$\eta^{(\prime)}$ productions in semileptonic B decays

Inspired by the new measurements on $B^{-}\to \eta^{(\prime)}\ell \bar\nu_{\ell}$ from the BaBar Collaboration, we examine the constraint on the flavor-singlet mechanism, proposed to understand the large branching ratios for $B\to \eta^{\prime} K$ decays. Based on the mechanism, we study the decays of $\bar B_{d,s}\to \eta^{(\prime)} \ell^{+} \ell^{-}$ and find that they are sensitive to the flavor-singlet effects. In particular, we show that the decay branching ratios of $\bar B_{d,s}\to \eta^{\prime} \ell^{+} \ell^{-}$ can be as large as $O(10^{-8})$ and $O(10^{-6})$, respectively.