Praxis Archives – Page 25 of 179

Stepping into the spotlight

François Englert and Peter Higgs — **Final summit** François Englert (left) and Peter Higgs (right) in Stockholm on 10 December 2013. Credit: A Mahmoud/Nobel Media

With the boson confirmed, speculation inevitably grew about the 2012 Nobel Prize in Physics. The prize is traditionally announced on the Tuesday of the first full week in October, at about midday in Stockholm. As it approaches, a highly selective epidemic breaks out: Nobelitis, a state of nervous tension among scientists who crave Nobel recognition. Some of the larger egos will have previously had their craving satisfied, only perhaps to come down with another fear: will I ever be counted as one with Einstein? Others have only a temporary remission, before suffering a renewed outbreak the following year.

Three people at most can share a Nobel, and at least six had ideas like Higgs’s in the halcyon days of 1964 when this story began. Adding to the conundrum, the discovery of the boson involved teams of thousands of physicists from all around the world, drawn together in a huge cooperative venture at CERN, using a machine that is itself a triumph of engineering.

The 2012 Nobel Prize in Physics was announced on Tuesday 9 October and went to Serge Haroche and David Wineland for taking the first steps towards a quantum computer. Two days later, I went to Edinburgh to give a colloquium and met Higgs for a coffee beforehand. I asked him how he felt now that the moment had passed, at least for this year. “I’m enjoying the peace and quiet. My phone hasn’t rung for two days,” he remarked.

That the sensational discovery of 2012 was indeed of Higgs’s boson was, by the summer of 2013, beyond dispute. That Higgs was in line for a Nobel prize also seemed highly likely. Higgs himself, however, knew from experience that in the Stockholm stakes, nothing is guaranteed.

Back in 1982, at dawn on 5 October in the Midwest and the eastern US, preparations were in hand for champagne celebrations in three departments at two universities. At Cornell, the physics department hoped they would be honouring Kenneth Wilson, while over in the chemistry department their prospect was Michael Fisher. In Chicago, the physicists’ hero was to be Leo Kadanoff. Two years earlier the trio had shared the Wolf Prize, the scientific analogue of the Golden Globes to the Nobel’s Oscars, for their work on critical phenomena connected with phase transitions, fuelling speculation that a Nobel would soon follow. At the appointed hour in Stockholm, the chair of the awards committee announced that the award was to Wilson alone. The hurt was especially keen in the case of Michael Fisher, whose experience and teaching about phase transitions, illuminating the subtle changes in states of matter such as melting ice and the emergence of magnetism, had inspired Wilson, five years his junior. The omission of Kadanoff and Fisher was a sensation at the time and has remained one of the intrigues of Nobel lore.

Fisher’s agony was no secret to Peter Higgs. As undergraduates they had been like brothers and remained close friends for more than 60 years. Indeed, Fisher’s influence was not far away in July 1964, for it was while examining how some ideas from statistical mechanics could be applied to particle physics that Higgs had the insight that would become the capstone to the theory of particles and forces half a century later. For this he was to share the 2004 Wolf Prize with Robert Brout (who sadly died in 2011) and François Englert – just as Fisher, Kadanoff and Wilson had shared this prize in 1980. Then as October approached in 2013 Higgs became a hot favourite at least to share the Nobel Prize in Physics, and the bookmakers would only take bets at extreme odds-on.

Time to escape

In 2013, 8 October was the day when the Nobel decision would be announced. Higgs’s experiences the year before had helped him to prepare: “I decided not to be at home when the announcement was made with the press at my door; I was going to be somewhere else.” His first plan was to disappear into the Scottish Highlands by train, but he decided it was too complicated, and that he could hide equally well in Edinburgh. “All I would have to do is go down to Leith early enough. I knew the announcement would be around noon so I would leave home soon after 11, giving myself a safe margin, and have an early lunch in Leith about noon.”

ATLAS and CMS physicists in Building 40 on 8 October 2013 — **Build up** ATLAS and CMS physicists gathered in Building 40 on 8 October 2013 for the announcement of the Nobel Prize in Physics. Credit: CERN-HI-1310243-06

Richard Kenway, the Tait Professor of Mathematical Physics at Edinburgh and one of the university’s vice principals, confirmed the tale. “That was what we were all told, and he completely convinced us. Right up to the actual moment when we were sitting waiting for the [Nobel] announcement, we thought he had disappeared off somewhere into the Highlands.” Some newspapers got the fake news from the department, and one reporter even went up into the Highlands to look for him.

As scientists and journalists across the world were glued to the live broadcast, the Nobel committee was still struggling to reach the famously reclusive physicist. The announcement of his long-awaited crown was delayed by about half an hour until they decided they could wait no longer. Meanwhile, Peter Higgs sat at his favourite table in The Vintage, a seafood bar in Henderson Street, Leith, drinking a pint of real ale and considering the menu. As the committee announced that it had given the prize to François Englert and Peter Higgs “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider”, phones started going off in the Edinburgh physics department.

Higgs finished his lunch. It seemed a little early to head home, so he decided to look in at an art exhibition. At about three o’clock he was walking along Heriot Row in Edinburgh, heading for his flat nearby, when a car pulled up near the Queen Street Gardens. “A lady in her 60s, the widow of a high-court judge, got out and came across the road in a very excited state to say, ‘My daughter phoned from London to tell me about the award’, and I said, ‘What award?’ I was joking of course, but that’s when she confirmed that I had won the prize. I continued home and managed to get in my front door with no more damage than one photographer lying in wait.” It was only later that afternoon that he finally learned from the radio news that the award was to himself and Englert.

