2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/182621We propose a new method for reconstructing an effective spin direction of a semi-leptonically decayed top quark. The method is simple: for instance, it does not require the spin information of the antitop quark in a ttbar event. The reconstructed effective spin is expected to be useful in hadron collider experiments. We demonstrate its usefulness in an analysis of the top decay vertex.10 pages, 6 figures; one reference added; version to appear in Phys.Lett.BHigh Energy Physics - PhenomenologyHigh Energy Physics - Experimenttext