Measurement of t-Channel Single Top-Quark Production in pp Collisions at sqrt(s) = 8 TeV with the ATLAS detector

We present a measurement of the $t$-channel single-top quark production cross-section in the lepton+jets channel with 5.8 fb$^{-1}$ of $\sqrt{s}$ = 8 TeV $pp$ collision data, taken with the ATLAS detector in 2012, using a neural network based discriminant. Selected events contain one lepton, missing transverse momentum, and two or three jets, including one which is $b$-tagged. The background model includes multijets, $W$+jets and top quark pair events, with smaller contributions from $Z$+jets and diboson events. We show data-background comparisons for kinematic distributions and measure the $t$-channel production cross-section by performing a combined binned maximum likelihood fit to the neural network output distribution for the observed data with two and three jets. The measured $t$-channel cross-section is $\sigma_{t}= 95 \pm 2 (\mathrm{stat.}) \pm 18 (\mathrm{syst.}) \mathrm{pb} = 95\pm 18$ pb, which is in good agreement with the Standard Model prediction. Using the ratio of the measured to the theoretically predicted cross section and assuming that the top-quark-related CKM matrix elements obey the relation $|V_{tb}|\gg |V_{ts}|, |V_{td}|$, the coupling strength at the $W$-$t$-$b$ vertex is determined to be $|V_{tb}|=1.04^{+0.10}_{-0.11}$. If it is assumed that $|V_{tb}|\leq 1$, a lower limit of $|V_{tb}|>0.80$ is obtained at the 95% CL.