Isospin symmetry of T_z=±3∕2→±1∕2 Gamow-Teller transitions in A=41 nuclei

Under the assumption that isospin T is a good quantum number, isobaric analog states and various analogous transitions are expected in isobars with mass number A . The strengths of T_z=±3∕2→±1∕2 analogous Gamow-Teller (GT) transitions and analogous M1 transitions within the A=41 isobar quartet are compared in detail. The T_z=+3∕2→+1∕2 GT transitions from the J^π=3∕2⁺ ground state of ⁴¹K leading to excited J^π=1∕2⁺ , 3∕2⁺ , and 5∕2⁺ states in ⁴¹Ca were measured using the (³He,t) charge-exchange reaction. With a high energy resolution of 35  keV , many fragmented states were observed, and the GT strength distribution was determined up to 10  MeV excitation energy (E_x) . The main part of the strength was concentrated in the E_x=4–6  MeV region. A shell-model calculation could reproduce the concentration, but not so well details of the strength distribution. The obtained distribution was further compared with two results of ⁴¹Ti β decay studying the analogous T_z=−3∕2→−1∕2 GT strengths. They reported contradicting distributions. One-to-one correspondences of analogous transitions and analog states were assigned up to E_x=6  MeV in the comparison with one of these ⁴¹Ti β -decay results. Combining the spectroscopic information of the analog states in ⁴¹Ca and ⁴¹Sc , the most probable J^π values were deduced for each pair of analog states. It was found that 5∕2⁺ states carry the main part of the observed GT strength, while much less GT strength was carried by 1∕2⁺ and 3∕2⁺ states. The gross features of the GT strength distributions for each J were similar for the isospin analogous T_z=±3∕2→±1∕2 transitions, but the details were somewhat different. From the difference of the distributions, isospin-asymmetry matrix elements of ≈8  keV were deduced. The Coulomb displacement energy, which is sensitive to the configuration of states, showed a sudden increase of about 50  keV at the excitation energy of 3.8  MeV . The strengths of several M1 transitions to the IAS in ⁴¹Ca were compared with the strengths of analogous GT transitions. It was found that ratios of the M1 and GT transition strengths were similar, suggesting that the contributions of the ℓτ term in M1 transitions are small.