This week, the ATLAS Collaboration announced a new high-precision measurement of the lifetime of the B0 meson. The B0 meson is composed of a bottom quark and a down antiquark. Measurements of its lifetime – the average time it exists before decaying – provide an exceptional probe of physics processes beyond the Standard Model.

The ATLAS Collaboration at CERN has observed top-quark pair production in lead-lead ion collisions, marking the first observation of this process in nucleus-nucleus interactions.

At this week’s Higgs2024 conference, the ATLAS Collaboration unveiled the first LHC search for tri-Higgs production – a process over 600,000 times rarer than the production of a single Higgs boson.

ATLAS researchers are using innovative new techniques in their analysis of off-shell Higgs-boson production.

The ATLAS Collaboration has released three major searches for new-physics phenomena, all utilising new advancements in particle tagging.

Two new studies from the ATLAS Collaboration explore how top-quark pairs are produced alongside heavy-flavour quarks, like bottom and charm.

New measurements by the ATLAS Collaboration show that studying Higgs-boson decays into tau-lepton pairs can reveal not only its interactions with fermions, but also give insights into Higgs-boson production at the LHC. ATLAS researchers performed two kinds of cross-section measurements in their new analysis of Higgs-boson decays to tau leptons.

At the BOOST 2024 conference, the ATLAS Collaboration presented a new technique that employs artificial intelligence (AI) to refine jet calibration, specifically focusing on jets originating from bottom quarks (b-jets).

As the most abundantly produced object in the ATLAS experiment, jets are critical to understanding a number of physics processes. In new results presented at the BOOST 24 conference in Genova (Italy), ATLAS scientists detailed two innovative approaches for more accurately quantifying jet properties.

The 16th International Workshop on Boosted Object Phenomenology, Reconstruction, Measurements, and Searches at Colliders (BOOST 2024) kicks off today in Genova (Italy). This year’s edition continues the tradition of bringing together leading experts from both theoretical and experimental backgrounds to discuss latest developments in the study of particle “jets”.

At the recent ICHEP 2024 conference held in Prague (Czech Republic), ATLAS physicists presented two innovative searches for R-parity-violating SUSY using data collected during the Run 2 of the LHC (2015 to 2018).

At the recent International Conference on High-Energy Physics (ICHEP) 2024, the ATLAS Collaboration presented a new measurement of the ttH(bb) process using the same Run-2 dataset, achieving a factor of two better expected ttH signal significance compared to the previous result.

The ATLAS Collaboration has just released the world’s most precise study of the Higgs boson’s interaction with bottom quarks and charm quarks. This new result is a re-analysis of data collected during Run 2 of the LHC (2015-2018). ATLAS researchers examined Higgs-boson decays to bottom and charm quarks (H→bb and H→cc) implementing significantly improved analysis techniques.

The ATLAS Collaboration has released its first search for new physics phenomena at the highest-ever collision energy of 13.6 TeV, targeting exotic events with two “displaced” leptons.

In a new result from the ATLAS Collaboration, physicists analysed the first Run-3 heavy-ion collision data collected in the autumn of 2023. Specifically researchers looked at “ultraperipheral” collisions, where ions pass at a distance precluding hadronic interactions yet close enough to interact through electromagnetic fields.

The 2024 International Conference on High Energy Physics (ICHEP) kicks off this week in Prague, Czech Republic. For over 70 years, ICHEP has gathered physicists from around the world to share the latest advancements in particle physics, astrophysics, cosmology, and accelerator science, and to discuss plans for major future facilities.

The ATLAS Collaboration has made a significant advancement in the understanding of the Higgs boson by investigating its production in association with W or Z bosons (known as “VH production”), where the Higgs boson decays to bottom quarks. For the first time, LHC researchers have studied VH production in a fully hadronic final state.

Researchers at the ATLAS Experiment release the first-ever direct search for new composite dark particles called dark mesons, presented this week at the Large Hadron Collider Physics (LHCP) Conference in Boston.

In a new analysis from the ATLAS Collaboration, physicists merged five di-Higgs studies of LHC Run 2 data. By combining the power of all these decay channels, researchers achieved the most sensitive probe of di-Higgs production and the Higgs self-coupling.

In a new study submitted to Physical Review Letters, ATLAS scientists used a new algorithm to search for long-lived particles (LLP) produced in the decay of Higgs bosons. These LLPs may leave a distinct signature of one or more hadronic “jets” of particles originating at a significantly displaced position from the proton–proton collision point.

