Measurements of the absolute branching fractions for the semileptonic decays D0 -> K-mu+nu_mu and D0 -> pi-mu+nu_mu

Based on the data sample of 33 pb$^{-1}$ collected at and around 3.773 GeV with the BESII detector at the BEPC collider, the absolute branching fractions for the semileptonic decays $D^0\to K^-\mu^+\nu_\mu$ and $D^0\to\pi^-\mu^+\nu_\mu$ have been measured. In the system recoiling against $7584\pm198\pm341$ singly tagged $\bar D^0$ mesons, $87.2\pm13.6$ events for $D^0\to K^-\mu^+\nu_\mu$ and $9.3\pm7.4$ events for $D^0\to\pi^-\mu^+\nu_\mu$ are observed. These yield the absolute branching fractions to be $BF(D^0\to K^-\mu ^+\nu_\mu)=(3.55\pm0.56\pm 0.59)%$ and $BF(D^0\to\pi^-\mu^+\nu_\mu)=(0.38\pm0.30\pm0.10)%$. The upper limit of the branching fraction for $D^0\to\pi^-\mu^+\nu_\mu$ is also set to be $BF(D^0\to\pi^-\mu^+\nu_\mu)<0.89%$ at 90% confidence level.