Identification of the Lowest $T=2$, $J^{\ddot{I}€=}{0}^{+}$ Isobaric Analog State in ${}^{52}$Co and Its Impact on the Understanding of ${\hat{I}}^2$-Decay Properties of ${}^{52}$Ni

Abstract

Masses of ${}^{52g,52m}$Co were measured for the first time with an accuracy of $\sim 10$ keV, an unprecedented precision reached for short-lived nuclei in the isochronous mass spectrometry. Combining our results with the previous ${\hat{I}}^2$-${\hat{I}}^3$ measurements of ${}^{52}$Ni, the $T=2$, $J^{\ddot{I}}€=0^{+}$ isobaric analog state (IAS) in ${}^{52}$Co was newly assigned, questioning the conventional identification of IASs from the ${\hat{I}}^2$-delayed proton emissions. Using our energy of the IAS in ${}^{52}$Co, the masses of the $T=2$ multiplet fit well into the Isobaric Multiplet Mass Equation. We find that the IAS in ${}^{52}$Co decays predominantly via ${\hat{I}}^3$ transitions while the proton emission is negligibly small. According to our large-scale shell model calculations, this phenomenon has been interpreted to be due to very low isospin mixing in the IAS.

Accepted for publication in PRL. 5 pages, 2figures