Measurement of the $D^0\to K^{-}\ddot{I}{€}^{+}{e}^{+}{e}^{-}$ branching fraction and search for $D^0\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}{e}^{+}{e}^{-}$ and $D^0\to K^{+}{K}^{-}{e}^{+}{e}^{-}$ decays at Belle

Abstract

We present a study of the rare charm meson decays $D^0\to K^{+}{K}^{-}{e}^{+}{e}^{-}$, $\ddot{I}{€}^{+}\ddot{I}{€}^{-}{e}^{+}{e}^{-}$, and $K^{-}\ddot{I}{€}^{+}{e}^{+}{e}^{-}$ using a 942 fb${}^{-1}$ data set collected by the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We use $D^0$ candidates identified by the charge of the pion in $D^{\ast }\to D^0\ddot{I}€$ decays and normalize the branching fractions to $D^0\to K^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}{€}^{+}$ decays. The branching fraction for decay $D^0\to K^{-}\ddot{I}{€}^{+}{e}^{+}{e}^{-}$ is measured to be (39.6 $\pm$ 4.5 (stat) $\pm$ 2.9 (syst)) $\times$ $10^{-7}$, with the dielectron mass in the $\ddot{I}/\ddot{I}‰$ mass region $675<m_{ee}<875$ MeV$/c^2$. We also search for $D^0\to h^{-}{h}^{(\prime )+}{e}^{+}{e}^{-}$ ($h^{(\prime )}=K,\ddot{I}€$) decays with the dielectron mass near the $\hat{I}\cdot$ and $\ddot{I}•$ resonances, and away from these resonances for the $K^{+}{K}^{-}{e}^{+}{e}^{-}$ and $\ddot{I}{€}^{+}\ddot{I}{€}^{-}{e}^{+}{e}^{-}$ modes. For these modes, we find no significant signals and set 90$\%$ confidence level upper limits on their branching fractions at the $\mathcal{O}$(10${}^{-7}$) level.