Precise determination of ${}_{\hat{I}}^{12}›$C level structure by ${\hat{I}}^3$-ray spectroscopy

Abstract

Level structure of the ${}_{\hat{I}}^{12}›$C hypernucleus was precisely determined by means of ${\hat{I}}^3$-ray spectroscopy. We identified four ${\hat{I}}^3$-ray transitions via the ${}^{12}$C$(\ddot{I}{€}^{+},K^{+}{\hat{I}}^3)$ reaction using a germanium detector array, Hyperball2. The spacing of the ground-state doublet $(2_1^{-},1_1^{-})$ was measured to be $161.5\pm 0.3\text{(stat)}\pm 0.3\text{(syst)}$\,keV from the direct $M1$ transition. Excitation energies of the $1_2^{-}$ and $1_3^{-}$ states were measured to be $2832\pm 3\pm 4$\,keV and $6050\pm 8\pm 7$\,keV, respectively. The obtained level energies provide definitive references for the reaction spectroscopy of $\hat{I}›$ hypernuclei.