Jobs – Page 23 of 511

Quo vadis, European particle physics?

The 2020 European strategy for particle physics justifiably singled out the Higgs boson as the most mysterious element of the Standard Model. Uncovering the particle’s true nature and answering the numerous questions raised by its interactions with other particles is set forth as the highest priority of the field. And this, the strategy concluded, requires the next dream machines: an e⁺e^– Higgs factory and, in the longer term, a 100 TeV hadron collider. Getting there will be no easy feat, and thus several intermediate steps, necessary for bringing this programme to fruition, have been set in motion.

Firstly, the European Committee for Future Accelerators (ECFA) was called upon by the CERN Council to formulate a global detector R&D roadmap for both short- and long-term experimental endeavours. A painstaking consultation process across the entire range of detector technologies – from gas, liquid and solid-state detectors to particle-
identification systems, calorimetry and blue-sky R&D – culminated in a 250-page document and the creation of detector R&D collaborations to focus on the most relevant topics. In parallel, the European Laboratory Directors Group has compiled an accelerator R&D roadmap spanning activities such as high-field magnets, high-gradient accelerating elements, plasma-wakefield acceleration, energy- recovery linacs, and more.

**Paris Sphicas**, National and Kapodistrian University of Athens and CERN, started his three-year term as ECFA chair in January 2024. Credit: P Sphicas

With the accelerator and detector development in the best of hands, what remains is to converge on the next machine: namely the e⁺e^– collider that takes us as close as we can to a full understanding of the Higgs boson and the electroweak and top-quark sectors. Thankfully, we already know a lot about the reach of such “HET” factories from previous studies, in particular those carried out during the previous strategy update. To encourage further work en route to the next strategy update, ECFA has put together a HET-factory study group that brings together both the linear and circular e⁺e^– detector communities. The goal is to solidify our understanding of the requirements that the physics places on the experiments and on the associated beams. A common software framework with more realistic detector simulation and a parallel study of detector structures are the other working areas in the study group. Good progress is visible, and the third and last major workshop on the HET-factory study will take place in October 2024.

Major players

The other major players in the global high-energy physics scene completed their corresponding strategy processes either several years ago (Japan with the ILC and China with the CEPC) or recently (US with the P5 process). All eyes are now turned to Europe as we enter the final stretch towards the next update of the European strategy. With the Future Circular Collider feasibility study due to be completed next year, all the elements needed for a fully informed decision on the future of European – and global – particle physics will soon be in place.

The entire field, and especially the younger generations, are most eagerly awaiting this decision

The next strategy process will build on the excellent work that took place in the context of the previous one, which culminated with a large community gathering in Granada. Taking into account the updated information, it is both expected and highly desirable that the process converges quickly, with a definitive recommendation on both the next e⁺e^– collider and the longer-term prospects. The entire field, and especially the younger generations, are most eagerly awaiting this decision. Today, in parallel with maximally exploiting the physics potential of the LHC, our most important duty is to ensure that current PhD candidates find themselves at the centre of future discoveries a few decades from now.

Is all this possible for Europe? Absolutely! CERN has an unparalleled track record on the world stage with the ISR, SppS and LEP legacies, as well as the tremendous success of the LHC. These have not only provided some of the greatest advances in our understanding of the fundamental elements of nature, but also serve as guarantors of CERN’s ability to continue advancing the energy frontier, keeping Europe at the leading edge of scientific knowledge. All that is currently needed is the final direction – and the start signal. Quo vadis European particle physics? Towards the next discovery frontier, to further unravel the mysteries of the fascinating universe we have come to inhabit.

The Many Voices of Modern Physics: Written Communication Practices of Key Discoveries

This book provides a rich glimpse into written science communication throughout a century that introduced many new and abstract concepts in physics. It begins with Einstein’s 1905 paper “On the Electrodynamics of Moving Bodies”, in which he introduced special relativity. Atypically, the paper starts with a thought experiment that helps the reader to follow a complex and novel physical mechanism. Authors Harmon and Gross analyse and explain the terminological text and bring further perspective by adding comments made from other scientists or science writers during the time. They follow this analysis style throughout the book, covering science from the smallest to the largest scales and addressing the controversies surrounding atomic weapons.

