Jobs – Page 79 of 521

Gennady Zinovjev 1941–2021

Gennady Zinovjev, a prominent theorist in the field of quantum chromodynamics (QCD) and the physics of strongly-interacting matter, a pioneer in experimental studies of relativistic heavy-ion collisions and a leader of the Ukraine–CERN collaboration, passed away on 19 October 2021 at the age of 80. In a career spanning more than 50 years, Genna, as he was known to most of his friends, made important theoretical contributions to many different topics, ranging from analytical and perturbative QCD to phenomenology, and from hard probes and photons to hadrons and particle chemistry. His scientific activities were concentrated around experimental facilities at CERN and the Joint Institute for Nuclear Research (JINR), Dubna. He was one of the key initiators of the NICA complex at JINR, played a pivotal role in Ukraine becoming an Associate Member State of CERN in 2016 and was one of the founding members of the ALICE collaboration.

Born in 1941 in Birobidzhan (Russian Far East), in 1963, Zinovjev graduated from Dnepropetrovsk State University, a branch of Moscow State University. From 1964 to 1967 he studied at the graduate school of the Laboratory of Theoretical Physics of JINR, after which he spent a year at the Institute of Mathematics and Computer Science of the Academy of Sciences of the Moldavian SSR (Kishinev now Chisinau). He was awarded a PhD in physics and mathematics in 1975 at the Dubna Laboratory of Theoretical Physics and then joined the Kiev Institute for Theoretical Physics (both now the Bogolyubov Institute for Theoretical Physics) of the National Academy of Sciences of Ukraine, firstly as a staff member and then, from 1986, as head of the department of high-energy-density physics. In 2006 he was awarded the Certificate of Honour of the Verkhovna Rada (Parliament) of Ukraine, and in 2008 was awarded the Davydov Prize of the National Academy of Sciences of Ukraine becoming a member of the Academy in 2012.

In the mid-1990s Zinovjev initiated Ukraine’s participation in ALICE, and soon started to play a key role in the conception and construction of the Inner Tracking System (ITS), and more generally in the creation of both the ALICE experiment and the collaboration. Overcoming innumerable practical and bureaucratic obstacles, he identified technical and technological expertise within the Ukrainian academic and research environment, and then managed and led the development and fabrication of novel ultra-lightweight electrical substrates for vertex and tracking detectors. These developments, which took place at the Kharkiv Scientific Research Technological Institute of Instrument Engineering, resulted in technologies and components that formed the backbone of the ITS 1 and ITS 2 detectors. He was the deputy chair of the ALICE collaboration board from 2011 to 2013 and also served as a member of the ALICE management board during that time.

Genna was one of those rare people who are equally comfortable with theory, experiment, science, politics and human interactions. He was a passionate scientist, deeply committed to the Ukrainian scientific community. He did not hesitate to make great personal sacrifices to pursue what he considered important for science, his students and colleagues. Equally influential was his prominent role as a teacher and mentor for a steady stream of talent, both experimentalists and theorists. Many of us in the heavy-ion physics community owe him a great deal. We will always remember him for his charismatic personality, great kindness, openness and generosity.

Overview of the ITER project, and our variable experiences in the development of some critical components of the magnets

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ITER has now reached the stage where about half of the large magnet components have arrived on site and many more are nearing completion at manufacturing locations distributed throughout the ITER partners. Although we still have several years of challenging on-site assembly ahead, the acceptance tests and first-of-a-kind assembly are teaching us a lot about the magnet quality and possible improvements for future tokamaks.

The webinar, presented by Neil Mitchell, will summarise the present status of manufacturing and assembly. Neil will then chose three areas, critical to magnet and tokamak performance, to describe in more detail:

1. Development of Nb₃Sn strands for fusion applications started in the 1980s and the selection of the material for the Toroidal and Central Solenoid Coils in the first phase of ITER 1988–1991 was a key driver of the overall tokamak parameters. The development, qualification and procurement, both before and after the decision to use it, gives us an unusual opportunity to look at the implementation of a novel technology in its entirety, with the expected and unexpected problems we encountered and how they were solved – or tolerated.

