Jobs – Page 185 of 530

Physics at its limits

Since Democritus, humans have wondered what happens as we slice matter into smaller and smaller parts. After the discovery almost 50 years ago that protons are made of quarks, further attempts to explore smaller distances have not revealed tinier substructures. Instead, we have discovered new, heavier elementary particles, which although not necessarily present in everyday matter are crucial components of nature’s fundamental make-up. The arrangement of the elementary particles and the interactions between them is now well described by the Standard Model (SM), but furthering our understanding of the basic laws of nature requires digging even deeper.

Quantum physics gives us two alternatives to probe nature at smaller scales: high-energy particle collisions, which induce short-range interactions or produce heavy particles, and high-precision measurements, which can be sensitive to the ephemeral influence of heavy particles enabled by the uncertainty principle. The SM was built from these two approaches, with a variety of experiments worldwide during the past 40 years pushing both the energy and the precision frontiers. The discovery of the Higgs boson at the LHC is a perfect example: precise measurements of Z-boson decays at previous lepton machines such as CERN’s Large Electron–Positron (LEP) collider pointed indirectly but unequivocally to the existence of the Higgs. But it was the LHC’s proton–proton collisions that provided the high energy necessary to produce it directly. With exploration of the Higgs fully under way at the LHC and the machine set to operate for the next 20 years, the time is ripe to consider what tool should come next to continue our journey.

Aiming at a high-energy collider with a clean collision environment, CERN has for several years been developing an e⁺e^– linear collider called CLIC. With an energy up to 3 TeV, CLIC would combine the precision of an e⁺e^– collider with the high-energy reach of a hadron collider such as the LHC. But with the lack so far of any new particles at the LHC beyond the Higgs, evidence is mounting that even higher energies may be required to fully explore the next layer of phenomena beyond the SM. Prompted by the outcome of the 2013 European Strategy for Particle Physics, CERN has therefore undertaken a five-year study for a Future Circular Collider (FCC) facility built in a new 100 km-circumference tunnel (see image below).

The FCC accelerator complex in the Geneva region, showing the LHC for comparison.

Such a tunnel could host an e⁺e^– collider (called FCC-ee) with an energy and intensity much higher than LEP, improving by orders of magnitude the precision of Higgs and other SM measurements. It could also house a 100 TeV proton–proton collider (FCC-hh) with a discovery potential more than five times greater than the 27 km-circumference LHC. An electron–proton collider (FCC-eh), furthermore, would allow the proton’s substructure to be measured with unmatchable precision. Further opportunities include the collision of heavy ions in FCC-hh and FCC-eh, and fixed-target experiments using the injector complex. The earliest that such a machine could enter operation is likely to be the mid 2030s, when the LHC comes to the end of its operational lifetime, but the long lead times for collider projects demand that we start preparing now (see timeline below). A Conceptual Design Report (CDR) for a 100 km collider is expected to be completed by the end of 2018 and hundreds of institutions have joined the international FCC study since its launch in 2014. An independent study for a similar facility is also under way in China.

The CDR will document the accelerator, infrastructures and experiments, as well as a plethora of physics studies proving FCC’s ability to match the long-term needs of global high-energy-physics programmes. The first FCC physics workshop took place at CERN in January to review the status of these studies and discuss the complementarity between the three FCC modes.

The post-LHC landscape

To chart the physics landscape of future colliders, we must first imagine what questions may or may not remain at the end of the LHC programme in the mid-2030s. At the centre of this, and perhaps the biggest guaranteed physics goal of the FCC programme, is our understanding of the Higgs boson. While there is no doubt that the Higgs was the last undiscovered piece of the SM, it is not the closing chapter of the millennia-old reductionist paradigm. The Higgs is the first of its kind – an elementary scalar particle – and it therefore raises deep theoretical questions that beckon a new era of exploration (figure 1, p39).

Consider its mass. In the SM there is no symmetry that protects the Higgs mass from large quantum corrections that drag it up to the mass scale of the particles it interacts with. You might conclude that the relatively low mass of the Higgs implies that it simply does not interact with other heavy particles. But there is good, if largely theoretical, evidence to the contrary. We know that at energies 16 orders of magnitude above the Higgs mass where general relativity fails to provide a consistent quantum description of matter, there must exist a full quantum theory that includes gravity. The fact that the Higgs is so much lighter than this scale is known as the hierarchy problem, and many candidate theories (such as supersymmetry) exist that require new heavy particles interacting with the Higgs. By comparing precise measurements of the Higgs boson with precision SM predictions, we are indirectly searching for evidence of these theories. The SM provides an uncompromising script for the Higgs interactions and any deviation from it would demand its extension.

Even setting to one side grandiose theoretical ideas such as quantum gravity, there are other physical reasons why the Higgs may provide a window to undiscovered sectors. As it carries no spin and is electrically neutral, the Higgs may have so-called “relevant” interactions with new neutral scalar particles. These interactions, even if they take place only at very high energies, remain relevant at low energies – contrary to interactions between new neutral scalars and the other SM particles. The possibility of new hidden sectors already has strong experimental support: although we understand the SM very well, it does not account for roughly 80% of all the matter in the universe. We call the missing mass dark matter, and candidate theories abound. Given the importance of the puzzle, searches for dark-matter particles will continue to play a central role at the LHC and certainly at future colliders.

