the basic features of the Standard Model (SM) of particle physics – also known as the Glashow–Weinberg–Salam (GSW) model – without many technical details. It is a remarkably accessible book that can be used for self learning by advanced undergraduates and beginning graduate students. All the basic building blocks are provided in a self-contained manner, so that the reader can acquire a good knowledge of quantum mechanics and electromagnetism before reaching the boundaries of the SM, which is the theory that best describes our knowledge of the fundamental interactions.

The topics that the book deals with include special relativity, basic quantum field theory and the action principle, continuous symmetries and Noether’s theorem, as well as basic group theory – in particular, the groups needed in the SM: U(1), SU(2) and SU(3). It also covers the relativistic treatment of fermions through the Dirac equation, the quantisation of the electromagnetic field and a first look at the theory of gauge transformations in a familiar context. This is followed by a reasonable account of quantum electrodynamics (QED), the most accurate theory tested so far. The quantisation rules are reviewed with clarity and a number of useful and classic computations are presented to familiarise the reader with the technical details associated with the computation of decay rates, scattering amplitudes, phase-space volumes and propagators. The book also provides an elementary description of how to construct and compute Feynman rules and diagrams, which are later applied to electron–electron scattering and electron–positron annihilation, and how the latter relates to Compton or electron–photon scattering. This lays the basic computational tools to be used later in the sections about electroweak and strong interactions.

At this point, before starting a description of the SM per se, the author briefly describes the historical Fermi model and then presents the main actors. The reader is introduced to the lepton doublet (including the electron, the muon, the tau and their neutrinos), the weak charged and neutral currents, and the vector bosons that carry the weak force (the Ws and the Z). This is followed by an analysis of electroweak unification and the introduction of the weak angle, indicating how the electromagnetic interaction sits inside the weak isospin and hypercharge. Then, the author deals with the quark doublets and the symmetry breaking pattern, using the Brout–Englert–Higgs mechanism, which gives mass to the vector bosons and permits the accommodation of masses for the quarks and leptons. We also learn about the Cabibbo–Kobayashi–Maskawa mixing matrix, neutrino oscillations, charge and parity (CP) violation, the solar neutrino problem, and so on. To conclude, the author presents the SU(3) gauge theory of the strong interactions and provides a description of some theories that go beyond the SM, as well as a short list of important open problems. All this is covered in just over 250 pages: a remarkable achievement. In addition, the book includes many interesting and useful computations.

This work is a very welcome addition to the modern literature in particle physics and I certainly recommend it, in particular for self study. I hope, though, that in the second edition the correct Weinberg is portrayed on p184… an extremely hilarious blunder.

Luis Alvarez-Gaume, CERN and SUNY (New York, US)

Technology Meets Research: 60 Years of CERN Technology, Selected Highlights
By Christian Fabjan, Thomas Taylor, Daniel Treille and Horst Wenninger (eds.)
World Scientific

Technology Meets Research: 60 Years of CERN Technology, Selected Highlights

This book, the 27th volume in the “Advanced Series on Directions in High Energy Physics”, presents a robust and accessible summary of 60 years of technological development at CERN. Over this period, the foundations of today’s understanding of matter, its fundamental constituents and the forces that govern its behaviour were laid and, piece by piece, the Standard Model of particle physics was established. All this was possible thanks to spectacular advances in the field of particle accelerators and detectors, which are the focus of this volume. Each of the 12 chapters is built using contributions from the physicists and engineers who played key roles in this great scientific endeavour.

After a brief historical introduction, the story starts with the Synchrocyclotron (SC), CERN’s first accelerator, which allowed – among other things – innovative experiments on pion decay and a measurement of the anomalous magnetic dipole moment of the muon. While the SC was a development of techniques employed elsewhere, the Proton Synchroton (PS), the second accelerator constructed at CERN and now the cornerstone of the laboratory’s accelerator complex, was built using the new and “disruptive” strong-focusing technique. Fast extraction from the PS combined with the van der Meer focussing horn were key to the success of a number of experiments with bubble chambers and, in particular, to the discovery of the weak neutral current using the large heavy-liquid bubble chamber Gargamelle.

The book goes on to present the technological developments that led to the discovery of the Higgs boson by the ATLAS and CMS collaborations at the LHC, and the study of heavy-quark physics as a means to understand the dynamics of flavour and the search for phenomena not described by the SM. The taut framework that the SM provides is evident in the concise reviews of the experimental programme of LEP: the exquisitely precise measurements of the properties of the W and Z bosons, as well as of the quarks and the leptons – made by the ALEPH, DELPHI, OPAL and L3 experiments – were used to demonstrate the internal consistency of the SM and to correctly predict the mass of the Higgs boson. An intriguing insight into the breadth of expertise required to deliver this programme is given by the discussion of the construction of the LEP/LHC tunnel, where the alignment requirements were such that the geodesy needed to account for local variations in the gravitational potential and measurements were verified by observations of the stars.

The rich scientific programme of the LHC and of LEP before it have their roots in the systematic development of the accelerator and detector techniques. The accelerator complex at CERN has grown out of the SC.

The book concisely presents the painstaking work required to deliver the PS, the Intersecting Storage Rings (ISR) and the Super Proton Synchrotron (SPS). Experimentation at these facilities established the quark-parton model and quantum chromodynamics (QCD), demonstrated the existence of charged and neutral weak currents, and pointed out weaknesses in our understanding of the structure of the nucleon and the nucleus. The building of the SPS was expedited by the decision to use single-function magnets that enabled a staged approach to its construction. The description of the technological innovations that were required to realise the SPS includes the need for a distributed, user-friendly control-and-monitoring system. A novel solution was adopted that exploited an early implementation of a local-area network and for which a new, interpretative programming language was developed.

