For many students, a summer internship is a rite of passage — and a gateway to future jobs. Looking for a valuable glimpse into what a future in physics might hold, dozens of university students from around the world headed to CERN to participate in the Summer Student Programme and engage with cutting-edge scientific research at the ATLAS Experiment. With the support of their supervisors, these students have been deepening their knowledge of particle physics, engineering and computing through challenging projects. These are the stories of 12 of these students.

The tenth edition of the annual conference on Large Hadron Collider physics (LHCP 2022) begins today in video-conference rooms around the world.

The 30th International Symposium on Lepton Photon Interactions at High Energies (Lepton Photon 2021) kicks off today. Explore the ATLAS results that will be presented.

The European Physical Society Conference on High Energy Physics (EPS-HEP 2021) kicks off today. Explore the ATLAS results that will be presented.

The ninth annual conference on Large Hadron Collider physics (LHCP 2021) begins today in video-conference rooms around the world.

The ATLAS Collaboration has just released a collection of 200 software packages that make up the Trigger and Data Acquisition System (TDAQ). With this new release, most ATLAS software is now open – reinforcing the Collaboration’s ongoing commitment to open science.

A new result from the ATLAS Collaboration, released for the Higgs 2020 conference, aims at enriching the Higgs picture by studying its WW* decays.

One of the great unexplained mysteries is the nature of dark matter. So far, its existence has only been established through gravitational effects observed in space; no dark-matter particles with the needed properties have (yet) been detected. Could the Higgs boson be the key to their discovery?

ATLAS scientists are implementing a new strategy in the search for physics beyond the Standard Model – one that combines measurements across the full spectrum of the Collaboration's research programme.

ATLAS researchers are broadening their extensive search programme to look for more unusual signatures of unknown physics, such as long-lived particles. A theory that naturally motivates long-lived particles is supersymmetry (SUSY). A new search from the ATLAS Collaboration – released this week for the 5th International Conference on Particle Physics and Astrophysics (ICPPA-2020) – looks for the superpartners of the electron, muon and tau lepton

In 2017, the ATLAS and CMS Collaborations announced the detection of a never-before-observed process: vector boson scattering.

It was in 2014, just a few months after my transition from ALICE to ATLAS, that I saw the mock-up for the first time: a full-scale wooden reproduction of the central portion of the ATLAS experiment, measuring some 8 metres high and wide.

With new data from the LHC, ATLAS physicists have measured jet-quenching phenomena in the quark–gluon plasma with help of Z bosons.

As major players in the field of particle physics, the LHC collaborations contributed many new results, most of which exploited the full Run-2 dataset, recorded in 2015 to 2018. ATLAS physicists contributed 35 new results, and gave 85 talks in the parallel and plenary sessions. Their contributions spanned a wide range of topics, from precision measurements and searches for new phenomena to detector performance and R&D, as well as diversity and outreach.

During the International Conference on High-Energy Physics (ICHEP 2020), the ATLAS Collaboration presented the first observation of photon collisions producing pairs of W bosons, elementary particles that carry the weak force, one of the four fundamental forces. The result demonstrates a new way of using the LHC, namely as a high-energy photon collider directly probing electroweak interactions. It confirms one of the main predictions of electroweak theory – that force carriers can interact with themselves – and provides new ways to probe it.

The ATLAS Collaboration has announced the first observation of two W bosons produced from the scattering of two photons — particles of light – at the International Conference on High-Energy Physics (ICHEP 2020).

The ATLAS and CMS experiments at CERN announce new results which show that the Higgs boson decays into two muons. These new results have pivotal importance for fundamental physics because they indicate for the first time that the Higgs boson interacts with second-generation elementary particles.

The ATLAS Collaboration has released a new study into a key building block of matter: leptons. This type of particle comes in three different families (flavours) and, according to the Standard Model, should follow strict rules. For instance, except for their mass, leptons of different flavours have identical properties – a feature known as lepton flavour universality. This was recently corroborated by a key measurement of the W-boson decay rates into leptons by the ATLAS Collaboration.

Physicists can study Higgs-boson couplings in several ways: by measuring the rates of different Higgs boson production mechanisms and decays, and also by studying the particle’s kinematic properties. The ATLAS Collaboration has just presented precise new measurements of these key quantities. Several of these measurements were updated to use the full LHC Run 2 dataset (2015–2018), to provide the best precision to date.

Today, at the International Conference for High Energy Physics (ICHEP 2020), the ATLAS Collaboration announced first results using the ATLAS Forward Proton (AFP) spectrometer. With this instrument, physicists directly observed and measured the long sought-after prediction of proton scattering when particles of light turn into matter.

In the contest for the heaviest known elementary particle, the top quark and Z boson rank first and third, respectively. When a proton–proton collision produces a top-quark pair together with a Z boson – a process known as ttZ production – their total mass can reach an impressive 440 GeV! The discovery of this highly energetic process thus required the record collision energy and rate of the LHC; no previous collider could come close.

The nature of dark matter remains one of the great unsolved puzzles of fundamental physics. Many theoretical scenarios postulate that dark matter particles could be produced in the intense high-energy proton–proton collisions of the LHC. While the dark matter would escape the ATLAS detector unseen, it could occasionally be accompanied by a visible jet of particles radiated from the interaction point. Today, at the International Conference in High-Energy Physics (ICHEP 2020), ATLAS presented a new search for novel phenomena in collision events with jets and high missing transverse momentum (MET).

Since the 1950s, one conference has stayed circled in red on every physicist's calendar: the International Conference on High­-Energy Physics (ICHEP). The fortieth edition of ICHEP kicks off today, bringing together particle physicists, astrophysicists and accelerator scientists to share the latest news in their fields. Originally planned as an in-person event in Prague, ICHEP2020 will instead be the very first all-virtual edition of the conference.

The ATLAS Collaboration has released a new paper on the search for the Higgs-boson decay to a pair of muons. The new study uses the entire dataset collected by the ATLAS experiment during Run 2 of the LHC (2015–2018) to give a first hint of this elusive process.

The first all-virtual BOOST workshop kicks off today, bringing together experts from the LHC experiments and the theory community. This is the twelfth conference on "Boosted Object Phenomenology, Reconstruction and Searches in High-Energy Physics" (BOOST 2020), hosting plenary-style talks and virtual poster presentations on the latest developments in hadronic physics.

How do you track a particle’s trajectory when your detector keeps moving? What if you find slight biases in your detector’s measurements? These were the challenges faced by the ATLAS Inner Detector during Run 2 of the LHC (2015–2018). Located at the heart of the experiment, the Inner Detector provides efficient and precise measurements of charged-particle tracks. In a new paper released today, physicists describe the complex solutions they developed to align the Inner Detector, ensuring the continued accuracy of the experiment.

As a community, we need to stay in contact, remain motivated and learn from each other's experiences. The work-from-home situation is one to which everyone has to adjust, balancing personal and professional lives, while accepting the effect of the ongoing pandemic on society. Despite these challenges, the ATLAS Early Career Scientist Board (ECSB) developed a series of events to boost the morale of the ECS community and to help people connect, even when they are sitting miles away from each other. I joined the ATLAS ECSB in March 2020, and to be honest, it has felt great to be a part of something that makes a difference in people’s lives – even if it’s just to laugh together.

Though an academic affair, poster sessions are also an opportunity to network and socialise with colleagues. Typically, a large hall will be filled with rows of poster stands, their authors standing anxiously beside them, anticipating whatever question may be posed by a passer-by. Finger food and drinks are usually served. Sometimes these encounters lead to in-depth discussions about a new result but, more often than not, they just serve as ice-breakers for would-be colleagues, or a kind of “physics buffet” for conference attendees to sample subjects outside their specialization. Could such an experience be recreated in an online conference?

