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One of the biggest open questions in particle physics today is how the Higgs boson interacts with itself. This “self-coupling” could help explain the evolution of the early Universe and the mechanism that gives mass to elementary particles. To try to shed light on this fundamental interaction, the ATLAS Collaboration has recently studied one of the “golden” decay channels of a pair of Higgs bosons, where one Higgs boson decays into two photons and the other into a pair of bottom quarks.
By combining the entire LHC Run 2 dataset (2015–2018) and a partial Run 3 dataset (2022–2024), the ATLAS team has significantly enhanced the statistical power of the analysis of this decay channel. The result, just published in Physics Letters B, marks the first ATLAS measurement based on over 300 inverse femtobarns (fb⁻¹) of proton–proton collision data, where one inverse femtobarn corresponds to approximately 100 trillion collisions.
Studying this decay channel is particularly challenging due to the extremely rare nature of Higgs boson pair production – predicted to occur once in a trillion proton–proton collisions – and the significant background from Standard Model processes that mimic this decay mode. To overcome these challenges, ATLAS physicists used advanced data analysis techniques, such as machine learning, to help to isolate the decay signal from the background.
As a result of these advancements and the addition of the partial Run 3 dataset, the ATLAS researchers set more stringent limits than they did before on the signal strength (the observed signal divided by the Standard Model prediction) and two key interaction parameters. These are the magnitude of the Higgs boson’s self-coupling divided by its Standard Model prediction, limited to be between −1.6 and 6.6, and the interaction strength between two Higgs bosons and two vector bosons (W or Z bosons) divided by its Standard Model prediction, limited to be between −0.5 and 2.6.
The results underscore the ATLAS Collaboration’s growing ability to explore Higgs boson pair production in this golden decay channel. They also lay the foundation for future measurements of the Higgs boson’s self-coupling – key to understanding the evolution of the Universe after the Big Bang. With the full Run 3 dataset soon to be available and the High-Luminosity LHC on the horizon, ATLAS is well positioned to push these studies even further – sharpening our understanding of the Higgs boson and exploring potential signs of physics beyond the Standard Model.
Read more on the ATLAS website.
ehatters Wed, 04/22/2026 - 10:17 Byline ATLAS collaboration Publication Date Wed, 04/22/2026 - 10:10Tens of kilometres above Earth’s surface, high-energy particles from outer space constantly strike the atmosphere, creating showers of energetic secondary particles that rain down from the sky. Approximately one of these particles passes through your head every second, but the “cosmic rays” that produce them are still not fully understood. In a recent paper, the ATLAS Collaboration describes how its first measurement of proton–oxygen collisions at the LHC could help us learn more about them.
Cosmic rays were discovered over a century ago by physicist Victor Hess in experiments conducted aboard hot-air balloons. Today, astrophysicists use detectors on the ground to image cosmic-ray showers and computer simulations of the showers to understand that data.
However, these simulations depend on properties of the strong force – one of the fundamental forces of the Universe – which is difficult to accurately model. Current simulations disagree with one another, making it difficult for astrophysicists to interpret their measurements of cosmic rays.
In part to help improve these simulations, the LHC was configured to collide protons with oxygen ions for the first time in July 2025. This meant physicists could study ‘recreated’ cosmic-ray collisions in more detail. The beam of protons acted as a cosmic ray, while the beam of oxygen ions played the role of Earth’s atmosphere, which is composed primarily of nitrogen and oxygen.
The new paper describes how ATLAS physicists analysed these collisions by measuring the tracks left in the experiment from electrically charged particles. They measured key properties of the collision, including how often the particles were created, how many were created, and the energies and angles at which they flew out.
They then compared the measured distributions of charged particles with the numbers predicted by various simulations typically used to interpret data from cosmic-ray observatories. These simulations, which are tuned to reproduce data from previous collisions of protons with heavier nuclei, disagree with one another.
The new ATLAS measurements achieve a precision level of a few percent, significantly improving knowledge of proton–oxygen collisions. Theorists can now use this input to refine their models and help shed more light on the mysterious high-energy particles arriving from our cosmos.