The book also describes the introduction of the new isotope separation online technique, which allows highly unstable nuclei to be studied, and its evolution into research on nuclear matter in extreme conditions at ISOLDE and its upgrades. The study of heavy-ion collisions in fixed target experiments at the SPS collider and now in the ALICE experiment at the LHC, has its roots in the early nuclear-physics programme as well. The SC, and later the PS, were ideal tools to create the intense low-energy beams used to test fundamental symmetries, to search for rare decays of hadrons and leptons, and to measure the parameters of the SM.

Reading this chronicle of CERN’s outstanding record, I was struck by its extraordinary pedigree of innovation in accelerator and detector technology. Among the many examples of groundbreaking innovation discussed in the book is the construction of the ISR which, by colliding beams head on, opened the path to today’s energy

frontier. The ISR programme created the conditions for pioneering developments such as the multi-wire proportional chamber, and the transition radiation detector as well as large-acceptance magnetic spectrometers for colliding-beam experiments. Many of the technologies that underpin the success of the proton–antiproton (Spp S) collider, LEP and the LHC, were innovations pioneered at the ISR. For example, the discovery of the W and Z bosons at the Spp S relied on the demonstration of stochastic cooling and antiproton accumulation. The development of these techniques allowed CERN to establish its antiproton programme, which encompassed the search for new phenomena at the energy frontier, as well as the study of discrete symmetries using neutral kaons at CPLEAR and the detailed study of the properties of antimatter.

The volume includes contributions on the development of the computing, data-handling and networking systems necessary to maximise the scientific output of the accelerator and detector facilities. From the digitisation and handling of bubble- and spark-chamber images in the SC era, to the distributed processing possible on the worldwide LHC computing grid, the CERN community has always developed imaginative solutions to its data-processing needs.

The book concludes with thoughtful chapters that describe the impact on society of the technological innovations driven by the CERN programme, the science and art of managing large, technologically challenging and internationally collaborative projects, and a discussion of the R&D programme required to secure the next 60 years of discovery.

The contributions from leading scientists of the day collected in this relatively slim book document CERN’s 60-year voyage of innovation and discovery, the repercussions of which vindicate the vision of those who drove the foundation of the laboratory – European in constitution, but global in impact. The spirit of inclusive collaboration, which was a key element of the original vision for the laboratory, together with the aim of technical innovation and scientific excellence, are reflected in each of the articles in this unique volume.

Kenneth Long, Imperial College, UK

Books received

A Primer on String Theory
By Volker Schomerus
Cambridge University Press

This textbook aims to provide a concise introduction to string theory for undergraduate and graduate students.

String theory was first proposed in the 1960s and has become one of the main candidates for a possible quantum theory of gravity. While going through alternate phases of highs and lows, it has influenced numerous areas of physics and mathematics, and many theoretical developments have sprung from it.

It was the intention of the author to include in the book just the fundamental concepts and tools of string theory, rather than to be exhaustive. As Schomerus states, there are already various textbooks available that cover this field in detail, from its roots to its most modern developments, but these might be dispersive and overwhelming for students approaching the topic for the first time.

The volume is composed of a brief historical introduction and two parts, each including various chapters. The first part is dedicated to the dynamics of strings moving in a flat Minkowski space. While these string theories do not describe nature, their study is helpful to understand many basic concepts and constructions, and to explore the relation between string theory and field theory on a two-dimensional “world”.

The second part deals with string theories for four-dimensional physics, which can be relevant to the description of our universe. In particular, the motion of superstrings on backgrounds in which some of the dimensions are curled up is studied (this phenomenon is called compactification). This part, in turn, includes three sections devoted to as many subtopics.

First, the author discusses conformal field theory, also dealing with the SU(2) Wess–Zumino–Novikov–Witten model. Then, he passes on to treat Calabi–Yau spaces and the associated string compactification. Finally, he focuses on string dualities, giving special emphasis to the AdS/CFT correspondence and its application to gauge theory.

A Student’s Guide to Dimensional Analysis
By Don S Lemons
Cambridge University Press

Dimensional analysis is a mathematical technique that allows one to deduce the relationship between different physical quantities from the dimensions of the variables involved in the system under study. It provides a method to simplify – when possible – the resolution of complex physical problems.

This short book provides an introduction to dimensional analysis, covering its history, methods and formalisation, and shows its application to a number of physics and engineering problems. As the author explains, the foundation principle of dimensional analysis is essentially a more precise version of the well known rule against “adding apples and oranges”; nevertheless, the successful application of this technique requires physical intuition and some experience. Most of the time it does not lead to the solution of the problem, but it can provide important hints about the direction to take, constraints on the relationship between physical variables and constants, or a confirmation of the correctness of calculations.

After a chapter covering the basics of the method and some historical notions about it, the book offers application examples of dimensional analysis in several areas: mechanics, hydrodynamics, thermal physics, electrodynamics and quantum physics. Through the solution of these real problems, the author shows the possibilities and limitations of this technique. In the final chapter, dimensional analysis is used to take a few steps in the direction of uncovering the dimensional structure of the universe.

Aimed primarily at physics and engineering students in their first university courses, it can also be useful to experienced students and professionals. Being concise and providing problems with solutions at the end of each chapter, the book is ideal for self study.

Compiled by Virginia Greco, CERN.

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