Suited and booted

On arrival in Stockholm in December 2013, after a stressful two-day transit in London, Higgs learned that one of the first appointments was to visit the official tailor. The costume was to be formal morning dress in the mid-19th-century style of Alfred Nobel’s time, including elegant shoes adorned with buckles. As Higgs recalled, “Getting into the shirt alone takes considerable skill. It was almost a problem in topology.” The demonstration at the tailor’s was hopeless. Higgs was tense and couldn’t remember the instructions. On the day of the ceremony, fortunately, “I managed somehow.” Then there were the shoes. The first pair were too small, but when he tried bigger ones, they wouldn’t fit comfortably either. He explained, “The problem is that the 19th-century dress shoes do not fit the shape of one’s foot; they were rather pointy.” On the day of the ceremony both physics laureates had a crisis with their shoes. “Englert called my room: ‘I can’t wear these shoes. Can we agree to wear our own?’ So we did. We were due to be the first on the stage and it must have been obvious to everyone in the front row that we were not wearing the formal shoes.”

Robert Brout in spirit completed a trinity of winners

On the afternoon of 10 December, nearly 2000 guests filled the Stockholm Concert Hall to see 12 laureates receive their awards from King Gustav of Sweden. They had been guided through the choreography of the occasion earlier, but on the day itself, performing before the throng in the hall, there would be first-night nerves for this once-in-a-lifetime theatre. Winners of the physics prize would be called to receive their awards first, while the others watched and could see what to expect when they were named. The scenery, props and supporting cast were already in place. These included former winners dressed in tail suits and proudly wearing the gold button stud that signifies their membership of this unique club. Among them were Carlo Rubbia, discoverer of the W and Z particles, who instigated the experimental quest for the boson and won the prize in 1984; Gerard ’t Hooft, who built on Higgs’s work to complete the theoretical description of the weak nuclear force and won in 1999; and 2004 winner Frank Wilczek, who had built on his own prize-winning work to identify the two main pathways by which the Higgs boson had been discovered.

Peter Higgs in July 2012 — **Showtime** (left) Peter Higgs and the author at Palermo airport on 2 July 2012 after attending the Erice summer school. Higgs was en route to CERN but was not aware of the ATLAS and CMS results. (right) Jane MacKenzie and Stephanie Hills guiding Peter Higgs at CERN two days later. Credits: F Close/J MacKenzie

After a 10-minute oration by the chair of the Nobel Foundation and a musical interlude, Lars Brink, chairman of the Nobel Committee for Physics, managed to achieve one of the most daunting challenges in science pedagogy, successfully addressing both the general public in the hall and the assembled academics, including laureates from other areas of science. The significance of what we were celebrating was beyond doubt: “With discovery of the Higgs boson in 2012, the Standard Model of physics was complete. It has been proved that nature follows precisely that law that Brout, Englert and Higgs created. This is a fantastic triumph for science,” Brink announced. He also introduced a third name, that of Englert’s collaborator, Robert Brout. In so doing, he made an explicit acknowledgement that Brout in spirit completed a trinity of winners.

Brink continued with his summary history of how their work and that of others established the Standard Model of particle physics. Seventeen months earlier the experiments at the LHC had confirmed that the boson is real. What had been suspected for decades was now confirmed forever. The final piece in the Standard Model of particle physics had been found. The edifice was robust. Why this particular edifice is the one that forms our material universe is a question for the future. Brink now made the formal invitation for first Englert and then Higgs to step forward to receive their share of the award.

Higgs, resplendent in his formal suit, and comfortable in his own shoes, rose from his seat and prepared to walk to centre-stage. Forty-eight years since he set out on what would be akin to an ascent of Everest, Higgs had effectively conquered the Hillary step – the final challenge before reaching the peak – on 4 July 2012 when the existence of his boson was confirmed. Now, all that remained while he took nine steps to reach the summit was to remember the choreography: stop at the Nobel Foundation insignia on the carpet; shake the king’s hand with your right hand while accepting the Nobel prize and diploma with the other. Then bow three times, first to the king, then to the bust of Alfred Nobel at the rear of the stage, and finally to the audience in the hall.

Higgs successfully completed the choreography and accepted his award. As a fanfare of trumpets sounded, the audience burst into applause. Higgs returned to his seat. The chairman of the chemistry committee took the lectern to introduce the winners of the chemistry prize. To his relief, Higgs was no longer in the spotlight.

All in a name

The saga of Higgs’s boson had begun with a classic image – a lone genius unlocking the secrets of nature through the power of human thought. The fundamental nature of Higgs’s breakthrough had been immediately clear to him. However, no one, least of all Higgs, could have anticipated that it would take nearly half a century and several false starts to get from his idea to a machine capable of finding the particle. Nor did anyone envision that this single “good idea” would turn a shy and private man into a reluctant celebrity, accosted by strangers in the supermarket. Some even suggested that the reason why the public became so enamoured with Higgs was the solid ordinariness of his name, one syllable long, unpretentious, a symbol of worthy Anglo-Saxon labour.

