We measure the branching fraction for the flavor-changing neutral-current process $B\to X_s{\ell }^{+}{\ell }^{-}$ with a sample of $89\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ events recorded with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ storage ring. The final state is reconstructed from $e^{+}{e}^{-}$ or ${\mu }^{+}{\mu }^{-}$ pairs and a hadronic system $X_s$ consisting of one $K^{\pm }$ or $K_S^0$ and up to two pions, with at most one ${\pi }^0$. We observe a signal of $40\pm 10(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 2(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})$ events and extract the inclusive branching fraction $\mathcal{B}(B\to X_s{\ell }^{+}{\ell }^{-})=\mathbf{(}5.6\pm 1.5(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 0.6(\mathrm{e}\mathrm{x}\mathrm{p}\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\pm 1.1(\mathrm{m}\mathrm{o}\mathrm{d}\mathrm{e}\mathrm{l}\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\mathbf{)}\times {10}^{-6}$ for $m_{{\ell }^{+}{\ell }^{-}}>0.2\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{/}{c}^2$.

• Received 3 April 2004

DOI:https://doi.org/10.1103/PhysRevLett.93.081802