Jobs – Page 110 of 527

Particles mean prizes

Just five research areas account for more than half of Nobel prizes, even though they publish only 10% of papers, reveals a study by social scientists John Ioannidis, Ioana-Alina Cristea and Kevin Boyack. The trio mapped the number of Nobel prizes in medicine, physics and chemistry between 1995 and 2017 to 114 fields of science, finding that particle physics came top with 14%, followed by cell biology (12%), atomic physics (11%), neuroscience (10%) and molecular chemistry (5%). The analysts also investigated whether Nobel success reflects immediate scientific impact, and found that the only key paper associated with a Nobel Prize which was the most cited that year pertains to the 2010 award to Andre Geim and Konstantin Novoselov for experiments with graphene. On average, more than 400 papers had greater impact than the work most closely associated with the prize-winners’ success within a year either side of the publication dates.

Particle-physics prize-winners in the period studied include: Perl and Reines (1995) for the discovery of the tau lepton and the detection of the neutrino; ’t Hooft and Veltman (1999) for contributions to electroweak theory; Davis and Koshiba (2002) for the detection of cosmic neutrinos; Gross, Politzer and Wilczek (2004) for asymptotic freedom; Nambu, Kobayashi and Maskawa (2008) for work on spontaneous symmetry breaking and quark mixing; Englert and Higgs (2013) for the Brout–Englert–Higgs mechanism; and Kajita and McDonald (2015) for the discovery of neutrino oscillations. The team also chose to class Mather and Smoot’s 2006 prize relating to the cosmic microwave background, Perlmutter, Schmidt and Riess’s 2011 award for the discovery of the accelerating expansion of the universe, and Weiss, Barish and Thorne’s 2017 gong for the observation of gravitational waves as particle-physics research.

The winners of this year’s Nobel prize in physics will be announced on Tuesday 6 October.

Horst Wenninger: 1938-2020

Former CERN director Horst Wenninger, who played key roles in the approval of the LHC and in establishing knowledge transfer at CERN, passed away on 16 July. Horst was universally trusted and his advice was sought regularly by colleagues. He knew his way around CERN like no one else, and knew whom to contact to get things done (and, crucially, how to get them to do it). Before becoming a physicist, Horst had considered becoming a diplomat. Somehow, he managed to combine the two professions, all in the interest of CERN. He cultivated the art of connecting scientists, engineers and administrators – always with the aim of achieving a clear goal.

Born in Wilhelmshaven, Germany in 1938, the third child of a naval officer, Horst earned his PhD in nuclear physics from Heidelberg University in 1966. Two years later he joined CERN to participate in the Big European Bubble Chamber (BEBC). From the outset Horst was inspired by CERN. Early on he saw the importance of the Laboratory for establishing peaceful worldwide collaboration and relished participating in the adventure.

He was soon identified as a leader, first as physics coordinator for the BEBC in 1974. In 1980 he went to DESY to work on electron–positron collider physics in preparation for LEP, returning to CERN in 1982 to lead the BEBC group. In 1984 he became head of the experimental facilities division, providing support for Omega, UA1 and UA2. For the R&D and construction of the LEP detectors Horst needed to implement a new style of collaboration: for the first time, major parts of the detectors had to be financed, developed and provided by outside groups with central CERN coordination. In 1990 he became leader of the accelerator technologies division, and in 1993 he was appointed LHC deputy project leader, where his profound knowledge of CERN was vital for the reassessment of the LHC project.

The wider community also benefited immensely from his contributions in advisory roles throughout his active life

Horst’s five-year term as CERN research and technical director began in 1994 – the year LHC approval was expected. The day before the crucial vote by the CERN Council in December of that year, the German delegation was still not authorised to vote in support of the project. In a latenight action Horst managed to arrange contact with the office of the German chancellor, with the mission to sway the minister responsible for the CERN decision. His cryptic reaction was conveniently interpreted by the supportive German delegate as a green light, a determined move for the good of CERN. Horst was later awarded the Order of Merit (First Class) of the German Republic.