In 2021, nine years after the discovery, we were reminiscing about the occasion when, to my surprise, Higgs suddenly remarked that it had “ruined my life”. To know nature through mathematics, to see your theory confirmed, to win the plaudits of your peers and join the exclusive club of Nobel laureates: how could all this equate with ruin? To be sure I had not misunderstood, I asked again the next time we spoke. He explained: “My relatively peaceful existence was ending. I don’t enjoy this sort of publicity. My style is to work in isolation, and occasionally have a bright idea.”

This is an edited extract from Elusive: How Peter Higgs Solved the Mystery of Mass, by Frank Close, published on 14 June (Basic Books, US) and 7 July (Allen Lane, UK)

You have to be able to explain ‘why’

On 4 July 2012, Sean Carroll was at CERN to witness the momentous announcements by ATLAS and CMS – but not in his usual capacity as a physicist. He was there as an accredited member of the media, sharing an overflow room with journalists to get first-hand footage for the final chapter of his book. The Particle at the End of the Universe ended up being the first big title on the discovery and went on to win the 2013 Royal Society Science Books Prize. “It got reviewed everywhere, so I am really grateful to the Higgs boson and CERN!”

Carroll’s publisher sensed an opportunity for a timely, expert-authored title in 2011, as excitement in ATLAS and CMS grew. He initially said “No” – it wasn’t his research area, and he preferred to present a particular point of view, as he did in his first popular work From Eternity to Here: The Quest for the Ultimate Theory of Time. “With the Higgs boson, there is no disagreement, he says. “Everyone knows what the boson is, what it does and why is it important.” After some negotiation, he received an offer he couldn’t refuse. It also delved into the LHC, the experiments and how it all works, with a dash of quantum field theory and particle physics more generally. “We were hoping the book would come out by the time they announced the discovery, but on the other hand at least I got to include the discovery in the book, and was there to see it.”

Show me the money

Books are not very lucrative, he says. “Back in the 1980s and 1990s, when the success of Hawking’s A Brief History of Time awoke the interest of publishers, if you had a good idea for a physics book you could make a million dollars. But it is very hard to earn enough to make a living. “It takes roughly a year, or more depending on how much you have to learn, and depends on luck, the book and the person writing it.” His next project is a series of three books aimed at explaining physics to the general reader. The first, The Biggest Ideas in the Universe: Space, Time and Motion, due out in September, covers Newtonian mechanics and relativity; the second covers quantum mechanics and quantum field theory, and the third complexity, emergence and large-scale phenomena.

Meanwhile, Carroll’s podcast Mindscape, in which he invites experts from different fields to discuss a range of topics, has produced 200 episodes since it launched in 2018 and attracts around 100,000 listeners weekly. “I thought that it was a very fascinating idea, basically your personal radio show, but I quickly learned that I didn’t have that many things to say all by myself,” he explains. “Then I realised it would give me an excuse to talk to lot of interesting people and stretch my brain a lot, and that worked out really well.”

Reaching out

As someone who fell in love with science at a young age and enjoyed speaking and writing, Carroll has clearly found his ideal career. But stepping outside the confines of research is not without its downsides. “Overall, I think it has been negative actually, as it’s hard for some scientists to think that somebody is both writing books and giving talks, and also doing research at the same time. There is a prejudice that if you are a really good researcher then that’s all you do, and anything else is a waste of time. But whatever it does to my career, it has been good in many ways, and I think for the field, because I have reached people who wouldn’t know about physics otherwise.”

We need to take seriously the responsibility to tell people what it is that we have learned about the universe, and why it’s exciting to explore further

Moreover, he says, scientists are obligated to communicate the results of their work. “When it comes to asking the public for lots of money you have to be able to explain why it’s needed, and if they understand some of the physics and they have been excited by other discoveries they are much more likely to appreciate that,” he says, citing the episode of the Superconducting Super Collider. “When we were trying to build the SSC, physicists were trying their best to explain why we needed it and it didn’t work. Big editorials in the New York Times clearly revealed that people did not understand the reasons why this was interesting, and furthermore thought that the kind of physics we do does not have any immediate or technological benefit. But they are all also curious like we are. And while we don’t all have to become pop-science writers or podcasters (just like I am not going to turn up on Tik Tok or do a demo in the street), as a field we really need to take seriously the responsibility to tell people what it is that we have learned about the universe, and why it’s exciting to explore further.”

Limbering up for the Einstein Telescope

On 14 April the government of the Netherlands announced that it intends to conditionally allocate €42 million to the development of the Einstein Telescope – a proposed next-generation gravitational-wave observatory in Europe. It also pledged a further €870 million for a potential future Dutch contribution to the construction. The decision was taken by the Dutch government based on the advice of the Advisory Committee of the National Growth Fund, stated a press release from Nikhef and the regional development agency for Limburg.

The Einstein Telescope (ET) is a triangular laser interferometer with sides 10 km-long that would be at least 10 times more sensitive than the Advanced LIGO and Virgo observatories, extending its scope for detections and enabling physicists to look back much further in cosmological time. To reach the required sensitivities, the interferometer has to be built at least 200 m underground in a geologically stable area. Its mirrors will have to operate in cryogenic conditions to reduce thermal disturbance, and be larger and heavier than those currently employed to allow for a larger and more powerful laser beam.

Activities have been taking place at two potential sites in Europe: the border region of South Limburg (the Euregio Meuse-Rhine) in the Netherlands; and the Sar-Grav laboratory in the Sos Enattos mine in Sardinia, Italy. For the Sardinia site, a similar proposal has been submitted to the Italian government and feedback is expected in July.

