A group of researchers including scientists from Nagoya University, the J-PARC Center, Tokyo Institute of Technology, Osaka University, Kyushu University, and Japan Atomic Energy Agency study the angular distribution of gamma-rays emitted from a neutron capture reaction with polarized neutrons. This is the basis of CP-violation research experiments using nuclear reactions.

In particle physics CP-violation is one of the origins of the matter universe; however, only tiny violations have thus far been observed. Unknown CP-violating processes are sought through various experiments. In some nuclear reactions, it appears that strong enhancements of symmetry violation occur. The enhancement mechanism can be tested by measuring the angular distribution of gamma rays emitted in nuclear reactions.

A high-performance neutron polarizer was developed and installed in the neutron beamline at J-PARC. It was clearly observed that the angular distribution of gamma-rays is dependent on the spin direction of incident neutrons. This result suggests a new method for studying the reaction mechanism in nuclei to reveal the origin of matter in the universe.

Learn more about the result at Press Release (Japanese).

Professor Masaaki Kitaguchi, KMI, who is actively involved in the project explained the details. “By understanding nuclear reactions, nuclei can be used as a micro laboratory for particle physics and astrophysics. KMI, Nagoya University has played a central role in several neutron physics experiments all over the world. The high-intensity neutron source at J-PARC and state of the art devices enable us to perform novel experiments with precision by controlling neutron beams. I am very excited about where we are now.”

Paper Information

“Transverse asymmetry of γ rays from neutron-induced compound states of ¹⁴⁰La,” Phys. Rev. C 101, 064624 – Published 25 June 2020
DOI：10.1103/PhysRevC.101.064624
URL: https://journals.aps.org/prc/abstract/10.1103/PhysRevC.101.064624