NA64

"The NA64 experiment (known as P348 at the proposal stage) is a fixed-​target experiment at the CERN SPS combining the active beam dump and missing energy techniques to search for rare events. The experiment will build and operate a fully hermetic detector placed on the H4 beam line with the primary goal to search for light dark bosons (Z') from dark sector that are coupled to photons, e.g. dark photons (A'), or sub-​GeV Z' coupled only to quarks. In some cases the Z' is coupled only to µ or tau, so we call the Z′ the dark leptonic gauge boson. The experiment is also capable to search for K_L -> invisible decay, which is complementary to K+ -> 𝜋+ + ν ν, and invisible decays of 𝜋0, η, η′, K_S mesons."