Furthermore, the SM cannot explain the origin of the matter–antimatter asymmetry that created enough matter for us to exist, otherwise known as baryogenesis. Since the asymmetry was created in the early universe when temperatures and energies were high, we must explore higher energies to uncover the new particles responsible for it. With the LHC we are only at the beginning of this search. Another outstanding question lies in the origin of the neutrino masses, which the SM alone cannot account for. As with dark matter, there are numerous theories for neutrino masses, such as those involving “sterile” neutrinos that are in the reach of lepton and hadron colliders. These and other outstanding questions might also imply the existence of further spatial dimensions, or larger symmetries that unify leptons and quarks or the known forces. The LHC’s findings notwithstanding, future colliders like the FCC are needed to explore these fundamental mysteries more deeply, possibly revealing the need for a paradigm shift.

Electron–positron potential

The capabilities of circular e⁺e^– colliders are well illustrated by LEP, which occupied the LHC tunnel from 1989 to 2000. Its point-like collisions between electrons and positrons and precisely known beam energy allowed the four LEP experiments to test the SM to new levels of precision. Putting such a machine in a 100 km tunnel and taking advantage of advances in accelerator technology such as superconducting radio-frequency cavities would offer even greater levels of precision on a larger number of processes. We would be able to change the collision energy in the range 91–350 GeV, for example, allowing data to be collected at the Z pole, at the WW production threshold, at the peak of ZH production, and at the top–antitop quark threshold. Controlling the beam energy at the 100 keV level would allow exquisite measurements of the Z- and W-boson masses, while the high luminosity of FCC-ee will lead to samples of up to 10¹³ Z and 10⁸ W bosons, not to mention several million Higgs bosons and top-quark pairs. The experimental precision would surpass any previous experiment and challenge cutting-edge theory calculations.

Technical timeline of the FCC project shown in comparison with previous and existing CERN colliders.

FCC-ee would quite literally provide a quantum leap in our understanding of the Higgs. Like the W and Z gauge bosons, the Higgs receives quantum electroweak corrections typically measuring a few per cent in magnitude due to fluctuations of massive particles such as the top quark. This aspect of the gauge bosons was successfully explored at LEP, but now it is the turn of the Higgs – the keystone in the electroweak sector of the SM. The millions of Higgs bosons produced by FCC-ee, with its clinically precise environment, would push the accuracy of the measurements to the per-mille level, accessing the quantum underpinnings of the Higgs and probing deep into this hitherto unexplored frontier. In the process, e⁺e^– → HZ, the mass recoiling against the Z has a sharp peak that allows a unique and absolute determination of the Higgs decay width and production cross-section. This will provide an absolute normalisation for all Higgs measurements performed at the FCC, enabling exotic Higgs decays to be measured in a model-independent manner.

The high statistics promised by the FCC-ee programme go far beyond precision Higgs measurements. Other signals of new physics could arise from the observation of flavour-changing neutral currents or lepton-flavour-violating decays by the precise measurements of the Z and H invisible decay widths, or by direct observation of particles with extremely weak couplings such as right-handed neutrinos and other exotic particles. Given the particular energy and luminosity of a 100 km e⁺e^– machine, the precision of the FCC-ee programme on electroweak measurements would allow new physics effects to be probed at scales as high as 100 TeV. If installed before FCC-hh, it would therefore anticipate what the hadron machine must focus on.

The energy frontier

The future proton–proton collider FCC-hh would operate at seven times the LHC energy, and collect about 10 times more data. The discovery reach for high-mass particles – such as Z´ or W´ gauge bosons corresponding to new fundamental forces, or gluinos and squarks in supersymmetric theories – will increase by a factor five or more, depending on the luminosity. The production rate of particles already within the LHC reach, such as top quarks or Higgs bosons, will increase by even larger factors. During its planned 25 years of data-taking, more than 10¹⁰ Higgs bosons will be created by FCC-hh, which is 10,000 times more than collected by the LHC so far and 100 times more than will be available by the end of LHC operations. These additional statistics will enable the FCC-hh experiments to improve the separation of Higgs signals from the huge backgrounds that afflict most LHC studies, overcoming some of the dominant systematics that limit the precision attainable from the LHC.

While the ultimate precision on most Higgs properties can only be achieved with FCC-ee, several demand complementary information from FCC-hh. For example, the direct measurement of the coupling between the Higgs and the top quark necessitates that they be produced together, requiring an energy beyond the reach of the FCC-ee. At 100 TeV, almost 10⁹ of the 10¹² produced top quarks will radiate a Higgs boson, allowing the top-Higgs interaction to be measured with a statistical precision at the 1% level – a factor 10 improvement over what is hoped for from the LHC. Similar precision can be reached for Higgs decays that are too rare to be studied in detail at FCC-ee, such as those to muon pairs or to a Z and a photon. All of these measurements will be complementary to those obtained with FCC-ee, and will use them as reference inputs to precisely correlate the strength of the signals obtained through various production and decay modes.

