Direct Measurements of the Branching Fractions for the Semileptonic Decays $D^0 \to K^-μ^+ν_μ$ and $D^0 \to π^-μ^+ν_μ$

Abstract

Based on the data sample of 33 pb$^{-1}$ collected at and around 3.773 GeV with the BES-II detector at the BEPC collider, the absolute branching fractions for the semileptonic decays $D^0\to K^-μ^+ν_μ$ and $D^0\toπ^-μ^+ν_μ$ have been measured. In the system recoiling against $7584\pm198\pm341$ singly tagged $\bar D^0$ mesons, $87.2\pm13.6$ events for $D^0\to K^-μ^+ν_μ$ and $9.3\pm7.4$ events for $D^0\toπ^-μ^+ν_μ$ are observed. These yield the absolute branching fractions to be $BF(D^0\to K^-μ^+ν_μ)= (3.55\pm0.56\pm0.59)%$ and $BF(D^0\toπ^-μ^+ν_μ)= (0.38\pm0.30\pm0.10)%$. The measured branching fraction for $D^0\to K^-μ^+ν_μ$ was previously used to determine the ratio $Γ(D^0\to K^-μ^+ν_μ)/ Γ(D^+\to \bar K^0μ^+ν_μ)$ combining the previously measured branching fraction for $D^+\to \bar K^0μ^+ν_μ$ by the BES Collaboration.