We study $B\ensuremath{\rightarrow}{K}^{(*)}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decays ($\ensuremath{\ell}=e$, $\ensuremath{\mu}$) based on a data sample of $657\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $B\overline{B}$ pairs collected with the Belle detector at the KEKB ${e}^{+}{e}^{\ensuremath{-}}$ collider. We report the differential branching fraction, isospin asymmetry, ${K}^{*}$ polarization, and the forward-backward asymmetry (${A}_{\mathrm{FB}}$) as functions of ${q}^{2}={M}_{\ensuremath{\ell}\ensuremath{\ell}}^{2}{c}^{2}$. The fitted ${A}_{\mathrm{FB}}$ spectrum exceeds the standard model expectation by 2.7 standard deviations. The measured branching fractions are $\mathcal{B}(B\ensuremath{\rightarrow}{K}^{*}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}})=({10.7}_{\ensuremath{-}1.0}^{+1.1}\ifmmode\pm\else\textpm\fi{}0.9)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ and $\mathcal{B}(B\ensuremath{\rightarrow}K{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}})=({4.8}_{\ensuremath{-}0.4}^{+0.5}\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$, where the first errors are statistical and the second are systematic, with the muon to electron ratios ${R}_{{K}^{*}}=0.83\ifmmode\pm\else\textpm\fi{}0.17\ifmmode\pm\else\textpm\fi{}0.08$ and ${R}_{K}=1.03\ifmmode\pm\else\textpm\fi{}0.19\ifmmode\pm\else\textpm\fi{}0.06$.
Measurement of the Differential Branching Fraction and Forward-Backward Asymmetry forB→K(*)l+l− | Litlas
