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In the quest to uncover the fundamental particles and forces of nature, one of the critical challenges facing high-energy experiments at the Large Hadron Collider (LHC) is ensuring the quality of the vast amounts of data collected. To do this, data quality monitoring systems are in place for the various subdetectors of an experiment and they play an important role in checking the accuracy of the data.
One such subdetector is the CMS electromagnetic calorimeter (ECAL), a crucial component of the CMS detector. The ECAL measures the energy of particles, mainly electrons and photons, produced in collisions at the LHC, allowing physicists to reconstruct particle decays. Ensuring the accuracy and reliability of data recorded in the ECAL is paramount for the successful operation of the experiment.
During Run 3 of the LHC, which is currently ongoing, CMS researchers have developed and deployed an innovative machine-learning technique to enhance the current data quality monitoring system of the ECAL. Detailed in a recent publication, this new approach promises to make the detection of data anomalies more accurate and efficient. Such real-time capability is essential in the fast-paced LHC environment for quick detection and correction of detector issues, which in turn improves the overall quality of the data. The new system was deployed in the barrel of the ECAL in 2022 and in the endcaps in 2023.
The traditional CMS data quality monitoring system consists of conventional software that relies on a combination of predefined rules, thresholds and manual inspections to alert the team in the control room to potential detector issues. This approach involves setting specific criteria for what constitutes normal data behaviour and flagging deviations. While effective, these methods can potentially miss subtle or unexpected anomalies that don't fit predefined patterns.
In contrast, the new machine-learning-based system is able to detect these anomalies, complementing the traditional data quality monitoring system. It is trained to recognise the normal detector behaviour from existing good data and to detect any deviations. The cornerstone of this approach is an autoencoder-based anomaly detection system. Autoencoders, a specialised type of neural network, are designed for unsupervised learning tasks.
An image from ECAL data with anomalous regions (left) which, when passed through the machine-learning system, produces the easily identifiable colour map on the right, showing anomalous regions in red and good regions in green. (Image: CMS experiment)The system, fed with ECAL data in the form of 2D images, is also adept at spotting anomalies that evolve over time thanks to novel correction strategies. This aspect is crucial for recognising patterns that may not be immediately apparent but develop gradually.
The novel autoencoder-based system not only boosts the performance of the CMS detector but also serves as a model for real-time anomaly detection across various fields, highlighting the transformative potential of artificial intelligence. For example, industries that manage large-scale, high-speed data streams, such as the finance, cybersecurity and healthcare industries, could benefit from similar machine-learning-based systems for anomaly detection, enhancing their operational efficiency and reliability.
CMS is just one of many experiments at CERN that is improving its performance using AI, automation and machine learning. Read more about this here.
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ndinmore Wed, 11/13/2024 - 16:40 Byline CMS collaboration Publication Date Wed, 11/13/2024 - 16:20The Large Hadron Collider (LHC) is like an immensely powerful kitchen, designed to cook up some of the rarest and hottest recipes in the Universe, like the quark–gluon plasma, a state of matter known to have existed shortly after the Big Bang. While the LHC mostly collides protons, once a year it collides heavy ions – such as lead nuclei – a key ingredient for preparing this primordial soup.
Today at 11.13 am, a new heavy-ion run began at the LHC, smashing together lead ions, containing 208 nucleons (82 protons and 126 neutrons), at an energy of 5.36 TeV per nucleon pair.
The LHC heavy-ion run will last almost three weeks, providing enough data for years’ worth of work for physicists, who analyse this data to seek to understand the Universe’s first moments.
Accelerator physicists at the CERN Control Centre are also gearing up to increase the machine’s luminosity performance compared with last year.
“We aim to achieve at least 30% more collisions per day than in 2023,” said Roderik Bruce, accelerator physicist and the LHC coordinator of the ion programme at CERN.
For this run, they have consolidated novel concepts that were introduced last year, such as crystal collimation and a new scheme to inject beams with shorter bunch spacing, making it possible to pack more lead ions in a beam for collisions that result in more physics data.
The ALICE experiment at CERN is dedicated to heavy-ion physics at the LHC. Its detector, specifically built for heavy-ion measurements, was upgraded during the last long shutdown to be able to collect and store many more collisions than before. The goal this year is to double the total sample collected in the ongoing LHC Run 3.
“We look forward to the large data sample from this run, which should allow us to get a first direct measurement of the temperature of the quark–gluon plasma and to study its other properties with unprecedented precision,” said Marco van Leeuwen, the ALICE spokesperson.
The other LHC experiments have also modified their detectors and data-taking capacity to make the most of the ongoing heavy-ion run.
