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.

Physics Briefing | 18 Jan 2018

Reaching out across cultures

This past Spring, I had the opportunity to travel to Taos, New Mexico, USA, to work with artist Agnes Chavez, on one of her “Projecting Particles” workshops. Her innovative programme aims to develop STEM (Science, Technology, Engineering, Math) skills in students aged 8 and up, employing a mixture of science education and artistic expression. It is a winning combination for everyone involved.

Blog | 05 Jan 2018

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.

Physics Briefing | 18 Dec 2017

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.

Physics Briefing | 15 Dec 2017

Explore virtual CERN with ATLAScraft

Enter the world of particle physics with the newly-launched ATLAScraft! Players can explore the CERN campus, shrink down to the size of a particle, and even conduct their own “experiments” in educational minigames.

News | 13 Dec 2017

Broken symmetry: searches for supersymmetry at the LHC

A commentary by ATLAS physicists Paul de Jong and George Redlinger on the history, progress and future of the search for supersymmetry.

Feature | 08 Dec 2017

Behind the scenes at ATLAS Week

A few times a year, the large LHC collaborations such as ATLAS organise an internal overview session. This photo essay will take you to the most recent of these “ATLAS Weeks” – giving you a glimpse behind the curtain, and exploring this essential part of the collaboration structure and life.

News | 06 Nov 2017

Noble nuclei open new doors in ATLAS physics

Take something you think you understand, change it and see what happens. Earlier this month, the ATLAS Experiment put this basic scientific principle to the test during the first Large Hadron Collider (LHC) xenon run.

News | 31 Oct 2017

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.

Physics Briefing | 26 Oct 2017

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.

Physics Briefing | 23 Oct 2017

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.

Physics Briefing | 05 Oct 2017

The art of physics

I have been doing some work with artists recently. Not that I’m planning a career change, you know: I just love to talk about my research to anyone who is prepared to listen, and lately it’s been with artists. Ruth Jarman and Joe Gerhardt, aka Semiconductor, are internationally renowned visual artists who in 2015 won the Collide@CERN Ars Electronica Award and spent a two-month residency at CERN. Like myself, they live in Brighton, which is also home to the University of Sussex, where I work.

Blog | 04 Oct 2017

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.

Physics Briefing | 03 Oct 2017

ATLAS LIVE: Celebrating 25 years of discovery

To celebration of its 25th anniversary, ATLAS is hosting a series of Facebook live events today, Monday 2 October 2017. Explore key locations around CERN - including the ATLAS control room, Building 40 and the ATLAS TileCal workshop - while learning about the physics, construction and history of the ATLAS Experiment.

News | 02 Oct 2017

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.

Physics Briefing | 27 Sep 2017

On top of the top: ATLAS highlights from the TOP2017 workshop

The ATLAS collaboration presented exciting new results at the 10th International Workshop on Top Quark Physics (TOP2017), held in Braga (Portugal). The conference, which concluded today, brought together experimental and theoretical physicists specializing in the heaviest known elementary particle: the top quark.

News | 22 Sep 2017

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.

Physics Briefing | 22 Sep 2017

Exploring the nature of the “ridge” in small systems

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”.

Physics Briefing | 28 Aug 2017

ATLAS sees first direct evidence of light-by-light scattering at high energy

Physicists from the ATLAS experiment at CERN have found the first direct evidence of high energy light-by-light scattering, a very rare process in which two photons – particles of light – interact and change direction. The result, published today in Nature Physics, confirms one of the oldest predictions of quantum electrodynamics (QED).

Press Statement | 14 Aug 2017

Exploring rare decays of the Higgs boson

Since discovering a Higgs boson in 2012, the ATLAS and CMS collaborations have been trying to understand whether this new particle is the Higgs boson as predicted by the Standard Model, or a Higgs boson from a more exotic model containing new, as yet undiscovered, particles. The answer lies in the properties of the Higgs boson.

Physics Briefing | 11 Aug 2017

5 fundamental parameters from top quark decay

For many physicists, discovering “new physics” means bringing to light a new particle. Another path to discovery lies in carefully measuring the properties of known particles and the interactions between them. The ATLAS experiment has now released new results on the top quark's interaction with the charged intermediate vector boson.

Physics Briefing | 03 Aug 2017

The invisible plan

As the Large Hadron Collider (LHC) smashes together protons at a centre-of-mass energy of 13 TeV, it creates a rich assortment of particles that are identified through the signature of their interactions with the ATLAS detector. But what if there are particles being produced that travel through ATLAS without interacting? These “invisible particles” may provide the answers to some of the greatest mysteries in physics.

Physics Briefing | 17 Jul 2017

ATLAS highlights from EPS-HEP 2017

The ATLAS Collaboration has presented important new results at the European Physical Society conference on High Energy Physics (EPS-HEP) in Venice (Italy), including the latest analyses of 13 TeV Run 2 data from the Large Hadron Collider (LHC).

News | 12 Jul 2017

Probing physics beyond the Standard Model with heavy vector bosons

Although the discovery of the Higgs boson by the ATLAS and CMS Collaborations in 2012 completed the Standard Model, many mysteries remain unexplained. For instance, why is the mass of the Higgs boson so much lighter than one would expect and why is gravity so weak?

Physics Briefing | 08 Jul 2017

New rare pairs of heavy friends in ATLAS

Observing rare productions of heavy elementary particles can provide fresh insight into the Standard Model of particle physics. In a new result, the ATLAS Experiment presents strong evidence for the production of a single top-quark in association with a Z boson.

Physics Briefing | 07 Jul 2017