Jobs – Page 34 of 508

Extreme detector design for a future circular collider

**Grand designs** The layout of the FCC-hh reference detector, with a diameter of 20 m and length of 50 m, comparable to the dimensions of the ATLAS detector but much heavier. The central detector houses the tracking, electromagnetic calorimetry and hadron calorimetry inside a 4 T solenoid with a free bore diameter of 10 m (purple). The forward parts are displaced by 10 m from the interaction point, with two forward magnet coils (solenoids shown) providing the required bending power. The muon system is placed outside the magnet coils. Source: CERN Yellow Reports Monographs CERN-2022-002

The Future Circular Collider (FCC) is the most powerful post-LHC experimental infrastructure proposed to address key open questions in particle physics. Under study for almost a decade, it envisions an electron–positron collider phase, FCC-ee, followed by a proton–proton collider in the same 91 km-circumference tunnel at CERN. The hadron collider, FCC-hh, would operate at a centre-of-mass energy of 100 TeV, extending the energy frontier by almost an order of magnitude compared to the LHC, and provide an integrated luminosity a factor of 5–10 larger. The mass reach for direct discovery at FCC-hh will reach several tens of TeV and allow, for example, the production of new particles whose existence could be indirectly exposed by precision measurements at FCC-ee.

The potential of FCC-hh offers an unprecedented opportunity to address fundamental unknowns about our universe

At the time of the kickoff meeting for the FCC study in 2014, the physics potential and the requirements for detectors at a 100 TeV collider were already heavily debated. These discussions were eventually channelled into a working group that provided the input to the 2020 update of the European strategy for particle physics and recently concluded with a detailed writeup in a 300-page CERN Yellow Report. To focus the effort, it was decided to study one reference detector that is capable of fully exploiting the FCC-hh physics potential. At first glance it resembles a super CMS detector with two LHCb detectors attached (see “Grand designs” image). A detailed detector performance study followed, allowing a very efficient study of the key physics capabilities.

The first detector challenge at FCC-hh is related to the luminosity, which is expected to reach 3 × 10³⁵ cm^–2s^–1. This is six times larger than the HL-LHC luminosity and 30 times larger than the nominal LHC luminosity. Because the FCC will operate beams with a 25 ns bunch spacing, the so-called pile-up (the number of pp collisions per bunch crossing) scales by approximately the same factor. This results in almost 1000 simultaneous pp collisions, requiring a highly granular detector. Evidently, the assignment of tracks to their respective vertices in this environment is a formidable task.

Longitudinal cross-section of the FCC-hh reference detector — **Far reaching** The longitudinal cross-section of the FCC-hh reference detector, showing the pseudorapidity values, η , covered by the various subdetectors. Source: CERN Yellow Reports Monographs CERN-2022-002

The plan to collect an integrated pp luminosity of 30 ab^–1 brings the radiation hardness requirements for the first layers of the tracking detector close to 10¹⁸ hadrons/cm², which is around 100 times more than the requirement for the HL-LHC. Still, the tracker volume with such high radiation load is not excessively large. From a radial distance of around 30 cm outwards, radiation levels are already close to those expected for the HL-LHC, thus the silicon technology for these detector regions is already available.

The high radiation levels also need very radiation-hard calorimetry, making a liquid-argon calorimeter the first choice for the electromagnetic calorimeter and forward regions of the hadron calorimeter. The energy deposit in the very forward regions will be 4 kW per unit of rapidity and it will be an interesting task to keep cryogenic liquids cold in such an environment. Thanks to the large shielding effect of the calorimeters, which have to be quite thick to contain the highest energy particles, the radiation levels in the muon system are not too different from those at the HL-LHC. So the technology needed for this system is available.

Looking forward

At an energy of 100 TeV, important SM particles such as the Higgs boson are abundantly produced in the very forward region. The forward acceptance of FCC-hh detectors therefore has to be much larger than at the LHC detectors. ATLAS and CMS enable momentum measurements up to pseudorapidities (a measure of the angle between the track and beamline) of around η = 2.5, whereas at FCC-hh this will have to be extended to η = 4 (see “Far reaching” figure). Since this is not achievable with a central solenoid alone, a forward magnet system is assumed on either side of the detector. Whether the optimum forward magnets are solenoids or dipoles still has to be studied and will depend on the requirements for momentum resolution in the very forward region. Forward solenoids have been considered that extend the precision of momentum measurements by one additional unit of rapidity.

**Forward momentum** Momentum resolution versus pseudorapidity, η, for the FCC-hh reference detector for a given transverse momentum, p_T. If dipole magnets instead of solenoids are used in the forward region, the momentum resolution can be significantly improved (dashed lines). Source: CERN Yellow Reports Monographs CERN-2022-002

A silicon tracking system with a radius of 1.6 m and a total length of 30 m provides a momentum resolution of around 0.6% for low-momentum particles, 2% at 1 TeV and 20% at 10 TeV (see “Forward momentum” figure). To detect at least 90% of the very forward jets that accompany a Higgs boson in vector-boson-fusion production, the tracker acceptance has to be extended up to η = 6. At the LHC such an acceptance is already achieved up to η = 4. The total tracker surface of around 400 m² at FCC-hh is “just” a factor two larger than the HL-LHC trackers, and the total number of channels (16.5 billion) is around eight times larger.

