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We report the first measurement of the lepton forward-backward asymmetry${\cal A}_{\rm FB}$ as a function of the squared four-momentum of the dileptonsystem, $q^2$, for the electroweak penguin process $B \rightarrow X_s \ell^+\ell^-$ with a sum of exclusive final states, where $\ell$ is an electron or amuon and $X_s$ is a hadronic recoil system with an $s$ quark. The results arebased on a data sample containing $772\times10^6$ $B\bar{B}$ pairs recorded atthe $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$collider. ${\cal A}_{\rm FB}$ for the inclusive $B \rightarrow X_s \ell^+\ell^-$ is extrapolated from the sum of 10 exclusive $X_s$ states whoseinvariant mass is less than 2 GeV/$c^2$. For $q^2 > 10.2$ GeV$^2$/$c^2$, ${\calA}_{\rm FB} < 0$ is excluded at the 2.3$\sigma$ level, where $\sigma$ is thestandard deviation. For $q^2 < 4.3$ GeV$^2$/$c^2$, the result is within1.8$\sigma$ of the Standard Model theoretical expectation.

Measurement of the Lepton Forward-Backward Asymmetry in $B \rightarrow X_s \ell^+ \ell^-$ Decays with a Sum of Exclusive Modes