QCD calculation of$B \to \pi l\bar v_l$ and the matrix element |V _bu|

Abstract

Using QCD sum rules for a two-point function involving beauty vector currents, together with current algebra-PCAC sum rules, we estimate the hadronic matrix element in$B \to \pi l\bar v_l$. We find$\Gamma \left( {\bar {\rm B}^0 \to \pi ^ + l\bar v_l } \right) = \left( {1.45 \pm 0.59} \right) \times 10^{13} \left| {V_{bu} } \right|^2 s^{ - 1}$. As a byproduct, the vector current contribution to the decay$B \to \rho l\bar v_l$ is also estimated.