Search for Leptonic Decays of Dark Photons at NA62

The NA62 experiment at CERN, configured in beam-dump mode, has searched for dark photon decays in flight to electron-positron pairs using a sample of 1.4×1017 protons on dump collected in 2021. No evidence for a dark photon signal is observed. The combined result for dark photon searches in lepton–antilepton final states is presented and a region of the parameter space is excluded at 90% confidence level, improving on previous experimental limits for dark photon mass values between 50 and 600 MeV/c2 and coupling values in the range 10−6 to 4×10−5. An interpretation of the e+e− search result in terms of the emission and decay of an axionlike particle is also presented. Published by the American Physical Society 2024