Measurement of the top quark pair production cross section in pp collisions at $\sqrt{s}=$ 7 TeV in $\mu$+$\tau$ final states with ATLAS.

A measurement of the cross section of top quark pairs production in proton$-$proton collisions at 7 TeV using events with an isolated $\mu$ and a $\tau$ lepton decaying hadronically is reported. Candidate events are selected requiring, in addition to a $\mu$ and a $\tau$ lepton, two or more jets in which at least one of them tagged as a jet originating from a $b$ quark, and large missing transverse energy. The analysis utilizes a multivariate technique based on boosted decision trees to identify $\tau$ leptons. A data sample collected by ATLAS corresponding to an integrated luminosity of 1.08 fb$^{-1}$ yields $\sigma(t \bar t) =142 \pm 21(stat.) \pm ^{20}_{16} (syst.) \pm 5 (lumi.)$ pb