The twelfth annual conference on Large Hadron Collider physics (LHCP 2024) kicks off today in Boston, USA. This week-long event will feature a detailed review of the latest experimental and theoretical results in collider physics, including several final studies of the LHC Run-2 dataset (collected in 2015-2018) and discussions on future research directions for the high-energy particle-physics community.

The ATLAS Collaboration has just published a search for two new Higgs bosons, X and S, that would interact with the Standard-Model Higgs boson.

If spotting one Higgs boson is interesting, what happens when you spot two? ATLAS researchers are looking for the production of two Higgs bosons using a new technique.

Using the full LHC Run-2 dataset, the ATLAS Collaboration measured Z boson production in association with both bottom (b) and charm (c) quarks, the latter for the first time in ATLAS.

New results released by the ATLAS Collaboration describe the significant advancements made in identifying electrons and photons.

The ATLAS Collaboration mourns the passing of renowned physicist Peter Higgs, whose theoretical work on elucidating the fundamental spontaneous symmetry-breaking mechanism by which elementary particles acquire mass reshaped our understanding of the Universe.

In a groundbreaking new result, the ATLAS Collaboration has measured the W-boson width for the first time at the Large Hadron Collider (LHC).

The ATLAS Collaboration has just released its first measurements using LHC Run-3 data of the production rates (“cross sections”) of W and Z bosons.

In a new result presented at Moriond EW, physicists at the ATLAS Collaboration tested lepton flavour universality between muons and electrons. The precision of the result stands as the best yet-achieved in W-boson decays by a single experiment and surpasses the world average.

This year, the start of Spring marks the beginning of the conference season for particle physicists! All eyes turn to La Thuile, Italy, where the annual Recontres de Moriond conferences will be held.

In a new result, researchers conducted a novel search of data collected during Run 2 of the LHC, searching for heavy new particles that could fit the 2HDM or 2HDM+S models.

In a new result, the ATLAS Collaboration reports the first evidence of a Higgs boson produced in association with a leptonically-decaying W or Z boson and decaying into a pair of tau leptons.

As we celebrate the 50th anniversary of the observation of neutral currents and the 40th anniversary of the W/Z boson discovery, we take a look back on the 13 years of ATLAS research into the weak force.

The ATLAS Collaboration has published three new results in this challenging area, using Boosted Decision Trees (BDTs) to isolate potential signals and ultimately set stringent constraints on the masses of SUSY particles.

On 16 November 2023 at 6pm CET, Dr. Ludovica Aperio Bella will give a live public talk on the ATLAS Youtube Channel about precision measurements at the LHC.

The ATLAS Collaboration has measured the production cross section of the J/ψ and ψ(2S) charmonium states in terms of the transverse momentum and the rapidity. For both states, they examined the widest range of transverse momentum so far, thus providing new input for theoretical models.

In a new result from the ATLAS Collaboration, physicists observed – for the first time – quantum entanglement between a pair of quarks. This is the highest-energy measurement of entanglement to date.

The ATLAS Collaboration has released two brand-new results searching for di-Higgs events in the full LHC Run-2 dataset. In one, researchers looked for events where one Higgs boson decays into two bottom quarks and the other decays into two photons. In the other, they looked for events where one Higgs boson decays into two bottom quarks, and the other into two tau leptons or W/Z bosons, which subsequently decay into leptons.

On 14 September at 6pm CEST, Dr. Martin Rybar and Dr. Peter Steinberg will give a live public talk on the ATLAS Youtube Channel on how the ATLAS experiment records heavy-ion collisions.

The ATLAS Collaboration at CERN observes the production of top-quark pairs in proton-lead ion collisions. ATLAS’ new result confirms and builds upon an earlier observation made by the CMS Collaboration, expanding it into a new decay channel.

For the very first time, the ATLAS Collaboration has searched for dark jets that closely resemble QCD jets. Instead of originating from Standard-Model particles, these dark jets would be produced through a new, heavy particle called the Z' boson.

The ATLAS Collaboration has prepared a variety of new results for the Quark Matter conference, focusing on the study of collisions involving lead ions, xenon, and lead ions with protons.

The ATLAS Collaboration has just released a new measurement of the production cross section of two Z bosons. This highlight result examines data collected during Run 3 of the LHC and pioneers the use of PHYSLITE, a new, reduced data format that requires significantly less storage.

In a new paper submitted to Phys. Rev. Lett., the ATLAS Collaboration pioneers the use of unsupervised machine learning to search for anomalous collision events which could be from new physics phenomena.

