Measurement of the Differential Branching Fraction and Forward-Backward Asymmetry for B → K(*)l+ l-

We study B -> Kd(*)l(+)l(-) decays (l = e,u) based on a data sample of 657 x 10(6) B (B) over bar pairs collected with the Belle detector at the KEKB e(+)e(-) collider. We report the differential branching fraction, isospin asymmetry, K* polarization, and the forward-backward asymmetry (A(FB)) as functions of q(2) = M(ll)(2)c(2). The fitted A(FB) spectrum exceeds the standard model expectation by 2.7 standard deviations. The measured branching fractions are B(B -> K*l(+)l(-)) = (10: 7(-1.0)(+1.1)) x 10(-7) and B(B -> Kl(+)l(-)) = (4.8 (+0.5)(-0.4) +/- 0.3) x 10(-7), where the first errors are statistical and the second are systematic, with the muon to electron ratios R-K* = 0.83 +/- 0: 17 +/- 0.08 and R-K = 1.03 +/- 0.19 +/- 0.06.