Novel probes of the strong force: precision jet substructure and the Lund jet plane

A hallmark of the strong force at the Large Hadron Collider (LHC) is the dramatic production of collimated jets of particles when quarks and gluons scatter at high energies. Particle physicists have studied jets for decades to learn about the structure of quantum chromodynamics – or QCD, the theory of the strong interaction – across a wide range of energy scales. Recent theoretical and experimental advancements in their study is now allowing ATLAS physicists to test the strong force in new ways.

Physics Briefing | 19 Apr 2020

Searching for new sources of matter–antimatter symmetry breaking in Higgs boson interaction with top quarks

When a particle is transformed into its antiparticle and its spatial coordinates inverted, the laws of physics are required to stay the same – or so we thought. This symmetry – known as “CP symmetry” (Charge conjugation and Parity symmetry) – was considered to be exact until 1964, when a study of the kaon particle system led to the discovery of “CP violation”. In a new result presented today, the ATLAS Collaboration performed a direct test of the CP properties of the interaction between the Higgs boson and top quarks. The result is based on an analysis of the full LHC Run-2 dataset, looking at collision events where the Higgs boson is produced in association with one or two top quarks, and in turn decays into two photons.

Physics Briefing | 07 Apr 2020

Measuring the beauty of the Higgs boson

Two years ago, the Higgs boson was observed decaying to a pair of beauty-quarks (H→bb), moving its study from the “discovery era” to the “measurement era”. In new results presented today, the ATLAS Collaboration studied the full LHC Run 2 dataset to give an updated measurement of H→bb, where the Higgs boson is produced in association with a vector boson (W or Z).

Physics Briefing | 07 Apr 2020

ATLAS Collaboration enters active “Safe Mode”

The global health crisis caused by COVID-19 has impacted every aspect of life. Much of the world’s population are sheltering in place, with ATLAS Collaboration members similarly affected.

News | 02 Apr 2020

ATLAS PhD Grant continues its support of up-and-coming talents

At an award ceremony in the Globe of Science and Innovation, the ATLAS Collaboration celebrated the new recipients of the ATLAS PhD Grant: Prajita Bhattarai, Hassnae El Jarrari and Albert Kong.

News | 11 Mar 2020

ATLAS Thesis Awards: And the winners are…

With over 5000 members in 181 institutions, contributions to the ATLAS Collaboration can take a variety of forms. Every February, ATLAS celebrates the outstanding work of one particular set of members: its PhD students.

News | 03 Mar 2020

Serving up new winter recipes with the ATLAS Early Career Scientist Board

In 2019, I joined the ATLAS Early Career Scientist Board (ECSB): a special advisory group dedicated to assisting the ATLAS Collaboration in building an environment where the full scientific potential of scientists at the start of their career can be realised. The board organises several activities for the ATLAS community (you may have seen all of our summer activities described in this blog). I was actively involved in the winter activities. They were all fantastic experiences to improve social relationships in a 5000-people collaboration.

Blog | 28 Feb 2020

25 years on: a single top quark partners with the Z boson

A quarter-century after its discovery, physicists at the ATLAS Experiment are gaining new insight into the heaviest-known particle: the top quark. The huge amount of data collected during Run 2 of the LHC (2015-2018) has allowed physicists to study rare production processes of the top quark in great detail, including its production in association with other heavy elementary particles.

Physics Briefing | 21 Feb 2020

Searching for natural supersymmetry using novel techniques

In new results presented today at CERN, the ATLAS Experiment’s search for supersymmetry (SUSY) reached new levels of sensitivity. The results examine a popular SUSY extension studied at the Large Hadron Collider (LHC): the “Minimal Supersymmetric Standard Model” (MSSM), which includes the minimum required number of new particles and interactions to make predictions at the LHC energies.

Physics Briefing | 18 Feb 2020

ATLAS Experiment releases 13 TeV Open Data for Science Education

The ATLAS Collaboration at CERN has just released the first open dataset from the Large Hadron Collider’s (LHC) highest-energy run at 13 teraelectronvolts (TeV). The new release is specially developed for science education, underlining the Collaboration’s long-standing commitment to students and teachers using open-access ATLAS data and related tools.

Press Statement | 10 Feb 2020

In conversation with Philippe Farthouat, a driving force behind ATLAS electronics

Philippe Farthouat has played a critical role in electronics development since the beginning of ATLAS, from design and prototyping to testing and installation. He has been the overall ATLAS electronics coordinator since 1999.

Portrait | 14 Jan 2020

Sharing the Excitement of ATLAS

This past week, I grabbed a last-minute opportunity to wander about and take in the beauty of my favourite particle physics detector. Located 100 meters under the French/Swiss border near Geneva, ATLAS is always a marvel to see and to explore. Although I have hosted hundreds of visits by its side, I never tire of the view and inevitably pull out my phone or camera to photograph it, yet again.

Blog | 22 Dec 2019

New open release streamlines interactions with theoretical physicists

What if you could test a new theory against LHC data? Better yet, what if the expert knowledge needed to do this was captured in a convenient format? This tall order is now on its way from the ATLAS Collaboration, with the first open release of full analysis likelihoods from an LHC experiment.

