CERN: News

ALICE sees “the ridge” in simplest collisions yet

abelchio — Fri, 31 Mar 2023 09:15:22 +0000

ALICE sees “the ridge” in simplest collisions yet

When atomic nuclei such as gold or lead nuclei collide at high energy in particle colliders, they can produce quark–gluon plasma (QGP) – a hot and dense state of matter predicted to have existed shortly after the Big Bang. One of the key features of QGP formation in such heavy-ion collisions is a long-range spatial correspondence, or correlation, between the particles that are created in the collisions. This collective phenomenon, which manifests as a ridge-like shape in data plots and is known as the ridge, was first observed in 2005 in heavy-ion collisions at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory in the US, and has since been observed at CERN’s Large Hadron Collider (LHC) in smaller collision systems such as collisions between protons.

At the Rencontres de Moriond conference today, the ALICE collaboration reported the observation of a ridge correlation in the simplest collision system yet. The result brings physicists a step closer to finding the origin of QGP-like collective phenomena in small collision systems.

The first observation of a ridge correlation in collisions other than heavy-ion collisions was made in 2010 by the CMS collaboration in “high-multiplicity” proton collisions that produce a relatively large number of particles. Soon after, CMS, ALICE and ATLAS observed the phenomenon also in collisions between protons and lead nuclei. These observations came as a surprise – such collision systems were expected to be too small and simple to develop QGP-like collective behaviour. Further studies have shown that the observed ridge correlations are indeed collective in nature, but the exact mechanisms that underpin this collective behaviour in these smaller and simpler systems remain to be identified.

Number of particle pairs (vertical axis) along two angular directions. A ridge-like shape is seen on the nearside on both sides of the peak. (Image: ALICE collaboration)

In its latest study, the ALICE collaboration set out to investigate whether a ridge correlation also occurs in “low-multiplicity” proton collisions that create a relatively small number of particles. The ALICE researchers analysed a large sample of proton collisions recorded by the collaboration during the second run of the LHC to investigate how the ridge effect depends on the number of particles produced in the collisions. They then plotted in a graph the number of particle pairs produced in a set of low-multiplicity collisions along two angular directions relative to the collision axis, and found a clear ridge-like shape.

Next, the ALICE team examined how the number of particle pairs associated with the ridge varied with multiplicity, and compared the results with previous results from electron–positron collisions recorded by the ALEPH experiment at the Large Electron–Positron Collider, the LHC’s predecessor. This comparison showed that, for the same multiplicity, the ridge correlation in proton collisions is stronger than that deduced for electron–positron collisions, in which no ridge correlation has so far been seen.

These new ALICE results, as well as future studies based on data from the third run of the LHC, should help physicists identify the mechanisms that govern collective behaviour in small collision systems.

_____

Find out more on the ALICE website.

abelchio Fri, 03/31/2023 - 11:15

Byline

Ana Lopes

Publication Date

Fri, 03/31/2023 - 11:07

Where does the Higgs boson come from?

katebrad — Thu, 30 Mar 2023 11:05:21 +0000

Where does the Higgs boson come from?

The discovery of the Higgs boson at the Large Hadron Collider (LHC) in 2012 was a triumph of theoretical and experimental physics, yet its implications are only just beginning to be understood. Precise measurements by the ATLAS and CMS collaborations show that this fundamental particle, which is responsible for generating the masses of elementary particles, behaves as predicted by the half-century-old Standard Model of particle physics. But where does the Higgs boson come from? And why is it so light that the LHC is able to produce it in droves? Such conundrums were discussed during a week-long workshop, Exotic Approaches to Naturalness, hosted by the CERN Theoretical Physics department from 30 January to 3 February.

