RARE DECAY B-]K-ASTERISK-GAMMA - A MORE PRECISE CALCULATION

Efforts to predict the rare exclusive decay B --> Kgamma from the wel l-known inclusive decay b --> sgamma are frustrated by the effect of t he large recoil momentum. We show how to reduce the large uncertainty in calculating this decay by relating B --> Kgamma to the semileptoni c process B --> rhoenuBAR using the heavy-quark symmetry in B decays a nd SU(3) flavor symmetry. A direct measurement of the q2 spectrum for the semileptonic decay can provide accurate information for the exclus ive rare decay.