Chiral Perturbation Theory for $B \rightarrow D^*$ and $B \rightarrow D$ Semileptonic Transition Matrix Elements at Zero Recoil

Abstract

Heavy quark symmetry predicts the value of $B \rightarrow D$ and $B \rightarrow D^*$ transition matrix elements of the current $\bar c γ_μ(1 - γ_5)b$, at zero recoil (where in the rest frame of the $B$ the $D$ or $D^*$ is also at rest). We use chiral perturbation theory to compute the leading corrections to these predictions which are generated at low momentum, below the chiral symmetry breaking scale.