Jobs – Page 13 of 505

EIC steps towards construction

**Shaping up** A schematic of the future Electron–Ion Collider at Brookhaven National Laboratory. Credit: BNL/T Bowman

The Electron–Ion Collider (EIC), located at Brookhaven National Laboratory and being built in partnership with Jefferson Lab, has taken a step closer to construction. In April the US Department of Energy (DOE) approved “Critical Decision 3A”, which gives the formal go-ahead to purchase long-lead procurements for the facility.

The EIC will offer the unique ability to collide a beam of polarised high-energy electrons with polarised protons, polarised lightweight ions, or heavy ions. Its aim is to produce 3D snapshots or “nuclear femtography” of the inner structure of nucleons to gain a deeper understanding of how quarks and gluons give rise to properties such as spin and mass (CERN Courier October 2018 p31). The collider, which will make use of infrastructure currently used for the Relativistic Heavy Ion Collider and is costed at between $1.7 and 2.8 billion, is scheduled to enter construction in 2026 and to begin operations in the first half of the next decade.

By passing the latest DOE project milestone, the EIC project partners can now start ordering key components for the accelerator, detector and infrastructure. These include superconducting wires and other materials, cryogenic equipment, the experimental solenoid, lead-tungstate crystals and scintillating fibres for detectors, electrical substations and support buildings. “The EIC project can now move forward with the execution of contracts with industrial partners that will significantly reduce project technical and schedule risk,” said EIC project director Jim Yeck.

More than 1500 physicists from nearly 300 laboratories and institutes worldwide are members of the EIC user group. Earlier this year the DOE and the CNRS signed a statement of interest concerning the contribution of researchers in France, while the UK announced that it will invest £58.8 million to develop the necessary detector and accelerator technologies.

BESIII passes milestone at the charm threshold

The BESIII collaboration has marked a significant milestone: the completion of its 15-year campaign to collect 20 fb^–1 of e⁺e^– collision data at the ψ(3770) resonance. The sample, collected in two main running periods, 2010–2011 and 2022–2024, is more than 20 times larger than the world’s previous charm-threshold data set collected by the CLEO-c experiment in the US.

BESIII is an experiment situated on the BEPCII storage ring at IHEP in Beijing. It involves more than 600 physicists drawn not only from China but also other nations, including Germany, Italy, Poland, the Netherlands, Sweden and the UK from the CERN member states. The detector has collected data at a range of running points with centre-of-mass energies from 1.8 to 4.95 GeV, most of which are inaccessible to other operating colliders. This energy regime allows researchers to make largely unique studies of physics above and below the charm threshold, and has led to important discoveries and measurements in light-meson spectroscopy, non-perturbative QCD, and charm and tau physics.

The ψ(3770), discovered at SLAC in 1977, is the lightest charmonium state above the open-charm threshold. Charmonium consists of a bound charm quark and anti-charm quark, whereas open-charm states such as D⁰ and D⁺ mesons are systems in which the charm quark co-exists with a different anti-quark. The ψ(3770) can decay into D and anti-D mesons, whereas charmonium states below threshold, such as the J/ψ, are too light to do so, and must instead decay through annihilation of the charm and anticharm quarks.

The sample is more than 20 times larger than the world’s previous charm-threshold data set

Open-charm mesons are also produced in copious quantities at the LHC and at Belle II. However, in ψ(3770) decays at BESIII they are produced in pairs, with no accompanying particles. This makes the BESIII sample a uniquely clean laboratory in which to study the properties of D mesons. If one meson is reconstructed, or tagged, in a known charm decay, the other meson in the event can be analysed in an unbiased manner. When reconstructed in a decay of interest, the unbiased sample of mesons can be used to measure absolute branching fractions and the relative phases between any intermediate resonances in the D decay.

“Both sets of information are not only interesting in themselves, but also vital for studies with charm and beauty mesons at LHCb and Belle II,” explains Guy Wilkinson of the University of Oxford. “For example, measurements of phase information performed by BESIII with the first tranche of ψ(3770) data have been essential input in the world-leading determination of the CP-violating angle γ of the unitarity triangle by LHCb in events where a beauty meson decays into a D meson and an accompanying kaon.” Exploitation of the full 20 fb^–1 sample will be essential in helping LHCb and Belle II realise their full potential in CP-violation measurements with larger data sets in the future, he adds. “Hence BESIII is very complementary to the higher energy experiments, demonstrating the strong synergies that exist between particle-physics facilities worldwide.”