In 2000 Horst helped launch the CERN technology transfer division and chaired the technology advisory board. Also, thanks largely to his drive, the 2017 book Technology Meets Research – 60 Years of CERN Technology: Selected Highlights was published. Horst retired from CERN in 2003, but continued to make major contributions. He was asked to provide guidance for the FAIR project at GSI Darmstadt, where he was instrumental in arranging the involvement of CERN accelerator experts and later steered the complex and delicate organisation of major international “in-kind” contributions. When, in 2019 the EU approved the “South-East European International Institute for Sustainable Technologies” (SEEIIST), Horst was appointed to coordinate the projects first phase.

Horst left his mark on CERN. The wider community also benefited immensely from his contributions in advisory roles throughout his active life. We have lost an outstanding colleague and a good friend from whose enthusiasm, advice and wisdom we all benefited tremendously.

Turning the screw on H → μμ

The first evidence for the coupling of the Higgs boson to a second-generation fermion, the muon, has been reported at the LHC. At the 40th International Conference on High Energy Physics, held from 28 July to 6 August, CMS reported a 3σ excess of H → μμ decay candidates compared to the expected sample under the hypothesis of no coupling between the Higgs boson and the muon. A similar analysis by the ATLAS collaboration yielded a 2σ excess for the coupling.

The latest measurements of the Higgs boson by ATLAS and CMS follow 5σ observations of its coupling to the tau lepton in 2015 and to the top and bottom quarks in 2018, all of which are third-generation fermions. Its couplings to W and Z bosons have also been established at 5σ confidence. Within present experimental accuracy, all couplings between the Higgs boson and other Standard Model particles correspond to the strength of interaction that would give the particles their observed masses, according to the Brout–Englert–Higgs mechanism. In this model, the particles acquire mass through spontaneous symmetry breaking; the W and Z as a result of a local gauge symmetry and the fermions, such as the muon, as a result of Yukawa couplings to the Higgs field – a novel type of interaction among fundamental particles that is not derived from a symmetry principle. Any deviation from the expected couplings would imply that the Higgs sector is more complicated than this minimal scenario.

Couplings to lighter particles are expected to be proportionately smaller and more difficult to observe. The decay to two muons, H → μμ, is expected to occur with a branching fraction of just one in 5000 Higgs-boson decays, and is overwhelmed by backgrounds from the Drell–Yan process.

The new results sharpen the question of why there is a hierarchy of particle masses
John Ellis

The new ATLAS and CMS analyses, which deploy the entire 13 TeV Run-2 data set, include events where the Higgs boson was produced according to four topologies gluon fusion, which accounts for the creation of 87% of the Higgs bosons observed at the LHC; vector-boson fusion; the production of a Higgs boson in association with a weak vector boson; and its production in association with a top quark–antiquark pair. Uniquely, CMS simulated the background to the vector-boson-fusion signal rather than fitting it from data – a procedure that would have incurred additional statistical uncertainty – resulting in the topology contributing roughly equal statistical power compared to gluon fusion.

Machine learning
“The first evidence in CMS was reached thanks to the excellent performance of our muon and tracking systems, and an improved signal/background discrimination with machine-learning techniques,” says Andrea Rizzi, CMS physics co-coordinator.

The signature for the decay is a small excess of events near a muon-pair invariant mass of 125 GeV – the mass of a Higgs boson. CMS reports an overall signal strength of 1.2 ± 0.4, while ATLAS finds a signal strength of 1.2 ± 0.6, with the uncertainties dominated by their statistical component. “Both measurements are compatible with the Standard Model,” says ATLAS physics coordinator Klaus Mönig. “Assuming the H → μμ coupling predicted by the Standard Model, and extrapolating the current results, the combined sensitivity could get near the observation threshold of 5σ at the end of Run 3, from 2022 to 2024.”

If there is only a single Higgs field, it should provide the masses for all the Standard-Model particles, but there may be additional Higgs fields that could make contributions to their masses. The new results therefore reduce the scope available to such multi-Higgs models, and sharpen the question of why there is a hierarchy of particle masses, says John Ellis of King’s College London. “Why is the Higgs coupling to the muon so different from its coupling to the tau lepton, whereas the couplings of the W boson to tau leptons and muons are equal to within a couple of percent? The more we learn about the Higgs, the more mysterious it seems!”

ICHEP’s online success

Originally set to take place in Prague, the International Conference of High Energy Physics (ICHEP) took place virtually from 28 July to 6 August. Running a major biennial meeting virtually was always going to be extremely difficult, but the local organisers rose to the challenge by embracing technologies such as Zoom and YouTube. To allow global participation, the conference was spread over eight days rather than the usual six, with presentations compressed into five-hour slots that were streamed twice: first as a live “premiere” and later as recorded “replay” sessions, for the benefit of participants in different time zones.