One respect in which a 100 TeV proton–proton collider would come to the fore is in revealing how the Higgs behaves in private. The Higgs is the only particle in the SM that interacts with itself. As the Higgs scalar potential defines the potential energy contained in a fluctuation of the Higgs field, these self-interactions are neatly defined as the derivatives of the scalar electroweak potential. With the Higgs boson being an excitation about the minimum of this potential, we know that its first derivative is zero. The second derivative of the potential is simply the Higgs mass, which is already known to sub-per-cent accuracy. But the third and fourth derivatives are unknown, and unless we gain access to Higgs self-interactions they could remain so. The rate of Higgs pair-production events, which in some part occur through Higgs self-interactions, would grow precipitously at FCC-hh and enable this unique property of the Higgs to be measured with an accuracy of 5% per cent. Among many other uses, such a measurement would comprehensively explore classes of baryogenesis models that rely on modifying the Higgs potential, and thus help us to understand the origin of matter.

Fig. 1. Together, FCC-ee, hh and eh can provide detailed measurements on the Higgs properties. The figure shows indicative precision in the determination of couplings to gauge bosons, quarks and leptons, as well as of the Higgs self-coupling, of its total width and of the invisible decay rate. Firmer estimates will appear in the CDR.

FCC-hh would also allow an exhaustive exploration of new TeV-scale phenomena. Indirect evidence for new physics can emerge from the scattering of W bosons at high energy, from the production of Higgs bosons at very large transverse momentum, or by testing the far “off-shell” nature of the Z boson via the measurement of lepton pairs with invariant masses in the multi-TeV region. The plethora of new particles predicted by most models of symmetry-breaking alternative to the SM can be searched for directly, thanks to the immense mass reach of 100 TeV collisions. The search for dark matter, for example, will cover the possible space of parameters of many theories relying on weakly interacting massive particles, guaranteeing a discovery or ruling them out. Theories that address the hierarchy problem will also be conclusively tested. For supersymmetry, the mass reach of FCC-hh pushes beyond the regions motivated by this puzzle alone. For composite Higgs theories, the precision Higgs coupling measurements and searches for new heavy resonances will fully cover the motivated territory. A 100 TeV proton collider will even confront exotic scenarios such as the twin Higgs, which are nightmarishly difficult to test. These theories predict very rare or exotic Higgs decays, possibly visible at FCC-hh thanks to its enormous Higgs production rates.

Beyond these examples, a systematic effort is ongoing to categorise the models that can be conclusively tested, and to find the loopholes that might allow some models to escape detection. This work will influence the way detectors for the new collider are designed. Work is already starting in earnest to define the features of these detectors, and efforts in the FCC CDR study will focus on comprehensive simulations of the most interesting physics signals. The experimental environment of a proton–proton collider is difficult due to the large number of background sources and the additional noise caused by the occurrence of multiple interactions among the hundreds of billions of protons crossing each other at the same time. This pile-up of events will greatly exceed those observed at the LHC, and will pose a significant challenge to the detectors’ performance and to the data-acquisition systems. The LHC experience is of immense value for projecting the scale of the difficulties that will have to be met by FCC-hh, but also for highlighting the increasing role of proton colliders in precision physics beyond their conventional role of discovery machines.

Asymmetric collisions

Smashing protons into electrons opens up a whole different type of physics, which until now has only been explored in detail by a single machine: the HERA collider at DESY in Germany. FCC-eh would collide a 60 GeV electron beam from a linear accelerator, external and tangential to the main FCC tunnel, with a 50 TeV proton beam. It would collect factors of thousands more luminosity than HERA while exhibiting the novel concept of synchronous, symbiotic operation alongside the pp collider. The facility would serve as the most powerful, high-resolution microscope to examine the substructure of matter ever built, with high-energy electron–proton collisions providing precise information on the quark and gluon structure of the proton.

Fig. 2. The complementary role of the ee, pp and ep colliders in probing a sterile neutrino of mass M and mixing angle θ with ordinary neutrinos.
Image credit: arXiv:1612.02728.

This unprecedented facility would enhance Higgs studies, including the study of the coupling to the charm quark, and broaden the new-physics searches also performed at FCC-hh and FCC-ee. Unexpected discoveries such as quark substructure might also arise. Uniquely, in electron–proton collisions new particles can be created in lepton–quark fusion processes or may be radiated in the exchange of a photon or other vector boson. FCC-eh could also provide access to Higgs self-interactions and extended Higgs sectors, including scenarios involving dark matter. If neutrino oscillations arise from the existence of heavy sterile neutrinos, direct searches at the FCC-eh would have great discovery prospects in kinematic regions complementary to FCC-hh and FCC-ee, giving the FCC complex a striking potential to shine light on the origin of neutrino masses.

Unknown unknowns

In principle, the LHC could have – and still could provide – answers to many of these outstanding questions in particle physics. That no new particles beyond the Higgs have yet been found, or any significant deviations from theory detected, does not mean that these questions have somehow evaporated. Rather, it shows that any expectations for early discoveries beyond the SM at the LHC – often based on theoretical, and in some cases aesthetic, arguments – were misguided. In times like this, when theoretical guidance is called into question, we must pursue experimental answers as vigorously as possible. The combination of accelerators that are being considered for the FCC project offer, by their synergies and complementarities, an extraordinary tool for investigating these questions (figure 2).

