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.
Categories: hep-ph hep-ex