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

Abstract

We have searched a sample of 9.6 x 10(6) B(B) over bar 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 x 10(-6) and B(B <right arrow> K*(892)l(+)l(-))m(ll>0.5GeV) < 3.3 x 10(-6). We also obtain an upper limit on the weighted average 0.65B(B <right arrow> Kl(+)l(-)) + 0.35B(B --> K*(892)l(+)l(-))m(ll>0.5GeV) < 1.5 x 10(-6). The weighted-average limit is only 50% above the standard model prediction.