Observation of the ${\hat{I}}^2$-delayed ${\hat{I}}^3$-proton decay of ${}^{56}$Zn and its impact on the Gamow Teller strength evaluation

Abstract

We report the observation of a very exotic decay mode at the proton drip-line, the ${\hat{I}}^2$-delayed ${\hat{I}}^3$-proton decay, clearly seen in the ${\hat{I}}^2$ decay of the $T_z$ = -2 nucleus ${}^{56}$Zn. Three ${\hat{I}}^3$-proton sequences have been observed after the ${\hat{I}}^2$ decay. Here this decay mode, already observed in the $sd$-shell, is seen for the first time in the $fp$-shell. Both ${\hat{I}}^3$ and proton decays have been taken into account in the estimation of the Fermi (F) and Gamow Teller (GT) strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.

Accepted for publication in PRL. (5 pages, 4 figures)