Physics Department - Extern RSS Feeds

NA64 uses the high-energy SPS muon beam to search for dark matter

The NA64 experiment started operations at CERN’s SPS North Area in 2016. Its aim is to search for unknown particles from a hypothetical “dark sector”. For these searches, NA64 directs an electron beam onto a fixed target. Researchers then look for unknown dark sector particles produced by collisions between the beam’s electrons and the target’s atomic nuclei.

Recently, the NA64 team started using a muon beam from the SPS to search for new particles that interact predominantly with muons – heavier versions of the electron – and could explain simultaneously the long-standing puzzle of the muon’s anomalous magnetic moment and the dark-matter (DM) problem. Their first results were accepted in the journal Physical Review Letters on 8 April.

In this paper, the NA64 collaboration sets new limits on the available parameter space – the window where the researchers could find a hypothetical dark boson Z’ coupling only to muons and tauons for given values of its mass and coupling strength. In the so-called vanilla model, the Z’ can only decay back into neutrinos and could provide an explanation of the muon’s anomalous magnetic moment puzzle. However, in extended models, it can also decay into DM candidates. This would solve the DM problem by predicting the observed relic density of DM particles created in the early universe. With these results, the NA64 collaboration demonstrates the great potential of muon beams in dark matter searches and in future new physics scenarios preferably coupled to muons.

“Muons scattering off the nuclei in the target could produce a hypothetical dark boson Z’, followed by its invisible decay into either a pair of neutrinos or a pair of dark-matter candidates, depending on the underlying model,” explains the deputy Technical Coordinator Laura Molina Bueno. “The signature of this production would be missing energy and momentum in our detectors.”

To search for this, a 160 GeV tertiary muon beam derived from the primary SPS proton beam is fired onto an electromagnetic calorimeter acting as an active target. The experimentalists then search for events in which one final-state muon has a momentum lower than 80 GeV with no detectable activity in the downstream calorimeters.

As no event matching these conditions was observed in the expected signal region, the researchers were able to exclude this region and conclude that, for the first model, the only possible mass window for a dark boson Z’ to explain the g-2 muon anomaly is from 6 MeV up to 40 MeV. Their results also indicate that light thermal dark matter coupled to the standard model via a (Lmu-Ltau) Z’ cannot be heavier than 40 MeV.

NA64 is among the first experiments searching for dark sectors weakly coupled to muons. The experimentalists are confident that they will cover the available parameter space in the future by using higher beam intensities. “Using a muon beam opens a new window to explore other well-motivated new physics scenarios, such as benchmark dark-photon models, scalar portals, millicharged particles or lepton-flavour violating processes,” concludes NA64 co-Spokesperson Paolo Crivelli.

anschaef Sat, 05/18/2024 - 08:34 Byline Kristiane Bernhard-Novotny Publication Date Sat, 05/18/2024 - 08:29

Nature Physics, Published online: 17 May 2024; doi:10.1038/s41567-024-02475-3

Ultrafast light pulses, if they are sufficiently intense, can induce phase transitions on ultrafast timescales. It is now shown that when a system is first excited by a weak preparatory pulse, this generates local changes in structure that transiently lower the energy barrier to the phase transition, enabling high-speed and energy-efficient transitions.

Accelerator Report: Already a fifth of the way there

The whole CERN accelerator complex and its associated experimental facilities have been fully operational for some time now, so the time is ripe to review the first part of this year’s run and look forward to what is still to come.

At the LHC, first collisions with just a few bunches occurred on 6 April. Meaningful physics data taking can only begin when collisions take place with at least 1200 bunches per beam, and this milestone was reached on 14 April. It means that, out of the 147 days allocated to proton-proton collisions this year, 32 have already been completed, representing just over 20% of the 2024 proton run.

During these initial 32 days, the LHC machine was available 67.2% of the time with stable beams in collision 45.2% of the time. The goal is to achieve a stable beam time ratio of at least 50%. Such figures are quite normal in the early stages of an annual run, a period during which various teething problems and challenges are identified and addressed, as discussed in my last report.