The Netherlands’ intended €42 million investment will go towards preparatory work such as innovation of the necessary technology, location research, building up a high-tech ecosystem and organisation, stated the press release, while the reservation of €870 million is intended to put the Netherlands in a strong position to apply in the future – together with Belgium and Germany – to host and build the ET.

It is fantastic that the cabinet embraces the ambition to make the Netherlands a world leader in research into gravity waves

“It is fantastic that the cabinet embraces the ambition to make the Netherlands a world leader in research into gravity waves,” said Nikhef director Stan Bentvelsen, who has been involved with the ET for several years. “These growth-fund resources form the basis for further cooperation with our partners in Germany and Belgium, and for research into the geological subsurface in the border region of South Limburg. A major project requires a careful process, and I am confident that we will meet the additional conditions.”

Housing the ET in the region could have a major positive impact on science, the economy and society in the Netherlands, said provincial executive member for Limburg Stephan Satijn. “With today’s decision, the cabinet places our country at the global forefront of high-tech and science. Limburg is the logical place to help shape this leading position. Not only because of the suitability of our soil, but also because we are accustomed to working together internationally and to connecting science and business.”

At the 12th ET symposium in Budapest on 7–8 June, the ET scientific collaboration was officially born – a crucial step in the project’s journey, said ad interim spokesperson Michele Punturo of the INFN: “We were a scientific community, today we are a scientific collaboration, that is, a structured and organised system that works following shared rules to achieve the common goal: the realisation of a large European research infrastructure that will allow us to maintain scientific and technological leadership in this promising field of fundamental physics research.”

In January, the ET was granted status as a CERN recognised experiment (RE43), with a collaboration agreement on vacuum technology already in place and a further agreement concerning cryogenics at an advanced stage.

Council decides new measures for Russia and Belarus

Open meeting of the June Council — **Open council** Delegates from CERN’s Member States during the open meeting of the June Council. Credit: CERN-PHOTO-202206-111-1

At its 208th meeting on 16 June, the CERN Council announced further measures in response to the continuing illegal military invasion of Ukraine by the Russian Federation with the involvement of the Republic of Belarus. The Council declared that it intends to terminate CERN’s International Cooperation Agreements (ICAs) with both countries at their expiration dates in 2024. However, the situation will continue to be monitored carefully and the Council stands ready to take any further decision in the light of developments in Ukraine.

CERN’s ICAs normally run for five years and are tacitly renewed for the same period unless a written notice of termination is provided by one party to the other at least six months prior to the renewal date. The ICA with the Russian Federation expires in December 2024, and that with the Republic of Belarus in June 2024.

The latest measures follow those already adopted at an extraordinary meeting of the Council on 8 March, and at the Council’s regular session on 25 March. In addition to the promotion of initiatives to support Ukrainian collaborators and Ukrainian scientific activity in high-energy physics, these measures included the suspension of Russia’s Observer status and the decision not to engage in new collaborations with Russia and its institutions until further notice (CERN Courier May/June 2022 p7).

The Council also decided in June to review CERN’s future cooperation with the Joint Institute for Nuclear Research (JINR) well in advance of the expiration of the current ICA in January 2025. This follows measures adopted at the previous Council sessions to suspend the Observer status of JINR and the participation of CERN scientists in all JINR scientific committees, and vice versa, until further notice. The Council reaffirmed that all decisions taken to date, along with the actions undertaken by the CERN management, which have had a marked impact on the involvement of the Russian Federation and the Republic of Belarus in the scientific programme of the organisation, remain in force.

Ukraine joined CERN as an Associate Member State in 2016 and Ukrainian scientists have long been active in many of the laboratory’s activities. Russian scientists also have a long and distinguished involvement with CERN, and Russia was granted Observer status in recognition of its contributions to the construction of the LHC. At the June Council meeting, the Member States reiterated their denunciation of the continuing illegal military invasion, recalling that the core values of CERN (CERN Courier September/October 2022 p49) have always been based upon scientific collaboration across borders as a driver for peace, and stressing that the aggression of one country against another runs counter to these values.

Tour de QCD and beyond

The 56th Rencontres de Moriond on QCD and High Energy Interactions took place at the Italian resort of La Thuile from 19 to 26 March. More than 100 participants, almost equally split between experimentalists and theorists, were treated to an exciting scientific programme and many in-person interactions, which were especially appreciated after two years of pandemic isolation.

Keeping with the tradition of Moriond, several new experimental results were presented by major experimental collaborations, with participants enjoying ample opportunities to debate cases where measurements and theoretical predictions do not agree. Held 10 years after the Higgs discovery, the conference started with a review of how the Higgs boson came of age – from early exploration to a precision era. An exciting mix of new precision results and interesting observations in Higgs physics were presented, including the first measurement of the Higgs-charm coupling as well as studies of off-shell Higgs production and di-Higgs production by the ATLAS and CMS collaborations.

The first observation of tqγ production by ATLAS as well as many measurements in top-quark physics, including a mass measurement based on single top quarks by CMS, were discussed. Many recent studies of Z and W bosons and their interactions were reported, including a new CMS result that resolved an earlier mild LEP tension in the decay rates of W bosons to leptons, and the observation of triple-W production at the LHC by ATLAS. The LHCb collaboration presented its first measurement of the W mass, while CMS discussed the first observation of WW and triple-J/ψ production in double-parton scattering.

