Praxis Archives – Page 38 of 179

In pursuit of the possible

**Giulia Zanderighi** leads the department of novel computational techniques in particle phenomenology at the Max Planck Institute for Physics in Munich. Credit: A Griesch/MPP

What do collider phenomenologists do?

I tend to prefer the term particle phenomenology because the collider is just the tool that we use. However, compared to other experiments, such as those searching for dark matter or axions, colliders provide a controlled laboratory where you decide how many collisions and what energy these collisions should have. This is quite unique. Today, accelerators and detectors have reached an immense level of sophistication, and this allows us to perform a vast amount of fundamental measurements. So, the field spans precision measurements of fundamental properties of particles, in particular of the Higgs boson, consistency tests of the Standard Model (SM), direct and indirect searches for new physics, measurements of rare decays, and much more. For essentially all these topics we have had new results in recent years, so it’s a very active and continuously evolving field. But of course we do not just measure things for the sake of it. We have big, fundamental questions and we are looking for hints from LHC data as to how to address them.

What’s hot in the field today?

One topic that I think is very cool is that we can benefit from the LHC, in its current setup, also as lepton collider. In fact, at the LHC we are looking at elementary collisions between the proton’s constituents, quarks and gluons. But since the proton is charged, it also emits photons, and one can talk about the photon parton-distribution function (PDF), i.e. the photonic content of protons. These photons can split into lepton pairs, so when one collides protons one is also colliding leptons. The fascinating thing is that the “content” of leptons in protons is rather democratic, so one can look at collisions between, say, a muon and a tau lepton – something that can’t be done even at future proposed lepton colliders. Furthermore, by picking up a lepton from one proton and a quark from the other proton, one can place new constraints on leptoquarks, and plenty of other things. This idea was already proposed in the 1990s, but was essentially forgotten because the lepton PDF was not known. Now we know this very precisely, bringing new possibilities. But let me stress that this is just one idea – there are many other new ideas out there. For instance, one major branch of phenomenology is to use machine learning or deep learning to recognise the SM and extract from data what is not SM-like.

I’m the first female director, which of course is a great responsibility

How does the Max Planck Institute differ from your previous positions, for example at CERN and Oxford?

A long time ago, somebody told me that the best thing that can happen to you in Germany is the Max Planck Society. It’s true. You are given independence and the means to fully focus on research and ideas, largely free of teaching duties or the need to apply for grants. Also, there are very valuable interactions with universities, be it in research or via the International Max Planck Research Schools for PhD students. Our institute in Munich is a very unique place. One can feel it immediately. As a guest in the theory department, for example, you get to sit in the Heisenberg office, which feels like going back in time. Our institute was founded in Berlin in 1917 with Albert Einstein as a first director. In 1958 the institute moved to Munich with Werner Heisenberg as director. After more than 100 years I’m the first female director, which of course is a great responsibility. But I also really loved both CERN and Oxford. At CERN I felt like I was at the centre of the world. It is such a vibrant environment, and I loved the proximity to the experiments and the chats in the cafeteria about calculations or measurements. In Oxford I loved the multidisciplinary aspect, the dinners in college sitting next to other academics working in completely different fields. I guess I’m lucky that I’ve been in so many and such different places.

What is the biggest challenge to reach higher precision in quantum-field-theory calculations of key SM processes?

Scattering processes — **Loops and legs** Calculating scattering processes at the LHC at next-to-next-to-leading order in QCD is a high priority for the field. Credit: D Dominguez/CERN

The biggest challenge is that often there is no single biggest challenge. For instance, for inclusive Higgs-boson production we have a number of theoretical uncertainties, but they are all quite comparable in size. This means that to reduce the overall uncertainty considerably, one needs to reduce all uncertainties, and they all have very different physics origins and difficulties – from a better understanding of the incoming parton densities and a better knowledge of the strong coupling constant, to higher order QCD or electroweak effects and effects related to heavy particles in virtual loops, etc. Computing power can be a liming factor for certain calculations, so making things numerically more efficient is also important. One of the main goals of the coming year will be the calculation of two to three scattering processes at the LHC at next-to-next-to-leading order (NNLO) in QCD. For instance, a milestone will be the calculation of top-pair production in association with a Higgs boson at that level of accuracy. This is the process where we can measure most directly the top-Yukawa coupling. The importance of this measurement can’t be overstressed. While the big discovery at the LHC is so far the Higgs boson, one should also remember that the Yukawa interaction is a new type of fundamental interaction, which is proportional to the mass of the particle, just like gravity, but yet so different from gravity. For some calculations, NNLO is already enough in terms of perturbative precision; going to N³LO doesn’t really add much yet. But there are a few cases where it helps already, such as super-clean Drell–Yan processes.

