Flavor-changing neutral current transitions are forbidden at tree level in the Standard Model and can only occur via higher order diagrams. Since the amplitudes for such loops are dominated by the heaviest known particles, and non-SM effects are expected to contribute at the same order as the SM, such processes are an ideal place to look for new physics.
We present a measurement of the inclusive branching fraction for the flavor-changing neutral current process B [arrow right] Xs [cursive l]+ [cursive l]- with a sample of 81.9 fb-1 , collected with the BABAR detector at the Stanford Linear Accelerator Center. The final state is reconstructed from e+e - or μ+ μ- pairs and a hadronic system consisting of one K± or K s and up to two pions, with at most one π0 . We observe a signal of 40 ± 10(stat) ± 2(syst) events and extract a branching fraction [Special characters omitted.] (B [arrow right] Xs [cursive l] + [cursive l]- ) = (5.6 ± 1.5(stat) ± 0.6(exp. syst) ± 1.1(model syst)) × 10-6 for mll > 0.2 GeV.