There are numerous instances in which the answer nature has offered was not a reply to the question first posed. For example, Michelson and Morley’s experiment designed to study the properties of the ether ended up disproving the existence of the ether and led to Einstein’s theory of special relativity. The Kamiokande experiment in Japan, originally built to observe proton decays, instead discovered neutrino masses. The LHC itself could have disproven the SM by discovering that the Higgs boson is not an elementary but a composite particle – and may still do so, with its future more precise measurements.

The possibility of unknown unknowns does not diminish the importance of an experiment’s scientific goals. On the contrary, it demonstrates that the physics goals for future colliders can play the crucial role of getting a new facility off the ground, even if a completely unanticipated discovery results. This is true of all expeditions into the unknown. We should not forget that Columbus set sail to find a westerly passage to Asia. Without this goal, he would not have discovered the Americas.

Doubting darkness

Erik Verlinde of the University of Amsterdam in the Netherlands photographed at CERN in April following his seminar on emergent gravity. Image credit: J Ordan/CERN.

What is wrong with the theory of gravity we have?

The current description of gravity in terms of general relativity has various shortcomings. Perhaps the most important is that we cannot simply apply Einstein’s laws at a subatomic level without generating notorious infinities. There are also conceptual puzzles related to the physics of black holes that indicate that general relativity is not the final answer to gravity, and important lessons learnt from string theory suggesting gravity is emergent. Besides these theoretical issues, there is also a strong experimental motivation to rethink our understanding of gravity. The first is the observation that our universe is experiencing accelerated expansion, suggesting it contains an enormous amount of additional energy. The second is dark matter: additional gravitating but non-luminous mass that explains anomalous galaxy dynamics. Together these entities account for 95 per cent of all the energy in the universe.

Isn’t the evidence for dark matter overwhelming?

It depends who you ask. There is a lot of evidence that general relativity works very well at length scales that are long compared to the Planck scale, but when we apply general relativity at galactic and cosmological scales we see deviations. Most physicists regard this as evidence that there exists an additional form of invisible matter that gravitates in the same way as normal matter, but this assumes that gravity itself is still described by general relativity. Furthermore, although the most direct evidence for the existence of dark matter comes from the study of galaxies and clusters, not all astronomers are convinced that what they observe is due to particle dark matter – for example, there appears to be a strong correlation between the amount of ordinary baryonic matter and galactic rotation velocities that is hard to explain with particle dark matter. On the other hand, the physicists who are carrying out numerical work on particle dark matter are trying to explain these correlations by including complicated baryonic feedback mechanisms and tweaking the parameters that go into their models. Finally, there is a large community of experimental physicists who simply take the evidence for dark matter as a given.

Is your theory a modification of general relativity, or a rewrite?

The aim of emergent gravity is to derive the equations that govern gravity from a microscopic quantum, while using ingredients from quantum-information theory. One of the main ideas is that different parts of space–time are glued together via quantum entanglement. This is due to van Raamsdonk and has been extended and popularised by Maldacena and Susskind with the slogan “EPR = ER”, where EPR is a reference to Einstein–Podolsky–Rosen and ER refers to the Einstein–Rosen bridge: a “wormhole” that connects the two parts of the black-hole geometry on opposite sides of the horizon. These ideas are being developed by many theorists, in particular in the context of the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence. The goal is then to derive the Einstein equations from this microscopic-quantum perspective. The first step in this programme was already made before my work, but until now most results were derived for AdS space, which describes a universe with a negative cosmological constant and therefore differs from our own. In my recent paper [arXiv:1611.02269] I extended these ideas to de Sitter space, which contains a positive dark energy and has a cosmological horizon. My insight has been that, due to the presence of positive dark energy, the derivation of the Einstein equations breaks down precisely in the circumstances where we observe the effects of “dark matter”.

How did the idea emerge?

The idea of emergent gravity from thermodynamics has been lingering around since the discovery by Hawking and Bekenstein of black-hole entropy and the laws of black-hole thermodynamics in the 1970s. Ted Jacobson made an important step in 1996 by deriving the Einstein equations from assuming the Bekenstein–Hawking formula, which expresses the microscopic entropy in terms of the area of the horizon measured in Planck units. In my 2010 paper [arXiv:1001.0785] I clarified the origin of the inertia force and its relation to the microscopic entropy in space, assuming that this is given by the area of an artificial horizon. After this work I started thinking about cosmology, and learnt about the observations that indicate a close connection between the acceleration scale in galaxies and the acceleration at the cosmological horizon, which is determined by the Hubble parameter. I immediately realised that this implied a relation between the observed phenomena associated with dark matter and the presence of dark energy.

Your paper is 50 pages long. Can you summarise it here?

The idea is that gravity emerges by applying an analogue of the laws of thermodynamics to the entanglement entropy in the vacuum. Just like the normal laws of thermodynamics can be understood from the statistical treatment of microscopic molecules, gravity can be derived from the microscopic units that make up space–time. These “space–time molecules” are units of quantum information (qubits) that are entangled with each other, with the amount of entanglement measured by the entanglement entropy. I realised that in a universe with a positive dark energy, there is a contribution to the entanglement entropy that grows in proportion to area. This leads to an additional force on top of the usual gravity law, because the dark energy “pushes back” like an elastic medium and results in the phenomena that we currently attribute to dark matter. In short, the laws of gravity differ in the low-acceleration regime that occurs in galaxies and other cosmological structures.