Read more on the ATLAS website.
ehatters Mon, 04/20/2026 - 17:33 Byline ATLAS collaboration Publication Date Tue, 04/21/2026 - 10:29According to our current understanding of the Universe, quarks are fundamental, point-like particles: basic building blocks that are not made up of smaller particles. A recent paper from the CMS Collaboration describes how it probed quarks to the scale of 10-20 metres to test this premise.
At this scale, no evidence of constituent particles was identified, but history shows that structures once considered fundamental can reveal deeper layers: matter was found to consist of molecules, which were then found to be made of atoms, which were in turn found to consist of a dense nucleus surrounded by a cloud of electrons.
Rutherford discovered the nucleus by sending a beam of helium nuclei onto a gold-foil target. These nuclei scattered off the gold atoms of the foil at various angles, which Rutherford then measured. By studying the distribution of the scattering angles, he was able to prove that atoms contained a point-like nucleus at the centre. This was possible because the helium beam in the experimental set-up had enough energy to probe the inside of the atoms.
The nucleus was then shown to be made of protons and neutrons, which were themselves later found to consist of quarks. LHC experiments including CMS are now continuing this quest, colliding particles at extremely high energies to probe the potential inner structure of quarks.
When two beams of protons collide within CMS, they break apart into their constituent quarks. These outgoing quarks become two jets – sprays of particles – that can be measured and used to reconstruct the scattering angle between the quarks.
The distribution of the scattering angle between the two jets can be compared to the distribution that would be expected if the quark was indeed a point-like particle. The recent results from the CMS Collaboration, which were based on data from the second run of the LHC, showed no significant disagreement with the scattering distribution of a point-like quark. This means that quarks are not likely to be larger than 10-20 metres if they are composite structures.
This size estimate is derived from the constraints on the energy scale at which quark ‘compositeness’ reveals itself. For the benchmark model of the recent CMS paper, which assumed that quarks were composite, the recent results set the most stringent limit to date at 37 TeV.
Similarly to how Rutherford was able to identify the components of the atom only because his beam of particles had enough energy, studying particle collisions with higher energies could help us to identify smaller potential structures within quarks. Data from the third run of the LHC and the upcoming High-Luminosity LHC could help to reduce the uncertainties on the measurement of the scattering angle, allowing us to identify even smaller structures and continue the search for the smallest building blocks of matter.
A collision event recorded by the CMS detector with two outgoing jets. (Image: CMS) ehatters Thu, 04/16/2026 - 14:57 Byline CMS collaboration Publication Date Thu, 04/16/2026 - 14:46It was with profound shock and sadness that we learned of the sudden passing of staff member Mark Rayner, Editor of CERN Courier magazine, on 23 March.
Mark was born in Hounslow, England, on 7 October 1983 and studied physics at Worcester College, University of Oxford, from 2002 to 2006. His journey in particle physics began in 2005, when he spent three months at CERN as a Summer Student working on tests of the ATLAS transition-radiation-tracker end caps. He continued at Oxford with a PhD, participating in the Muon Ionisation Cooling Experiment (MICE) based at the Rutherford Appleton Laboratory. His thesis described the development of a novel technique for characterising the MICE muon beam and demonstrating its suitability for a muon cooling measurement, an essential step on the path towards a possible neutrino factory and muon collider. In 2011, Mark moved from accelerator physics to neutrino physics, joining the University of Geneva both as a lecturer and as a researcher working on the T2K, Hyper-Kamiokande and BabyMIND experiments, to which he contributed with data analysis and detector development.
A passionate educator and communicator, Mark trained as an apprentice physics teacher at Ecole Internationale de Genève in 2018. The following year he joined CERN as a senior fellow working on the CERN Courier magazine, disseminating the latest developments in global high-energy physics. He played a major role in the launch of the CERN Courier website and rose quickly to become the magazine’s deputy editor. When his fellowship ended, Mark moved to the World Economic Forum, where he managed the production of a portfolio of publications and tools relating to education, skills and learning and served as lead author for the Future of Jobs report 2023.
