NA64 searching for hidden sectors at the CERN SPS

NA64 is a fixed target experiment at the CERN SPS to search for hidden sectors. In this talk, we will present our latest results on the search for a new sub-GeV vector gauge boson ($A'$) mediated dark matter ($\chi$) production. The $A'$, called dark photon, could be generated in the reaction $e^-Z \to e^-ZA’$ of 100 GeV electrons dumped against an active target which is followed by the prompt invisible decay $A'\to \chi\chi$. The experimental signature of this process would be a clean event with an isolated electron and large missing energy in the detector. This allows us to set new limits on the $\gamma-A'$ mixing strength and constrain models with light thermal dark matter or light scalar, Majorana or pseudo-Dirac thermal dark matter. Preliminary results on the search for the $X\to e^+e^-$ decay of a new light $X$ boson which could explain a recently observed anomaly in the $^8$Be transitions will be also discussed.