The CMS detector has increased its data-collecting speed from 20 gigabytes to 30 gigabytes per second. This means the CMS detector can now collect and study all the collision data instead of having to filter data during the heavy-ion run.
Similarly, the ATLAS detector is now fully adapted to new data acquisition systems, significantly enhancing its trigger for particle jets and leptons. It has also refined its trigger strategies for ultra-peripheral collisions, which occur when two heavy ions pass very close to each other but don’t actually collide head-on, enabling studies of physics in extreme electromagnetic fields.
The LHCb detector will record lead–lead collision data with a 70% increase in instantaneous luminosity compared to last year, enabling it to collect a large data sample and study rare processes, such as the production of beauty hadrons, with high precision. As a new addition, this year LHCb will be able to inject neon and argon gases into its special SMOG2 system to collect lead–neon and lead–argon data alongside lead–lead collision data.
Studying the quark–gluon plasma reveals how the building blocks of matter emerged in the early Universe, just a hundredth of a billionth of a second after the Big Bang. The heavy-ion run is a unique opportunity at the LHC to study matter in its most extreme conditions.
ALICE heavy ion run team at the ALICE Control Roomckrishna Wed, 11/06/2024 - 17:05 Byline Chetna Krishna Publication Date Wed, 11/06/2024 - 17:30
To help to shed light on the nature of elusive neutrino particles, CERN’s Neutrino Platform enables a global community of neutrino experts to develop and prototype different projects for next-generation neutrino experiments. From DUNE at LBNF in the United States to T2K in Japan, developments for far and near detectors are advancing well. Alongside this, novel identification techniques for neutrino beams are vital to strongly reduce systematic uncertainties on key observables – such as the flavour-dependent neutrino flux. These techniques are being developed in the framework of the Physics Beyond Colliders study, in particular by the ENUBET and NuTAG collaborations.
ENUBET aims to exploit the fact that every time a neutrino is produced, it is accompanied by a charged lepton that can be detected and identified in a calorimeter with very good resolution. To detect these charged leptons, physicists envision a fully instrumented 40-metre-long decay tunnel. The collaboration has just completed a first successful test of its demonstrator’s full data acquisition system.
NuTAG proposes to follow the concept of a tagged neutrino beam to study neutrino oscillations using silicon detector technology. A proof-of-principle of this technique has been recently demonstrated at the NA62 experiment at CERN, where two tagged neutrino candidates have been found for the first time.
Combining these two concepts would result in a tagged neutrino beam with full particle identification. At the moment, a feasibility study is under way to find a suitable site for a possible first implementation.
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This is a short summary of this article published in the newsletter of CERN’s EP department.
anschaef Wed, 10/30/2024 - 14:32 Byline Kristiane Bernhard-Novotny Publication Date Wed, 10/30/2024 - 14:29Antimatter might sound like something out of science fiction, but at the CERN Antiproton Decelerator (AD), scientists produce and trap antiprotons every day. The BASE experiment can even contain them for more than a year—an impressive feat considering that antimatter and matter annihilate upon contact. The CERN AD hall is the only place in the world where scientists are able to store and study antiprotons. But this is something that scientist working on the BASE experiment hope to change one day with their subproject BASE-STEP: an apparatus designed to store and transport antimatter.
Yesterday, the team of scientists and engineers took an important step towards this goal by transporting a cloud of 70 protons in a truck across CERN’s main site. “If you can do it with protons, it will also work with antiprotons,” said Christian Smorra, the leader of BASE-STEP. “The only difference is that you need a much better vacuum chamber for the antiprotons.” This is the first time that loose particles have been transported in a reusable trap that scientists can then open in a new location and then transfer the contents into another experiment. The end goal is to create an antiproton-delivery service from CERN to experiments located at other laboratories.
Antimatter is a naturally occurring class of particles that is almost identical to ordinary matter except that the charges and magnetic properties are reversed. This has baffled scientists for decades because according to the laws of physics, the Big Bang should have produced equal amounts of matter and antimatter. These equal-but-opposite particles would have quickly annihilated with each other; leaving a simmering but empty Universe. Physicists suspect that there are hidden differences that can explain why matter survived and antimatter all but disappeared.
The BASE experiment aims to answer this question by precisely measuring the properties of antiprotons, such as their intrinsic magnetic moment, and then comparing these measurements with those taken with protons. However, the precision the experiment can achieve is limited by its location.
“The accelerator equipment in the AD hall generates magnetic field fluctuations that limit how far we can push our precision measurements,” said BASE spokesperson Stefan Ulmer. “If we want to get an even deeper understanding of the fundamental properties of antiprotons, we need to move out.”