In a new study presented at the EPS-HEP 2023 conference, the ATLAS Collaboration combed through the full LHC Run-2 dataset (recorded 2015-2018) in search for magnetic monopoles and HECOs (see Figure 1). The result places some of the tightest limits yet on the production rate of magnetic monopoles.

In new results presented today, the ATLAS Collaboration provides its most comprehensive overview of the searches for weakly-interacting supersymmetric particles. By developing new search algorithms and exploiting machine learning techniques, researchers have probed deep into this difficult-to-reach territory.

The ATLAS Collaboration has announced the first observation of two different tri-boson processes: the simultaneous production of a W boson with two photons (Wγγ) and the production of a W boson, a Z boson and a photon (WZγ). The production of a Z boson with two photons (Zγγ) was first observed in 2016 using data from LHC Run 1 (2010-2013). In a new publication, the ATLAS Collaboration expanded the scope of this initial observation using Run 2 data.

Vector boson scattering processes play a special role within the Standard Model, as they are closely related to the Higgs mechanism and can proceed via an exchange of a Higgs boson. By studying these processes, ATLAS physicists are exploring multiple new-physics models, including anomalous self-interactions of the W bosons and extended Higgs sector with additional Higgs bosons.

This week, ATLAS physicists presented four exciting new results about jet tagging using AI algorithms at the BOOST 2023 conference held at Lawrence Berkeley National Lab (USA).

The ATLAS Collaboration has released two new results explaining how detector timing measurements and calorimeter signal calibration using artificial intelligence (AI) are being used to further improve the quality of data recorded by the experiment.

The 15th International Workshop on Boosted Object Phenomenology, Reconstruction, Measurements, and Searches at Colliders (BOOST 2023) kicks off today in Lawrence Berkeley National Lab, California (USA). The conference brings together experts from the LHC experiments and the theory community to discuss new approaches for using “jets” of particles in studies of Quantum Chromodynamics (QCD) and searches physics beyond the Standard Model.

This week, at the Lepton-Photon Conference in Melbourne (Australia), the ATLAS Collaboration presented its measurement of the Higgs-boson mass in studies of Higgs decays to two photons using the full LHC Run 2 dataset (“H→yy” or the diphoton channel), and a new combination of this measurement with the 2022 measurement of the Higgs-boson mass in studies of the Higgs decays to four leptons (the “H→4l channel”).

The summer conference season is here! While for some, summer means slowing down – for ATLAS researchers, it means the start of new conferences, with more new results to be presented! This season, experimental physics and theorists will be traveling to Melbourne, Australia, for the International Symposium on Lepton Photon Interactions at High Energies (Lepton Photon), and to Hamburg, Germany, for the European Physical Society Conference on High Energy Physics ( EPS-HEP).

When studying the shape of LHC collision events, physicists ask: how similar or different is their energy flow? The ATLAS Collaboration recently published a measurement of new collision event shapes in high-energy multijet events at the LHC.

For Run 3 of the LHC (2022–ongoing), the ATLAS Collaboration decided to change how it stores and processes conditions data. The significant efforts that went into this change – and the motivations for them – were presented at the 26th International Conference on Computing in High Energy and Nuclear Physics in May.

What happens if dark-matter particles are produced inside a jet of Standard-Model particles? This leads to a novel detector signature known as semi-visible jets! The ATLAS Collaboration has come up with a new search for semi-visible jets, looking for them in a general production mode where two protons interact by exchanging an intermediate particle, which is then converted into two jets.

At the 2023 LHCP conference, ATLAS physicists presented precise new measurements of the W± and Z boson transverse momentum distributions at two centre-of-mass energies: 13 TeV and, for the first time, 5.02 TeV. These results give unprecedented information on these transverse-momentum shape spectra, providing crucial input for other studies of these bosons.

The ATLAS Collaboration just released new measurements of the production rate (or cross-section) of Higgs bosons at 13.6 TeV using data collected in the second half of 2022.

The eleventh annual conference on Large Hadron Collider physics (LHCP 2023) kicks off today in Belgrade (Serbia) signaling the return of this week-long event to its face-to-face format. The programme of this edition covers the wide spectrum of Large Hadron Collider physics and technology, from several final studies of the LHC Run-2 dataset (2015-2018) to detailed assessments of the upgraded accelerators and detectors for Run 3.

