Briefings

Studying “Little Bangs”: exotic collisions probe the size of quark-gluon plasma

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.

Physics Briefing | 13 July 2021

The hunt for higgsinos reaches new limits

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

Physics Briefing | 10 June 2021

Heavyweight champions: a search for new heavy W’ bosons with the ATLAS detector

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.

Physics Briefing | 9 June 2021

ATLAS measures the polarisation of top quarks and antiquarks

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. 

Physics Briefing | 8 June 2021

New search for charming decay of the Higgs boson

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.

Physics Briefing | 7 June 2021

Twice the Higgs, twice the challenge

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).

Physics Briefing | 29 March 2021

ATLAS finds further confirmation of evidence for four top quark process

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.

Physics Briefing | 24 March 2021

Better late than never: ATLAS searches for late-decaying new particles

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.

Physics Briefing | 23 March 2021

Deeper insight into Higgs boson production using W bosons

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.

Physics Briefing | 22 March 2021

The supersymmetric bottom quark and its friends

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. 

Physics Briefing | 16 March 2021

Studying top quarks at high and not-so-high energies

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.

Physics Briefing | 11 March 2021

The power of position: aligning the ATLAS muon spectrometer

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

Experiment Briefing | 4 March 2021

ATLAS finds evidence of a rare Higgs boson Dalitz decay to two leptons and a photon

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.

Physics Briefing | 2 February 2021

Studying the Higgs boson in its most common – yet uncommonly challenging – decay channel

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.

Physics Briefing | 1 December 2020

Refining the picture of the Higgs boson

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

Physics Briefing | 19 November 2020

ATLAS uses the Higgs boson as a tool to search for 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?

Physics Briefing | 29 October 2020

Higgs boson probes for new phenomena

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.

Physics Briefing | 28 October 2020

Leptons at a distance: a new search for long-lived particles

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

Physics Briefing | 7 October 2020

Z bosons zoom through quark–gluon plasma as jets quench

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

Physics Briefing | 25 August 2020

ATLAS observes W-boson pair production from light colliding with light

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).

Physics Briefing | 5 August 2020

New ATLAS result marks milestone in the test of Standard Model properties

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.

Physics Briefing | 3 August 2020

New measurements of the Higgs boson find strength in unity

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.

Physics Briefing | 31 July 2020

Looking forward: ATLAS measures proton scattering when light turns into matter

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.

Physics Briefing | 30 July 2020

ATLAS probes interactions between heavyweights of the Standard Model

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.

Physics Briefing | 30 July 2020

Jetting into the dark side: a precision search for dark matter

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).

Physics Briefing | 27 July 2020