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Nature Physics, Published online: 04 April 2024; doi:10.1038/s41567-024-02457-5

The occurrence of propagating spiral waves in multicellular organisms is associated with key biological functions. Now this type of wave has also been observed in dense bacterial populations, probably resulting from non-reciprocal cell–cell interactions.

Nature Physics, Published online: 04 April 2024; doi:10.1038/s41567-024-02412-4

Leggett modes can occur when superconductivity arises in more than one band in a material and represent oscillation of the relative phases of the two superconducting condensates. Now, this mode is observed in Cd3As2, a Dirac semimetal.

Nature Physics, Published online: 04 April 2024; doi:10.1038/s41567-024-02465-5

The ferromagnet CrVI6 serves as a material platform to demonstrate the topological Kerr effect in two-dimensional magnets. This can be used to identify skyrmions by magneto-optical means.

The CMS experiment at CERN measures a key parameter of the Standard Model

Last week, at the annual Rencontres de Moriond conference, the CMS collaboration presented a measurement of the effective leptonic electroweak mixing angle. The result is the most precise measurement performed at a hadron collider to date and is in good agreement with the prediction from the Standard Model.

The Standard Model of Particle Physics is the most precise description to date of particles and their interactions. Precise measurements of its parameters, combined with precise theoretical calculations, yield spectacular predictive power that allows phenomena to be determined even before they are directly observed. In this way, the Model successfully constrained the masses of the W and Z bosons (discovered at CERN in 1983), of the top quark (discovered at Fermilab in 1995) and, most recently, of the Higgs boson (discovered at CERN in 2012). Once these particles had been discovered, these predictions became consistency checks for the Model, allowing physicists to explore the limits of the theory’s validity. At the same time, precision measurements of the properties of these particles are a powerful tool for searching for new phenomena beyond the Standard Model – so-called “new physics” - since new phenomena would manifest themselves as discrepancies between various measured and calculated quantities.

The electroweak mixing angle is a key element of these consistency checks. It is a fundamental parameter of the Standard Model, determining how the unified electroweak interaction gave rise to the electromagnetic and weak interactions through a process known as electroweak symmetry breaking. At the same time, it mathematically ties together the masses of the W and Z bosons that transmit the weak interaction. So, measurements of the W, the Z or the mixing angle provide a good experimental cross-check of the Model.

The two most precise measurements of the weak mixing angle were performed by experiments at the CERN LEP collider and by the SLD experiment at the Stanford Linear Accelerator Center (SLAC). The values disagree with each other, which had puzzled physicists for over a decade. The new result is in good agreement with the Standard Model prediction and is a step towards resolving the discrepancy between the latter and the LEP and SLD measurements.

“This result shows that precision physics can be carried out at hadron colliders,” says Patricia McBride, CMS spokesperson. “The analysis had to handle the challenging environment of LHC Run 2, with an average of 35 simultaneous proton-proton collisions. This paves the way for more precision physics at the High-Luminosity LHC, where five times more proton pairs will be colliding simultaneously.”

Precision tests of the Standard Model parameters are the legacy of electron-positron colliders, such as CERN’s LEP, which operated until the year 2000 in the tunnel that now houses the LHC. Electron-positron collisions provide a perfect clean environment for such high-precision measurements. Proton-proton collisions in the LHC are more challenging for this kind of studies, even though the ATLAS, CMS and LHCb experiments have already provided a plethora of new ultra-precise measurements. The challenge is mainly due to huge backgrounds from other physics processes than the one being studied and to the fact that protons, unlike electrons, are not elementary particles. For this new result, reaching a precision similar to that of an electron-positron collider seemed like an impossible task, but it has now been achieved.

The measurement presented by CMS uses a sample of proton-proton collisions collected from 2016 to 2018 at a centre-of-mass energy of 13 TeV and corresponding to a total integrated luminosity of 137 fb−1, meaning about 11.000 million million collisions! 

The mixing angle is obtained through an analysis of angular distributions in collisions where pairs of electrons or muons are produced. This is the most precise measurement performed at a hadron collider to date, improving on previous measurements from ATLAS, CMS and LHCb.