This summer, BEPCII will undergo an upgrade that will increase its luminosity. Over the rest of the decade more data will be taken above and below the charm threshold. In the longer term, there are plans, elsewhere in China, for a Super Tau Charm Facility – an accelerator that would build on the BEPCII and BESIII programme with datasets that are two orders of magnitude larger.

New subdetectors to extend ALICE’s reach

ALICE components — **Upgrade ahead** ALICE’s new forward calorimeter (left) and the components of the Inner Tracker System 3. Credit: ALICE

The LHC’s dedicated heavy-ion experiment, ALICE, is to be equipped with an upgraded inner tracking system and a new forward calorimeter to extend its physics reach. The upgrades have been approved for installation during the next long shutdown from 2026 to 2028.

With 10 m² of active silicon and nearly 13 billion pixels, the current ALICE inner tracker, which has been in place since 2021, is the largest pixel detector ever built. It is also the first detector at the LHC to use monolithic active pixel sensors (MAPS) instead of the more traditional hybrid pixels and silicon microstrips. The new inner tracking system, ITS3, uses a novel stitching technology to construct MAPS of 50 µm thickness and up to 26 × 10 cm² in area that can be bent around the beampipe in a truly cylindrical shape. The first layer will be placed just 2 mm from the beampipe and 19 mm from the interaction point, with a much lighter support structure that significantly reduces the material volume and therefore its effect on particle trajectories. Overall, the new system will boost the pointing resolution of the tracks by a factor of two compared to the present ITS detector, strongly enhancing measurements of thermal radiation emitted by the quark–gluon plasma and enabling insights into the interactions of charm and beauty quarks as they propagate through it.

The new forward calorimeter, FoCal, is optimised for photon detection in the forward direction. It consists of a highly granular electromagnetic calorimeter, composed of 18 layers of 1 × 1 cm² silicon-pad sensors paired with tungsten converter plates and two additional layers of 30 × 30 μm² pixels, and a hadronic calorimeter made of copper capillary tubes and scintillating fibres. By measuring inclusive photons and their correlations with neutral mesons, as well as the production of jets and charmonia, FoCal will add new capabilities to explore the small Bjorken-x parton structure of nucleons and nuclei.

Technical design reports for the ITS3 and FoCal projects were endorsed by the relevant CERN review committees in March. The construction phase has now started, with the detectors due to be installed in early 2028 in order to be ready for data taking in 2029. The upgrades, in particular ITS3, are also an important step on the way to ALICE 3 – a major proposed upgrade of ALICE that, if approved, would enter operation in the mid-2030s.

First DESI results shine a light on Hubble tension

The expansion of the universe has been a well-established fact of physics for almost a century. By the turn of the millennium the rate of this expansion, referred to as the Hubble constant (H₀), had converged to a value of around 70 km s^–1 Mpc^–1. However, more recent measurements have given rise to a tension: whereas those derived from the cosmic microwave background (CMB) cluster around a value of 67 km s^–1 Mpc^–1, direct measurements using a local distance-ladder (such as those based on Cepheids) mostly prefer larger values around 73 km s^–1 Mpc^–1. This disagreement between early- and late-universe measurements, respectively, stands at the 4–5σ level, thereby calling for novel measurements.

One such source of new information are large galaxy surveys, such as the one currently being performed by the Dark Energy Spectroscopic Instrument (DESI). This Arizona-based instrument uses 5000 individual robots that optimise the focal plane of the detector to allow it to measure 5000 galaxies at the same time. The goal of the survey is to provide a detailed 3D map, which can be used to study the evolution of the universe by focussing on the distance between galaxies. During its first year of observation, the results of which have now been released, DESI has provided a catalogue of millions of objects.

Primordial imprints

Small fluctuations in the density of the early universe resulted not only in signatures in the CMB, as measured for example by the Planck probe, but also left imprints in the distribution of baryonic matter. Each over-dense region is thought to contain dark matter, baryonic matter and photons. The gravitational force from dark matter on the baryons is countered by radiation pressure from the photons. From the small over-densities, baryons are dragged along by photon pressure until these two types of particles decoupled during the recombination era. The original location of the over-density is surrounded by a sphere of baryonic matter, which typically is at a distance referred to as the sound horizon. The sound horizon at the moment of decoupling, denoted r_d, leaves an imprint that has since evolved to produce the density fluctuations in the universe that seeded large-scale structures.