2. High-voltage insulation in superconducting magnets is a frequently overlooked area that demands many new technologies. It is the area in the ITER magnets that has created the most quality issues on magnet acceptance and is clearly an area where more engineering attention is required.

3. The need for improvements in overall integration of the magnets into the tokamak, and in particular maintainability and repairability, is being demonstrated as we assemble components into the cryostat. The assembly is proceeding well in terms of quality but at the same time, the complexity shows that for a nuclear power plant, we need improvements.

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After completing his PhD at Cambridge University on the fluid mechanics of turbomachinery, Neil Mitchell entered the nuclear fusion world in 1981 during the completion of the JET tokamak, and participated extensively in the early superconducting strand and conductor development programme of the EU in the 1980s, as well as in the design/manufacturing of several small copper-magnet-based magnetic fusion devices, including COMPASS at UKAEA. He was involved in the prototype manufacturing and testing of the superconductors that eventually became the main building blocks of the ITER magnets, and participated in the development and first tests of facilities such as Fenix at LLNL and Sultan at PSI. He has filled several positions within the ITER project after joining as one of the founder members in 1988, in particular, as the section leader for the ITER conductor in the 1990s with the highly successful construction and test of the CSMC in Japan and TFMC in Europe, and then after as division head responsible for the magnet procurement. He was responsible for finalising the magnet design, negotiating the magnet in-kind procurement agreements with the ITER Home Institutes and direct contracts, following and assisting the industrial production qualification and ramp up in multiple suppliers in EU, Japan, Korea, China, US and Russia. The ITER conductor production was completed in 2016 and now with the completion of the first-of-kind magnets, the delivery to the site of several coils and the placement of the first PF coil in the cryostat, he is working as an advisor to the ITER director. He is deeply involved in problem solving in the interfaces to the ITER on-site construction as the ITER magnets are delivered, contributing to the magnet control and commissioning plans, and advising the EU on the design of a next-generation fusion reactor.

Ideas not equations

When it was first published in 1984, James E Dodd’s The Ideas of Particle Physics used very little maths, but was full of clear and concise explanations – a strong contrast with the few other reference books that were available at the time. The first edition was written prior to the start of LEP, just after the discovery of the W and Z bosons. The fourth edition, published in 2021, brings it up to date while keeping its signature style.

At the time of my PhD, 30 years ago, Dodd’s book was revolutionary and helped me enormously. Over the years I have recommended it to countless students, to complement lectures and internet resources. But I had not looked at the updated versions until now. In keeping with the original, the new edition states explicitly that it is not a textbook: it contains no mathematical derivations, and no complicated formulae are written down. This is not at all to say that it is an easy read – it is not! But Dodd and Ben Gripaios, who joins the original author for this expanded fourth edition, convey the beauty of fundamental physics, and some of the phrases border on poetic: “Viewed picturesquely, it is as if the world of physical reality conducts itself while hovering over an unseen sea of negative-energy electrons.”

Some of the phrases border on poetic

The second half of the updated book follows on from where the first edition left off. Precision measurements at LEP and the discovery of the gauge bosons and the top quark are all described with the same excitement and eye for beauty as the earlier discoveries. However, the LHC receives fewer words than the World Wide Web, with its almost five-decades-long journey reduced to a couple of milestones. The hunt for the Higgs boson is also glossed over and fails to capture the excitement of the past couple of decades. More problematically, the description of the role the Higgs boson plays in spontaneous symmetry breaking is muddled.

The latter chapters redeem the text by detailing many of the theories that have arisen over the past 30 to 40 years, and how they may address the many remaining questions in fundamental physics. Indeed, while the first edition perhaps gave the impression that there was not much more to learn about the universe, the fourth edition shows how little we understand, and gives good pointers to where we may find answers.

As a tome on the evolutionary nature of particle physics, with concepts rather than mathematics at the forefront, The Ideas of Particle Physics remains an excellent book, predominantly aimed at graduate students, as a complement to courses and other reference works.