The Higgs boson is the simplest known particle: a “fragment of vacuum” with no charge or spin. As with all elementary particles, it is an excitation, or quantum, of a more fundamental entity called a field – the uniquely featureless Brout–Englert–Higgs field, which fills all space uniformly. This field is understood to have come into existence during an epochal “electroweak” phase transition a fraction of a nanosecond after the Big Bang; whereas, previously, elementary particles such as the electron had moved at the speed of light, they were forever after forced to interact with this quantum molasses, which imbued them with the property of mass. But if this picture is true, the Higgs boson itself should gain mass from the interactions of known particles with its parent field. Totting up these so-called quantum corrections would suggest a value for the Higgs-boson mass that is many orders of magnitude larger than is observed. Apart from putting it beyond the reach of any conceivable experiment, such a heavyweight Higgs would not allow the universe as we know it to have formed.

Aware of this paradox (called the electroweak hierarchy problem) long before the Higgs boson was discovered, and guided by the possible existence of particles and forces beyond those described by the Standard Model, physicists have come up with various explanations. One is that the Higgs boson is made of more basic entities held together by very strong forces, which circumvents the impact of quantum corrections. Another is that space-time possesses additional “supersymmetric” dimensions that would imply the existence of an entirely new mirror-world of particles that cancel out the troublesome quantum corrections from standard ones. So far, however, no evidence for such “natural” solutions to the electroweak hierarchy problem has been found.

Enter Exotic Approaches to Naturalness, which drew on such concepts as generalised symmetries, ultraviolet/infrared mixing, weak-gravity conjectures and “magic zeroes” to try to explain the Higgs boson’s mass, and other unnatural numbers in physics. If the language is abstruse, it’s because participants of the February workshop were encouraged to challenge conventions and to plant seeds of ideas at the edge of knowledge – including those that reject the concept of naturalness entirely. The latter would be a radical break from past successes. After all, the mass of the Higgs boson is not the only seemingly unnatural number in nature: where physicists were once perplexed about why the electrical energy of the electron does not grow infinitely large at short distances, for instance, the mystery vanished with the discovery that the electron has an antimatter partner, the positron, that cancels out the unphysical divergence. The unnatural mass of the Higgs boson might even be linked to the exceedingly small but non-zero value of the cosmological constant, which is responsible for the accelerating expansion of the universe.

“This workshop provided us with a fantastic forum to bring a fresh perspective on naturalness problems, both in a variety of physical systems and for particle physics specifically,” says workshop co-organiser Tim Cohen of CERN. “Our community has been pondering the Higgs’s naturalness problem for decades, and yet many of us suspect that we have not found the right idea yet. If we can eventually understand how nature has addressed the electroweak hierarchy problem, there is a very high likelihood of learning something that will change our perspective on fundamental physics, and the reductionist philosophy that has served us since the beginning of our discipline.”

While theorists let their imaginations run free, the conclusion of the CERN workshop was clear: the path ahead will be guided by data. Larger samples of Higgs bosons to be collected by ATLAS and CMS in the coming years – and by experiments at a dedicated “Higgs factory” proposed to follow the LHC – will enable physicists to study the unique interaction of the Higgs boson with itself. This will provide information about the precise shape and form of the Brout–Englert–Higgs field and the nature of the electroweak phase transition, and possibly tell us whether the Higgs boson is natural or weirdly fine-tuned for our existence.

katebrad Thu, 03/30/2023 - 13:05

Byline

Matthew Chalmers

Publication Date

Thu, 03/30/2023 - 12:54

A spring awakening: CERN’s accelerators gear up for 2023

ndinmore — Mon, 27 Mar 2023 10:11:55 +0000

A spring awakening: CERN’s accelerators gear up for 2023

The days are getting longer, the trees are getting greener and it is time, too, for the CERN accelerator complex to reawaken. Following the year-end technical stop (YETS) – a 17-week period in which the accelerators undergo maintenance and minor upgrades – each accelerator in the chain has, in turn, restarted for the 2023 data-taking season. Each restart is an important step in the process of conveying protons from their source to their final destination in the Large Hadron Collider (LHC). While most major upgrades of the machines were carried out during the long shutdown before the start of LHC Run 3, the accelerator upgrades performed during the YETS will improve physics data taking for the second year of the run.

