Search for invisible decays of a dark photon using $e^{+}{e}^{-}$ annihilation data at BESIII

We report a search for a dark photon using $14.9$~fb${}^{-1}$ of $e^{+}{e}^{-}$ annihilation data taken at center-of-mass energies from 4.13 to 4.60~GeV with the BESIII detector operated at the BEPCII storage ring. The dark photon is assumed to be produced in the radiative annihilation process of $e^{+}{e}^{-}$ and to predominantly decay into light dark matter particles, which escape from the detector undetected. The mass range from 1.5 to 2.9~GeV is scanned for the dark photon candidate, and no significant signal is observed. The mass dependent upper limits at the 90$\mathrm{\%}$ confidence level on the coupling strength parameter $\epsilon$ for a dark photon coupling with an ordinary photon vary between $1.6\times {10}^{-3}$ and $5.7\times {10}^{-3}$.