Praxis Archives – Page 19 of 179

A game changer for CERN

**Dreaming big** Science Gateway project leader Patrick Geeraert. Credit: M Chalmers

How did the idea for Science Gateway come about?

I was on detachment at the European Southern Observatory (ESO) in Garching when I was called back to CERN in 2017. The idea for a flagship education and outreach project was already quite advanced, and since I had triggered the construction of ESO’s Supernova planetarium and visitor centre during my mandate as director of administration, the CERN Director-General (DG) thought I could build on this for CERN. There had been various projects for buildings based around the Globe in the past, but they never quite took off. However, the then-new directorate wanted to create a new space for education and outreach targeting the general public of all ages. The DG also made it clear that a large auditorium for CERN events should be part of any plan, and that the entire construction should be financed by donations. I started to work on the concept.

The Italian architect Renzo Piano had visited CERN independently and fell in love with our values. When he left, he said: “If one day I can do something for you, don’t hesitate.” A few months later he proposed to draw the building. In June 2018 he showed us his first mockup, the “space station” design you see today. It crossed the Route de Meyrin and encroached on land designated for agricultural use on the north side and the CERN kindergarten on the south side. The design complicated matters, but on the other hand it was really inspiring. My first thought was that the budget I had will not be sufficient because what is expensive when you do construction are the facades, and here we had five buildings, complicated ones, with some parts suspended. But it was so original, so much in the DNA of CERN, that we thought, okay, let it be five.

What will be in the buildings?

There are three “pavilions” and two “tubes”. On the north side of the Science Gateway, we have a 900-seat auditorium where we can host large CERN meetings such as collaboration weeks, as well as hiring the venue out. It’s modular so we can split it in up to three different rooms and host independent events if needed. This element of the building caused most of the headaches. The second pavilion will house the reception, shop and restaurant. On the upper floor we have the two large lab spaces, where we will have two school groups at a time. Between the restaurant and the auditorium we have a natural amphitheatre where we can also hold events.

Then we enter the two tubes straddling the Route de Meyrin, which are exhibition areas. The first is about CERN – engaging visitors with accelerators, detectors, data acquisition and IT, etc. In the second tube, one half is a journey back to the Big Bang and the other is about open questions such as dark matter, dark energy, extra dimensions and such topics, where we will have art pieces to engage visitors. The third pavilion is an exhibition about the quantum world. The bridge linking the buildings is 220 m long and you can walk from one side to the other unimpeded.

How was the construction managed, and when will the building be open to the public?

The first problem was that the north side of the Science Gateway, previously a temporary car park, was on agricultural land. We had to reclassify that piece of land for it to be authorised to build on, which is extremely complicated in Geneva. The process usually takes at least 10 years if it is successful at all, and we got it done in one. We had a very constructive process with our host authorities, whom I would like to thank warmly for their support, and the Renzo Piano team had made a case with drawings and models to help communicate our vision. We got the building permit in September 2019 and launched a procurement process for the construction and for the scenographers regarding the exhibitions. In November 2020 we signed the contract with the construction companies and they started to erect the site barracks at the end of 2020. The construction is due to be completed this summer. It was an extremely aggressive schedule, made more difficult by the pandemic and factors relating to Russia’s invasion of Ukraine. The inauguration will very likely be in the first week of October, with first visitors in the next day. I would like to thank the competent and dedicated work of all CERN’s departments and services that have contributed to the success of this project.

Who is the Science Gateway for?

The main objective is to inspire the next generation to engage in STEM (science, technology, engineering, mathematics) studies and careers. To do that, first you need to have a programme for different age ranges. Whereas traditionally we target 16 years and above, Science Gateway will start with workshops for visitors as young as five. The exhibitions are suited to all ages above eight. Ideally, we want to engage visitors before they reach high school because that’s typically when girls start to think that STEM subjects are not for them. Another important audience is parents, so Science Gateway is also geared towards families and to show adults what it means to be a scientist along with showing diverse role models. The exhibits and installations are developed by a mix of in-house and outside expertise. For the labs, we rely on our education team, which has the experience of S’Cool LAB, but now that we have extended the age range of our audiences, we will also work closely with, for instance, the LEGO foundation, one of our donors, who are very strong in education programmes for children aged 5 to 12. Finally, Science Gateway is an opportunity for us to engage with VIPs and decision makers, to bring support to fundamental research and explain its impact on society.

How many visitors do you expect?

A lot! Currently we have more than 300,000 demands for guided tours per year and we can only satisfy about half of them. From those 300,000, more than 70% are based more than 800 km away. The Science Gateway will allow us to welcome up to 500,000 people per year, which is more than 1000 per day on average. We will continue to attract schools and visitors from all CERN member states and beyond, that’s for sure, and increase capacity for hands-on lab activities in particular. We also expect many more local visitors. Entry will be free, and we will be open to visitors all year, every day except Mondays. The Science Gateway will only be closed on 24, 25 and 31 December, and 1 January. For groups of 12 or more, people have to book in advance. But individuals and families can just show up on the day and access the auditorium, exhibition tubes, restaurant and the quantum-world pavilion. On the campus, they will also find temporary exhibitions in the Globe, and Ideasquare will also propose activities. Visitors can book a guided tour in the morning for that same day. Guided tours will remain at the same level as today, and we are trying to reduce pressure on existing restaurants on the Meyrin site with the new Science Gateway restaurant.

How is the Science Gateway funded?

The construction, landscaping, exhibitions and everything you will see in the building on day one are all funded from donations, with the main ones comings from Stellantis Foundation and a private foundation in Geneva. CERN is very grateful to all donors for their generosity. It’s about CHF 90 million in total, with some donors sponsoring particular exhibits or spaces. For the operations, the cost is estimated at around CHF 4 million per year. This will be funded from a mix of income from the infrastructure (for example, the shop, restaurant, parking and auditorium) and some limited CERN budget. The operational costs are for staffing in addition to maintenance of the equipment, cleaning and maintaining the forest that surrounds the building.

What is the operational model?