The transportable trap being carefully loaded in the truck before going for a road trip across CERN's main site. (Image: CERN)This is where BASE-STEP comes in. The goal is to trap antiprotons and then transfer them to a facility where scientists can study them with a greater precision. To be able to do this, they need a device that is small enough to be loaded onto a truck and can resist to the bumps and vibrations that are inevitable during ground transport. The current apparatus — which includes a superconducting magnet, cryogenic cooling, power reserves, and a vacuum chamber that traps the particles using magnetic and electric fields — weighs 1000 kilograms and needs two cranes to be lifted out of the experimental hall and onto the truck. Even though it weighs a tonne, BASE-STEP is much more compact than any existing system used to study antimatter. For example, it has a footprint that is five times smaller than the original BASE experiment as it has to be narrow enough to fit through ordinary laboratory doors.
During the rehearsal, the scientists used trapped protons as a stand-in for antiprotons. Protons are a key ingredient of every atom, the simplest of which is hydrogen (one proton and one electron.) But storing protons as loose particles and then moving them onto a truck is a challenge because any tiny disturbance will draw the unbonded protons back into an atomic nucleus.
“When it’s transported by road, our trap system is exposed to acceleration and vibrations, and laboratory experiments are usually not designed for this”, Smorra said. “We needed to build a trap system that is robust enough to withstand these forces, and we have now put this to a real test for the first time.” However, Smorra noted that the biggest potential hurdle isn’t currently the bumpiness of the road but traffic jams.“If the transport takes too long, we will run out of helium at some point,” he said. Liquid helium keeps the trap’s superconducting magnet at a temperature below 8.2 Kelvin: its maximum operating temperature. If the drive takes too long, the magnetic field will be lost and the trapped particles will be released and vanish as soon as they touch ordinary matter.
“Eventually we want to be able to transport antimatter to our dedicated precision laboratories at the Heinrich Heine University in Düsseldorf, which will allow us to study antimatter with at least 100-fold improved precision,” Smorra said. “In the longer term, we want to transport it to any laboratory in Europe. This means that we need to have a power generator on the truck. We are currently investigating this possibility.”
After this successful test, which included ample monitoring and data taking, the team plans to refine its procedure with the goal of transporting antimatter next year. “This is a totally new technology that will open the door for new possibilities of study, not only with antiprotons but also with other exotic particles, such as ultra-highly-charged ions,” Ulmer said.
Another experiment, PUMA, is preparing a transportable trap. Next year, it plans to transport antiprotons next year 600 metres from the AD hall to CERN’s ISOLDE facility in order to use it to study the properties and structure of exotic atomic nuclei.
The BASE-STEP team celebrating the successful transport at the end of the operation. The green signal on the computer screen shows that the 70 loose protons are still "alive", maintained by the magnetic field in the trap. (Image: CERN)cmenard Fri, 10/25/2024 - 10:58 Byline Sarah Charley Publication Date Fri, 10/25/2024 - 11:40
18 October 2024 · Voir en français
Part 19 of the CERN70 feature series. Find out more: cern70.cern
Jürgen Schukraft joined CERN’s heavy-ion programme in 1986 and was the first spokesperson for the ALICE experiment at the Large Hadron Collider
On 7 November 2010, lead nuclei collided in the Large Hadron Collider (LHC) for the first time. In the control room of ALICE, the LHC’s heavy-ion experiment, a celebratory atmosphere reigned. This was the beginning of a new chapter in CERN’s heavy-ion programme, which had started 25 years earlier.
In the 1980s, theoretical work had indicated that high-energy heavy-ion collisions – using, for example, lead or gold nuclei – would allow quark–gluon plasma, a state of matter thought to have existed at the very start of the Universe, to be reproduced. Less than 10 microseconds after the Big Bang, the Universe was too hot and dense for quarks and gluons to bond together to form protons and neutrons, the constituents of atomic nuclei as we know them. Quarks and gluons moved around freely in a sort of primordial soup known as quark–gluon plasma.
In 1986, the programme’s first experiments were carried out using relatively light nuclei, such as oxygen and sulphur nuclei, which were fired by the SPS (Super Proton Synchrotron) accelerator at targets made of heavier elements, such as gold and lead. These experiments collected promising clues, but did not produce conclusive results confirming the existence of the much-talked-about primordial soup. A second programme started in 1994 with lead ion beams. A total of seven large experiments (and other smaller ones) measured different aspects of the collisions. The combined results collected by these experiments allowed CERN to announce the discovery of a “new state of matter” in February 2000. At the same time, the Brookhaven National Laboratory in the United States started up its Relativistic Heavy Ion Collider (RHIC). In 2005, the Brookhaven Laboratory announced that it had observed quark–gluon plasma and its characteristics were unexpected. The plasma behaved like an almost perfect liquid with practically no viscosity.
