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May 1, 2020
The ATLAS and CMS collaborations used the full LHC Run 2 dataset to obtain new insights into the interaction
Image above: ATLAS and CMS's event displays where the Higgs boson is produced in association with top quarks (Image: CERN).
Recent years have seen the study of the Higgs boson progress from the discovery age to the measurement age. Among the latest studies of the properties of this unique particle by the ATLAS and CMS collaborations are measurements that shed further light on its interaction with top quarks – which, as the heaviest elementary particle, have the strongest interactions with the Higgs boson. In addition to allowing a determination of the strength of the top-Higgs interaction, the analyses open a new window on charge-parity (CP) violation.
Discovered unexpectedly more than 50 years ago, CP violation reveals a fundamental asymmetry in nature that causes rare differences in the rates of processes involving matter particles and their antimatter counterparts, and is therefore thought to be an essential ingredient to explaining the observed abundance of matter over antimatter in the universe. While the Standard Model of particle physics can explain CP violation, the amount of CP violation observed so far in experiments – recently in the behaviour of charm quarks by the LHCb collaboration – is too small to account for the cosmological matter–antimatter imbalance. Searching for new sources of CP violation is thus of great interest to physicists.
In their recent studies, the CMS and ATLAS teams independently performed a direct test of the properties of the top–Higgs interaction. The studies are based on the full dataset of Run 2 of the LHC, which allowed for more precise measurements and analyses of the collision events where the Higgs boson is produced in association with one or two top quarks before decaying into two photons. The detection of this extremely rare association, which was first observed by the two collaborations in 2018, required the full capacities of the detectors and analysis techniques.
Large Hadron Collider (LHC). Animation Credit: CERN
As predicted by the Standard Model, no signs of CP violation were found in the top–Higgs interaction by either experiment. The top–Higgs production rate, a measure of the strength of the interaction between the particles, was also found by both experiments to be in line with previous results and consistent with the Standard Model predictions.
Following these first investigations of CP violation in the top–Higgs interaction, ATLAS and CMS physicists plan to study other Higgs-boson decay channels as part of the decades-long search for the origin of the universe’s missing antimatter.
Note:
CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.
The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.
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Related articles:
ATLAS searches for rare Higgs boson decays into a photon and a Z boson
https://orbiterchspacenews.blogspot.com/2020/04/atlas-searches-for-rare-higgs-boson.html
LHCb finds new hints of possible Standard Model deviations
https://orbiterchspacenews.blogspot.com/2017/04/lhcb-finds-new-hints-of-possible.html
Long live the doubly charmed particle
https://orbiterchspacenews.blogspot.com/2018/05/long-live-doubly-charmed-particle.html
LHCb announces a charming new particle
https://orbiterchspacenews.blogspot.com/2017/07/lhcb-announces-charming-new-particle.html
Related links:
ATLAS: https://home.cern/science/experiments/atlas
Compact Muon Solenoid (CMS): http://home.cern/about/experiments/cms
Large Hadron Collider (LHC): http://home.cern/topics/large-hadron-collider
For more information about European Organization for Nuclear Research (CERN), Visit: http://home.cern/
Image (mentioned), Animation (mentioned), Text, Credits: CERN/Thomas Hortala.
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