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ATLAS Briefings
ATLAS studies the dynamics of very high-momentum top quarks
– 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.Read more →
Measurements of weak top quark processes gain strength
– 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.Read more →
Searching for supersymmetric Higgs bosons on the compressed frontier
– 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.Read more →
Squeezing sleptons at the LHC
– 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.Read more →
ATLAS finds evidence of the Higgs boson produced in association with a pair of top quarks
– 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.Read more →
Photon-tagged jet quenching in the quark-gluon plasma
– 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.Read more →
Studying fragments of the top quark
– 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.Read more →
Hunting down forbidden decays of the top quark
– 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.Read more →
ATLAS and CMS look forward with the top quark
– 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.Read more →
Finding a haystack in a field of haystacks
– 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.Read more →
