First Observation of the Semileptonic Decay $\hat{I}{›}_c^{+}\to p{K}^{-}{e}^{+}\hat{I}{½}_e$

Abstract

Using $4.5{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data samples collected at the center-of-mass energies ranging from 4.600~GeV to 4.699~GeV with the BESIII detector at the BEPCII collider, a first study of the semileptonic decays $\hat{I}{›}_c^{+}\to p{K}^{-}{e}^{+}\hat{I}{½}_e$, $\hat{I}{›}_c^{+}\to \hat{I}›(1520)e^{+}\hat{I}{½}_e$ and $\hat{I}{›}_c^{+}\to \hat{I}›(1405)e^{+}\hat{I}{½}_e$ is performed. The $\hat{I}{›}_c^{+}\to p{K}^{-}{e}^{+}\hat{I}{½}_e$ decay is observed with a significance of $8.2\ddot{I}ƒ$ and the branching fraction is measured to be $\mathcal{B}(\hat{I}{›}_c^{+}\to p{K}^{-}{e}^{+}\hat{I}{½}_e)=(0.88\pm 0.17_{stat.}\pm 0.07_{syst.})\times 10^{-3}$. We also report evidence of $\hat{I}{›}_c^{+}\to \hat{I}›(1520)e^{+}\hat{I}{½}_e$ and $\hat{I}{›}_c^{+}\to \hat{I}›(1405)e^{+}\hat{I}{½}_e$ with significances of $3.3\ddot{I}ƒ$ and $3.2\ddot{I}ƒ$, respectively, and measure $\mathcal{B}(\hat{I}{›}_c^{+}\to \hat{I}›(1520)e^{+}\hat{I}{½}_e)=(1.02\pm 0.52_{stat.}\pm 0.11_{syst.})\times 10^{-3}$ and $\mathcal{B}(\hat{I}{›}_c^{+}\to \hat{I}›(1405)[\to p{K}^{-}]e^{+}\hat{I}{½}_e)=(0.42\pm 0.19_{stat.}\pm 0.04_{syst.})\times 10^{-3}$. Combining these with the inclusive semileptonic $\hat{I}{›}_c^{+}$ branching fraction measured by BESIII, the relative fraction is determined to be $[\mathcal{B}(\hat{I}{›}_c^{+}\to p{K}^{-}{e}^{+}\hat{I}{½}_e)/\mathcal{B}(\hat{I}{›}_c^{+}\to X{e}^{+}\hat{I}{½}_e)]=(2.1\pm 0.4_{stat.}\pm 0.2_{syst.})\%$, which provides a clear confirmation that semileptonic $\hat{I}{›}_c^{+}$ decays are not saturated by the $\hat{I}›{\ell }^{+}\hat{I}{½}_{\ell }$ final state.

13 pages, 9 figures and 2 tables