ISSN - 00319007, EISSN - 10797114, Physical Review Letters, 2009, vol. 103, p. -
Measurement of the differential branching fraction and forward-backward asymmetry for b→K(*)l+l-
We study B→K(*)ℓ+ℓ- decays (ℓ=e, μ) based on a data sample of 657×106 BB̄ 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 (AFB) as functions of q2=Mℓ2c2. The fitted AFB 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±0.9)×10-7 and B(B→Kℓ+ℓ-)=(4.8-0.4+0.5±0.3)×10-7, where the first errors are statistical and the second are systematic, with the muon to electron ratios RK*=0.83±0.17±0.08 and RK=1.03±0.19±0. 06. © 2009 The American Physical Society.