Read more:

• CMS Physics Analysis Summary
• CMS Physics Briefing

angerard Wed, 04/03/2024 - 11:01 Publication Date Wed, 04/03/2024 - 16:00

CERN and the Swiss Arts Council announce the artists selected for the sixth edition of Connect

Connect is an art residency programme launched by Arts at CERN and Pro Helvetia in 2021. Dedicated to Swiss-based artists working at the intersection of science and artistic research, this research-led residency invites them to come to CERN to explore ideas and develop new work.

The selected duo is composed of Robin Meier Wiratunga and Vimala Pons. Meier Wiratunga is an artist and composer who seeks to understand how humans, insects and objects think. Collaborating closely with scientific researchers, Meier Wiratunga's work blends machine learning with insights from animal intelligence, creating constellation scores where musical patterns emerge as ‘thinking tools'. Vimala Pons is an actress who has worked in independent and auteur cinema.

Meier Wiratunga and Pons will dedicate their residency at CERN to developing their proposal titled Guided Meditations for the End of the Universe. This project aims to delve into cosmological theories about the end of the Universe to transform them into meditative and embodied experiences. Employing an anthropological approach to engage with science, the artists intend to employ spoken voice recordings, electronic music, light environments and sonified data from particle events.

Now in its sixth edition, Connect has become a pivotal platform for Swiss-based artists to expand their artistic practice in dialogue with the field of physics and science at CERN. This collaboration framework between Arts at CERN and Pro Helvetia will continue through the next year with an iteration in Chile and India, sustaining its mission to foster interactions and dialogue between artistic and scientific communities.

“We find ourselves in a challenging yet exciting time, as we witness the emergence of a strong and vibrant infrastructure devoted to the integration of artistic activity within the sciences,” says Mónica Bello, Curator and Head of Arts at CERN. “This is a transformational and promising development that presents unprecedented opportunities for cultural innovation. Connect is evidence of these dynamics, and I am proud to see that our partnership with Pro Helvetia is advancing further, bringing in new residents with different perspectives and backgrounds and strengthening the confluence of art and science in Switzerland.”

“This sixth edition of Connect continues to reaffirm the significance of the interface between art, science and technology. The quality and diversity of applications received illustrate the rich interdisciplinarity inherent in this dynamic field, and the extent to which it is part of current artistic practice. We are happy to foster dialogue and innovation at this remarkable intersection and are very pleased about the ongoing collaboration with Arts at CERN,” explains Philippe Bischof, Director of Pro Helvetia.

The jury of Connect was formed by Mónica Bello, Curator and Head of Arts at CERN; Giulia Bini, Head of Program and Curator of “Enter the Hyper-Scientific” at EPFL Lausanne; and Federica Martini, Head of the CCC - Critical Curatorial Cybermedia Master at HEAD Genève.

angerard Tue, 04/02/2024 - 16:09 Publication Date Wed, 04/03/2024 - 14:00

Nature Physics, Published online: 01 April 2024; doi:10.1038/s41567-024-02445-9

Topological magnetic spin structures such as skyrmions and merons have the potential to be used in magnetic information devices. Now multistep transformations between such structures are demonstrated in a centrosymmetric material.

Nature Physics, Published online: 01 April 2024; doi:10.1038/s41567-024-02477-1

Despite their potential device applications, experimental realizations of proximity-induced Fulde–Ferrell–Larkin–Ovchinnikov states are rare. Now Josephson junctions based on a dilute magnetic topological insulator provide evidence of such a state.

CERN to change name for 70th Anniversary The Organization’s new logo. The correct usage of the branding can be found on the Design Guidelines website.

Since its inception in 1954, CERN has grown from a small group of physicists from a handful of countries to a thriving international hub for science and technology. This is why, on the occasion of the Laboratory’s 70th Anniversary, the time has come for the name to be adapted to reflect its new role in society. The new name, the Network of Experiments for Research and Development in Society, will come into force on 1 October 2024, at the Laboratory’s 70th birthday party.

The acronym CERN was borne from an intergovernmental meeting of UNESCO in Paris in December 1951. This is when the first resolution concerning the establishment of a European Council for Nuclear Research (in French Conseil Européen pour la Recherche Nucléaire, or CERN) was adopted. Two months later, an agreement was signed establishing the provisional Council – and the name “CERN” stuck. However, today, our understanding of matter goes much deeper than the nucleus, and “CERN” is now widely viewed across the scientific community as an outdated and exclusionary name.

