Measurement of the W boson polarisation in top quark decays in 0.70 fb$^{-1}$ of pp collisions at sqrt(s)=7 TeV with the ATLAS detector

Measurements of the helicities of W bosons in top quark decays and angular asymmetries are presented in this note. Final states with one or two charged leptons, missing transverse energy and at least four or two jets, respectively, were considered. At least one of the jets in the single lepton final state is required to be b-tagged. Data collected by the ATLAS experiment at a centre-of-mass energy of 7 TeV were used, corresponding to an integrated luminosity of 0.70/fb. The results are in agreement with the Standard Model. As the polarisation of the W bosons in top quark decays is sensitive to the structure of the Wtb-vertex the measurements were used to set limits on anomalous contributions to the Wtb-vertex.