Constraints on the Hubble constant assuming the flat ΛCDM model — **Hubble tension** 68% credible-interval constraints on the Hubble constant assuming the flat ΛCDM model, showing: DESI baryon acoustic oscillation measurements in combination with other data (blue, bold); corresponding results from the Sloan Digital Sky Survey and combinations thereof (blue); CMB anisotropy measurements from Planck and the Atacama Cosmology Telescope (orange); and measurements using Cepheids or tip-of-the-red-giant branch distance ladders (green). Source: arXiv:2404.03002

This imprint, and how it has evolved over the last 13 billion years, depends on a number of parameters in the standard ΛCDM model of cosmology. Measuring the baryon distribution therefore allows many of the ΛCDM parameters to be constrained. Since the DESI data measure the combination of H₀ and r_d, a direct measurement of H₀ is not possible. However, by using additional data for the sound horizon, taken from CMB measurements and Big Bang nucleosynthesis theory, the team finds values of H₀ that cluster around 67.5 km s^–1 Mpc^–1 (see “Hubble tension” figure). This is consistent with early-universe measurements and differs by more than 3σ from late-universe measurements.

Although these new results do not directly resolve the Hubble tension, they do hint at one potential solution: the need to revise the ΛCDM model. The measurements also allow constraints to be placed on the acceleration of the universe, which depends on the dark-energy equation of state, w. While this is naturally assumed to be constant at w = –1, the DESI first-year results better match a time-evolving equation of state. Although highly dependent on the analysis, the DESI data so far provide results that differ from ΛCDM predictions by more than 2.5σ. The data from the remaining four years of the survey are therefore highly anticipated as these will show whether a change to the standard cosmological model is required.

Strengthening science in Europe

Why theoretical cosmology?

I was first trained as a mathematician, and then as a physicist. I’ve always worked at the interface between theory and data, where one of the most interesting things is to test cosmological models inspired by some fundamental theory. For example, you can create a model based on string theory or on a non-perturbative approach to quantum gravity, and then use data to constrain the quantum gravity theory. Today we receive a wealth of data from different kinds of experiments, which allows us to test early-universe models without relying on ad hoc ideas. Although it is not something I directly work on, the current tension in the value of the Hubble constant serves as an example. This of course could be telling us something about new physics, but it seems to me it is more likely to be an issue with the way we interpret data and apply the same models across different scales. Supernovae are taken as “standard candles” when measuring the expansion rate of the universe, for example, and one may wonder how correct this assumption is. It is important to perform systematic studies of the raw data before we rush to new theories.

My current work mainly bears on gravitational waves. I am also editor-in-chief of the journal General Relativity and Gravitation. I joined the LIGO collaboration the year of the discovery, studying the implications of gravitational-wave background searches for new physics. I am working on similar studies for the proposed Einstein Telescope. Gravitational waves allow us to test high-energy models beyond the Standard Model at energy scales that are above those that can be reached by accelerators. There are also new results coming from pulsar timing arrays. We live in a time where many exciting results are coming fast.

How big is the European Physical Society, and what led you to be elected president?

The European Physical Society (EPS) is the federation of all national physics societies in Europe. It was founded in 1968 by particle physicist Gilberto Bernardini, who contributed to the foundation of CERN and later became director of the Synchrocyclotron division and directorate member for research.

Several years ago, following the LIGO/Virgo discoveries, I initiated the gravitational physics division of the EPS and, in doing so, entered the EPS council. Then I was elected a member of the executive committee and was eventually contacted to run for election. I admit that I was reluctant at first because it’s another task with a lot of responsibilities. But it turned out I was elected, and I took up the position formally on April 27th. I am proud to have been elected as president and I will do my best to serve the EPS and respect the confidence that representatives of so many European national societies have put in me.

What do you hope to achieve during your two-year mandate?

I have several goals as president. The most important one is to strengthen the position of Europe. What do I mean by that? There are important issues that we all face together, such as our economic independence (for instance, sources of energy, technological advances in electronics, biophysics and medical applications) and the preservation of the environment. The EPS can play a role by building teams of experts to address these issues, to be in a position to advise policy makers at the European level.

The proposed Future Circular Collider — **Collider talk** The EPS can support constructive dialogue about major projects such as the proposed Future Circular Collider at CERN. Credit: Pixel Rise

Scientific policy is another example. We live in an era with very large changes in the scale of experiments, the size of datasets, as well as advanced data-analysis techniques such as artificial intelligence. We should be able to have a say about how these things are dealt with and what the priorities are. The EPS can have a solid dialogue with large experimental teams and important research centres such as CERN. We can pass the message, for example via the national physics societies, and provide lists of experts able to advise politicians on such matters.

