$l$-forbidden $M1$ strengths near ${}^{100}$Sn from knockout reactions in Cd and Sn

Abstract

Neutron knockout reactions on beams of ${}^{104,102}$Cd, and ${}^{104}$Sn are presented. States in the residual ${}^{103,101}$Cd and ${}^{103}$Sn nuclei are populated, including low-lying $7/2^{+}$ states of $\hat{I}½g_{7/2}$ character. These states have half-lives $\approx 400$ ps due to their low energy and hindered $B(M1;7/2^{+}\to 5/2^{+})$ strengths. The excited-state half-lives were measured using their Doppler-shifted lineshapes, and the resulting $B(M1)$ strengths are compared to Valence Space In Medium Similarity Renormalization Group (VS-IMSRG) calculations. The VS-IMSRG calculations under-predict the $l$-forbidden $M1$ strengths in the ${}^{100}$Sn region, as well as in other regions of the nuclear chart near ${}^{40}$Ca and ${}^{208}$Pb.

9 pages + 1 page supplementary material, 13 figures, accepted in PRC