Is there a level of precision of LHC measurements beyond which indirect searches for new physics are no longer fruitful?

We will never rule out precision measurements as a route to search for new physics. We can always extend the reach and enhance the sensitivity of indirect searches. By increasing precision, we are exploring deeper in the ultraviolet region, where we can start to become sensitive to states exchanged in the loops that are more and more heavy. There is a limit, but we are very far from it. It’s like looking with a better and better microscope: the better the resolution, the more one can explore. However, the experimental precision has to go hand in hand with theoretical precision, and this is where the real challenge for phenomenologists lies. Of course, if you have a super precise measurement but no theory prediction, or vice versa, then you can’t do much with it. With the Higgs boson I am confident that the theory calculations will not be the deal breaker. We will eventually hit the wall in terms of experimental precision, but you can’t put a figure on where this will happen. Until you see a deviation you are never really done.

How would you characterise the state of particle physics today?

When I entered the field as a student, there were high expectations that supersymmetry would be discovered quickly at the LHC. Now things have turned out to be different, but this is what makes it exciting and challenging – even more so, because the same mysteries are still there. We have big, fundamental questions. We have hints from theory, from experiments. We have a powerful, multi-purpose machine – the LHC – that is only just getting started and will provide much more data. Of course, expectations like the quick discovery of supersymmetry have not been fulfilled, but nature is how it is. I think that progress in physics is driven by experiments. We have beautiful exceptions where progress comes from theory, like general relativity, or the postulation of the mechanism for electroweak symmetry breaking. When I think about the Higgs mechanism, I am still astonished that such a simple and powerful idea postulated in 1964 turns out to be realised in nature. But these cases, where theory precedes experiments, are the exception not the rule. In most cases progress in physics comes from observations. After all, it is a natural science, it is not mathematics.

There are some questions that are really tough, and we may never really see an answer to. But with the LHC there are many other smaller questions we certainly can address, such as understanding the proton structure or studying the interaction potential between nucleons and strange baryons, which are relevant to understand the physics of neutron stars, and these are still advancing knowledge. The brightest minds are attracted to the biggest problems, and this will always draw young researchers into the field.

Is naturalness a good guiding force in fundamental research?

Yes. We have plenty of examples where naturalness, in the sense of a quadratic sensitivity to an unknown ultraviolet scale, leads to postulating a new particle: the energy of the electron field (leading to the positron), the charged and neutral pion mass difference (leading to the rho-meson) or the kaon transition rates and mixing, which led to the postulation of the existence of the charm quark in 1970, before its direct discovery in 1974 at SLAC and Brookhaven. In everyday life we constantly assume naturalness, so yes, it is puzzling that the Higgs mass appears to be fine-tuned. Certainly, there is a lot we still don’t understand here, but I would not give up on naturalness, at least not that easily. In the case of the electroweak naturalness problem, it is clear that any solution, such as supersymmetry or compositeness, will also leave an imprint in the Higgs couplings. So the LHC can, in principle, tell us about naturalness even if we do not discover new physics directly; we just have to measure very precisely if the Higgs boson couplings align on a straight line in the mass-versus-coupling plane.

The presence of dark matter is overwhelming in the universe and it is embarrassing that we know little to nothing about its nature

Which collider should follow the LHC?

That is the billion-dollar question – I mean, the 25 billion-dollar question! To me one should go for the machines that explore as much as possible the new energy frontier, namely a 100 TeV hadron collider. It is a compromise between what we might be able to achieve from a machine-building/accelerator/engineering point of view and really exploring a new frontier. For instance, at a 100 TeV machine one can measure the Higgs self-coupling, which is intimately connected with the Higgs potential and to the profound question of the stability of the vacuum.

Which open question would you most like to see answered during your career?

Probably the nature of dark matter. The presence of dark matter is overwhelming in the universe and it is embarrassing that we know little to nothing about its nature and properties. There are many exciting possibilities, ranging from the lightest neutral states in new-physics models to a non-particle-like interpretation, like black holes. Either way, an answer to this question would be an incredible breakthrough.

How to find a Higgs boson

Finding Higgs bosons can seem esoteric to the uninitiated. The spouse of a colleague of mine has such trouble describing what their partner does that they read from a card in the event that they are questioned on the subject. Do you experience similar difficulties in describing what you do to loved ones? If so, then Ivo van Vulpen’s book How to find a Higgs boson may provide you with an ideal gift opportunity.