How did the community react to the paper?

Submitting work that goes against a widely supported theory requires some courage, and the fact that I have already demonstrated serious work in string theory helped. Nevertheless, I do experience some resistance – mainly from researchers who have been involved in particle dark-matter research. Some string theorists find my work interesting and exciting, but most of them take a “wait and see” attitude. I am dealing with a number of different communities with different attitudes and scientific backgrounds. A lot of it is driven by sociology and past investments.

How often do you work on the idea?

Emergent gravity from quantum entanglement is now an active field worldwide, and I have worked on the idea for a number of years. I mostly work in the evening for around three hours and perhaps one hour in the morning. I also discuss these ideas with my PhD students, colleagues and visitors. In the Netherlands we have quite a large community working on gravity and quantum entanglement, and recently we received a grant together with theorists from the universities of Groningen, Leiden, Utrecht and Amsterdam, to work on this topic.

Within a month of your paper, Brouwer et al. published results supporting your idea. How significant is this?

My theory predicts that the gravitational force due to a centralised mass exhibits a certain scaling relation. This relation was already known to hold for galaxy rotation curves, but these can only be measured up to distances of about 100 kilo-parsec because there are no visible stars beyond this distance. Brouwer and her collaborators used weak gravitational lensing to determine the gravitational force due to a massive galaxy up to distances of one mega-parsec and confirmed that the same relation still holds. Particle dark-matter models can also explain these observations, but they do so by adjusting a free parameter to fit the data. My prediction has no free parameters and hence I find this more convincing, but more observations are needed before definite conclusions can be drawn.

Is there a single result that would rule your theory in or out?

If a dark-matter particle would be discovered that possesses all the properties to explain all the observations, then my idea would be proven to be false. Personally I am convinced this will not happen, although I am still developing the theory further to be able to address important dynamical situations such as the Bullet Cluster (see “How dark matter became a particle”) and the acoustic oscillations that explain the power spectrum of the cosmic microwave background. One of the problems is that particle dark-matter models are so flexible and can therefore easily be made consistent with the data. By improving and extending the observations of gravitational phenomena that are currently attributed to dark matter, we can make better comparisons with the theory. I am hopeful that within the next decade the precision of the observations will have improved and the theory will be developed to a level that decisive tests can be performed.

How would emergent gravity affect the rest of physics?

Our perspective on the building blocks of nature would change drastically. We will no longer think in terms of elementary particles and fundamental forces, but units of quantum information. Hence, the gauge forces responsible for the electroweak and strong interactions will also be understood as being emergent, and this is the way that the forces of nature will become unified. In this sense, all of our current laws of nature will be seen as emergent.

Birth of the high-energy network

A career networking event at CERN organised by the LHC experiment collaborations in 2016.
Image credit: S Bennett/CERN.

With over 60 years of history and currently more than 13,000 users from all over the world, CERN clearly has great potential to bring together a varied alumni community. Today, CERN alumni are distributed around the world, pursuing their careers and passions across many fields including industry, economics, information technology, medicine and finance. Several have gone on to launch successful start-ups, some of them directly applying CERN-inspired technologies.

Setting up and nurturing this important network is a strategic objective for CERN management. Following 12 months of careful preparation, the new CERN Alumni Programme will be launched in June this year.

The new community, united by a shared pride in having contributed to CERN’s scientific endeavours, will provide an opportunity for alumni to maintain links with the Organization. It will allow them to continue to share CERN’s values and support its activities, and serve as a valuable resource for members of personnel in the transition to work outside the laboratory. Physicists, in particular, often consider CERN as a “prime environment” that comes just after academia. The prospect of having to leave CERN may be daunting, with no guarantee that one’s professional future will offer a similar environment and possibilities. However, preliminary statistics on the CERN alumni community demonstrate that professional experience at CERN nurtures skills and talents that are highly sought after by employers and can aid the development of alumni careers in many different fields.

The CERN Alumni Programme has been purposely designed to be inclusive. Former users, associates, students, fellows, staff, and any member of personnel who has held a contract of either employment or association with CERN, may join the alumni community simply by registering. Current members of personnel will also be able to register and interact with the alumni, as well as partner companies. The final objective is to establish a dynamic, long-lasting and high-energy network of engaged members.

Since November 2016 it has been possible for previous and current members of personnel who wish to become members of the network to leave their contact details on the alumni webpage (see below), which CERN will use to contact them once the new web platform is up and running. Registered members of the CERN alumni community will have access to dedicated editorial content, opportunities to exchange experiences and establish contacts with other alumni, in addition to career development opportunities. The aim is to gather a large number of members, whether they are former colleagues still working in academia, have set up their own businesses, have moved into completely different professional environments, or have retired but wish to stay connected.

CERN alumni will themselves be actively involved in building the community, which will evolve with them. The advisory board of the new programme will include representatives from the community as well as members of CERN management. Alumni will be able to set up thematic groups within the community based on factors such as regional interests and scientific topics. A mobile app will help them to stay connected with news, events and networking activities that are published by the community.

