Upper limits on parity-violating terms in nuclear electromagnetic operators and nuclear structure effects

Parity-violating (PV) nuclear experiments offer a suitable tool for investigating parity conservation in the electromagnetic interaction of nucleons. It has been estimated that PV electromagnetic vertices induced by weak interactions are very small. Thus, any sizeable PV nucleon electromagnetic couplings indicate the presence of a genuine PV electromagnetic interaction. The upper limit to such a PV electromagnetic interaction can be estimated from the existing experimental value for the circular polarization of γ-rays emitted in the radiative capture of a thermal neutron (n+p → d+γ). This estimate is consistent with the value for the circular γ-polarization measured in deformed nuclei (¹⁸¹Ta, ¹⁷⁷Hf). Useful additional information can be extracted from the measurement of the γ-asymmetry in the n+p → d+γ reaction and from the measurements of circular polarization in the decays of selected spherical nuclei (²⁰³Tl, ¹¹¹In, ⁶³Cu). Extensive theoretical analysis taking into account nuclear structure effects shows that the decay of ⁶³Cu is particularly suitable for this purpose.