The only exception from written evaluations of scientific papers is the chapter “Astronomical value”, in which the authors revisit the times of great astronomers such as Galileo Galilei or the Herschel siblings William and Caroline. The authors show that, even back then researchers were in need of sponsors and supporters to fund their research. In Galilei’s case, he regularly presented his findings to the Medici family and fuelled fascination in his patrons so that he was able to continue his work.

While writing the book, Gross, a rhetoric and communications professor, died unexpectedly, leaving Harmon, a science writer and editor at Argonne National Laboratory in communications, to complete the work.

While somewhat repetitive in style, readers can pick a topic of interest from the table of contents and see how scientists and communicators interacted with their audiences. While in-depth scientific knowledge is not required, the book is best targeted at readers who are familiar with the basics of physics and who want to gain new perspectives on some of the most important breakthroughs during the past century and beyond. Indeed, by casting well-known texts in a communication context, the book offers analogies and explanations that can be used by anyone involved in public engagement.

Extremely Brilliant Source illuminates Paganini’s favourite violin

Intense beams of synchrotron X-rays produced at the European Synchrotron Radiation Facility (ESRF) in Grenoble have revealed the inner workings of Niccolò Paganini’s favourite violin. Renowned for its acoustic prowess, the 280 year-old “Il Cannone” ranks among the most important instruments in the history of Western music. To help understand and preserve the precious artefact, the Municipality of Genoa in Italy and the Premio Paganini teamed up with researchers at the ESRF’s new BM18 beam line to study the structural status of the wood and its bonding.

Using multi-resolution propagation phase-contrast X-ray microtomography, a non-destructive technique widely used at the ESRF for palaeontology, the team was able to reconstruct a 3D image of the violin at the level of its cellular structure. In addition to revealing Il Cannone’s conservation status and structure, the results hint at the interventions made by luthiers throughout the instrument’s life.

In few months, we will be able to work on much larger instruments, up to the size of a double bass
Paul Tafforeau, ESRF

Inaugurated in 1994, the ESRF was the first “third generation” synchrotron, using periodic magnetic arrays called undulators to deliver the world’s brightest X-ray beams. It consists of a 844 m-circumference 6 GeV electron storage ring with almost 50 experimental stations serving around 5000 users per year across a wide range of disciplines. The study of Paganini’s violin was made possible by an EUR 330 million upgrade called the Extremely Brilliant Source, which came online in 2020. With an increased X-ray brightness and coherent flux 100 times higher than before, the facility allows complex materials to be imaged more quickly and in greater detail.

“We had to deal with some logistical and technical challenges, but the ESRF team did an incredible job to make this dream a reality,” says Paul Tafforeau, ESRF scientist in charge of BM18. “I hope that this experiment will be the first in a long series. In few months, we will be able to work on much larger instruments, up to the size of a double bass.”

CMS closes in on tau g–2

The CMS collaboration has reported the first observation of ?? → ?? in pp collisions. The results set a new benchmark for the tau lepton’s magnetic moment, surpassing previous constraints and paving the way for studies probing new physics.

For the tau lepton’s less massive cousins, measurements of magnetic moments offer exceptional sensitivity to beyond-the-Standard-Model (BSM) physics. In quantum electrodynamics (QED), quantum effects modify the Dirac equation, which predicts a gyromagnetic factor g precisely equal to two. The first-order correction, an effect of only α/2π, was calculated by Julian Schwinger in 1948. Taking into account higher orders too, the electron anomalous magnetic moment, a = (g–2)/2, is one of the most precisely measured quantities in physics and is in remarkable agreement with QED predictions. The g–2 of the muon has also been measured with high precision and shows a persiste nt discrepancy with certain theoretical predictions. By contrast, however, the tau lepton’s g–2 suffers from a lack of precision, given that its short lifetime makes direct measurements very challenging. If new-physics effects scale with the squared lepton mass, deviations from QED predictions in this measurement would be about 280 times larger than in the muon g–2 measurement.

