First measurement of the ratio B(t -> Wb)/B(t -> Wq) and associated limit on the Cabibbo-Kobayashi-Maskawa element vertical bar V-tb vertical bar - Affolder, T; Akimoto, H; Akopian, A; Albrow, MG; Amaral, P; Amendolia, SR; Amidei, D; Anikeev, K; Antos, J; Apollinari, G; Arisawa, T; Asakawa, T; et al. (2001)