The CERN accelerator complex. (Image: CERN)

It all began on 13 February 2023, when Linac4 started beam commissioning: a short period of adjusting the machine before operation began on 17 February. This linear accelerator is responsible for supplying protons to the whole accelerator chain. It consists of a hydrogen ion source and several accelerating structures (known as radiofrequency cavities) that forward the ions to the PSB (Proton Synchrotron Booster). During the YETS, the Linac4 source was upgraded. Alessandra Lombardi, senior accelerator physicist at CERN, explains: “The novelty is in the extraction. While the new source is similar to the previous one, it allows a 30% increase in the peak current of the beam.” An increase in peak current means that the beams running through the accelerators have the potential for higher intensity.

On 3 March, the PSB began beam commissioning. Here, the hydrogen ions accelerated by Linac4 are stripped of their electrons, leaving only protons. These beams of protons are further accelerated in four synchrotron rings, supplying a small number of experiments and the next accelerator in the chain: the Proton Synchrotron (PS).

The Proton Synchrotron Booster. (PSB) (Image: CERN)

The PS, which began its 2023 operation on 10 March, is responsible for supplying proton beams to a variety of experiments, including n_TOF, the Antiproton Decelerator and those in the East Area, as well as to the Super Proton Synchrotron (SPS), the next accelerator in the chain. During the YETS, the beamlines between the PS and SPS underwent upgrades to make beam transfer more efficient. Until 2016, when a process called “multi-turn extraction” was introduced, the process of transferring beams from the PS to the SPS resulted in beam loss. Because the circumference of the SPS is eleven times that of the PS, the transfer involved circulating a beam five times around the PS, filling ten of the SPS’s eleven sections. This left some space for the machine to direct the beam. For 2023, this method has been improved upon even further, with the introduction of barrier buckets. These help synchronise the beam’s injection into the next accelerator with its gap, preventing further beam loss and improving the efficiency of the whole complex.

On 17 March, the SPS began beam commissioning. Adjusting and preparing this accelerator for physics is the final step before proton beams can circulate in the LHC again. The SPS was also upgraded for 2023. Mike Barnes, one of CERN’s senior engineers, explains: “We have kicker systems in all the accelerators, many of which have had work carried out. All these systems must be recommissioned and tested before being handed back to the CERN Control Centre for operations.” Kicker systems act like switches on train tracks: they change the direction of the beam to transfer it to the next accelerator. He continues: “In the SPS kicker system, four modules were upgraded to reduce the amount of heat that the beam deposits in them. These four modules previously limited high-intensity beam operation in the SPS.”

Furthermore, in the LHC, one of the injection kicker magnets was replaced with a new design during the YETS. This, like much equipment installed in the LHC tunnel, will be tested as part of the preparations for the LHC’s next run: the High-Luminosity LHC.

Installation of the SPS's new injection kicker magnets. (Image: CERN)

The whole process of restarting the machines is extremely complex, involving many people across multiple groups at CERN. The LHC restart is different every year due to the continuous machine upgrades and, at every stage of the restart, each individual machine needs to be adjusted to make the physics run as efficient and productive as possible. Following a commissioning period from 28 March, collisions in the LHC are expected to commence on 22 April, supplying its experiments with more efficiency and a higher beam intensity than ever before.

Accelerator report: the CERN accelerator complex is awakening from hibernation

ndinmore Mon, 03/27/2023 - 12:11

Byline

Naomi Dinmore

Publication Date

Wed, 03/29/2023 - 09:30

As Indico passes 1 million events, CERN and UN host joint workshop to discuss growth of this open source platform for organising events

ndinmore — Fri, 24 Mar 2023 15:03:21 +0000

As Indico passes 1 million events, CERN and UN host joint workshop to discuss growth of this open source platform for organising events

Over one million events have now been organised at CERN using Indico, a free and open source platform created at the Organization in 2004. On 20 and 21 March, representatives of CERN, the United Nations Office at Geneva (UNOG) and other organisations met for a workshop on Indico and its future development and growth.

Indico can be used to organise conferences, book meeting rooms, archive presentations and much more. Today it is used by over 200 organisations, including 11 UN agencies, such as the Joint UN Programme on HIV/AIDS (UNAIDS), the UN Educational, Scientific and Cultural Organization (UNESCO), the Office of the UN High Commissioner for Refugees (UNHCR) and the UN Environment Programme (UNEP).

