Direct Measurements of Absolute Branching Fractions for D0 and D+   Inclusive Semimuonic Decays
  By analyzing about 33 $\rm pb^{-1}$ data sample collected at and around 3.773 GeV with the BES-II detector at the BEPC collider, we directly measure the branching fractions for the neutral and charged $D$ inclusive semimuonic decays to be $BF(D^0 \to \mu^+ X) =(6.8\pm 1.5\pm 0.7)%$ and $BF(D^+ \to \mu^+ X) =(17.6 \pm 2.7 \pm 1.8)%$, and determine the ratio of the two branching fractions to be $\frac{BF(D^+ \to \mu^+ X)}{BF(D^0 \to \mu^+ X)}=2.59\pm 0.70 \pm 0.25$. 
BES Collaboration: M. Ablikim, et al