Measurement of the top quark pair production cross-section with ATLAS in $pp$ collisions at $\sqrt{s}=7$ TeV in the single-lepton channel using semileptonic $b$ decays

The cross section for top quark pair production in $pp$ collisions at $\sqrt{s} = 7 $TeV is measured using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected requiring a single high-$p_{T}$ isolated electron or muon, missing transverse momentum and jets. Semileptonic $b$ decays are identified by a lower momentum muon close to a jet, leading to substantially different sources of systematic uncertainty compared with other measurements. With a data sample corresponding to 4.66$\,fb^{-1}$ of integrated luminosity the top quark pair production cross section is measured to be \begin{equation*} \sigma_{t\bar{t}}= 165 \pm 2 ({\rm stat.}) \pm 17 ({\rm syst.}) \pm 3 ({\rm lumi.})~{\rm pb} \end{equation*} in agreement with theoretical predictions based on perturbative QCD and with other measurements which used different techniques or decay channels.