It is evident that the FCC-hh reference detector is more challenging than the LHC detectors, but not at all out of reach. The diameter and length are similar to those of the ATLAS detector. The tracker and calorimeters are housed inside a large superconducting solenoid 10 m in diameter, providing a magnetic field of 4 T. For comparison, CMS uses a solenoid with the same field and an inner diameter of 6 m. This difference does not seem large at first sight, but of course the stored energy (13 GJ) is about five times larger than the CMS coil, which needs very careful design of the quench protection system.

For the FCC-hh calorimeters, the major challenge, besides the high radiation dose, is the required energy resolution and particle identification in the high pile-up environment. The key to achieve the required performance is therefore a highly segmented calorimeter. The need for longitudinal segmentation calls for a solution different from the “accordion” geometry employed by ATLAS. Flat lead/steel absorbers that are inclined by 50 degrees with respect to the radial direction are interleaved with liquid-argon gaps and straight electrodes with high-voltage and signal pads (see “Liquid argon” figure). The readout of these pads on the back of the calorimeter is then possible thanks to the use of multi-layer electrodes fabricated as straight printed circuit boards. This idea has already been successfully prototyped within the CERN EP detector R&D programme.

The considerations for a muon system for the reference detector are quite different compared to the LHC experiments. When the detectors for the LHC were originally conceived in the late 1980s, it was not clear whether precise tracking in the vicinity of the collision point was possible in this unprecedented radiation environment. Silicon detectors were excessively expensive and gas detectors were at the limit of applicability. For the LHC detectors, a very large emphasis was therefore put on muon systems with good stand-alone performance, specifically for the ATLAS detector, which is able to provide a robust measurement of, for example, the decay of a Higgs particle into four muons, with the muon system alone.

**Liquid argon** A cross section through the liquid-argon electromagnetic calorimeter using inclined absorber plates and highly granular readout boards (top), and measurements of the electrical properties of a readout electrode prototype for such a calorimeter at CERN (bottom). Source: CERN Yellow Reports Monographs CERN-2022-002 (top); CERN EP R&D Annual Report 2022 (bottom)

Thanks to the formidable advancement of silicon-sensor technology, which has led to full silicon trackers capable of dealing with around 140 simultaneous pp collisions every 25 ns at the HL-LHC, standalone performance is no longer a stringent requirement. The muon systems for FCC-hh can therefore fully rely on the silicon trackers, assuming just two muon stations outside the coil that measure the exit point and the angle of the muons. The muon track provides muon identification, the muon angle provides a coarse momentum measurement for triggering and the track position provides improved muon momentum measurement when combined with the inner tracker.

The major difference between an FCC-hh detector and CMS is that there is no yoke for the return flux of the solenoid, as the cost would be excessive and its only purpose to shield the magnetic field towards the cavern. The baseline design assumes the cavern infrastructure can be built to be compatible with this stray field. Infrastructure that is sensitive to the magnetic field will be placed in the service cavern 50 m from the solenoid, where the stray field is sufficiently low.

**Higgs self-coupling** The precision of the Higgs self-coupling measurement at FCC-hh (in terms of the expected negative log–likelihood scan as a function of the trilinear self-coupling modifier) in all channels, and their combination. The dashed line represents the sensitivity obtained including statistical uncertainties only; the solid line corresponds to the inclusion of systematic uncertainties. Source: CERN Yellow Reports Monographs CERN-2022-002

The high granularity and acceptance of the FCC-hh reference detector will result in about 250 TB/s of data for calorimetry and the muon system, about 10 times more than the ATLAS and CMS HL-LHC scenarios. There is no doubt that it will be possible to digitise and read this data volume at the full bunch-crossing rate for these detector systems. The question remains whether the data rate of almost 2500 TB/s from the tracker can also be read out at the full bunch-crossing rate or whether calorimeter, muon and possible coarse tracker information need to be used for a first-level trigger decision, reducing the tracker readout rate to the few MHz level, without the loss of important physics. Even if the optical link technology for full tracker readout were available and affordable, sufficient radiation hardness of devices and infrastructure constraints from power and cooling services are prohibitive with current technology, calling for R&D on low-power radiation-hard optical links.

Benchmarks physics

The potential of FCC-hh in the realms of precision Higgs and electroweak physics, high mass reach and dark-matter searches offers an unprecedented opportunity to address fundamental unknowns about our universe. The performance requirements for the FCC-hh baseline detector have been defined through a set of benchmark physics processes, selected among the key ingredients of the physics programme. The detector’s increased acceptance compared to the LHC detectors, and the higher energy of FCC-hh collisions, will allow physicists to uniquely improve the precision of measurements of Higgs-boson properties for a whole spectrum of production and decay processes complementary to those accessible at the FCC-ee. This includes measurements of rare processes such as Higgs pair-production, which provides a direct measure of the Higgs self-coupling – a crucial parameter for understanding the stability of the vacuum and the nature of the electroweak phase transition in the early universe – with a precision of 3 to 7% (see “Higgs self-coupling” figure).

Moreover, thanks to the extremely large Higgs-production rates, FCC-hh offers the potential to measure rare decay modes in a novel boosted kinematic regime well beyond what is currently studied at the LHC. These include the decay to second-generation fermions, muons, which can be measured to a precision of 1%. The Higgs branching fraction to invisible states can be probed to a value of 10^–4, allowing the parameter space for dark matter to be further constrained. The much higher centre-of-mass energy of FCC-hh, meanwhile, significantly extends the mass reach for discovering new particles. The potential for detecting heavy resonances decaying into di-muons and di-electrons extends to 40 TeV, while for coloured resonances like excited quarks the reach extends to 45 TeV, thus extending the current limit by almost an order of magnitude. In the context of supersymmetry, FCC-hh will be capable of probing stop squarks with masses up to 10 TeV, also well beyond the reach of the LHC.

