Parity and Time Reversal Invariance Violation in Neutron-Nucleus Scattering

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 θ-term and the quark chromo-EDM. PV effects have random sign for all target nuclei except for 232 Th, 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.

Searches for Exotic Interactions Using Neutrons

“…Subsequent progress in the measurement of nucleon-nucleon parity violation in two-and few-nucleon systems [77,78], combined with progress in atomic physics enabling measurements of nuclear anapole moments [79], can soon be used to provide the input information needed to confront the predictions of nuclear statistical spectroscopy [80,81] for parity-odd effects in neutron-nuclear resonances. Searches for parity violation in p-wave resonances in heavy nuclei not yet measured [82] and in the (n, γ) cascades from p-wave neutron capture [83] can also provide important new information.…”