Neutron Diffraction and Optics of a Noncentrosymmetric Crystal. New Feasibility of a Search for Neutron EDM

Recently strong electric fields (up to 10 V/cm) have been discovered, which affect the neutrons moving in noncentrosymmetric crystals. Such fields allow new polarization phenomena in neutron diffraction and optics and provide, for instance, a new feasibility of a search for the neutron electric dipole moment (EDM). A strong interplanar electric field of the crystal and a sufficiently long time for the neutron passage through the crystal for Bragg angle close to π/2 in the case of Laue diffraction make it possible to reach the sensitivity achieved with the most sensitive now magnetic resonance method using ultra cold neutrons (UCN method). A series of experiments was carried out in a few last years on study of the dynamical diffraction of polarized neutrons in thick (1–10 cm) quartz crystals, using the forward diffraction beam and Bragg angles close to 90◦. As well new neutron optics phenomena were investigated. The following effects was first observed: • the effect of an essential time delay of a diffracting neutron inside the crystal for Bragg angles close to π/2; • the phenomenon of a neutron beam depolarization in time of Laue diffraction by noncentrosymmetric α-quartz crystal; • the effect of a neutron-optical spin rotation for neutrons moving through a noncentrosymmetric crystal with the energies and directions far from the Bragg ones; • the controlled spin rotation effect for the Bragg reflected (from a smal part of crystal near its exit face) neutrons in a slightly deformed quartz crystal. The feasibility of experiment on a search for neutron EDM using Laue diffraction in crystals without a center of symmetry was tested at the reactors: WWR-M in Gatchina and HFR in Grenoble. It was shown that the sensitivity can reach (3− 6) · 10 e · cm per day for the available quartz crystal and cold neutron beam flux.