Studies with Ultra-cold and Cold Neutrons

The experimental search for neutron electric dipole moment (EDM-experiment) is considered to be one of the crucial experiments in physics as it should explain the nature of violation in relation to time reversal. In practically every work concerning T-violation, possible effects are estimated basing on normalization to the upper limit of neutron EDM. So far it has been the most sensitive method for experimental progress in the T-violation problem. More than a half of 50-year EDM-experiment history is described by ultra-cold neutron methodology. A considerable contribution to this problem has been made at PNPI. Here the EDM neutron limit was reduced from 3·10 e·cm down to 1·10 e·cm (see Fig. 1), which allowed to reject a number of theoretical ideas about the nature of T-violation.