Claudia Gemme, researcher at INFN in Genova, has had a varied career with the ATLAS Collaboration. From her work on the construction and commissioning of the ATLAS Pixel detector, to a career in physics analysis and the ATLAS Publication Committee, she now leads a key upgrade of the ATLAS detector: the ATLAS Inner Tracker (ITk).

The eighth Large Hadron Collider Physics (LHCP 2020) conference concluded today, 30 May, in Zoom rooms around the world. Instead of descending on Paris to meet, particle physicists held the conference fully online for the first time. As a result, LHCP 2020 welcomed some 1300 registered participants – nearly triple its previous record of attendance. A bumper crop of new ATLAS results were prepared for the conference covering a broad range of topics, from precise measurements of the Standard Model to novel searches for new physics. These new results probed the full dataset collected during Run 2 of the LHC (2015-2018) – a proven gold mine for ATLAS’ rich physics programme.

This week, at the LHCP 2020 conference, the ATLAS Collaboration presented a precise measurement of lepton flavour universality using a brand-new technique. Physicists examined collision events where pairs of top quarks decay to pairs of W bosons, and subsequently into leptons. They then measured the relative probability that this lepton is a muon or a tau-lepton – a ratio known as R(τ/μ). According to the Standard Model, R(τ/μ) should be unity – but there has been long-standing tension with this prediction, ever since it was measured at the Large Electron-Positron (LEP) collider in the 1990s.

Supersymmetry offers an elegant solution to the limitations of the Standard Model, extending it to give each elementary particle a “superpartner” with different spin properties. Yet SUSY also contains interactions that would cause phenomena not observed in nature, such as the decay of protons. This has traditionally been avoided by requiring the conservation of a property known as “R-parity” (or “matter-parity”), which incorporates the baryon number, lepton number and spin. ATLAS physicists are also considering SUSY models with R-parity violation (or “RPV”), which would allow the lightest SUSY particle to be observed decaying directly into Standard Model particles.

In a new result released today, the ATLAS Collaboration announced strong evidence of the production of four top quarks. This rare Standard Model process is expected to occur only once for every 70 thousand pairs of top quarks created at the LHC and has proven extremely difficult to measure.

Light-by-light scattering is a very rare phenomenon in which two photons – particles of light – interact, producing another pair of photons. Direct observation of this process at high energy had proven elusive for decades, until it was first seen by the ATLAS Collaboration in 2016 and established in 2019. In a new measurement, ATLAS physicists are using light-by-light scattering to search for a hyped phenomenon beyond the Standard Model of particle physics: axion-like particles.

The eighth annual conference on Large Hadron Collider physics (LHCP 2020) kicks off today in video-conference rooms around the world. This week-long event is usually an opportunity for physicists from around the world to meet in person and share the latest news from their LHC experiments. This year, due to the COVID-19 pandemic, the conference is being held online.

The ATLAS Collaboration is exploring novel ways to search for new phenomena. Alongside an extensive research programme often inspired by specific theoretical models – ranging from quantum black holes to supersymmetry – physicists are applying new model-independent methods to broaden their searches. ATLAS has just released the first model-independent search for new particles using a novel technique called “weak supervision”.

Could the Higgs boson decay into dark matter? As dark matter does not interact directly with the ATLAS detector, physicists look for signs of “invisible particles”, inferred through momentum conservation of the proton–proton collision products. The ATLAS Collaboration searched the full LHC Run-2 dataset, setting the strongest limits on the Higgs boson decaying to invisible dark-matter particles to date.

The ATLAS Collaboration has just released a new result searching for the Higgs-boson decay to a Z boson and a photon. This result uses the full LHC Run-2 dataset, analysing almost four times as many Higgs-boson events as the previous ATLAS result.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Eight years of operation. Over 10,000 trillion high-energy proton collisions. One critical new particle discovery. Countless new insights into our universe. The Large Hadron Collider (LHC) has been breaking records since data-taking began in 2010 – and yet, for ATLAS and its fellow LHC experiments, a golden era of exploration is only just beginning.

In the Standard Model of particle physics, elementary particles acquire their masses by interacting with the Higgs field. This process is governed by a delicate mechanism: electroweak symmetry breaking (EWSB). Although EWSB was first proposed in 1964, it remains among the least understood phenomena of the Standard Model as a large dataset of high-energy particle collisions is required to probe it.

This week, at the European Physical Society Conference on High-Energy Physics (EPS-HEP) in Ghent, Belgium, the ATLAS Collaboration at CERN released new measurements of Higgs boson properties using the full LHC Run-2 dataset. Critically, the new results examine two of the Higgs boson decays that led to the particle’s discovery in 2012: H→ZZ*→4ℓ, where the Higgs boson decays into two Z bosons, in turn decaying into four leptons (electrons or muons); and H → γγ, where the Higgs boson decays directly into two photons.

A key interaction not yet observed by LHC experiments is the production of “double Higgs”. The Standard Model predicts that the Higgs field can interact with itself to create a Higgs boson pair. The rate with which this happens is critical, as it allows physicists to directly probe the potential energy of the Higgs field, which is responsible for mass of particles. Deviations from the expectation would be a strong hint of new physics.

Today, at the European Physical Society Conference on High-Energy Physics (EPS-HEP) in Ghent, Belgium, the ATLAS Collaboration released a new preliminary result searching for Higgs boson decays to a muon and antimuon pair (H → μμ). The new, more sensitive result uses the full Run-2 dataset, analysing almost twice as many Higgs boson events as the previous ATLAS result.

Among the most intriguing particles studied by the ATLAS collaboration is the top quark. As the heaviest known fundamental particle, it plays a unique role in the Standard Model of particle physics and – perhaps – in yet unseen physics beyond the Standard Model. A new ATLAS result, presented today at the European Physical Society Conference on High-Energy Physics (EPS-HEP) in Ghent, Belgium, examines the full Run 2 dataset to find evidence of charge asymmetry in top-quark pair events, with a significance of four standard deviations.

ATLAS physicists are in Ghent, Belgium, this week for the European Physical Society Conference on High-Energy Physics (EPS-HEP) 2019. Since its establishment in 1971, the EPS-HEP conference has brought together the high-energy particle physics community every two years to discuss the latest results in field. This year, several hundred physicists from around the world are expected to attend.

Simulation and supersymmetry, two things that have defined Zachary Marshall’s career. Zach is a researcher with Lawrence Berkeley National Lab. He is currently the co-convener of the ATLAS Supersymmetry group, leading the team searching for supersymmetry and all its various manifestations, building on his previous work as convenor of the ATLAS Simulation group.

The large amount of data delivered by the LHC in Run 2 (2015-2018) has not only allowed the ATLAS Experiment to probe previously unexplored territory for rare Standard Model processes and new physics, but also to measure already known processes to better precision. In both cases, but particularly the latter, a precise measurement of the integrated luminosity of the dataset is essential. In other words, how many proton collisions actually occurred in ATLAS during Run 2.

Dipole magnets are probably the best-known source of magnetic fields. They consist of a north and south pole; while one end magnetically attracts, the opposite repels. If you cut a magnet in half, you are left with two magnets, each with its own north and south pole. This apparent absence of an isolated magnetic pole - or “magnetic monopole” - has puzzled physicists for more than a century. It would seem perfectly natural for this particle to be present in our universe; Maxwell’s equations would reflect complete symmetry between electricity and magnetism if particles with magnetic charge were observed. So far the mystery remains: while every known particle in our universe is either electrically charged or neutral, none have been found to be magnetically charged.