Beyond bumps

CCJanFeb22_FN_CLEAN — **Stunning agreement** Fits to beyond-the-Standard-Model couplings by four of the major fitting groups. Effective-field-theory coefficients C₉^μ and C₁₀^μ can affect both lepton-flavour universality and the golden decays B_s,d→μ⁺μ^–. Credit: B. Capdevila, M. Fedele, S. Neshatpour, and P. Stangl

The inaugural CERN Flavour Anomalies Workshop took place on 20 October as part of this year’s Implications of LHCb Measurements and Future Prospects meeting. More than 500 experimentalists and theorists met in a hybrid format via Zoom and in person. Discussion centered on the longstanding tensions in B-physics measurements, and new project ideas. The workshop was dedicated to the memory of long-time LHCb collaborator Sheldon Stone (Syracuse), who made a plentiful contribution to CERN’s flavour programme.

The central topic of the workshop was the b anomalies: a persistent set of tensions between predictions and measurements in a number of semileptonic b-decays which are not as clear as unexpected peaks in invariant mass distributions. Instead, they manifest themselves as modifications to the branching fractions and angular distributions of certain flavour-changing neutral-current (FCNC) b-decays which have become more significant over the past decade. The latest LHCb measurement of the ratio (R_K) of B⁺ decays to a kaon and a muon or electron pair differs from the Standard Model (SM) by more than 3σ, and the ratio (R_K*) of B⁰ decays to an excited kaon and a muon or electron pair differs by more than 2σ. LHCb has also seen several departures from theory in measurements of angular distributions at the level of roughly 3σ significance. Finally, and coherent with these FCNC effects, BaBar, Belle and LHCb analyses of charged-current b→cτ^–ν̄ decays support lepton-flavour-universality (LFU) violation at a combined significance of roughly 3σ. Though no single measurement is statistically significant, the collective pattern is intriguing.

Four of the major fitting groups showed a stunning agreement in fits to effective-field-theory parameters

But how robust are the SM predictions for these observables? Efforts include both theory-only and data-driven approaches for distinguishing genuine signs of beyond-the-SM (BSM) effects from hard-to-understand hadronic effects. A further aim is to understand what type of BSM models could produce the observed effects. Of particular interest was the question of how to incorporate information from high-pT searches at the LHC experiments. ATLAS and CMS are ramping up their efforts, and their ongoing B-physics programmes will hopefully soon confirm and complement LHCb’s results. Both experiments reported on work to address the main bottlenecks: the reconstruction of low-momentum leptons, and trigger challenges foreseen as a result of increased luminosities in Run 3. The complementarity of B-physics and direct searches was clear from results such as ATLAS and CMS searches for leptoquarks compatible with the flavour anomalies.

Theory consensus

The workshop saw, for the first time, a joint theory presentation by four of the major b→sℓ⁺ℓ^– fitting groups. They showed a stunning agreement in fits to effective-field-theory parameters which register as nonzero in the presence of BSM physics (see figure). The fits use observables that either probe LFU or help to constrain troublesome hadronic uncertainties. The observables include the now famous R_K, R_K* and R_pK (which studies Λ_b⁰ baryon decays to a proton, a charged kaon and a pair of muons or electrons), whose measurements are dominated by LHCb results; and results on the branching fraction for B_s→μ⁺μ^– from ATLAS, CMS and LHCb. Though the level of agreement diminishes when other observables and measurements are included, dominantly due to the different theoretical assumptions made by the four groups, all agree that substantial tensions with the SM are unavoidable.

New results from LHCb included first measurements of the LFU-sensitive ratios R_K*+ (which concerns B⁺→K*⁺ℓ⁺ℓ^– decays) and R_Ks (which concerns B⁰→K_S⁰ℓ⁺ℓ^– decays), and new measurements of branching fractions and angular observables for the decay B_s→ϕμ⁺μ^–, which is at present hampered by significant theory uncertainties. By contrast, many theoretical predictions for b→cτ^–ν̄ processes are now more precise than measurements, with the promise of further improvements thanks to dedicated lattice-QCD studies. Larger and more diverse datasets will be needed to reduce the experimental uncertainties.