“The word “nuclear” doesn’t really reflect the full breadth of scientific research we do here,” says Noah Lott, Head of Rebranding at the Organization. “Network of Experiments for Research and Development in Society indicates the range of particle physics, computing, engineering and technology research that takes place at the Laboratory, as well as its impact on society.”

“We are also no longer just a European organisation, as we have grown to a global community encapsulating more than 80 countries,” adds Ivana Reed, spokesperson for international relations at the Laboratory. “We feel that everyone, no matter who they are, will feel accepted and proud to be associated with NERDS.”

A dedicated working group – the Decision for a Unified Moniker Board – was created in 2021 to assess potential options for the new name. “NERDS is so much more memorable and inclusive than CERN,” explains Wirall Geex, president of the working group. “Since we are a global network of varied experiments, we hope the new name will remove negative stereotypes about the type of people who work at the Organization,” he adds, pushing up his glasses.

NERDS was chosen by the working group out of a list of names put forward by the CERN community. Among the high contenders were A Large International Experimental Network (ALIEN), the High Energy Laboratory for Physics (HELP), and the initial frontrunner, the Global Organization for Discovery (GOD). However, following a spirited debate in the working group, GOD was discarded on account of unfortunate echoes of the “God particle” – the controversial name accidentally given to the Higgs boson in 1993.

NERDS looks forward to continuing to be at the forefront of scientific research for the next 70 years and beyond.

ndinmore Wed, 03/27/2024 - 19:02 Publication Date Mon, 04/01/2024 - 09:00

Accelerator Report: Protons or Easter eggs? Let’s hope for both

Beam commissioning is progressing well across the entire accelerator complex, with initial completion achieved in the first machines of the chain. Last week, the first physics experiments started in the East Area, behind the PS, and others will follow suit shortly.

A Cell-Coupled-Drift-Tube-Linac (CCDTL) ready to be tested in SM18. (Image: CERN)

However, despite the overall positive momentum of beam commissioning, challenges have arisen along the way, highlighting the complexities involved. Last week, some of the components of one of the Linac4 accelerating structures, specifically the Cell-Coupled-Drift-Tube-Linacs (CCDTLs) 3 and 4, presented some issues. Both CCDTLs rely on a single klystron*, a high-power microwave amplifier crucial for providing accelerating power to the structures, which, in turn, transfer the power to the protons, which are then accelerated.

The high-voltage and high-frequency amplifier chain, including the klystron, experienced frequent voltage breakdowns, resulting in a significant drop in accelerating voltage within the two CCDTLs. This disruption severely perturbed the beam, rendering it unusable for the PS Booster. Experts intervened multiple times, initially focusing on fine-tuning the parameters of the amplifier chain and later on cleaning and replacing various components suspected to be causing the breakdowns.

By 22 March, a set of parameters was established to allow the acceleration of beams with a low proton intensity, enabling commissioning activities to continue in the downstream machines, including the LHC. However, these parameters did not meet the requirements for generating the full-blown physics beams that will be required in the coming weeks. On 24 March, a collaborative effort with experts from various groups convened in the CERN Control Centre (CCC) to conduct a final assessment. This evaluation aimed to determine whether the klystron needed replacing.

After re-establishing the parameters suitable for high-intensity beam acceleration, the beam was switched back on. Unfortunately, within the first hour, at least two high-voltage breakdowns occurred – the team thus concluded that the klystron replacement was necessary.

To maintain commissioning activities in the downstream machines, parameters allowing low-intensity beam acceleration were reinstated. This allowed operations to continue until Monday morning, when the klystron replacement process started. Such an intervention typically requires two to three days before beam operations can be restored.

The new klystron is in place, ready to feed the CCDTLs 3 and 4. (Image: CERN)

Meanwhile, commissioning activities in the downstream machines have been suspended and the start of physics at the n_TOF facility, behind the PS, has been postponed (it was originally scheduled to start on 25 March). Commissioning of the North Area's secondary beams began on 22 March instead of 25 March. Thanks to this head start, the incident in Linac4 does not impact the overall schedule for the North Area, where physics is still scheduled to start on 10 April.

In Linac4, the old klystron has been removed, and the new one had been installed and tested by 26 March. Beam was sent to the PS Booster at 5 p.m. that day and, at 9 p.m., the LHC beam commissioning activities resumed. Since then, they have been progressing well.