Last but not least is education. We need to adapt the programmes offered to the students because there is huge demand for soft skills, and I am not sure they are adequately provided. We also need to offer opportunities to welcome students and early-career researchers from regions around the world that need support. We should collaborate with them and provide scholarships to enable them to spend time at a facility such as CERN or DESY and develop key skills.

To achieve all that, we should strengthen the links between the EPS and the national societies (be they small or large). We represent the interest of all physicists in Europe equally. We also need to have a more active dialogue with our colleagues in North America and Asia because we share common challenges. Of course, to do that requires hard work and commitment.

How can the EPS support fundamental research such as particle physics?

We have a high-energy physics division, of course. From my point of view, we need to accentuate the motivation for exploring the laws of the universe. CERN obviously plays a key role in this because colliders are one of the basic experimental devices to do so. Gravitational-wave observatories are another example. These experiments have to go hand-in-hand because they have a common ambition. The EPS can give an extra voice to the scientific aspects of this enterprise. Of course, the question of financing next-generation experiments remains to be solved, as well as the balance between fundamental science and applied research. For me there is no doubt that such experiments should continue. Unfortunately, today one often has to state the implications for industry and the applications for society. This can sometimes be difficult to square with curiosity-driven science.

If approved, would a new collider at CERN take away funding from other fields?

This is a very simplistic view. Science funding is not a zero-sum game. As CERN did for the LHC, it’s good to find external sources. Money can’t go to everyone in equal amounts, so we need a way to set scientific priorities in Europe. First and foremost, this should take into account the scientific case. Then we should look at the number of countries that are interested and the level of investments that have been made – for example, also involving industry.

Money can’t go to everyone in equal amounts, so we need a way to set scientific priorities in Europe

Is the scientific case for the Future Circular Collider sufficiently clear in this respect?

If the argument is to find super-symmetry, or particles predicted by some other framework of physics beyond the Standard Model, then I’m afraid it will fail. Of course, in scientific working groups you need to go into specifics such as which hypotheses will be tested, and which signatures are possible. But such detail is a trap when engaging with broader audiences because we can’t be sure that such things exist at the energies we can explore. Instead, the argument should be that we try to understand better the elementary particles and laws. We need to pass the message to politicians, to the person on the street and to scientists that there are some important questions that can only be addressed with future colliders. While CERN and particle physicists should not be defensive, they should be clearer about what the role and ultimate hope of a collider is. Then there is no argument that can go against it. This is something that could be elaborated by the high-energy physics division of the EPS, for example by providing a document stating the views of particle physicists. We should also be prepared for a critical dialogue, to identify the strengths and weaknesses of the arguments. One should in any case ensure that anyone invited to give their views should have an established scientific reputation within their field, a prerequisite that is not met in some high-level discussions and media outlets.

Does the existence of several future-collider options pose a problem from a communications perspective?

I think it’s problematic if, scientifically, a consensus cannot be reached. There is something similar going on in the gravitational-wave community, where divisions exist about where to build the Einstein Telescope and which configuration it should have. This may lead to a healthy process of course, but discussions should be kept between experts. Indeed, it can weaken the case for a new experiment if scientists are seen to be disagreeing strongly.

What effects are current political shifts in Europe having on physics?

I’m afraid that there could be very negative effects. To this we have to add the risks created by the conflicts we see expanding. One effect could also be the changes in priorities for funding. As one of the largest scientific societies, we need to keep supporting collaborations among scientists no matter their country of origin, ethnicity, gender, or any other discriminating factor. We also need to provide financial support where possible, for example as we have done recently for Ukrainian colleagues to participate in our activities, and to make statements in response to events going way beyond the world of physics.

Sabbatical in space

Sławosz Uznański had to bide his time. Since its foundation in 1975, the European Space Agency (ESA) had only opened four selection rounds for new astronauts. When a fresh opportunity arose in 2021, Uznański’s colleagues in CERN’s electric power converters group were supportive of his ambitions to take an extended sabbatical in space. Now confirmed as one of 17 astronauts selected from among more than 22,000 applicants, Uznański is in training for future missions to the International Space Station (ISS).

His new colleagues are a diverse bunch, including geologists, medical doctors, astrophysicists, biologists, biotechnologists, jet fighter pilots and helicopter pilots. His own background is as a physicist and systems engineer. Following academic work studying the effect of radiation on semiconductors, Uznański spent 12 years at CERN working on powering existing infrastructure and future projects such as the Future Circular Collider. He’s most proud of being a project leader in reliability engineering and helping to design and deploy a new radiation-tolerant power-converter control system to the entire LHC accelerator complex.

