Evidence of a higher nodal band α+44Ca cluster state in fusion reactions and a clustering in 48Ti

In the nucleus Ti-48, whose structure is essential in evaluating the half-life of the neutrinoless double-beta decay (0 nu beta beta) of Ca-48, the existence of the alpha cluster structure is shown for the first time. A unified description of scattering and structure is performed for the alpha + Ca-44 system. By using a global potential, which reproduces experimental alpha + Ca-44 scattering over a wide range of incident energies, E-alpha = 18-100 MeV, it is shown that the observed (alpha + Ca-44 )-fusion excitation function at E-alpha = 9-18 MeV is described well. The bump at E-alpha = 10.2 MeV is found to be due to a resonance which is a 7- state of the higher nodal band with the (alpha + Ca-44 )-cluster structure in Ti-48. The local potential (alpha + Ca-44)-cluster model locates the ground band of Ti-48 in agreement with experiment and reproduces the enhanced B(E2) values in the ground band well. This shows that collectivity due to alpha clustering in Ti-48 should be taken into account in the evaluation of the nuclear matrix element in the 0 nu beta beta double-beta decay of Ca-48.

Automated summary

In the nucleus Ti-48, the presence of alpha cluster structure is identified, which is crucial for evaluating the half-life of the neutrinoless double-beta decay of Ca-48. Utilizing a global potential, the scattering and structure of the alpha + Ca-44 system are effectively described. Furthermore, the local potential model shows that alpha clustering affects the nuclear matrix element in the double-beta decay process of Ca-48.