On 27 March, beams entered into “test” collisions at the target energy of 6.8 TeV in the LHC. These were not yet stable beams, which meant that the experiments did not take data. Collisions for physics at 6.8 TeV are expected to take place on 8 April.

______

* A klystron is a high-power microwave amplifier used to generate high-power radiofrequency (RF) signals at a specific frequency. It operates on the principle of velocity modulation, where bunches of electrons are alternately accelerated and decelerated within a resonant cavity structure. This modulation process results in the amplification of the RF signal.

anschaef Wed, 03/27/2024 - 15:59 Byline Rende Steerenberg Publication Date Thu, 03/28/2024 - 10:49

CERN and STFC support environmentally sustainable physics CERN Director-General, Fabiola Gianotti, and STFC Executive Chair, Mark Thomson, sign a new agreement to support the development of more sustainable particle accelerators (Image: CERN)

On 22 March, CERN and the UK’s Science and Technology Facility Council (STFC) signed a new agreement to collaborate on the research and development of advanced new technologies to make future particle accelerators significantly more sustainable.

Minimising the environmental impact of particle physics activities, ensuring their sustainability and energy efficiency is one of the key recommendations of the last update of the European Strategy for Particle Physics, published in 2020.

“CERN is fully committed to fostering sustainability across its existing and forthcoming projects, actively engaging in a variety of initiatives,” explains Mike Lamont, CERN Director of Accelerators and Technology. “These include sourcing renewable energy, implementing heat recovery schemes, and forging collaborations with industry to explore innovative applications of sustainable technology, such as high-power electricity distribution in various contexts. Our philosophy in this regard aligns well with that of the STFC and we look forward for exploiting the potential of this collaboration – together we are stronger.”

The agreement will act as a framework to better direct CERN and STFC’s funding, expertise and technological investment to minimise environmental impact. It provides guidance and recommendations that consider the entire lifecycle of accelerator facilities from design and construction to operation and decommissioning.

The agreement also outlines a proposal for STFC to establish a new Centre of Excellence in Sustainable Accelerators (CESA) at the Daresbury Laboratory in the UK. CESA would conduct original research in sustainable accelerator technologies and train accelerator scientists, technicians and engineers in the skills required to develop new accelerators with sustainability at the heart of the design.

For more details, see the UKRI website.

katebrad Wed, 03/27/2024 - 10:29 Publication Date Wed, 03/27/2024 - 10:28

Spring at CERN, your photos Ice-white blossom in front of ISOLDE (Image: Sanje Fenkart) (Image: CERN)

Blossom, blue sky and buildings proved the winning combination for our “spring at CERN” photo competition. Congratulations to Sanje Fenkart from the IR department, who wins not just one CAGI Chocopass, but two, allowing her and a friend to spend a day exploring Geneva and tasting from a range of chocolate shops.

Thank you to all of you who sent in your photos. They are beautiful and are now available in a CC-BY photo collection, shown as a slideshow here:

We’d like to thank the International Geneva Welcome Centre (CAGI) for their sweet (pun intended) gesture of offering these prizes. The CAGI cultural kiosk is located in CERN’s main building and is open from Monday to Friday from 8:30 a.m. to 11:00 a.m. and from 11:30 a.m. to 2:30 p.m. It offers numerous discounts for local activities and events both in Switzerland and in France. Find out more here: https://www.cagi.ch/en/cultural-kiosk-agenda/

katebrad Wed, 03/27/2024 - 10:03 Byline Internal Communication Publication Date Wed, 03/27/2024 - 16:46

Nature Physics, Published online: 27 March 2024; doi:10.1038/s41567-024-02447-7

Even by shining classical light on a single opening, one can perform a double-slit experiment and discover a surprising variety of quantum mechanical multi-photon correlations — thanks to surface plasmon polaritons and photon-number-resolving detectors.

Nature Physics, Published online: 27 March 2024; doi:10.1038/s41567-024-02466-4

Two adjacent layers flowing at different velocities in the same fluid are subject to flow instabilities. This phenomenon is now studied in atomic superfluids, revealing that quantized vortices act as both sources and probes of the unstable flow.