Mark returned to CERN as a staff member in 2024, and as Editor of the CERN Courier. Over a short period, his talent for language and his creativity in graphics and data journalism raised the bar for CERN’s flagship publication. He also paid particular attention to improving the visibility of gender diversity in the Courier and to developing the magazine’s online presence, enabling him to connect particle physics with new audiences. He took great pride in his work and in engaging with authors to shape their stories, and was widely recognised for his dignity and professionalism both among his colleagues and members of the international particle-physics community.
Above all, Mark cared deeply about everything he did, and especially about the well-being of others. His pursuit of excellence and his remarkable attention to detail set a standard that inspired those around him, and this is reflected in the deeply motivated team that he built and nurtured. He was highly cultured and sang in the Geneva Gospel Choir.
Mark was a man of great warmth and spirit and of quiet generosity, whose presence brought light to those fortunate enough to know him. He will be remembered with great respect and will be profoundly missed.
His friends and colleagues
ehatters Tue, 04/14/2026 - 13:08 Publication Date Tue, 04/14/2026 - 12:59The top quark, the heaviest and most short-lived elementary particle known, has long been thought to decay too quickly to form bound states. However, a new result from the CMS Collaboration, presented this week at the Rencontres de Moriond conference, strengthens last year's observation that top quarks may, in fact, briefly pair up with their antimatter counterparts. This fleeting bound state – known as toponium – would be the most massive composite particle ever observed, completing the family of quark–antiquark states bound by the strong nuclear force.
Most matter around us is made of atoms, in which electrons cling to protons through the electromagnetic force. But protons themselves are not elementary. They belong to a broad family of composite particles called hadrons, in which quarks are held together by the strong nuclear force. Among them, the simplest are pairings of a quark with its own antiquark, which provide an especially clean window on the workings of the strong force. For decades, such states have been known for every type of quark but the most elusive: the top.
First discovered more than 30 years ago at the Tevatron accelerator near Chicago, the top quark has been extensively studied ever since, with experiments at the LHC going so far as to measure quantum entanglement between top quarks and antiquarks. Even when produced alongside its antiquark, the top typically decays before any bound state can form. Yet the hundreds of millions of top quark–antiquark pairs produced at the LHC, effectively making it a top-quark factory, provide such an enormous dataset that the rarest phenomena can leave a detectable trace.
The first hints of toponium appeared in searches for heavy Higgs-boson-like particles that could decay into a top quark–antiquark pair. An unexpected excess of collision events was observed at a mass close to twice the mass of the top quark, which is more characteristic of a bound state rather than a new fundamental particle. Detailed studies by the CMS and ATLAS experiments confirmed this excess using events in which both top quarks decay into leptons (electrons or muons).
The new CMS study approaches the problem from a different angle, examining events in which one top quark decays into a bottom quark, a charged lepton and a neutrino while the other decays into quarks that produce sprays, or “jets”, of particles. “Isolating the signal in this decay channel was challenging,” says Otto Hindrichs, a researcher at the University of Rochester who developed a new AI-assisted technique to reconstruct these collision events.
“Instead of reconstructing the mass of the top quark–antiquark pair directly, we focused on the relative velocity of the top quark and antiquark,” explains Yu-Heng Yu, a graduate student involved in the analysis. “If they form a bound state, their relative velocity should be much smaller than when they are produced independently,”
These new techniques proved highly effective. They resulted in the observation of an excess with a statistical significance of more than five standard deviations – the gold standard for a discovery in high-energy physics. The result provides a new, statistically independent confirmation of toponium production.
“Toponium is heavier than the heaviest known atomic nucleus, oganesson, making it the most massive bound state ever observed,” says Regina Demina, leader of the CMS group at the University of Rochester. “Its discovery deepens our understanding of the strong nuclear force and its ability to bind the fundamental constituents of matter.”
