ATLAS observes interaction between Higgs boson and 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.
Argonne’s High Energy Physics Division has been a collaborator on the ATLAS detector since 1994. Standing 151 feet long, 80 feet tall and 80 feet wide and comprising more than 100 million sensors, ATLAS has earned the title of the largest particle detector ever built. As one of six particle detectors located along the Large Hadron Collider’s (LHC’s) 16-mile ring, ATLAS identifies and analyzes the elementary particles emitted after a high-energy collision between two protons.
The announcement was made June 4, 2018, at the 6th Large Hadron Collider Physics Conference.
The result exploits the full dataset delivered to ATLAS by the LHC and establishes the signal with a statistical significance of 6.3 standard deviations. It concurs with a recent observation by the CMS Collaboration with a significance of 5.2 standard deviations using a smaller dataset.
“This measurement constitutes a landmark achievement in the exploration of the Higgs mechanism and the interaction of Standard Model particles with the Higgs boson. It provides direct evidence that the heaviest known particle, the top quark, interacts with the predicted large strength with the Higgs boson” said Karl Jakobs, ATLAS spokesperson. The signal for this production has slowly built up over years of accumulating data, with first evidence reported by ATLAS last December.
As only one percent of all Higgs bosons are produced in association with top quarks, its observation was extremely challenging. ATLAS physicists examined five years of collision data to arrive at this result. Argonne has made important contributions to the result, especially in the Multivariate Analysis (MVA) and fit studies.
“This is one of the most demanding searches carried out by the ATLAS Collaboration, requiring significant collaborative effort from a large number of scientist teams throughout the world, and Argonne’s contributions to the ATLAS experiment helped make this observation possible,” said Argonne senior physicist James Proudfoot (HEP).
The success of this result hints at the new analysis possibilities of the ATLAS experiment. Thanks to the wealth of data being produced by the LHC and the excellent performance of the ATLAS experiment, physicists will be able to study the Higgs boson in further rare and experimentally challenging interactions for the first time. Such studies will continue to challenge the limits of the Standard Model and may open new avenues of discovery.
Image: ATLAS Collaboration/CERN: Visualization of an event from the tt̄H(γγ) analysis. The event contains two photon candidates displayed as green towers in the electromagnetic calorimeter, and six jets (b-jet) shown as yellow (blue) cones.