On 5 May at 4pm CEST, ATLAS physicists Dr. Stefanie Morgenstern and Dr. Liaoshan Shi will give a live tour of the ATLAS Control Room on the ATLAS and CERN Youtube Channels.

In the new results presented at the Moriond conferences, the ATLAS Collaboration tested the CP invariance of Higgs-boson interactions with vector bosons (W or Z bosons).

The ATLAS Collaboration has just published the most precise measurement to date of the production cross section of top-quark pairs. The measured value is 829 ± 15 picobarns and has a relative uncertainty of just 1.8%.

The ATLAS Collaboration has released the most detailed analysis to date of the production of top-quark pairs alongside a W boson.

The ATLAS Collaboration at CERN announces the observation of the simultaneous production of four top quarks. This is one of the rarest – and heaviest – processes ever observed at the Large Hadron Collider (LHC), with a total particle mass of almost 700 GeV.

The ATLAS Collaboration at CERN has released a precise new measurement of the Z-boson transverse momentum. This has allowed researchers to determine the strength of the strong force. Their result has less than 1% uncertainty, making it the most precise determination of the strong force ever made by a single experiment.

The ATLAS Collaboration has measured the W boson mass to be 80360 MeV with an uncertainty of 16 MeV – in agreement with the Standard Model.

The ATLAS Collaboration has released an impressive set of searches for leptoquarks interacting with third-generation leptons or quarks – placing valuable constraints on leptoquark parameters.

The ATLAS Collaboration has released two new studies of the tau lepton, investigating whether this elementary particle may actually be composite in nature.

The winter conference season has begun! This month, all roads lead to La Thuile in the Italian Alps, where experimental physicists and theorists will take part in some of the most important particle physics meetings of the year. The La Thuile and Rencontres de Moriond conferences promise not to disappoint, with topical sessions ranging from heavy-ion and neutrino physics, to dark matter searches and astroparticle observations.

The ATLAS Collaboration has just released its most precise luminosity measurement to date. They studied four years of measurements (2015-2018), covering the entire Run 2 of the LHC to assess the amount of luminosity delivered to the ATLAS experiment.

The ATLAS Collaboration has performed an extensive search for new, high-mass particles that can decay to a pair of W bosons. As many theoretical models predict the existence of such high-mass particles, physicists were able to investigate the validity of several models at once across a large energy range.

The ATLAS Collaboration has just released its first Run 3 measurements, studying data collected in the first half of August 2022. Researchers have measured the interaction strength (or cross-section) of two well-known processes: the production of a pair of top quarks and the production of a Z boson.

In a highlight result presented at the Higgs 2022 conference, the ATLAS Collaboration studied the production of off-shell Higgs bosons with a high invariant mass decaying into two on-shell Z bosons using the data collected during LHC Run 2 (2015-2018). For their new search, ATLAS physicists focused on events where the two Z bosons decay into four charged leptons (ZZ→4l channel) or two charged leptons plus two neutrinos (ZZ→ 2l2v channel), as they offered the highest signal sensitivity.

The ATLAS Collaboration has partnered with Seal Storage Technology in a pilot project to explore their decentralised cloud storage platform as an efficient and cost-effective option for archival data storage

The ATLAS Collaboration celebrated its 30th anniversary on 1 October 2022.

On 6 October at 2pm CET, Dr. Hideyuki Oide will give a live public talk on the ATLAS Youtube Channel on the LHC's search for new, long-lived particles.

The ATLAS Collaboration has been looking for signs of dark photons in data collected by the experiment during LHC Run 2 (2015-2018). Their newest search targets, for the first time in ATLAS, the production of a Higgs boson in association with a Z boson, with subsequent decay of the Higgs into a photon and a dark photon.

In a new analysis presented at the ICHEP 2022 conference, ATLAS physicists found evidence of a four-charm-quark excess. Like the LHCb Collaboration, ATLAS sees both the X(6900) particle and a broad structure at threshold.

In a new result presented at ICHEP 2022, ATLAS physicists set out to measure proton scattering at microradian angles and study this quantum interference.

In a new result presented at the ICHEP 2022 conference, ATLAS physicists have been able to observe events with both a W and Z boson simultaneously polarised longitudinally for the very first time.

The 2022 International Conference on High Energy Physics (ICHEP) kicks off this week in Bologna, Italy. The ATLAS Collaboration will be unveiling a wide range of new results, exploring the full potential of the dataset collected during LHC Run 2 (2015-2018).