CMS figure 1 — **Fig. 1.** Observed and expected distributions of the number of additional tracks within 1 mm of the di-tau vertex. The ?? → ?? signal is visible at low multiplicities. Credit: CMS Collaboration

Experimental insights on g–2 can be indirectly obtained by measuring the exclusive production of tau–lepton pairs created in photon–photon collisions. As charged particles pass each other at relativistic velocities in the LHC beampipe, they generate intense electromagnetic fields, leading to photon–photon collisions. The production of tau lepton pairs in photon collisions was first observed by the ATLAS and CMS collaborations in Pb–Pb runs. The CMS collaboration has now observed the same process in proton–proton (pp) data. When photon collisions occur in pp runs, the protons can remain intact. As a result, final-state particles can be produced exclusively, with no other particles coming from the same production vertex.

Tau–lepton tracks were isolated within just a millimetre around the interaction vertex

Separating these low particle multiplicity events from ordinary pp collisions is extremely challenging, as events “pile up” within the same bunch crossing. Thanks to the precise tracking capabilities of the CMS detector, tau–lepton tracks were isolated within just a millimetre around the interaction vertex. Figure 1 shows the resulting excess of ?? → ?? events rising above the estimated backgrounds when few additional tracks were observed within the selected 1 mm window.

CMS figure 2 — **Fig. 2.** Constraints set by the new CMS result on the anomalous magnetic moment of the tau lepton, in comparison with past measurements. Credit: CMS Collaboration

This process was used to constrain a_? using an effective-field-theory approach. BSM physics affecting g–2 would modify the expected number of ?? → ?? events, with the effect increasing with the di-tau invariant mass. Compared to Pb–Pb collisions, the pp data sample provides a more precise g–2 value because of the larger number of events and of the higher invariant masses probed, thanks to the higher energy of the photons. Using the invariant-mass distributions collected in pp collisions during the full LHC Run 2, the CMS collaboration has not observed any statistically significant deviations from the Standard Model. The tightest constraint ever on a_? was set, as shown in figure 2. The uncertainty is only three times larger than the value of Schwinger’s correction.

Science needs cooperation, not exclusion

In the aftermath of World War II, nations came together and formed the United Nations (UN) with the purpose, as stated in the first article of the UN charter, “… to take effective collective measures for the prevention and removal of threats to the peace”. With more than 100 ongoing wars and military conflicts, we are further away than ever from this ideal. This marks a significant failure of diplomacy to prevent those wars.

In a similar spirit as the UN, CERN was founded in 1954 to bring nations together through peaceful scientific collaboration. Remarkably, just one year after its foundation, cooperation between CERN and Soviet scientists began via the Joint Institute for Nuclear Research in Dubna and the Institute for High Energy Physics in Protvino. In 2014, on the occasion of CERN’s 60th anniversary, former Director-General Rolf Heuer wrote that “CERN has more than fulfilled the hopes and dreams of advancing science for peace”.

The invasion of Ukraine by the army of the Russian Federation at the end of February 2022 and the suffering inflicted on countless innocent civilians, including scientists, is against international law and must be condemned in the strongest terms. Despite pro-war statements from some Russian institutes, many Russian physicists oppose the war and immediately signed petitions against it.

Lyn Evans (LHC project leader), Luciano Maiani (CERN’s Director-General at the time), Alexander Skrinsky and Kurt Hübner atop the last batch of dipole and quadrupoles magnets delivered from Novosibirsk, destined to form the transfer lines carrying protons from the SPS into the LHC. Credit: Lauren Guiraud/CERN

In March 2022, as a reaction to the war in Ukraine, many national Western science institutions put bans on their historical scientific cooperation with Russian institutions. This move unexpectedly also concerned international organisations such as CERN, whose governing Council deliberated on the renewal of existing cooperation agreements with Russian and Belarusian institutes, and, regrettably, decided to stop them in 2024.

Limiting international scientific collaboration is against the advancement of knowledge, which is not just a global public good but a powerful instrument for intercultural dialogue and peace – especially during times of crisis. If we take the UN charter seriously, we must ask which measures are appropriate for the prevention and removal of threats to the peace. After all, as one Ukrainian colleague put it, do sanctions against Russian science institutes help to stop the war?

Limiting international scientific collaboration is against the advancement of knowledge, which is not just a global public good but a powerful instrument for intercultural dialogue and peace

After some two years of both economic and scientific sanctions, the answer would appear to be “no”. While we have continued to work together with our Russian and Belarusian colleagues at CERN, and had many discussions among us within experimental collaborations, people with whom we worked together for decades now risk becoming excluded from their experiments and from CERN and other institutes.