Other organisations using Indico include the GSI Helmholtz Centre for Heavy Ion Research, the Cherenkov Telescope Array and the software company Canonical; representatives of each of these three organisations were also present at the event. In total, the workshop saw 50 experts come together to discuss further development plans for Indico.

Much discussion at the event focused on approaches for further growing the Indico community and coordinating development efforts. In addition to CERN and UNOG, important recent contributions to Indico have recently been made by the Max Planck Society for the Advancement of Science and the Institute of Electrical and Electronics Engineers.

The workshop was split across the CERN Meyrin Data Centre building and the UN’s Palais Des Nations. Tim Smith, head of the CERN IT department’s Communication, Education and Outreach section, gave the keynote speech at the event. “Collaboration and sharing knowledge are founding principles of CERN, built into the Organization’s DNA,” says Smith. “Indico is one of many examples of technologies developed to fulfil CERN needs which now is having significant positive impact on wider society.”

Other talks during the workshop focused on topics such as accessibility, searchability, using Indico in conjunction with CERN’s “CERNBox” storage platform, and even harnessing artificial intelligence technologies to improve Indico.

“This workshop happens at a time when we’ve reached the milestone of 1 million events having been organised at CERN using Indico; we’re very proud of this, but it's even more impressive to see how Indico has grown outside CERN,” says Pedro Ferreira, head of the Conferencing Technology section in the CERN IT department. “We’ve identified several priorities for future collaboration, including work on accessibility and further support for multilingualism.”

“The Indico Workshop 3.5 was a real success,” says Kira Kruglikova, director of the Division of Administration at UNOG. “This first joint workshop, co-organised by CERN and the UN, is another example of the strong collaboration between our two organisations and the respective teams.”

“The team felt enriched by the two working days with the Indico community and by the opportunity to share and learn from each other’s experiences and best practices,” continues Kruglikova. “The outcomes of the workshop exemplify the bright future of our project, and we look forward to contributing further with new ideas and concrete development to the success of Indico and its community.”

Find out more about Indico on the official website.

ndinmore Fri, 03/24/2023 - 16:03

Byline

Andrew Purcell

Publication Date

Fri, 03/24/2023 - 15:38

ICRC and CERN cooperate on R&D in technologies for humanitarian action

ndinmore — Fri, 24 Mar 2023 10:27:28 +0000

ICRC and CERN cooperate on R&D in technologies for humanitarian action

Today, International Committee of the Red Cross (ICRC) representatives from its Delegation for Cyberspace came to CERN for the first in a series of knowledge-sharing sessions on using free and open source technologies to support the vital humanitarian work they carry out across the globe. These technologies are being explored as a means to pursue neutrality, impartiality and independence of humanitarian action in a digital environment. CERN and the ICRC have signed a cooperation agreement that will see members of CERN’s IT department provide training on selected technologies, as well as sharing their experience.

Technologies to be covered include Indico, CERN’s popular platform for organising events; CERNBox, which is used to store and share data; Newdle, which was created at CERN to aid meeting scheduling; CERN’s Single-Sign On solution for authentication; and OpenStack, a popular open source cloud-computing tool to which CERN contributes and which is used at CERN to manage the computers in its data centre.

The ICRC is an independent, neutral organisation that works to ensure humanitarian protection and assistance for victims of armed conflict and other situations of violence. It takes action in response to emergencies and at the same time promotes respect for international humanitarian law and its implementation in national law.

At today’s event, the ICRC was represented by six members of its Luxembourg-based Delegation for Cyberspace and of its Geneva-based Data Protection Office Tech Hub. They are responsible for carrying out research and development and exploring and testing the technology relevant for the deployment of services to populations affected by armed conflict and other situations of violence by digital means, in a neutral, impartial and independent manner. Their aim is also to explore how to adapt the ICRC’s way of working, as well as the work of the International Red Cross and Red Crescent Movement as a whole and the wider humanitarian community, for the benefit of people affected by humanitarian emergencies globally.

