Limits to second-class nucleonic and mesonic currents

Abstract

Second-class currents, i.e those of irregular G-parity in the definition of Weinberg, induce differences between the ft -values for positive and negative electron emission in the mirror beta-decay of complex nuclei and, together with weak magnetism, there affect various correlation phenomena. Such currents might arise either from (strong-interaction-clad) NNeν vertex terms or from the in-flight decay of exchange mesons, most probably ω→πeν, or from both, in the manner first explored in detail by Kubodera, Delorme and Rho. The nucleonic and mesonic effects can be (partially) disentangled only by studying a suite of cases and inter-relating those cases through suitable many-body wave-functions. Present data are analyzed to show that, at the 90% CL, the amplitudes of second-class (strong-interaction-clad)-nucleonic-vertex and meson-exchange terms are both at least an order of magnitude below those of corresponding first-class terms. These experimental upper limits are themselves about one order of magnitude larger than the values expected from mu, md symmetry-breaking. Evidences from particle physics are quantitatively comparable to, and consistent with, those from nuclear structure physics but are less detailed and less surely based.