# Dark Photon Search in the Mass Range Between 1.5 and 3.4 GeV/$c^2$

## TL;DR

This study searches for dark photons in the 1.5 to 3.4 GeV/c^2 mass range using electron-positron collision data, finding no evidence but setting competitive upper limits on their coupling strength.

## Contribution

First search for dark photons in this mass range at BESIII, providing new constraints on their properties with no observed signal.

## Key findings

- No significant dark photon signal observed.
- Set 90% CL upper limits on mixing strength.
- Provided competitive constraints compared to previous experiments.

## Abstract

Using a data set of 2.93 fb$^{-1}$ taken at a center-of-mass energy $\sqrt{s}$ = 3.773 GeV with the BESIII detector at the BEPCII collider, we perform a search for an extra U(1) gauge boson, also denoted as a dark photon. We examine the initial state radiation reactions $e^+e^-\rightarrow e^+e^-\gamma_{\rm ISR}$ and $e^+e^-\rightarrow \mu^+\mu^-\gamma_{\rm ISR}$ for this search, where the dark photon would appear as an enhancement in the invariant mass distribution of the leptonic pairs. We observe no obvious enhancement in the mass range between 1.5 and 3.4 GeV/$c^{2}$ and set a 90% confidence level upper limit on the mixing strength of the dark photon and the Standard Model photon. We obtain a competitive limit in the tested mass range.