GT matrix elements of the mirror beta decays in the fp-shell region

Study of the Gamow-Teller (GT) matrix elements, especially their quenching with respect to the shell model prediction, is one of the important current subjects in nuclear physics. A systematic study of the GT matrix elements in the sd-shell region has been extensively carried out with a full-space (sd)n shell-model calculation by Brown, Chung and Wildenthal. They have derived a quenching factor of ρ = 0.76 ± 0.073 from a comparison between the theoretical and the experimental GT matrix elements. This factor is considered to be a renormalization actor of the axial-vector coupling constant, gA, or of the single-particle GT matrix elements, and is to be compared with the theoretical estimates of the second-order configuration mixing, meson-exchange and isobar-excitation processes. In the fp-shell region such a fully systematic analysis has been made only recently, because of the lack of experimental data and the difficulty of large-scale shell model calculations in this region. Since the Tz = ± 1/2 mirror nuclei have a strong superallowed β transition between the two ground states, once can easily single out the GT transition strength or the GT matrix element left-angle σ right-angle from an experimental log ft value. In this the authors describe the present experimental and theoretical situations for the study of the GT matrix elements in the OF7/2-1p3/2 region, especially the data on the mirror beta transitions