As the end of the year approaches, it may not be too early to collect wishes for 2022. The most prevalent wishes involve new analysis results from ATLAS, CMS and LHCb on these burning topics, and a 2022 workshop to happen in person!

First observation of WWW production

**Fig. 1.** Example Feynman diagrams for the leading-order production of WWW events. Credit: CERN

The W boson was first directly observed in 1983 using the Super Proton Synchrotron proton–antiproton collider at CERN, resulting in a Nobel Prize the following year. Almost four decades later, the ATLAS collaboration has observed the simultaneous production of three W bosons for the first time.

The possible new interactions are represented by operator terms with anomalous triple and quartic gauge couplings

The study of multi-boson processes involving boson self-interactions provides unique insight into the nature of electroweak symmetry breaking and therefore enables rigorous tests of the Standard Model (SM). Likewise, deviations from SM predictions could indicate hints of beyond-Standard Model physics through, for example, interactions that exist at energies beyond the current reach of the LHC which avoid the requirement to create the particle directly. These effects could potentially result from interactions with virtual particles in loops or new amplitudes generated by a tree-level exchange. In an effective field theory (EFT) approach, the possible new interactions are represented by operator terms with anomalous triple and quartic gauge couplings, both of which are present in WWW production.

Signal events

At leading order, the WWW signal is produced through the different mechanisms presented in the Feynman diagrams shown in figure 1. While there are many decay modes, ATLAS used four final-state channels where the signal-to-background ratio is big enough to observe the signal. The first three channels result from the decay of two of the Ws into charged lepton–neutrino pairs, with the same electric- charge sign of the charged leptons, and the decay of the third W into a pair of quarks observed as hadronic jets: the two-lepton (2l) channel, with flavour combinations ee, eμ and μμ. Additionally, WWW production is measured in the three-lepton (3l) channel, where each W decays into a charged lepton–neutrino pair, requiring no same-flavour opposite-sign charged-lepton pairs, and thus reducing the Z-boson background.

**Fig. 2.** The BDT distribution of the WWW three-lepton channel. Credit: CERN

A multivariate analysis using a boosted decision tree (BDT) was used to discriminate the signal from the background, with the BDT trained using 12 discriminating input variables in the 2l channel and 11 input variables in the 3l channel. A binned maximum likelihood fit was performed on the BDT distributions with four free-floating parameters: the signal strength and three normalisation factors for the dominant WZ background. The BDT distributions were fitted in the four signal regions simultaneously with the trilepton invariant mass distribution in three WZ control regions (WZ plus 0, 1, ≥ 2 jets). The resulting BDT distribution for the 3l channel is shown in figure 2.

The large event samples (139 fb^–1) provided by the full Run-2 data set, the implementation of multivariate techniques, and an improved ATLAS detector and reconstruction performance enabled the observation and the cross-section measurement of this rare process. The observed (expected) significance of the measurement is 8.2 (5.4) standard deviations compared to the hypothesis with no WWW signal. The cross section is measured to be 850 ± 100 (stat.) ± 80 (syst.) fb, as derived from the observed signal strength (the ratio of measured to predicted yields) of 1.66 ± 0.28. The observed signal significance is within 2.4σ of the SM prediction. The full Run-3 data set is anticipated to more than double the number of signal events and will enable a more precise measurement of WWW production. Higher precision cross-section measurements and detailed differential distributions will elucidate the compatibility with the SM, and an EFT approach can quantify the sensitivity to anomalous gauge couplings in a search for new physics.

Quark–gluon plasma narrows jets

**Fig. 1.** Hadrons from a jet (ovals) are reclustered into a tree structure, and the low-energy, wide-angle particles are removed in order to identify the first “hard” splitting, shown in dark purple. Credit: CERN

A new measurement by the ALICE collaboration has demonstrated for the first time that jets become narrower after “quenching” in quark–gluon plasma (QGP). RHIC and LHC data show that the QGP behaves like a strongly-coupled liquid with very low viscosity, but it is an open question how this arises from the asymptotic limit of weakly-coupled quarks and gluons at short lengths. The new results provide quantitative new insights into the hot and dense medium created in heavy-ion collisions and how it modifies the substructure of jets and dissipates part of their energy.

