# Observation of $\psi(3686) \rightarrow e^{+}e^{-}\chi_{cJ}$ and $\chi_{cJ} \rightarrow e^{+}e^{-}J/\psi$

## TL;DR

This paper reports the first observation and measurement of branching fractions for specific rare decays of the $ ext{psi}(3686)$ and $ ext{chi}_cJ$ particles into electron-positron pairs and J/psi, using a large dataset from BESIII.

## Contribution

First observation of $ ext{psi}(3686)
ightarrow e^{+}e^{-} ext{chi}_cJ$ and $ ext{chi}_cJ
ightarrow e^{+}e^{-}J/ ext{psi}$ decays with measured branching fractions.

## Key findings

- Branching fractions for $ ext{psi}(3686)$ decays into $e^{+}e^{-} ext{chi}_cJ$ measured.
- Branching fractions for $ ext{chi}_cJ$ decays into $e^{+}e^{-}J/ ext{psi}$ measured.
- Ratios of branching fractions relative to radiative decays reported.

## Abstract

Using $4.479 \times 10^{8}$ $\psi(3686)$ events collected with the BESIII detector, we search for the decays $\psi(3686) \rightarrow e^{+}e^{-}\chi_{c0,1,2}$ and $\chi_{c0,1,2} \rightarrow e^{+}e^{-}J/\psi$. The decays $\psi(3686) \rightarrow e^{+}e^{-}\chi_{c0,1,2}$ and $\chi_{c0,1,2} \rightarrow e^{+}e^{-}J/\psi$ are observed for the first time. The measured branching fractions are $\mathcal{B}(\psi(3686) \rightarrow e^{+}e^{-}\chi_{c0,1,2}) = (11.7 \pm 2.5 \pm 1.0)\times10^{-4}$, $(8.6 \pm 0.3 \pm 0.6)\times10^{-4}$, $(6.9 \pm 0.5 \pm 0.6)\times10^{-4}$, and $\mathcal{B}(\chi_{c0,1,2} \rightarrow e^{+}e^{-}J/\psi) = (1.51 \pm 0.30 \pm 0.13)\times10^{-4}$, $(3.73 \pm 0.09 \pm 0.25)\times10^{-3}$, $(2.48 \pm 0.08 \pm 0.16)\times10^{-3}$. The ratios of the branching fractions $\frac{\mathcal{B}(\psi(3686) \rightarrow e^{+}e^{-}\chi_{c0,1,2})}{\mathcal{B}(\psi(3686) \rightarrow \gamma\chi_{c0,1,2})}$ and $\frac{\mathcal{B}(\chi_{c0,1,2} \rightarrow e^{+}e^{-}J/\psi)}{\mathcal{B}(\chi_{c0,1,2} \rightarrow \gamma J/\psi)}$ are also reported.