Hear and be heard
When I came to CERN as a student in the early 1980s, I was fascinated by the open and international spirit. It was an unforgettable experience to be able to talk openly to scientists from the Soviet Union, the German Democratic Republic, or other countries. I was excited to listen to different viewpoints and thrilled that science could offer a way to understand each other and to work towards a better world.

Unfortunately, the discussion about sanctions in science and the sanctions themselves have contributed to an atmosphere of mistrust and fear. Today, I am shocked when hearing that young students are afraid of discussing political matters with their colleagues, and that they are not accepted to summer schools because they were born and have studied in the wrong country. I am afraid that this next generation of scientists will remember how they were treated.

With the acceptance of sanctions in science — sanctions which are not endorsed by UN agencies — we allow the dominance of politics over scientific cooperation. It is fatal to impose a failed policy on the scientific community, which has long provided the language to communicate and cooperate across all borders.

The Science4Peace forum, which was created in response to restrictions on scientific cooperation implemented as a result of Russia’s invasion of Ukraine, convened a panel discussion in spring 2023 at which experts from different fields in science, ranging from IUPAP to particle physicists and climate researchers, expressed their opposition to sanctions in science. A subsequent report “Beyond a year of sanctions in science” concluded with a statement of the famous conductor Daniel Barenboim at a concert he gave with his East-West orchestra in Ramallah in 2005: “This is not going to bring peace, what it can bring is understanding, patience and courage to listen to the narratives of the other”. Perhaps, we should take this also as our motto in science, and against exclusion and sanctioning of colleagues, even in difficult times.

Igor Golutvin 1934–2023

Igor Anatolievich Golutvin, an outstanding scientist who founded new directions and research techniques in particle physics, died on 13 September 2023.

Born on 8 August 1934 in Moscow, Golutvin graduated from MIPT in 1957 and started his work at JINR in 1958. Several generations of detectors for large-scale physics facilities were developed under his supervision at the JINR Synchrophasotron, the IHEP accelerator in Serpukhov, and at the Proton Synchrotron and the LHC at CERN.

Golutvin became one of the pioneers of the CMS experiment, driving the cooperation of Russia and other JINR member states via the Russia and Dubna Member States (RDMS) CMS collaboration. Over the past 30 years, under his supervision, RDMS physicists have completed the development of unique detectors for CMS. Igor was also instrumental in initiating Grid computing for CMS in Russia. He was awarded the 2014 Cherenkov Prize of the Russian Academy of Sciences for his outstanding contribution to the development of CMS. In recent years, he played an important role in the preparation of upgrades for CMS, in particular concerning the calorimeters.

During his work at JINR, Golutvin established a scientific school and trained a team of active, qualified physicists and engineers. Within the framework of cooperation between CMS Russia and other JINR member states, he brought together like-minded people with the aim of preserving Russian scientific schools, built unique teams of engineers and physicists, and developed favourable conditions for attracting gifted young physicists, which he saw as extremely important for the implementation of long-term scientific projects.

Igor was a member of the equipment committee of the International Committee for Future Accelerators, an editorial board member of the journal Nuclear Instruments and Methods, a directorate member of the CMS collaboration at CERN, head of the collaboration of the institutes of Russia and JINR in CMS, and the organiser and head of numerous international and Russian scientific conferences and symposia.

He was also a professor/full member of the Russian Academy of Engineering Sciences, Russian Academy of Natural Sciences, International Academy of Sciences, Honoured Scientist of the Russian Federation and chief researcher for CMS at VBLHEP. For many years of fruitful work, Golutvin was awarded numerous state and scientific awards and prizes.

A year of celebrations

2024 marks CERN’s 70th anniversary, with a packed programme of events that connect CERN’s heritage with its exciting future. This will culminate in a grand celebration for the CERN community on 17 September followed by a high-level official ceremony on 1 October. Kicking off proceedings in CERN Science Gateway on 30 January is a public event exploring CERN’s science. Two events on 7 March and 18 April will showcase how innovation and technologies in high-energy physics have found applications in daily life and medicine, while the transformative potential of global collaboration is the topic of a fourth public event in mid-May. Events in June and July will focus on open questions in the field and on the future facilities needed to address them, and public events will also be organised in CERN’s member states and beyond. The full programme can be found at: cern70.web.cern.ch/.

