Study of the semileptonic charm decays D 0 → π - ℓ + v and D 0 → K - ℓ + v

We investigate the decays ${D}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\ell}}^{+}\ensuremath{\nu}$ and ${D}^{0}\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{\ensuremath{\ell}}^{+}\ensuremath{\nu}$, where $\ensuremath{\ell}$ is $e$ or $\ensuremath{\mu}$, using approximately $7\text{ }\text{ }{\mathrm{f}\mathrm{b}}^{\ensuremath{-}1}$ of data collected with the CLEO III detector. We find ${\mathrm{R}}_{0}\ensuremath{\equiv}\mathcal{B}({\mathrm{D}}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\mathrm{e}}^{+}\ensuremath{\nu})/\mathcal{B}({\mathrm{D}}^{0}\ensuremath{\rightarrow}{\mathrm{K}}^{\ensuremath{-}}{\mathrm{e}}^{+}\ensuremath{\nu})=0.082\ifmmode\pm\else\textpm\fi{}0.006\ifmmode\pm\else\textpm\fi{}0.005$. 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 $|{f}_{+}^{\ensuremath{\pi}}(0){|}^{2}|{V}_{cd}{|}^{2}/|{f}_{+}^{K}(0){|}^{2}|{V}_{cs}{|}^{2}={0.038}_{\ensuremath{-}0.007\ensuremath{-}0.003}^{+0.006+0.005}$.