The High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) is scheduled to begin colliding protons in 2026. This major improvement to CERN’s flagship accelerator will increase the total number of collisions in the ATLAS experiment by a factor of 10. To cope with this increase, ATLAS is preparing a complex series of upgrades including the installation of new detectors using state-of-the-art technology, the replacement of ageing electronics, and the upgrade of its trigger and data acquisition system.

This April marked the 10th anniversary of the International School of Trigger and Data Acquisition (ISOTDAQ). It was a fantastic event that united researchers in physics, computing and engineering, ranging from undergraduate students to post-doctoral scientists. The goal of the school was to teach the "arts and crafts" of triggering and data-acquisition for high-energy physics experiments through a series of lectures and hands-on laboratory exercises.

The management of the ATLAS experiment begins a new term this Spring, with Spokesperson Karl Jakobs (University of Freiburg) continuing to steer the collaboration through Long Shutdown 2 to the start of Run 3 of the Large Hadron Collider (LHC).

One of the most complete theoretical frameworks that includes a dark matter candidate is supersymmetry. Dark matter is an unknown type of matter present in the universe, which could be of particle origin. Many supersymmetric models predict the existence of a new stable, invisible particle - the lightest supersymmetric particle (LSP) – which has the right properties to be a dark matter particle. The ATLAS Collaboration has recently reported two new results on searches for an LSP where it exploited the experiment’s full “Run 2” data sample taken at 13 TeV proton-proton collision energy. The analyses looked for the pair production of two heavy supersymmetric particles, each of which decays to observable Standard Model particles and an LSP in the detector.

At an award ceremony in the Globe of Science and Innovation, the recipients of the 2019 ATLAS PhD Grant were celebrated in the presence of CERN & Society donors and members of the ATLAS community. The ATLAS PhD Grant has supported up-and-coming talents in particle physics since 2014 and this year saw a new donor take up its cause.

This week, particle physicists from around the world gathered in La Thuile, Italy, for the annual Rencontres de Moriond conference on Electroweak Interactions and Unified Theories. It was one of the first major conferences to be held following the recent completion of the Large Hadron Collider’s (LHC) second operation period (Run 2). The ATLAS Collaboration unveiled a wide range of new results, including new analyses using the full Run-2 dataset, as well as some high-profile studies of Higgs, electroweak and heavy-ion physics.

The Higgs boson was discovered in 2012 by the ATLAS and CMS experiments, but its rich interaction properties (its coupling to other particles) have remained a puzzle. Thanks to an unprecedented amount of Higgs bosons produced at the LHC, all of the main Higgs boson production and decay modes have now been observed.

At the Rencontres de Moriond (La Thuile, Italy), the ATLAS Collaboration presented an updated measurement of ttH production in the diphoton channel. The result examines the full Run-2 dataset – 139 fb^-1 collected between 2015 and 2018 – to observe ttH production in a single channel with a significance of 4.9 standard deviations.

Today, at the Rencontres de Moriond conference (La Thuile, Italy), the ATLAS collaboration released evidence for the simultaneous production of three W or Z bosons in proton–proton collisions at the Large Hadron Collider (LHC). The W and Z bosons are the mediator particles of the weak force – one of the four known fundamental forces – which is responsible for the phenomenon of radioactivity as well as an essential ingredient to our Sun's thermonuclear process.

Light-by-light scattering is a very rare phenomenon in which two photons – particles of light – interact, producing again a pair of photons. The ATLAS Collaboration has reported the observation of light-by-light scattering with a significance beyond 8 standard deviations.

When we look around us, at all the things we can touch and see – all of this is visible matter. And yet, this makes up less than 5% of the universe.

Could a Grand Unified Theory resolve the remaining mysteries of the Standard Model? If verified, it would provide an elegant description of the unification of SM forces at very high energies, and might even explain the existence of dark matter and neutrino masses. ATLAS physicists are searching for evidence of new heavy particles predicted by such theories, including a neutral Z’ gauge boson.

On Valentine’s Day 2019, the ATLAS Collaboration took a break from the usual rhythm of scientific discussion to showcase some of its most junior members. In a celebration in CERN’s Main Auditorium, the collaboration held its 10th annual ATLAS Thesis Awards.

Long Shutdown 2 (LS2) of the Large Hadron Collider commenced last week, as the accelerator powered down and the entry to the ATLAS cavern opened wide. Over the next two years, teams from across the ATLAS Collaboration will be upgrading and consolidating their experiment. On the agenda: the refurbishments of key electronics, the maintenance of various detector components and – critically – the installation of new detectors.

Beams in the Large Hadron Collider came to a stop today, closing out four years of record-breaking operation for the ATLAS experiment. Run 2 saw the extraordinary exploration of the high-energy frontier, as the ATLAS experiment brought new understanding of particle physics.

Martine Bosman is one of the pioneers behind the Tile Calorimeter. Over her long career with the Collaboration, she has held several key roles: from convenor of the Radiation Task Force and the Top Quark Group to Collaboration Board Chair.

For several decades, particle physicists having been trying to better understand Nature at the smallest distances by colliding particles at the highest energies. While the Standard Model of particle physics has successfully explained most of the results that have arisen from experiments, many phenomena remain baffling. Thus, new particles, forces or more general concepts must exist and – if the history of particle physics is any indication – they could well be revealed at the high-energy frontier.

On 11 October 2018, during its semestrial collaboration meeting at CERN, ATLAS celebrated outstanding achievements of its collaboration members with an awards ceremony. Established in 2014, the Outstanding Achievement Awards give recognition to excellent contributions made to the collaboration in all areas, excluding physics analysis.

The study of hadrons – particles that combine together quarks to form mesons or baryons – is a vital part of the ATLAS physics programme. Their analysis has not only perfected our understanding of the Standard Model, it has also provided excellent opportunities for discovery. On 20 September 2018, at the International Workshop on the CKM Unitarity Triangle (CKM 2018), ATLAS revealed the most stringent experimental constraint of the very rare decay of the B0 meson into two muons (μ).

The Brout-Englert-Higgs (BEH) mechanism is at the core of the Standard Model, the theory that describes the fundamental constituents of matter and their interactions. It introduces a new field, the Higgs field, through which the weak bosons (W and Z) become massive while the photon remains massless. The excitation of this field is a physical particle, the Higgs boson, which was discovered by the ATLAS and CMS collaborations in 2012.

The ATLAS Collaboration at CERN’s Large Hadron Collider (LHC) has – at long last – observed the Higgs boson decaying into a pair of bottom (b) quarks. This elusive interaction is predicted to make up almost 60% of the Higgs boson decays and is thus primarily responsible for the Higgs natural width. Yet it took over six years after the 2012 discovery of the Higgs boson to accomplish this observation.

While the Standard Model has proven tremendously successful, much experimental evidence points to it not being a complete description of our universe. The search for “new physics” is therefore an important component of the ATLAS experimental programme, where a number of analyses are looking for signs of new heavy particles decaying to different final states. Though these searches have not yet found a significant signal, they have allowed physicists to place stringent constraints on different new physics scenarios. These can be further tightened by combining different analysis channels and approaches.

“Multiculturalism” isn’t just a buzzword for ATLAS, it’s a way of life. With members of over 90 different nationalities – spanning every populated continent – ATLAS is a cultural experiment as much as it is a scientific one. Our new ATLAS Around the World series invites you to meet people from every nationality represented in the collaboration, to gain an insight into the individual journeys that brought them to particle physics. All are from very different backgrounds, but share the common goal of understanding our universe.