Readers will feel like they are talking physics over a drink with van Vulpen, who is a lecturer at the University of Amsterdam and a member of the ATLAS collaboration. Originally published as De melodie van de natuur, the book’s Dutch origins are unmistakable. We read about Hans Lippershey’s lenses, Antonie van Leeuwenhoeck’s microbiology, Antonius van den Broek’s association of charge with the number of electrons in an atom, and even Erik Verlinde’s theory of gravity as an emergent entropic force. Though the Higgs is dangled at the end of chapters as a carrot to get the reader to keep reading, van Vulpen’s text isn’t an airy pamphlet cashing in on the 2012 discovery, but a realistic representation of what it’s like to be a particle physicist. When he counsels budding scientists to equip themselves better than the North Pole explorer who sets out with a Hugo Boss suit, a cheese slicer and a bicycle, he tells us as much about himself as about what it’s like to be a physicist.

Van Vulpen is a truth teller who isn’t afraid to dent the romantic image of serene progress orchestrated by a parade of geniuses. 9999 out of every 10,000 predictions from “formula whisperers” (theorists) turn out to be complete hogwash, he writes, in the English translation by David McKay. Sociological realities such as “mixed CMS–ATLAS” couples temper the physics, which is unabashedly challenging and unvarnished. The book boasts a particularly lucid and intelligible description of particle detectors for the general reader, and has a nice focus on applications. Particle accelerators are discussed in relation to the “colour X-rays” of the Medipix project. Spin in the context of MRI. Radioactivity with reference to locating blocked arteries. Antimatter in the context of PET scans. Key ideas are brought to life in cartoons by Serena Oggero, formerly of the LHCb collaboration.

The weak interaction is like a dog on an attometre-long chain.

Attentive readers will occasionally be frustrated. For example, despite a stated aim of the book being to fight “formulaphobia”, Bohr’s famous recipe for energy levels lacks the crucial minus sign just a few lines before a listing of –3.6 eV (as opposed to –13.6 eV) for the energy of the ground state. Van Vulpen compares the beauty seen by physicists in equations to the beauty glimpsed by musicians as they read sheet music, but then prints Einstein’s field equations with half the tensor indices missing. But to quibble about typos in the English translation would be to miss the point of the book, which is to allow readers “to impress friends over a drink,” and talk physics “next time you’re in a bar”. Van Vulpen’s writing is always entertaining, but never condescending. Filled with amusing but perceptive one-liners, the book is perfectly calibrated for readers who don’t usually enjoy science. Life in a civilisation that evolved before supernovas would have no cutlery, he observes. Neutrinos are the David Bowie of particles. The weak interaction is like a dog on an attometre-long chain.

This book could be the perfect gift for a curious spouse. But beware: fielding questions on the excellent last chapter, which takes in supersymmetry, SO(10), and millimetre-scale extra dimensions, may require some revision.

Black holes attract 2020 Nobel Prize

Penrose, Ghez and Genzel — **Space–time pioneers** From left: Nobel winners Roger Penrose, Andrea Ghez and Reinhard Genzel. Credit: Creative Commons

The 2020 Nobel Prize in Physics, announced on 6 October, has recognised seminal achievements in the theoretical and experimental understanding of black holes. One half of the SEK 10 million ($1.15 million) award went to Roger Penrose of the University of Oxford “for the discovery that black-hole formation is a robust prediction of the general theory of relativity”. The other half was awarded jointly to Andrea Ghez of the University of California, Los Angeles and Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics “for the discovery of a supermassive compact object at the centre of our galaxy”, after the pair led separate research teams during the 1990s to identify a black hole at the centre of the Milky Way.

You might ask where the greatest entropy is in the universe – by an absolutely enormous factor it is in black holes
Roger Penrose

As soon as Einstein had completed his theory of general relativity in 1915, it was clear that solutions in the vicinity of a spherically symmetric, non-rotating mass allow space–time to be “pinched” to a point, or singularity, where known physics ceases to apply. Few people, including Einstein himself, however, thought that black holes really exist. But 50 years later, Penrose invented a mathematical tool called a trapped surface to show that black holes are a natural consequence of general relativity, proving that they each hide a singularity. His groundbreaking article (Phys. Rev. Lett. 14 57) is heralded as the first post-Einsteinian result in general relativity.

Penrose is also known for the “Penrose process”, whereby a particle–antiparticle pair that forms close to the event horizon of a black hole can become separated, with one of the two particles falling into the black hole and the other one escaping and carrying away energy and angular momentum. He also proposed twistor theory, which has evolved into a rich branch of theoretical and mathematical physics with potential relevance to the unification of general relativity and quantum mechanics, among many other contributions.

