Combination of cross-section measurements of associated production of a single top-quark and a W boson at sqrt[s] = 8 TeV with the ATLAS and CMS experiments

A combination of cross-section measurements for the associated production of a top quark and a $W$ boson in proton-proton collisions at $\sqrt{s}=8\,\,\rm TeV$ by the ATLAS and CMS experiments is presented. The two measurements are based on integrated luminosities of $20.3\,\,\rm fb^{-1}$ and $12.2\,\,\rm fb^{-1}$, respectively. The combined production cross section of a single top quark and a $W$ boson is determined as $\sigma_{tW} = 25.0\pm1.4\;(\text{stat.})\pm4.4\;(\text{syst.})\pm0.7\;(\text{lumi.})\,\,\text{pb} = 25.0\pm4.7\,\,\text{pb}$, in agreement with the NLO+NNLL expectation. A $95\%$ C.L. lower limit on the magnitude of the CKM matrix element $V_{tb}$ of $|V_{tb}|>0.79$ is extracted from the cross-section measurement. $$\textit{ }$$ $\,\,\,\,\,\,\,\textit{The following have been revised with respect to the version dated September 29, 2014:}$ $~~~~~~~~~~~~~~~~~~\textit{The uncertainties for ATLAS and CMS have been updated in Fig. 1.}$