Observation of the semileptonic decays $D^0\to K_S^0\ddot{I}{€}^{-}\ddot{I}{€}^0{e}^{+}\hat{I}{½}_e$ and $D^{+}\to K_S^0\ddot{I}{€}^{+}\ddot{I}{€}^{-}{e}^{+}\hat{I}{½}_e$

Abstract

By analyzing $e^{+}{e}^{-}$ annihilation data corresponding to an integrated luminosity of 2.93 $\mathrm{f}{\mathrm{b}}^{-1}$ collected at a center-of-mass energy of 3.773 GeV with the \text{BESIII} detector, the first observation of the semileptonic decays $D^0\to K_S^0\ddot{I}{€}^{-}\ddot{I}{€}^0{e}^{+}\hat{I}{½}_e$ and $D^{+}\to K_S^0\ddot{I}{€}^{+}\ddot{I}{€}^{-}{e}^{+}\hat{I}{½}_e$ is reported. With a dominant hadronic contribution from $K_1(1270)$, the branching fractions are measured to be $\mathcal{B}(D^0\to K_1(1270{)}^{-}(\to K_S^0\ddot{I}{€}^{-}\ddot{I}{€}^0)e^{+}\hat{I}{½}_e)=(1.69_{-0.46}^{+0.53}\pm 0.15)\times 10^{-4}$ and $\mathcal{B}(D^{+}\to {\bar{K}}_1(1270{)}^0(\to K_S^0\ddot{I}{€}^{+}\ddot{I}{€}^{-})e^{+}\hat{I}{½}_e)=(1.47_{-0.40}^{+0.45}\pm 0.20)\times 10^{-4}$ with statistical significance of 5.4$\ddot{I}ƒ$ and 5.6$\ddot{I}ƒ$, respectively. When combined with measurements of the $K_1(1270)\to K^{+}\ddot{I}{€}^{-}\ddot{I}€$ decays, the absolute branching fractions are determined to be $\mathcal{B}(D^0\to K_1(1270{)}^{-}{e}^{+}\hat{I}{½}_e)=(1.05_{-0.28}^{+0.33}\pm 0.12\pm 0.12)\times 10^{-3}$ and $\mathcal{B}(D^{+}\to {\bar{K}}_1(1270{)}^0{e}^{+}\hat{I}{½}_e)=(1.29_{-0.35}^{+0.40}\pm 0.18\pm 0.15)\times 10^{-3}$. The first and second uncertainties are statistical and systematic, respectively, and the third uncertainties originate from the assumed branching fractions of the $K_1(1270)\to K\ddot{I}€\ddot{I}€$ decays.

19pages