Luminosity production is also progressing according to schedule, as can be seen in the graph below. So far, the integrated luminosity collected has reached 17.5 fb-1, which is nearly 20% of the 2024 target of 90 fb-1. To reach this target, we need an average of about 0.8 fb-1 per day. Recently we have seen a record production of 1.23 fb-1 in just 24 hours, which demonstrates the LHC’s impressive potential to meet and possibly even exceed our target.

The predicted and achieved luminosity curves for ATLAS and CMS. The blue areas indicate the machine development (MD) periods, the red area the Van de Meer run, and the green one the technical stop. (Image: CERN)

Today, the LHC is performing the Van de Meer run, a crucial process used to calibrate the luminosity measurements in the four main LHC experiments (ALICE, ATLAS, CMS, LHCb).

This follows the first block of machine development (MD) sessions that took place on 13-15 May, during which experts conducted various tests and studies, including further investigation into the collimator hierarchy breaking that occurred in April.

On 18 May, the LHC will resume its primary task of producing luminosity. This production period will continue until the second MD block that is scheduled to start on 5 June and will be followed by a 5-day technical stop to carry out essential preventive and corrective maintenance before the summer holiday season. During the summer, the LHC will continue its luminosity production.

An overview of the beam availability of the different injectors and experimental facilities. The availability of each machine takes into account the non-availability of the upstream machines. (Image: CERN)

Not only is the LHC performing well, but the injector complex is also achieving a high level of beam availability for its experimental users. Physics in the injector complex kicked off on 22 March in the PS East Area. With the run scheduled to end on 2 December, the East Area has already completed over 20% of its 2024 run. Meanwhile the antimatter factory, which was the last facility in the injector complex to start beam operation, began delivering antiprotons to its experiments on 22 April, so just over 10% of its scheduled physics time for 2024 has now elapsed.

Linac4, the first link in the proton injector chain, has posted an average availability of 97.3% since its start after Long Shutdown 2 (LS2). It has posted availability of 95.7% so far in 2024, about 1.6% less than usual. This can mainly be attributed to a series of faults that led to the replacement of a klystron in March.

The injectors will continue their routine beam delivery to the experimental facilities until 12 June, when they too will interrupt beam production for a 4-day technical stop. Afterwards, it will be business as usual once more and the experiments can look forward to good beam delivery over the summer.

As we continue through the year, the achievements so far set a promising pace for the remaining months.

anschaef Thu, 05/16/2024 - 11:56 Byline Rende Steerenberg Publication Date Wed, 05/15/2024 - 11:52

Nature Physics, Published online: 16 May 2024; doi:10.1038/s41567-024-02520-1

Cold and ultracold molecules

Nature Physics, Published online: 16 May 2024; doi:10.1038/s41567-024-02523-y

Max out the gap

Nature Physics, Published online: 16 May 2024; doi:10.1038/s41567-024-02524-x

Trapped by memory

Nature Physics, Published online: 16 May 2024; doi:10.1038/s41567-024-02494-0

A single light-emitting dye molecule precisely placed within the tiny gap of a metal nanodimer boosts light–matter coupling — a step closer to the development of quantum devices operating at room temperature.

Nature Physics, Published online: 16 May 2024; doi:10.1038/s41567-024-02501-4

It’s time to tackle space debris

Nature Physics, Published online: 16 May 2024; doi:10.1038/s41567-024-02528-7

Social activities are common in many research groups, often based around outdoor activities such as hiking. We argue that there are more inclusive ways to bring a team together.

Nature Physics, Published online: 16 May 2024; doi:10.1038/s41567-024-02503-2

UNESCO has now formally adopted World Metrology Day as a UNESCO International Day to be observed on 20 May each year — the theme of 2024 is sustainability. Shanay Rab and Richard Brown take a look at its origin.

Nature Physics, Published online: 16 May 2024; doi:10.1038/s41567-024-02499-9

Ultracold atoms are a well-established platform for quantum sensing and metrology. This Review discusses the enhanced sensing capabilities that molecules offer for a range of phenomena, including symmetry-violating forces and dark matter detection.

