Radiative decay B → lνγ in the light cone QCD approach

We calculate the rate for the decay Bu → lνγ using the light cone QCD sume rules. We find Br(Bu → lνγ) ≃ 2 · 10. The results are used to test the applicability of the constituent quark model approximation to the same process.The latter estimate is proportional to 1/mu, where mu ≃ Λ̄u is the ”constituent quark mass”, indicating that the process is of long distance type. We find that the two approaches yield similar results for the total rate with the choice mu ≃ 480 MeV . This indicates that the constituent quark model may be used for estimates of the radiative ”annihilation” contribution to this and other radiative decays. We point out that this decay may be useful for the measurement of |Vub|. submitted to Physics Letters B ∗ On sabbatical leave from Dept. of Applied Math., Univ. of Western Ontario, London, Ontario, Canada