“I really had to have a good idea of the space–time geometry. Not just 3D, you had to think of the whole 4D space–time… I do most of my thinking in visual terms, rather than writing down equations,” said Penrose in an interview with the Nobel Foundation following the award. “Black holes have become more and more important, also in ways that people don’t normally appreciate. They are the basis of the second law of thermodynamics… You might ask where the greatest entropy is in the universe – by an absolutely enormous factor it is in black holes.”

Preparatory ‘pre-lab’ proposed for ILC

ILC accelerating module — **Down the line** How an accelerating module for the International Linear Collider (ILC) might look. Credit: R Hori/KEK

On 10 September the International Committee for Future Accelerators (ICFA) announced the structure and members of a new organisational team to prepare a “pre-laboratory” for an International Linear Collider (ILC) in Japan. The ILC International Development Team (ILC-IDT), which consists of an executive board and three working groups governing the pre-lab setup, accelerator, and physics and detectors, aims to complete the preparatory phase for the pre-lab on a timescale of around 1.5 years.

We hope that the effort by our Japanese colleagues will result in a positive move by the Japanese government
Tatsuya Nakada

The aim of the pre-lab is to prepare the ILC project, should it be approved, for construction. It is based on a memoranda of understanding among participating national and regional laboratories, rather than intergovernmental agreements, explains chair of the ILC-IDT executive board Tatsuya Nakada of École Polytechnique Fédérale de Lausanne. “The ILC-IDT is preparing a proposal for the organisational and operational framework of the pre-lab, which will have a central office in Japan hosted by the KEK laboratory,” says Nakada. “In parallel to our activities, we hope that the effort by our Japanese colleagues will result in a positive move by the Japanese government that is equally essential for establishing the pre-laboratory.”

In June the Linear Collider Board and Linear Collider Collaboration, which were established by ICFA in 2013 to promote the case for an electron–positron linear collider and its detectors as a worldwide collaborative project, reached the end of their terms in view of ICFA’s decision to set up the ILC-IDT.

The ILC has been on the table for almost two decades. Shortly after the discovery of the Higgs boson in 2012, the Japanese high-energy physics community proposed to host the estimated $7 billion project, with Japan’s prime minister at that time, Yoshihiko Noda, stressing the importance of establishing an international framework. In 2018 ICFA backed the ILC as a Higgs factory operating at a centre-of-mass energy of 250 GeV – half the energy set out five years earlier in the ILC’s technical design report.

Higgs factory

An electron–positron Higgs factory is the highest-priority next collider, concluded the 2020 update of the European strategy for particle physics (ESPPU). The ESPPU recommended that Europe, together with its international partners, explore the feasibility of a future hadron collider at CERN at the energy frontier with an electron–positron Higgs factory as a possible first stage, noting that the timely realisation of the ILC in Japan “would be compatible with this strategy”. Two further proposals exist: the Compact Linear Collider at CERN and the Circular Electron–Positron Collider in China. While the ILC is the most technically ready Higgs-factory proposal (see p35), physicists are still awaiting a concrete decision about its future.

In March 2019 Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT) expressed “continued interest” in the ILC, but announced that it had “not yet reached declaration” for hosting the project, arguing that it required further discussion in formal academic decision-making processes. In February KEK submitted an application for the ILC project to be considered in the MEXT 2020 roadmap for large-scale research projects. KEK withdrew the application the following month, announcing the move in September following the establishment of the ILC-IDT.

The ministry will keep an eye on discussions by the international research community
Koichi Hagiuda

“The ministry will keep an eye on discussions by the international research community while exchanging opinions with government authorities in the US and Europe,” said Koichi Hagiuda, Japanese minister of education, culture, sports, science and technology, at a press conference on 11 September.

Steinar Stapnes of CERN, who is a member of the ILC-IDT executive board representing Europe, says that clear support from the Japanese government is needed for the ILC pre-lab. “The overall project size is much larger than the usual science projects being considered in these processes and it is difficult to see how it could be funded within the normal MEXT budget for large-scale science,” he says. “During the pre-lab phase, intergovernmental discussions and negotiation about the share of funding and responsibilities for the ILC construction need to take place and hopefully converge.”

CERN publishes first environmental report

Safety engineering and environment group members — **Greener pastures** Members of the CERN safety engineering and environment group at one of around 100 environment monitoring stations on and around the laboratory’s sites. Credit: CERN-PHOTO-201504-073-3

“It is our vision for CERN to be a role model for environmentally responsible research,” writes CERN Director-General Fabiola Gianotti in her introduction to a landmark environmental report released by the laboratory on 9 September. While CERN has a longstanding framework in place for environmental protection, and has documented its environmental impact for decades, this is its first public report. Two years in the making, and prepared according to the Global Reporting Initiative Sustainability Reporting Standards, it details the status of CERN’s environmental footprint, along with objectives for the coming years.