An event display showing a collision between a beam of sulphur ions and a target containing gold atoms, recorded in 1991 by the NA35 experiment, one of the first experiments in CERN's heavy ion programme. (Image: CERN)During this time, at CERN, the Large Hadron Collider collaborations were preparing to assemble their detectors. In 1993, a group of scientists led by Jürgen Schukraft had proposed the construction of a detector for the study of heavy-ion collisions, in order to carry on the programme that had started a few years earlier at the SPS. Known as ALICE (A Large Ion Collider Experiment), the experiment was designed to identify the multitude of particles emitted by heavy-ion collisions. With the first proton collisions, which were followed by lead-ion collisions in 2010, ALICE started exploring the strong interaction and quark-gluon plasma.
In 15 years of operation, ALICE, along with the other LHC experiments, has produced a large quantity of detailed results that allow us to better understand the state of matter at the very beginning of the Universe. The experiment has, for example, studied the behaviour of plasma and determined the characteristics of its flow. It has also observed the phenomenon of jet quenching, which reveals the energy loss of quarks and gluons in plasma, and has defined more precisely the production of the various particles in heavy-ion collisions.
Recollections It took 20 years to build the ALICE detector, 40 minutes to take the first data, one hour for preliminary analysis, two days for the (almost) final results, and three days to agree on the author list. The ship had set sail, and the physics journey into ALICE’s wonderland had begun in earnest.After two years at the Intersecting Storage Rings (ISR), Jürgen Schukraft joined CERN’s heavy-ion programme when it started data taking in 1986. He worked on the North Area experiments NA34 and NA45 before starting at ALICE, CERN’s heavy-ion experiment at the Large Hadron Collider (LHC), for which he was the first spokesperson from 1993 to 2011.
“The beginning of the heavy-ion programme at CERN in the 1980s was both exciting and confusing. We made a big leap in energy with SPS and thought that it might be enough to create a quark–gluon plasma (QGP). Everyone was in a “gold rush” mood, but nobody knew what we would find or when. During the programme’s first days, Austrian TV came to CERN wanting to film the “first detection of the quark–gluon plasma” live. They were disappointed when they realised that it would take more time...
Even though we found two striking signatures that were predicted for a QGP, the first results were confusing. Better theory was needed, and more data. From 1994, we could use heavy ions (lead), which made all the difference. Plus, a new generation of bespoke detectors opened new possibilities, and evidence that we were looking at something “different” was accumulating. In early 2000, CERN announced “compelling evidence” for a new state of matter. Yet, we still couldn’t be sure if this “new state” was the real QGP or only a precursor, or even an imposter.
The centre of action moved to Brookhaven National Lab with the startup of RHIC in summer 2000. By 2005, BNL declared that yet another new state of matter had been found – a “strongly interacting perfect liquid” – an even more fluid substance (with less internal friction) than superfluid helium. Around the same time, the SPS confirmed another crucial prediction, the “melting” of hadron masses in the QGP and also precisely measured the QGP temperature, far above the predicted threshold. By then we knew, in hindsight, that we had been dealing with the QGP all along.
Back at CERN, we were busy inventing new detector technologies for the LHC, building and assembling the (for us) gigantic ALICE experiment, and writing thousands of pages of technical documents. After an aborted attempt the year before, the LHC saw “first light” during a short proton–proton test run in November 2009. The packed ALICE control room erupted in applause when the first collision “event” popped up on the screen. The display looked good, the detectors worked and decades of preparation had come to a successful end.
A young fellow sitting quietly in the back of the room had single-handedly reconstructed and analysed the 284 (!) events that we netted during the test. Within an hour, he interrupted our celebration with the first actual physics result, the density of produced particles. It looked good, and the next morning, literally in the shower, I had the crazy idea to see if we could push this all the way to publication. The following days were the most intense and exhilarating of my life. The detector had worked out of the box, but of course not perfectly; in intense meetings twice a day, with a 24-hour task force of a few dozen people, we sorted out one problem after another. By day five, one minute after midnight, the paper was submitted – a full week before the first scheduled LHC collisions. It took 20 years to build the ALICE detector, 40 minutes to take the first data, one hour for preliminary analysis, two days for the (almost) final results, and three days to agree on the author list. The ship had set sail, and the physics journey into ALICE’s wonderland had begun in earnest.