In terms of dark-matter searches, FCC-hh has immense potential – particularly for probing scenarios of weakly interacting massive particles such as higgsinos and winos (see “Dark matters” figure). Electroweak multiplets are typically elusive, especially in hadron collisions, due to their weak interactions and large masses (needed to explain the relic abundance of dark matter in our universe). Their nearly degenerate mass spectrum produces an elusive final state in the form of so-called “disappearing tracks”. Thanks to the dense coverage of the FCC-hh detector tracking system, a general-purpose FCC-hh experiment could detect these particle decays directly, covering the full mass range expected for this type of dark matter.

A detector at a 100 TeV hadron collider is clearly a challenging project. But detailed studies have shown that it should be possible to build a detector that can fully exploit the physics potential of such a machine, provided we invest in the necessary detector R&D. Experience with the Phase-II upgrades of the LHC detectors for the HL-LHC, developments for further exploitation of the LHC and detector R&D for future Higgs factories will be important stepping stones in this endeavour.

Future colliders are particle observatories

In no other field of science is the promise of revolutionary discovery the only standard by which future proposals are held. Yet in particle physics a narrative persists that the current lack of new physics beyond the Standard Model (SM) is putting the future of the field in doubt. This pessimism is misguided.

Take cosmology and astrophysics. These are fundamental sciences whose aim is nothing more than to better understand the objects within their remit. Telescopes and other instruments point at the universe at large, observing to ever higher precision, farther than ever before, in new, previously inaccessible regimes. The Gaia, JWST and LIGO instruments, which cost between $1–10 billion each, had clear scientific cases: to simply do better science.

Not once in ESA’s list of Gaia science objectives is dark matter or dark energy mentioned. Gaia’s scientific potential is fulfilled not by the promise of new physics discoveries but by improving precision astrometry, uncovering more of the known astrophysical objects and testing further the standard cosmological model. JWST is a success if it makes sharper observations and peers out farther than ever, regardless of whether it discovers new types of exotic phenomena or sees the same objects as before but better. LIGO was not considered a failure for having discovered gravitational-wave signals in agreement with Einstein’s general theory of relativity; nor is the future of gravitational-wave observatories in doubt as a consequence.

Particle physics is pushing the boundaries of our understanding in the other direction – looking inwards rather than outwards. The discovery of the Higgs boson, like that of gravitational waves, opens an entirely new window for probing our universe. Its agreement with the SM until now does nothing to diminish the need for a future Higgs observatory. Higgs aside, new elementary particle processes are continually being unveiled, from the long-predicted quantum scattering of light by light to complex interactions involving multiple bosons or fermions, most recently in the spectacular observation of four top quarks by ATLAS and CMS.

Gaia, JWST and LIGO had clear scientific cases: to simply do better science

Moreover, unlike cosmology and astrophysics, particle physics can do more than observe. It is an experimental science in the truest sense: set up the initial conditions, repeat the experiment, then analyse what comes out. The ability to directly manipulate the elementary building blocks of our world both complements and works symbiotically with astrophysical and cosmological observations. We need all eyes open on the universe to make progress; blinding one eye will not make the other sharper.

A better name can help

In this spirit, the CERN Future Circular Collider (FCC) is a bold and ambitious proposal for ensuring another thriving century of particle physics. As a multi- generational project, it would be our era’s cathedral to knowledge and wonder about the universe. However, the FCC cannot always remain a future collider if it ever becomes reality. When it comes to be renamed, the CERN International Particle Observatory would be more apt. This better reflects the role of colliders as general-purpose tools to do good science.

**Tevong You** is an assistant professor in theoretical physics at King’s College London. Credit: Branco Weiss Fellowship

The International Particle Observatory will cost around $10 billion for a high-precision observatory, starting in the 2040s. A high-energy observatory would then follow in the 2070s. Is it worth it? Should we not be more concerned with climate change? Both questions must be put in the context of other areas of government spending and the value of fundamental physics. For example, an Olympic Games funded by a single nation, for a month’s worth of entertainment, costs about $10 billion. The same price tag shared across multiple countries over decades, to uncover fundamental knowledge that stands for all time, is a pittance by comparison. Furthermore, studies have shown that the economic return of investment in CERN outweighs the cost. We get back more than we put in.

The value of the enterprise itself benefits society in myriad indirect ways, which does not place it at odds with practical issues such as climate change. On the contrary, a new generation of particle-physics experiments stimulating cutting-edge engineering, technology, computing and data analysis, while fostering international collaboration and inspiring popular culture, creates the right conditions for tackling other problems. Particle physics helps humanity prosper in the long run, and has already played an indispensable role in creating our modern world.

Building an International Particle Observatory is a win–win proposition. It pays for itself, contributes to a better society, improves our understanding of the universe by orders of magnitude, and advances our voyage of exploration into the unknown. We just need to shift our narrative to one that emphasises the tremendous range of fundamental science to be done. A better name can help.

An insight into the European Spallation Source

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The European Spallation Source (ESS) is a European project with 13 members states and two host states. In this talk, Mats Lindroos will give examples of the science that will be done at ESS both in applied physics and fundamental physics. He will speak about the in-kind model, which made it possible to build this facility on a greenfield site in a country without any previous experience of much of the required technology.