“We have proton collisions in the ATLAS experiment.” At 16.47 CEST, the Large Hadron Collider (LHC) officially kicked off its third period of operation (Run 3). The LHC is colliding proton beams at a world-record-breaking energy of 13.6 tera electron volts (TeV). The higher beam energy and intensity of Run 3 will allow the ATLAS experiment to push the very limits of its physics research.

In the most recent effort to constrain the Higgs self-coupling constant, ATLAS physicists used the full Run 2 dataset (collected during 2015-2018) to perform a combined study on the production of a single Higgs boson and two Higgs bosons. This single-Higgs analysis was featured in a paper released in Nature today, looking back on 10 years of Higgs boson research at the ATLAS Experiment

The ATLAS Collaboration at CERN has released its most comprehensive overview of the Higgs boson. The new paper, published in the journal Nature, comes exactly ten years after ATLAS announced the discovery of the Higgs boson. In celebration of this anniversary, a special all-day symposium on the Higgs boson is currently underway at CERN.

The ATLAS experiment at the Large Hadron Collider (LHC) is on the eve of a new data harvest with the restart of the LHC for Run 3. The upcoming four-year run will provide a dataset nearly twice the size of what was collected in Run 2 (2015–2018).

ATLAS researchers are exploring the potential of High Performance Computing (HPC). HPC harnesses the power of purpose-built supercomputers constructed from specialised hardware, and is used widely in other scientific disciplines.

The ATLAS Collaboration has just released a new measurement of the CP properties of H→ττ interactions. The study of H→ττ allows researchers to understand the CP-nature of Higgs boson interactions.

The ATLAS Collaboration has released a new combined search for heavy vector bosons, which includes 13 individual searches studying different final states. The new combination includes, for the first time, a dedicated search for heavy particles decaying to third-generation leptons (taus).

Using the full Run-2 dataset, the ATLAS Collaboration has published four analyses searching for flavour-changing neutral currents in the production and decay of the top quark. The results study top-quark processes involving all four neutral bosons: the photon, gluon, Z boson and Higgs boson.

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

The ATLAS Collaboration finds evidence of parton mass, colour-charge and radiation-pattern dependence in quark-gluon-plasma induced energy loss.

At the recent Quark Matter 2022 conference in Krakow, Poland, members of the ATLAS Collaboration presented a new study of “jets” of particles travelling through the QGP. The result provides new insight into dijet suppression due to interactions with the nuclear medium.

Today at the Quark Matter 2022 Conference, the ATLAS Collaboration announced the observation of tau-lepton pairs created when particles of light – or photons – interact during lead-ion collisions. The result opens a new avenue for measuring how magnetic the tau lepton is – a property sensitive to new particles beyond the Standard Model.

Where is all the new physics? Could it be sneaking past the standard searches? ATLAS researchers have developed innovative ways to search for new particles, improving their search programme to ensure they have the best chance of discovering new physics in Run 3 of the LHC.

The ATLAS Collaboration performed a new search for exotic Higgs-boson decays using the full dataset of 13 TeV proton-proton collisions delivered by the LHC between 2015 and 2018.

Many theories suggest that the Higgs boson discovered in 2012 by the ATLAS Experiment is but the first to be observed from a larger Higgs family. A new ATLAS analysis searches for the presence of a new singly-charged Higgs boson.

On 31 March 2022 at 8pm CEST, Dr. David Rousseau will give a live public talk on the ATLAS Youtube Channel on the role artificial intelligence plays in particle physics research.

The ATLAS Collaboration announces the first observation of “tqγ production”: the associated production of a single top quark and a photon in proton-proton collisions at the LHC.

The ATLAS Collaboration has devised a range of new strategies to look for long-lived particles with various possible characteristics. Four new results from this effort were presented at the recent Lepton-Photon and La Thuile conferences.

The winter conference season is in full swing! 2022 marks the return of full auditoriums and coffee-break chats, as the La Thuile and Rencontres de Moriond conferences welcome participants to venues in the Italian Alps. These are the first large-scale, international particle physics conferences to be held in person in the COVID era – reuniting experimentalists and theorists after almost two years of virtual meetings.

The ATLAS trigger system operated extremely successfully during Run 1 (2009–2013) and Run 2 (2015–2018) of the LHC. It is now undergoing various upgrades in preparation for the upcoming Run-3 data-taking period, which will see a moderate increase in the rate of collisions inside the experiment.

