Small energy transfer at the ultra-cold neutron reflection from solid surface

Serious disagreement exists between the experimental values for the probability of small energy up-scattering of ultra-cold neutrons (UCN) at their reflection from solid surfaces. We performed new measurement of the UCN up-scattering from the copper surface to the whole energy range higher than the boundary energy of the reflecting copper foil. Significant value (∼2.5×10−4∼2.5×10−4) has been observed for the probability of the UCN up-scattering to the μeV energy range. We found strong dependence of the effect on the incident UCN energy.