News | 12 Dec 2019

African scientists take on new ATLAS machine-learning challenge

Cirta is a new machine-learning challenge for high-energy physics on Zindi, the Africa-based data-science challenge platform. Launched this autumn at the International Conference on High Energy and Astroparticle Physics (TIC-HEAP), Constantine, Algeria, Cirta challenges participants to provide machine-learning solutions for identifying particles in LHC experiment data.

News | 20 Nov 2019

ATLAS probes the quark-gluon plasma in a new study of photo-produced muon pairs

The electromagnetic fields of the Lorentz-contracted lead nuclei in heavy-ion collisions at the LHC act as intense sources of high-energy photons, or particles of light. This environment allows physicists to study photon-induced scattering processes, that can not be studied elsewhere. A key process examined by ATLAS physicists involves the annihilation of photons into pairs of oppositely charged muons. The ATLAS Collaboration recently released a new, comprehensive measurement of this process.

Physics Briefing | 19 Nov 2019

Ensuring high-quality data at ATLAS

During Run 2, ATLAS achieved an exceptionally high data-quality efficiency for a hadron collider, with over 95% of the 13 TeV proton-proton collision data certified for physics analysis. In a new paper released today, the ATLAS data quality team summarises how this excellent result was achieved.

Physics Briefing | 13 Nov 2019

In conversation with Masaya Ishino, a key player behind ATLAS' successful Run 2

Masaya Ishino is a researcher and professor with the University of Tokyo. He joined the ATLAS Collaboration in 2001, and has been instrumental to the development, construction and operation of the muon spectrometer. Masaya was elected ATLAS Run Coordinator in 2017, playing a key role in the record-breaking Run 2 operation.

Portrait | 07 Oct 2019

ATLAS highlights from TOP2019

As the heaviest elementary particle, the top quark is appropriately named. It is ideally suited for precision measurements that test the limits of our understanding and could provide indirect hints at new physics. Physicists from around the world gathered in Beijing, China, last week at the annual TOP2019 conference to exchange the latest news, results and ideas on the top quark. For the ATLAS collaboration, TOP2019 proved a great success, with several excellent talks and posters presented by its members.

News | 04 Oct 2019

Record crowds at ATLAS for the CERN Open Days

On 14-15 September 2019, CERN opened its doors to the public for its first Open Days since 2013. This massive event saw over 75,000 visitors descend upon the Organization – many of whom eagerly anticipated underground visits to the LHC and its experiments.

News | 23 Sep 2019

New ATLAS members, welcome on board

This summer was rich with events regularly organised by the ATLAS Early Career Scientists Board (ECSB): Induction Day, Career Q&A and the Ice Cream event. The ECSB is a special advisory group dedicated to assisting the ATLAS Collaboration in building an environment where the full scientific potential of young scientists can be realised. It consists of seven early career scientists, representing various career levels, nationalities, genders and home institutions. I have been in the thick of things as a new member of the ECSB and had a lot of new experiences. Each event was full of fantastic people and brought to its participants tonnes of useful information.

Blog | 18 Sep 2019

ATLAS Experiment welcomes the public for CERN Open Days

The ATLAS Experiment will be opening its doors to the world on 14 and 15 September 2019 for the CERN Open Days. This weekend-long event will be an exciting opportunity for members of the public to explore the world’s largest particle-physics laboratory – host to the most powerful particle accelerator ever built, the Large Hadron Collider (LHC) – and take part in over 100 activities around the CERN campus.

News | 06 Sep 2019

Searching for Higgs boson interactions with the lightest charged lepton

Does the Higgs boson follow all of the rules set by the Standard Model? Since discovering the particle in 2012, the ATLAS and CMS Collaborations have been hard at work studying the behaviour of the Higgs boson. Any unexpected observations could be a sign of new physics beyond the Standard Model.

Physics Briefing | 06 Aug 2019

ATLAS delivers new direct measurement of the top-quark decay width with improved precision

As the heaviest known particle, the top quark plays a key role in studies of fundamental interactions. Due to its short lifetime, the top quark decays before it can turn into a hadron. Thus, its properties are preserved and transferred to its decay products, which can in turn be measured in high-energy physics experiments. Such studies provide an excellent testing ground for the Standard Model and may provide clues for new physics.

Physics Briefing | 06 Aug 2019

ATLAS releases new search for strong supersymmetry

New particles sensitive to the strong interaction might be produced in abundance in the proton-proton collisions generated by the LHC – provided that they aren’t too heavy. These particles could be the partners of gluons and quarks predicted by supersymmetry (SUSY), a proposed extension of the Standard Model of particle physics that would expand its predictive power to include much higher energies. In the simplest scenarios, these “gluinos” and “squarks” would be produced in pairs, and decay directly into quarks and a new stable neutral particle (the “neutralino”), which would not interact with the ATLAS detector. The neutralino could be the main constituent of dark matter.

Physics Briefing | 05 Aug 2019

Zooming in on top-quark production

As the heaviest known elementary particle, the top quark has a special place in LHC physics. Top quark-antiquark pairs are copiously produced in collisions recorded by the ATLAS detector, providing a rich testing ground for theoretical models of particle collisions at the highest accessible energies. Any deviations between measurements and predictions could point to shortcomings in the theory – or first hints of something completely new.

Physics Briefing | 05 Aug 2019