Find out more on the CMS website.
roryalex Tue, 03/24/2026 - 11:35 Byline CMS collaboration Publication Date Wed, 03/25/2026 - 11:31According to the theory of supersymmetry, there is a mirror world of hypothetical particles that could help resolve several physics puzzles, such as the surprisingly small mass of the Higgs boson and the nature of dark matter. The ATLAS Collaboration at the Large Hadron Collider (LHC) has conducted new searches for these so-called supersymmetric (SUSY) particles using machine-learning techniques. The results of these searches, presented this week at the Moriond conference, have placed some of the strongest bounds yet on the properties of SUSY particles.
Supersymmetry proposes that each particle in the Standard Model has a “superpartner”. The higgsino is the SUSY counterpart of the Higgs boson and is the subject of many SUSY searches. But detecting the higgsino, if it exists, is far from simple. The higgsino would not appear on its own but as a mixture of other SUSY particles, creating states known as neutralinos and charginos. Theorists predict that the lightest neutralino could be stable and, therefore, a strong candidate for dark matter. The other, heavier neutralinos and charginos would decay into this stable SUSY particle. However, these decays are expected to produce very little energy and the resulting low-energy particles would be extremely difficult to detect.
By deploying machine-learning techniques, the ATLAS Collaboration has been able to significantly improve the experiment’s sensitivity to low-energy particles. ATLAS now reports the results of two new searches for signs of SUSY particles in analyses of data from the LHC’s second run, which was collected between 2015 and 2018.
One of these searches involved hunting for signs of a disappearing track left by a chargino decaying into a stable neutralino, which is invisible to the detectors, and a low-energy pion. The pion follows a highly curved trajectory that is extremely difficult to identify in a busy proton–proton collision, causing the chargino’s track to “disappear”. The ATLAS Collaboration additionally searched for signs of heavier neutralinos decaying into the lightest and only stable neutralino and two low-momentum leptons, such as electrons. The researchers deployed neural networks to search deep into the low-momentum region of pions and leptons to find signs of them being produced through the decay of SUSY particles.
No signs of these SUSY particles were observed in either of these searches. However, these results have now set some of the most stringent limits yet on the masses and lifetimes of charginos and neutralinos, superseding the longstanding limits set by the Large Electron–Positron Collider, the LHC’s predecessor.
These limits help guide future searches for SUSY particles at the LHC and the High-Luminosity LHC. The search continues for the mirror world of SUSY.
roryalex Thu, 03/19/2026 - 09:25 Byline Rory Harris Publication Date Thu, 03/19/2026 - 11:23The LHCb experiment at CERN’s Large Hadron Collider (LHC) has discovered a new particle consisting of two charm quarks and one down quark, a similar structure to the familiar proton, but with two heavy charm quarks replacing the two up quarks of the proton, thus quadrupling its mass. The discovery, presented at the ongoing Moriond conference, will help physicists better understand how the strong force binds protons, neutrons and other composite particles together.
Quarks are fundamental building blocks of matter and come in six flavours: up, down, charm, strange, top and bottom. They usually combine in groups of twos and threes to form mesons and baryons, respectively. Unlike the stable proton, however, most of these mesons and baryons, which are collectively known as hadrons, are unstable and short-lived, making them a challenge to observe. Producing them requires smashing together high-energy particles in a machine such as the Large Hadron Collider (LHC). These unstable hadrons will quickly decay, but the more stable particles that are produced as a result of this decay can be detected and the properties of the original particle can therefore be deduced.
Researchers have used this approach many times to find new hadrons, and the new particle just announced by the LHCb Collaboration brings the total number of hadrons discovered by LHC experiments up to 80.
“This is the first new particle identified after the upgrades to the LHCb detector that were completed in 2023, and only the second time a baryon with two heavy quarks has been observed, the first having being observed by LHCb almost 10 years ago,” says LHCb Spokesperson Vincenzo Vagnoni. “The result will help theorists test models of quantum chromodynamics, the theory of the strong force that binds quarks into not only conventional baryons and mesons but also more exotic hadrons such as tetraquarks and pentaquarks.”
