Weak Nucleon Currents in Light Nuclei

Abstract

We have studied the axial vector current in the nuclear weak processes. The strengths of the main axial vector and induced tensor currents are well established. As compared with these, the strength of the induced pseudoscalar has been not too well-known yet. We have studied it by analyzing the experimental data on the nuclear recoil polarizations in muon capture and the ft values and beta-ray angular distributions in the A = 12 system. The nucleon current in the light nuclei can be assumed to have the same form as that of the free nucleon except for the difference in the momentum transfer, if we adopt reasonable nuclear wave functions and take into account effects of the exchange currents. We adopted the general Op-shell wave functions together with the full effects of the core polarization of 2ℏω. The Hartree-Fock condition is also taken into consideration. Our result gives the ratio, g_P/g_A which is very close to the canonical value based on PCAC. The experimental data on the ft value and axial charge are well reproduced. This means that the renormalization mechanism for g_A and g_P can be mostly understood in terms of the meson exchange currents in the light nuclei like A = 12.