The CERN Alumni Programme kick-off event will be held on 2–3 February 2018. In addition to offering unique networking opportunities, it will be possible to visit the LHC and its experiments as well as experimental areas that are usually not accessible to the public. Inspiring seminars and several panel sessions will complete the programme. The event is designed to be a valuable experience for all different types of alumni, from young scientists who have recently left CERN to those with long-standing careers in different fields, and many others.

We are aware that it will be a challenge to reach all of our alumni spread across the planet over such a long period. If you are one of them, do not hesitate to leave your contact details at https://alumni.cern/. It is the best way to show your interest, join the new community and stay connected with CERN. We also invite you to get in touch with any questions by emailing alumni.relations@cern.ch. We will be very happy to welcome you back to CERN again!

Synchrotron Radiation: Basics, Methods and Applications

By S Mobilio, F Boscherini and C Meneghini (eds)
Springer

Observed for the first time in 1947 – and long considered as a problem for particle physics as it can cause particle beams to lose energy – synchrotron radiation is today a fundamental tool for characterising nanostructures and advanced materials. Thanks to its characteristics in terms of brilliance, spectral range, time structure and coherence, it is extensively applied in many scientific fields, spanning material science, chemistry, nanotechnology, earth and environmental sciences, biology, medical applications, and even archaeology and cultural heritage.

The book reports the lecture notes of lessons held at the 12th edition of the School on Synchrotron Radiation, held in Trieste, Italy, in 2013 and organised by the Italian Synchrotron Radiation Society in collaboration with Elettra-Sincrotrone Trieste. The book is organised in four parts. The first describes the emission of synchrotron and free-electron laser sources, as well as the basic aspects of beamline instrumentation. In the second part, the fundamental interactions between electromagnetic radiation and matter are illustrated. The third part discusses the most important experimental methods, including different types of spectroscopy, diffraction and scattering, microscopy and imaging techniques. An overview of the numerous applications of these techniques to various research fields is then given in the fourth section. In this, a chapter is also dedicated to the new generation of synchrotron radiation sources, based on free-electron lasers, which are opening the way to new applications and more precise measurements.

This comprehensive book is aimed at both PhD students and more experienced researchers, since it not only provides an introduction to the field but also discusses relevant topics of interest in depth.

The European Research Council

By Thomas König
Polity Press

Established in 2007 to fund frontier-research projects, the European Research Council (ERC) has quickly become a fundamental instrument of science policy at European level, as well as a quality standard for academic research. This book traces the history of the creation and development of the ERC, drawing on the first-hand knowledge of the author, who was scientific adviser to the president of the ERC for four years. It covers the period between the early 2000s – when a group of strong-minded scientists pushed the idea of allocating (more) money to research projects selected for the quality of the proposals, judged by independent, competent and impartial reviewers – and when the first ERC programme cycle was concluded in 2013.

The author is particularly interested in the politics behind those events and shows how the ERC could translate into reality thanks to the fact that the European Commission decided to support it, using a much more strategic, planned and technical approach. He also describes the way that the ERC was implemented and the creation of its scientific council, discusses the “hybrid” nature of the ERC – being somewhere between a programme and an institution – and the consequent frictions in its early days, as well as the process to establish a procedure for selecting applications for funding.

While telling the story of the ERC from a critical perspective and examining its challenges and achievements, the book also offers a view of the relationship between science and policy in the 21st century.

The Many Faces of Maxwell, Dirac and Einstein Equations: A Clifford Bundle Approach (2nd edition)

By Waldyr A Rodrigues Jr and Edmundo Capelas de Oliveira
Springer

The Many Faces of Maxwell, Dirac and Einstein Equations
In theoretical physics, hardly anything is better known than the Einstein, Maxwell and Dirac equations. The Dirac and Maxwell equations (as well as the analogous Yang–Mills equations) form the basis of the modern description of matter via the electrodynamic, weak and strong interactions, while Einstein’s equations of special and general relativity are the foundations of the theory of gravity. Taken together, these three equations cover scales from the subatomic to the large-scale universe, and are the pillars on which the standard models of cosmology and particle physics are built. Although they constitute core information for theoretical physicists, they are rarely, if ever, presented together.

This book aims to remedy the situation by providing a full description of the Dirac, Maxwell and Einstein equations. The authors go further, however, by presenting the equations in several different forms. Their aim is twofold. On one hand, different expressions of these famous formulae may help readers to view a given equation from new and possibly more fruitful perspectives (when the Maxwell equations are written in the form of the Navier–Stokes equations, for instance, they allow a hydrodynamic interpretation of the electrodynamic field). On the other hand, casting different equations in similar forms may shed light on the quest for unification – as happens, for example, when the authors rewrite Maxwell’s equations in Dirac-like form and use this to launch a digression on supersymmetry.

Another feature of the book concerns concepts in differential geometry that are widely used in mathematics but about which there is little knowledge in theoretical physics. An example is the torsion of space–time: general differential manifolds are naturally equipped with a torsion in addition to the well-known curvature, and torsion also enters into the description of Lie algebras, yet the torsional completion of Einstein gravity, for instance, has been investigated very little. In the book, the authors take care of this issue by presenting the most general differential geometry of space–time with curvature and torsion. They then use this to understand conservation laws, more specifically to better grasp the conditions under which these conservation laws may or may not fail. Trivially, a genuine conservation law expresses the fact that a certain quantity is constant over time, but in differential geometry there is no clear and unambiguous way to define an absolute time.