In 2017, LHCb reported the discovery of a very similar particle, which consists of two charm quarks and one up quark. This up quark is the only difference between this particle and the new one, which has a down quark in its place. Despite the similarity, the new particle has a predicted lifetime that is up to six times shorter than its counterpart, due to complex quantum effects. This makes it even more challenging to observe.
By analysing data from proton–proton collisions recorded by the LHCb detector during the third run of the LHC, the LHCb Collaboration observed the new baryon with a statistical significance of 7 sigma, well above the threshold of 5 sigma required to claim a discovery.
“This major result is a fantastic example of how LHCb’s unique capabilities play a vital role in the success of the LHC,” says Mark Thomson, CERN Director-General. “It highlights how experimental upgrades at CERN directly lead to new discoveries, setting the stage for the transformative science we expect from the High-Luminosity LHC. These achievements are only possible thanks to the exceptional performance of CERN’s accelerator complex and the teams who make it all work and to the commitment of the scientists on the LHCb experiment.”
Further information:
LHCb presentation at Moriond is available here.
LHCb news article.
A hadron collider’s energy reach is defined by the circumference of its tunnel and the strength of its dipole magnets. Next-generation hadron colliders look set to have tunnels more than three times longer than the LHC. Further expansion of the energy frontier depends on the ability of accelerator physicists to increase the strength of the magnets.
This is one of the hardest problems in applied superconductivity – and exactly the sort of challenge that can inspire spinoff applications, from energy-efficient power transmission in cities to sustainable air travel. This edition’s cover illustrates a high-temperature superconducting cable developed by Amalia Ballarino’s team at CERN in collaboration with Airbus.
Elsewhere in these pages: meet Fermilab’s new director, Norbert Holtkamp; boost into the rest frame of charged particles in a bent crystal; the most important tool you’ve never heard of; a milestone for the HiLumi LHC; an Eiffel honour for women physicists; all you need to know about little red dots; Michael S Turner on the coming revolutions in high-energy physics and cosmology; and much more.
ehatters Thu, 03/12/2026 - 10:12 Byline Mark Rayner Publication Date Thu, 03/12/2026 - 10:06The NA62 Collaboration has dramatically reduced the uncertainty in its measurement of an extremely rare particle decay, in results just presented at the 2026 La Thuile conference.
The study of rare decays gives physicists the chance to probe the Standard Model of particle physics. Researchers can determine what is known as the branching ratio of a decay, which describes how many particles decay through a particular process as a fraction of the total number of decays that occur. The branching ratio of the decay that the NA62 Collaboration has studied – the decay of a positively charged kaon into a positively charged pion and neutrino–antineutrino pair (written K+→π+νν) – can be predicted theoretically with a very high degree of precision. Thanks to this ‘theoretical cleanliness’, this particular kaon decay is extremely sensitive to new physics beyond the Standard Model but, with a predicted branching ratio of less than one in 10 billion, it is extremely rare and very challenging to observe.
The NA62 experiment was designed to study the K+→π+νν process in depth and therefore produces a lot of kaons, which is why it is also known as the “kaon factory”. The kaons are created by firing a high-intensity beam of protons from the Super Proton Synchrotron at a beryllium target. This produces nearly a billion particles every second, of which around 6% are kaons whose decay products can be studied in great detail using the NA62 detectors.
In 2024, the NA62 Collaboration reported having observed this process with a statistical significance of five standard deviations, the gold standard in particle physics for claiming a discovery. Now, the researchers have included the data recorded in 2023–2024 in their analyses and used improved data analysis techniques based on cutting-edge machine learning algorithms. The results, combined with the previous data taken since the experiment began, have significantly refined their understanding of the ultra-rare kaon decay.
With the full dataset, the NA62 Collaboration obtained an updated value of the K+→π+νν branching ratio of 9.6 +1.9 −1.8 × 10−11 , with an uncertainty 40% smaller than before.
“This is the most sensitive dataset we have analysed yet,” said lead data analyst Joel Swallow. “The fact that we can see clearly and measure with precision something so rare and elusive is a great success from a technological point of view.”