Also reviewed will be the status of the project with beam on target planned for 2025 and the start of the full user programme in 2027.

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Mats Lindroos has a PhD in subatomic physics from Chalmers University of technology in Gothenburg, Sweden, and since 2014, is adjunct professor at Lund’s university. He worked at CERN from 1993–2009 starting as a research fellow at the ISOLDE facility and from 1995 as a staff member in the CERN accelerator sector. He has among other tasks been responsible for PS Booster operation and technical coordination of the CERN ISOLDE facility. He has also been project leader of several CERN projects and had leading roles in several EC-supported design studies for future nuclear physics and neutrino facilities. Mats co-authored a book in 2009 on a future neutrino beam concept, beta-beams. Since 2009 he has been head of the accelerator division and sub-project leader at the European Spallation Source ERIC (ESS) in Lund.

EPS announces 2023 awards

The High Energy and Particle Physics Division of the European Physical Society (HEPP-EPS) has announced the winners of this year’s awards.

Cecilia Jarlskog shares the High Energy and and Particle Physics Prize 2023 with the Data Bay and RENO collaboration for their work on neutrino mixing angle. Credit: J. Junthunen

The EPS High Energy and Particle Physics Prize is awarded for an outstanding contribution in a experimental, theoretical or technological achievement. This year, the recipients are Cecilia Jarlskog for the discovery of an invariant measure of CP violation in both quark and lepton sectors; and the Daya Bay and RENO collaborations for the observation of short-baseline reactor electron-antineutrino disappearance, providing the first determination of the neutrino mixing angle, which paves the way for the detection of CP violation in the lepton sector.

The 2023 Giuseppe and Vanna Cocconi Prize (honouring contributions in particle astrophysics and cosmology in the past 15 years) is awarded to the SDSS/BOSS/eBOSS collaborations for their outstanding contributions to observational cosmology, including the development of the baryon-acoustic oscillation measurement into a prime cosmological tool, using it to robustly probe the history of the expansion rate of the Universe back to one-fifth of its age providing crucial information on dark energy, the Hubble constant, and neutrino masses.

The SDSS IV collaboration is part of the awardees of the High-Energy Prize. Credit: SDSS

The 2023 Gribov Medal is awarded to Netta Engelhardt for her groundbreaking contributions to the understanding of quantum information in gravity and black-hole physics. This medal goes to early-career researchers working in theoretical physics or field theory.

Valentina Cairo is receiving the Young Experimental Physicist Prize for her contribution to the ATLAS inner tracker. Credit: P. Butti

The 2023 Young Experimental Physicist Prize of the High Energy and Particle Physics Division of the EPS – for early-career experimental physicists – is awarded to Valentina Cairo for her outstanding contributions to the ATLAS experiment: from the construction of the inner tracker, to the development of novel track and vertex reconstruction algorithms and to searches for di-Higgs boson production.

Honouring achievements in outreach, education, and the promotion of diversity, the 2023 Outreach Prize of the High Energy and Particle Physics Division of the EPS is awarded to Jácome (Jay) Armas. It recognizes his outstanding combination of activities on science communication, most notably for the “Science & Cocktails” event series, revolving around science lectures which incorporate elements of the nightlife such as music/art performances and cocktail craftsmanship and reaching out to hundreds of thousands in five different cities world-wide.

All awards will be presented at the EPS Conference on High Energy Physics, which will take place in Hamburg from 21 to 25 August.

Full citations can be found here: http://eps-hepp.web.cern.ch/eps-hepp/prizes.php

RadiaSoft rewrites the rulebook on modelling and optimisation of multi-stage accelerators

Modelling of beam dynamics — **Design and optimisation** Sirepo aggregates a portfolio of codes to facilitate the modelling of beam dynamics for a range of particle acceleration schemes. Dedicated applications within Sirepo include more specific simulation software covering use-cases for magnets (above), X-ray beamlines, control systems, plasmas, neutronics and machine learning. (Courtesy: RadiaSoft)

“Robust software solutions that deliver step-function advances in accelerator design, engineering and research productivity.” Writ large, that’s the unifying goal shaping the day-to-day work of physicists and software engineers at RadiaSoft, a Boulder, Colorado-based company that specialises in the provision of high-level research, design and scientific consulting services in beamline physics, accelerator science and associated machine-learning technologies. Theirs is a wide-ranging remit that spans electron linacs, free-electron lasers (FELs), synchrotron radiation generated in electron rings, high-intensity proton synchrotrons and accumulator rings, with the RadiaSoft team bringing creativity and novel solutions to the design and simulation of high-power particle beams and directed radiation.

Founded in 2013, RadiaSoft has spent the past decade establishing a heavyweight customer base with organisations large and small. Customers include US Department of Energy (DOE) national laboratories (among them Fermilab, Brookhaven National Laboratory and SLAC National Accelerator Laboratory); academic research centres (at institutions such as UCLA and Texas A&M University); as well as industry partners like Best Medical, Modern Hydrogen and Radiabeam.

“As an R&D company, we work across an expansive canvas encompassing accelerator physics, enabling platform technologies and engineering for multi-stage accelerator facilities,” Jonathan Edelen, an accelerator physicist and president of RadiaSoft, told CERN Courier. “We work collaboratively with our scientific customers – often funded under the US government’s Small Business Innovation Research (SBIR) programme – and help them tackle physics and engineering problems that they don’t have the expertise or time to solve on their own.”

