B -> K^* gamma from D -> K^* l nu

TL;DR

This paper predicts the B -> K^* gamma decay rate by relating it to measured D -> K^* l nu form factors using heavy quark symmetries, and finds good agreement with experimental data.

Contribution

It introduces a novel method combining heavy quark spin and flavor symmetries to predict rare B decay rates from semileptonic D decays.

Findings

Prediction agrees well with experimental data

Implications for |Vub| extraction from B -> rho l nu

Demonstrates effectiveness of symmetry-based extrapolation

Abstract

The B -> K^* gamma branching fraction is predicted using heavy quark spin symmetry at large recoil to relate the tensor and (axial-)vector form factors, using heavy quark flavor symmetry to relate the B decay form factors to the measured D -> K^* l nu form form factors, and extrapolating the semileptonic B decay form factors to large recoil assuming nearest pole dominance. This prediction agrees with data surprisingly well, and we comment on its implications for the extraction of |Vub| from B -> rho l nu.