Test of parity violation and time reversal invariance in slow neutron absorption reactions

Measurements of helicity asymetries in slow neutron absorption reactions have been performed by detecting capture γ-rays. Large enhancements of parity-violation effect observed in these reactions are explained by interference between s- and p-wave resonances. The weak matrix element in hadronic reaction has been deduced from the results. Violation of time reversal invariance is being searched for in reactions in which large enhancement of the parity violation effect occurs. The same order of enhancement is expected in violation of time reversal invariance. The difference between the probability for helicity flip (+ → −) and that for (− → +) during transmission through a transversely polarized target is being measured. Recently, 139 La nuclei in LaAlO 3 crystal have been polarized successfully. The crystal is useful for the target, since the highest enhancement of the parity violation effect has been found for the 139 La target. The perspective of the experiment is shown.