An important property of the QGP is its ability to “resolve” nearby partons as effectively independent colour charges above the medium’s characteristic resolution scale – a parameter that is very poorly predicted by theory, but thought to be in the vicinity of a femtometre or less. In recent years, jet quenching has been proposed to determine this scale. Jets originate from a single quark or gluon that showers into more partons, either by radiating a gluon or splitting into a quark–antiquark pair. When a jet moves through the medium, each individual splitting results in two distinct colour charges that, depending on their angular separation and the medium’s resolution length, can interact as one coherent object or two independent charges. At the LHC, we can put our understanding of this resolution scale to test using special measurements of the angular structure of jets. This allows us to test whether wider jets are more likely to be resolved.

ALICE “groomed” jets using track clustering

The angle between the two prongs of the “hard” splitting — **Fig. 2.** The distribution of the angle between the two prongs of the “hard” splitting measured by ALICE, in both proton–proton and Pb–Pb collisions. The lower panel shows the Pb–Pb/p–p ratio in comparison with theoretical models. Credit: CERN

To identify the relevant two-prong splittings, ALICE “groomed” jets using track clustering. The algorithm reclusters and unwinds the jet shower to find the first parton splitting satisfying a grooming condition (figure 1). The excellent tracking resolution in ALICE allows for very precise measurements of jet substructure even at small angular distance scales. The angular width of the jet was found to be significantly modified in Pb–Pb compared to pp collisions (figure 2). In particular, wider splittings are suppressed in Pb–Pb compared to pp collisions, demonstrating that the interaction of jets with the QGP filters out wide jets.

This measurement is the first of its kind to be fully corrected for large background effects, allowing direct quantitative comparisons with theoretical calculations of jet quenching. Most theoretical models describe the general narrowing trend seen in the data, despite the different implementations of jet-medium interactions. The data is consistent with models implementing an incoherent interaction in which the medium resolves the splittings (Pablos, L_res = 0). Interestingly, however, another calculation demonstrates this narrowing effect with a fully coherent interaction, in which the jet splittings are not resolved, but by modifying the initial quark and gluon fractions (Yuan, quark). While the precision of the data currently precludes a precise extraction of the medium’s resolving power within a given model, the measurement places quantitative constraints on medium properties, and demonstrates for the first time a direct modification to the angular structure of jets in heavy-ion collisions. This opens the door to increasingly precise measurements with the high-precision data anticipated in LHC Run 3.

LHCb studies the intrinsic charm of the proton

**Fig. 1.** gc → Zc scattering is sensitive to valence-like intrinsic charm. Credit: CERN

The possibility that the proton wave function may contain a |uudcc> component in addition to the g → cc splitting arising from perturbative gluon radiation has been debated for decades. In favour of such “intrinsic charm” (IC), light-front QCD (LFQCD) calculations predict that non-perturbative IC manifests as percent-level valence-like charm content in the parton distribution functions (PDFs) of the proton. On the other hand, if the charm–quark content is entirely perturbative in nature, the charm PDF should resemble that of the gluon and decrease sharply at large momentum fractions, x. The proton could also contain intrinsic beauty, but suppressed by a factor of order m²_c/m²_b. The picture for intrinsic strangeness is somewhat murkier due to the lighter mass of the strange quark.

Measurements of charm-hadron production in deep-inelastic scattering and in fixed-target experiments, with typical momentum transfers below Q = 10 GeV, have been interpreted as evidence both for and against the IC predicted by LFQCD. Even though such experiments are in principle sensitive to valence-like c-quark content, interpreting low-Q data is challenging since it requires a careful theoretical treatment of hadronic and nuclear effects. Recent global PDF analyses, which also include measurements by ATLAS, CMS and LHCb, are inconclusive and can only exclude a relatively large IC component carrying more than a few percent of the momentum of the proton.

Using its Run-2 data, LHCb recently studied IC by making the first measurement of the fraction of Z+jet events that contain a charm jet in the forward region of proton–proton collisions. Since Zc production is inherently at large Q, above the electroweak scale, hadronic effects are small. A leading-order Zc production mechanism is gc → Zc scattering (figure 1), where in the forward region one of the initial partons must have large x, hence Zc production probes the valence-like region.

