HQET and form factor effects in B→K(*)l+l-

We examine the rates for the exclusive decays B→K(*)l+l-. We use the scaling predictions of the heavy quark effective theory to extract the necessary form factors from fits to data available in D→K(*)lν, B→K(*)ψ('), and the rare decay B→K*γ. 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→K*l+l- are sensitive to the forms chosen for the form factors, while the lepton polarization asymmetry in bar B0→ bar K(*)0μ+μ- is largely independent of the choice of form factors. Contributions from charmonium resonances dominate the spectra and integrated rates. In our open-quote open-quote best close-quote close-quote scenario, we find B(bar B0→ bar K0μ+μ-)=2.0±0.3x10-6 and B(bar B0→ bar K*0μ+μ-)=8.1±2.0x10-6. We also make predictions for other polarization observables in these decays. copyright 1996 The American Physical Society