A Science Gateway operations group has been created from the former visits service. With the exception of a small increase in industrial services contracts and two fellows, there are basically no recruitments. We will heavily rely on volunteers, from members of the personnel to users and other people linked with CERN. We already have a pool of guides who provide on average 16,000 hours per year on guided tours and we need to double that amount to ensure the Science Gateway operates as required. We will encourage more people to become guides and start training in July. We want to emphasise that, in addition to the rewards of engaging visitors with CERN’s science, this experience will be useful to their professional lives. We are also considering giving certificates and possibly accreditations. Ideally we should have about 650 guides each giving 48 hours per year.

What is the environmental philosophy behind Science Gateway?

We want to pass on the message that we’re sustainable. We’ll be carbon neutral when we are in the operations phase, and solar panels on the roof of the three pavilions will produce much more energy than we need, with 40% going back into the CERN grid. The use of geothermal probes was explored but had to be abandoned due to local geology. Heating and cooling will be provided by heat exchangers powered by our solar panels. In the restaurant we will avoid single-use plastics, and lights will be dimmed in the evening and switched off at night. There will also be a charge for parking to encourage visitors to come by public transport. We wanted to show the link between science and nature, and that’s why we have the forest, with 400 trees and 13,000 shrubs.

How does it feel to see the project coming to completion?

When we started discussions six or so years ago, I thought I had less than a 10% chance of success because the project was so ambitious and had to be completely funded by donations. . However, it was strongly supported by the directorate, which was also very active in raising funds. The fact that it was to be built on agricultural land was another factor. There were more reasons for it to fail than to succeed. But the challenge was worth it. The phase during which we were doing the design of the construction with the architects was really interesting. I think we had 50 different versions, trying to define a design that would fit both the architects’ vision and our programme. With the construction, things start to become less fun. But we are almost there now and the Science Gateway will be a game changer for CERN, so I’m pretty proud of it. I had planned to retire at the end of the construction, but now I’ve decided to stay a bit longer and see the first steps of CERN’s new big baby.

Event celebrates 50 years of Kobayashi–Maskawa theory

Quarks change their flavour through the weak interaction, and the strength of the flavour mixing is parametrised by the Cabibbo–Kobayashi–Maskawa (CKM) matrix, which is an essential part of the Standard Model. This year marks the 60th anniversary of Nicola Cabibbo’s paper describing the mixing between down and strange quarks. It also marks the 50th anniversary of the paper by Makoto Kobayashi and Toshihide Maskawa, published in February 1973, which explained the origin of CP violation by generalising the quark mixing to three generations. To celebrate the magnificent accomplishments of quark-flavour physics during the past 50 years and to discuss the future of this important topic, a symposium was held at KEK in Tsukuba, Japan on 11 February, attracting about 150 participants from around the globe, including Makoto Kobayashi himself.

Opening the event, Masanori Yamauchi, director-general of KEK, summarised the early history of Kobayashi-Maskawa (KM) theory and the ideas to test it as a theory of CP violation. He recalled his time as a member of the Belle collaboration at the KEKB accelerator, including the memorable competition with the BaBar experiment at SLAC during the late 1990s and early 2000s, which finally led to the conclusion that KM theory explains the observed CP violation. Kobayashi and Maskawa shared one half of the 2008 Nobel Prize in Physics “for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature”.

The scientific sessions were initiated by Amarjit Soni (BNL), who summarised various ideas to measure CP violation from cascade decays of B mesons including the celebrated papers by A I Sanda and co-workers in 1980–1981, which gave a strong motivation to build B factories. Stephen Olsen (Chung Ang University), who was one of the leaders of the Belle collaboration, looked back at the situation in the early 1980s when B-meson mixing was first observed, and emphasised the role of the accelerator physicists who achieved the 100-fold increase in luminosity that was necessary to measure CP angles. Adrian Bevan (Queen Mary University of London) added a perspective from the BaBar experiment, while the more recent impressive development by the LHCb experiment was summarised by Patrick Koppenburg (Nikhef).

Theoretical developments remain an integral part of quark-flavour physics. Matthias Neubert (University of Mainz) gave an overview of the theoretical tools developed to understand B-meson decays, which include heavy-quark symmetry, heavy-quark effective field theory, heavy-quark expansion and QCD factorisation, and Zoltan Ligeti (LBNL) summarised concurrent developments of theory and experiment to determine the sides of the CKM triangle. Lattice QCD also played a central role in the determination of the CKM matrix elements by providing precision computation of non-perturbative parameters, as discussed by Aida El-Khadra (University of Illinois).

There are valuable lessons from the KM paper when applied to the search beyond the Standard Model

The B sector is not the only place where CP violation is observed. Indeed, it was first observed in kaon mixings, and important pieces of information have been obtained since then. A number of theoretical ideas dedicated to the study of kaon CP violation were discussed by Andrzej Buras (Technical University of Munich), and experimental projects were overviewed by Taku Yamanaka (Osaka University).

There are still unsolved mysteries around quark-flavour physics. The most notable is the origin of the fermion generations, which may only be understood by accumulating more data to find any discrepancy with the Standard Model. SuperKEKB/Belle II, the successor of KEKB/Belle, plans to accumulate 50 times more data in the coming decades, while LHCb will continue to improve the precision of measurement in hadronic collisions. Nanae Taniguchi (KEK) reported the current status of SuperKEKB/Belle II, which has been in physics operation since 2019 and has already broken peak-luminosity records in e⁺e^– collisions. Gino Isidori (University of Zurich) gave his view on the possible shape of physics to come. “There are valuable lessons from the KM paper, which are still valuable today, when applied to the search beyond the Standard Model,” he concluded.

As a closing remark, Makoto Kobayashi reminisced about the time when he built the theory as well as the time when the KEKB/Belle experiment was running. “I was able to watch the development of the B factory so closely from the very beginning,” he said. “I am grateful to the colleagues who gave me such a great opportunity.”

