Direct measurement of the absolute branching fraction for $D^+ \to {\bar K}^0μ^+ν_μ$ and determination of $ Γ(D^0 \to K^-μ^+ν_μ)/Γ(D^+ \to {\bar K}^0μ^+ν_μ)$

Abstract

The absolute branching fraction for the decay $D^+ \to {\bar K}^0μ^+ν_μ$ is determined using $5321 \pm 149 \pm160$ singly tagged $D^-$ sample from the data collected around 3.773 GeV with the BESII detector at the BEPC collider. In the system recoiling against the singly tagged $D^-$ mesons, $28.7 \pm 6.4$ events for $D^+ \to {\bar K}^0μ^+ν_μ$ are observed. These yield the absolute branching fraction to be $BF(D^+ \to {\bar K}^0μ^+ν_μ) = (10.3\pm2.3\pm0.8)%$. The ratio of the two partial widths for the decays $D^0 \to K^-μ^+ν_μ$ and $D^+ \to {\bar K}^0μ^+ν_μ$ is determined to be $Γ(D^0 \to K^-μ^+ν_μ)/Γ(D^+ \to {\bar K}^0μ^+ν_μ) = 0.87 \pm 0.24 \pm 0.15$.