Single-top quark studies in ATLAS

We present the result of searches for single top-quark production in the t and Wt-channels in 7 TeV proton-proton collisions with the ATLAS detector using 0.7~fb$^{-1}$ luminosity. The t-channel search is based on the selection of events with a single lepton (muon or electron), jets and missing transverse energy. The Wt-channel analysis is based on the selection of events with one or two leptons, jets and missing transverse energy. The t-channel production cross section is measured by two different techniques, one following a cut-based approach and one fitting the distribution of a multivariate discriminant constructed with a neural network. The cut-based analysis combines the 2-jet and 3-jet data sets and measures $\sigma_{t}= 90^{+32}_{-22};$pb. The observed significance is 7.6~standard deviations. A simple cut-based approach is used to select the Wt contribution. After selection, we observe 287 data events compared to a prediction of 293 events, with a predicted signal purity of 16%. The following upper limits at 95% CL are determined on the Wt associated production cross-section~:$\sigma(pp -> Wt+X) < $39(41) pb for the observed (expected) limit.