Rare $B$-Decays and Heavy to Light Semileptonic Transitions in the Isgur and Wise Limit

Abstract

From the experimental branching ratios for $B^{-}-->{\rho }^0{l}^{-}{\bar{\nu }}_l$ and $D^{+}-->{\text{overl}K}^{\ast 0}({\text{overl}K}^0)e^{+}{\nu }_e$ one finds, in the Heavy Quark Limit of $HQET$, $|V_{bu}|=(8.1\pm 1.7)x10^{-3}$, larger but consistent with the actual quoted range $(2-7)x10^{-3}$. In the same framework one predicts for $R(B-->K^{\ast }\gamma )=(2\pm 2)10^{-2}$.

Comments: 9 pages, 1 Figure avalaible on request from SANTORELLI@NA.INFN.IT