According to the Standard Model, most particles get their mass through an interaction with the Higgs field. If dark-matter particles acquire their mass in the same way, a Higgs boson created in an LHC collision might sometimes decay into a pair of “invisible” dark-matter particles. The ATLAS Collaboration has released a new search for invisible Higgs-boson decays using the full Run-2 dataset.

On 17 February 2022 at 8pm CET, Dr. Karolos Potamianos will give a live public talk on the ATLAS Youtube Channel on the study of the electroweak force and the role it plays in the Universe.

Physicists from the ATLAS Collaboration have combined two measurements of the interaction strength of the Higgs boson with two different pairs of quarks. This allows physicists to test a hypothesis that the Higgs boson interacts with charm quarks (which are second-generation quarks) in the same way it interacts with beauty quarks (third-generation quarks).

The ATLAS Collaboration has completed the installation of “Phase-I” upgrades of the Liquid Argon Calorimeter (LAr). The upgrades improve the read-out speed of the calorimeter’s electronics and provide more efficient event-selection capabilities. These improvements will be pivotal for data-taking during the coming high-intensity runs of the LHC.

The ATLAS Collaboration has just released a new paper combining LHC and HERA data to determine Parton Distribution Functions (PDFs), which describe what fraction of a proton’s momentum is taken by its constituent quarks and gluons.

The ATLAS Collaboration has released updated measurements of the Higgs boson properties using the full LHC Run-2 dataset (recorded 2015-2018).

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.

Could there be another source of asymmetry in the Universe? ATLAS physicists are studying the differences between positively- and negatively-charged electrons and muons, looking for signs of charge–lepton-flavour symmetry breaking.

According to the Standard Model, the Higgs boson can interact with itself, resulting in the simultaneous production of two Higgs bosons ("di-Higgs production"). In a new result, the ATLAS Collaboration combines three di-Higgs decay channels to reach the best limits yet on di-Higgs production.

On 22 November 2021 at 8pm CET, Dr. Heather Russell will give a live public talk on the ATLAS Youtube Channel on the "trigger", the ATLAS event selection system.

Following several years of development, ATLAS Collaboration has launched a new "multithreaded" release of its analysis software, Athena.

The ATLAS Collaboration is breathing new life into its LHC Run-2 dataset, recorded from 2015 to 2018. Physicists will be reprocessing the entire dataset – nearly 18 PB of collision data – using an updated version of the ATLAS offline analysis software (Athena). Not only will this improve ATLAS physics measurements and searches, it will also position the Collaboration well for the upcoming challenges of Run 3 and beyond.

On 23 September 2021 at 8pm CEST, Dr. Maria Moreno Llácer will give a live public talk on the ATLAS Youtube Channel on the top quark. She will explain what makes this quark such a unique particle and describe the role it plays in the search for new physics.

Finding the differences between these types of matter – while extremely challenging – could reveal well-hidden effects that hint at the existence of new particles and interactions. In a new result presented at the TOP 2021 conference, the ATLAS Collaboration probed the heaviest-known elementary particle, the top quark, in search of these effects.

In a new study, the ATLAS Collaboration looked for Z bosons decaying into an electron and an anti-muon, or into a muon and a positron.

The ATLAS Collaboration releases new measurements of the Higgs-boson decay to tau leptons. The result provides new insight into the “Yukawa coupling”, a key interaction of the Higgs boson.

One of the long-term goals of the LHC is to measure the Higgs-boson self-coupling, which in turn can give us clues about the formation of the early Universe. This self-coupling can only be measured directly by studying the production of pairs of Higgs bosons (HH).

The ATLAS Collaboration has released a new result searching for pairs of Higgs bosons (HH) produced by new particles. The Higgs bosons would then each decay into pairs of bottom (b) quarks – known as the '4b decay channel'.

The ATLAS Collaboration announces the first observation of “WWW production”: the simultaneous creation of three massive W bosons in high-energy LHC collisions.

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

What can particles of light – photons – tell us about the inner workings of the Standard Model? A new paper from the ATLAS Collaboration measures pairs of photons to improve the understanding of a fundamental force of Nature – the strong force – and thus scrutinise the theoretical models that underpin high-energy physics research.

In celebration of the lowering of the first New Small Wheel detector, CERN is hosting a 360° live event from the ATLAS cavern! Tune in on Thursday 15 July at 5pm CEST.

A new result from the ATLAS Collaboration studies the interactions of photons – particles of light – with lead nuclei at the Large Hadron Collider (LHC). Using new data collection techniques, physicists revealed an unexpected similarity to the experimental signatures of the quark–gluon plasma.

