Rare decayB→K*γ: A more precise calculation

Efforts to predict the rare exclusive decay $B\to K^{*}\gamma$ from the well-known inclusive decay $b\to s\gamma$ are frustrated by the effect of the large recoil momentum. We show how to reduce the large uncertainty in calculating this decay by relating $B\to K^{*}\gamma$ to the semileptonic process $B\to \rho e\overline{\nu }$ using the heavy-quark symmetry in $B$ decays and SU(3) flavor symmetry. A direct measurement of the $q^2$ spectrum for the semileptonic decay can provide accurate information for the exclusive rare decay.