Jobs – Page 52 of 504

Upsilon suppression in heavy-ion collisions

CMS figure 1 — **Fig. 1.** The nuclear modification factor R_AA of the three ϒ states, as a function of <N_part> (besides the centrality-integrated values). The error bars (boxes) represent the statistical (systematic) uncertainties. The boxes at unity represent global systematic uncertainties, for both the ϒ(2S) and ϒ(3S) points (open), and for only the ϒ(2S) (purple) or ϒ(3S) (green) mesons. Source: CMS-PAS-HIN-21-007

The bound states of a heavy quark and its antiquark, called quarkonia, have long been regarded as ideal probes to study the quark–gluon plasma (QGP) formed in high-energy heavy-ion collisions. The golden signature is the suppression of their production yield in lead–lead (PbPb) collisions with respect to extrapolations from proton–proton (pp) collisions, caused by modifications of the binding potential in the QGP. The suppression of the different quarkonium states is expected to depend on their binding energies. Quarkonia can also be produced by recombination processes. The ϒ states (bound states of b quarks and antiquarks) are much less affected by recombination effects than charmonium states, given the very small probability that b quarks are produced. A comparison of their suppression patterns is particularly informative because of the different binding energies of the ϒ(1S), ϒ(2S) and ϒ(3S) states.

The suppression of quarkonium production is quantified via the nuclear modification factor R_AA, defined as the ratio between the yield in nucleus–nucleus (AA) collisions and the yield extrapolated from pp data. Previous measurements of R_AA for the ϒ mesons by experiments at RHIC and the LHC revealed a significant suppression of the ϒ(1S) state and a larger suppression for the ϒ(2S) state. However, these experiments could only set upper limits for the ϒ(3S) state due to its very low production yield. The CMS experiment recently changed this situation by presenting the first observation of the ϒ(3S) meson in heavy-ion collisions. The ϒ mesons are detected using their decay to two muons. The analysis used the large PbPb data sample collected in 2018 and extracted the ϒ(3S) signals from the large background of muon pairs by using a boosted decision tree algorithm.

The new R_AA results are shown together with the previously published ϒ(1S) values as a function of the average number of nucleons participating in the PbPb collisions, <N_part> (figure 1). Collisions with larger <N_part> show a bigger overlap between the two nuclei, producing a larger and hotter QGP. As previously observed, the degree of suppression increases from peripheral to central collisions, i.e. as N_part increases, indicating a more substantial dissociation effect at higher QGP temperatures. The new ϒ(3S) suppression measurement completes the picture of suppression patterns for five different quarkonium states, which was started 35 years ago at the CERN SPS with the J/ψ and ψ(2S) results of NA38. The stage is set for a deeper understanding of deconfinement in the QGP.

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.

X-ray polarisation probes extreme physics

Accretion disk around magnetar 4U 0142+61 — **Magnetar** Artistic depiction of the accretion disk around the magnetar 4U 0142+61, located in the Cassiopeia constellation 13,000 lights years away. Credit: NASA/JPL-Caltech/R Hurt (SSC)

X-ray astronomy has been around for more than 50 years and remains responsible for a wealth of discoveries. Astronomical breakthroughs have been the result of detailed measurements of the X-ray arrival time, direction and energy. But the fourth measurable parameter of X-rays, their polarisation, remains largely unexplored. Following the first rough measurements of a handful of objects in the 1970s by Martin Weisskopf and co-workers, there was a hiatus in X-ray polarimetry due to the complexity of the detection mechanism. In recent years, in parallel with the emergence of gamma-ray polarimetry, interest in the field has returned. Indeed, after some initial measurements using the Chinese–Italian PolarLight Cubesat launched in October 2018, X-ray polarimetry has reached full maturity with the launch of the first large-scale dedicated observatory in December 2021: the Imaging X-ray Polarimetry Explorer (IXPE), a joint project by NASA and the Italian Space Agency, led by Weisskopf.

The IXPE mission uses gas pixel detectors to measure the polarisation for a range of astronomical sources in the 2-8 keV energy range. Incoming X-rays are absorbed in a gas which results in the emission of a photoelectron, the azimuthal emission direction of which is correlated with the polarisation vector of the incoming photon. Tracking the path of the electron therefore allows the polarisation to be inferred. Accurately measuring the emission direction of the low-energy photoelectron, especially in a space-based detector, has been one of the main IXPE challenges and required decades of detector development.