On 1 July 2021, Dr. Hongtao Yang will be giving a live public talk, sharing the story of the Higgs boson's discovery by the ATLAS and CMS experiments. He will explain what ATLAS physicists have learned about this fascinating particle so far, and describe the next steps in its exploration.

The ATLAS Collaboration has released three new searches for "higgsinos" - the super-partner of the Higgs boson.

A new search from the ATLAS Collaboration, released this week at the Large Hadron Collider Physics conference (LHCP 2021), sets limits on the mass of the W’ boson.

In a new result presented by the ATLAS Collaboration, physicists have measured – for the first time – the full polarisation vectors for both top quarks and antiquarks.

At the LHCP2021 conference, the ATLAS Collaboration presents a new direct search for the decay of the Higgs boson to charm quarks. Observing this decay would give physicists new insight into the Higgs boson’s relationship with the second generation of matter particles.

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

Soon after the Big Bang, the Universe was too hot for normal matter to exist. Instead, it was made up of an extremely hot liquid of quarks and gluons: the quark-gluon plasma (QGP). In this live talk, Dr. Anne Marie Sickles explains how physicists at the ATLAS experiment are studying the QGP and what they've have learned.

Making a scientific breakthrough in 2021 requires more than just a microscope – most scientists rely on powerful computers and ingenious software to carry out their research. In this live talk, Dr. James Catmore explains the advanced computing and software techniques used by the ATLAS Experiment.

In the post-Higgs discovery era, scientists at the Large Hadron Collider (LHC) have been hard at work studying the Higgs boson’s properties. One property that remains to be experimentally verified is whether the Higgs boson can couple to itself (self-coupling).

In a new result released this week, the ATLAS Collaboration studied the production of four top quarks at once in LHC collisions. This is the heaviest particle final state ever seen at the LHC, and provides physicists with a unique opportunity to study the top quark’s relationship to the Higgs boson.

A new result from the ATLAS Collaboration – debuted at the virtual Moriond Electroweak conference – sets itself apart from more traditional LHC searches. Typically, physicists will look for new particles produced in LHC collisions that immediately decay to known or invisible particles. This analysis, in contrast, looks for new particles that live for roughly a hundred nanoseconds or more before decaying.

The Higgs boson reveals its properties to the outside world twice: during production and decay. ATLAS’ new result studies the Higgs boson at both of these moments, looking at its production via two different methods and its subsequent decay into two W bosons.

Since 1966, Les Rencontres de Moriond has united experimentalists and theorists for weeks of scientific discussion. 2021 is no exception – but instead of in-person chats over coffee in La Thuile (Italy), physicists will be sharing their new findings in online meetings.

The special status of the top and bottom quarks makes them key players in the search for phenomena not foreseen by the Standard Model. New ATLAS results set strong constraints on the production of supersymmetric bottom quarks and of possible dark-matter particles.

CERN’s Large Hadron Collider (LHC) is famous for colliding protons at world-record energies – but sometimes it pays to dial down the energy and see what happens under less extreme conditions.

In new results released this week, ATLAS physicists describe novel techniques used to accurately align the muon spectrometer.

ATLAS finds first evidence of the Higgs boson decaying to two leptons and a photon. This is one of the rarest Higgs boson decays yet seen at the LHC, with striking features that presented unique challenges for the ATLAS experiment.

New results from the ATLAS Collaboration focus on different production modes of the Higgs boson decaying into b-quarks, capitalising on the power of machine learning to better discriminate this particular process from other proton collision events.

Journey into the ATLAS Experiment! On Thursday 26th November, Prof. Daniela Bortoletto gave a live public talk on Youtube describing how particle detectors like ATLAS find elementary particles.

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

Dark Matter plays a crucial role in the evolution of our Universe. On Thursday 29th October, Dr. Christian Ohm gave a live public talk on Youtube on the extraordinary mystery of Dark Matter.

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

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

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 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.

On Thursday 28 May, Dr. Laura Jeanty gave a public talk live on YouTube on the underlying symmetries of the Universe, and how they are studied by particle physics experiments.

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).

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.

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.

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.

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.

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.

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.

Today, at the Large Hadron Collider Physics (LHCP) conference in Puebla, Mexico, and at the SUSY2019 conference in Corpus Christi, USA, the ATLAS Collaboration presented numerous new searches for SUSY based on the full Run-2 dataset (taken between 2015 and 2018), including two particularly challenging searches for electroweak SUSY. Both target particles that are produced at extremely low rates at the LHC, and decay into Standard Model particles that are themselves difficult to reconstruct. The large amount of data successfully collected by ATLAS in Run 2 provides a unique opportunity to explore these scenarios with new analysis techniques.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 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).