**Fig. 2.** The measured production cross-section ratio (grey bands) for three intervals of forward Z rapidity, compared to theory predictions without IC (purple circles), with the charm PDF shape allowed to vary, hence permitting IC (orange squares), and with IC as predicted by LFQCD with a mean momentum fraction of 1% (red triangles). The predictions are offset in each interval to improve visibility. Credit: CERN

The spectrum observed by LHCb exhibits a sizable enhancement at forward Z rapidities (figure 2), consistent with the effect expected if the proton wave function contains the |uudcc> component predicted by LFQCD. Incorporating these results into global PDF analyses should strongly constrain the large-x charm PDF, both in size and shape – and could reveal that the proton contains valence-like intrinsic charm.

These results demonstrate the unique sensitivity of the LHCb experiment to the valence-like content of the proton. Looking forward to Run 3, increased luminosity will lead to a substantial improvement in the precision of this measurement, which should provide an even clearer picture of just how charming the proton is.

Muon detector probes long-lived particles

New ways to detect long-lived particles (LLPs) are opening up avenues for searching for physics beyond the Standard Model (SM). LLPs could provide evidence for a hidden dark sector of particles that includes dark-matter candidates and could be studied via “portal interactions” with the visible universe. By employing the CMS experiment’s muon spectrometer in a novel way, the collaboration has recently deployed a powerful new technique for detecting LLPs that decay between 6 and 10 metres from the primary interaction point.

An LLP decaying in the endcap muon spectrometer volume should produce a particle shower when its decay products interact with the return yoke of the CMS solenoid. The secondary particles produced by the shower would traverse the gaseous regions of the cathode-strip chamber (CSC) detector and produce a large multiplicity of signals on the wire anodes and strip cathodes. Localised hits are reconstructed by combining these signals using a density-based clustering algorithm. This is the first time the CSC detectors have been used as a sampling calorimeter to try to detect and identify LLP decays.

**Fig. 1.** Distributions of the number of hits in the cluster (N_hits) in the search region. Signal models where the Higgs boson plays the role of the dark-portal messenger are shown (dashed lines). The Higgs boson is assumed to decay to dark-sector scalar particles with masses of 7 (red), 15 (orange), 40 (cyan) or 55 GeV (purple), while the dark scalar decays with a macroscopic displacement to quarks. Credit: CERN

Searching for CSC clusters with a sufficiently large number of hits suppresses background processes while maintaining a high efficiency for detecting potential LLP decays. The large amount of steel in the CMS return yoke nearly eliminates “punch-through” hadrons that are not fully stopped by the calorimeter, potentially mimicking the signature of an LLP. The largest remaining source of backgrounds is known LLPs produced by SM processes such as the neutral kaon, K_L. These particles are copiously produced in LHC collisions and, on rare occasions, traverse the material without being stopped. Kaons are predominantly produced with much lower energies than the signal LLPs and therefore result in clusters with a smaller number of hits. Requiring clusters with more than 130 CSC hits suppresses these dominant background events to a negligible level (see figure 1).

This search improves on the previous best results by more than a factor of six

Using the full Run-2 dataset, the CMS collaboration detected no excess of particle-shower events above the expected backgrounds, setting constraints on a benchmark-simplified model of scalar LLP production mediated by the Higgs boson (a so-called Higgs portal model). This search improves on the previous best results by more than a factor of six (two) for an LLP mass of 7 GeV (≥ 15) GeV for a proper decay length (cτ) of the scalar larger than 100 m. It is the first to be sensitive to LLP decays with cτ up to 1000 m and masses between 40 and 55 GeV at branching ratios of the Higgs to a pair of LLPs below 20%.

This novel approach to identifying showers in muon detectors opens up an exciting new programme of searches for LLPs in a wide variety of theoretical models. Potential frameworks range from Higgs-portal models to other portals to a dark sector, including neutrinos, axions and dark photons. The on-going development of a dedicated Level-1 and High-Level Trigger focusing on particle showers detected in the CMS muon spectrometer promises an order of magnitude improvement in the discovery sensitivity for LLPs in the forthcoming run of the LHC.