Several sessions were devoted to flavour measurements and anomalies, including possible lepton-flavour universality violations in B-meson decays. LHCb presented the most precise value of the CKM matrix angle γ measured in a single experiment, as well as the most precise measurement of the charm-mixing parameter y_CP. New results on lepton-flavour universality attracted a lot of attention. Among them are LHCb’s measurement of the ratio of Br(B⁺ → K⁺μ⁺μ^–) to Br(B⁺ → K⁺e⁺e^–), which is 3.1σ away from the SM, new LHCb limits on rare B⁰ decays, and the CMS measurement of the Drell–Yan forward–backward asymmetry difference between di-muons and di-electrons. The status of selected Standard Model (SM) calculations was described with the conclusion that the predictions are robust and therefore possible deficiencies of the SM a very unlikely source of the flavour anomalies. A number of talks demonstrated that there are many ways to accommodate the flavour anomalies into a consistent physics picture, which predicts subtle signals at the LHC that could have easily evaded detection so far.

Several speakers emphasised the importance of new creative analysis concepts

Continuing the topic of searches for new physics, several speakers emphasised the importance of new creative analysis concepts, including searching for anomalous energy losses, non-pointing tracks, delayed photons, displaced jets, displaced collimated leptons and tagging missing mass with forward detectors. Among the results of many interesting searches presented at Moriond, a 3σ excess in the number of highly ionising particles reported by the ATLAS collaboration caused some excitement and discussion, indicating that further studies (and statistics!) are very much needed.

Several talks presented theoretical predictions at high orders of perturbative QCD for basic SM processes at the LHC and future lepton colliders, such as the Drell–Yan and jet-production processes. These tour de force computations, representing cutting-edge applications of quantum field theory to collider physics, force us to think about how such advances in the theory of hard hadron collisions can be used to search for physics beyond the SM. Several talks addressed this issue by considering specific physics examples pointing towards new, exciting opportunities during LHC Run 3.

Emphasising the need for a refined knowledge of the fundamental input parameters used to describe hadron collisions, four new extractions of the strong coupling constant were reported, based on HERA, CDF, LEP and CMS data. The role of precision deep-inelastic scattering (HERA) and W/Z (ATLAS/CMS) data in constraining parton distribution functions was clearly elucidated.

An element of nonperturbative QCD that keeps theorists on their toes is hadronic spectroscopy

Turning towards the non-perturbative sector of QCD, a measurement of Λ_c production down to zero transverse momentum allowed the ALICE collaboration to extract the total charm cross-section in pp collisions. Interestingly, the fraction of Λ_c is significantly above the e⁺e^– baseline. Jet substructure measurements presented by ALICE and CMS allow a detailed comparison to Monte Carlo event generators. Furthermore, the first direct observation of the dead-cone effect, a suppression of forward gluon radiation in case of a massive emitter, was presented by the ALICE collaboration using charm-tagged jets.

An element of non-perturbative QCD that keeps theorists on their toes is hadronic spectroscopy. This trend continued at Moriond where the discoveries of several new states were presented, including the same-sign doubly charmed T⁺_cc(c–c–u–d) (LHCb) and the Z^–_cs (c–c–s–u) (BES III). The exploration of the χ_c1, earlier known as X(3872), with the hope of revealing its molecular or tetraquark nature, continues in pp as well as in PbPb collisions.

The best constraint of the charm diffusion coefficient in the quark–gluon plasma (ALICE), jet quenching studies with Z-hadron correlations (CMS) and surprising results on ridge structures in γp and γPb collisions (ATLAS) were presented during a dedicated heavy-ion session. Interestingly, by studying the abundant nuclei produced in heavy-ion collisions, the ALICE collaboration ruled out simple coalescence models for antideuteron production in PbPb collisions.

Finally, the current status of the muon anomalous magnetic moment was reviewed. The experimental value presented last year by the Fermilab g-2 collaboration shows a 1.5–4.2σ discrepancy with the SM prediction, depending on the theoretical baseline. An interesting comparison between continuum and lattice computations of the hadronic vacuum polarisation contributions was presented, and a new lattice result on hadronic light-by-light scattering was described, indicating that this “troublemaking” contribution is being brought under theoretical control.

Exciting experimental results and developments in the theory of QCD and high-energy interactions that, perhaps, remained somewhat hidden during the pandemic years, were on full display at Moriond, making the 56th edition of this conference a resounding success.

It all starts in the workshop

**Tailor-made** Florian Hofmann in front of a 5-axis milling and turning machine in the MME workshop. Credit: B Pérez Tapia

State-of-the-art particle accelerators and detectors cannot be bought off the shelf. They come to life in workshops staffed by teams of highly skilled engineers and technicians – such as heavy-machinist Florian Hofmann from Austria, who joined CERN in October 2019.

Florian is one of several hundred engineers and technicians employed by CERN to develop, build and test equipment, and keep it in good working order. He works in the machining and maintenance workshop of the mechanical and materials engineering (MME) group, which acts as a partner to many projects and experiments at CERN. “We tightly collaborate with all CERN colleagues and we offer our production facility and knowledge to meet their needs,” he explains. “Sometimes the engineers, the project leaders or even the scientists come to see how the parts of their work come together. It is a nice and humbling experience for me because I know they have been conceiving components for a very long time. Our doors are open and you don’t need special permission – everyone can come round!”