“Through this collaboration, we aim to develop new research-and-development opportunities for cooperation related to the use of free and open source software development, as well as to cybersecurity,” says Enrica Porcari, Head of the CERN IT Department. “We will work to further the sharing of knowledge, experience and tools in this area.”

“We will also identify new challenges as they emerge and develop guidance to help equip the humanitarian and academic sectors with the tools necessary to navigate them,” continues Porcari. “This is an important opportunity for us to further boost CERN’s positive impact upon society.”

CERN is at the heart of the open science movement, which is underpinned by sharing open data and creating open tools. The ICRC and CERN share institutional features and interests, including neutrality, impartiality, independence, openness, data protection and cybersecurity. Both organisations recognise the importance of openness and building pillars of knowledge. They both value suitable, affordable, easy-to-use computing tools that enable them to pursue their respective mandates, from protecting vulnerable populations to advancing science.

“This collaboration with CERN is an essential enabler for furthering our exploration in the area of neutrality, impartiality and independence of humanitarian action in the digital space,” says Massimo Marelli, Head of the ICRC Delegation for Cyberspace in Luxembourg. “Specifically, to do this, we will work with CERN to set up their free and open source software tools in the Delegation for Cyberspace environment and test new functionalities and tools as well as operating modalities.”

At today’s event, initial plans were made for more in-depth training sessions later in the year. Find out more about this important new cooperation, which will further boost the positive impact CERN technologies have on wider society, in an announcement published today on the ICRC website.

CERN works closely with other international organisations in Geneva to boost its positive impact upon society. For example, CERN hosts UNOSAT, the United Nations Satellite Centre, and has an agreement with the United Nations Office at Geneva to collaborate on Indico, a popular open source platform for organising events.

ndinmore Fri, 03/24/2023 - 11:27

Byline

Andrew Purcell

Publication Date

Fri, 03/24/2023 - 11:19

ATLAS and CMS observe simultaneous production of four top quarks

ndinmore — Fri, 24 Mar 2023 09:23:49 +0000

ATLAS and CMS observe simultaneous production of four top quarks

Today, at the Moriond conference, the ATLAS and CMS collaborations have both presented the observation of a very rare process: the simultaneous production of four top quarks. They were observed using data from collisions during Run 2 of the Large Hadron Collider (LHC). Both experiments’ results pass the required five-sigma statistical significance to count as an observation – ATLAS’s observation with 6.1 sigma, higher than the expected significance of 4.3 sigma, and CMS’s observation with 5.5 sigma, higher than the expected 4.9 sigma – making them the first observations of this process.

The top quark is the heaviest particle in the Standard Model, meaning it is the particle with the strongest ties to the Higgs boson. This makes top quarks ideal for looking for signs of physics beyond the Standard Model.

There are a variety of ways to produce a top quark. Most commonly, they are observed in quark and antiquark pairs, and occasionally on their own. According to Standard Model theory, four top quarks – consisting of two top quark–antiquark pairs – can be produced simultaneously. The rate of production is, however, predicted to be 70 thousand times lower than that of top quark–antiquark pairs, which makes four-top-quark production elusive. Evidence for this phenomenon has previously been found by ATLAS in 2020 and 2021, and by CMS in 2022. However, until today, there had never been an observation.

As well as being rare, four-top-quark production is notoriously difficult to detect. When physicists search for a particular event, they look for its “signature”: the properties of the final particles of a decay. These provide clues to the short-lived events they are looking for. Every top quark decays into a W boson and a bottom quark. The W boson can then decay into either a charged lepton and a neutrino or a quark–antiquark pair. This means that the signature of four-top-quark events can be highly varied, containing from zero to four charged leptons and up to 12 jets produced by the quarks. This makes looking for the signature of four-top-quark production challenging.

To help search for these events, both ATLAS and CMS used novel machine-learning techniques to build the algorithms that select four-top-quark candidate events. The analyses use the spectacular four-top-quark signature with multiple electrons, muons and (bottom-quark-tagged) jets to separate the events with four top quarks from the background due to other Standard Model processes with larger production rates. Both ATLAS and CMS searched for event signatures containing two or more leptons.