Given the energy consumption of large particle accelerators, environmental impact is a topic of increasing importance for high-energy physics research worldwide. Among the recommendations of the 2020 update of the European strategy for particle physics was a strong emphasis on the need to continue with efforts to minimise the environmental impact of accelerator facilities and maximise the energy efficiency of future projects.

When the Large Hadron Collider (LHC) is operating, CERN uses an average of 4300 TJ of electricity every year (30–50% less when not in operation) – enough energy to power just under half of the 200,000 homes in the canton of Geneva. “This is an inescapable fact, and one that CERN has always taken into consideration when designing new facilities,” states Frédérick Bordry, director for accelerators and technology.

Action plan

An energy-management panel established at CERN in 2015 has already led to actions, including free cooling and air-flow optimisation, better optimised LHC cryogenics, and the implementation of SPS magnetic cycles and stand-by modes, which significantly reduce energy consumption. The LHC delivered twice as much data per Joule in its second run (2015–2018) compared to its first (2010–2013), states the new report. With the High-Luminosity LHC due to deliver a tenfold increase in luminosity towards the end of the decade, CERN has made it a priority to limit the increase in energy consumption to 5% up to the end of 2024, with longer-term objectives to be set in future reports.

CERN procures its electricity mainly from France, whose production capacity is 87.9% carbon-free. In terms of direct greenhouse-gas emissions, the 192,000 tonnes of carbon-dioxide equivalent emitted by CERN in 2018 is mainly due to fluorinated gases used in the LHC detectors for cooling, particle detection, air conditioning and electrical insulation. CERN has set a formal objective that, by 2024, direct greenhouse emissions will be reduced by 28% by replacing fluorinated gases – which were designed in the 1990s to be ozone-friendly – with carbon dioxide, which has a global-warming potential several thousand times lower.

CERN has set a formal objective that, by 2024, direct greenhouse emissions will be reduced
by 28%

Other areas of environmental significance studied in the report include radiation exposure, noise and waste. CERN commits to limit the emission of ionising radiation to no more than 0.3 mSv per year – less than a third of the annual dose limit for public exposure set by the European Council. The report states that the actual dose to any member of the public living in the immediate vicinity of CERN due to the laboratory’s activities is below 0.02 mSv per year, which is less than the exposure received from cosmic radiation during a transatlantic flight.

A 2018 measurement campaign showed that noise levels at CERN have not changed since the early 1990s, and are low by urban standards. Nevertheless, CERN has have invested 0.7 million CHF to reduce noise at its perimeters to below 70 dB during the day and 60 dB at night (which corresponds to the level of conversational speech). The organisation has also introduced approaches to preserve the local landscape and protect flora, including 15 species of orchid growing on CERN’s sites.

Waste not

Water consumption, mostly drawn from Lac Léman, has slowly decreased over the past 10 years, the report notes, and CERN commits to keeping the increase in water consumption below 5% to the end of 2024, despite a growing demand for cooling from upgraded facilities. CERN also eliminates 100% of its waste, states the report, and has a recycling rate of 56% for non-hazardous waste (which comprises 81% of the total). A major project under construction since last year will see waste hot water from the cooling system for LHC Point 8 (where the LHCb experiment is located) channeled to a heating network in the nearby town of Ferney-Voltaire from 2022, with LHC Points 2 and 5 being considered for similar projects.

CERN plans to release further environment reports every two years. “Today, more than ever, science’s flag-bearers need to demonstrate their relevance, their engagement, and their integration into society as a whole,” writes Gianotti. “This report underlines our strong commitment to environmental protection, both in terms of minimising our impact and applying CERN technologies for environmental protection.”

Jacques Séguinot 1932–2020

Jacques Séguinot, a founding father of the ring-imaging Cherenkov detector, passed away on 12 October.

Born in 1932 in a small village in Vendée, Jacques studied electromechanical engineering at the University of Caen and received his PhD in physics in 1954. His solid engineering base was visible in every experiment that Jacques designed and built throughout his long career, which followed a classic French academic path – from a stagiaire de recherche in 1954 to a directeur de recherche in 1981, which he held until his official retirement in 1990.