This was the first ICHEP meeting since the publication of the update of the European strategy for particle physics, which presented an ambitious vision for the future of CERN. Though VIP-guest Peter Gabriel – rock star and human rights advocate – may not have been aware of this when delivering his opening remarks, his urging that delegates speak up for science and engage with politicians resonated with the physicists virtually present.

Many scientific highlights were covered at ICHEP and it is only possible to scratch the surface here. The results from all four major LHC experiments were particularly impressive and the collective progress in understanding the properties of neutrinos shows no sign of slowing down.

Higgs physics
ATLAS and CMS presented the first evidence for the decay of the Higgs boson into a pair of muons. Combined, the results provide strong evidence for the coupling of the Higgs boson to the muon, with the strength of the coupling consistent with that predicted in the Standard Model. Prior to these new results, the Higgs had only been observed to couple to the much heavier third-generation fermions and the W and Z gauge bosons. The measurements also provide further evidence for the linearity of the Higgs coupling, now over four orders of magnitude (from the muon to top quark), indicating the universality of the Standard-Model Higgs boson as the mechanism through which all Standard Model particles acquire mass. These are highly non-trivial statements.

ATLAS also presented a combined measurement of the Higgs signal strength, which describes a common scaling of the expected Higgs-boson yields in all processes, of 1.06 ± 0.07. In this measurement, the experimental and theoretical uncertainties are now roughly equal, emphasising the ever-increasing importance of theoretical developments in keeping up with the experimental progress; a feature that will ultimately determine the precision that will be reached by the LHC and high-luminosity LHC (HL-LHC) Higgs physics programmes.

The range of Standard Model measurements presented at ICHEP 2020 by ATLAS and CMS was truly impressive

More generally, the precision we are seeing from the ATLAS and CMS Run 2 proton–proton data is truly impressive, and an exciting indication of what is to come as the integrated luminosity accumulated by the experiments ramps up, and then ramps up again in the HL-LHC era. One interesting new example was the first observation of WW production from photon–photon collisions, where the photons are radiated from the incoming proton beams. This is a neat measurement that demonstrates the breadth of physics accessible at the LHC.

Overall, the range of Standard Model measurements presented at ICHEP 2020 by ATLAS and CMS was truly impressive and we should not forget that it is still relatively early in the LHC programme. In parallel, direct searches for new phenomena, such as supersymmetry and the “unexpected”, continues apace. Results from direct searches at the energy frontier were covered in numerous parallel session presentations. The current status was summarised succinctly by Paris Sphicas (Athens) in his conference summary talk: “Looked for a lot of possible new things. Nothing has turned up yet. Still looking intensively.”

Flavour physics
Over the last few years, a number of deviations from theoretical predictions have been observed in B-meson decays to final states with leptons. Discrepancies have been observed in ratios of decays to different lepton species, and in the angular distribution of decay products. Taken alone, each of these discrepancies are not particularly significant, but collectively they may be telling us something new about nature. At ICHEP 2020, the LHCb experiment presented their recently published results on the angular analysis in B⁰ → K^*0 μ⁺μ^–. The overall picture remains unchanged. The full analysis of the LHCb Run-2 data set, including updated measurements of the relative rates of the muon and electron decay modes (R_K and R_K*), is eagerly awaited.

The search for rare kaon decays continues to attract interest

The search for rare kaon decays continues to attract interest. One of the most impressive results presented at ICHEP was the recent observation by NA62 of the extremely rare kaon decay, K⁺ → π⁺νν̄. Occurring only once in every 10 billion decays, this is an incredibly challenging measurement and the new NA62 result is the first statistically significant observation of this decay, based on just 17 events. Whilst the observed rate is consistent with the Standard Model expectation, its observation opens up a new future avenue for exploring the possible effects of new physics.

