W-polarisation and constraints on Wtb-vertex

The structure of the $Wtb$-vertex can be tested using single top and $t\bar t$ events collected at the LHC. The measurement of the t-channel single top quark production cross section by the CMS Collaboration was used to constrain the $V_{tb}$ CKM matrix element while the measurement of the helicities of $W$ bosons and angular asymmetries in top quark decays by the ATLAS Collaboration were used to constrain possible new physics contributions to the $Wtb$-vertex.