Before joining CERN, Florian began studying atmospheric physics at the University of Innsbruck. After two semesters, he realised that even though he liked science he preferred not to practise it, so decided to change to engineering and programming. After completing his studies and working in diverse fields such as automotive, tool making and water power plants, he joined CERN. Like many of his colleagues, his expertise and genuine curiosity for his work helps Florian to find tailor-made solutions for CERN’s challenging projects, every one of which is different, he explains. “Years ago the job used to be a traditional mechanics job, but today the cutting-edge technologies involved make this the Formula One of production.”

Heavy metal

Florian is currently working on aluminium joints for the vacuum tank of the kicker magnets for the Proton Synchrotron, a fundamental component on which the technicians collaborate with many other groups. The workshop is also contributing to numerous important projects such as the FRESCA2 cryostat, which is visible at the entry of the workshop, and the crab cavities for the High-Luminosity LHC upgrade. The radio-frequency quadrupole for Linac4, which now drives all proton production at CERN, was built here, as was the cryostat for the ICARUS neutrino detector now taking data at Fermilab and parts of the AMS-02 detector operating on the International Space Station. In the 1960s, the workshop was responsible for the construction of the Big European Bubble Chamber, now an exhibit in the CERN Microcosm.

Today, the cutting-edge technologies involved make this the Formula One of production

Before any heavy-machinery work begins, the machining team simulates the machining process to avoid failures or technical issues during fabrication. Although the software is highly reliable, Florian and his co-workers have to stand by to control and steer the machine, modifying commands when needed and ensuring that the activity is carried out as required. Every machine has one person in charge, the so-called technical referent, but the team receives basic training on multiple machines to allow them to jump onto a different one if necessary. The job stands out for its dynamism, Florian explains. “At the MME workshop, we perform many diverse manufacturing processes needed for accelerator technologies, not only milling and turning of the machine but also welding of exotic materials, among others. The possibilities are countless.”

Florian’s enthusiasm reflects the mindset of the MME workshop team, where everyone is aware of their contributions to the broader science goals of CERN. “This is a team sport. When you join a club you need it to have good management, and I think that here, because of our supervisors and our group responsibility, you are made to feel like everyone is pushing in the same direction.” Being curious, eager to learn and open-minded are important skills for CERN technicians, he adds.

“When you come to CERN you always leave with more than you can bring, because the experience of contributing to science, to bring nations together towards a better world, is really rewarding. I think everybody needs to ask themselves what they want and what kind of world they want to live in.”

Less, better, recover

Energy consumed and delivered — **Greener physics** Energy consumed (blue) and per luminosity delivered (green) by previous (solid circles) and future (open circles) LHC runs. Credit: S Claudet

The famous “Livingston diagram”, first presented by cyclotron co-inventor Milton Stanley Livingston in 1954, depicts the rise in energy of particle accelerators as a function of time. To assess current and future facilities, however, we need complementary metrics suited to the 21st century. As the 2020 update of the European strategy for particle physics demonstrated, such metrics exist: instead of weighing up colliders solely on the basis of collision energy, they consider the capital cost or energy consumption with respect to the luminosity produced.

Applying these metrics to the LHC shows that the energy used during the upcoming Run 3 will be around three times lower than it was during Run 1 for similar luminosity performance (see “Greener physics” figure). The High-Luminosity LHC (HL-LHC) will operate with even greater efficiency. In fact, CERN accelerators have drawn a similar power for a period of 40 years despite their vastly increased scientific output: from 1 TWh for LEP2 to 1.2 TWh for the LHC and possibly 1.4 TWh at the HL-LHC.

The GWh/fb^–1 metric has now been adopted by CERN as a key performance indicator (KPI) for the LHC, as set out in CERN’s second environmental report published last year. It has also been used to weigh up the performance of various Higgs factories. In 2020, for example, studies showed that an electron–positron Future Circular Collider is the most energy efficient of all proposed Higgs factories in the energy range of interest. But this KPI is only part of a larger energy-management effort in which the whole community has an increasingly important role to play.

In 2011, with the aim to share best practices amongst scientific facilities, CERN was at the origin of the Energy for Sustainable Science at Research Infrastructures workshop series. A few years later, prompted by the need for CERN to move from protected-tariff to market-based electricity contracts, the CERN energy management panel was created to establish solid forecasts and robust monitoring tools. Each year since 2017, we send virtual “electricity bills” to all group leaders, department heads and directors, which has contributed to a change of culture in the way CERN views energy management.

Best practice

Along with the market-based energy contract, energy suppliers have a duty by law (with tax-incentive mechanisms) to help their clients consume less. A review of energy consumption and upgrades conducted between CERN and its electricity supplier EDF in 2017 highlighted best practices for operation and refurbishment, leading to the launch of the LHC-P8 (LHCb) heat-recovery project for the new city area of Ferney-Voltaire. Similar actions were proposed for LHC-P1 (ATLAS) to boost the heating plant at CERN’s Meyrin site, and heat recovery has been considered as a design and adjudication parameter for the new Prevessin Computer Centre. Besides an attractive 5–10 year payback time, such programmes make an important contribution to reducing CERN’s carbon footprint.

**Serge Claudet** is chair of the CERN energy management panel. Credit: S Claudet

Energy efficiency and savings are an increasingly important element in each CERN accelerator infrastructure. Completed during Long Shutdown 2, the East Area renovation project led to an extraordinary 90% reduction in energy consumption, while the LHC Injectors Upgrade project also offered an opportunity to improve the injectors’ environmental credentials. Energy economy was also the primary motivation for CERN to adopt new regenerative power converters for its transfer lines. These efforts build on energy savings of up to 100 GWh/y since 2010, for example by introducing free cooling and air-flow optimisation in the CERN Computer Centre, and operating the SPS and the LHC cryogenics with the minimum of necessary machines. CERN buildings are also aligning with energy- efficiency standards, with the renovation of up to two buildings per year planned over the next 10 years.