Neutrino physics
Neutrino physics continues to be one of the most active areas of research in particle physics, so it was not surprising that the neutrino parallel sessions were the best attended of the conference. This is a particularly interesting time, with long-baseline neutrino oscillation experiments becoming sensitive to the neutrino mass ordering, and beginning to provide constraints on CP violation. Updates were presented by the NOvA experiment in the USA and the T2K experiment in Japan. Both experiments favour the normal-ordering hypothesis, although not definitively, and there is currently a slight tension between the CP violation results from the two experiments. It is worth noting that the combined interpretation of the two experiments is quite complex. The NOvA and T2K collaborations are working on a combined analysis to clarify the situation.

There were also a number of presentations on the next generation of long-baseline neutrino oscillation experiments, DUNE in the US and Hyper-Kamiokande in Japan, which aim to make the definitive discovery of CP violation in the neutrino sector. In the context of DUNE, the progress with liquid-argon time-projection- chamber (LArTPC) detector technology is impressive. It was particularly pleasing to see a number of physics results from MicroBooNE at Fermilab, and the single-phase DUNE detector prototype at CERN (ProtoDUNE-SP), that are based on the automatic reconstruction of LArTPC images – a longstanding challenge.

Virtual success
A vast range of high-qualify scientific research was covered in the 800 parallel session presentations and summarised in the 44 plenary talks at ICHEP 2020. The quality of the presentations was high, and speakers coped well with the challenge of pre-recording talks. The “replay” sessions worked extremely well too – an innovation that is likely to persist in the post-COVID world. About 3000 people registered for the meeting, which is more than double the previous two events. It was particularly pleasing to learn that almost 2500 connected to the parallel sessions.

Despite the many successes, we all missed the opportunity to meet colleagues in person; it is often the informal discussions over coffee or in restaurants and bars that generate new ideas and, importantly, lead to new collaborations. Whilst virtual conferences are likely to remain a feature in the post- COVID world, they will not replace in-person events.

Paul Murphy 1930–2020

Murphy was a long-time leader of particle physics at the University of Manchester. Credit: Murphy family

Leading member of the UK particle-physics community, Paul Murphy, passed away on 26 August. Paul was a keen and brilliant physicist who was head of the particle-physics group at the University of Manchester from 1965 until his retirement in 1990. He started his PhD as a Fulbright Scholar theoretician in Fermi’s group in Chicago, but later discovered that his real talent lay in experimentation. Styling himself as a “gas and glue” man, Paul was one of the few physicists at the time who could design and make spark chambers that worked.

He then went to Liverpool to work on the 400 MeV cyclotron before joining the Rutherford Laboratory and going to UC Berkeley to study hyperons at the 6 GeV Bevatron. On returning in the early 1960s, he and John Thresher carried out a series of experiments to determine the spin-parity of pion-nucleon resonances, for which they were awarded the Rutherford medal and prize by the UK Institute of Physics.

Aged only 34, Paul moved to Manchester to become a professor, heading up the newly formed high-energy physics group. As well as leading the group into two experiments at the new electron synchrotron, NINA, at the Daresbury Laboratory, he spearheaded the development of particle detectors at Manchester and built the group’s strong reputation in this area. First were the wire spark chambers with digital instead of photographic readout, a version of which was then used in the CERN, Holland, Lancaster, Manchester (CHLM) experiment that concentrated on proton–proton diffraction scattering at the CERN ISR facility. Paul then led the group developing (quieter) large-area drift chambers that were used to detect muons, first at the JADE experiment at DESY, which helped to discover the gluon, and then at LEP’s OPAL experiment at CERN. His sharp physics mind led him to be a pioneer at the start of each new accelerator facility, for instance realising the potential for NINA to produce a useable beam of neutral kaons.

Paul was a firm believer in making the most of wherever he found himself. He played a major role in national and international particle physics, chairing and contributing to many strategic decision-making bodies. He was also an engaging educator at all levels, often livening up his lectures with many anecdotes.

Paul was a passionate humanitarian and loved people; he wanted to show everyone he met that he valued them, for example, by learning how to welcome them in their own language. His insight into people and physics alike was extraordinary, and his penchant for making a little friendly mischief never far from the surface.

John Thompson: 1939-2020

John Thompson, a senior physicist at the UK’s Rutherford Appleton Laboratory (RAL), passed away on 20 August.

