# Search for rare decay $J/ \psi \to \phi e^+ e^-$

## TL;DR

This study searches for the rare decay $J/\psi \to \phi e^+ e^-$ using a large dataset, finds no signal, and sets an upper limit on its branching fraction, which is still above Standard Model expectations.

## Contribution

First search for the decay $J/\psi \to \phi e^+ e^-$ with a large dataset, establishing an upper limit on its branching fraction.

## Key findings

- No signal observed for the decay.
- Upper limit on branching fraction set at $1.2 \times 10^{-7}$.
- Limit is about ten times higher than Standard Model prediction.

## Abstract

Using a data sample of $448.1\times10^6$ $\psi(3686)$ events collected at $\sqrt{s}=$ 3.686 GeV with the BESIII detector at the BEPCII, we search for the rare decay $J/\psi \to \phi e^+ e^-$ via $\psi(3686) \to \pi^+\pi^- J/\psi $. No signal events are observed and the upper limit on the branching fraction is set to be $\mathcal{B}(J/\psi \to \phi e^+ e^-) < 1.2 \times 10^{-7}$ at the 90\% confidence level, which is still about one order of magnitude higher than the Standard Model prediction.