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.