Marcello Ciafaloni 1940–2023

Internationally known theorist Marcello Ciafaloni passed away in Florence, Italy on 8 September 2023. Born in 1940 in the small town of Teramo in southern Italy, he was admitted for his higher education to the selective Scuola Normale Superiore in Pisa where he graduated in 1965. Since 1980 he was a full professor in theoretical physics at the University of Florence.

As a research associate at Berkeley (1969–1970) and a fellow at CERN (1972–1974), Ciafaloni initially focused his research on high-energy soft hadronic physics and produced important results in the context of Reggeon field theory. Towards the end of the seventies, he shifted his attention to perturbative QCD, in particular to hard processes and small-x physics where sophisticated re-summation techniques are needed. Since then, and throughout his career, he produced many fundamental results in perturbative QCD, including his single-author contribution to the celebrated CCFM equation (where the first C stands for his name), an important ingredient for QCD-based event generators.

Since 1987, Ciafaloni added a second dimension to his research spectrum by devoting part of his activity to the gravitational scattering of strings, a thought-experiment for understanding string theory’s version of quantum gravity. This work originated from one of his periodic visits to the CERN TH division and involved, besides Marcello, Daniele Amati and myself.

The so-called ACV collaboration carried on until 2007 (with long visits by Marcello at CERN in 1995 and 2001), but my own collaboration with Marcello continued until 2018, when his health started deteriorating. More recently, the techniques used for this “academic” problem turned out to be relevant for describing real black-hole mergers and the ensuing gravitational radiation.

I had the great privilege of working with Marcello on many occasions throughout his career. His deep knowledge of physics and his passion were only matched by his amazing technical skills. He had set very demanding standards for himself and pursued them with great intellectual honesty and much generosity towards his students and collaborators. His passing is a big loss for our community.

Bite-sized travels in particle physics

Faszinierende Teilchenphysik is certainly not the first popular book about elementary particle physics, and it won’t be the last. But its unique and clever structure make it stand out.

Think of it as a collection of short stories, organised in 12 chapters covering all ground from underlying theories and technologies to the limits of the Standard Model and ideas beyond it. The book begins with a gentle introduction to the world of particles and finishes by linking the infinitely small to the infinitely large. Each double-page spread within these chapters features a different topic in particle physics, its players, rules of play, tools, concepts and mysteries. Turn a page, and you find a new topic.

Among these 150 spreads, which are referred to as “articles” by the diverse team of authors, the reader can learn about neutrinos, lattice QCD, plasma acceleration, Feynman diagrams, multi-messenger astronomy and much more. Each one manages to convey both the fascination of the subject as well as all the central ideas and open questions within the two allocated pages. This makes for a great way of reading: the article about antimatter, for example, cross-references to the article about baryogenesis, so flip from page 18 to page 304 to dig deeper into the antimatter mystery. Not sure what a baryon is? Check the glossary, then maybe jump on the article about matter and antimatter, CP violation or symmetries. There is no need to read this book from cover to cover. On the contrary, browsing is so deeply embedded in its concept that it even features a flip-book illustration of a particle collision on the bottom right-hand-side of each spread. With a bit more care for captivating illustrations and graphic design, it could pass as a Dorling Kindersley-style travel guide to particle physics.

The authors, who are based at different universities and labs in Germany, have backgrounds covering theoretical and experimental particle physics, astroparticle physics, accelerator and nuclear physics, and science communication. They have obviously put as much thought into this publication as they put in hours, because they manage to write about each topic in a way that is easy to follow, even if it’s hard to digest. Puns, comparisons to everyday life and drawings to accompany the articles make for a full browsing experience, and the references within the text and at the bottom of each page show how everything is connected deep down.

When I received Faszinierende Teilchenphysik for review, one of the authors jokingly accompanied it with the words “this book is meant for retired engineers and for aunts looking for a present for their science-student-to-be nieces.” That may well be the case, but this book’s target audience is much wider. Physics fans and amateurs will enjoy sinking their teeth into a new world of interlinked topics; undergraduates will value it as a quick reference source that is less obscure and more fun to read than Wikipedia; and physics professionals will find it a useful refresher for topics beyond their expertise. The book even dedicates its final article to those questioning whether it is worth spending money and brain power on tiny particles, ending with a passionate case for the many benefits of fundamental research – not just spin-offs such as tumour therapy or artificial intelligence, but in pushing boundaries of knowledge outward.

