Precision Measurements of $\mathcal{B}[\ddot{I}ˆ(3686)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ]$ and $\mathcal{B}[J/\ddot{I}ˆ\to l^{+}{l}^{-}]$

Abstract

Based on $(106.41\pm 0.86)\times 10^6$ $\ddot{I}ˆ(3686)$ events collected with the BESIII detector at the BEPCII collider, the branching fractions of $\ddot{I}ˆ(3686)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ$, $J/\ddot{I}ˆ\to e^{+}{e}^{-}$, and $J/\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ are measured. We obtain $\mathcal{B}[\ddot{I}ˆ(3686)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ]=(34.98\pm 0.02\pm 0.45)$, $\mathcal{B}[J/\ddot{I}ˆ\to e^{+}{e}^{-}]=(5.983\pm 0.007\pm 0.037)$ and $\mathcal{B}[J/\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}]=(5.973\pm 0.007\pm 0.038)$. The measurement of $\mathcal{B}[\ddot{I}ˆ(3686)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ]$ confirms the CLEO-c measurement, and is apparently larger than the others. The measured $J/\ddot{I}ˆ$ leptonic decay branching fractions agree with previous experiments within one standard deviation. These results lead to $\mathcal{B}[J/\ddot{I}ˆ\to l^{+}{l}^{-}]=(5.978\pm 0.005\pm 0.040)$ by averaging over the $e^{+}{e}^{-}$ and $\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ channels and a ratio of $\mathcal{B}[J/\ddot{I}ˆ\to e^{+}{e}^{-}]/\mathcal{B}[J/\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}]=1.0017\pm 0.0017\pm 0.0033$, which tests $e$-$\hat{I}¼$ universality at the four tenths of a percent level. All the measurements presented in this paper are the most precise in the world to date.

13 pages, 6 figures; To be submitted to PRD