AMS’s second new life

In 2011, the Alpha Magnetic Spectrometer (AMS) was installed on the International Space Station (ISS). Since then, it has recorded more than 200 billion cosmic ray events and, while most of their sources are known, a few signatures in the data could point to dark matter. The detector’s latest upgrade will enable scientists to investigate this further.

AMS collects cosmic ray particles that reach Earth coming either directly from the Sun or from far-away sources such as stars ending in supernovae or black holes. Most of the cosmic rays that AMS detects are protons, but heavy nuclei like iron or silicon also reach the detector. However, one signature is particularly intriguing. AMS has detected an unusually high flux of positrons – the antimatter partners of electrons. Positrons and other antimatter particles are rare in the Universe and hence not expected to be seen in the observed data at the strength found by AMS. Their origin is not yet confirmed; they could come from pulsars (fast rotating remnants of stars that emit regular signals), a yet-unknown astrophysical source or dark matter. The observed positron flux fits very well with dark matter models. But in order to investigate this more accurately, the AMS collaboration is now working on refurbishing the detector.

The main upgrade will be a new detector layer with a higher number of silicon strips that will increase the acceptance of recording infalling particles by 300%. “By 2030, AMS will extend the energy range of the positron flux and reduce the error by a factor of two compared with current data,” says AMS spokesperson Sam Ting (MIT). This will allow the detector to investigate the positron signature even further.

A second important addition will be three new radiative surfaces. Because AMS is exposed to direct sunlight, it was painted white to reflect excess heat and remain at operational temperatures. After 13 years in the demanding conditions of space, the paint has degraded and, to compensate for this, the new radiators will keep AMS cool again.

Astronauts training at NASA’s “Neutral Buoyancy Lab” on a full-scale ISS model submerged under water where they learn to mount the new AMS upgrade parts (Image: Corrado Gargiulo/NASA)

Currently, all the parts of the new upgrade, including electronics and hardware, are being built as “validation” and “qualification” models. If they pass all the tests happening at CERN, INFN Perugia and IABG in Germany, the final flight model will go into production. Astronauts are already training with the prototypes in space-like environments on Earth. In 2026, when the upgrade is launched, the astronauts will mount the new detector parts onto AMS during spacewalks. “Everything is going very, very fast,” says chief engineer Corrado Gargiulo (CERN). “This is a requirement, otherwise we arrive too late at the ISS for the upgrade to make sense.” Indeed, the mission now has an end date. NASA has scheduled the deorbiting of the ISS for 2030 and, until then, AMS will have plenty of cosmic ray events to record to explore the positron signature.

A mock-up detector for the next AMS upgrade, which will be installed during the next anticipated spacewalk for AMS.  Another part of the upgrade includes a large power distribution system (PDS) radiator to restore AMS’s optimal thermal performance. (Image: Chetna Krishna/CERN)

ckrishna Tue, 03/26/2024 - 13:40 Byline Sanje Fenkart Publication Date Tue, 04/02/2024 - 10:00

The delicate balance of lepton flavours

In a talk at the ongoing Rencontres de Moriond conference, the ATLAS collaboration presented the result of its latest test of a key principle of the Standard Model of particle physics known as lepton flavour universality. The precision of the result is the best yet achieved by a single experiment in decays of the W boson and surpasses that of the current experimental average.

Most elementary particles can be classed into groups or families with similar properties. For example, the lepton family includes the electron, which forms the negatively charged cloud of particles surrounding the nucleus in every atom, the muon, a heavier particle found in cosmic rays, and the tau-lepton, an even heavier short-lived particle only seen in high-energy particle interactions.

As far as physicists know, the only difference between these particles is their mass, as generated through their different strengths of interaction with the fundamental field associated with the Higgs boson. In particular, a remarkable feature of the Standard Model is that each lepton type, or “flavour”, is equally likely to interact with a W boson, the electrically charged carrier of the weak force that is one of the four fundamental forces of nature. This principle is known as lepton flavour universality.

High-precision tests of lepton flavour universality, as obtained by comparing the rates of decay of the W boson into an electron and an electron neutrino, into a muon and a muon neutrino or into a tau-lepton and a tau neutrino, are therefore sensitive probes of physics beyond the Standard Model. Indeed, if lepton flavour universality holds, these decay rates should be equal (within negligible mass-dependent corrections).

