Physics Briefings

ATLAS finds evidence of the Higgs boson produced in association with a pair of top quarks

26th October 2017 – 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.

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Photon-tagged jet quenching in the quark-gluon plasma

23rd October 2017 – 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.

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Studying fragments of the top quark

5th October 2017 – 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. 

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Hunting down forbidden decays of the top quark

3rd October 2017 – 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.

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ATLAS and CMS look forward with the top quark

27th September 2017 – 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.

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Finding a haystack in a field of haystacks

21st September 2017 – 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.

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Exploring the nature of the “ridge” in small systems

28th August 2017 – 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”.

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