Neutrino pheno week back at CERN

Supernova 1987A — **Treasure trove** More than 35 years on, supernova 1987A (the double-ring structure at the centre of the image shows its remnant, as observed today) is still a topic of active discussion, including at Neutrino Platform Pheno Week. Credit: NASA

Since its inception in 2013, the CERN Neutrino Platform has evolved into a worldwide hub for both experimental and theoretical neutrino physics. Besides its multifaceted activities in hardware development – including most notably the ProtoDUNE detectors for the international long-baseline neutrino programme in the US – the platform also hosts a vibrant group of theorists.

From 13 to 17 March this group once again hosted the CERN Neutrino Platform Pheno Week, after a COVID-related hiatus of more than three years. With about 100 in-person participants and 200 more on Zoom, the meeting has become one of the largest in the field – a testament to the ever-growing popularity of neutrinos among particle physicists, even though neutrinos are the most elusive among all known elementary particles.

Talks at the March event reflected the full breadth of the subject, with the first days devoted to novel theoretical models explaining the peculiar relations observed among neutrino masses and mixing angles, and to understanding the way in which neutrinos interact with nuclei. The latter topic is particularly complex, given the vast range of energies in which neutrinos are studied – from non-relativistic cosmic background neutrinos with sub-meV energies to PeV-scale neutrinos observed in neutrino telescopes. An especially popular topic has also been the possibility of discovering physics beyond the Standard Model in the neutrino sector. In fact, because of their ability to mix with hypothetical “dark sector” fermions – that is, fermions potentially related to the physics of dark matter, or even dark matter itself – neutrinos offer a unique window to new physics.

The second part of the workshop was devoted to the neutrino’s role in astrophysics and cosmology. “There’s actually a two-way relationship between neutrinos and the cosmos,” explained invited speaker John Beacom (Ohio State University). “On the one hand, astrophysical and cosmological observations can teach us a lot about neutrino properties. On the other, neutrinos are unique cosmic messengers, and from observations at neutrino telescopes we can learn fascinating things about stars, galaxies and the evolution of the universe.” In recent years, for instance, neutrinos have allowed physicists to shed new light on the century-old problem of where ultra-high-energy cosmic rays come from. And the next galactic supernova – an event that happens on average every 30 to 100 years – will be a treasure trove of new information, given that we expect to observe tens of thousands of neutrinos from such an event. At the same time, cosmology sets the strongest upper limits on the absolute scale of neutrino masses, and with the next generation of cosmological surveys we have every expectation to achieve an actual measurement of this quantity. This is interesting because neutrino oscillations, while establishing that neutrinos have non-zero mass, are only sensitive to differences of squared masses, not to the absolute mass scale.

The programme of the Neutrino Platform Pheno Week closed with a tour of the ProtoDUNE experiments, giving the mostly theory-oriented audience an impression of how the magnificent machines testing our theories of the neutrino sector are being developed and assembled.

An extraordinary harvest of new results

The 57th Recontres de Moriond conference on electroweak interactions and unified theories, which took place from 18 to 25 March on the Alpine slopes of La Thuile in Italy, saw over 150 physicists meet in person for week packed with physics. More than 100 talks on the latest experimental results and theoretical ideas were actively debated, not only during the sessions but also during the breaks and meal times, in a stimulating and congenial atmosphere. The talks covered all the important areas of electroweak physics, with experiment and theory providing complementary approaches to some of the most pressing problems in particle physics and cosmology.

Neutrinos first
Neutrino masses and mixing provide a unique window on the only new physics so far seen beyond the Standard Model. The measured mass differences and mixing parameters provide a consistent picture suggesting the presence of a new scale potentially at approximately 10¹⁵ GeV. However, to complete this picture two fundamental elements are missing: the absolute mass scale of neutrinos and the determination, via neutrinoless double beta decay, of whether neutrinos have a Majorana nature. Also of fundamental importance are the mass-squared ordering of neutrinos, the maximality (or not) of atmospheric mixing, and the measurement of leptonic CP violation. All these questions were addressed by a range of new experimental results, many of which were presented for the first time.

NOvA and T2K presented a very consistent picture of the PMNS framework with a slight preference of the normal over the inverted ordering

The KATRIN collaboration reported an absolute upper limit on the electron-neutrino mass of 800 meV and is expected to reach a limit of 200 meV eventually. With a detailed analysis of their tritium decay spectrum, the team was also able to exclude rapid oscillations of electron neutrinos with potential sterile neutrinos and to set a limit on cosmic-neutrino local over-densities. The KamLandZEN, CUPID-Mo and Majorana Demonstrator experiments showed first results on neutrinoless double-beta decay searches in different systems. KamLandZEN had the largest number of radionuclei, providing upper limits on the effective electron neutrino mass between 36 and 156 meV (depending on model assumptions) and is expected to reach 20 meV with more data. CUPID-Mo and Majorana Demonstrator experiments are expected to eventually reach stronger limits down to approximately 10 meV. The latter experiment, based on germanium detectors, also reported interesting bounds on models for wave-function collapse.

Moriond_2023_young_researchers — Young researchers presenting their work during the Moriond Gravitation conference sessions, which was held in parallel. Credit: L Fayard

The long-baseline ν_μ oscillation experiments NOvA and T2K presented analyses of their latest intermediate dataset, showing a very consistent picture of the PMNS framework with a slight preference (at the one or two standard-deviation level) of the normal over the inverted ordering and the upper over the lower octant for θ₂₃. Both experiments are sensitive to electron-neutrino appearance. NOvA, however, provided the first evidence for electron anti-neutrino appearance and a first long-baseline measurement of sin²θ₂₃, in very good agreement with the reactor neutrino data. Both experiments exclude CP conserving values of δ_CP of 0 or π at 90% confidence. IceCUBE with its DeepCORE extension also presented stunning atmospheric neutrino-oscillation results comparable with SuperKamiokande and long-baseline experiment sensitivities. All these experiments provide strong supporting evidence of the validity of the three neutrino-flavour paradigm.