Preparing for orbit

For now, Uznański’s astronaut training is mostly theoretical, preparing him for the ISS’s orbit-trajectory control, thermal control, communications, data handling, guidance, navigation and power generation, where he has deep expertise. But lift-off may not be far away, and one of his reserve-astronaut colleagues, Marcus Wandt, is already sitting up in the ISS capsule.

“I had the chance, in January, to see him launch from Cape Canaveral. And then, thanks to my operational experience at CERN, being in the control room, I came back directly to Columbus Control Center in Munich. Throughout the whole mission, I was in the control room, to support the mission and learn what I might live through one day.”

Rather than expertise or physical fitness, Uznański sees curiosity as the golden thread for astronauts – not least because they have to be able to perform any type of experiment that is assigned to them. As a Polish astronaut, he will have responsibility for the scientific experiments that are intended to accompany his country’s first mission to the ISS, most likely in late 2024 or early 2025. Among 66 proposals from Polish institutes, a dozen or more are currently being considered to fly.

CERN is extremely open in terms of technologies and I very much identify myself with that

The experiments are as diverse as the astronauts’ professional backgrounds. One will non-invasively monitor astronauts’ brain activity to help develop human–machine interfaces for artificial limbs. Another – a radiation monitor developed at CERN – plays on the fact that shielded high-energy physics environments have a similar radiation environment to the ISS in low-earth orbit. Uznański hopes that this technology can be commercialised and become another example of the opportunities out there for budding space entrepreneurs.

“I think we are in a fascinating moment for space exploration,” he explains, pointing to the boom in the commercial sector since 2014. “Space technology has gotten really democratised and commercialised. And I think it opens up possibilities for all types of engineers who build systems with great ideas and great science.”

Open science is a hot topic here. It’s increasingly possible to access venture capital to develop related technologies, notes Uznański, and the challenge is to ensure that the science is used in an open manner. “There is a big overlap between CERN culture and ESA culture in this respect. CERN is extremely open in terms of technologies and I very much identify myself with that.”

However societies choose to shape the future of open science in space, the two organisations are already partnering on several projects devoted to the pure curiosity that is dear to Uznański’s heart. These range from Euclid’s study of dark energy (CERN Courier May/June 2023 p7) to the ongoing study of cosmic rays by the Alpha Magnetic Spectrometer (AMS). With AMS due for an upgrade in 2026 (CERN Courier March/April 2024 p7), he cannot help but hope to be on that flight.

“If the opportunity arises, it’s a clear yes from me.”

Peter Higgs 1929–2024

Peter Higgs, an iconic figure in modern science who in 1964 postulated the existence of the eponymous Higgs boson, passed away on 8 April 2024 at the age of 94.

Peter Higgs was born in Newcastle upon Tyne in the UK on 29 May 1929. His family moved around when he was young and he suffered from childhood asthma, so he was often taught at home. However, from 1941 to 1946 he attended Cotham Grammar School in Bristol, one of whose alumni was Paul Dirac. He went on to study physics at King’s College London, where he got his bachelor’s degree in 1950 and his PhD for research in molecular physics in 1954. After periods at the University of Edinburgh, Imperial College and University College London, in 1960 he settled at the University of Edinburgh where he remained for the rest of his career.

Seeds of success

Following his PhD, Higgs’s research interests shifted to field theory, with a first paper on vacuum expectation values of fields in 1956, followed by a couple of papers on general relativity. Then, in 1964, came his two famous papers introducing spontaneous gauge symmetry breaking into relativistic quantum field theory and showing how a vector boson could acquire a mass in a consistent manner – as long as it was accompanied by a massive scalar boson.

Related ideas had been discussed previously by Phillip Anderson and Yoichiro Nambu in the context of non-relativistic condensed-matter physics, namely in models of superconductivity, where a condensate of electron pairs enables a photon to acquire an effective mass. Anderson conjectured that a similar mechanism should be possible in a relativistic theory, but he did not develop the idea. On the other hand, Nambu used spontaneous symmetry breaking to describe the properties of the pion, but also did not discuss the extension to a relativistic vector boson.

