SEARCH FOR PRODUCTION OF AN INVISIBLE DARK PHOTON FROM π 0 DECAYS AT NA62

A search for an invisible dark photon A has been performed, exploiting theefficient photon-veto capability and high resolution tracking of the NA62detector at CERN. The signal stems from the chain $K^+ \rightarrow \pi^+ \pi^0$ followed by $\pi^0 \rightarrow A' \gamma$. No significant statistical excess has been identified. Upper limits onthe dark photon coupling to the ordinary photon as a function of the dark photonmass have been set, improving on the previous limits over the mass range 60–110MeV/c$^2$ .