Measurement of angular distribution of γ-rays in the resonance reaction of ¹³⁹La for T-Violation search experiment

The parity violation in the neutron capture reaction of ¹³⁹La was discovered with the enhancement million times larger than that in proton-proton scattering. The enhancement was observed at the neutron energy of 0.75 eV, which corresponds to p-wave resonance on the tail of large s-wave resonance peak. This was explained as the result of the entrance channel interference between the s- and p-wave amplitudes. The enhancement of T-violation is theoretically predicted with the same mechanism. The enhancement depends on the mixture of s- and p- partial waves in the compound state. 

The mixture affects the angular distribution of γ-ray from the compound nuclei. A clear distribution of γ-rays from the ¹³⁹La p-wave resonance was measured at J-PARC. The ratio of the partial p-wave neutron width to the neutron width in the entrance channel was determined by analysis on the s-p mixing framework. The R&D for the experiment has also started including the dynamical nuclear polarization technique. We will discuss the feasibility of T-violation search with lanthanum target.