Longstanding neutrino anomalies were discussed in detail. The reactor-neutrino deficit interpretation in terms of the existence of a sterile neutrino species is incompatible with several short baseline data. The significance of the LSND and MiniBooNE short-baseline low-energy excess was revisited in the light of new backgrounds. The long-standing gallium anomaly was further verified and confirmed by the independent experiment BEST. The BEST observations are, however, also not compatible with a simple sterile-neutrino oscillation pattern. The PROSPECT reactor-neutrino experiment also showed first results excluding the gallium anomaly in terms of an oscillation with a sterile neutrino. Finally, a peaking anomaly, in the range 5-7 MeV, was observed by several experiments (including RENO, DayaBay, NEOS, Chooz and PROSPECT). This anomaly cannot be easily interpreted in terms of fundamental neutrino physics. Instead, nuclear models have been discussed in detail and should be looked at carefully.

Finally, the results of CONUS, a Coherent neutrino scattering experiment based on high precision germanium detectors, set limits on light vector mediators and the neutrino magnetic moment.

The three-neutrino paradigm is standing tall with some anomalies that need to be further clarified, in particular the BEST gallium anomaly.

On the theoretical side, it was shown that leptogenesis is possible for any right-handed neutrino masses above about 0.1 GeV, which, if light enough, can be probed by the proposed SHiP experiment at CERN, as well as FCC-ee and HL-LHC. Neutrino experiments such as COHERENT were analysed in the framework of Standard Model Effective Field Theory.

The IceCUBE experiment also showed splendid multi-messenger results from high- and ultrahigh-energy neutrino observations and pointed out their ability to probe the Standard Model with ultrahigh-energy neutrinos that have travelled cosmic distances. These neutrinos are expected to be even mixtures of the three neutrino species; any deviation would be a clear sign of new physics. The cosmic-neutrino data also highlighted the missing data in neutrino-nucleon interactions in the range of a few 100 GeV to 10 TeV. At this year’s Moriond conference, the birth of collider neutrino physics was also presented, with the first results from the FASERν and SND experiments. FASERν showed the first unambiguous observation of neutrinos from proton-proton collisions at LHC point 1.

Overall the three neutrino paradigm is standing tall with some anomalies that still need to be further clarified, in particular the BEST gallium anomaly.

From neutrinos to quarks

From a theoretical point of view, neutrino and heavy-quark physics are two sides of the same coin: they provide information related to the flavour problem, namely the unexplained origin of quark and lepton families, masses and mixings. The fact that in the Standard Model fermion mass hierarchies arise from Yukawa couplings does not make it more satisfactory. The recently observed anomalies in semi-leptonic B decays exhibiting unexpected lepton-flavour patterns have raised numerous speculations and have in particular suggested that the flavour scale might be right around the corner at the TeV scale, motivating models discussed at the conference involving a new Z’ gauge boson or a scalar or a vector leptoquark from a twin Pati-Salam theory of flavour.

However, the recent results from LHCb on the main anomalies have shed new light on the question. LHCb discussed their recent reanalysis of the R(K) and R(K*) ratio of decay rates of B→K^(*)μμ /ee with the inclusion of an additional background from misidentified electrons are now in excellent agreement with the Standard Model. LHCb also presented a new result on the measurement of the R(D*) ratio of decay rates including fully hadronic τ decays and a new combined measurement of the R(D) and R(D*) ratios. With these new measurements from LHCb the R(D*) ratio agrees with the Standard Model predictions. A tension at the 3 standard deviations level is still observed, mostly due to the R(D) ratio.

Alternatively, D-meson decays were extensively discussed as a promising new playground for discovering new physics due to the richness of new data available, and the efficiency of the GIM mechanism for the charm quark and SU(3) flavour symmetry leading to easily verifiable null tests of the Standard Model.

Results of various rare decay and new resonance searches were presented by LHC experiments, with for example the ambitious searches of the extremely rare decay mode of the D meson in two muons, the observation by the CMS experiment of the decay of the η meson to four muons and the search for states decaying to di-charmonium states as J/ψ/J/ψ or J/ψ/ψ_2S to four muons, which could correspond to four charm tetra-quark states.

Leaving no stone unturned, the LHC experiments have presented a whole host of new results of searches for new phenomena beyond the Standard Model

A highlight of the conference was the strong contribution from the Belle II experiment in all areas of heavy flavour physics, including: several measurements of b→s transitions, including a fully inclusive measurement; several time dependent CP-violation observables, which yield precisions on the CKM parameter sin(2β) on a par with the current world’s best measurements in those channels; as well as new input to the |V_ub| and |V_cb| puzzle (the tension between exclusive and inclusive measurements which suffer from different theoretical uncertainties), with an exclusive measurement in the golden B→πlν mode and an inclusive measurement of the B→D*lν decay.

Moriond_ew_2023_theory_experiment — Triggered by the sheer amount of new results, fruitful discussions for further collaborations emerged during the breaks. Pictured: Marumi Kado and Stephen King (authors) in conversations. Credit: L Fayard

LHCb presented nice new results in the b→sss transition in the φφ channel showing that no CP- violating effect is seen, with results separated in different polarisation modes. LHCb also presented a new measurement of the CKM angle γ in the B^±→D[K^∓π^±π^∓π^±]h^± (h = π, K) channel and an overall combination yielding a precision of approximately 3.7º.

Finally, a status report was given by the KOTO experiment which is searching for the extremely rare K_L→πνν process. The two first runs (starting in 2015 until 2018) have allowed the collaboration to identify two new backgrounds and provide methods to mitigate them since 2019. With these improvements the KOTO experiment should reach sensitivities at the 10^-10 level, close to the expected branching fraction in the Standard Model of 3×10^-11. All measurements shown so far are compatible with the CKM paradigm.

Also in the quark sector, the latest measurements and the prospects in measurements of the neutron electric dipole moment were presented, providing strong constraints on new physics scenarios at high energy scales.