There will be no future large-scale science projects without major energy-efficiency and recovery objectives

This year, a dedicated team at CERN is being put together concerning alignment with the ISO50001 energy-management standard, which could bring significant subsidies. A preliminary evaluation was conducted in November 2021, demonstrating that 54% of ISO expectations is already in place and a further 15% is easily within reach.

The mantra of CERN’s energy-management panel is “less, better, recover”. We also have to add “credible” to this list, as there will be no future large-scale science projects without major energy-efficiency and recovery objectives. Today and in the future, we must therefore all work to ensure that every MWh of energy consumed brings demonstrable scientific advances.

Claude Bouchiat 1932–2021

Theoretical physicist Claude Bouchiat, who was born in Saint-Matré (southern France) on 16 May 1932, passed away in Paris on 25 November. He was a frequent visitor to the CERN theory group.

Bouchiat studied at the École Polytechnique in 1953–1955, and discovered theoretical high-energy physics after listening to a seminar by the late Louis Michel. In 1957, having been impressed by a conference talk given by C N Yang during a short visit to Paris, he decided to extend Michel’s results on the electron spectrum in muon decays to include the effects of parity violation. This work led to the Bouchiat–Michel formula. He then joined the theoretical physics laboratory (newly created by Maurice Lévy) at the University of Orsay where, together with Philippe Meyer, he founded a very active group in theoretical particle physics. In the 1960s, during several visits to CERN, he collaborated with Jacques Prentki. In 1974 Bouchiat and Meyer moved to Paris and established the theoretical physics laboratory at the École Normale Supérieure (ENS).

Bouchiat’s research covered a large domain that extended beyond particle physics. With Prentki and one of us (JI) he studied the leading divergences of the weak interactions, which was a precursor to the introduction of charm, and with Daniele Amati and Jean-Loup Gervais showed how to build dual diagrams satisfying the unitarity constraints. The trio also extended the anomaly equations in the divergence of the axial current to non-abelian theories. In the early 1970s, Bouchiat and collaborators used quantum field theory in the infinite momentum frame to shed light on the parton model. In 1972, with Meyer and JI, he formulated the anomaly cancellation condition for the Standard Model, establishing the vanishing sum of electric charges for quarks and leptons as essential for the mathematical consistency of the theory.

Probably his most influential contribution, carried out with his wife Marie-Anne Bouchiat, was the precise computation of parity-violation effects resulting from virtual Z-boson exchange between electrons and nuclei. They pointed out an enhancement in heavy atoms that rendered the tiny effect amenable to observation. This work opened a new domain of experimental research, starting first at ENS, which played an important role alongside the high-energy experiments at SLAC in confirming the structure of the weak neutral current. Examples of Bouchiat’s contributions outside particle physics include his studies of the elasticity properties of DNA molecules and of the geometrical phases generated by non-trivial space topology in various atomic and solid-state physics systems.

During his 60-year-long career, Claude Bouchiat had a profound influence on the development of French theoretical high-energy physics. He helped nurture generations of young theorists, and many of his former students are well-known physicists today.

The LHC experience up close

ATLAS end-cap calorimeter and toroidal magnet — **Higgs quest** One ATLAS end-cap calorimeter and the toroidal magnet in 2007. Credit: C Marcelloni/CERN-EX-0702016-10

With this ambitious book, the authors have produced a unique and excellent account of particle physics that goes way beyond a description of the LHC project. Its 600 pages are a very pleasant, although tough in places, read. The book serves as a highly valuable refresher of modern concepts of particle physics, recalling theoretical ideas as well as explaining advanced detector technologies and analysis methods that set the stage for the LHC experiments and the Higgs-boson discovery. Even though the focus converges on the Higgs boson, the full LHC project and its rich physics playground are well covered, and furthermore embedded in the broader context of particle physics and cosmology, as the subtitle indicates.

In a way, it is a multi-layered book, which makes it appealing for the selective reader. Each layer is in itself of great value and highly recommendable. The overarching presentation is attractive, with great photos, nicely prepared graphics and diagrams, and a clear structure guiding readers through the many chapters. Quite unique are the more than 50 inserted text boxes, typically one to three pages long, which explain in a concise way the concepts used in the main text. Experts may wish to skip some of them, but they are very educational (at least as a refresher) for most readers, as they were for me. The text boxes are ideal for students and science enthusiasts of all ages, although some are more demanding than others.

To start, the authors take the reader off into a substantial 170-page introduction to particle physics in general, and to the Standard Model (SM) in particular. Its theoretical ideas and their mathematical formulations, as well as its key experimental foundation, are clearly presented. The authors also explore with a broad view what the SM cannot explain. Some material in these introductory chapters are the most demanding parts of the book. The theoretical text boxes are a good opportunity for physics students to recall previously-acquired mathematical notions, but they are clearly not meant for non-experts, who can readily skip them and concentrate more on the very nicely documented historical accounts. A short and accessible chapter “Back to the Big Bang” concludes the introductions by embedding particle physics into the broader picture of cosmology.

