Updates tagged: “Physics Results”

ATLAS observes direct interaction of Higgs boson with top quark

The ATLAS Collaboration at CERN has announced the observation of Higgs bosons produced together with a top-quark pair. Observing this extremely rare process is a significant milestone for the field of High-Energy Physics. It allows physicists to test critical parameters of the Higgs mechanism in the Standard Model of particle physics.

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Stronger together: combining searches for new heavy resonances

While the Standard Model has proven tremendously successful, much experimental evidence points to it not being a complete description of our universe. The search for “new physics” is therefore an important component of the ATLAS experimental programme, where a number of analyses are looking for signs of new heavy particles decaying to different final states. Though these searches have not yet found a significant signal, they have allowed physicists to place stringent constraints on different new physics scenarios. These can be further tightened by combining different analysis channels and approaches.

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Could a new type of quark fix the “unnaturalness” of the Standard Model?

While the discovery of the Higgs boson at the Large Hadron Collider (LHC) in 2012 confirmed many Standard Model predictions, it has raised as many questions as it has answered. For example, interactions at the quantum level between the Higgs boson and the top quark ought to lead to a huge Higgs boson mass, possibly as large as the Planck mass (>1018 GeV). So why is it only 125 GeV? Is there a mechanism at play to cancel these large quantum corrections caused by the top quark (t)? Finding a way to explain the lightness of the Higgs boson is one of the top (no pun intended) questions in particle physics.

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ATLAS reveals key results at ICHEP 2018

Feynman. Salam. Weinberg. For the past 50 years, the International Conference on High­Energy Physics (ICHEP) has been the meeting place of giants in the field. Now, a new type of giant dominates: the thousands­-strong collaborations of Large Hadron Collider (LHC) physicists.

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Higgs boson observed decaying to b quarks – at last!

Today, at the 2018 International Conference on High Energy Physics in Seoul, the ATLAS experiment reported a preliminary result establishing the observation of the Higgs boson decaying into pairs of b quarks, furthermore at a rate consistent with the Standard Model prediction. 

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Combined measurements of Higgs boson couplings reach new level of precision

Higgs boson couplings manifest themselves in the rate of production of the Higgs boson at the LHC, and its decay branching ratios into various final states. These rates have been precisely measured by the ATLAS experiment, using up to 80 fb–1 of data collected at a proton-proton collision energy of 13 TeV from 2015 to 2017. Measurements were performed in all of the main decay channels of the Higgs boson: to pairs of photons, W and Z bosons, bottom quarks, taus, and muons. The overall production rate of the Higgs boson was measured to be in agreement with Standard Model predictions, with an uncertainty of 8%. The uncertainty is reduced from 11% in the previous combined measurements released last year.

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Precision leads to puzzles

The top quark is a unique particle due to its phenomenally high mass. It decays in less than 10-24 seconds, that is, before it had time to interact with any other particles. Therefore many of its quantum numbers, such as its spin, are transferred to its decay particles. When created in matter-antimatter pairs, the spins of the top quark and the antitop quark are expected to be correlated to some degree.

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Quarks observed to interact via minuscule “weak lightsabers”

Two among the rarest processes probed so far at the LHC, the scattering between W and Z bosons emitted by quarks in proton-proton collisions, have been established by the ATLAS experiment at CERN.

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Summary of new ATLAS results for ICHEP 2018

The 2018 International Conference on High Energy Physics (ICHEP) kicked off this week in Seoul, South Korea. The ATLAS Collaboration will be unveiling a wide range of new results at ICHEP 2018, including major developments in the measurement of Higgs boson properties, observations of key electroweak production processes, new high precision tests of the Standard Model, and combinations of searches extending the reach to new physics.

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Highlights from LHCP2018

Physicists from around the globe assembled this week at the Centre Domenico in Bologna, Italy, the site of Europe’s oldest university, to attend the sixth annual conference on Large Hadron Collider Physics (LHCP2018). The 425 participants enjoyed picturesque architecture, world-renowned cuisine, and a full menu of recent physics results from the LHC. A sample platter of a few of the tasty morsels is presented.

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