HQET and form factor effects inB→K(*)ℓ+ℓ−

We examine the rates for the exclusive decays $B\to K^{\mathrm{}(*)\mathrm{}}{\ell }^{+}{\ell }^{-}$. We use the scaling predictions of the heavy quark effective theory to extract the necessary form factors from fits to data available in $D\to K^{\mathrm{}(*)\mathrm{}}\ell \nu$, $B\to K^{\mathrm{}(*)\mathrm{}}{\psi }^{(\prime )}$, and the rare decay $B\to K^{*}\gamma$. We use different parametrizations of form factors, and find that integrated decay rates are not very sensitive to the forms chosen. However, the decay spectra and the forward-backward asymmetry in $B\to K^{*}{\ell }^{+}{\ell }^{-}$ are sensitive to the forms chosen for the form factors, while the lepton polarization asymmetry in ${\overline{B}}^0\to {\overline{K}}^{\mathrm{}(*)0}{\mu }^{+}{\mu }^{-}$ is largely independent of the choice of form factors. Contributions from charmonium resonances dominate the spectra and integrated rates. In our "best" scenario, we find $\mathcal{B}({\overline{B}}^0\to {\overline{K}}^0{\mu }^{+}{\mu }^{-})=2.0\mathrm{}\pm 0.3\times {10}^{-6\mathrm{}}$ and $\mathcal{B}({\overline{B}}^0\to {\overline{K}}^{\mathrm{}(*)0}{\mu }^{+}{\mu }^{-})=8.1\mathrm{}\pm 2.0\times {10}^{-6\mathrm{}}$. We also make predictions for other polarization observables in these decays.