Heavy axion opportunities at the DUNE near detector

Abstract

While the QCD axion is often considered to be necessarily light ($\ensuremath{\lesssim}\mathrm{eV}$), recent work has opened a viable and interesting parameter space for heavy axions, which solve both the strong $CP$ and the axion quality problems. These well-motivated heavy axions, as well as the generic axionlike particles, call for explorations in the GeV mass realm at collider and beam dump environments. The primary upcoming neutrino experiment, Deep Underground Neutrino Experiment, is simultaneously also a powerful beam dump experiment, enabled by its multipurpose near detector complex. In this study, we show with detailed analyses that the Deep Underground Neutrino Experiment near detector has a unique sensitivity to heavy axions for masses between 20 MeV and 2 GeV, complementary to other future experiments.