With the precision of the current result, the kaon decay appears to occur as predicted by theory and sets powerful constraints on new physics beyond the Standard Model.
“This stress test of the Standard Model is remarkable given the extreme rareness and theoretical cleanliness of the process that we investigated,” said NA62 spokesperson Giuseppe Ruggiero. “We have demonstrated once again that our current leading theory of nature has incredible predictive power.”
roryalex Wed, 03/04/2026 - 11:59 Byline Rory Harris Publication Date Wed, 03/04/2026 - 11:58In the first few microseconds after the Big Bang, the Universe was in an extremely hot and dense state of matter known as quark–gluon plasma (QGP), which can be reproduced with high-energy collisions between heavy ions such as lead nuclei. In a paper published today in Nature Communications, the ALICE Collaboration reports observing a remarkable common pattern in proton–proton, proton–lead and lead–lead collisions at the Large Hadron Collider (LHC), shedding new light on possible QGP formation and evolution in small collision systems.
Physicists initially believed that colliding small systems, such as protons, could not generate the extreme temperatures and pressures needed to form QGP. But in recent years, signatures of QGP have been observed in proton–proton and proton–lead collisions at the LHC, indicating that the size of the collision system may not be a limiting factor in QGP creation.
A key signature of QGP formation is anisotropic flow, where the particles produced in a collision are not emitted evenly but in preferred directions. For particles moving at intermediate speeds (or momenta), this anisotropic flow depends on the number of quarks they contain: particles that are made up of three quarks (baryons) exhibit stronger flow than those that are composed of two quarks (mesons). The leading explanation for this difference is something called quark coalescence – the process through which the quarks in the QGP combine into larger particles. And as baryons contain one more quark than mesons, they inherit more flow.
In its new study, the ALICE Collaboration measured the anisotropic flow of multiple meson and baryon species produced in proton–proton and proton–lead collisions, by carefully isolating the particles that were genuinely flowing together. The analysis showed that, like in heavy-ion collisions, the anisotropic flow was much stronger for baryons than for mesons at intermediate momenta.
(Right) A proton–proton collision at the LHC in which many particles were created and tracked by the ALICE detector. (Left) Illustration of the anisotropic flow of mesons and baryons that ALICE has studied using data from such collisions, with the large arrows representing the preferred directions. (Image: ALICE/CERN)“This is the first time we have observed, for a large interval in momentum and for multiple species, this flow pattern in a subset of proton collisions in which an unusually large number of particles are produced,” says David Dobrigkeit Chinellato, Physics Coordinator of the ALICE experiment. “Our results support the hypothesis that an expanding system of quarks is present even when the size of the collision system is small.”
The ALICE researchers went on to compare the new flow measurements to predictions from simulations that assume QGP formation and its evolution. They found that models that incorporate the anisotropic flow of quarks and their subsequent coalescence into mesons and baryons successfully explain the observed flow pattern, whereas models that exclude either process fail to capture it. However, even the successful models are not exactly right. There are still discrepancies between the models and data that are largely linked to uncertainties in the modelling of the proton’s substructure and the initial geometry of the collisions.
“We expect that, with the oxygen collisions that were recorded in 2025, which bridge the gap between proton collisions and lead collisions, we will gain new insights into the nature and evolution of the QGP across different collision systems,” said Kai Schweda, ALICE Spokesperson.
roryalex Fri, 02/20/2026 - 16:43 Byline ALICE collaboration Publication Date Fri, 03/20/2026 - 11:40The CMS Collaboration has shown, for the first time, that machine learning can be used to fully reconstruct particle collisions at the LHC. This new approach can reconstruct collisions more quickly and precisely than traditional methods, helping physicists better understand LHC data.
Each proton–proton collision at the LHC sprays out a complex pattern of particles that must be carefully reconstructed to allow physicists to study what really happened. For more than a decade, CMS has used a particle-flow (PF) algorithm, which combines information from the experiment’s different detectors, to identify each particle produced in a collision. Although this method works remarkably well, it relies on a long chain of hand-crafted rules designed by physicists.
