Search for dark sector and rare decays at BESIII

Abstract

The BESIII experiment has collected a large data sample of charmonium, charm mesons, hyperons, and other light mesons. These data provide a unique opportunity to explore the dark sector and rare decays. We present recent dark sector results from the BESIII experiment, including searches for sub-GeV dark matter in $\eta \to {\pi }^0+\text{invisible}$ and $J/\psi \to \varphi +\text{invisible}$, searches for dark baryon particles in ${\Xi }^{-}\to {\pi }^{-}+\mathrm{invisible}$, and searches for light vector bosons in ${\chi }_{cJ}\to J/\psi X$, where $X\to e^{+}{e}^{-}$. In addition, we also present the recent rare decay searches, including a search for $\psi \to e\mu$, as well as searches for several baryon number and lepton number violation processes, and searches for various charmonium weak decays.

contribution to the 2026 Electroweak session of the 60th Rencontres de Moriond