Transverse polarization of top quark pairs at the Tevatron and the Large Hadron Collider

We investigate the prospects to observe effects of transverse polarization of top quarks in pp,pp → ttX. QCD absorptive parts generate a polarization of top quarks and antiquarks transverse to the production plane in the partonic processes qq → tt and gg → tt, which reaches values of a few percent. These perturbative QCD effects are decreased at the hadronic level. A measurement through momentum correlations among the t and t decay products will be difficult both at an upgraded Tevatron and at the LHC.