RADIATIVE DECAY B-]L-NU-GAMMA IN THE LIGHT-CONE QCD APPROACH

We calculate the rate for the decay B-u --> l nu gamma using the light cone QCD sum rules. We find Br(B-u --> l nu gamma) similar or equal t o 2 x 10(-6). The results are used to test the applicability of the co nstituent quark model approximation to the same process. The latter es timate is proportional to 1/m(u)(2), where m(u) similar or equal to <( Lambda)over bar>(u) 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 m(u) similar or equal to 480 MeV. This indicates that the constituent quark model may be used for estimates of the radiative ''annihilation'' contributi on to this and other radiative decays. We point out that this decay ma y be useful for the measurement of \V-ub\.