The first direct observation of four-top-quark production is an exciting new step in learning more about this fascinating particle. Both experiments look forward to continuing to study this phenomenon during LHC Run 3.

ndinmore Fri, 03/24/2023 - 10:23

Byline

Naomi Dinmore

Publication Date

Fri, 03/24/2023 - 09:36

Arts at CERN and Copenhagen Contemporary to collaborate through Collide International award

angerard — Fri, 17 Mar 2023 10:17:17 +0000

Arts at CERN and Copenhagen Contemporary to collaborate through Collide International award

Today, we are pleased to announce a three-year partnership between CERN and Copenhagen Contemporary through Collide, Arts at CERN’s flagship international residency programme.

Arts at CERN is designed to generate creative connections between science and the arts through a broad programme of artistic residencies, art commissions and exhibitions. Over the past decade, Arts at CERN has brought arts and science together in new configurations, in collaboration with leading cultural institutions around the globe. The Collide residency programme was established in 2012 to foster networks with international organisations, creating new links between art and fundamental science worldwide.

Copenhagen Contemporary is Copenhagen’s international art centre, displaying installation art created by world-renowned artists and new emerging talents. Located in the former B&W welding building and offering 7000 m² of industrial halls, Copenhagen Contemporary displays large-scale installation art and creates collaborative partnerships and events across cultural genres, locally and internationally. Since 2016, Copenhagen Contemporary has hosted exhibitions featuring, among others, James Turrell, Carsten Höller, Pierre Huyghe, Bruce Nauman, Yoko Ono, Anselm Kiefer, Wu Tsang, and Larissa Sansour.

“For over 10 years, the Collide programme has allowed us to forge bonds of a new kind with different cities across our Member States,” explains Charlotte Warakaulle, CERN’s Director for International Relations. “We are delighted to see this international network expand with Copenhagen, which has such important traditions in particle physics, technology development, innovation and artistic expression. Bringing these dimensions together in Copenhagen will enable us to take these vital, creative encounters across communities even further.”

“At Copenhagen Contemporary we are excited and proud to bring the prestigious Collide programme to Scandinavia and offer artists a unique opportunity to develop their work in dialogue with world-leading scientists and researchers. Art and science share a deep curiosity to understand the world and our place in it. But their methods and end goals are different. Through art, the great conversation about the human condition is constantly renewed. We want to make this programme an opportunity to investigate how technology affects our life and might change our destiny,” says Marie Laurberg, Director of Copenhagen Contemporary.

The first edition of Collide Copenhagen has now been officially launched. Artists from any country in the world are invited to submit their proposals for a fully-funded two-month residency, split between CERN and Copenhagen Contemporary. The selected artist or artistic collective will devote this period to artistic research and artistic exploration, working side-by-side with physicists, engineers, laboratory staff and the Arts at CERN and Copenhagen Contemporary teams. For the first edition and the following annual calls, in 2024 and 2025, Arts at CERN and Copenhagen Contemporary will invite artists to reflect on the impact of science and research in contemporary culture. Proposals that consider the role of advanced technologies and novel scientific models as major topics in contemporary culture are welcome. Collide Copenhagen is especially aiming for artistic proposals that reflect on themes such as artificial intelligence, the modelling and analysis of vast datasets, the emergence of quantum technologies, and the interpretation of these themes from philosophical and ethical standpoints. The artists selected for the 2023–2025 editions will become part of an ambitious exhibition at Copenhagen Contemporary in 2025, investigating technology’s impact on humanity.

The application deadline is 8 May 2023. Conditions and guidelines for the call are on the Arts at CERN website. An international jury of experts will review the proposals and the decision will be announced in late June 2023.

angerard Fri, 03/17/2023 - 11:17

Publication Date

Thu, 03/23/2023 - 14:00

Accelerator Report: Preparing for the upcoming LHC restart

anschaef — Wed, 22 Mar 2023 12:33:18 +0000

Accelerator Report: Preparing for the upcoming LHC restart

Last week, the SPS accelerated its first beam of the year. In the early hours of Friday, 17 March, the PS sent the “LHC individual bunch beam” (LHCindiv) down the TT2/TT10 transfer lines to the SPS door. After clearing some interlocks, the beam was quickly injected into the accelerator. For the SPS operators, the machine physicists and the equipment experts, the meticulous process of adjusting the thousands of machine parameters then began, with countless iterations between observations on the beam and fine-tuning of the parameters. At 8 o’clock in the evening, the day ended with satisfaction after the beam was injected and accelerated on many different cycles.

