Constraints on dark axion portal: Missing energy and fermion EDMs

We study a model in which a new interactions between the Standard Model (SM) photon and both the dark photon ( γ D ) and an axionlike particles (ALP or a ) are described by the dark axion portal operator. The implications of this dark axion portal scenario for electron fixed-target experiments are presented. In particular, we investigate the missing energy signatures associated with production of dark photons and their subsequent invisible decays into stable dark sector fermions, γ D → χ χ ¯ . We discuss the discovery potential for such a scenario and derive projected sensitivity curves for the NA 64 e and LDMX experiments. Furthermore, novel constraints of the NA 64 e for 9.37 × 10 11 electrons on target are derived by considering two production mechanisms for invisible states: (i) the bremsstrahlung-like emission of an a γ D pair, e N → e N γ * ( → a γ D ) , and (ii) the exclusive vector meson photoproduction, γ * N → N V , followed by the invisible decays of vector mesons, V → a γ D . Additionally, the constraints on the parameter space of C P -violating, fermion-specific ALP and dark photon couplings are established. These constraints are derived from current experimental bounds on the electric dipole moments (EDMs) of SM fermions, incorporating loop-induced contributions to the EDMs of the electron, muon, and neutron.