Improved upper limits on the flavor-changing neutral current decays B→Kℓ⁺ℓ- and B→K*(892)ℓ⁺ℓ-

We have searched a sample of 9.6×106 B¯B events for the flavor-changing neutral current decays B→Kℓ⁺ℓ- and B→K*(892)ℓ⁺ℓ-. We subject the latter decay to the requirement that the dilepton mass m_ℓℓ exceed 0.5 GeV. There is no indication of a signal. We obtain the 90% confidence level upper limits B(B→Kℓ⁺ℓ-) < 1.7×10^-6 and B(B→K*(892)ℓ⁺ℓ-)_{mℓℓ>0.5Gev}< 3.3×10^-6. We also obtain an upper limit on the weighted average 0.65B B(B→Kℓ⁺ℓ-)+0.35B(B→K*(892)ℓ⁺ℓ-)_{mℓℓ>0.5Gev} < 1.5×10^-6. The weighted-average limit is only 50% above the standard model prediction.