This can be tested by measuring the ratios of the W boson’s rates of decay into the different lepton flavours. One of the challenges associated with such measurements at the Large Hadron Collider (LHC) is the collection of a pure (“unbiased”) sample of W bosons. In a paper released by Nature Physics in 2021, ATLAS reported the world’s most precise measurement of the ratio of the W boson’s rate of decay into a tau-lepton versus its rate of decay into a muon, demonstrating that collision events in which a pair of top quarks is produced provide an abundant and clean sample of W bosons.

In a recent paper, ATLAS released a new measurement, this time addressing the ratio of the W boson’s rate of decay into a muon versus its rate of decay into an electron. While the combination of all previous measurements showed that this ratio is within about 0.6% of unity, corresponding to equal decay rates, there was still room for improvement.

The new ATLAS result is based on a study of its full dataset from the second run of the LHC, collected between 2015 and 2018. The analysis looked at over 100 million top-quark-pair collision events. The top quark decays promptly into a W boson and a bottom quark, so this sample provides 100 million pairs of W bosons. By counting the number of these events with two electrons (and no muon) or two muons (and no electron), physicists can test whether the W boson decays more often into an electron or a muon.

However, it's not that simple. The Z boson, the electrically neutral carrier of the weak force, can also decay into a pair of electrons or muons, leaving a similar experimental signature to that of a top-quark pair. Since the combined mass of the leptons in Z-boson events clusters around the Z-boson mass of 91 GeV, this background process can be estimated and subtracted.

Moreover, as a result of measurements conducted in the 1990s at CERN’s Large Electron–Positron (LEP) collider, the LHC’s predecessor, and at the Stanford Linear Collider (SLC), the ratio of the Z boson’s rate of decay into two muons versus its rate of decay into two electrons is known to be equal to unity within 0.3%. Thus, in this ATLAS analysis, the Z boson’s decay rate ratio was determined as a reference measurement, allowing researchers to reduce uncertainties coming from the reconstruction of electrons and muons. Additionally, as many measurement uncertainties are similar in the events with two electrons and those with two muons, they were found to have only a minor effect on the measured decay rate ratio.

The final result from this new ATLAS analysis is a ratio of 0.9995, with an uncertainty of 0.0045, perfectly compatible with unity. With an uncertainty of only 0.45%, the result is more precise than all previous measurements combined (see figure below). For now, lepton flavour universality survives intact.

Measurements of the ratio of the W boson’s rate of decay into a muon versus its rate of decay into an electron. The new ATLAS result is shown in the last row as an open blue circle. Previous measurements are shown above using solid symbols, and the Particle Data Group average of all previous results is shown using a black diamond. (Image: ATLAS/CERN) abelchio Tue, 03/26/2024 - 10:33 Byline ATLAS collaboration Publication Date Tue, 03/26/2024 - 10:17

Computer Security: Day of the open firewall

With ongoing vulnerability scans of CERN’s internet presence performed by an external specialised company, the Computer Security team’s plans to perform penetration testing against selected targets visible to the internet, and the possibility of CERN joining a so-called Bug Bounty programme (a Bulletin article on this will come soon), we are preparing for an increasingly thorough assessment of the weaknesses, misconfigurations and vulnerabilities inside CERN – on the campus network, the technical network and the networks dedicated to the different experiments.

Given that the CERN networks are many, vast and interconnected in a complex manner, with tens of thousands of registered devices, thousands of them regularly or permanently connected, a large proportion of unmanaged “bring-your-own” devices or unpatchable and inherently vulnerable devices of the Internet of Things, a very large number of heterogenous virtual machines and containers running arbitrary applications, and about ten thousand websites leading to millions of webpages, vulnerability scanning and penetration testing of such an environment is complex, complicated and tedious. That’s why we have decided to lower CERN’s outer perimeter firewall protections for 24 hours on the first Monday of next month so that any external third party interested in poking/hacking/breaking into CERN can do so. The open firewall, allowing any incoming traffic, will facilitate not only the work of the aforementioned external company, but also that of the students affiliated with our WhiteHat programme, Bug Bounty hunters hoping for an entry on our Kudos page and any other benign or malicious attacker.

