Direct Measurements of the Branching Fractions for $D^0\to K^{-}{e}^{+}\hat{I}{½}_e$ and $D^0\to \ddot{I}{€}^{-}{e}^{+}\hat{I}{½}_e$ and Determinations of the Form Factors $f_{+}^K(0)$ and $f^{\ddot{I}}{€}_{+}(0)$

Abstract

The absolute branching fractions for the decays $D^0\to K^{-}{e}^{+}\hat{I}{½}_e$ and $D^0\to \ddot{I}{€}^{-}{e}^{+}\hat{I}{½}_e$ are determined using $7584\pm 198\pm 341$ singly tagged ${\bar{D}}^0$ sample from the data collected around 3.773 GeV with the BES-II detector at the BEPC. In the system recoiling against the singly tagged ${\bar{D}}^0$ meson, $104.0\pm 10.9$ events for $D^0\to K^{-}{e}^{+}\hat{I}{½}_e$ and $9.0\pm 3.6$ events for $D^0\to \ddot{I}{€}^{-}{e}^{+}\hat{I}{½}_e$ decays are observed. Those yield the absolute branching fractions to be $BF(D^0\to K^{-}{e}^{+}\hat{I}{½}_e)=(3.82\pm 0.40\pm 0.27)$ and $BF(D^0\to \ddot{I}{€}^{-}{e}^{+}\hat{I}{½}_e)=(0.33\pm 0.13\pm 0.03)$. The vector form factors are determined to be $|f_{+}^K(0)|=0.78\pm 0.04\pm 0.03$ and $|f^{\ddot{I}}{€}_{+}(0)|=0.73\pm 0.14\pm 0.06$. The ratio of the two form factors is measured to be $|f^{\ddot{I}}{€}_{+}(0)/f_{+}^K(0)|=0.93\pm 0.19\pm 0.07$.

6 pages, 5 figures