The Rare Decay $B\to K^{\ast }\gamma$: A More Precise Calculation

Abstract

Efforts to predict the rare exclusive decay $B\to K^{\ast }\gamma$ 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 $B\to K^{\ast }\gamma$ to the semileptonic process $B\to \rho e\bar{\nu }$ 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.

Comments: 15 pages, UTPT-93-02, in REVTEX with one figure in eps