CERN 70th anniversary exhibition at Geneva Airport

To honour its 70 years of contributions to scientific knowledge, technological innovation and international collaboration, CERN has put together a rich and diverse programme, at CERN and across its Member States, Associate Member States and beyond. This programme includes exhibitions, the first of which can now be visited at Geneva Airport as part of a collaboration between the two organisations. Inaugurated on 2 May, the exhibition’s three components will occupy the wall leading to the security check before entering the departure lounge, the “Panorama” terrace and the international terminal until autumn 2024.

Find out more on the “CERN and its neighbours” website.

anschaef Wed, 05/15/2024 - 12:09 Byline Zoe Nikolaidou Publication Date Wed, 05/15/2024 - 12:07

Computer Security: WhiteHat & Zebra trainings are back

Vulnerabilities and weaknesses lurk all over the digital place: unprotected file uploads, generous SQL queries, unfiltered input fields, disclosed passwords… They are the entry point for cross-site scripting, remote code execution or root privilege escalation, and the first step towards fostering the patient-zero-like compromise of a server, a service or the whole of CERN; the first step towards losing protected, restricted or confidential information; the first step that can result in mild to serious reputational damage for the Lab.

A plethora of means exists to protect against that. On the one hand, the Computer Security team is scanning for vulnerabilities and weaknesses in the hope of detecting them early and mitigating them fast. On the other, hand-in-hand with the Computer Security team, you, as an excellent software developer and experienced programmer, have followed the right courses to put in place a secure software programming and code development life-cycle, including sound system architecture and choice of components, apply best practices for managing and building your software in a secure fashion, and are aware of (and can avoid!) potential supply chain traps.

The CERN WhiteHat Challenge
While external students continue hacking into CERN and finding “juicy” stuff, we are glad to announce that the WhiteHatChallenge is back at CERN after a two-year hiatus. Designed as two half-days of training on ethics and integrity, focusing on penetration testing and vulnerability scanning, it should bring you up to speed on detecting suboptimal configurations and weaknesses in your web services and websites. While penetration testing is a marathon that requires lots of training and practice, this WhiteHat training should at least get you up and walking. It will cover the concepts for breaking into and abusing web applications, the use of the appropriate tools, and a Capture the Flag (CTF) tournament as a homework exercise to sharpen your skills. Hopefully it will give you a taste for becoming ─ after lots more fun training ─ an experienced penetration tester, hacker and participant in worldwide CTF tournaments! So, join us! All details for afternoon 1 and afternoon 2 can be found on Indico ─ no registration necessary.

Zebra Alliance Incident Response Exercise
And if you want to experience the pressure when the going really gets tough, see how incident response is conducted in reality. The Zebra Alliance has been hacked yet again (after previous attacks in 2022 and 2023)! And once again, it’s up to you and your peers in the room to figure out what happened. How did the attacker get in? What was their technique and intrusion vector? What’s their name (so the police can apprehend them)? No prior knowledge of security, incident response or even IT is needed. All you need is a laptop, the curiosity to dig and the eagerness to learn and tackle the challenge. As seats are limited, however, we kindly request that you register on Indico.

Have fun at both of these events! We hope to see you soon!

______

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

anschaef Wed, 05/15/2024 - 11:33 Byline Computer Security team Publication Date Wed, 05/15/2024 - 11:29

Unveiling the science of tomorrow: FCC Study takes centre stage at La Roche-sur-Foron exhibition

The Future Circular Collider (FCC) study took centre stage at the International Fair of Haute-Savoie/Mont Blanc in La Roche-sur-Foron from 27 April to 6 May. An information booth, overflowing with interactive exhibits, captivating presentations and branded goodies, showcased the proposed research infrastructure’s scientific potential, alongside the applications of particle physics research in everyday contexts.

The FCC study envisages a next generation particle collider that could succeed the LHC at CERN, currently the most powerful collider in the world. The FCC aspires to offer the broadest possible exploration of the Universe's mysteries via high-precision and high-energy studies of the elementary constituents of matter and the forces governing their interactions.