In early 1964 Walter Gilbert (later a winner of the Nobel Prize in Chemistry) wrote a paper arguing that Anderson and Nambu’s ideas for generating mass for a vector boson could not work in a relativistic theory. This was Higgs’s cue: a few weeks later he wrote a first paper pointing out a potential loophole in Gilbert’s argument (though not a specific model). He sent his paper to the journal Physics Letters, which quickly accepted it for publication. A few days later, he wrote a second paper, which contained an explicit model for mass generation, but was taken aback when the same journal rejected this paper as not being of practical interest. Undeterred, Higgs tweaked his paper to make his message more explicit, and submitted it to Physical Review Letters, where it was accepted.

Unknown to Higgs, François Englert and Robert Brout had already sent a paper describing a similar model to the same journal, where it was published ahead of Higgs’s paper. Both papers postulated a scalar field with a non-zero vacuum expectation value that gave mass to a vector boson. However, there was a key difference: Higgs pointed out explicitly that his model predicted the existence of a massive scalar boson, whereas this was not mentioned in the Englert–Brout paper. For this reason, the particle he predicted became known as the Higgs boson. Shortly after the publication of the Higgs and Englert–Brout papers, Gerry Guralnik, Carl Hagen and Tom Kibble published an article referring to their papers and filling in some aspects of the theory, but also not mentioning the existence of the massive scalar boson.

In 1965 Higgs went for a sabbatical to the University of North Carolina, where he continued working on his theory. Remarkably prescient, he wrote a third paper discussing how his boson could decay into a pair of massive gauge bosons as well as calculating associated scattering processes. However, he encountered scepticism about the validity of his theory, and neither his nor the other pioneering mass-generation papers garnered significant attention for several years.

This started to change in 1967 and 1968 when Steven Weinberg and Abdus Salam incorporated the mass-generation mechanism into their formulation of the electroweak sector of the Standard Model. But interest only really took off a few years later, after Gerard ’t Hooft and Martinus Veltman showed that spontaneously broken gauge theories are renormalisable and hence could be used to make accurate and reliable predictions for comparison with experiment, and when neutral weak interactions were discovered in the Gargamelle bubble chamber at CERN in 1973.

The search begins

During the 1970s interest in the experimental community moved towards searches for the massive intermediate vector bosons, the W and Z. However, it seemed to Mary Gaillard, Dimitri Nanopoulos and myself that the key long-term target should be the Higgs boson, the capstone of the structure of the Standard Model, and in 1975 we wrote a paper describing its phenomenology. At the time the existence of the Higgs boson was still regarded with some scepticism, and we ended our paper by writing that “We do not want to encourage big experimental searches for the Higgs boson, but we do feel that people performing experiments vulnerable to the Higgs boson should know how it may turn up.” I met Peter Higgs for the first time around 1980, and he was clearly flattered by our interest in his boson, but unprepared for the subsequent interest in the big experimental searches that followed.

Higgs pointed out explicitly that his model predicted the existence of a massive scalar boson

Searching for the Higgs boson moved to the top of the agenda following the discovery of the W and Z at CERN in 1983, when the Superconducting Super Collider project was launched in the US, followed by the first LHC workshop in 1984. Being a profoundly modest man, Higgs followed these developments from a distance as a somewhat bemused spectator. In the 1990s, precision experiments at LEP and elsewhere confirmed predictions of the Standard Model with high accuracy – if and only if the Higgs boson (or something very like it) was included in the theoretical calculations. Higgs became quietly confident in the reality of his boson. By the time the LHC started accumulating collisions at an energy of 7 and 8 TeV, anticipation of its possible discovery was growing.

Following early hints at the end of 2011, the word went around that on 4 July 2012 the ATLAS and CMS experiments would give a joint seminar presenting their latest results. I was tasked with locating Higgs and persuading him that he might find the results interesting. Somewhat reluctantly, he decided to come to CERN for the seminar, and he had no cause to regret it. He wiped tears from his eyes when the discovery of a new particle resembling his boson was announced, and confessed that he had never expected to see it in his lifetime.

Famously, in October 2013 as the Nobel Prize was being announced, Higgs went missing, in order to avoid being thronged by the media. Some months previously, in a pub in Edinburgh, he had told me that the existence of the Higgs boson was not a “big deal”, but I assured him that it was. Without his theory, electrons would fly away from nuclei at the speed of light and atoms would not exist, and radioactivity would be a force as strong as electricity and magnetism. His prediction of the existence of the particle that bears his name was a deep insight, and its discovery was the crowning moment that confirmed his understanding of the way the universe works.

Peter Higgs is survived by his two sons, a daughter-in-law and two grandchildren.