The new CMS machine-learning-based particle-flow (MLPF) algorithm approaches the task fundamentally differently, replacing much of the rigid hand-crafted logic with a single model trained directly on simulated collisions. Instead of being told how to reconstruct particles, the algorithm learns how particles look in the detectors, like how humans learn to recognise faces without memorising explicit rules.
When benchmarked using data mimicking that from the current LHC run, the performance of the new machine-learning algorithm matched that of the traditional algorithm and, in some cases, even exceeded it. For example, when tested on simulated events in which top quarks were created, the algorithm improved the precision with which sprays of particles – known as jets – were reconstructed by 10–20% in key particle momentum ranges.
The new algorithm also allows a collision to be fully reconstructed far more quickly than before, because it can run efficiently on modern electronic chips known as graphics processing units (GPUs). Traditional algorithms typically need to run on central processing units (CPUs), which are often slower than GPUs for such tasks.
“New uses of machine learning could make data reconstruction more accurate and directly benefit CMS measurements, from precision tests of the Standard Model to searches for new particles,” says Joosep Pata, lead developer of the new MLPF algorithm. “Ultimately, our goal is to get the most information out of the experimental data as efficiently as possible.”
While the new algorithm was tested under current LHC data conditions, it is predicted to be even more useful for data from the High-Luminosity LHC. Due to start running in 2030, the LHC upgrade will deliver approximately five times more particle collisions, posing a significant challenge to the LHC experiments. By teaching detectors to learn directly from data, physicists are not just improving performance, they are redefining what is possible in experimental particle physics.
Find out more about the algorithm on the CMS website and more about machine learning in particle physics through this CERN colloquium.
ehatters Thu, 02/12/2026 - 11:58 Byline CMS collaboration Publication Date Wed, 02/18/2026 - 12:35Antonino Zichichi, one of the most influential figures in high-energy physics, passed away on Monday, 9 February 2026 at the age of 96.
A native of Sicily, he graduated from the University of Bologna in the early 1950s and joined CERN in 1955, becoming one of the pioneers of CERN’s experimental programme. He participated in the first muon g - 2 experiment, which started to take data in 1959 at the Synchrocyclotron. He later led an experiment at the Proton Synchrotron (PS) at which antideuteron was discovered in 1965, confirming that a nucleus of antimatter could exist.
Appointed professor at the University of Bologna in 1960, Zichichi led the Bologna-CERN-Frascati collaboration and participated in numerous CERN experiments, including at the Intersecting Storage Rings, the Super Proton Synchrotron and the L3 experiment at the Large Electron-Positron collider, and in experiments carried out in Italy and the United States. Throughout his career, he authored several hundred scientific papers. His contributions include the study of lepton pairs produced in hadron interactions, the proposition of the existence of a heavy lepton, the development of a new method for searching for such a heavy lepton in electron-positron interactions, the evidence of the effective energy in quantum chromodynamics as well as studies of proton structure and stability.
Zichichi also played a crucial role in developing innovative detection technologies, securing Italian funding for the Lepton Asymmetry Analyser (LAA) project at CERN. This allowed the development of microelectronics at CERN which, together with the design of silicon strip and pixel detectors, would later become an essential component of the experiments at the Large Hadron Collider. He was particularly involved in the ALICE experiment, serving for over 20 years as the project leader of one of the experiment’s key subdetectors, the Time-of-Flight detector, and overseeing the large-scale implementation of the Multigap Resistive Plate Chamber, a detection technology that was later adopted by several other experiments.
Antonino Zichichi at CERN in 2018. (Image: CERN)A visionary leader, Zichichi was instrumental in establishing major research facilities. The Laboratori Nazionali del Gran Sasso was created under his presidency of the Italian National Institute of Nuclear Physics (INFN) (1977–1982). He was one of the founders of the European Physical Society, which he chaired between 1978 and 1980. He was also co-founder of the World Federation of Scientists, which focused on addressing planetary emergencies through science, and of the World Laboratory, an association supporting scientific research in developing countries.