The Adventure of the Large Hadron Collider — Credit: World Scientific

Next, the LHC and the ATLAS and CMS experiments enter the stage. The LHC project and its history is introduced with a brief reminder of previous hadron colliders (ISR, Spp–S and Tevatron). The presentation of the two general-purpose detectors comes with a short refresher on particle detection and collider experiments. Salient technical features, and collaboration aspects including some historical anecdotes, are covered for ATLAS and CMS. The book continues with the start-up of the machine, including the scary episode of the September 2008 incident, followed by the breathtaking LHC performance after the restart in November 2009 with Runs 1 and 2, until Long Shutdown 2, which began in 2019.

The story of the Higgs-boson discovery is set within a comprehensive framework of the basics of modern analysis tools and methods, a chapter again of special value for students. Ten years later, it is a pleasure to read from insiders how the discovery unfolded, illustrated with plenty of original physics plots and photographs conveying the excitement of the 4 July 2012 announcement. A detailed description of the rich physics harvest testing the Higgs sector as well as challenging the SM in general provides an up-to-date collection of results from the LHC’s first 10 years of physics operations.

A significant chapter “Quest for new physics” follows, giving the reader a good impression of the many searches hunting for physics beyond the SM. Their relations to, and motivations from, theoretical speculations and astroparticle-physics experiments are explained in an accessible and attractive way.

A book about the LHC wouldn’t be complete without an excursion to the physics and detectors of flavour and hot and dense matter. With the dedicated experiments LHCb and ALICE, respectively, the LHC has opened exciting new frontiers for both fields. The authors cover these well in a lean chapter introducing the physics and commenting on the highlights so far.

A look ahead and conclusion round off this impressive document about the LHC’s main mission, the search for the Higgs boson. Much more SM physics has since been extracted, as is amply documented. However, as the last chapter indicates, the journey to find directions to new physics beyond the SM must go on, first with the high-luminosity upgrades of the LHC and its experiments, and then preparing for future colliders reaching either much higher precision on the Higgs-boson properties or higher energies for exploring higher mass particles. Current ideas for such projects that could follow the LHC are briefly introduced.

The authors are not science historians, but central actors as experimental physicists fully immersed in the LHC adventure. They deliver lively first-hand and personal accounts, all while carefully respecting the historical facts. Furthermore, the book is preceded by a bonus track: the reader can enjoy an inspiring and substantial foreword by Carlo Rubbia, founding father and tireless promoter for the LHC project in the 1980s and early 1990s.

I can only enthusiastically recommend this book, which expands significantly on the French version published in 2014, to all interested in the adventure of the LHC.

Picture a scientist

“If you had to picture a scientist, what would it look like?” That is the question driving the documentary film Picture a Scientist, first released in April 2020 and screened on 10 February this year at the CERN Globe of Science and Innovation. Directed by Emmy-nominated Sharon Shattuck and Ian Cheney, whose previous productions include From This Day Forward (2016) and The Long Coast (2020), respectively, the 97 minute film tackles the difficulties faced by women in STEM careers. It is centered on the experiences of three US researchers – molecular biologist Nancy Hopkins (MIT), chemist Raychelle Burks (St. Edward’s University) and geologist Jane Willenbring (UC San Diego) – among others who have faced various forms of discrimination during their careers.

Hopkins talks about the difficulties she faced as a student in the 1950s and 1960s, when the education system didn’t offer many maths and science lessons to girls, and shares an experience of sexual harassment involving a famous biologist during a lab visit. Willenbring also experienced various mistreatments, including inappropriate nicknames and harassment from a colleague during a 1999 field trip in Antarctica. The film describes how these two anecdotes are just the tip of the iceberg of discrimination that has historically affected female scientists and is still present today. Less visible examples include being ignored in meetings, being treated as a trainee, receiving inappropriate emails and not getting proper credit for work.

Burks, who is Black, explains how the situation is even worse for women of different ethnic groups, as they are even more underrepresented in science. During her childhood, she recalls, most female Black scientists were fictional, such as Star Trek’s communications officer Nyota Uhura.

Being a scientist does not rely on race or gender but only on the love for science

The film highlights the importance of female scientists speaking out to help people see beyond the tip of the iceberg and allow them to act. Hopkins recounts how she once wrote a letter to the president of MIT in which she described systemic and invisible discrimination such as office space being larger for men than for women. Supported and encouraged by female colleagues, it led to a request to the dean of MIT for greater equality. Another example ultimately led the president of Boston University to dismiss the male researcher who had bullied Willenbring, after receiving many reports of gender harassment.

However, even though progress has been made, the film makes it clear – for example through graphs showing the considerable underrepresentation of women in science – that there is still much to do. “By its own nature science itself should be always evolving,” says Burks: we should be able to identify the idea of a scientist as someone fascinated about research rather than based on its stereotype.

Videos recreating scenes of the bullying described and footage from old TV shows showing the historical mistreatment of women complement candid accounts from those who have experienced discrimination, allowing the viewer to understand their experiences in an impactful way. Some scenes are hard to watch, but are necessary to understand the problem and therefore take steps to increase the recognition of women in STEM careers.

This film raises the often silenced voice of female scientists who have been discriminated against, and makes it clear that being a scientist does not rely on race or gender but only on the love for science. “If you believe that passion and ability for science is evenly distributed among the sexes, then if you don’t have women, you have lost half of the best people,” states Hopkins. “Can we really afford to lose those top scientists?”

Topics

Reset your password

Registration complete