Accelerator sustainability in focus

The world is facing a crisis of anthropogenic climate change, driven by excessive CO₂ emissions during the past 150 years. In response, the United Nations has defined goals in a race towards zero net-carbon emission. One of these goals is to ensure that all projects due to be completed by 2030 or after have a net-zero carbon operation, with a reduction in embodied carbon by at least 40% compared to current practice. At the same time, the European Union (EU), Japan and other nations have decided to become carbon neutral by around 2050.

These boundary conditions put large-scale science projects under pressure to reduce CO₂ emissions during construction, operation and potentially decommissioning. For context: given the current French energy mix, CERN’s annual 1.3 TWh electricity consumption (which is mostly used for accelerator operation) corresponds to roughly 50 kt CO₂e global warming potential (GWP), while recent estimates for the construction of tunnels for future colliders are in the multi-100 kt CO₂e GWP range.

Green realisation

To discuss potential ways forward, a Workshop on Sustainability for Future Accelerators (WSFA2023) took place on 25–27 September in Morioka, Japan within the framework of the recently started EU project EAJADE (Europe–America–Japan Accelerator Development and Exchange). Around 50 international experts discussed a slew of topics ranging from life-cycle assessments (LCAs) of accelerator technologies with carbon-reduction potential to funding initiatives towards sustainable accelerator R&D, and local initiatives aimed at the “green” realisation of future colliders. With the workshop being held in Japan, the proposed International Linear Collider (ILC) figured prominently as a reference project – attracting considerable attention from local media.

The general context of discussions was set by Beate Heinemann, DESY director for particle physics, on behalf of the European Laboratory Directors Group (LDG). The LDG recently created a working group to assess the sustainability of accelerators, with a mandate to develop guidelines and a minimum set of key indicators pertaining to the methodology and scope of reporting of sustainability aspects for future high-energy physics projects. Since LCAs are becoming the main tool to estimate GWP, a number of project representatives discussed their take on sustainability and steps towards performing LCAs. Starting with the much-cited ARUP study on linear colliders published in 2023 (edms.cern.ch/document/2917948/1), there were presentations on the ESS in Sweden, the ISIS-II neutron and muon source in the UK, the CERN sustainability forum, the Future Circular Collider, the Cool Copper Collider and other proposed colliders. Also discussed were R&D items for sustainable technologies, including CERN’s High Efficiency Klystron Project, the ZEPTO permanent-magnet project, thin film-coated SRF cavities and others.

A second big block in the workshop agenda was devoted to the “greening” of future accelerators and potential local and general construction measures towards achieving this goal. The focus was on Japanese efforts around the ILC, but numerous results can be re-interpreted in a more general way. Presentations were given on the potential of concrete to turn from a massive carbon source into a carbon sink with net negative CO₂e balance (a topic with huge industrial interest), on large-scale wooden construction (e.g. for experimental halls), and on the ILC connection with the agriculture, forestry and fisheries industries to reduce CO₂ emissions and offset them by increasing CO₂ absorption. The focus was on building an energy recycling society by the time the ILC would become operational.

What have we learnt on our way towards sustainable large-scale research infrastructures? First, that time might be our friend: energy mixes will include increasingly larger carbon-free components, making construction projects and operations more eco-friendly. Also, new and more sustainable technologies will be developed that help achieve global climate goals. Second, we as a community must consider the imprint our research leaves on the globe, along with as many indicators as possible. The GWP can be a beginning, but there are many other factors relating, for example, to rare-earth elements, toxicity and acidity. The LCA methodology provides the accelerator community with guidelines for the planning of more sustainable large-scale projects and needs to be further developed – including end-of-life, decommissioning and recycling steps – in an appropriate manner. Last but not least, it is clear that we need to be proactive in anticipating the changes happening in the energy markets and society with respect to sustainability-driven challenges at all levels.

Igor Savin 1930–2023

Igor Savin, honorary director of the Veksler and Baldin Laboratory of High Energy Physics (VBLHEP) at JINR, Dubna died on 8 July 2023 after a long illness. Born in Bryansk region, Russia in 1930, he graduated from Lomonosov Moscow State University and started his work in Dubna in 1955. He gained international prestige by studying interference in K-meson decays in experiments at CERN, which confirmed the violation of CP invariance. In 1967 he defended his PhD thesis based on the results of his work, and in 1974 his DSc thesis. The latter included classic results on kaon regeneration that were obtained by an international collaboration including physicists from Bulgaria, Hungary, Czechoslovakia and East Germany formed under Savin’s leadership. The collaboration conducted a series of experiments at the U-70 accelerator in Protvino, showing that the regeneration cross section decreases as a function of the kaon momentum in line with the Pomeranchuk theorem on the asymptotic equality of total cross sections for particles and antiparticles.