As an additional important point, the book contains a thorough discussion about the role of active transformations for physical fields (to be distinguished from passive transformations, which are simply a change in co-ordinates). Active transformations are fundamental, both to define the transformation properties of specific fields and also to investigate their properties from a purely kinematic point of view without involving field equations. A section is also devoted to exotic or new physical fields, such as the recently introduced “ELKO” field.

Aside from purely mathematical treatments, the book contains useful comments about fundamental principles (such as the equivalence principle) and physical effects (such as the Sagnac effect). The authors also pay attention to clarifying certain erroneous concepts that are widespread in physics, such as assigning a nonzero rest mass to the photon.

In summary, the book is well suited for anyone who has an interest in the differential geometry of twisted–curved space–time manifolds, and who is willing to work on generalisations of gravity, electrodynamics and spinor field theories (including supersymmetry and exotic physics) from a mathematical perspective. Perhaps the only feature that might discourage a potential reader, which the authors themselves acknowledge in the introduction, is the considerable amount of sophisticated formalism and mathematical notation. But this is the price one has to pay for such a vast and comprehensive discussion about the most fundamental tools in theoretical physics.

Infinitesimal: How a Dangerous Mathematical Theory Shaped the Modern World

By Amir Alexander
One World

CCboo1_03_17 — Infinitesimal: How a Dangerous Mathematical Theory Shaped the Modern World

Lying midway between the history and the philosophy of science, this book illuminates a fascinating period in European history during which mathematics clashed with common thought and religion. Set in the late 16th and early 17th centuries, it describes how the concept of infinitesimals – a quantity that is explicitly nonzero and yet smaller than any measurable quantity – took a central role in the debate between ancient medieval ideas and the new ideas arising from the Renaissance. The former were represented by immutable divine order and the principle of authority, the latter by social change and experimentation.

The idea of indivisible quantities and their use in geometry and arithmetic, which had already been developed by ancient Greek mathematicians, underwent its own renaissance 500 years ago, at the same time as Martin Luther launched the Reformation. The consequences for mathematics and physics were enormous, giving rise to unprecedented scientific progress that continued for the following decades and centuries. But even more striking is that the new way of thinking built around the concept of infinitesimals crossed the borders of science and strongly influenced society, up to the point that mathematics became the main focus of the struggle between the old and new orders.

This book is divided into two parts, each devoted to a particular geographical area and period in which this battle took place. The first part leads the reader to late 16th century Italy, where the flourishing and creative ideas of the Renaissance had given birth to a prolific number of mathematicians and scientists. Here, the prominent figure of Galileo Galilei – together with Evangelista Torricelli, Bonaventura Cavalieri and others – was at the forefront of the new mathematical approach involving the concept of infinitesimals. This established the basis of inductive reasoning, which makes broad generalisations from specific observations, and led to a new science founded on experience. On the opposite side, the religious congregation of the Jesuits used these same mathematical developments in its fight against heresy and the Reformation. To them, the traditional mathematical approach was a solid basis for the absolute truth represented by the Catholic faith and the authority of the Pope. The fierce opposition of the Jesuit mathematicians led Galileo and the “infinitesimalists” to damnation, with irreparable consequences for the ancient tradition of Italian mathematicians.

The second part of the book moves the reader to 17th century England, just after the English Civil War in the years of Cromwell’s republic and the Restoration. In that context, the new ideas represented by infinitesimals were not only condemned by the Anglican Church but also opposed by political powers. Here, the leading figure of Thomas Hobbes took the stage in the fight against the indivisibles and the inductive method. For him, traditional Euclidean geometry – which, contrary to induction, used deduction to achieve any result from a few basic statements – was the highest expression of an ordered philosophical system and a model for a perfect state. Hobbes was also concerned about the threat to the principle of authority that emanated from traditional mathematical thought. In his struggle against infinitesimals, he was confronted by the members of the newly founded Royal Society, eager for scientific progress. Among them was John Wallis, who considered mathematical knowledge as a “down–up” inductive system in which calculus played the role of experiments in physics. Solving many of the toughest mathematical problems of his times by infinitesimal procedures, Wallis defeated traditional geometry – and Thomas Hobbes with it. The triumph of Wallis made way for scientific progress and the advance of thought that opened the door to the Enlightenment.

This book is excellently written and its mathematical concepts are clearly explained, making it fully accessible to a general audience. With his fascinating narrative, the author intrigues the reader, depicting the historical background and, in particular, recounting the plots of the Holy See, the Jesuits’ fight for power, the Reformation, the absolutist power of the kings, and the early steps of Europeans towards democracy and freedom of thought. The book includes extensive notes at the end, a useful index of concepts, a timeline and a “dramatis personae” section, which is divided between “infinitesimalists” and “non-infinitesimalists”. Finally, the images and portraits included in the book enhance the enjoyment for the reader.

Sri Lanka signs International Co-operation Agreement with CERN

Susil Premajayantha and Charlotte Warakaulle with the signed documents.
Image credit: M Brice/CERN

On 8 February, Sri Lanka and CERN entered into an International Co-operation Agreement (ICA) concerning scientific and technical co-operation in high-energy physics. The agreement was signed by Susil Premajayantha, Sri Lankaʼs hon. minister of science, technology and research, and Charlotte Warakaulle, CERNʼs director for international relations.