The information booth at the International Fair of Haute-Savoie/Mont Blanc provided a unique opportunity for residents and visitors to articulate their views on the project and engage in constructive dialogue with the FCC team. Acknowledging the importance of transparency and community involvement, the project team is committed to openly addressing the hurdles inherent in such a monumental scientific endeavour. CERN’s participation in the International Fair of Haute-Savoie/Mont Blanc, enhanced by the valuable help of volunteers from the FCC team, resulted in meaningful discussions with more than 2000 members of the local community on topics ranging from the required technological advancements to sustainability measures.

More information about the FCC study:

https://fcc.web.cern.ch

https://fcc-faisabilite.eu

 

ndinmore Wed, 05/15/2024 - 10:27 Publication Date Wed, 05/15/2024 - 10:18

Nature Physics, Published online: 15 May 2024; doi:10.1038/s41567-024-02490-4

Thousands of Iranians study at German universities every year, but many struggle with the German academic system. Here, we offer some advice.

Nature Physics, Published online: 15 May 2024; doi:10.1038/s41567-024-02502-3

Experience under the spotlight

Nature Physics, Published online: 15 May 2024; doi:10.1038/s41567-024-02504-1

Active cell contraction drives hole nucleation, fracture and crack propagation in a tissue monolayer through a process reminiscent of dewetting thin films.

Nature Physics, Published online: 15 May 2024; doi:10.1038/s41567-024-02496-y

Many recent experiments have stored quantum information in bosonic modes, such as photons in resonators or optical fibres. Now an adaptation of the classical spherical codes provides a framework for designing quantum error correcting codes for these platforms.

Hunting for millicharged particles at the LHC

The LHC family of experiments continues to grow. Alongside the four main experiments, a new generation of smaller experiments is contributing to the search for particles predicted by theories beyond the Standard Model, our current theory of particle physics. Recently, the FORMOSA demonstrator, which hunts for millicharged particles, has been installed in the cavern containing the FASER detector, 480 meters downstream from the ATLAS interaction point. It will now collect its first data.

Some theories predict the existence of millicharged elementary particles that would have a charge much smaller than the electron charge. If they exist, they would give clues to a theory beyond the Standard Model and could be considered as candidates for dark matter.

The FORMOSA demonstrator aims to prove the feasibility of the full experiment, which is intended to be installed in a proposed underground hall located about 620 metres away from the ATLAS interaction point. This experimental area – the Forward Physics Facility – is under study within the Physics Beyond Colliders initiative and is expected to host several experiments that will search for long-lived particles predicted by theories beyond the Standard Model. These particles would be produced by collisions at the centre of the ATLAS detector and would interact feebly with Standard Model particles. If approved, the experiments, among them the the proposed FASERν 2 and FLArE experiments, could start taking data when the High-Luminosity LHC is switched on in 2029.

The FORMOSA demonstrator comprises scintillators. When interacting with a charged particle, the scintillators emit photons that are subsequently converted into an electrical signal. While cosmic muons or those from ATLAS collisions may also strike the scintillators, millicharged particles typically deposit much less energy into each layer, distinguishing them from muons that traverse the detector.

“Initial studies with so-called no-beam data and source tests look already promising. This marks an important step towards achieving the goal to run the demonstrator this year and a great demonstration of the collaborative spirit of the projects within the Forward Physics Facility,” says project leader Matthew Citron from University of California, Davis.

Millicharged particles have become a particular focus of research in recent years. The MilliQan detector, located 33 meters away from the CMS interaction point, as well as MoEDAL-MAPP close to LHCb, started data taking during LHC Run 3. In 2020, a study carried out with a smaller demonstrator, MilliQan had ruled out the existence of millicharged particles for a range of masses and charges. Thanks to a higher volume of detection and its location in the far forward region of the LHC collisions, the FORMOSA experiment hopes to extend this search.

cmenard Tue, 05/14/2024 - 08:59 Byline Kristiane Bernhard-Novotny Publication Date Tue, 05/14/2024 - 16:20

Nature Physics, Published online: 13 May 2024; doi:10.1038/s41567-024-02492-2

The properties of quantum matter arise from the combined effects of dimensionality, interactions and quantum statistics. An experiment now studies what happens to ultracold bosons when the dimensionality of the system changes continuously between one and two dimensions.