John obtained his PhD in nuclear physics for work on the Van de Graaff accelerator at the University of Liverpool in the early 1960s before moving to the University of Manitoba, Canada to work on particle physics. He then took a post at Daresbury Laboratory in the UK to work on experiments using the 5 GeV electron synchrotron, NINA. His first experiment involved a measurement of the total hadron photoproduction cross sections for energies from 1 to 4 GeV. These precise measurements have never been superseded and remain the definitive values documented by the Particle Data Group.

John was central to the formation of Daresbury’s LAMP group, which focused on a series of hadronic photoproduction experiments. He played a leading role in the development of the 480-element lead–glass array for studies of neutral particle production in the final phase of the LAMP experiment.

During this period, following the discovery of deep inelastic scattering at SLAC and DESY, John together with his colleagues became involved in the plans to study deep inelastic scattering at the higher energies afforded by the Super Proton Synchrotron (SPS) at CERN. He became a founding member of the European Muon Collaboration (EMC), which would go on to do experiments in the high-intensity muon beam at CERN.

John was a first rate, hands-on experimental physicist

As NINA came to the end of its life and Daresbury moved to host one of the first dedicated “light sources”, John moved with other colleagues in particle physics to RAL. Interested in the production of high-energy photons at the EMC, he organised the transfer of the LAMP lead–glass array from the UK to CERN to study the production of photons in the forward direction. In the final phase of the EMC activities he successfully led a team from RAL that implemented the change to a polarised target – a very difficult procedure that had to be done in just a few months.

In the 1980s John led the RAL group into the ALEPH experiment at CERN’s Large Electron Positron collider, LEP. The group undertook the task of building the end cap electromagnetic calorimeters, which operated successfully during the 11 years of ALEPH operations. John became heavily involved with early results for which the calorimeter performance was crucial, such as its use in counting the number of neutrino species from the radiative return reaction e⁺e^– → µµγ. During the LEP2 period in the late 1990s, John’s major contribution concerned the measurement of the W mass and width. This led to a highly productive collaboration between the Imperial College and RAL ALEPH teams, and saw John become instrumental in guiding the students. Following his retirement from RAL, he was appointed visiting professor at Imperial where he was lead author on the publication of the final ALEPH W mass measurements. He continued to advise and guide students, and took charge of graduate lectures until recently, when failing health made it difficult for him to do so.

John was a first rate, hands-on experimental physicist. He had a talent for understanding the difficulties of others and involving himself selflessly to help them progress. He always had a patient, calm, happy and relaxed manner, and will be sadly missed.

Terascale summer school goes global

In a joint venture by physicists at DESY, the first Terascale Summer School took place online from 23 July to 12 August, providing more than 160 undergraduate students from over 30 countries with an engaging introduction to the world of particle and astroparticle physics. Following a wide-ranging three weeks of teaching, an impromptu fortnight-long online tutorial, which only concluded yesterday, focused on strong interactions and Monte Carlo techniques, allowing students to deepen their knowledge through practical exercises.

Terascale chat — Terascale’s online format encouraged students to ask questions. Credit: I Melzer-Pellmann

As the school had been forced online due the ongoing pandemic, the organisers settled upon a reduced programme with just one or two 45 minutes lectures per day. Active moderation was key, with students typing questions in the chat box, and the moderator interrupting the lecturer when appropriate, to give the participants a chance to speak up. This format conferred upon less brash participants a more comfortable way to ask questions, several students noted. When one brave pioneer had broken the ice, queries flowed every few minutes – a resonance effect characterised by a lively, stimulating and relaxed atmosphere which boosted concentration levels.

With its global reach and breathing space for students to explore concepts independently, Terascale 2020’s compact online format may merit consideration during less extraordinary times too.

Neutrinos confirm rare solar fusion process

Despite being our closest star, much remains to be learned about the exact nature of the Sun and how it produces its energy. Two different fusion processes are thought to be at play in the majority of stars: the direct fusion of hydrogen into helium, which is thought to be responsible for approximately 99% of the Sun’s energy; and the fusion of hydrogen into helium via the six-stage carbon-nitrogen-oxygen (CNO) process (see diagram below). Although theorised in the 1930s, direct proof of this fusion process was missing. As a result, the amount of energy produced through the CNO cycle and the amount of elements such as carbon and nitrogen in the Sun’s core could only be estimated from models. Recently, the international Borexino collaboration directly detected neutrinos produced in the CNO cycle, providing the first direct proof of this process.

