Measurement of the fiducial and total single top-quark $t$-channel production cross-sections with the ATLAS detector at $\sqrt{s}= 8$ TeV

Detailed measurements of t-channel single top-quark production cross-section are presented. They use 20.2 fb$^{−1}$ of data collected by the ATLAS experiment in proton–proton collisions at a centre-of-mass energy of 8 TeV at the LHC. Total and fiducial cross-sections are measured for both top-quark and top-antiquark production. In this analysis, the signal is extracted from background processes, by employing a neural network based selection. The cross-sections are measured with respect to the visible phase-space (fiducial cross-section) and extrapolated to the full phase-space (total cross-section). The fiducial cross-section is measured with a precision of 5.8% (top quark) and 7.8% (top antiquark), respectively. The total cross-sections are measured to be $\sigma$tot(tq)=56.7+4.3−3.8pb and $\sigma$tot(t$^¯$q)=32.9+3.0−2.7pb for top-antiquark production, in agreement with the Standard Model prediction. In addition, the ratio of top-quark to top-antiquark production cross-sections is determined to be Rt=1.72$\pm$0.09. The cross-section ratio is compared with several PDF-set predictions. The measurement of the production cross-section enables the determination of the CKM-matrix element Vtb without assuming the unitarity of the CKM-matrix. The measured value of |Vtb| = 1.029 $\pm$ 0.048.