Superdeformed and Triaxial States in ${}^{42}\mathrm{Ca}$

Shape parameters of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in ${}^{42}\mathrm{Ca}$ were determined from $E2$ matrix elements measured in the first low-energy Coulomb excitation experiment performed with AGATA. The picture of two coexisting structures is well reproduced by new state-of-the-art large-scale shell model and beyond-mean-field calculations. Experimental evidence for superdeformation of the band built on $0_2^{+}$ has been obtained and the role of triaxiality in the $A\sim 40$ mass region is discussed. Furthermore, the potential of Coulomb excitation as a tool to study superdeformation has been demonstrated for the first time.

Figure 1

Low-lying excited states in ${}^{42}\mathrm{Ca}$, considered in the present analysis [34]. Transitions observed in the current experiment are marked in red. Level and transition energies are given in keV.

Figure 2

The $\gamma$-ray spectrum observed in the ${}^{42}\mathrm{Ca}+{}^{208}\mathrm{Pb}$ Coulomb excitation experiment in coincidence with backscattered particles registered in one of the MCP detectors and Doppler corrected for the projectile. The lines not originating from ${}^{42}\mathrm{Ca}$ are marked as follows: (filled square) lead isotopes, (filled triangle) 511 keV, (filled circle) ${}^{43}\mathrm{Ca}$. Insets show portions of the spectrum zoomed on the 1600–3000 keV and 850–1300 keV energy ranges, the latter also presenting the spectrum collected with the ${}^{197}\mathrm{Au}$ target (in red, multiplied by a factor of 3 for presentation purpose).

Figure 3

Potential energy surfaces resulting from deformation-constrained Hartree-Fock calculations with (a) SM interaction, and, (b) BMF, variation after the particle number projection (PN-VAP), Gogny D1S interaction. Spatial densities corresponding to each minimum found in BMF calculations are also shown in (b).