Speaker
Description
Vector boson scattering is one of the recent remarkable observations at the Large Hadron Collider. The longitudinal polarization modes of the massive vector bosons are strongly tied to the electroweak symmetry breaking mechanism. With the Standard Model predicted Higgs boson playing a crucial role in regularizing the scattering amplitude of these longitudinally polarized bosons, vector boson scattering is a pivotal process in experimentally probing the symmetry breaking mechanism. A golden channel for measuring vector boson scattering at the collider is the electroweak production of two W bosons with the same electric charges. Owing to its largest quark- to gluon- induced production ratio among other diboson combinations, the process was also the first target of the ATLAS vector boson scattering program, with evidence made in 2014 and observation in 2019. With the entire Run 2 datasets of proton-proton collisions at 13 TeV, corresponding to an integrated luminosity of 139 /fb, the differential cross-section of this process is measured.
The process is studied in the leptonic decay channels of the W bosons, effectively suppressing many Standard Model backgrounds. The process pp->l+-nu l+-nu jj is measured with the final state consisting of two leptons of like charges, two jets, and missing transverse energy. The characteristic vector boson scattering signature of two tagging jets, with a large di-jet invariant mass, separated by large angles, is used to tag electroweak-induced production. A combination of Monte Carlo-based predictions and data-driven approaches is used to estimate the various backgrounds. A statistical model of profile likelihood is used to constrain the background predictions and reduce the uncertainties following which the events are unfolded, and the cross-section is extracted. The fiducial differential cross-sections are measured in the leptonic channel as a function of several kinematic variables and are found to be consistent with the Standard Model predictions within uncertainties.
The results are additionally interpreted in the context of physics beyond the Standard Model. Constraints are obtained on the structure of quartic vector boson interactions in the framework of effective field theory. Model independent upper limits are obtained at 95% confidence level on the product of the cross section and branching fraction for vector boson fusion production of doubly charged Higgs bosons as a function of mass from 200 to 3000 GeV, and interpreted in the context of Georgi-Machacek model.
| Collaboration / Activity | ATLAS |
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