His first studies saw him spend several months at the French cosmic-ray laboratory on the Col du Midi near Mont Blanc, after which he worked on accelerator-based experiments: first at Saturne (CEA Saclay), and from 1964 onwards at CERN’s Proton Synchrotron studying strong interactions with pion and kaon beams. At the end of the 1960s, Jacques began a long and fruitful collaboration with Tom Ypsilantis, leading to a seminal 1977 paper establishing a new particle identification technology that became known as the RICH (Ring Imaging Cherenkov Counter).

The idea was to use the recently introduced multiwire proportional chamber, filled with a photosensitive gas, to detect and localise ultraviolet photons emitted by fast charged particles in a radiating medium, and to use a suitable optical arrangement to create a ring pattern whose radius depends on the particle speed. Combined with magnetic analysis, the RICH made it possible to identify a particle’s mass in a wide range of energies. In further work, Séguinot and Ypsilantis developed algorithms to optimise the momentum resolution of the detectors, as well as adapting radiators to cover different momentum ranges where other technologies were ineffective.

The early RICH devices were successfully deployed at the fixed-target experiments OMEGA at CERN and E605 at Fermilab. The ability of the detector to extend over most of the solid angle around the target or colliding-beam intersections also made it particularly relevant for experiments at the newly commissioned LEP and SLD accelerators. The RICH detector at LEP’s DELPHI experiment came close to the original design, with nearly 4π angular coverage, and Jacques’ contribution to this detector was key.

In view of the growing interest in meson factories, Jacques and Tom worked on faster RICH devices with shorter photo-conversion lengths, and also on CsI solid photo-converters. This led to applications in the RICH for CLEO at the CESR storage ring, the CsI-based RICH detectors in CERN’s ALICE, COMPASS and other experiments. Another very ambitious R&D programme, which started in the mid-1990s, aimed at developing highly segmented photodetectors sensitive to visible light. Jacques saw the potential of such hybrid photo detectors (HPD) for applications in medical imaging, and proposed an innovative PET device in which matrices of long scintillation crystals are read from both sides by HPDs. In the meantime, SiPM photodetectors had become available, with a number of practical advantages over HPDs. In the AX–PET collaboration, Jacques and several others built a fully operational axial PET with SiPM readout.

The high-energy physics community has lost an excellent detector physicist with an extraordinary sense of engineering. His groundbreaking ideas live on, including in the most recent detectors such as Belle II in Japan. But we will also remember Jacques’ fine personality, patience and decency.

Willem de Boer 1948–2020

Willem (“Wim”) de Boer passed away on 13 October, aged 72. Wim studied physics at the University of Delft and graduated in 1974 with a thesis on the dynamic orientation of nuclei at low temperatures, which laid the foundation of polarised targets in high-energy physics. Following a CERN fellowship, he joined the University of Michigan, Ann Arbor and worked on polarised proton–proton scattering at the ANL synchrotron, where he found an unexplained difference in the cross sections for parallel and antiparallel spins.

In 1975 Wim took up a position at the Max Planck Institute for Physics in Munich where he stayed, interrupted by a sabbatical at SLAC in 1987, for 14 years. In Munich he joined the team working on the CELLO experiment at DESY, where he took responsibility for the data-acquisition system. The CELLO years were instrumental for precision studies of QCD, out of which the triple-gluon coupling and the running of the strong coupling constant emerged – a subject Wim pursued ever after.

Following his appointment to a professorship at the University of Karlsruhe in 1989, Wim created research groups at LEP’s DELPHI experiment, the AMS-02 experiment on the International Space Station, and he coordinated a group at the LHC’s CMS experiment. Having studied the running of the coupling constants of the weak, electromagnetic and strong interactions, Wim found, together with Ugo Amaldi and Hermann Fürstenau, that these could only meet in a unified way at high energies if phenomena beyond the Standard Model, such as supersymmetry, existed. This was published in their seminal 1991 paper “Comparison of grand unified theories with electroweak and strong coupling constants measured at LEP”, which led to the expectation that a new energy domain would open up at the TeV scale with the lightest supersymmetric particle constituting dark matter. The paper has been cited almost 2000 times.

Wim contributed a multitude of ideas, studies and publications to each of the experiments he worked on, driven by the single question: where is supersymmetry? He looked for dark-matter signals at the lowest energies in our galaxy using earth-bound observatories, balloon experiments and satellites, at signals from direct production at LEP and the LHC, and in anomalous decay modes of bottom mesons using data from the Belle and BaBar experiments, among others.

It is our belief that Wim was most fascinated by AMS-02. Not only did he and his group contribute an electronic readout system to the detector, he also saw it take off from Cape Canaveral with the penultimate Space Shuttle flight in 2011, celebrated by the visit of the whole crew of astronauts to Karlsruhe later that year.

