2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/207606Top pair production at LHC is the ideal place to search for nonstandard Wtb couplings in t -> W b -> l nu b decays. The lb forward-backward asymmetry in the W rest frame is very sensitive to sigma_{mu nu} couplings, and can spot one-loop QCD corrections to the decay vertex with more than 5 sigma statistical significance. We discuss the potential of this asymmetry to signal nonstandard gamma_mu and sigma_{mu nu} couplings and compare with top-antitop spin correlation asymmetries, which have a lower sensitivity. We also briefly summarise the results for Tevatron.LaTeX, 12 pages, 2 PS figures. One reference added. To be published in PRDHigh Energy Physics - PhenomenologyHigh Energy Physics - Experimenttext