Observation of the Decay $B\to K{\ell }^{+}{\ell }^{-}$

Abstract

We report a search for the flavor-changing neutral current decay $B\to K^{(\ast )}{\ell }^{+}{\ell }^{-}$ using a 29.1 fb${}^{-1}$ data sample accumulated at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB $e^{+}{e}^{-}$ storage ring. We observe the decay process $B\to K{\ell }^{+}{\ell }^{-}(\ell =e,\mu )$, for the first time, with a branching fraction of $\mathcal{B}(B\to K{\ell }^{+}{\ell }^{-})=(0.75_{-0.21}^{+0.25}\pm 0.09)\times 10^{-6}$.

submitted to Physical Review Letter

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