Lattice-QCD studies have made remarkable progress in recent years, with hadronic contributions to muon g-2 being more or less under control, more so in the case of light-by-light contributions, which agree well with other results, and less so regarding the hadronic vacuum polarisation with errors being driven down by the BMW collaboration, which by itself seems to lead to more consistency with the FNAL and BNL results. However, the BMW results are not yet fully confirmed either by other lattice groups or the R-ratio from experiment, with the recent VEPP data being out of line with previous experiments.

Higher precision from lattice calculations has also led to the so-called Cabibbo anomaly reported at Moriond, whereby the unitarity of the first row of the CKM matrix seems to be violated by 2.7σ. If confirmed by future experiments and lattice calculations, this could be a signal for new physics.

In addition, in the lepton flavour sector Belle II presented their first and already the world’s most precise tau-mass measurement, which agrees with previous measurements. With only approximately half the luminosity accumulated by the Belle experiment, Belle II presented measurements surpassing the Belle precision, thus displaying the excellent performance of the experiment.

Dark searches

A variety of dark-matter candidates were discussed including: primordial black hole with improved limits using 21 cm hydrogen astronomy; weakly interacting massive particles (WIMPs) from new electroweak fermion multiplets with heavier masses; heavy singlet dilaton-like scalars; keV neutrinos from an inverse seesaw model; axions or axion-like particles with an extended window of masses arising from non-standard cosmology; and ultralight dark matter such as dark photons whose interactions with the detector could be simulated by the software package DarkELF. An interesting proposal for axion detectors that can double up as high-frequency gravitational wave detectors was also discussed.

A flurry of results of searches for dark-sector particles at the LHC, Belle II, Babar, NA62, BES and PADME were shown.

The XENONnT collaboration presented new results, unblinded for the occasion, with an exposure of 95.1 days corresponding to 1.1 tonne-year. LZ also presented their latest results with a similar exposure. The two experiments, along with the PandaX xenon-based experiment, are now exploring new territory at low WIMP-nucleon cross sections.

These very low cross sections motivate further searches for the existence of a dark sector with dark photons or axion-like particles. A flurry of results of searches for dark-sector particles at the LHC, Belle II, Babar, NA62, BES and the PADME experiment were shown. PADME, a fixed-target e⁺e^– experiment, also presented their ability to directly probe an anomaly which was also seen in ¹²C and ⁴He.

Theories of new heavy particles were also discussed, ranging from an analysis of the minimal supersymmetric Standard Model which showed that gluinos of 1 TeV and stop squarks of 500 GeV could still have escaped detection, to theories of two Higgs-doublet models plus a Higgs singlet, which might be responsible for the 95 GeV diphoton events, to the observation that vector-like fermions (which come in opposite chirality pairs) have the right properties to avoid a metastable universe.

Electroweak searches at the LHC

The LHC experiments presented results from a host of searches for new phenomena beyond the Standard Model, leaving no stone unturned. These looked for signatures of models motivated by theories addressing the shortcomings of the Standard Model, astrophysical and cosmological observations such as dark matter that could be interpreted as the existence of a fundamental field, and experimental anomalies observed such as in the lepton-flavour or muon g-2 anomalies. These searches place very important limits on the presence of new phenomena up to the few-TeV scale. With 20 times more data, the High-Luminosity LHC (HL-LHC) will provide invaluable opportunities to significantly increase the search domain and bring potential for discoveries.

The LHC experiments also presented a series of new results based on W and Z production, coinciding very well with the 40th anniversary of the W and Z boson discoveries at the CERN SppS. The CMS collaboration showed a measurement of the τ polarisation. This measurement can be directly translated in terms of a measurement of the weak mixing angle with a precision of approximately 10%, which is close to the precision reached by e⁺e^– experiments. The CMS collaboration also presented a measurement of the invisible width of the Z boson that is more precise than the direct invisible-width measurements performed at LEP. ATLAS showed the precise measurement of the Z boson transverse momentum differential cross section integrated over the full phase space of leptons produced in the Z decay, and with it was able to provide the current most precise measurement of α_Swith a precision comparable to the current world average or estimates using lattice QCD. ATLAS also presented a new measurement of the W-boson mass using a re-analysis of 7 TeV data collected in 2011, yielding a value slightly lower (by 10 MeV) and with a precision improved to 16 MeV, thus increasing the experimental tension with the recently published CDF measurement.

The LHC results have already obtained precision and sensitivity to processes that were thought to be unreachable prior to the start of operations.

ATLAS and CMS also showed results for more complex and rare processes equally highlighting the remarkable progresses made at the precision frontier. Both experiments showed an observation of the four top quarks production process and ATLAS presented the observation of two new tri-boson production processes, WZγ and Wγγ. ATLAS also presented a new measurement of the associated production of a W boson in association with a pair of top quarks which is a key background to numerous very important processes, as for instant the associated production of a Higgs boson with a pair of top quarks.

The results presented at this year’s Moriond elctroweak session show how LHC results have already obtained precision and sensitivity to processes that were thought to be unreachable prior to the start of operations. An outstanding example discussed in detail was the progress made in the search for di-Higgs production by ATLAS and CMS, a cornerstone of the HL-LHC physics programme to constrain the Higgs boson trilinear self-coupling. These results showed that combined, experiments should reach the sensitivity for the observation of this process at the LHC. Another example which was also discussed is the race to reach sensitivity to the Higgs-boson decays to charm quarks, where new methods based on deep learning techniques are making significant progress.

To further improve on the expected precision reach at the HL-LHC, intermediate goals at Run 3 are extremely important. Both ATLAS and CMS presented new results on measurements of Z boson, top, and Higgs boson production with LHC Run 3 data taken in 2022.

This year’s Moriond conference showed an extraordinary harvest of new results, giving an opportunity to take stock on the open questions and see the remarkable progress made since last year.

A celebration of physics in the Balkans

The 11th General Conference of the Balkan Physical Union (BPU11 Congress) took place from 28 August to 1 September 2022 in Belgrade, with the Serbian Academy of Science and Arts as the main host. Initiated in 1991 in Thessaloniki, Greece, and open to participants globally, the series provides a platform for reviewing, disseminating and discussing novel research results in physics and related fields.