The Borexino detector was specifically developed to detect the extremely rare interactions between solar neutrinos and a highly pure liquid scintillator. It comprises 278 tonnes of scintillator held in a nylon balloon deep under the mountains at Gran Sasso National Laboratory in Italy. In 2012 the experiment detected neutrinos from the main solar fusion process. Now, one year before the end of its scheduled operations, the Borexino team has fully probed the solar energy production. The discovery of the CNO process was complicated both by the lower flux of neutrinos compared to that from the main fusion process, and by the large similarity between the signal and one of the main irreducible background processes taking place in the detector.

In the six-stage CNO cycle a proton is absorbed by a carbon nucleus, followed by a nuclear decay, followed by a second and third absorption of a proton, followed by another decay, the absorption of a fourth proton and finally a decay into a carbon nucleus, a helium nucleus and the release of around 25 MeV of energy. Source: Creative Commons/Borb.

Battling background
Despite minimising backgrounds from cosmic rays, trace amounts of radioactive nuclei which leak into the active volume of Borexino produce a background of the same magnitude as the sought-after signal. The most important background for the CNO analysis was ²¹⁰Bi, a product of ²¹⁰Pb of which trace amounts can diffuse into the scintillator from the nylon balloon surface. Since the energy spectrum of the beta-decay of ²¹⁰Bi resembles that induced by neutrinos produced in the CNO process, the key to detecting the CNO neutrinos was to directly measure the ²¹⁰Bi-induced background. This was made possible by delving into the fluid dynamics of the liquid scintillator.

The ²¹⁰Bi in Borexino’s scintillator produces ²¹⁰Po, which undergoes alpha decay with a half-life of 134 days. As the alpha decay is relatively easy to identify, the team used ²¹⁰Po decays to deduce the number of ²¹⁰Bi decays in the detector. However, as the different isotopes move around in the liquid it cannot be guaranteed that the ²¹⁰Bi distribution is equal to ²¹⁰Po unless the flow in the detector is well understood. To overcome this, the collaboration had to reduce the flow of the scintillator material by stabilising the temperature, both through insulation and direct temperature regulation. After the ²¹⁰Po decay distribution inside the detector was found to be stable over times exceeding its half-life, an area with low ²¹⁰Po activity was identified and used to measure the CNO neutrinos with a well-understood and relatively low background.

This was made possible by delving into the fluid dynamics of the liquid scintillator

The spectral measurements performed of the CNO cycle exclude a non-detection with a statistical significance of more than five sigma. The measured solar-neutrino flux (7.2^+3.0₋1.7 counts per day per 100 tonnes of target, at 68% confidence) furthermore agrees with models which predict that 1% of the energy produced in the Sun comes from the CNO process. Additionally, the results shine light on the density of elements other than hydrogen and helium — the metallicity — of the Sun’s core, which in recent years has been debated to potentially differ from that on the solar surface. The Borexino results indicate that the density is likely similar although more precise measurements with future detectors are required for precision measurements.

This groundbreaking study, which required not only some of the most precise techniques used in particle physics but also complex fluid-dynamics simulations, confirms predictions made almost a century ago. In doing so it provides a first probe into the processes at the core of the Sun and thus of other stars. Although it has now been proved that the CNO process is responsible for only a fraction of the Sun’s energy, for heavier and therefore hotter stars it is predicted to be the dominant fusion process, making future high-precision studies important to understand the evolution of the universe in general.

An intuitive approach to teaching

This elementary textbook, suitable for either advanced undergraduate or introductory postgraduate courses, is a gem. Its author, Andrew Larkoski, is a phenomenologist with expertise in QCD, and a visiting professor at Reed College. It is worth mentioning that Reed College is also home to David J. Griffiths, who is the author of several successful textbooks, including his well-known “Introduction to Elementary Particles” (Wiley, 2nd edition, 2008). Larkoski’s book has a similar scope to Griffiths’ and certainly lives up to its legacy.

Larkoski begins with an introduction to special relativity and the standard preliminaries to particle physics, such as the Dirac equation, Fermi’s Golden rule and a very accessible introduction to group theory. The book also features a superb 30-page chapter on experimental concepts and statistics — an excellent resource for any student starting a particle-physics project for the first time. The main menu follows: matrix element and cross-sections calculations for QED, QCD and weak interactions. The book includes a nice introduction to electroweak unification, the basics of flavour physics, neutrino oscillations, and an accessible discussion on parton evolution and jets. The latter will be particularly useful for students of LHC physics. The book closes with an insightful chapter on open problems in particle physics.