Committed to science education and outreach, he founded the Ettore Majorana Foundation and Centre for Scientific Culture in Erice, Sicily in 1963, which became a hub for international scientific collaboration, particularly through its International School of Subnuclear Physics, where he served as director.
Zichichi received numerous honours and awards for his contributions to science, including the Knight Grand Cross of the Order of Merit of the Italian Republic, the Enrico Fermi Award from the Italian Physical Society, and recognition from academic institutions worldwide.
A full obituary will appear later in the CERN Courier.
cmenard Mon, 02/09/2026 - 12:16 Publication Date Mon, 02/09/2026 - 12:00What is the fate of the Universe? Why is there more matter than antimatter? What lurks beyond the Standard Model?
Each of these questions requires further study of the Higgs boson. Each is explored in the latest edition of the CERN Courier, the international magazine for particle physicists. Physicists have been studying the Higgs boson intensively since its discovery in 2012, but many questions remain unanswered. The High-Luminosity LHC, which will succeed the LHC in 2030, will provide a dataset of 380 million Higgs bosons, a sample more than ten times larger than any studied to date. LHC physicists Valentina Cairo and Steven Lowette explore what physicists expect to learn from this exceptional dataset. Leading accelerator physicists Gianluigi Arduini, Philip Burrows and Jacqueline Keintzel then report on the findings of a working group that was mandated to compare seven proposals for large-scale colliders to follow the High-Luminosity LHC.
Credit: Photographic reproduction by Guillaume Piolle of Wassily Kandinsky’s Yellow-Red-Blue, Public DomainThe Higgs boson is thought to have first given mass to elementary particles in a Universe-wide reconfiguration of fundamental forces that rippled throughout the cosmos a fraction of a second after the Big Bang. This edition of the Courier also explores another such shift, first imagined by physicists Roberto Peccei and Helen Quinn, that may have taken place even earlier. If correct, the fruit of this theory would be a new elementary particle known as the axion. CERN theorist Clara Murgui explains how this theory has the potential to solve two deep puzzles in fundamental science. Representatives of the MADMAX and ALPHA experiments describe two innovative new ways that will be used to search for the axion in the next ten years.
Also in the January/February edition: the community says farewell to Chen-Ning Yang; news from a busy two months in neutrino physics; the first indirect evidence for primordial monsters; and much more.
cmenard Fri, 01/16/2026 - 14:46 Publication Date Fri, 01/16/2026 - 14:39
Physicists can be allies, wrote Wassily Kandinsky, “who test matter again and again, who tremble before no problem, and who finally cast doubt on that very matter which was yesterday the foundation of everything, so that the whole universe is shaken.”
This edition of CERN Courier offers two examples of physics to shake the universe. Each spontaneously breaks the symmetry of a field, plunging the vacuum into a potential well shaped like the rim of a hat, releasing a torrent of energy into the universe.
Peccei–Quinn symmetry breaking would explain the fine tuning of the Standard Model to produce no CP violation in the strong interaction, while also yielding a dark-matter candidate, the QCD axion. Two ingenious experiments are smashing the limits of cavity haloscopes to search for the QCD axion over the next 10 years.
Electroweak symmetry breaking is thought to have given mass to elementary particles. Its smoking gun was the Higgs boson, but very little is known about how it took place in the early universe. Much depends on the shape of the Higgs potential, which we have barely even begun to probe. In this issue, Valentina Cairo and Steven Lowette explore what can be learnt at the High-Luminosity LHC.
These projections provide an important input to the 2026 update to the European Strategy for Particle Physics. The biggest decision concerns seven large-scale collider projects that the community has proposed as possible successors to the High-Luminosity LHC. Like Kandinsky’s geometric constructivism at the Bauhaus, they are a harmony of lines, arcs and circles.
Read the digital edition of this new issue on the CERN Courier website.
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ehatters Wed, 01/14/2026 - 15:36 Byline Mark Rayner Publication Date Fri, 01/16/2026 - 08:05
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