Search for the Decay B+→K+τ∓μ±

Abstract

We present a search for the lepton flavor violating decay B + → K + τ ∓ μ ± using 383 × 10 6 B ¯¯¯ B events collected by the BABAR experiment. The branching fraction for this decay can be substantially enhanced in new physics models. The kinematics of the tau from the signal B decay are inferred from the K + , μ , and other B in the event, which is fully reconstructed in one of a variety of hadronic decay modes, allowing the signal B candidate to be fully reconstructed. We observe no excess of events over the expected background and set a limit of B ( B + → K + τ μ ) < 7.7 × 10 − 5 at 90% confidence level, where the branching fraction is for the sum of the K + τ − μ + and K + τ + μ − final states. We use this result to improve a model-independent bound on the energy scale of flavor-changing new physics.