The SPS operations team continued to work over the weekend, making particle orbit measurements around the SPS and determining whether improvements could or needed to be made. This is done through a “beam-based realignment campaign”: the particle orbits in the horizontal and vertical planes are measured for two types of beam, namely the LHCindiv beam and a low intensity beam destined for fixed-target physics in the SPS North Area. This orbit data is carefully analysed and used to calculate whether mechanical displacement of some of the quadrupole magnets could improve the orbit, i.e. whether the excursion of the beam in the vacuum chamber can be reduced so that the particle beam can move more smoothly through the SPS vacuum chambers for the remainder of the year, minimising possible particle losses. This week, beam production will be briefly interrupted so that our colleagues working on transport and geodetic metrology can enter the SPS tunnel to move the selected magnets, sometimes by only a fraction of a millimetre. Immediately afterwards, the SPS operators will re-inject the beam and quantify and validate the orbit correction. From that moment onwards the fine adjustments to prepare the necessary beams will continue, in order to be ready to inject beams into the LHC next week.

The SPS super cycle. On the left: at 7.00 a.m., the LHCindiv beam has just been injected (but not yet accelerated) and dumped on the internal dump. On the right: the progress made during the day is clearly visible, with various types of beam injected and accelerated. (Images: CERN)

On the LHC side, most of the maintenance activities have been completed, the machine has been closed and the Departmental Safety Officer, with support from the access and safety system team and the OP group, has validated the LHC access and safety system – a necessary condition for switching on the LHC and injecting beams. The hardware commissioning is progressing well and the power converters are being switched on and tested gradually. The objective is to be ready to inject the first beam of 2023 into the LHC next week.

anschaef Wed, 03/22/2023 - 13:33

Byline

Rende Steerenberg

Publication Date

Wed, 03/22/2023 - 13:31

New LHC experiments enter uncharted territory

ckrishna — Wed, 22 Mar 2023 09:42:09 +0000

New LHC experiments enter uncharted territory

Although neutrinos are produced abundantly in collisions at the Large Hadron Collider (LHC), until now no neutrinos produced in such a way had been detected. Within just nine months of the start of LHC Run 3 and the beginning of its measurement campaign, the FASER collaboration changed this picture by announcing its first observation of collider neutrinos at this year’s electroweak session of the Rencontres de Moriond. In particular, FASER observed muon neutrinos and candidate events of electron neutrinos. “Our statistical significance is roughly 16 sigma, far exceeding 5 sigma, the threshold for a discovery in particle physics,” explains FASER’s co-spokesperson Jamie Boyd.

In addition to its observation of neutrinos at a particle collider, FASER presented results on searches for dark photons. With a null result, the collaboration was able to set limits on previously unexplored parameter space and began to exclude regions motivated by dark matter. FASER aims to collect up to ten times more data over the coming years, allowing more searches and neutrino measurements.

FASER is one of two new experiments situated at either side of the ATLAS cavern to detect neutrinos produced in proton collisions in ATLAS. The complementary experiment, SND@LHC, also reported its first results at Moriond, showing eight muon neutrino candidate events. “We are still working on the assessment of the systematic uncertainties to the background. As a very preliminary result, our observation can be claimed at the level of 5 sigma,” adds SND@LHC spokesperson Giovanni De Lellis. The SND@LHC detector was installed in the LHC tunnel just in time for the start of LHC Run 3.

