Search for FCNC in single-top quark production in ATLAS

Flavour Changing Neutral Currents (FCNC) are strongly suppressed in the Standard Model due to the Glashow-Iliopoulos-Maiani (GIM) mechanism. Although absent at tree level, small FCNC contributions are expected at one-loop level, determined by the CKM mixing. For the top quark, within the framework of the Standard Model, the expected FCNC branching fractions to gauge bosons, e.g. t$Rightarrow$q+gluon, are predicted to be at the level of $10^{-13}$. 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. This 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. The top quark then decays as usual via the SM process, t$Rightarrow$W+b, An upper limit on the production cross section at 95% confidence level has been extracted using 35 $pb^{-1}$ from the first ATLAS data taken in 2010.