Study of the Rare Decay B Mesons Decaying to X Mesons Positive and Negative Leptons at BaBar

摘要

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 (yields) X(sub s)(ell)(sup +)(ell)(sup -) with a sample of 81.9 fb(sup -1), collected with the BABAR detector at the Stanford Linear Accelerator Center. The final state is reconstructed from e(sup +)e(sup -) or (mu)(sup +)(mu)(sup -) pairs and a hadronic system consisting of one K(sup (+-)) or K(sub s) and up to two pions, with at most one (pi)(sup 0). They observe a signal of 40 (+-) 10(stat) (+-) 2(syst) events and extract a branching fraction (Beta)(B (yields) X(sub s)(ell)(sup +)(ell)(sup -)) = (5.6 (+-) 1.5(stat) (+-) 0.6(exp. syst) (+-) 1.1(model syst)) x 10(sup -6) for m(sub ll) > 0.2 GeV.