Measurement of the Electroweak Penguin ProcessB→Xsℓ+ℓ−

We report the first measurement of the branching fraction for the inclusive decay $B\to X_s{\ell }^{+}{\ell }^{-}$, where $\ell$ is either an electron or a muon, and $X_s$ is a hadronic recoil system that contains an $s$ quark. We analyzed a data sample of $65.4\times {10}^6$ $B$ meson pairs collected with the Belle detector at the KEKB $e^{+}{e}^{-}$ asymmetric-energy collider. We find $\mathcal{B}(B\to X_s{\ell }^{+}{\ell }^{-})=[6.1\pm 1.4(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}{)}_{-1.1}^{+1.4}(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})]\times {10}^{-6}$ for dilepton masses greater than $0.2\mathrm{G}\mathrm{e}\mathrm{V}/c^2$.