Göttingen 2012 – scientific programme

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T: Fachverband Teilchenphysik

T 34: Top-Quark: Produktion 3

T 34.10: Talk

Wednesday, February 29, 2012, 19:00–19:15, ZHG 104

Single Top Quark Production through Flavour Changing Neutral Currents — •Muhammad Alhroob¹, Dominic Hirschbuehl², and Ian Brock¹ — ¹Physikalisches Institute, Bonn, Germany — ²University of Wuppertal, Wuppertal, Germany

Flavour Changing Neutral Currents (FCNC) are extremely suppressed in the Standard Model due to the Glashow-Iliopoulos-Maiani (GIM) mechanism. There are, however, extensions of the SM, like supersymmetry (SUSY) and the 2-Higgs doublet model, which predict the presence of FCNC contributions already at tree level and significantly enhance the FCNC decay branching ratios compared to the Standard Model predictions. Our analysis concentrates on single top-quark production through FCNC, where the u(c) quark interacts with a gluon to produce a single top quark without any associated production. Data collected with the ATLAS detector at a center-of-mass energy of √s=7 TeV and corresponding to an integrated luminosity of 2.05 fb⁻¹ are used. Candidate events with a leptonic top-quark decay signature are classified into signal- and background-like events using a neural network. No signal is observed in the output distribution and a Bayesian upper limit on the production cross-section is placed. The observed 95% C.L. upper limit on the cross-section multiplied by the t → Wb branching fraction is measured to be σ_{qg→ t} × B (t→ Wb)<3.9 pb. This upper limit is converted into an upper limit of the coupling strength.