0 5 10 15 excitation e n ergy [MeV] 0 5 10 15 0 + 2 + 4 + 6 + 8 + 0 + 2 + 4 + 6 + 8 + 10 + 12 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 0 + 2 + 1 4 + 6 + 0 + 2 + 2 4 + 6 + 8 + 10 + (12 $^{+}$) 2 + 5 3 + (2 , 3 , 4) + 2 + 3 2 + 4 (4 $^{+}$) 4 + Theory Exp GS GS SD0 SD0 SD2 (SD2) FIG. 4: Level scheme of $^{40}$Ar is shown. In experimental data, the GS, the SD band (SD0), candidate states of the side band of the SD band (SD2), and other low-lying J π ≤ 4 + states are listed. The experimental data are taken from Refs. 17 and 24. GCM. The K π = 0 + GS band, the K π = 0 + SD band (SD0), and the K π = 2 + SD band (SD2) are obtained by the GCM calculation. The energy levels of the GS and SD0 bands agree with the experimental data. The observed J π = 2 + 5 (3.92 MeV), 3 + (4.23 MeV), and (2 , 3 , 4) + (5.17 MeV) states are tentatively assigned as members of the SD2 band in this study because their excitation energies are similar to calculated ones of the SD2 band and the candidates states decay to the members of the SD0 band. Dominant components of the GS band are the deformed-basis AMD wave functions around the GS minimum on the energy curve, and those of the SD0 and SD2 bands are the basis wave functions around the SD minimum with the triaxial deformations. Owing to the triaxial deformations around the SD local minimum, the SD2 band appears. The members of the SD0 and SD2 bands are dominated by the | K | = 0 and 2 components, respectively, projected from a single deformed- basis AMD wave function at ( β, γ ) = (0 . 478 , 11 . 2 $^{◦}$) up to high spin states. Both the SD0 and SD2 bands show rigid rotor-like behavior. The calculated level spacings in the SD0 band members show the rotational band spectra and match experimental data, and those of the SD2 band members are consistent with experimental data. The energy gap between the J π = 0 + SD0 and the J π = 2 + SD2 states is slightly overestimated, and it may indicate that the triaxiality of the SD states is underestimated. 7