2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/40600We present a new sum rule which does not contain any Landau-pole effect and allows a determination of Vub/Vcb with a theoretical error of O(5%).LaTex file, 5 pages, talk given at the LEPTRE Conference, Rome 18-20 April 2001,to be published in the proceedings, no figures; some typos correctedHigh Energy Physics - Phenomenologytext