New constraints on ALP couplings to electrons and photons from ArgoNeuT and the MiniBooNE beam dump

Beam dumps and fixed-target experiments have been very sensitive probes of such particles and other physics beyond the Standard Model by considering the production of new states from the primary interaction in the beam dump. In a proton beam dump, there are many secondary interactions taking place in electromagnetic showers which may be additional production channels for pseudoscalar bosons or axionlike particles (ALPs). The targetless configuration of the MiniBooNE experiment, which collected data from 1.86 x 1020 protons impinging directly on the steel beam dump, is an excellent test of sensitivity to these production channels of ALPs in the MeV mass region. Using the null observation of the MiniBooNE dump mode data, we set new constraints on ALPs coupling to electrons and photons produced through a multitude of channels and detected via both scattering and decays in the MiniBooNE detector volume. We find that the null result rules out parameter space that was previously unconstrained by laboratory probes in the 10-100 MeV mass regime for both electron and photon couplings. Lastly, we make the case for performing a dedicated analysis with 1.25 x 1020 protons on target of data collected by the ArgoNeuT experiment, which we show to have complementary sensitivity and set the stage for future searches.