While the discovery of the Higgs boson at the Large Hadron Collider (LHC) in 2012 confirmed many Standard Model predictions, it has raised as many questions as it has answered. For example, interactions at the quantum level between the Higgs boson and the top quark ought to lead to a huge Higgs boson mass, possibly as large as the Planck mass (>10¹⁸ GeV). So why is it only 125 GeV? Is there a mechanism at play to cancel these large quantum corrections caused by the top quark (t)? Finding a way to explain the lightness of the Higgs boson is one of the top (no pun intended) questions in particle physics.

Since the beginning of ATLAS, collaboration members have devoted hours, days, weeks and months teaching High Energy Physics (HEP) to anyone willing to listen. But sometimes those willing to listen do not have the means, especially when oceans and continents separate them from our experiment in Geneva. How can we overcome these geographical distances to allow anyone interested in HEP to learn?

Feynman. Salam. Weinberg. For the past 50 years, the International Conference on High­Energy Physics (ICHEP) has been the meeting place of giants in the field. Now, a new type of giant dominates: the thousands­-strong collaborations of Large Hadron Collider (LHC) physicists.

What a start it's been to my first conference! I was lucky enough to join the 39th International Conference on High Energy Physics (ICHEP), the biggest conference in High Energy Physics. About 1000 physicists are currently gathered in Seoul, presenting results from all across the field. Getting to visit South Korea plus hearing about cutting-edge physics sounded like a 5-star recipe to me!

Today, at the 2018 International Conference on High Energy Physics in Seoul, the ATLAS experiment reported a preliminary result establishing the observation of the Higgs boson decaying into pairs of b quarks, furthermore at a rate consistent with the Standard Model prediction.

Higgs boson couplings manifest themselves in the rate of production of the Higgs boson at the LHC, and its decay branching ratios into various final states. These rates have been precisely measured by the ATLAS experiment, using up to 80 fb^–1 of data collected at a proton-proton collision energy of 13 TeV from 2015 to 2017. Measurements were performed in all of the main decay channels of the Higgs boson: to pairs of photons, W and Z bosons, bottom quarks, taus, and muons. The overall production rate of the Higgs boson was measured to be in agreement with Standard Model predictions, with an uncertainty of 8%. The uncertainty is reduced from 11% in the previous combined measurements released last year.

The top quark is a unique particle due to its phenomenally high mass. It decays in less than 10-24 seconds, that is, before it had time to interact with any other particles. Therefore many of its quantum numbers, such as its spin, are transferred to its decay particles. When created in matter-antimatter pairs, the spins of the top quark and the antitop quark are expected to be correlated to some degree.

Two among the rarest processes probed so far at the LHC, the scattering between W and Z bosons emitted by quarks in proton-proton collisions, have been established by the ATLAS experiment at CERN.

The 2018 International Conference on High Energy Physics (ICHEP) kicked off this week in Seoul, South Korea. The ATLAS Collaboration will be unveiling a wide range of new results at ICHEP 2018, including major developments in the measurement of Higgs boson properties, observations of key electroweak production processes, new high precision tests of the Standard Model, and combinations of searches extending the reach to new physics.

Many questions in particle physics are related to the existence of particle mass. The “Higgs mechanism,” which consists of the Higgs field and its corresponding Higgs boson, is said to give mass to elementary particles.

Physicists from around the globe assembled this week at the Centre Domenico in Bologna, Italy, the site of Europe’s oldest university, to attend the sixth annual conference on Large Hadron Collider Physics (LHCP2018). The 425 participants enjoyed picturesque architecture, world-renowned cuisine, and a full menu of recent physics results from the LHC. A sample platter of a few of the tasty morsels is presented.

A long-standing member of the ATLAS Collaboration, CERN physicist Nick Ellis was one of the original architects of the ATLAS Trigger. Working in the 1980s and 1990s, Nick led groups developing innovative ways to move and process huge quantities of data for the next generation of colliders. It was a challenge some thought was impossible to meet. Nick currently leads the CERN ATLAS Trigger and Data Acquisition Group and shared his wealth of experience as a key part of the ATLAS Collaboration.

A decisive property of the Higgs boson is its affinity to mass. The heavier a particle is, the stronger the Higgs boson will couple to it. While physicists have firmly established this property for heavy W and Z bosons (force carriers), more data are needed to measure the Higgs boson coupling to the heavy fermions (matter particles). These interactions, known as Yukawa couplings, are very interesting as they proceed through a quite different mechanism than the coupling to force-carrying bosons in the Standard Model.

Many theoretical models predict that new physics, which could provide answers to these questions, could manifest itself as yet-undiscovered massive particles. These include massive new particles that would decay to much lighter high-momentum electroweak bosons (W and Z). These in turn decay, and the most common signature would be pairs of highly collimated bundles of particles, known as jets.

According to the Standard Model, quarks, charged leptons, and W and Z bosons obtain their mass through interactions with the Higgs field, whose fluctuation gives rise to the Higgs boson. To test this theory, ATLAS takes high-precision measurements of the interactions between the Higgs boson and these particles. While experiments had observed and measured the Higgs boson decaying to pairs of W or Z bosons, photons or tau leptons, the Higgs coupling to quarks had – until now – not been observed.

The ATLAS Collaboration at CERN has announced the observation of Higgs bosons produced together with a top-quark pair. Observing this extremely rare process is a significant milestone for the field of High-Energy Physics. It allows physicists to test critical parameters of the Higgs mechanism in the Standard Model of particle physics.

The ATLAS experiment has just completed a new search for evidence of supersymmetry (SUSY), a theory that predicts the existence of new “super-partner” particles, with different properties from their Standard Model counterparts. This search looks for SUSY particles decaying to produce two leptons and scrutinises the invariant mass distribution of these leptons, hoping to find a bump.

In October 2017, the ATLAS experiment recorded collisions of xenon nuclei for the first time. While massive compared to a proton, xenon nuclei are smaller than the lead ions typically collided in the LHC. The xenon-xenon collision data, combined with previous results from the analysis of lead-lead collisions, provide the first opportunity to examine heavy ion collisions in a system that is distinctly smaller in size. This allows physicists to study in detail the role of the collision geometry for observables often associated with the quark-gluon plasma.

Heavy ion collisions at the Large Hadron Collider (LHC) form a hot, dense medium called the quark-gluon plasma (QGP), in which the primary constituents are thought to be quarks and gluons produced in the initial interactions of the nuclei. Besides typical heavy ion collisions, where the nucleons in the colliding nuclei undergo multiple strong interactions with each other, there is also a class of “ultraperipheral” collisions. In these collisions, the nuclei are far enough apart to miss each other, but the surrounding electromagnetic field of one nucleus is able to interact both with the other nucleus (“photonuclear” interactions) and with the other electromagnetic field (“photon-photon” interactions).

Following the first “beam splash” tests in early-April, the ATLAS experiment awaited the next milestone on the road to data-taking: "stable beams". This is when the LHC proton beams are aligned, squeezed, focused and finally steered to collide head-to-head. It is an important test, as it allows us to verify that the collision mechanism is ready to take data that are good for physics studies.

Each year, around mid-spring, the giant LHC accelerator wakes up from its winter maintenance and gets ready for a new feverish period of data taking. But before smashing protons once again, some tests have to be done, to check that everything is in order and that the machine can accelerate and collide particles properly, as it did before the shutdown.