According to Edelen, the secret of RadiaSoft’s success lies in combining “broad and deep technical domain knowledge” with a wealth of prior project experience at large-scale accelerator facilities plus the development of customised solutions for smaller operations. “That collective know-how,” he said, “allows us to tackle all manner of design and optimisation problems in accelerator science. We work on projects ranging from fundamental studies of esoteric beam dynamics to the simulation and design of RF control systems to the development of machine-learning algorithms for accelerator controls.”

Software innovation

All of this core expertise in accelerator physics and engineering doesn’t stand alone in the RadiaSoft corporate portfolio. Underpinning the consultancy’s value proposition is a software development team that majors on the realisation of intuitive, powerful graphical user interfaces for open-source, high-performance simulation codes. This same team – which aggregates many years of experience working with all sorts of simulation packages for accelerator physics and subsystems – is the driving force behind RadiaSoft’s flagship product Sirepo.

Sirepo is a browser-based, computer-aided engineering (CAE) gateway with graphical user interface. The platform supports over a dozen community-developed particle-accelerator simulation codes, a specialised machine-learning application, a controls-modelling application and a private JupyterHub instance. Users can build simulations with drag-and-drop inputs, collaborate in real-time with shareable URLs, or download their simulations to work from the command line.

Jonathan Edelen: “Sirepo Omega is all about convergence, automation and enhanced workflow efficiency.” (Courtesy: RadiaSoft)

“Sirepo makes it easier for users to learn and run these simulation codes, many of which can be difficult to work with,” explained Edelen. “Equally important, RadiaSoft handles all of the dependency packaging, installation and versioning of the codes within Sirepo, while our cloud-based computing architecture allows users to share their simulations by simply sending a URL to colleagues.”

At a granular level, Sirepo aggregates a portfolio of codes to facilitate the modelling of beam dynamics for a range of particle acceleration schemes. Users can employ elegant, for example, to study varied configurations such as linacs and rings, while OPAL can model electron guns, beamlines and linacs with space charge, wake fields and coherent synchrotron radiation. Meanwhile, MAD-X is used for large-scale lattice design, with options for optimisation and export for use in other tracking codes within Sirepo. Users can also delve into time-dependent, 3D modelling for FELs, with Genesis offering simulation for single-pass FELs and extensions to cover oscillators or multi-stage set-ups. Sirepo’s interoperability means that the user can easily coordinate these codes for an end-to-end simulation of the beamline.

Other dedicated applications within Sirepo act as a repository for more specific simulation software for use-cases with magnets, X-ray beamlines, control systems, plasmas, neutronics and machine learning. “The codes within Sirepo are used in the design and optimisation of accelerator facilities worldwide,” noted Edelen, “and are relevant through the full life-cycle of an accelerator – from new-build through commissioning, acceptance and regular operations.”

Next up in the evolution of the RadiaSoft simulation environment is Sirepo Omega. Due to go live over the summer, this unified workflow manager will enable scientific users to create series simulations within the Sirepo “sandbox” – the outputs from one simulation automatically flowing along the simulation chain to generate a final result (with users, if they wish, able to probe individual simulations on a localised basis throughout the workflow).

“Sirepo Omega is all about convergence, automation and enhanced workflow efficiency,” said Edelen. For example, all coordinate transformations between different simulations are handled automatically by Sirepo Omega, while users can track particles automatically through all the sub-simulations. “The user will also get plots and summarised outputs in one convenient location, so there’s no need to go digging into each application to retrieve the results,” Edelen added.

Optimisation is better by design

Another foundational building block of the RadiaSoft service offering is rsopt, a Python framework for testing and running black-box optimisation problems in accelerator science and engineering. As such, the rsopt library and workflow manager give scientists a high degree of modularity when it comes to the choice of optimisation algorithms and code execution methods (including easy-to-use functionality for logging and saving results). Integration with Sirepo also enables templating for a number of codes related to particle accelerator simulation, making it straightforward to parse existing input files and use them without any additional modification.

“As well as ease-of-use and maintainability, rsopt combines a lot of powerful utilities for typical accelerator optimisation problems,” explained Chris Hall, senior scientist at RadiaSoft. A case study in this regard might be an accelerator code representing the design for an FEL – a common requirement being to minimise the bunch length or maximise the peak current while minimising emittance growth.

Chris Hall: “rsopt combines a lot of powerful utilities for typical accelerator optimisation problems.” (Courtesy: RadiaSoft)

A recent RadiaSoft collaboration involved the use of the rsopt library for the simulation and training of a non-destructive beam diagnostic capable of characterising the transverse and longitudinal profiles of ultrashort, high-brightness electron beams in FELs and next-generation colliders. “One of the attractions of rsopt,” added Hall, “is the ability to carry out various samplings to generate data for machine-learning models or to get a better understanding of your problem space.”

What’s more, interoperability is hard-wired into rsopt to enable platform-independent execution and scaling to massively parallel systems. “This means users can easily move their code execution between computational environments and utilise algorithms from multiple libraries without having to refactor their own code,” noted Hall.

The future’s bright for RadiaSoft. Having established a sustainable R&D business model in North America over the past 10 years, international expansion is the next step on the group’s commercial roadmap. “Watch this space,” Edelen concluded. “The task for us right now is finding the right path to grow our R&D activity by collaborating with scientists and engineers at large-scale accelerator facilities in Europe.”

For more information about Sirepo, sign up on CERN Courier for the RadiaSoft webinar End-to-end simulation of particle accelerators using Sirepo (19 July).

End-to-end simulation of particle accelerators using Sirepo

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This webinar will give a high-level overview of how scientists can model particle accelerators using Sirepo, an open-source scientific computing gateway.

