Ultra-cold neutron (UCN) are neutrons with kinetic energies low enough that they can be trapped in material and magnetic bottles until they decay.  UCN typically have velocities below 8 meters per second.  At these low energies UCN can only travel a few meters upward against gravity.  The free neutron decays into an electron, proton, and neutrino in about 900 seconds.  The ability to contain UCN makes them ideal for studying fundamental physics of the neutron.  These studies can lead to a better understanding of nature and the Standard Model.