The new agreement follows an Expression of Interest signed in June 2015 by Sri Lanka ambassador Ravinatha Aryasinha and the then Director-General Rolf-Dieter Heuer, which already incorporated Sri Lanka into CERN’s high-school teacher and summer-student programmes. Previously, scientists from Sri Lankan universities have participated in LHC experiments within the frameworks of sabbatical leave or similar programmes, whereas others have participated as visiting scientists employed by universities in a third country.

With the partnership now formalised via the new ICA, students, scientists, engineers and research institutes in Sri Lanka will be able to benefit from broader and more sustained participation in CERN, and thus be exposed to cutting-edge technology and research in high-energy physics.

“ICAs help to strengthen the global network for particle physics, which is essential for the future of the discipline and for fundamental research more generally,” says Warakaulle. “It is significant to see that a smaller, developing country is emphasising fundamental research and making the connection with CERN a priority. It testifies to an understanding of the value of fundamental research, which is commendable in a country that is facing other challenges. It also further enhances the CERN connection with South Asia, following the associate memberships of Pakistan and India.”

European computing cloud takes off

Scope of the pilot phase for the European Open Science Cloud.

A European scheme to make publicly funded scientific data openly available has entered its first phase of development, with CERN one of several organisations poised to test the new technology. Launched in January and led by the UK’s Science and Technology Facilities Council, a €10 million two-year pilot project funded by the European Commission marks the first step towards the ambitious European Open Science Cloud (EOSC) project. With more than 30 organisations involved, the aim of the EOSC is to establish a Europe-wide data environment to allow scientists across the continent to exchange and analyse data. As well as providing the basis for better scientific research and making more efficient use of data resources, the open-data ethos promises to address societal challenges such as public-health or environmental emergencies, where easy access to reliable research data may improve response times.

The pilot phase of the EOSC aims to establish a governance framework and build the trust and skills required. Specifically, the pilot will encourage selected communities to develop demonstrators to showcase EOSC’s potential across various research areas including life sciences, energy, climate science, material science and the humanities. Given the intense computing requirements of high-energy physics, CERN is playing an important role in the pilot project.

The CERN demonstrator aims to show that the basic requirements for the capture and long-term preservation of particle-physics data, documentation, software and the environment in which it runs can be satisfied by the EOSC pilot. “The purpose of CERN’s involvement in the pilot is not to demonstrate that the EOSC can handle the complex and demanding requirements of LHC data-taking, reconstruction, distribution, re-processing and analysis,” explains Jamie Shiers of CERN’s IT department. “The motivation for long-term data preservation is for reuse and sharing.”

Propelled by the growing IT needs of the LHC and experience gained by deploying scientific workloads on commercial cloud services, explains Bob Jones of CERN’s IT department, CERN proposed a model for a European science cloud some years ago. In 2015 this model was expanded and endorsed by members of EIROforum. “The rapid expanse in the quantities of open data being produced by science is stretching the underlying IT services,” says Jones. “The Helix Nebula Science Cloud, led by CERN, is already working with leading commercial cloud service providers to support this growing need for a wide range of scientific use cases.”

The challenging EOSC project, which raises issues such as service integration, intellectual property, legal responsibility and service quality, complements the work of the Research Data Alliance and builds on the European Strategy Forum on Research Infrastructure (ESFRI) road map. “Our goal is to make science more efficient and productive and let millions of researchers share and analyse research data in a trusted environment across technologies, disciplines and borders,” says Carlos Moedas, EC commissioner for research, science and innovation.

Milestone for US dark-matter detector

Photomultiplier tubes surrounded by polytetrafluoroethylene for the LZ experiment, which is managed by Lawrence Berkeley National Laboratory.
Image credit: LBNL.

The US Department of Energy (DOE) has formally approved a key construction milestone for the LUX-ZEPLIN (LZ) experiment, propelling the project towards its April 2020 goal for completion. On 9 February the project passed a DOE review and approval stage known as “Critical Decision 3”, which accepts the final design and formally launches construction. The LZ detector, which will be built roughly 1.5 km underground at the Sanford Underground Research Facility in South Dakota and be filled with 10 tonnes of liquid xenon to detect dark-matter interactions, is considered one of the best bets to determine whether dark-matter candidates known as WIMPs exist.

The project stems from the merger of two previous experiments: LUX (Large Underground Xenon) and ZEPLIN (ZonEd Proportional scintillation in LIquid Noble gases). It was first approved in 2014 and currently has about 250 participating scientists in 37 institutions in the US, UK, Portugal, Russia and Korea. The detector is expected to be at least 50 times more sensitive to finding signals from dark-matter particles than its predecessor LUX, and will compete with other liquid-xenon experiments under development worldwide in the race to detect dark matter. A planned upgrade to the current XENON1T experiment (called XENONnT) at Gran Sasso National Laboratory in Italy and China’s plans to advance the PandaX-II detector, for instance, are both expected to have a similar schedule and scale to LZ.

The LZ collaboration plans to release a Technical Design Report later this year. “We will try to go as fast as we can to have everything completed by April 2020,” says LZ project director Murdock Gilchriese. “We got a very strong endorsement to go fast and to be first.”

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