Improved Upper Limits on the FCNC Decays $B\to K\ell^{+}\ell^{-}$ and $B\to K^{*}(892)\ell^{+}\ell^{-}$

TL;DR

This paper reports improved upper limits on the rare flavor-changing neutral current decays of B mesons to K and K* mesons with lepton pairs, constraining new physics beyond the Standard Model.

Contribution

The study provides the most stringent upper limits to date on these decay branching fractions, narrowing the gap to Standard Model predictions.

Findings

No signal observed for the decays.

Upper limits on branching fractions are set at 1.7 and 3.3 times 10^{-6}.

Weighted average limit is only 50% above Standard Model expectations.

Abstract

We have searched a sample of 9.6 million BBbar events for the flavor-changing neutral current decays B -> K l^+ l^- and B -> K^*(892) l^+ l^-. We subject the latter decay to the requirement that the dilepton mass exceed 0.5 GeV. There is no indication of a signal. We obtain the 90% confidence level upper limits on the branching fractions Br(B -> K l^+ l^-) < 1.7 \times 10^{-6} and Br(B -> K^*(892) l^+ l^-) < 3.3 \times 10^{-6}. We also obtain an upper limit on the weighted average 0.65 Br(B -> K l^+ l^-) + 0.35 Br(B -> K^*(892) l^+ l^-) < 1.5 \times 10^{-6}. The weighted-average limit is only 50% above the Standard Model prediction.