In 1974 Igor Savin led a small group of physicists from Dubna to visit CERN to identify an experiment where JINR’s participation would be significant. Thanks to his enthusiasm and organisational talent, this led to the first large-scale joint CERN–JINR project, NA4 at the SPS, which was approved in 1975 and finished in 1995. He led the JINR team participating in the study of deep inelastic scattering of muons from nucleons and nuclei. This research established γ/Z interference in the electroweak interactions of muons on nuclei, indicating the existence of an intermediate Z-boson discovered at CERN a year and a half later, and enabled the structure functions of protons and deuterons to be measured at percent levels. The latter were shown to be in agreement with the new theory of strong interactions, QCD, and proved that the structure functions of free and bound nucleons in the nucleus differ. This first equal cooperation between JINR and CERN contributed to the development at Dubna of the most advanced technologies and promoted strong collaboration with the global scientific community.

Igor Savin founded a new scientific direction at JINR: the experimental and theoretical study of the spin structure of nucleons and nuclei, which has gone from strength to strength. Igor headed the JINR group in the SMC experiment at CERN, in which the spin-dependent structure functions of protons and deuterons were measured and a small contribution of the valence quarks to the nucleon spin was found. He also led the JINR team in the COMPASS experiment at CERN and actively participated in the HERMES experiment at DESY to further study the nucleon spin structure in electron scattering reactions on longitudinally and transversely polarised nucleons.

As director of VBLHEP JINR, Igor Savin paid great attention to the development of international scientific cooperation, which is the backbone of the laboratory. The main task was to perform research at external accelerators at IHEP, CERN, DESY, Brookhaven and other world centres. His work has been recognised with numerous awards, including the gold medal of the Czech Academy of Sciences and the medals of the Hungarian People’s Republic and the German Democratic Republic. He was a scientist with a worldwide reputation, who helped create the glorious history of JINR. On the occasion of his 90th birthday, Carlo Rubbia said: “Igor, your anniversary celebration represents for all of us a unique result to which we have been involved over many decades and of which we are extremely proud”.

Igor Savin leaves a deep mark on science and a bright memory to everyone who had the honour and privilege to call him their friend, colleague or mentor. A wonderful man and a true scientist will be missed by all who knew and loved him.

Fritz Nolden 1953–2023

Our long-time colleague Fritz Nolden passed away on 28 December 2023 at the age of 70.

After studying physics at the Technical University of Munich and completing his diploma thesis under the supervision of Paul Kienle, Fritz Nolden began working at GSI Darmstadt in July 1985. His work focused on aspects of the planned Experimental Storage Ring (ESR) in Bernhard Franzke’s group. Initially he dealt with general questions regarding the interpretation and design of the storage ring and related beam-dynamics aspects. Here he benefited from his ability to work on theoretical problems, which played a major role in his further career and which, as he always liked to emphasise, was the greatest motivation and basis for his work.

After working intensively in the construction and commissioning of the ESR, Nolden increasingly found time to deal with the theory and structure of stochastic cooling. This led to the completion of his doctoral thesis at the Technical University of Munich in 1995 on theoretical aspects of a stochastic cooling system at the ESR. He was responsible for the commissioning of this system at the ESR in the same year, and worked on a variety of problems that arose during the operation of the ESR facility, both theoretically and experimentally. Colleagues from the research departments also appreciated his support, in both words and actions, when planning and carrying out experiments at the ESR.

In addition to his ongoing willingness to ensure the operation of the ESR in a jointly responsible position, he also increasingly took on tasks in planning the storage rings for FAIR and in particular their stochastic-cooling systems. Many criteria and specifications of these systems go back to his theoretical work and planning activities.

Until his retirement in 2017, Nolden continued to support the operation of the ESR with all his expertise and commitment. After his retirement, he still visited GSI regularly to discuss current issues with colleagues and share his wealth of experience with them. He was a sought-after conversation partner because he not only brought his expertise to the discussions, but also liked to season his comments with subtle humour.

Fritz’s professional contributions were also valued by many international colleagues, for whom he was an open and competent partner in scientific exchange. Worth mentioning here are his many years of exchange with colleagues at CERN and his consulting work at the IMP Lanzhou.

We mourn the loss of a colleague with excellent specialist knowledge, great interest and commitment in his tasks for GSI and FAIR, who always showed a friendly manner and a great openness to all the problems that were brought to his attention.

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