One of the first lead-ion collision recorded by ALICE in 2010 (Image: CERN)And what an expedition it was. In the years since, the LHC heavy-ion programme has helped to resolve most of the earlier puzzles. Notably, we understood the confusing ups and downs of charmonium suppression as an unanticipated consequence of the QGP. With heavy-ion results also coming in from the other three large LHC experiments, we measured the properties of the QGP with ever-increasing sophistication and precision. And early on, still with proton beams, we tripped over another surprise – the first, and arguably still the most unexpected, LHC discovery. A feeble, but distinct, very long-range correlation between particles, never before seen in any elementary collisions, was announced in 2010 to a packed auditorium by the CMS Spokesperson with an apology (“we present this signal to the scrutiny of the scientific community because we didn’t succeed in killing it”). The mysterious result spawned many different explanations, which were mostly ad hoc, speculative, or outright weird. Today, after a plethora of painstaking and detailed measurements, including crucially in proton–nucleus collisions, and alongside great strides in theory, we understand this correlation – unexpectedly appearing in “lowly” proton–proton collisions – as a precursor or onset of the hot and dense matter phenomena we had considered the exclusive territory of heavy-ion reactions.
Forty years after seeing (or rather, understanding) not much in those first light-ion collisions at the SPS, we are now regularly exploring and testing with remarkable detail and precision QCD (quantum chromodynamics), the theory of the strong interaction, in the regime where it actually is strong. Along the way, we have found traces and shadows of the QGP everywhere we looked, including in the lightest of systems. Such are the surprises and adventures of exploring nature at the frontiers of our understanding, and it has been a privilege – and lots of fun – to be part of it for so long.”
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This interview is adapted from the 2004 book “Infinitely CERN”, published to celebrate CERN’s 50th anniversary, updated by Jürgen Schukraft in 2024.
Jürgen Schukraft was the first spokesperson of the ALICE experiment at the Large Hadron ColliderThe ND280 detector, an essential part of the T2K (Tokai to Kamioka) neutrino experiment in Japan, has undergone a significant upgrade to enhance its ability to precisely measure neutrino interactions. T2K aims to study neutrinos to improve our understanding of matter-antimatter asymmetry in the universe.
At the start of its second data collection phase in June 2024, the upgraded near detector ND280, which contains multiple subdetectors assembled and tested at CERN, was used for the first time. This marks the end of an extraordinary journey that started in 2017 as an R&D project between T2K and CERN’s Neutrino Platform.
A time projection chamber for the ND280 Upgrade, built and tested at CERN. (Image: CERN)After all the parts arrived in Japan, the detector was tested on the surface before being lowered it into its final position about 50 metres below ground in late 2023. “ND280 passed its first crucial test with flying colours in December 2023,” says Stefano Levorato, researcher at INFN. “It was so incredible to see the first event displays with the neutrino tracks.”
Read more on the BE-EA website and in the CERN Courier.
ndinmore Thu, 09/12/2024 - 15:49 Byline Kristiane Bernhard-Novotny Publication Date Mon, 09/16/2024 - 15:49The CMS collaboration welcomes its tenth management team: spokesperson Gautier Hamel de Monchenault and deputy spokespersons Anadi Canepa and Hafeez Hoorani. The new team began their mandate on 1 September 2024 and will represent the CMS collaboration until 31 August 2026. This is the tenth spokesperson team of the CMS experiment since the signing of its letter of intent just over 30 years ago.
The next two years will represent a unique time in the history of CMS with the confluence of detector operations, analysis of unprecedented proton–proton and heavy-ion collision datasets, and the ambitious upgrade of the detector in preparation for the High Luminosity phase of the LHC. Thanks to an exceptionally versatile particle physics detector and the ingenuity and creativity of a diverse collaboration, CMS will continue to address the most fundamental particle physics questions, including advancing research into the Higgs boson.
The CMS collaboration thanks the outgoing spokesperson Patricia McBride, and deputy spokespersons Lucia Silvestris and Wolfgang Adam for their incredible work from 2022 to 2024.
For detailed biographies of the new spokesperson team, visit the CMS website.
ndinmore Tue, 09/03/2024 - 13:52 Byline CMS collaboration Publication Date Tue, 09/03/2024 - 13:49
The Hellenic Society for the Study of High Energy Physics (HeSSHEP) promotes the scientific work of the Greek scientists, informs the general public and the Greek state on matters concerning the subject of High Energy Physics, organizes an workshop and conferences.
