Electron scattering and charged pion photoproduction on12C and13C

Electron scattering and charged pion photoproduction at 200 MeV on¹²C and¹³C have been studied by the nuclear shell model to investigateM1 andE2 nuclear form factors of the isovector type. Starting with the Op-shell model of Hauge-Maripuu, the effects of core polarization by theM 3Y force and the one-pion-exchange current are taken into account. The effect of core polarization is found to be essential in both electron scattering and pion photoproduction, while the meson-exchange current, which also improves the calculated results, gives contributions of about 10%–15%.     

Beta-ray spectra of 12B and 12N and conserved vector current

In order to investigate spectral shape factors of ¹²B and ¹²N, we make a new formalism of β-decay theory, where the radial wave functions of leptons are treated with no approximation and, therefore, the nuclear matrix elements are electron-energy dependent. With this formalism we can show strong support for the conserved vector current hypothesis in analyzing the experimental data which were given by Wu, Lee and Mo in 1963 and revised by them in 1977 using the latest experimental results on the end-point energies and branching ratios of the inner β-groups, in addition to the correct Fermi functions for the positron. In fact, the average slopes of the spectral shape factors for ¹²B and ¹²N are in excellent agreement with those in our theory. Recent experimental data given by the Heidelberg group are also in good agreement with the theory if we analyze the difference of the average slopes for ¹²B and ¹²N. There are, however, small discrepancies with the theory in their individual values. The relation of the present formalism with traditional theories of β-decay is discussed.     

Induced pseudoscalar interaction in weak nucleon current and muon capture in hyperfine states of muonic deuterium

Muon capture rate in muonic deuterium can be calculated with less ambiguities in nuclear wave functions, since we know the bound and scattering states of the two nucleons with higher accuracy theoretically. It is, however, dependent on the pion-nucleon-delta coupling constant through the exchange current effect. This dependence is considerably reduced for the ratio of the capture rates from two hyperfine states of muonic deuterium. This ratio is, therefore, useful to study the strength of the induced pseudoscalar term. Several other physical quantities in light nuclei are also introduced here for the same purpose.     

Spin control and structure of weak nucleon currents in A= 8, 12, 20 and 41

The β-ray angular distributions from purely spin aligned ¹²B and ¹²N were precisely remeasured using a further refined spin-manipulation technique. We determined the amount of a g-parity violating induced tensor form factor in a weak axial vector current as 2M f_T/f_A= +0.22 ± 0.05\ (stat.) ± 0.15\ (syst.) ± 0.05\ (theor.). The result is consistent with the theoretical prediction in the framework of which induced tensor form factor is proportional to u- and d-quark mass difference. To study the g-parity violation in weak nucleon current systematically, we have started to measure the alignment correlation terms of ⁸Li, ⁸B, ²⁰F and ⁴¹Sc. This revised version was published online in August 2006 with corrections to the Cover Date.