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

The relative branching fraction RK = Γ(D0 → K−μ+v)/Γ(D0 → μ−X) has been measured by Fermilab experiment E653, using D0 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 D0 decay variables Mmin and pTh. We find RK = 0.472 ± 0.051 (stat) ± 0.040 (sys), and use a world average of the D0 → Klv branching fraction to obtain the D0 inclusive semimuonic branching fraction B(D0 → μ+X) = (7.67 ± 1.13)%.