Until now, neutrino experiments have only studied neutrinos coming from space, Earth, nuclear reactors or fixed-target experiments. While astrophysical neutrinos are highly energetic, such as those that can be detected by the IceCube experiment at the South Pole, solar and reactor neutrinos generally have lower energies. Neutrinos at fixed-target experiments, such as those from the CERN North and former West Areas, are in the energy region of up to a few hundred gigaelectronvolts (GeV). FASER and SND@LHC will narrow the gap between fixed-target neutrinos and astrophysical neutrinos, covering a much higher energy range – between a few hundred GeV and several TeV.

One of the unexplored physics topics to which they will contribute is the study of high-energy neutrinos from astrophysical sources. Indeed, the production mechanism of the neutrinos at the LHC, as well as their centre-of-mass energy, is the same as for the very-high-energy neutrinos produced in cosmic-ray collisions with the atmosphere. Those “atmospheric” neutrinos constitute a background for the observation of astrophysical neutrinos: the measurements by FASER and SND@LHC can be used to precisely estimate that background, thus paving the way for the observation of astrophysical neutrinos.

Another application of these searches is measuring the production rate of all three types of neutrinos. The experiments will test the universality of their interaction mechanism by measuring the ratio of different neutrino species produced by the same type of parent particle. This will be an important test of the Standard Model in the neutrino sector.

ckrishna Wed, 03/22/2023 - 10:42

Byline

Kristiane Bernhard-Novotny

Chetna Krishna

Publication Date

Wed, 03/22/2023 - 10:25

HiLumi News: New CERN niobium–tin magnet energises the HL-LHC programme

anschaef — Tue, 21 Mar 2023 12:58:05 +0000

HiLumi News: New CERN niobium–tin magnet energises the HL-LHC programme

The magnet programme is one of the keystones of the HL-LHC project. At its heart is the development of triplet quadrupole magnets, which will focus the very intense beam around the collision points at ATLAS and CMS. The niobium–tin compound from which the coils are built allows them to reach the 12 T magnetic fields required by the HL-LHC.

Despite the complexity of Nb₃Sn coils and magnet manufacturing, as of early 2023, the technology is being validated for use inside particle accelerators. Twenty 4.2-metre-long magnets (MQXFA) are being produced in the United States – seven of which have successfully passed their individual tests and will be assembled two by two in cold masses as an in-kind contribution to the HL-LHC.

The third prototype of the longer version of the magnet developed at CERN (MQXFBP3, 7.2-m-long) was the first to reach nominal current, plus an operational margin, in a test carried out in late 2022. After this success, the results of the months-long test of its successor, MQXFB02, had teams across the HL-LHC project celebrating: not only does this new magnet also reach nominal current plus operational margin, but it does so with a larger temperature margin. Moreover, it demonstrated resilience in an endurance test to simulate its long-term behaviour in the HL-LHC. A similar test was carried out on a US magnet in 2022.

MQXFB02 is the fruit of the second leg of the “three-leg” strategy that was implemented after performance limitations were observed in the first two MQXFB prototypes. This second leg involved technical improvements in the magnet assembly to eliminate the coil overstress during keying and bladdering operations. Powering for the test started in November 2022 and ended at the beginning of March this year.

(Image: CERN)

The quadrupole magnet reached nominal current, plus a 300 A operational margin (16.53 kA), with two quenches at 1.9 K in the first powering cycle. At 4.5 K, it quenched at nominal current plus 200 A, thus proving a temperature margin of ~2.7 K. This performance limitation is similar to that observed in the first three prototypes, but at a higher current level. The magnet’s resilience was assessed through three warm-up and cool-down cycles, which all reached nominal current at 1.9 K without quenches. Over more than three months of testing, a total of 500 powering cycles and 48 high current quenches, both provoked and spontaneous, were performed – none of them caused performance degradation. This combination of performance and resilience is the base of the acceptance criteria for operation in the HL-LHC.

Given these good results, the magnet will be recovered from its cold mass and, in April 2023, a new cold mass will be manufactured, including, this time, a nested corrector from the CIEMAT collaboration. The cold mass will then be tested again, in its final configuration, in SM18 in 2024.

anschaef Tue, 03/21/2023 - 13:58

Publication Date

Tue, 03/21/2023 - 13:56