The ATLAS collaboration is continuing to scour the wealth of data provided by the LHC for any signs of physics beyond the particles and interactions described by the Standard Model. One approach is to search for new forces in addition to the Standard Model’s electroweak and strong interactions. Such forces could be propagated by new massive bosons playing the role the W and Z bosons have in mediating the electroweak force.

Why is gravity so much weaker than the other forces of nature? This fundamental discrepancy, known as the “hierarchy problem”, has long been a source of puzzlement. Since the discovery of a scalar particle, the Higgs boson, with a mass of 125 GeV near that of the W and Z bosons mediating the weak force, the hierarchy problem is more acute than ever.

Physicists from the ATLAS, CMS and LHCb collaborations have just launched the TrackML challenge – your chance to develop new machine learning solutions for the next generation of particles detectors.

Every spring, hundreds of universities around the world open their doors to high-school students for a day to give them hands-on experience in particle physics. The International Masterclass programme gives students the chance to use real data collected by the ATLAS detector and other LHC experiments to test the Standard Model and search for new particles.

The ATLAS Collaboration at CERN has released new studies of the Higgs boson using 13 TeV data collected in 2015 and 2016. The results further corroborate the Standard Model nature of the Higgs boson, and open doors to fresh searches for new physics.

It’s kick off at the Large Hadron Collider! Proton beams are circulating once again in the accelerator, marking the start of a new year of exploration for the ATLAS experiment.

I met beautiful people in Los Angeles earlier this month: smart, talented students, all destined for great careers. They welcomed me to their high schools and their after-school programmes, all well-equipped with computing, electronics, a robotics lab and, above all, a brilliant staff of teachers.

The ATLAS collaboration has released a set of comprehensive results that illuminate the properties of the Higgs boson with improved precision, using its decay into two photons with LHC collisions recorded at a centre-of-mass energy of 13 TeV.

What do you do when you produce more data than you can handle? This might seem like a strange question for experimental physicists, but it’s a problem that the ATLAS detector faces every day. While the LHC continues to produce ever-higher rates of proton collisions, the detector can only record data at a fixed rate. Therefore, tough choices must be made about what events to keep. This is not a decision made lightly – what if the thrown-away data contain some long-sought new particles beyond those of the Standard Model.

Discovering the Higgs boson can be likened to finding a new continent. While a momentous event in itself, the most exciting part remains the exploration of the new land! In a new result presented today at the Rencontres de Moriond, the ATLAS collaboration examined the Higgs boson decaying into two W bosons

In a paper published today in the European Physical Journal C, the ATLAS Collaboration reports the first high-precision measurement at the Large Hadron Collider (LHC) of the mass of the W boson. This is one of two elementary particles that mediate the weak interaction – one of the forces that govern the behaviour of matter in our universe. The reported result gives a value of 80370±19 MeV for the W mass, which is consistent with the expectation from the Standard Model of Particle Physics, the theory that describes known particles and their interactions.

The top quark – the heaviest known fundamental particle – plays a unique role in high-energy physics. Studies of its properties have opened new opportunities for furthering our knowledge of the Standard Model. In a new paper submitted to Physical Review D, the ATLAS collaboration presents a comprehensive measurement of high-momentum top-quark pair production at 13 TeV.

The production of top quarks in association with vector bosons is a hot topic at the LHC. ATLAS first reported strong evidence for the production of a top quark in association with a Z boson at the EPS 2017 conference. In a paper submitted to the Journal of High-Energy Physics, the ATLAS experiment describes the measurement of top-quark production in association with a W boson in 13 TeV collisions.

This past Spring, I had the opportunity to travel to Taos, New Mexico, USA, to work with artist Agnes Chavez, on one of her “Projecting Particles” workshops. Her innovative programme aims to develop STEM (Science, Technology, Engineering, Math) skills in students aged 8 and up, employing a mixture of science education and artistic expression. It is a winning combination for everyone involved.

The Standard Model has a number of puzzling features. For instance, why does the Higgs boson have a relatively low mass? Could its mass arise from a hidden symmetry that keeps it from being extremely heavy? And what about dark matter? While the Standard Model has some (almost) invisible particles, like neutrinos, those particles can’t account for all of the dark matter observed by cosmological measurements.

Supersymmetry (SUSY) is an extension of the Standard Model that predicts the existence of “superpartners” with slightly different properties compared to their Standard Model counterparts. Physicists have been searching for signs of SUSY for over forty years, so far without success, which makes us think that SUSY particles — should they exist — are also heavier than particles in the Standard Model. However, in order for SUSY to help mitigate some problems with the Higgs boson sector of the Standard Model, SUSY particles should not be too heavy. And if some SUSY particles are relatively light, then they should be produced copiously at CERN’s Large Hadron Collider (LHC). So for SUSY to remain an attractive theory of nature, it must be hiding in plain sight in LHC data.

Enter the world of particle physics with the newly-launched ATLAScraft! Players can explore the CERN campus, shrink down to the size of a particle, and even conduct their own “experiments” in educational minigames.

A commentary by ATLAS physicists Paul de Jong and George Redlinger on the history, progress and future of the search for supersymmetry.

A few times a year, the large LHC collaborations such as ATLAS organise an internal overview session. This photo essay will take you to the most recent of these “ATLAS Weeks” – giving you a glimpse behind the curtain, and exploring this essential part of the collaboration structure and life.

Take something you think you understand, change it and see what happens. Earlier this month, the ATLAS Experiment put this basic scientific principle to the test during the first Large Hadron Collider (LHC) xenon run.

The ATLAS collaboration has presented evidence of “ttH production”, a rare process where a pair of top quarks emits a Higgs boson. Observing this process would provide new insight into the Higgs mechanism and allow for new studies of how unknown physics might (or might not) change the behaviour of this fundamental particle.

Collisions of lead nuclei in the LHC form the hot, dense medium known as the quark-gluon plasma (QGP). Experimentally, the QGP is characterized by the collective flow of emerging quarks and gluons. They fragment into highly collimated “jets” of particles that in turn lose energy through a phenomenon known as “jet quenching”. Studying this effect can help improve our understanding of quantum chromodynamics, the theory of the strong nuclear interaction that governs the behaviour of the QGP.

Using Run 1 data, ATLAS reports a new differential production rate measurement of top quark pairs and a precise new determination of the top quark mass.

I have been doing some work with artists recently. Not that I’m planning a career change, you know: I just love to talk about my research to anyone who is prepared to listen, and lately it’s been with artists. Ruth Jarman and Joe Gerhardt, aka Semiconductor, are internationally renowned visual artists who in 2015 won the Collide@CERN Ars Electronica Award and spent a two-month residency at CERN. Like myself, they live in Brighton, which is also home to the University of Sussex, where I work.

Ordinary matter is made of just three kinds of elementary particles: up and down quarks, which form the atomic nucleus, and electrons, which surround the nucleus. But the rest of nature is not so straightforward: heavier forms of quarks and leptons are produced regularly at particle accelerators.

To celebration of its 25th anniversary, ATLAS is hosting a series of Facebook live events today, Monday 2 October 2017. Explore key locations around CERN - including the ATLAS control room, Building 40 and the ATLAS TileCal workshop - while learning about the physics, construction and history of the ATLAS Experiment.

The top quark, the heaviest known elementary particle, has a unique place in the Standard Model. By precisely measuring its properties, ATLAS physicists can probe physics beyond our current understanding.

The ATLAS collaboration presented exciting new results at the 10th International Workshop on Top Quark Physics (TOP2017), held in Braga (Portugal). The conference, which concluded today, brought together experimental and theoretical physicists specializing in the heaviest known elementary particle: the top quark.