Wim’s career saw him work across detectors using gases, liquids, silicon and diamonds, and study their performance in magnetic fields and high-radiation backgrounds. He also investigated the use of detectors for medical and technical applications. His last R&D effort began only a few weeks before his death: the development of a novel cooling system for high-density batteries.

Our field has lost a great all-round physicist with unparalleled creativity and diligence, a warm collegiality and a very characteristic dry humour. Well aware of his rapid illness, his last words to his family were: “Hij gaat nog niet, want hij heeft nog zoveel ideeën!” (roughly “He’s not going yet, because he still has so many ideas!). He will be missed deeply.

American Physical Society announces 2021 awards

Henry Sobel (Top) and Edward Kearns (Bottom). Credit: UCI/Boston University

W.K.H. Panofsky Prize

The W K H Panofsky Prize in experimental particle physics has been awarded to Henry Sobel, professor emeritus of the University of California, Irvine and Edward Kearns of Boston University for pioneering and leadership contributions to large underground experiments for the discovery of neutrino oscillations and sensitive searches for baryon-number violation. As the US co-spokesperson, Sobel is heavily involved with Japan’s Super-Kamiokande experiment (Super-K), and is also involved in the next-generation neutrino experiments – DUNE, in the US and Hyper-K in Japan. Kearns is also involved in Super-K and DUNE, along with being a member of the Tokai-To-Kamioka (T2K) experiment and active in the search for dark matter using techniques based on cryogenic noble liquids.

J.J. Sakurai Prize

The J J Sakurai Prize for theoretical physics has been given to Vernon Barger of the University of Wisconsin-Madison for pioneering work in collider physics contributing to the discovery and characterisation of the W boson, top quark and Higgs boson, and for the development of incisive strategies to test theoretical ideas with experiments.

Robert R. Wilson Prize

In the field of accelerators, Yuri Fyodorovich Orlov, formerly of Cornell University, was awarded the Robert R Wilson Prize for his pioneering innovation in accelerator theory and practice. Orlov received the news shortly before his passing on 27 September.

Maria Goeppert Mayer Award

Phiala E Shanahan of the Massachusetts Institute of Technology has been granted the Mario Goeppert Mayer Award, which recognises an outstanding contribution to physics research by a women, “for key insights into the structure and interactions of hadrons and nuclei using numerical and analytical methods”.

Chanda Prescod-Weinstein Credit: University of New Hampshire

Edward A.Bouchet Award

The Edward A Bouchet Award, which promotes the participation of underrepresented minorities in physics, has been awarded to Chanda Prescod-Weinstein of the University of New Hampshire for her contributions to theoretical cosmology and particle physics and for co-creating the Particles for Justice movement.

Herman Feshbach Prize

The Herman Feshbach Prize in theoretical nuclear physics has been awarded to Berndt Mueller of Brookhaven National Laboratory for his contributions to the identification of quark-gluon plasma signatures.

Henry Primakoff Award

The 2021 Henry Primakoff Award for early-career particle physics has gone to Jaroslav Trnka of the University of California, Davis for seminal work on the computation of particle scattering amplitudes.

Dwight Nicholson Medal

The 2020 Dwight Nicholson Medal for Outreach has been given to Michael Barnett of Lawrence Berkeley National Laboratory “for a lifetime of innovations in outreach bringing the discoveries and searches of particle physicists and cosmologist to multitudes of students and lay people around the world.”

Yuri Orlov 1924–2020

Yuri Orlov, a world-renowned accelerator physicist and a leading figure in the worldwide campaign for human rights in Soviet Russia, passed away at the end of September at the age of 96.

Yuri was born in Moscow in 1924. He studied and worked there until 1956, when a critical pro-democracy speech he gave at the Institute for Theoretical and Experimental Physics resulted in him being fired and banned from scientific work. He then moved to the Yerevan Physics Institute in Armenia where he earned his first doctorate (“Nonlinear theory of betatron oscillations in the strong-focusing synchrotron”) in 1958, followed by the award of a second doctorate in 1963. While in Yerevan, he designed the 6 GeV electron synchrotron, became head of the electromagnetic interaction laboratory, and was elected to the Armenian Academy of Sciences.

In 1972 Yuri returned to Moscow and joined the influential dissident movement that included Andrei Sakharov and Aleksandr Solzhenitsyn. When the final documents of the Helsinki Conference on Security and Co-operation in Europe were signed in 1975, Yuri founded the Moscow Helsinki Group with the aim of having all human rights guaranteed in the Helsinki documents accorded to all citizens of the Soviet Union. As was to be expected, Yuri was arrested in 1977, tried in a political mock trial in 1978 and convicted to seven years in a labour camp in Perm.