As usual, any ethical party probing CERN during those 24 hours is supposed to stop their activity before any damage or destruction is done and to report all their findings immediately to us so that they can be addressed, controlled, mitigated and fixed. For those cases where the scans and tests are performed by malicious actors, our network-based intrusion detection system connected to the outer perimeter firewall will stay alert and monitor all activities in the hope of identifying their ill-doing well in time, as we managed to in the past. The Computer Security team will, exceptionally, cover its duties 24/7. Of course, we cannot guarantee that no damage will be done by any malicious attacker, but we are counting on the robustness, resilience and up-to-dateness of your systems, devices, virtual machines/containers and websites. This risk is also the reason why we will open the firewall for just 24 hours: this tight time window should keep any collateral damage low.

So, stay tuned for next Monday, 1 April, 00:00 to 23:59, the day when we shall learn more about the security of CERN’s internal networks, and subsequently further improve all the systems connected to it.  

________

Do you want to learn more about computer security incidents and issues at CERN? Follow our Monthly Report. For further information, questions or help, check our website or contact us at Computer.Security@cern.ch.

anschaef Mon, 03/25/2024 - 23:22 Byline Computer Security team Publication Date Mon, 03/25/2024 - 23:22

Nature Physics, Published online: 26 March 2024; doi:10.1038/s41567-024-02436-w

Interactions of atmospheric neutrinos with quantum-gravity-induced fluctuations of the metric of spacetime would lead to decoherence. The IceCube Collaboration constrains such interactions with atmospheric neutrinos.

First observation of photons-to-taus in proton–proton collisions by CMS

In March 2024, the CMS collaboration announced the observation of two photons creating two tau leptons in proton–proton collisions. It is the first time that this process has been seen in proton–proton collisions, which was made possible by using the precise tracking capabilities of the CMS detector. It is also the most precise measurement of the tau’s anomalous magnetic moment and offers a new way to constrain the existence of new physics.

The tau, sometimes called tauon, is a peculiar particle in the family of leptons. In general, leptons, together with quarks, make up the “matter” content of the Standard Model (SM). The tau was only discovered in the late 1980s at SLAC, and its associated neutrino – the tau neutrino – completed the tangible matter part upon its discovery in 2000 by the DONUT collaboration at Fermilab. Precise research for the tau is rather tricky though, as its lifetime is very short: it remains stable for only 290·10-15 s (a hundred quadrillionth of a second).

The two other charged leptons, the electron and the muon, are rather well studied. A lot is also known about their magnetic moments and their associated anomalous magnetic moments. The former can be understood as the strength and orientation of an imaginary bar magnet inside a particle. This measurable quantity, however, needs corrections at the quantum level arising from virtual particles tugging at the magnetic moment, deviating it from the predicted value. The quantum correction, referred to as anomalous magnetic moment, is of the order of 0.1%. If the theoretical and experimental results disagree, then this anomalous magnetic moment, al , opens doors to physics beyond the SM.

The anomalous magnetic moment of the electron is one of the most precisely known quantities in particle physics and agrees perfectly with the SM. Its muonic counterpart, on the other hand, is one of the most investigated ones, into which research is ongoing. Although theory and experiments have mostly agreed so far, recent results give rise to a tension that requires further investigation.

For the tau, however, the race is still going. It is especially hard to measure its anomalous magnetic moment, aτ, due to the tau’s short lifetime. The first attempts to measure aτ after the tau’s discovery came with an uncertainty that was 30 times higher than the size of the quantum corrections. Experimental efforts at CERN with the LEP and LHC detectors improved the constraints, reducing the uncertainties to 20 times the size of the quantum corrections.

In collisions, researchers look for a special process: two photons interacting to produce two tau leptons, also called a di-tau pair, which then decay into muons, electrons, or charged pions, and neutrinos. So far both ATLAS and CMS have observed this in ultra-peripheral lead–lead collisions. Now, CMS reports on the first observation of the same process during proton–proton collisions. These collisions offer a higher sensitivity to physics beyond the SM as new physics effects increase with the collision energy. With the outstanding tracking capabilities of the CMS detector, the collaboration was able to isolate this specific process from others, by selecting events where the taus are produced without any other track within distances as small as 1 mm. “This remarkable achievement of detecting ultra-peripheral proton–proton collisions sets the stage for many groundbreaking measurements of this kind with the CMS experiment,” said Michael Pitt, from the CMS analysis team.