CERN unveils roadmap for quantum technology

Launched one year ago, the CERN Quantum Technology Initiative (QTI) will see high-energy physicists and others play their part in a global effort to bring about the next “quantum revolution”, whereby phenomena such as superposition and entanglement are exploited to build novel computing, communication, sensing and simulation devices (CERN Courier September/October 2020 p47).

On 14 October, the CERN QTI coordination team announced a strategy and roadmap to establish joint research, educational and training activities, set up a supporting resource infrastructure, and provide dedicated mechanisms for exchange of knowledge and technology. Oversight for the CERN QTI will be provided by a newly established advisory board composed of international experts nominated by CERN’s 23 Member States.

As an international, open and neutral platform, describes the roadmap document, CERN is uniquely positioned to act as an “honest broker” to facilitate cross-disciplinary discussions between CERN Member States and to foster innovative ideas in high-energy physics and beyond. This is underpinned by several R&D projects that are already under way at CERN across four main areas: quantum computing and algorithms; quantum theory and simulation; quantum sensing, metrology and materials; and quantum communication and networks. These projects target applications such as quantum-graph neural networks for track reconstruction, quantum support vector machines for particle classification, and quantum generative adversarial networks for physics simulation, as well as new sensors and materials for future detectors, and quantum-key-distribution protocols for distributed data analysis.

Education and training are also at the core of the CERN QTI. Building on the success of its first online course on quantum computing, the initiative plans to extend its academia–industry training programme to build competencies across different R&D and engineering activities for the new generation of scientists, from high-school students to senior researchers.

Co-chairs of the CERN QTI advisory board, Kerstin Borras and Yasser Omar, stated: “The road map builds on high-quality research projects already ongoing at CERN, with top-level collaborations, to advance a vision and concrete steps to explore the potential of quantum information science and technologies for high-energy physics”.

2021 Nobel Prize recognises complexity

Parisi, Hasselmann and Manabe — **Climate pioneers** Nobel winners (from left) Giorgio Parisi, Klaus Hasselmann and Syukuro Manabe. Credits: B Sabatini; J Knop/MPG; N Manabe

On 5 October, Syukuro Manabe (Princeton), Klaus Hasselmann (MPI for Meteorology) and Giorgio Parisi (Sapienza University of Rome) were announced as the winners of the 2021 Nobel Prize in Physics for their groundbreaking contributions to the understanding of complex physical systems, which provided rigorous scientific foundations to our understanding of Earth’s climate. Sharing half the 10 million Swedish kronor award, Manabe and Hasselmann were recognised “for the physical modelling of Earth’s climate, quantifying variability and reliably predicting global warming”. Parisi, who started out in high-energy physics, received the other half of the award “for the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales”.

In the early 1960s, Manabe developed a radiative-convective model of the atmosphere and explored the role of greenhouse gases in maintaining and changing the atmosphere’s thermal structure. It was the beginning of a decades-long research programme on global warming that he undertook in collaboration with the Geophysical Fluid Dynamics Laboratory, NOAA. Hasselmann, who was founding director of the Max Planck Institute for Meteorology in Hamburg from 1975 to 1999, developed techniques that helped establish the link between anthropogenic CO₂ emissions and rising global temperatures. He published a series of papers in the 1960s on non-linear interactions in ocean waves, in which he adapted Feynman-diagram formalism to classical random-wave fields.

Parisi, a founder of the study of complex systems, enabled the understanding and description of many different and apparently entirely random materials and phenomena in physics, biology and beyond, including the flocking of birds. Early in his career, he also made fundamental contributions to particle physics, the most well-known being the derivation, together with the late Guido Altarelli and others, of the “DGLAP” QCD evolution equations for parton densities. “My mentor Nicola Cabibbo was usually saying that we should work on a problem only if working on the problem is fun,” said Parisi following the announcement. “So I tried to work on something that was interesting and which I believed that had some capacity to add something.”

As per last year, the traditional December award ceremony will take place online due to COVID-19 restrictions.

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