X-ray polarimetry has reached full maturity with the launch of the first large-scale dedicated observatory

IXPE has already observed a range of sources. Its first public results, posted on arXiv on 18 May, concern a magnetar, a highly magnetic neutron star, called 4U 0142+61, which rotates around its axis in about 8 s and has a magnetic field of 10¹⁰ T. IXPE’s first ever measurement of polarised emission from a magnetar in the X-ray region shows this extreme object to have an energy-integrated polarisation degree of 12%, while in the thermal (2–4 keV) range this is about 12%, and as high as 41% for emission at higher energies (5.5–8 keV). The polarisation angles of the two emission components are orthogonal.

The results appear to agree best with a model where the thermal emission stems from a condensed iron atmosphere: the higher energy emission would be a result of some thermal photons being up-scattered to higher energies when interacting with charged particles following the magnetic field lines. However, since other models link the emission to a gaseous atmosphere heated by a constant bombardment of particles, measurements of additional magnetars are needed.

Fundamental physics

Apart from providing novel insights into neutron-star properties, time-resolved studies of the emission during the rotation period hints at more fundamental physics at play. The spectral profile of 4U 0142+61 was found to be rather constant during the rotation, indicating that the emission does not come from hot-spots, such as the poles, but rather from a large area on the surface. As the magnetic field over such a large area would, however, be expected to vary significantly, so would the polarisation angle of the emitted X-rays. As a result, the net polarisation seen on Earth would largely be blurred out, resulting in a much lower polarisation degree than is observed.

An intriguing explanation for this, note the authors, is vacuum birefringence – an effect predicted to be important in the presence of extreme magnetic fields, but which has never been observed. While for the magnetar the polarisation angle of the emission varies with the emission location, it gets altered as the photons travel through the strong magnetic field in which continuous electron–positron pairs affect their propagation. Only when the magnetic field is weak enough, at around 100 times the radius of the star, does the polarisation angle get frozen. Since this angle is aligned with the magnetic field, which at this point is smoother, the emission will realign the emission travelling towards Earth and allow for a net polarisation.

Although the polarisation degrees measured by IXPE are not high enough to definitively prove vacuum birefringence, the results give a clear hint. Furthermore, the measurements of 4U 0142+61 are only the first of many performed by the IXPE team. Throughout the coming months, detailed measurements of galactic objects such as the Crab Nebula, as well as extra-galactic sources, are predicted to be released. Among these objects there will be other magnetars, the X-ray emission from which will soon bring further understanding of these extreme objects and potentially confirm the existence of vacuum birefringence.

Superconducting magnets: an enabling technology for the discovery of the Higgs boson

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This webinar is focused on the technology of the superconducting magnets used in the LHC. After reviewing the equations for an electromagnet, we show how superconductivity enables much larger magnetic fields in very compact devices, thanks to the possibility of increasing the current density in the windings by more than two order of magnitudes with respect to resistive conductors. We then outline the development of superconducting accelerator magnets from the ISR quadrupoles, up to the LHC and beyond.

We conclude by describing the successive increases of LHC energy since 2008 up to the 6.8 TeV per beam recently achieved, and show how the control of field imperfections has been an essential element for reaching the ultimate luminosity.

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Ezio Todesco was born in Bologna Italy, where he got a PhD in physics. In the 90’s, after a master thesis at CERN, he worked at the Italian national institute of nuclear physics (INFN) on topics related to nonlinear dynamics of particle accelerators, and long-term stability in the planned Large Hadron Collider. He joined the magnet group at CERN in 1998, and has been in charge of the field quality follow-up of the LHC main dipoles and quadrupole during the five-year-long magnet production. After the completion of the production phase, he has been in charge of the magnetic field model of the LHC, following the initial commissioning and the successive energy increases up to 13 TeV centre of mass. Then, he has been involved in the studies of the LHC luminosity upgrade, and he leads the interaction region magnets for HL-LHC since the beginning of the project in 2015.

Why not watch our other related Higgs boson anniversary webinars?

• RF technology for LHC and HL-LHC

• The LHC cryogenics and its adaptation to the operational parameters for beams, related physics and energy preservation

RF technology for LHC and HL-LHC

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This webinar, presented by Frank Gerigk, will provide an overview of the LHC RF system, its superconducting cavities and RF power system. It also introduce the changes, which will be implemented to accelerate the high-intensity beams of the HL-LHC era.

