Search for sub-GeV invisible particles in inclusive decays of $J/\psi$ to $\varphi$

BESIII Collaboration, M. Ablikim, M. N. Achasov +696

A search for an invisible particle, $X$, with a mass between 0 and 0.96 $\text{GeV}/{\text{c}}^2$, is performed in the process $J/\psi \to \varphi +X$ using $(8774.0\pm39.4)\times…