Measurement of the B --> Xs l+ l- Branching Fraction Using a Sum over Exclusive Modes

Abstract

We present a measurement of the branching fraction for the flavor-changing neutral current process B --> Xs l+ l- based on a sample of 88.9 \times 10^6 Upsilon(4S) --> BBbar events recorded with the BaBar detector at the PEP-II e+e- storage ring. The final state is reconstructed from pairs of electrons or muons and a hadronic system consisting of one K+/- or K0s and up to two pions, with at most one pi0. Summing over both lepton flavors, we observe a signal of 41 +/- 10(stat) +/- 2(syst) events with a statistical significance of 4.6 sigmas. The inclusive branching fraction is determined to be BF(B --> Xs l+ l-) = [6.3 +/- 1.6(stat) +1.8 -1.5(syst)] 10^{-6} for m(l+ l-) > 0.2 GeV/c^2. All results are preliminary.