As soon as Yuri Orlov’s ordeal became known in Europe and North America, physicists began to protest against the treatment of their colleague. At CERN, where several physicists had had personal contacts with Yuri, the Yuri Orlov Committee was founded with Georges Charpak as one of its founding members. The long-standing fruitful scientific collaboration with the Soviet Union was challenged and the support of eminent political leaders of the CERN member states was solicited.

Surviving a total of seven years of labour camp under extreme conditions, Yuri was deported to Siberia for a period of five years. Because of continuing international pressure, he was then deported to the US in 1986, where he was offered a position at Cornell University. Soon after his forced emigration, Yuri visited CERN and he spent a sabbatical there in 1988/1989 working in the accelerator division to develop the idea of ion “shaking”. He joined the muon g-2 experiment at Brookhaven National Laboratory and worked on Brookhaven proposals to measure the electric dipole moments of protons, electrons and deuterons. At Cornell he pursued this work as well as an alternative design for the proposed B-factory, and wrote on the foundations of quantum mechanics. In 2008 he was named a professor of physics and professor of government, and taught physics and human rights until his retirement in 2015.

Yuri authored or co-authored more than 240 scientific papers and technical reports, and wrote a memoir, Dangerous Thoughts: Memoirs of a Russian Life (William Morrow & Co, 1991). Among the many honours Yuri received are the American Physical Society’s 2006 Sakharov prize “For his distinction as a creative physicist and as a life-long, ardent leader in the defence and development of international human rights, justice and the freedom of expression for scientists”, and the APS 2021 Wilson Prize for outstanding achievements in the physics of particle accelerators, of which he was notified shortly before his death.

Yuri’s example as a scientist committed to the freedom of science, its cultural dimension in world affairs and his defence of the human right of expression of one’s convictions is an example and inspiration to all of us.

Glen Lambertson 1926–2020

Glen Lambertson, one of the early giants of US accelerator physics, passed away on 30 August aged 94. Glen is best known for the injection/extraction magnet that bears his name. His greatest achievements, however, were, to quote from the American Physical Society (APS) 2006 Wilson Prize citation, “… fundamental contributions … in the area of beam electrodynamics including the development of beam instrumentation for the feedback systems that are essential for the operation of high luminosity electron and hadron colliders”.

Glen’s studies at the University of Colorado were interrupted by World War II, during which he saw action serving in the legendary 10th Mountain Division. Severely wounded in Northern Italy, his life was saved by the newly discovered wonder drug “penicillin”. (Incidentally, he remained an avid skier well into his 80s.) After the war he completed his degree at Colorado in engineering physics and did graduate work at the University of California, quickly becoming involved with accelerators. His first contact was as an operator of the 184-Inch Synchrocyclotron, where he commented that Ernest Lawrence would often reach over his shoulder to “tweak a knob”.

Glen played a large part in the design of the magnet system for the Bevatron at Lawrence Berkeley National Laboratory, and in 1960 was instrumental in the retrofitting of a resonant extraction system for this machine, vastly improving its performance and effectiveness as a discovery tool for the newly established field of particle physics. His patent for the “Lambertson magnet” is dated 1965, and this concept is still widely used for the injection and extraction of beams in synchrotrons and storage rings.

In the mid-1970s Glen was a major contributor to the ESCAR project – a first attempt to build a small (4 GeV) superconducting accelerator to provide data and experience for future large superconducting machines. While funds were not available to complete the project, two quadrants of dipoles were built and successfully tested, along with the necessary cryogenic and control-system infrastructures. Later in the 1970s, following the developments in stochastic cooling by Simon Van der Meer, Glen led the successful experiment to demonstrate stochastic cooling at the Fermilab 200 MeV cooling test ring. His techniques were transferred to rings at Fermilab and Brookhaven.

His most productive studies were in beam instabilities, in particular the instrumentation to detect and control electron-cloud instabilities. He was a key figure in the successful commissioning of both the PEP-II B-factory at SLAC, and the Advanced Light Source at Berkeley. He also had close contacts with CERN, serving as a visiting scientist in 1993 and later playing an important role in calculating the impedance of injection-line components for the LHC.

Glen’s work was widely recognised. In addition to the APS Wilson prize, he was an APS fellow and also won the US Particle Accelerator School Prize for Achievement in Accelerator Science and Technology.

His always relaxed demeanour and sage advice were a constant inspiration to us, and we forgave him his incredibly awful puns. Rest in peace, Glen!

Topics

Reset your password

Registration complete