Multiboson production provides a unique way to probe Electroweak Symmetry Breaking (EWSB) and physics beyond the Standard Model (SM). With the discovery of the Higgs boson, the default model is that EWSB occurs according to the Higgs mechanism. Devia
tions from the SM in Higgs and gauge boson properties due to new physics at a higher energy scale can be parameterized by higher-dimension operators in an Effective Field Theory (EFT). We present sensitivity studies for dimension-6 and dimension-8 operators in an EFT by looking for anomalous vector boson scattering and triboson production, at proton-proton colliders with center-of-mass energies of 14 TeV, 33 TeV and 100 TeV, respectively.
Single-top production processes have been studied using 0.7 fb-1 of data from 7 TeV center-of-mass energy proton-proton collisions collected with the ATLAS detector at the LHC. Single-top is electroweak top production and the standard model includes
three production modes. Each contains a Wtb vertex, allowing the possibility of a direct measurement of the CKM matrix element |Vtb|. Single-top could also be sensitive to new physics, such as flavor changing neutral currents or heavy W bosons. Using cut-based selections, a limit of < 39.1 pb is set for dilepton Wt production and < 26.5 pb for s-channel production. For the t-channel measurement, both cut-based and neural network analyses are performed and the cross-section is measured to be 90 +32 -22 pb, where 65 +28 -19 pb is expected according to standard model.
Single-top production has been studied with the ATLAS detector using 0.7 fb-1 of 2011 data recorded at 7 TeV center-of-mass energy. The measurement of electroweak production of top-quarks allows probes of the Wtb vertex and a direct measurement of th
e CKM matrix element |V_tb|. It is also expected to be sensitive to new physics such as flavor changing neutral currents or heavy W production. The t-channel cross-section measurements are performed using both a cut-based and neural network approach, while a cut-based selection in the dilepton channel is used to derive a limit on the associated (Wt) production. An observed cross-section of 90 +32 -22 pb (65 +28 -19 pb expected) is obtained for the t-channel, which is consistent with the Standard Model expectation. For the Wt production, an observed limit of < 39.1 pb (40.6 pb expected) is derived, which corresponds to about 2.5 times the Standard Model expectation.
