Precision Measurements of the Semileptonic Charm Decays $D^0 \to π^- \ell^+ ν$ and $D^0 \to K^- \ell^+ ν$

Abstract

We investigate the decays $D^0\toπ^-\ell^+ν$ and $D^0\to K^-\ell^+ ν$, where $\ell$ is $e$ or $μ$, using approximately 7 ${\rm fb}^{-1}$ of data collected with the CLEO III detector. We find $R_0\equiv {\cal B}(D^0\to π^-e^+ν)/{\cal B}(D^0\to K^-e^+ν)= 0.082 \pm 0.006 \pm 0.005$. Fits to the kinematic distributions of the data provide parameters describing the form factor of each mode. Combining the form factor results and $R_0$ gives $|f^π_{+}(0)|^2 |V_{cd}|^2/|f^K_{+}(0)|^2 |V_{cs}|^2 = 0.038^{+0.006+0.005}_{-0.007-0.003}$.