Improved Upper Limits on the Flavor-Changing Neutral Current Decays $B \to K ℓ^{+} ℓ^{-}$ and $B \to K^{*} (892) ℓ^{+} ℓ^{-}$

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15 October 2001

journal article
research article
Published by American Physical Society (APS) in Physical Review Letters

Vol. 87 (18) , 181803
https://doi.org/10.1103/physrevlett.87.181803

Abstract

We have searched a sample of

9.6 \times 10^{6}

B \bar{B}

events for the flavor-changing neutral current decays

B \to K ℓ^{+} ℓ^{-}

and

B \to K^{*} (892) ℓ^{+} ℓ^{-}

. We subject the latter decay to the requirement that the dilepton mass

m_{ℓ ℓ}

exceed 0.5 GeV. There is no indication of a signal. We obtain the

90 %

confidence level upper limits

B (B \to K ℓ^{+} ℓ^{-}) < 1.7 \times 10^{- 6}

and

B (B \to K^{*} (892) ℓ^{+} ℓ^{-})_{m_{ℓ ℓ} > 0.5 GeV} < 3.3 \times 10^{- 6}

. We also obtain an upper limit on the weighted average

0.65 B (B \to K ℓ^{+} ℓ^{-}) + 0.35 B (B \to K^{*} (892) ℓ^{+} ℓ^{-})_{m_{ℓ ℓ} > 0.5 GeV} < 1.5 \times 10^{- 6}

. The weighted-average limit is only

50 %

above the standard model prediction.

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