NA64—Search for Dark Sector Particles

NA64 is a fixed target dark matter experiment at the CERN SPS searching for dark photons ($A'$) in the sub-GeV mass range at the secondary beamlines of the CERN North Area. It uses the electron beam from the H4 beamline and the muon beam from the M2 beamline with an aim to detect the dark photons from the interaction of the beam in an active target, an electromagnetic calorimeter (ECAL). This chapter includes the description of the experiment including the signature to hunt for these elusive particles as well as the current results. Some of the future planned searches will also be described.