In order to produce rare physics phenomena, such as the Higgs boson or possible signs of new physics, the Large Hadron Collider (LHC) collides tens of millions of protons per second. Under such conditions, around 20 simultaneous proton-proton interactions occur in each beam crossing. Thus, additional collisions called “pile-up” are recorded along with the collision of interest. Together, they form a single event for analysis.

When ultra-relativistic heavy ions collide, a new state of hot and dense matter – the quark–gluon plasma (QGP) – is created. One of the key features for this state is the observation of long-range azimuthal angle correlations between particles emitted over a wide range of pseudorapidity. This phenomenon is often referred to as the “ridge”.

Physicists from the ATLAS experiment at CERN have found the first direct evidence of high energy light-by-light scattering, a very rare process in which two photons – particles of light – interact and change direction. The result, published today in Nature Physics, confirms one of the oldest predictions of quantum electrodynamics (QED).

Since discovering a Higgs boson in 2012, the ATLAS and CMS collaborations have been trying to understand whether this new particle is the Higgs boson as predicted by the Standard Model, or a Higgs boson from a more exotic model containing new, as yet undiscovered, particles. The answer lies in the properties of the Higgs boson.

For many physicists, discovering “new physics” means bringing to light a new particle. Another path to discovery lies in carefully measuring the properties of known particles and the interactions between them. The ATLAS experiment has now released new results on the top quark's interaction with the charged intermediate vector boson.

As the Large Hadron Collider (LHC) smashes together protons at a centre-of-mass energy of 13 TeV, it creates a rich assortment of particles that are identified through the signature of their interactions with the ATLAS detector. But what if there are particles being produced that travel through ATLAS without interacting? These “invisible particles” may provide the answers to some of the greatest mysteries in physics.

The ATLAS Collaboration has presented important new results at the European Physical Society conference on High Energy Physics (EPS-HEP) in Venice (Italy), including the latest analyses of 13 TeV Run 2 data from the Large Hadron Collider (LHC).

Although the discovery of the Higgs boson by the ATLAS and CMS Collaborations in 2012 completed the Standard Model, many mysteries remain unexplained. For instance, why is the mass of the Higgs boson so much lighter than one would expect and why is gravity so weak?

Observing rare productions of heavy elementary particles can provide fresh insight into the Standard Model of particle physics. In a new result, the ATLAS Experiment presents strong evidence for the production of a single top-quark in association with a Z boson.

Since the discovery of the elusive Higgs boson in 2012, researchers have been looking beyond the Standard Model to answer many outstanding questions. An attractive extension to the Standard Model is Supersymmetry (SUSY), which introduces a plethora of new particles, some of which may be candidates for Dark Matter.

The ATLAS collaboration has released a new preliminary measurement of the Higgs boson mass using 2015 and 2016 LHC data. The number of recorded Higgs boson events has more than tripled since the first measurement of the Higgs boson was released, using 2011/2012 data. An improved precision in the measurement of the Higgs boson mass has been made possible by both the increased collision energy of 13 TeV and improved collision rate.

Since resuming operation for Run 2, the LHC has been producing about 20,000 Higgs bosons per day in its 13 TeV proton–proton collisions. At the end of 2015, the data collected by the ATLAS and CMS collaborations were already enough to re-observe the Higgs boson at the new collision energy. Now, having recorded more than 36,000 trillion collisions between 2015 and 2016, ATLAS can perform ever more precise measurements of the properties of the Higgs boson

Cosmological and astrophysical observations based on gravitational interactions indicate that the matter described by the Standard Model of particle physics constitutes only a small fraction of the entire known Universe. These observations infer the existence of Dark Matter, which, if of particle nature, would have to be beyond the Standard Model.

Until now, the Higgs boson had been observed decaying to photons, tau leptons, and W and Z bosons. However, these impressive achievements represent only 30% of the Higgs boson decays! The Higgs boson’s favoured decay to a pair of b-quarks, which was predicted to happen around 58% of the time and thus drives the short lifetime of the Higgs boson, had so far remained elusive. Observing this decay would fill in one of the big missing pieces of our knowledge of the Higgs sector. It would confirm that the Higgs mechanism is responsible for the masses of quarks and might also provide hints of new physics beyond our current theories. All in all, it is a vital missing piece of the Higgs boson puzzle!

If you are interested in particle physics, you probably hear a lot about the huge amount of data that is recorded by experiments like ATLAS. But where does this data come from? Roughly speaking: first you have to plan, build and maintain an experiment and in the end you need people to analyse the data you’ve recorded. But what happens in between? What happens in the day-to-day life of people in the ATLAS control room, who are responsible for keeping all that great data coming?

From the chaotic moments after the Big Bang to present day proton collisions in the ATLAS Experiment, the new planetarium show Phantom of the Universe takes viewers on the hunt for dark matter. The show has been awarded an honourable mention for outstanding and innovative production at the 11^th International FullDome Festival in Germany.

Discovered almost 100 years ago by Ernest Rutherford, the proton was one of the first particles to be studied in depth. Yet there’s still much about it that remains a mystery. Where does its mass and spin come from? What is it made of? To answer these questions, ATLAS physicists are using “jets” of particles emitted by the LHC as a magnifying glass to examine the inner structure of the proton.

More than 400 physicists from around the world visiting Shanghai to hear the latest LHC results, at the fifth annual Large Hadron Collider Physics (LHCP17) conference. It was a wonderful opportunity for Chinese particle physicists and students, who do not often have the chance to travel abroad! Even for me, although I have been working on the LHC for almost 10 years, this was still my first time attending such a high-level conference to hear the first-rate physics results from all four experiments at the Large Hadron Collider.

Geneva, 23 May 2017. A new season of record-breaking kicked off today, as the ATLAS experiment began recording first data for physics of 2017. This will be the LHC’s third year colliding beams at an energy of 13 tera electron volts (TeV), allowing the ATLAS Experiment to continue to push the limits of physics.

The fifth annual Large Hadron Collider Physics (LHCP2017) conference was held this week at Shanghai Jiao Tong University in a leafy suburb in the former French concession in Shanghai, China. This year there were more participants than ever before: 470 people from universities across the globe. ATLAS presented an interesting set of new results exploiting the high statistics of the combined 2015 and 2016 dataset.

The start of the 2017 run marks the conclusion of a maintenance period known as the Extended Year-End-Technical-Stop (EYETS). This upkeep is vital for the health and well-being of the detector, ensuring that ATLAS can thrive for the months of high-intensity operation that follow.

Supersymmetry is an extension to the Standard Model that may explain the origin of dark matter and pave the way to a grand unified theory of nature. For each particle of the Standard Model, supersymmetry introduces an exotic new “super-partner,” which may be produced in proton-proton collisions. Searching for these particles is currently one of the top priorities of the LHC physics program. A discovery would transform our understanding of the building blocks of matter and the fundamental forces, leading to a paradigm shift in physics similar to when Einstein’s relativity superseded classical Newtonian physics in the early 20^th century.

Supersymmetry (SUSY) is one of the most attractive theories extending the Standard Model of particle physics. SUSY would provide a solution to several of the Standard Model’s unanswered questions, by more than doubling the number of elementary particles, giving each fermion a bosonic partner and vice versa. In many SUSY models the lightest supersymmetric particle (LSP) constitutes dark matter.

