The main aim of the NA64 experiment is to search for unknown particles from a hypothetical “dark sector”. These particles could be dark photons, which would carry a new force between visible matter and dark matter, in addition to gravity, or they could make up dark matter themselves.
For these searches, NA64 directs an electron beam of 100–150 GeV energy from the Super Proton Synchrotron (SPS) onto a fixed target. Researchers then look for unknown dark- sector particles produced by collisions between the SPS beam’s electrons and the target’s atomic nuclei. The search can either be done by looking for ordinary particles, such as electrons, into which the new particles would decay, or for the “missing” collision energy the dark-sector particles would carry away.
NA64 also searches for axions and axion-like particles that could explain the puzzling symmetry properties of the strong force or serve as a mediator of a new force. The experiment looks for the production of such particles in interactions between high-energy photons generated by the SPS beam’s electrons in the target and virtual photons from the target’s atomic nuclei.
The NA64 team will also use a muon beam from the SPS to search for new particles that interact predominantly with muons – heavier versions of the electron – and could explain the long-standing puzzle with the muon’s anomalous magnetic moment. It also plans to use hadronic beams from the SPS to look for invisible decays of neutral kaons and of other mesons to probe new physics phenomena, as well as to look for a candidate for mirror-type dark matter.