The scientific scope of BPU11 covered the full landscape of physics via 139 lectures (12 plenary and 23 invited) and 150 poster presentations. A novel addition was five roundtables dedicated to high-energy physics (HEP), widening participation, careers in physics, quantum and new technologies, and models of studying physics in European universities with a focus on Balkan countries. The hybrid event attracted about 476 participants (325 on site) from 31 countries, 159 of whom were students, and demonstrated the high level of research conducted in the Balkan states.

Roadmaps to the future

The first roundtable “HEP – roadmaps to the future” showed the strong collaboration between CERN and the Balkan states. Four out of 23 CERN Member States come from the region (Bulgaria, Greece, Serbia and Romania); two out of three Associate Member States in the pre-stage to membership are Cyprus and Slovenia; and two out of seven Associate Member States are Croatia and Turkey. A further four countries have cooperation agreements with CERN, and more than 400 CERN users come from the Balkans.

Kicking off the HEP roundtable discussions, CERN director for research and computing Joachim Mnich presented the recently launched accelerator and detector R&D roadmaps in Europe. Paris Sphicas (CERN and the University of Athens) reported on the future of particle-physics research, during which he underlined the current challenges and opportunities. These included: dark matter (for example the search for WIMPs in the thermal parameter region, the need to check simplified models such as axial-vector and di-lepton resonances, and indirect searches); supersymmetry (the search for “holes” in the low-mass region that will exist even after the LHC); neutrinos (whether neutrinos are Majorana or Dirac particles, their mass measurement and exploration of a possible “sterile” sector); as well as a comprehensive review of the Higgs sector.

CERN’s Emmanuel Tsesmelis, who was awarded the Balkan Physical Union charter and honorary membership in recognition of his contributions to cooperation between the Balkan states and CERN, reflected on the proposed Future Circular Collider (FCC). Describing the status of the FCC feasibility study, due to be completed by the end of 2025, he stressed that the success of the project relies on strong global participation. His presentation initiated a substantial discussion about the role of the Balkan countries, which will be continued in May 2023 at the 11th LHCP conference in Belgrade.

The roundtable devoted to quantum technologies (QTs), chaired by Enrique Sanchez of the European Physical Society (EPS), was another highlight with strong relevance to HEP. Various perspectives on the different QT sectors – computing and simulation, communication, metrology and sensing – were discussed, touching upon the impact they could have on society at large. Europe plays a leading role in quantum research, concluded the panel. However, despite increased interest in QTs, including at CERN, issues such as how to obtain appropriate funding to enhance European technological leadership, remain. Discussions highlighted the opportunities for new generations of physicists from the Balkans to help build this “second quantum revolution”.

In addition to the roundtables, four high-level scientific satellite events took place, attracting a further 150 on-site participants: the COST Workshop on Theoretical Aspects of Quantum Gravity; the SEENET–MTP Assessment Meeting and Workshop; the COST School on Quantum Gravity Phenomenology in the Multi-Messenger Approach; and the CERN–SEENET–MTP–ICTP PhD School on Gravitation, Cosmology and Astroparticle Physics. The latter is part of a unique regional programme in HEP initiated by SEENET–MTP (Southeastern European Network in Mathematical and Theoretical Physics) and CERN in 2015, and joined by the ICTP in 2018, which has contributed to the training of more than 200 students in 12 SEENET countries.

The BPU11 Congress, the largest event of its type in the region since the beginning of the COVID-19 pandemic, contributed to closer cooperation between the Balkan countries and CERN, ICTP, SISSA, the Central European Initiative and others. It was possible thanks to the support of the EPS, ICTP and CEI-Trieste, CERN, EPJ, as well as the Serbian ministry of science and institutions active in physics and mathematics in Serbia. In addition to the BPU11 PoS Proceedings, several articles based on invited lectures will be published in a focus issue of EPJ Plus “On Physics in the Balkans: Perspectives and Challenges”, as well as in a special issue of IJMPA.

Unconventional music @ CERN

Honouring the 100th anniversary of Einstein’s Nobel prize, the Swedish embassy in Bern collaborated with CERN for an event connecting science and music, held at the CERN Globe of Science and Innovation on 19 October. The event was originally planned for 2021 but was postponed due to the pandemic.

Brian Foster (University of Oxford) talked about Einstein’s love for music and playing the violin, which was underlined with many photos showing Einstein with some of the well-known violinists of the time. Around the period Einstein was awarded the Nobel prize, Russian engineer Lev Termen invented the theremin, consisting of two antennae and played without physical contact. This caught Einstein’s attention and it is said that he even played the theremin himself once.

Delving further into the unconventional, LHC physicists performed Domenico Vicinanza’s (GEANT and Anglia Ruskin University) “Sonification of the LHC”, for which the physicist-turned composer mapped data recorded by the LHC experiments between 2010 and 2013 into music. First performed in 2014 on the occasion of CERN’s 60th anniversary, Vicinanza’s piece is intended as a metaphor for scientific cooperation, in which different voices and perspectives can reach the same goal only by playing together.

There followed the debut of an even more unconventional piece of music by The Stone Martens – a Swiss and Swedish “noise collaboration” improvised by Henrik Rylander and Roland Bucher. By sending the output of his theremin through guitar-effects pedals, Rylander created a unique sound. Together with Bucher’s self-made “noise table”, with which he sampled acoustic instruments and everyday objects, the duo created a captivating, otherworldly sound collage that was well received by the 160-strong audience. The event closed with an unconventional Bach concerto for two violins in which these unique sounds were fused with traditional instruments. Anyone interested in experiencing the music for themselves can find a recorded version at https://indico.cern.ch/event/1199556/.

A powerful eye opener into the world of AI

The appearance of the word “for” rather than “in” in the title of this collection raises the bar from an academic description to a primer. It is neither the book’s length (more than 800 pages), nor the fact that the author list resembles a who’s who in artificial intelligence (AI) research carried out in high-energy physics that makes this book live up to its premise; it is the careful crafting of its content and structure.

