Weak Radiative B Decays

Abstract

We study the (tree-level) weak radiative decays of $B$ mesons. We present a numerical estimate for the inclusive $b \to X_c \gamma (\gamma)$ modes based on the free-quark decay. We then review what is known for the $B \to D^\star \gamma$ modes in the framework of heavy quark effective theory and chiral perturbation theory. Finally, we extend these ideas to the double radiative decay modes $B \to D \gamma \gamma$. We find that the $b \to X_c \gamma \gamma$ rate is about an order of magnitude larger than the corresponding $b \to X_s \gamma \gamma$ rate. We also find the branching ratio for the $B \to D \gamma \gamma$ mode with most favorable CKM angles at the few $\times10^{-8}$ level, comparable to predictions for $B \to K \gamma \gamma$.