  Heavy QCD axions are well-motivated extensions of the QCD axion that address
the quality problem while still solving the strong CP problem. Owing to the
gluon coupling, critical for solving the strong CP problem, these axions can be
produced in significant numbers in beam dump and collider environments for
axion decay constants as large as PeV, relevant for addressing the axion
quality problem. In addition, if these axions have leptonic couplings, they can
give rise to long-lived decay into lepton pairs, in particular, dominantly into
muons above the dimuon threshold and below the GeV scale in a broad class of
axion models. Considering existing constraints, primarily from rare meson
decays, we demonstrate that current and future neutrino facilities and
long-lived particle searches have the potential to probe significant parts of
the heavy QCD axion parameter space via dimuon final states.