With the huge amount of proton–proton collisions delivered by the LHC in 2015 and 2016 at the increased collision energy of 13 TeV, ATLAS has entered a new era of Higgs boson property measurements. The new data allowed ATLAS to perform measurements of inclusive and differential cross sections using the “golden” H->ZZ*->4l decay.

Ever since the LHC collided its first protons in 2009, the ATLAS Collaboration has been persistently studying their interactions with increasing precision. To this day, it has always observed them to be as expected by the Standard Model. Though it remains unrefuted, physicists are convinced that a better theory must exist to explain certain fundamental questions: What is the nature of the dark matter? Why is the gravitational force so weak compared to the other forces?

Up to now, ATLAS has measured the energies and positions of jets using the finely segmented calorimeter system, in which both electrically charged and neutral particles interact. However, the inner detector tracking system provides more precise measurements of charged particle energies and positions. A recent ATLAS paper describes a particle flow algorithm that extrapolates the charged tracks seen by the inner detector to the calorimeter regions.

With the year’s first proton beams now circulating in the Large Hadron Collider, physicists have today recorded “beam splashes” in the ATLAS experiment

A new age of exploration dawned at the start of Run 2 of the Large Hadron Collider, as protons began colliding at the unprecedented centre-of-mass energy of 13 TeV. The ATLAS experiment now frequently observes highly collimated bundles of particles (known as jets) with energies of up to multiple TeV, as well as tau-leptons and b-hadrons that pass through the innermost detector layers before decaying. These energetic collisions are prime hunting grounds for signs of new physics, including massive, hypothetical new particles that would decay to much lighter – and therefore highly boosted – bosons.

The 52nd Rencontres de Moriond conference was held in La Thuile, Italy, from the 18 March to 1 April. The first week, which ran until 25 March, was devoted to the theme "Electroweak interactions and unified theories", while the second week was based on the theme of “QCD and high energy interaction”.

The fundamental forces of nature are intimately related to corresponding symmetries. For example, the properties of electromagnetic interactions (or force) can be derived by requiring the theory that describes it to remain unchanged (or invariant) under a certain localised transformation. Such an invariance is referred to as a symmetry, just as one would refer to an object as being symmetric if it looks the same after being rotated or reflected. The particular symmetry related to the forces acting among particles is called gauge symmetry.

High-energy photon pairs at the LHC are famous for two things. First, as a clean decay channel of the Higgs boson. Second, for triggering some lively discussions in the scientific community in late 2015, when a modest excess above Standard Model predictions was observed by the ATLAS and CMS collaborations.

At this year’s Rencontres de Moriond, the ATLAS collaboration presented the first results examining the combined 2015/2016 LHC data at 13 TeV proton–proton collision energy. Thanks to outstanding performance of the CERN accelerator complex last year, this new dataset is almost three times larger than that available at ICHEP, the last major particle physics conference held in August 2016.

Nature has surprised physicists many times in history and certainly will do so again. Therefore, physicists have to keep an open mind when searching for phenomena beyond the Standard Model.

There are many mysteries the Standard Model of particle physics cannot answer. Why is there an imbalance between matter and anti-matter in our Universe? What is the nature of dark matter or dark energy? And many more. The existence of physics beyond the Standard Model can solve some of these fundamental questions. By studying the head-on collisions of protons at a centre-of-mass energy of 13 TeV provided by the LHC, the ATLAS Collaboration is on the hunt for signs of new physics.

In new results presented at the Moriond Electroweak conference, the ATLAS Collaboration has sifted through the full available data sample of the LHC’s 13 TeV proton collisions in search of a specific SUSY particle: the heavy partner to the top quark, called the “top squark” or “stop”

Many of the most important unanswered questions in fundamental physics are related to mass. Why do elementary particles, which we have observed and measured at CERN and other laboratories, have the masses they do? And why are they so different, with the mass of the top quark more than three hundred thousand times that of the electron? The presence of dark matter in our universe is inferred because of its mass but, if it is a particle, what is it? While the Standard Model has been a tremendously successful theory in describing the interactions of sub-atomic particles, we must look to even larger masses in search of answers and, potentially, new supersymmetric particles

Every March for the past 50 years, particles physicists have been heading to the mountains. The terminus of this migration? Les Rencontres de Moriond, one of the year’s first major conference for high-energy physics.

Karl Jakobs from the University of Freiburg is a familiar face at CERN and in the ATLAS Experiment. He’s been part of the collaboration since the signing of the ATLAS Letter of Intent in 1992, having taken on various coordination roles, and followed the experiment through all its phases. Now, after twenty-five years with the collaboration, Karl is moving into the main office as spokesperson.

From detector development to detailed searches for new physics, ATLAS PhD students publish dozens of outstanding theses every year. Since 2010, a few have been celebrated at the annual ATLAS Thesis Awards.

Motivated. Outstanding. Enthusiastic. These are the criteria used when selecting the recipients of the ATLAS PhD Grant. It’s a tough competition.

What precision measurement of the inclusive W+, W− and Z/γ∗ production cross sections can tell us about the true nature of the proton.

For the first time, ATLAS has measured the kinematics of the top quark and of the tt̅ system in 13 TeV events containing two charged leptons, two neutrinos and two jets (called “dilepton” events).

2016 has been a record-breaking year. The LHC surpassed its design luminosity and produced stable beams a staggering 60% of the time – up from 40% in previous years, and even surpassing the hoped for 50% threshold. While all of the ATLAS experiment rejoiced – eager to analyse the vast outpouring of data from the experiment – its computing experts had their work cut out for them.

The ATLAS collaboration is now reporting the first measurement of the W mass using LHC proton-proton collisions data at a centre-of-mass energy at 7 TeV. The ATLAS result matches the best single-experiment measurement of the W mass performed by the CDF collaboration.

HiggsHunters is the first mass-participation citizen science project for the Large Hadron Collider, allowing non-experts to get directly involved in physics analysis. Since its launch in 2014 on the Zooniverse platform, over 30,000 people from 179 countries have participated in the project. Their work has led to the project’s first publication on arXiv.

Am I going to dedicate my entire life to high-energy physics? Am I qualified to work in another field, if I wish to? These are questions we may ask ourselves as we near the end of a contract. On Tuesday 29 November, the four experiments, ATLAS, ALICE, CMS and LHCb, organized a meeting with some of their former physicists who had decided to take the plunge into the business world.

Here at ATLAS, we like to consider ourselves pretty decent at tracking down particles. In fact, we do it every day. Just because a proton-proton collision doesn’t produce the next Nobel Prize winning particle doesn’t mean we can ignore it. Teams of physicists are still combing through every single event, rebuilding known particles out of the signals they leave us

Whether searching for signs of new physics, or making precise measurements of known interactions, it is essential to know the total number of proton-proton collisions that the LHC delivers in ATLAS. This parameter, known as “luminosity”, is a vital part of ATLAS analysis.

The 2016 ATLAS Outstanding Achievement Awards ceremony was held at CERN on 20 October. Now in its third year, the awards give recognition to excellent contributions made to the collaboration, with an emphasis on activities carried out in the first year of Run 2.

Ever since the age of 10, as far as I remember, I have been fascinated by technical and natural sciences, especially physics. I loved building (and repairing) experiments or things. As a result, in high school I happily attended an advanced course in physics and continued my studies at RWTH Aachen University (Germany).

My colleagues and I are in town to attend the 22^nd International Conference on Computing in High Energy and Nuclear Physics (CHEP 2016, for short). I like to think of us as the nerds of the nerds. Computing, networking, software, middleware, bandwidth, and processors are the topics of discussion, and there is indeed much to talk about.

