The ATLAS Collaboration, an international team of physicists including Peter Onyisi from the University of Texas at Austin, 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.
Physicists hypothesized forty years ago that quarks get their masses from the Higgs field. Today's announcement, made jointly with a second team at the LHCP conference in Bologna, is the first direct proof that this hypothesis is correct. It also allows physicists to test other critical parameters of the Higgs mechanism in the Standard Model of particle physics.
The observations were made with the Large Hadron Collider (LHC) at CERN, the European Organization for Nuclear Research.
The ATLAS announcement was made jointly with the CMS Collaboration, another team using data from a different set of detectors at the LHC. The ATLAS result establishes the signal with a statistical significance of 6.3 standard deviations (exceeding five standard deviations, considered the gold standard). It concurs with the observation by the CMS Collaboration, which had 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," says Karl Jakobs, ATLAS Spokesperson. "It provides direct evidence that the heaviest known particle, the top quark, interacts with the predicted large strength with the Higgs boson."
The signal for this production has slowly built up over years of accumulating data, with the first evidence reported by ATLAS last December.
As only 1 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.
The new result may also provide insight into one of the most puzzling aspects of the Standard Model: the wide range of masses among fermions, the class of particles that constitute matter and include quarks and leptons. Understanding the nature of the top quark mass would go a long way to solving this open question.
"The measurement gives a strong indication that the Higgs boson has a key role in the large value of the top quark mass," says Cerutti. "While this is certainly a key feature of the Standard Model, this is the first time it has been verified experimentally with overwhelming significance."
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.
Other current members of the ATLAS team from UT Austin are postdoctoral researcher Rohin Narayan and graduate students Harish Potti and Aaron Webb. Former UT Austin members include Yuriy Ilchenko and Victor Rodriguez.
This press release was adapted from a release by the ATLAS Collaboration.
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