Measurement of the inclusive branching fraction for $\ddot{I}ˆ(3686)\to K_S^0+\text{anything}$

Abstract

Using 5.9~pb${}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected at center-of-mass energies from 3.640 to 3.701 GeV with the BESIII detector at the BEPCII Collider, we measure the observed cross sections of $e^{+}{e}^{-}\to K_S^{0}X$ (where $X=\text{anything}$). From a fit to these observed cross sections with the sum of continuum and $\ddot{I}ˆ(3686)$ and $J/\ddot{I}ˆ$ Breit-Wigner functions and considering initial state radiation and the BEPCII beam energy spread, we obtain for the first time the product of $\ddot{I}ˆ(3686)$ leptonic width and inclusive decay branching fraction $\hat{I}{“}_{\ddot{I}ˆ(3686)}^{ee}\mathcal{B}(\ddot{I}ˆ(3686)\to K_S^{0}X)=(373.8\pm 6.7\pm 20.0)$ eV, and assuming $\hat{I}{“}_{\ddot{I}ˆ(3686)}^{ee}$ is $(2.33\pm 0.04)$ keV from PDG value, we measure $\mathcal{B}(\ddot{I}ˆ(3686)\to K_S^{0}X)=(16.04\pm 0.29\pm 0.90)\%$, where the first uncertainty is statistical and the second is systematic.

11 pages, 5 figures