Search for Time Reversal Violation using Compound Nuclei

Abstract

Time reversal violation beyond the Standard Model of elementary particles is one of the biggest problems in particle physics. The parity violation caused by weak interaction is largely enhanced in compound nuclei. There is a theoretical prediction that T-violating effects can also be enhanced by this mechanism in these nuclei implying that T-violation can be searched for with an enhanced sensitivity. We are planning an experiment to search for the T-violation beyond the Standard Model using compound nuclei in J-PARC. In order to estimate the enhancement of the T-violation, the angular distribution of the (n,γ) reaction was measured with ¹³⁹La, which is a possible candidate nucleus for the T-violation search, by using a germanium γ-ray detector assembly at J-PARC. A clear angular dependence of the γ-rays from the p-wave resonance was found. The result indicates that the enhancement of the T-violation in the neutron absorption reaction of ¹³⁹La is on the order of 10⁶.