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.

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

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.

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.

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.

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.

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.

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!

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.

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.

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 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.

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.

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).

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.

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.

One of the most direct ways to search for the unexpected is to look for new particles, often with multi-TeV mass. These heavy particles are featured in beyond the Standard Model theories and could be created at the Large Hadron Collider.

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.

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.

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 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.

On 25 February 2016 in CERN's Main Auditorium, the ATLAS collaboration announced the winners of the 2015 ATLAS Thesis Awards: Javier Montejo Berlingen, Ruth Pöttgen, Nils Ruthmann, and Steven Schramm. The winners were selected by the ATLAS Thesis Awards Committee for their outstanding contributions to the collaboration in the context of a PhD thesis. A total of 33 nominations were received, all of a very high standard and encompassing major achievements in all areas of ATLAS results and activities.

Heavy-ion physics is the study of the hot dense medium created shortly after the Big Bang. Physicists examine this medium in three collision systems: lead-lead, proton-lead and proton-proton collisions.

The new results confirm that the ridges in proton-proton, proton-nucleus, and nucleus-nucleus collisions have a similar origin. The results also show that the observed weak dependence on the numbers of charged particles and the centre-of-mass energy should provide strong constraints on the mechanism responsible for producing the ridge in proton-proton, and, maybe, proton-nucleus collisions.

This week, physicists from around the world are gathering at the Top 2015 workshop in Ischia, Italy to discuss the latest measurements of the top quark. As the heaviest known fundamental particle, the top quark plays a special role in the search for "new physics".

Today, at the Large Hadron Collider Physics conference (LHCP2015), the ATLAS and CMS collaborations presented the most precise measurements yet of Higgs boson properties. By combining Run 1 data from both experiments, the new measurements paint a clear picture of how the Higgs boson is produced, decays, and interacts with other particles.

Most of the matter in the universe is made not of stuff we understand, but of invisible “dark matter” particles. We have yet to observe these mysterious particles on Earth, presumably because they interact so weakly with normal matter. The high energy collisions in the Large Hadron Collider provide our best current hope of making dark matter particles, and thus giving us a better understanding what most of the universe is made of.

One of the most basic quantities in particle physics, the rate at which protons scatter off of one another (the cross section), cannot be calculated from the theory of strong interactions, quantum chromodynamics. It must instead be measured, and those measurements can then be used to tune the numerical models of LHC proton–proton collisions.

W and Z bosons are the massive carriers of the weak force, responsible for radioactive decays. These bosons also couple closely to the Higgs boson. W and Z bosons are produced at a large rate in proton-proton collisions at the LHC, where ATLAS physicists have now measured the rates for W and Z boson production using 13 TeV proton-proton collisions

ATLAS Outreach Co-coordinator Kate Shaw has been awarded the 2015 European Physical Society (EPS) Outreach prize "for her contributions to the International Masterclasses and for her pioneering role in bringing them to countries with no strong tradition in particle physics".

A new set of techniques is being used to identify highly energetic top quarks, W and Z bosons, and Higgs bosons decaying to quarks and, ultimately, to hadrons measured in ATLAS. Signatures of these “boosted” Standard Model particles are particularly useful when searching for massive new particles and measuring processes at high energies.

After a shutdown of more than two years, Run 2 of the Large Hadron Collider (LHC) has restarted with proton–proton collisions at a centre-of-mass energy of 13 TeV. This new phase will allow the LHC experiments to explore nature and probe the physical laws governing it at scales never reached before.

With a precision of just under 14% − currently dominated by our ability to understand how many proton-proton collisions have occurred at ATLAS (i.e. luminosity) − this measurement is able to confirm that quantum chromodynamics, the theory of the strong interaction, still seems to be going strong!

Previous studies of two-particle angular correlations in proton-proton, proton-lead, and lead-lead collisions at the LHC have provided important insight on the physics of the particle production process. On 24 July, Atlas presented new preliminary measurements of two-particle correlations...

Jets are collimated sprays of hadrons generated from quarks and gluons, produced either directly in the proton-proton collision or as a part of the decay of W bosons, Z bosons, Higgs bosons, top quarks or new particles yet to be discovered. In fact, all W, Z and Higgs bosons decay most often to quarks which form jets.