The speaker, Jonathan Edelen, will work through examples using three of Sirepo’s applications that best highlight the different modelling regimes for simulating a free-electron laser.

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Jonathan Edelen, president, earned a PhD in accelerator physics from Colorado State University, after which he was selected for the prestigious Bardeen Fellowship at Fermilab. While at Fermilab he worked on RF systems and thermionic cathode sources at the Advanced Photon Source. Currently, Jon is focused on building advanced control algorithms for particle accelerators including solutions involving machine learning.

CERN shares beampipe know-how for gravitational-wave observatories

The direct detection of gravitational waves in 2015 opened a new window to the universe, allowing researchers to study the cosmos by merging data from multiple sources. There are currently four gravitational wave telescopes (GWTs) in operation: LIGO at two sites in the US, Virgo in Italy, KAGRA in Japan, and GEO600 in Germany. Discussions are ongoing to establish an additional site in India. The detection of gravitational waves is based on Michelson laser interferometry with Fabry-Perot cavities, which reveals the expansion and contraction of space at the level of ten-thousandths of the size of an atomic nucleus, i.e. 10^-19m. Despite the extremely low strain that needs to be detected, an average of one gravitational wave is measured per week of measurement by studying and minimising all possible noise sources, including seismic vibration and residual gas scattering. The latter is reduced by placing the interferometer in a pipe where ultrahigh vacuum is generated. In the case of Virgo, the vacuum inside the two perpendicular 3 km-long arms of the interferometer is lower than 10^-9 mbar.

While current facilities are being operated and upgraded, the gravitational-wave community is also focusing on a new generation of GWTs that will provide even better sensitivity. This would be achieved by longer interferometer arms, together with a drastic reduction of noise that might require cryogenic cooling of the mirrors. The two leading studies are the Einstein Telescope (ET) in Europe and the Cosmic Explorer (CE) in the US. The total length of the vacuum vessels envisaged for the ET and CE interferometers is 120 km and 160 km, respectively, with a tube diameter of 1 to 1.2 m. The required operational pressures are typical to those needed for modern accelerators (i.e. in the region of 10^-10 mbar for hydrogen and even lower for other gas species). The next generation of GWTs would therefore represent the largest ultrahigh vacuum systems ever built.

The next generation of gravitational-wave telescopes would represent the largest ultrahigh vacuum systems ever built.

Producing these pressures is not difficult, as present vacuum systems of GWT interferometers have a comparable degree of vacuum. Instead, the challenge is cost. Indeed, if the previous generation solutions were adopted, the vacuum pipe system would amount to half of the estimated cost of CE and not far from one-third of ET, which is dominated by underground civil engineering. Reducing the cost of vacuum systems requires the development of different technical approaches with respect to previous-generation facilities. Developing cheaper technologies is also a key subject for future accelerators and a synergy in terms of manufacturing methods, surface treatments and installation procedures is already visible.

Within an official framework between CERN and the lead institutes of the ET study – Nikhef in the Netherlands and INFN in Italy – CERN’s TE-VSC and EN-MME groups are sharing their expertise in vacuum, materials, manufacturing and surface treatments with the gravitational-wave community. The activity started in September 2022 and is expected to conclude at the end of 2025 with a technical design report and a full test of a vacuum-vessel pilot sector. During the workshop “Beampipes for Gravitational Wave Telescopes 2023”, held at CERN from 27 to 29 March, 85 specialists from different communities encompassing accelerator and gravitational-wave technologies and from companies that focus on steel production, pipe manufacturing and vacuum equipment gathered to discuss the latest progress. The event followed a similar one hosted by LIGO Livingston in 2019, which gave important directions for research topics.

Plotting a course
In a series of introductory contributions, the basic theoretical elements regarding vacuum requirements and the status of CE and ET studies were presented, highlighting initiatives in vacuum and material technologies undertaken in Europe and the US. The detailed description of current GWT vacuum systems provided a starting point for the presentations of ongoing developments. To conduct an effective cost analysis and reduction, the entire process must be taken into account — including raw material production and treatment, manufacturing, surface treatment, logistics, installation, and commissioning in the tunnel. Additionally, the interfaces with the experimental areas and other services such as civil engineering, electrical distribution and ventilation are essential to assess the impact of technological choices for the vacuum pipes.

The selection criteria for the structural materials of the pipe were discussed, with steel currently being the material of choice. Ferritic steels would contribute to a significant cost reduction compared to austenitic steel, which is currently used in accelerators, because they do not contain nickel. Furthermore, thanks to their body-centred cubic crystallographic structure, ferritic steels have a much lower content of residual hydrogen – the first enemy for the attainment of ultrahigh vacuum – and thus do not require expensive solid-state degassing treatments. The cheapest ferritic steels are “mild steels” which are common materials in gas pipelines after treatment to fight corrosion. Ferritic stainless steels, which contain more than 12% in weight of dissolved chromium, are also being studied for GWT applications. While first results are encouraging, the magnetic properties of these materials must be considered to avoid anomalous transmission of electromagnetic signals and of the induced mechanical vibrations.