Artificial intelligence is not new to our field. On the contrary, some of the concepts and algorithms have been pioneered in high-energy physics. Artificial Intelligence for High Energy Physics credits this as well as reaching into very recent AI research. It covers topics ranging from unsupervised machine-learning techniques in clustering to workhorse tools such as boosted decision trees in analyses, and from recent applications of AI in event reconstruction to simulations at the boundary where AI can help us to understand physics.

Each chapter follows a similar structure: after setting the broader context, a short theoretical introduction into the tools (and, where possible, the available software) is given, which is then applied and adapted to a high-energy physics problem. The ratio of in-depth theoretical background to AI concepts and the focus on applications is well balanced, and underlines the work of the editors, who avoided duplication and cross-reference individual chapters and topics. The editors and authors have not only created a selection of high-quality review articles, but a coherent and remarkably good read. Takeaway messages in the chapter for distributed training and optimisation stand out, and one might wish that this concept found more resonance throughout the book.

Artificial Intelligence for High Energy Physics — Credit: World Scientific

Sometimes, the book can be used as a glossary, which helps to bridge the gaps that seem to exist simply because high-energy physicists and data scientists use different names for similar or even identical things. While the book can certainly be used as a guide for a physicist in AI, an AI researcher with the necessary physics knowledge may not be served quite so well.

In an ideal world, each chapter would have a reference dataset to allow the reader to follow the stated problems and learn through building and exercising the described pipelines. This, however, would turn the book from a primer into a textbook for AI in high-energy physics. To be fair, wherever possible the authors of the chapters have used and referred to publicly available datasets, and one chapter is devoted to the issue of arranging a community data competition, such as the TrackML challenge in 2018.

As for the most important question – have I learned something new? – the answer is a resounding “yes”. While none of the broad topics and their application to high-energy physics will come as a surprise to those who have been following the field in recent years, there are neat projects and detailed applications showcased in this book. Furthermore, reading about a familiar topic in someone else’s words can be a powerful eye opener.

Meenakshi Narain 1964–2023

Experimental particle physicist Meenakshi Narain, an inspirational leader and champion of diversity, died unexpectedly on 1 January 2023 in Providence, RI. Considered by many as a “force of nature”, Meenakshi’s impact on the physics community has left an indelible mark.

Meenakshi grew up in Gorakhpur, India and emigrated to the US in 1984 for graduate school at SUNY Stony Brook. Her PhD thesis, based on data taken by the CUSB-II detector at CESR, utilised inclusive photon spectra from upsilon decays for both spectroscopy measurements and searches for exotic particles, including the Higgs boson. In 1991 Meenakshi joined Fermilab as a postdoc on the DØ experiment, where she was a principal player in the 1995 discovery of the top quark, leading a group searching for top anti–top pair production in the dilepton channel. Over the next decade, as a Fermilab Wilson Fellow and a faculty member at Boston University, she made seminal contributions to measurements of top-quark pair and single-top production, as well as to the top-quark mass, width and couplings.

In 2007, upon joining the faculty at Brown University, Meenakshi joined the CMS experiment at the LHC. In addition to pioneering a number of exotic searches for high-mass resonances, new heavy gauge bosons and top-quark partners, she continued to make innovative contributions to precision top-quark measurements. Her foundational work on b- and c-quark identification also paved the way for Higgs boson searches and measurements. As a leader of the CMS upgrade studies group, Meenakshi coordinated physics studies for several CMS technical design reports for the High-Luminosity LHC upgrade, and an impressive number of results for the CERN yellow reports. She was also a key contributor to the US CMS outer tracker upgrade.

The tutorials and workshops Meenakshi organised as co-coordinator of the LHC Physics Center (LPC) were pivotal in advancing the careers of many young scientists, whom she cared about deeply. As chair of the US CMS collaboration board, she was a passionate advocate for the LHC research programme. She created an inclusive, supportive community that participated in movements such as Black Lives Matter, and tackled numerous challenges imposed by the COVID-19 pandemic.

A strong voice for women and under-represented minorities in physics, Meenakshi was the founding co-chair of the CMS diversity office and the driving force behind the CMS task force on diversity and inclusion and the CMS women’s forum. She mentored a large group of students, post-docs and scientists from diverse backgrounds, and created PURSUE – an internship programme that provides summer research opportunities at CMS to students from minority-serving institutions.

Meenakshi’s illustrious career has been recognised via numerous accolades and positions of responsibility. She is remembered for her recent co-leadership of the Snowmass energy-frontier study, her service on HEPAP and her new appointment to the P5 subpanel, in addition to her new position as the first woman to chair the physics department at Brown. She will be remembered as a brilliant scientist, a beloved mentor and an inspiring leader who made the world a better, more equitable and inclusive place.

Lars Brink 1943–2022

It is with great sadness that we learnt of the passing of Lars Brink on 29 October 2022 at the age of 78. Lars Brink was an emeritus professor at Chalmers University Göteborg, Sweden and a member of the Royal Swedish Academy. He started his career as a fellow in the CERN theory group (1971–1973), which was followed by a stay at Caltech as a scientific associate (1976–1977). In subsequent years he was a frequent visitor at CERN, Caltech and ITP Santa Barbara, before becoming a full professor of theoretical physics at Chalmers in 1986, which under his guidance became an internationally leading centre for string theory and supersymmetric field theories.

Lars held numerous other appointments, in particular as a member and chairperson on the board of NORDITA, the International Center for Fundamental Physics in Moscow, and later as the chairperson of the advisory board of the Solvay Foundation in Brussels. Since 2004 he was an external scientific member of the Max Planck Institute for Gravitational Physics in Golm. During his numerous travels Lars was welcomed by many leading institutions all over the world. He also engaged in many types of community service, such as the coordination of the European Union network “Superstring Theory” since 2000. Most importantly, he served on the Nobel Committee for physics many years, and as its chairperson for the 2013 Nobel Prize in Physics awarded to François Englert and Peter Higgs.