Join this webinar to:
• Learn about the technology that accelerates LHC protons from 450 GeV to 7 TeV.
• Appreciate the development of the superconducting cavities used in the LHC.
• Understand how the LHC system will be modified for HL-LHC and how crab cavities will increase the number of collisions.

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Frank Gerigk is the leader of the Radio Frequency (RF) Group at CERN. After graduating at the Technical University Berlin in 1999, he came to CERN as a fellow to work on RF and beam dynamics for linear accelerators. In 2002, he became staff member at the Rutherford Appleton Laboratory in the UK, continuing with beam dynamics and focussing on halo development in hadron beams. After his return to CERN in 2005, Frank joined the RF group and soon became responsible for the Linac4 RF cavities. He became section leader for Linac RF in 2012, and then for Superconducting RF in 2018. Since 2020 he has been leading the RF group in the new Systems Department.

Why not sign up for our other related Higgs boson anniversary webinars?

• Superconducting magnets: an enabling technology for the discovery of the Higgs boson

• The LHC cryogenics and its adaptation to the operational parameters for beams, related physics and energy preservation

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.

Sylvie Rosier-Lees 1961–2022

Sylvie Rosier-Lees left us on 14 March 2022 following a long illness, which she endured with immense courage. Following her studies at the Ecole normale supérieure de Fontenay-Saint-Cloud, Sylvie began her research career in 1985 with a thesis on the L3 experiment at LEP. There were several of us – new to the Laboratoire d’Annecy de Physique des Particules (LAPP) at the time – with the idea of strengthening the existing L3 team, and Sylvie was our first student. Her inquisitive mind, tenacity and ability to face experimental problems – in particular concerning the calibration of the BGO crystals – quickly made her stand out within the collaboration.

Before becoming a highly regarded specialist in supersymmetry, she studied the identification of B mesons produced in Z decays, which made it possible to contribute to the first measurements of the B°–B° mixing parameter as well as the forward–backward asymmetry. Supersymmetry and the search for the neutralino set Sylvie on the quest for dark matter, to which she subsequently dedicated her entire career. In 2000 she joined the Alpha Magnetic Spectrometer (AMS) collaboration – a particle-physics detector installed on the International Space Station to identify and measure fluxes of cosmic rays. She took over responsibility for the readout electronics of the electromagnetic calorimeter, introducing independent rapid triggering based solely on calorimetry. Resistance to radiation, extended temperature range, low power consumption and operation in vacuum were all technical challenges that were met thanks to Sylvie’s scientific rigour and exceptional human qualities. She had an enthusiasm and leadership that motivated and led to the success of everyone in her team. More than 15 years after its completion in 2005 and more than 10 years after its first signal on 19 May 2011, the calorimeter’s electronics are still smoothly providing data. With AMS, she searched for dark matter via deformations of antiparticle fluxes, for example in the fraction of positrons detected, one of the first AMS publications

In 2005 Sylvie created a HESS group at LAPP. The Namibia-based gamma-ray telescope had entered its second phase with the construction of the fifth telescope, the largest with a focal length of 36 m. Sylvie took up the challenge of an ambitious mechanical project to load and unload the camera – a cube 2.5 m high and weighing 2.6 tonnes – from its data-taking position 5 m from the ground to a shelter at ground level. She then explored the potential of the facility for dark-matter searches, since its size allowed the detection threshold of photons to be lowered to 50 GeV.

Throughout her career, Sylvie maintained close ties with phenomenologists and theorists. This collaboration began at LEP within the framework of a national supersymmetry group, where she coordinated an influential working group on the Minimal Supersymmetric Standard Model. Subsequently, with theorists, she obtained a lower bound on the mass of the lightest neutralino, a candidate for dark matter, by combining astrophysical, cosmological and collider observables. She also notably contributed to the development of an extension of the still widely used micrOMEGAs code, making it possible to calculate the spectrum of positrons and antiprotons coming from the annihilation of dark-matter particles in the galaxy.

Always positive with students, Sylvie supervised or co-supervised around 10 theses. All these elements earned her the 2017 Joliot-Curie Prize awarded by the French Physical Society. Her enthusiasm, energy and good humour are sorely missed. We are thinking of Jean-Pierre, her husband, and her sons Edouard and Arthur.

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.

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