Four solutions regarding the design and manufacturing of the pipes and their support system were discussed at the March workshop. The baseline is a 3 to 4 mm-thick tube similar to the ones operational in Virgo and LIGO, with some modifications to cope with the new tunnel environment and stricter sensitivity requirements. Another option is a 1 to 1.5 mm-thick corrugated vessel that does not require reinforcement and expansion bellows. Additionally, designs based on double-wall pipes were discussed, with the inner wall being thin and easy to heat and the external wall performing the structural role. An insulation vacuum would be generated between the two walls without the cleanliness and pressure requirements imposed on the laser beam vacuum. The forces acting on the inner wall during pressure transients would be minimised by opening axial movement valves, which are not yet fully designed. Finally, a gas-pipeline solution was also considered, which would be produced by a half-inch thick wall made of mild steel. The main advantage of this solution is its relatively low cost, as it is a standard approach used in the oil and gas industry. However, corrosion protection and ultrahigh vacuum needs would require surface treatment on both sides of the pipe walls. These treatments are currently under consideration. For all types of design, the integration of optical baffles (which provide an intermittent reduction of the pipe aperture to block scattered photons) is a matter of intense study, with options for position, material, surface treatment, and installation reported. The transfer of vibrations from the tunnel structure to the baffle is also another hot topic.

The manufacturing of the pipes directly from metal coils and their surface treatment can be carried out at supplier facilities or directly at the installation site. The former approach would reduce the cost of infrastructure and manpower, while the latter would reduce transport costs and provide an additional degree of freedom to the global logistics as storage area would be minimized. The study of in-situ production was brought to its limit in a conceptual study of a process that from a coil could deliver pipes as long as desired directly in the underground areas: The metal coil arrives in the tunnel; then it is installed in a dedicated machine that unrolls the coil and welds the metallic sheet to form the pipe to any length.

These topics will undergo further development in the coming months, and the results will be incorporated into a comprehensive technical design report. This report will include a detailed cost optimization and will be validated in a pilot sector at CERN. With just under two and a half years of the project remaining, its success will demand a substantial effort and resolute motivation. The optimism instilled by the enthusiasm and collaborative approach demonstrated by all participants at the workshop is therefore highly encouraging.

Proton structure consists of three distinct regions

Researchers at Jefferson lab in the US have gained a deeper understanding of the role of gluons in providing mass to visible matter. Based on measurements of the photoproduction of J/ψ particles, the findings suggest that the proton’s structure has three distinct regions, with an inner core driven by gluonic interactions making up most of its mass.

Although the charge and spin of the proton have been extensively studied for decades, relatively little is known about its mass distribution. This is because gluons, which despite being massless provide a sizeable contribution to the proton’s mass, are neutral and thus cannot be studied directly using electromagnetic probes. The Jefferson team instead used the gluonic gravitational form factors (GFFs). Similar to electromagnetic form factors, which provide information about a hadron’s charge and magnetisation distributions, the GFFs (technically the matrix elements of the proton’s energy–momentum tensor) encode mechanical properties of the proton such as its mass, density, pressure and shear distributions.

To access the GFFs, the team measured the threshold cross section of exclusive J/ψ photoproduction at different energies by forcing photons with energies between 9.1 and 10.6 GeV to interact with a liquid hydrogen target. Gluons dominate the production of J/ψ at small momentum transfer since J/ψ mesons share no valence quarks with the proton. Due to the J/ψ’s vector quantum numbers, this process can occur at certain energies by gluons in scalar (dilaton-like) and tensor (graviton-like) states. The researchers fed their cross-section results into QCD models describing the gluonic GFFs and extracted the parameters defining the GFFs, enabling them to deduce one mass radius and one scalar radius.

We need a new generation of high-precision J/ψ experiments to get a better picture
Zein-Eddine Meziani

The analysis revealed a scalar proton radius of 1 fm, which is substantially larger than both the charge radius (around 0.85 fm) and the proton mass radius (0.75 fm). This led the team to propose that the proton structure consists of three distinct regions: an inner core that makes up most of the mass radius and is dominated by the tensor gluonic field structure, followed by the charge radius resulting from the relativistic motion of quarks, all enveloped in a larger confining scalar gluon density.

“Given that the proton’s scalar gluon radius is the largest we need to understand how this converts to our understanding of the gluonic structure of nuclei. For example, what would be the scalar radius of ⁴He compared to its charge radius?” says study leader Zein-Eddine Meziani of Argonne. The team plans to extend its studies to include the J/ψ muon final state decay, doubling the statistics of the current measurement, and to extract the gluon pressure distribution. “It is hard to say much right now, but this is a field in its infancy and the direct role of gluons in nuclei is not well understood,” adds Meziani. “We need a new generation of high-precision J/ψ experiments to get a better picture.”

Giorgio Brianti 1930–2023

John Adams (former Director General, left) and Giorgio Brianti (right). Credit: CERN

Giorgio Brianti, a pillar of CERN throughout his 40-year career, passed away on 6 April at the age of 92. He played a major role in the success of CERN and in particular the LEP project, and his legacy lives on across the whole of the accelerator complex.

Giorgio began his engineering studies at the University of Parma and continued them for three years in Bologna, where he obtained his laurea degree in May 1954. Driven by a taste for research, he learned, thanks to his thesis advisor, that Edoardo Amaldi was setting up an international organization in Geneva called CERN and was invited to meet him in Rome in June 1954. In his autobiography – written for his family and friends – Giorgio describes this meeting as follows: “Edoardo Amaldi received me very warmly and, after various discussions, he said to me: ‘you can go home: you will receive a letter of appointment from Geneva soon’. I thus had the privilege of participating in one of the most important intellectual adventures in Europe, and perhaps the world, which in half a century has made CERN ‘the’ world laboratory for particle physics.”

