Unexpected distribution of ν1 f7/2 strength in 49Ca

The calcium isotopes have emerged as a critical testing ground for new microscopically derived shell-model interactions, and a great deal of experimental and theoretical focus has been directed toward this region. We investigate the relative spectroscopic strengths associated with 1 f(7/2) neutron hole states in Ca-47,Ca-49 following one-neutron knockout reactions from Ca-48,Ca-50. The observed reduction of strength populating the 7/2(1)(-) state in Ca-49, as compared to Ca-47, is inconsistent with shell-model calculations using both phenomenological interactions such as GXPF1, and interactions derived from microscopically based two-and three-nucleon forces. The result suggests a fragmentation of the l = 3 strength to higher-lying states as suggested by the microscopic calculations, but the observed magnitude of the reduction is not reproduced in any shell-model description.