PERTURBATIVE QCD ANALYSIS OF B-MESON DECAYS

The resummation of large QCD radiative corrections, including leading and next-to-leading logarithms, in the pion electromagnetic form facto r is reviewed. A similar formalism is applied to exclusive processes i nvolving heavy mesons, and leads to Sudakov suppression for the semile ptonic decay B-->pi l nu. It is found that, with the inclusion of Suda kov effects, a perturbative QCD analysis of this decay is reliable for the energy fraction of the pion above 0.4. Combining predictions from soft pion theorems we estimate that the upper limit of the matrix ele ment /V-ub/ is 2.8-4.8X10(-3) from different models of the B meson wav e function.