Experiments with Gravitationally-bound Ultracold Neutrons at the European Spallation Source ESS

Experiments with gravitationally-bound ultracold neutrons have made substantial progress in the last decade. They have been contributing to answer scientific questions ranging from gravity tests at micron distances, the direct search for dark matter particles as axions, and dark energy realizations. Comparing the present accuracy of around 10-14 eV - achieved with a gravity resonance spectroscopy technique - with the by many orders of magnitude expected smaller size of inevitable systematic errors, one may conclude that the present experiments are heavily restricted by the limited strength of today's ultracold neutron (UCN) sources.We propose to build a dedicated UCN source at the European Spallation Source in order to perform experiments with gravitationally-bound UCN.