Giorgio had boundless admiration for John Adams, who had been recruited by Amaldi a year earlier, recounting: “John was only 34 years old, but had a very natural authority. To say that we had a conversation would be an exaggeration, due to my still very hesitant English, but I understood that I was assigned to the magnet group”. After participating in the design of the main bending magnets for the Proton Synchrotron, Giorgio was sent by Adams to Genoa for three years to supervise the construction of 100 magnets made by the leading Italian company in the sector, Ansaldo. Upon his return, he was entrusted with the control group and in 1964 he was appointed head of the synchro-cyclotron (SC) division. After only four years he was asked to create a new division to build a very innovative synchrotron – the Booster – capable of injecting protons into the PS and significantly increasing the intensity of the accelerated current. He described this period as perhaps his happiest from a technical point of view. Adams – who had been appointed Director General of the new CERN-Lab II to construct the 400 GeV Super Proton Synchrotron (SPS) – also entrusted Giorgio with designing and building the experimental areas and their beam lines. The 40th anniversary of their inauguration was celebrated with him in 2018 and the current fixed-target experimental programme profits to this day from his foresight.

Giorgio has left us not only an intellectual but also a spiritual legacy

In January 1979 Giorgio was made head of the SPS division, but only two years later he was called to a more important role, that of technical director, by the newly appointed Director General Herwig Schopper. As Giorgio writes: “The main objectives of the mandate were to build the LEP… which was to be installed in a 27 km circumference tunnel over 100 m deep, and to complete the SPS proton-antiproton program, a very risky enterprise, but whose success in 1982 and 1983 was decisive for the future of CERN”. The enormous technical work required to transform the SPS into a proton-antiproton collider that went on to discover the W and Z bosons took place in parallel with the construction of LEP and the launch of the Large Hadron Collider (LHC) project, which Giorgio personally devoted himself to starting in 1982.

The LHC occupied Giorgio for nearly 15 years, starting from almost nothing. As he writes: “It was initially a quasi-clandestine activity to avoid possible reactions from the delegates of the Member States, who would not have understood an initiative parallel to that of the LEP. The first public appearance of the potential project, which already bore the name Large Hadron Collider, took place at a workshop held in Lausanne and at CERN in the spring of 1984.”

The LHC project received a significant boost from Carlo Rubbia, who became Director General in 1989 and appointed Giorgio as director of future accelerators. While LEP was operating at full capacity during these years, under his leadership new technologies were developed and the first prototypes of high-field superconducting magnets were created. The construction programme for the LHC was preliminarily approved in 1994, under the leadership of Chris Llewellyn Smith. In 1996, one year after Giorgio’s retirement, the final approval was granted. Giorgio continued to work, of course! In particular, in 1996 he agreed to chair the advisory committee of the Proton Ion Medical Machine Study, a working group established within CERN aimed at designing and developing a new synchrotron for medical purposes for the treatment of radio-resistant tumours with carbon ion beams. The first centre was built in Italy, in Pavia, by the Italian Foundation National Centre for Oncological Hadrontherapy (CNAO). He was also an active member of the editorial board of the book “Technology meets Research,” which celebrated 60 years of interaction at CERN between technology and fundamental science.

Giorgio has left us not only an intellectual but also a spiritual legacy. He was a man of great moral rigour, with a strong and contemplative Christian faith, determined to achieve his goals but mindful not to hurt others. He was very attached to his family and friends. His intelligence, kindness, and generosity shone through his eyes and – despite his reserved character – touched the lives of everyone he met.

Altarelli awards honour young scientists

On 27 March, during the 30th edition of the Deep-Inelastic Scattering and Related Subjects workshop (DIS2023) held in Michigan, Adinda de Wit and Yong Zhao received the 2023 Guido Altarelli Awards for experiment and theory. The prizes, named after CERN’s Guido Altarelli, who made seminal contributions to QCD, recognise exceptional achievements from young scientists in deep-inelastic scattering and related subjects.

CMS collaborator Adinda de Wit (University of Zurich) was awarded the experimental prize for her achievements in understanding the nature of the Higgs boson, including precision studies of its couplings and decay channels. She received her PhD from Imperial College London, then took up a postdoc position at DESY followed by the University of Zurich and is presently at LLR. Co-convener of the CMS Higgs physics analysis group and past co-convener of the CMS Higgs combination and properties group, de Wit also received the Herta-Sponer-Prize by the German Physical Society.

Yong Zhao (Argonne National Laboratory) was awarded the theory prize for fundamental contributions to ab initio calculations of parton distributions in lattice QCD. He received his PhD from the University of Maryland, and then held postdoc positions at Brookhaven and MIT before joining Argonne laboratory as an assistant physicist. Yong also received the 2022 Kenneth G. Wilson Award for Excellence in Lattice Field Theory for fundamental contributions to calculations of parton physics on lattice.

During the award ceremony, Nobel laureate Giorgio Parisi joined in via Zoom to reminisce about his collaboration with Altarelli. Together they contributed to QCD evolution equations for parton densities, known as the Altarelli-Parisi or DGLAP equations.

The DIS series covers a large spectrum of topics in high-energy physics. One part of the conference is devoted to the most recent results from large experiments at Brookhaven, CERN, DESY, Fermilab, Jlab and KEK, as well as corresponding theoretical advances. The workshop demonstrated how DIS and related subjects permeate a broad range of physics topics from hadron colliders to spin physics, neutrino physics and more. The next workshop will be held in Grenoble, France from 8-12 April 2024.

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