Parity and Time Reversal Invariance Violation in Neutron-Nucleus Scattering

TL;DR

This paper investigates parity and time-reversal violation effects in neutron-nucleus scattering, highlighting enhanced effects near resonances, analyzing their origins, and proposing methods to extract fundamental interaction constants from experimental data.

Contribution

It introduces a statistical theory for calculating PV and PTRIV effects in neutron reactions, and suggests experimental approaches to determine underlying CP-violating interaction strengths.

Findings

PV effects are enhanced near p-wave resonances.

PV effects show a consistent positive sign in 232Th, indicating possible regular contributions.

A ratio estimate of PTRIV to PV effects is provided.

Abstract

Parity violating (PV) as well as parity and time-reversal invariance violating (PTRIV) effects are enhanced a million times in neutron reactions near p-wave compound resonances. We present the calculation of such effects using a statistical theory based on the properties of chaotic eigenstates and discuss a possibility to extract the strength constants of PTRIV interactions from the experimental data, including nucleon-nucleon and pion-nucleon CP-violating interactions, the QCD theta-term and the quark chromo-EDM. PV effects have random sign for all target nuclei except for 232Th, where PV effects of a positive sign have been observed for ten statistically significant p-wave resonances, with energy smaller than 250 eV. This may be an indication of a possible regular (non-chaotic) contribution to PV effects. We link this regular effect to the doublets of opposite parity states in the rotation spectra of nuclei with an octupole deformation and suggest other target nuclei where this hypothesis may be tested. We also discuss a permanent sign contribution produced by doorway states. An estimate of the ratio of PTRIV effects to PV effects is presented. Although a polarised target is not needed for the measurement of PV effects, for the interpretation of the results, it may be convenient to do both PV and PTRIV experiments with a polarised target.