And if you’re afraid that your school German might let you down, don’t worry: the English edition is already in the works and due to come out in 2024.

Complexity, Entropy and the Physics of Information

“This quantum business is so incredibly important and difficult that everyone should busy himself with it,” wrote Einstein in a 1908 letter, cited by John Wheeler at the workshop “Complexity, Entropy and the Physics of Information” held at the Santa Fe Institute in 1989. More than a century after Einstein’s letter, many fundamental questions connecting physics and information remain unanswered.

The book Complexity, Entropy and the Physics of Information consists of 32 essays capturing the talks given at the Santa Fe workshop. Building on the fundamental work by Claude Shannon, the aim of the workshop was to explore fundamental questions relating to the foundations of quantum theory and quantum information science. Most of the questions raised are still relevant today, as many contributions to this two-volume reprint of proceedings demonstrate.

The workshop started with Wheeler’s famous talk “It from bit”, in which he aimed to “deduce the quantum from existence”. Those remain a guiding principle in the life of a researcher in the field. Indeed, in a talk at the QTML 2023 conference held at CERN, Max Welling (University of Amsterdam) motivated his recent work on “General Message Belief Propagation” for quantum computations using Wheeler’s principle, linking machine-learning models to thermodynamics.

William Wootters’ contribution, on the other hand, builds on the work of John Bell, who showed that quantum mechanics is inherently non-local, i.e. that correlations between spatially separated systems are stronger than what is allowed in a hidden-variable theory. In contrast, Wootter focusses on the locality of quantum mechanics – specifically stating that local measurements on parts of a system and correlations between those measurements allow the state of an ensemble to be determined. Furthermore, Benjamin Schumacher presents his thoughts on the “physics of communication” and discusses the connections between information and entropy. He promotes the idea that “it is not the number of available signals but rather their distinguishability that matters in communication.”

Wojciech Zurek focusses on the implications of a quantum measurement, which converts a collection of possible alternatives to a definite outcome and thus decreases the statistical entropy. In this regard, he discusses the connections between physical and statistical entropy (Shannon entropy) and the algorithmic information content of the data (Kolmogorov complexity). Applications in non-equilibrium systems highlight the fundamental cost of information erasure that was first mentioned by Landauer in 1961.

Charles Bennett asks “what is complexity?” and presents various suitable notions for a “formal measure of complexity” based on computational theory, information theory and thermodynamics. He thus highlights the notion of “logical depth”, which is the execution time needed to generate the object of interest by a near-incompressible universal computer program. The behaviour of complexity measures in dynamical systems exhibiting self-organisation and phase transitions are also discussed.

A noteworthy collection of essays

Tommaso Toffoli explores whether the principles of mechanics are universal and fundamental because they emerge from an extremely fine-grained underlying structure, in which case they would be of mathematical rather than physical origin. This mode of thought is in line with statistical mechanics, where laws emerge due to collective effects in systems with many elements.

In his contribution, Edwin Jaynes focuses on the meaning of probability in quantum mechanics, which he regards not as a “physically real thing” but relevant for quantifying the role of incomplete information and the precision with which a theory is able to predict results. In case of its infiniteness, the theory is unable to predict this quantity and, hence, the uncertainty is infinite. But he stresses that it does not mean that the physical quantity is infinite.

This is just snapshot of the many rich contributions. Besides quantum information theory, the book also touches on cosmology, quantum gravity and dynamical systems. An introduction from Seth Lloyd, who attended the Santa Fe workshop, also provides valuable context to the significance of the proceedings.

Complexity, Entropy and the Physics of Information forms a noteworthy collection of essays linking information, computation and complexity, as well as physics and especially quantum mechanics. As it contains many individual essays grouped thematically, readers may pick out topics based on their own interest. I would recommend this work for anyone who is interested in this area, especially researchers and students working in quantum physics and computational theory.

Topics

Reset your password

Registration complete

Major players