This new method offers a new way to constrain the tau anomalous magnetic moment, which the CMS collaboration tried out immediately. While the significance will be improved with future run data, their new measurement places the tightest constraints so far, with higher precision than ever before. It reduces the uncertainty from the predictions down to only three times the size of the quantum corrections. “It is truly exciting that we can finally narrow down some of the basic properties of the elusive tau lepton,” said Izaak Neutelings, from the CMS analysis team. “This analysis introduces a novel approach to probe tau g-2 and revitalises measurements that have remained stagnant for more than two decades,” added Xuelong Qin, another member of the analysis team.

Further material: 3D interactive version of the event display with all tracks here.

sandrika Mon, 03/25/2024 - 16:27 Publication Date Mon, 03/25/2024 - 17:00

World Wide Web at 35 Tim Berners-Lee invented and developed the World Wide Web as an essential tool for high energy physics at CERN from 1989 to 1994. Together with a small team he conceived HTML, http, URLs, and put up the first server and the first 'what you see is what you get' browser and html editor. (Image: CERN)

Thirty-five years ago, a young computer expert working at CERN wrote a proposal that combined accessing information with a desire for broad connectivity and openness. This proposal went on to become the World Wide Web (WWW), whose impact on society has been profound.  

Sir Tim Berners-Lee’s first proposal in March 1989 was for an internet-based hypertext system to link and access information across different computers. In November 1990, this “web of information nodes in which the user can browse at will” was formalised as a proposal, “WorldWideWeb: Proposal for a HyperText Project”, by Berners-Lee, together with a CERN colleague, Robert Cailliau. By Christmas that year, Berners-Lee had implemented key components, namely html, http and URL, and created the first Web server, browser and editor (WorldWideWeb). This server is now exhibited in the Laboratory’s new visitor centre, CERN Science Gateway.

CERN released the WWW software into the public domain on 30 April 1993, making it freely available for anyone to use and improve. This decision encouraged the use of the Web, and society to benefit from it.

Now, thirty-five years since his original proposal, Sir Tim Berners-Lee reflects on the web’s trajectory in an open letter and states how we, as engaged citizens, can "re-shape a digital future that prioritises human well-being, equity, and autonomy".

katebrad Mon, 03/25/2024 - 15:36 Publication Date Wed, 03/27/2024 - 16:24

Brazil becomes Associate Member State of CERN

Brazil has become the first Associate Member State of CERN in the Americas, following official notification that the country has completed its internal approval procedures in respect of the agreement signed in March 2022 granting it that status and of the Protocol on Privileges and Immunities of the Organization. The starting date of Brazil’s status as an Associate Member State is 13 March 2024.

Formal cooperation between CERN and Brazil started in 1990 with the signature of an International Cooperation Agreement, allowing Brazilian researchers to participate in the DELPHI experiment at the Large Electron–Positron Collider (LEP). Over the past decade, Brazil’s experimental particle-physics community has doubled in size. At the four main Large Hadron Collider (LHC) experiments alone, about 200 Brazilian scientists, engineers and students collaborate in fields ranging from hardware and data processing to physics analysis.

Today, Brazilian institutes participate in all the main experiments at the LHC – ALICE, ATLAS, CMS and LHCb and their ongoing and planned upgrades – as well as in ALPHA at the anti-proton decelerator. They are also involved in experiments at ISOLDE, ProtoDUNE at the Neutrino Platform and instrumentation projects such as Medipix. Following on from their participation in the RD51 collaboration, Brazilian teams are also contributing to setting up the DRD1 and DRD3 R&D collaborations for future detectors. Brazilian nationals also participate very actively in CERN training and outreach programmes.

Beyond particle physics, CERN and Brazil’s National Centre for Research in Energy and Materials (CNPEM) have also been formally cooperating since December 2020 on accelerator technology R&D and its applications.

As an Associate Member State, Brazil is entitled to appoint representatives to attend meetings of the CERN Council and the Finance Committee. Its nationals are eligible to apply for limited-duration staff positions and CERN’s graduate programmes, and its industry is entitled to bid for CERN contracts, increasing opportunities for industrial collaboration in advanced technologies.

angerard Fri, 03/22/2024 - 09:06 Publication Date Fri, 03/22/2024 - 17:00