The ATLAS Open Data platform is inspiring new ways to teach high-energy physics. Universities can incorporate the data into their curriculum, giving their students hands-on analysis experience and introducing them to the world of research.

For many students, summer means sun and beach volleyball. For some, though, it is an opportunity to learn at ATLAS! Thanks to CERN’s Summer Student Programme, every year dozens of university students come to ATLAS to spend their holidays in this unique environment. During these three months they alternate between lectures and work, always supported by their supervisors. This summer, ATLAS hosted 50 students from 31 different countries. Here are some of their stories.

The strong force is one of the four fundamental interactions of Nature. It governs the interactions between quarks and gluons, and is thus responsible for the stability of ordinary matter. In the proton-proton collisions at the Large Hadron Collider, the strong force is seen in the production of collimated sprays of mesons and baryons, known as hadron jets. The ATLAS Collaboration has released the measurement of the inclusive jet production cross sections at the new 13 TeV energy frontier.

The International Conference on High Energy Physics (ICHEP) wraps up its 38th edition today in Chicago. For ATLAS, it brings to a close an intense period of analysis. The collaboration presented 64 new sets of results at the conference, ranging from detector performance studies to measurements of Standard Model processes to searches for new physics. All in all, a rather stellar turnout.

For those of you with an affinity for Twitter, you’ll know that the ICHEP press crew have been utilising all of their dark arts to bring you the most interesting results as they’re presented at ICHEP 2016.

ATLAS has performed measurements of boson-pair production using data from 13 TeV proton-proton collisions that began in 2015. The cross-section (a measure of the production frequency) of the WW boson pair production was measured and was compared to a previous measurement in 8 TeV collisions.

One of the highlights of last year’s physics results was the appearance of an excess in the search for a new particle decaying into two photons ("the di-photon channel"). New results in this channel were presented at the ICHEP conference in Chicago on Friday, 5 August.

The LHC’s jump in energy to 13 TeV in Run 2, together with the copious amount of collisions delivered over the last 12 months, has allowed the ATLAS experiment to collect a data sample that is more than equivalent to the one collected during Run 1.

ATLAS physicists have been eagerly searching the collected data for evidence of the production of the supersymmetric top quark (squark). Recent ATLAS results feature five separate searches for this elusive particle.

The ATLAS experiment has been searching for the process in which a pair of top quarks is produced, where one is a “virtual” particle that emits a Higgs boson on the way to becoming a “real” particle. This process is referred to as ttH production after the particles that are produced.

The nature of dark matter remains one of the greatest mysteries in physics. While extraordinary, the Standard Model can not explain dark matter, whose existence is well established by cosmological measurements.

Results using record-breaking 2016 data will be presented at the International Conference on High Energy Physics (ICHEP) in Chicago, 3-10 August.

On Friday 29 July, the ATLAS experiment at CERN released the data from 100 trillion proton-proton collisions to the public. This includes the world’s first open release of 8 TeV data, gathered from the Large Hadron Collider in 2012, making it the most current high-energy physics open data.

My work involves analyzing data to try to understand how nature works at the most fundamental level, by searching for new particles and ways in which they interact. Specifically, I am looking at the top quark, which is the heaviest fundamental particle known to exist, with a mass of about 180 times that of a proton.

For a long time, physicists have assumed that space-time has four dimensions in total – three of space and one of time – in agreement with what we see when we look around us. However, some theorists have proposed that there may be other spatial dimensions that we don’t experience in our daily lives.

The ATLAS collaboration has now released the final results on the search for new physics in the di-photon channel using 2015 data.

ATLAS has published hundreds of studies of LHC data, with the Higgs boson discovery being perhaps the best known. Amongst the Run 1 searches there was one which stood out: the diboson excess.

When the protons from the LHC collide, they sometimes produce W and Z bosons, the massive carriers of the weak force responsible for radioactive decays. These bosons are produced in abundance at the LHC and ATLAS physicists have now precisely measured their production rates using 13 TeV proton-proton collision data recorded in 2015.

ATLAS has released a new precise measurement of the mass of the top quark, the heaviest known elementary particle.

2016 is set to be an outstanding year for the ATLAS experiment and the Large Hadron Collider. We’re expecting up to 10 times more data compared to 2015, which will allow us to make precise measurements of many known physics processes and to search for new physics.

The Large Hadron Collider Physics (LHCP2016) conference kicked off today in Lund, Sweden. Held annually, the LHCP conference is an opportunity for experimental and theoretical physicists to discuss results from across the high-energy physics community. From Standard Model Physics and Heavy Ion Physics to Supersymmetry and other Beyond Standard Model investigations, the conference unites the disciplines to examine recent progress and consider future developments.

Friday morning, 29 April 2016: what was expected to be a productive shift turned out to be very different.

PP@LHC is an Italian conference with important contributions by foreign institutes, focused on the proton-proton physics performed at the LHC by the ATLAS, CMS and LHCb experiments. The aim of this year’s edition was not only to give an overview on the current status of LHC research, but to focus on future challenges with the upcoming new data.

From techno beats to classical melodies, from jazz swinging to pop and rock riffs – the ATLAS experiment can play them all. Thanks to Quantizer, a platform that translates ATLAS events into notes and rhythms, one of the most complex scientific instruments in the world will not only search for new physics, but also generate music.

Spring is now in full bloom at the ATLAS experiment which recorded the year’s first collisions for physics on Monday, 9 May. Event displays from these collisions were immediately streaming on the ATLAS live website, with some shared across social media platforms.

ATLAS is back and better than ever! With 13 TeV beams circulating in the Large Hadron Collider, the ATLAS experiment is now recording data for physics. This milestone marks the start of the second year of “Run 2” as ATLAS continues its exploration of 13 TeV energy frontier.

ATLAS scientists have just released a new publication with results based on an analysis of the early Run 2 data collected in 2015 using 13 TeV proton-proton collisions.

According to classical electrodynamics, the electromagnetic energy (and mass) of a point-like electron should be infinite. This is of course not the case! The solution of the riddle is antimatter - the ‘vacuum’ around every electron is filled with a cloud of electrons and anti-electrons and the combined energy turns out to be finite.

The third day of the Moriond QCD conference was dedicated to quantum chromodynamics (QCD), the theory that describes strong interactions itself.

Here we are at the second blog from the Moriond QCD conference and, as promised, I will discuss a bit of physics.

This morning the Large Hadron Collider (LHC) circulated the first proton-proton beams of 2016 around its 27 kilometre circumference. The beams were met with great enthusiasm in the ATLAS Control Centre as they passed through the ATLAS experiment.

My name is Mario Campanelli, and I am a physicist who has been working for about 9 years on the ATLAS experiment, as part of the academic staff of University College London. This is the first time I write a blog, but I do have quite an experience in communicating science to the public, having guided visitors around CERN since I started working there as a PhD student 20 years ago, and also having written two books for the general public. Since Saturday I have been in La Thuile, a mountain resort in the Italian Alps, for the Rencontres de Moriond - arguably the most important winter conference in particle physics.

The ATLAS Collaboration uses two selections in this search, one optimised for Higgs-like particles that are expected to have a strong signal compared to background with both photons in the central region of the detector (the “spin-0” selection) and a second optimised for graviton-like particles (the “spin-2” selection) which often have at least one photon close to the LHC proton beam axis.

Almost four years following the discovery of the Higgs boson, LHC experiments are now more than ever exploring the possibility of new particles and new effects beyond the Standard Model.

The results presented by the ATLAS collaboration during the Moriond Electroweak 2016 conference set new limits on a potential extended Higgs sector.