Measurement of Γ(D0 → K−μ+ν)/Γ(D0→ μ+X using a D∗ tag

Abstract The relative branching fraction R K = Γ ( D 0 → K − μ + v )/ Γ ( D 0 → μ − X ) has been measured by Fermilab experiment E653, using D 0 mesons produced by 600 GeV π − . The semimuonic decay sample of 232 events was identified by the decay chain D ∗+ → D 0 π + , D 0 → μ + h − X , where h is a hadron. The Kμv component was extracted from the joint distribution of these events in the D 0 decay variables M min and p Th . We find R K = 0.472 ± 0.051 (stat) ± 0.040 (sys), and use a world average of the D 0 → Klv branching fraction to obtain the D 0 inclusive semimuonic branching fraction B ( D 0 → μ + X ) = (7.67 ± 1.13)%.