A very nice collection of unsolved exercises will serve as an invaluable resource for lecturers. Many refer to processes currently being studied at the LHC and other projects. The book’s modernity is also evident through mentions throughout the text on the latest results in dark matter and neutrino physics, and a discussion on how the Higgs boson discovery was made.

Analogies are drawn between Feynman diagrams and electrical circuits

A particularly attractive feature of Larkoski’s writing is his use of intuitive and conceptual discussions: dimensional analysis is used often in calculations to get an idea of what we expect; analogies are drawn between Feynman diagrams and electrical circuits; connections between space curvature and quantum chromodynamics are pointed out, just to mention some of the very many examples you can find in the book.

One point that the lecturers should be aware of is that Larkoski employs the Weyl basis of Dirac γ-matrices, whereas Griffiths, Thomson (Modern Particle Physics, Cambridge, 2013), Halzen & Martin (Quarks and Leptons, Wiley, 1984), and other popular textbooks which currently form the backbone of many university courses, use the Dirac basis. As a result, both equations and Feynman rules look different, and care will be required when multiple textbooks are used in the same course. In general, Larkoski is closer to Thomson and Griffiths, as it does not include the wide range of calculations of Halzen & Martin, which is slightly more advanced.

Larkoski’s new book will certainly find its way among the most popular particle physics textbooks. Its clear and intuitive presentation will doubtlessly deepen the understanding of students who read it, and inspire lecturers to a more conceptual approach to teaching.

Radiation rules of thumb

Don Cossairt and Matthew Quinn’s recently published book summarises both basic concepts of the propagation of particles through matter and fundamental aspects of protecting personnel and environments against prompt radiation and radioactivity. It constitutes a compact and comprehensive compendium for radiation-protection professionals working at accelerators. The book’s content originates in a course taught by Cossairt, a longstanding and recently retired radiation expert at Fermilab at numerous sessions of the US Particle Accelerator School (USPAS) since the early 1990s. It is also available as a Fermilab report which has stood the test of time as one of the standard health-physics handbooks for accelerator facilities for more than 20 years. Quinn, the book’s co-author, is the laboratory’s radiation-physics department manager.

Radiation-protection book cover — Credit: CRC Press

The book begins with a short overview of physical and radiological quantities relevant for radiation protection assessments, and briefly sketches the mechanisms for energy loss and scattering during particle transport in matter. The introductory part concludes with chapters on the Boltzmann equation, which in this context describes the transport of particles through matter, and its solution using Monte Carlo methods. The following chapters illustrate the radiation fields which are induced by the interactions of electron, hadron and ion beams with beamline components. The tools described in these chapters are parametrised equations, handy rules-of-thumb and graphs of representative particle spectra and yields which serve for back-of-the-envelope calculations and describe the fundamental characteristics of radiation fields.

Practical questions

The second half of the book deals with practical questions encountered in everyday radiation-protection assessments, such as the selection of the most efficient shielding material for a given radiation field, the energy spectra to be expected outside of shielding where personnel might be present, and lists of radiologically relevant nuclides which are typically produced around accelerators. It also provides a compact introduction to activation at accelerators. The final chapter gives a comprehensive overview of radiation-protection instrumentation traditionally used at accelerators, helping the reader to select the most appropriate detector for a given radiation field.

Nowadays, assessments are more readily and accurately obtained with Monte Carlo simulations

Some topics have evolved since the time when the material upon which the book is based was written. For example, the “rules-of-thumb” presented in the text are nowadays mostly used for cross-checking results obtained with much more powerful and user-friendly Monte Carlo transport programs. The reader will not, however, find information on the use and limitations of such codes. For example, the chapter on aspects of radiation dose attenuation through passage ways and ducts as well as environmental doses due to prompt radiation (“skyshine”) gives only analytical formulae, while assessments are nowadays more readily and accurately obtained with Monte Carlo simulations. There is risk, however, that such codes be treated as a “black box”, and their results blindly believed. In this regard, the book gives many tools necessary for obtaining rough but valuable estimates for setting up simulations and cross-checking results.

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