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.

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

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

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

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

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

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

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

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