Constraint on the coupling of axionlike particles to matter via an ultracold neutron gravitational experiment

We present a new constraint for the axion monopole-dipole coupling in the range of $1\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$\char21{}a few mm, previously unavailable for experimental study. The constraint was obtained using our recent results on the observation of neutron quantum states in the Earth's gravitational field. We exploit the ultimate sensitivity of ultracold neutrons (UCN) in the lowest gravitational states above a material surface to any additional interaction between the UCN and the matter, if the characteristic interaction range is within the mentioned domain.