Lars was a world-class theoretical physicist, with many pioneering contributions, especially to the development of supergravity and superstring theory, as well as many other topics. One of his earliest contributions was a beautiful derivation of the critical dimension of the bosonic string (with Holger Bech Nielsen), obtained by evaluating the formally divergent sum over zero-point energies of the infinitely many string oscillators; this derivation is now considered a standard textbook result. In 1976, with Paolo Di Vecchia and Paul Howe, he presented the first construction of the locally supersymmetric world-sheet Lagrangian for superstrings (also derived by Stanley Deser and Bruno Zumino) which now serves as the basis for the quantisation of the superstring and higher loop calculations in the Polyakov approach. His seminal 1977 work with Joel Scherk and John Schwarz on the construction of maximal (N = 4) supersymmetric Yang–Mills theory in four dimensions laid the very foundation for key developments of modern string theory and the AdS/CFT correspondence that came to dominate string-theory research only much later. Independently of Stanley Mandelstam, he proved the UV finiteness of the N = 4 theory in the light-cone gauge in 1983, together with Olof Lindgren and Bengt Nilsson – another groundbreaking result. Equally influential is his work with Michael Green and John Schwarz on deriving supergravity theories as limits of string amplitudes. More recently, he devoted much effort to a reformulation of N = 8 supergravity in light-cone super-space (with Sudarshan Ananth and Pierre Ramond). His last project before his death was a reevaluation and pedagogical presentation of Yoichiro Nambu’s seminal early papers (with Ramond).

Lars received numerous honours during his long career. In spite of these achievements he remained a kind, modest and most approachable person. Among our many fondly remembered encounters we especially recall his visit to Potsdam in August 2013, when he revived an old tradition by inviting the Nobel Committee to a special retreat for its final deliberations. The concluding discussions of the committee thus took place in Einstein’s summer house in Caputh. Of course, we were all curious for any hints from the predictably tight-lipped Swedes in advance of the official Nobel announcement, but in the end the only useful information we got out of Lars was that the committee had crossed the street for lunch to eat mushroom soup in a local restaurant!

He leaves behind his wife Åsa, and their daughters Jenny and Maria with their families, to whom we express our sincere condolences. We will remember Lars Brink as a paragon of scientific humility and honesty, and we miss a great friend and human being.

How to find your feet in industry

The sixth annual LHC Career Networking Event, which took place at CERN on 21 November 2022, attracted more than 200 scientists and engineers (half in person) seeking to explore careers beyond CERN. Seven former members of the LHC-experiment collaborations and representatives from CERN’s knowledge transfer group discussed their experiences, good and bad, upon transitioning to the diverse employment world outside particle physics. Lively Q&A sessions and panel discussions enabled the audience to voice their questions and concerns.

While the motivations for leaving academia expressed by the speakers differed according to their personal stories, common themes emerged. The long time-scales of experimental physics coupled with job instability and the glacial pace of funding cycles for new projects, for example, sometimes led to demotivation, whereas the speakers found that industry had exciting shorter-term projects to explore. Several speakers sought a better work–life balance in subjects they could enthuse about, having previously experienced a sense of stagnation. Another factor related to that balance was the better ratio between salary and performance, and hours worked.

Case studies

Caterina Deplano, formerly an ALICE experimentalist, and Giorgia Rauco, ex-CMS, described the personal constraints that led them to search for a job in the local area, and showed that this need not be a limiting factor. Both assessed their skills frankly and opted for further training in their target sectors: education and data science, respectively. Deplano’s path to teaching in Geneva led her to go back and study for four years, improving her French-language skills while obtaining a Swiss teaching qualification. The reward was apparent in the enthusiasm with which she talked about her students and her chosen career. Rauco explained how she came to contemplate life outside academia and talked participants through the application process, emphasising that finding the “right” employment fit had meant many months of work with frequent disappointments, the memory of which was erased by the final acceptance letter. Both speakers gave links to valuable resources for training and further education, and Rauco offered some top-tips for prospective transitioners: be excited for what is coming next, start as soon as possible if you are thinking about changing and don’t feel guilty about your choice.

Maria Elena Stramaglia, formerly ATLAS, described the anguish of deciding whether to stay in academia or go to industry, and her frank assessment of transferable skills weighed up against personal desires and her own work–life balance. Her decision to join Hitachi Energy was based on the right mix of personal and technical motivation, she said. In moving from LHCb to data science and management, Albert Puig Navarro joined a newly established department at Proton (the developers of ProtonMail, which was founded by former ATLAS members; CERN Courier September/October 2019 p53), in which he ended up being responsible for hiring a mix of data scientists, engineers and operations managers, conducting more than 200 interviews in the process. He discussed the pitfalls of over-confidence, the rather different requirements of the industrial sector, and the shift in motivations between pure science and industry. Cécile Deterre, a former ATLAS physicist now working on technology for sustainable fish farming, focussed on CV-writing for industrial job applications, during which she emphasised transferable skills and how to make your technical experience more accessible to future employers.

With one foot still firmly in particle physics, Alex Winkler, formerly CMS, joined a company that makes X-ray detectors for medical, security and industrial applications; in a serendipitous exception among the speakers, he described how he was head-hunted while contemplating life beyond CERN, and mentioned the novel pressures implicit in working in a for-profit environment. Massimo Marino, ex-ATLAS, gave a lively talk about his experiences in a number of diverse environments: Apple, the World Economic Forum and the medical energy industries, to name a few. Diverting along the way to write a series of books, his talk covered the personal challenges and expectations in different roles and environments over a long career.

Throughout the evening, which culminated in a panel session, participants had the opportunity to quiz the speakers about their sectors and the personal decisions and processes that led them there. Head of CERN Alumni Relations Rachel Bray also explained how the Alumni Network can help facilitate contact between current CERN members and their predecessors who have left the field. The interest shown by the audience and the detailed testimonials of the speakers demonstrated that this event remains a vital source of information and encouragement for those considering a career transition.

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