$^{12}$ C中前2个$^+$态的重取向效应测量：扁形变的确认
Reorientation-effect measurement of the first 2$^+$ state in $^{12}$C: confirmation of oblate deformation
摘要：
在TRIUMF/ISAC II设施上使用TIGRESS $γ-$射线光谱仪进行的库仑激发重取向效应测量，允许根据粒子$-γ$符合数据首次确定$^{12}$ C中的$\langle 2^+_1\mid\mid \hat{E2} \mid\mid 2^+_1\rangle$对角矩阵元素。用手性NN N $^4$ LO 500和NN+3 NF 350相互作用计算了$^{12}$ C基态和第一激发态（2 $^+_1$）的核极化率.一致的预测显示出比先前预期的更大的极化率。将2 $^+_1$态的极化率引入到当前和以前的$^{12}$ C的库仑激发重取向效应分析中。光谱四极矩的$Q_{_S}(2_1^+)= +0.053(44)$ eb和$Q_{_S}(2_1^+)= +0.08(3)$ eb的测定，分别产生的加权平均值$Q_{_S}(2_1^+)= +0.071(25)$ eb，与最近的从头计算。本测量结果证实了$^{12}$ C的2 $^+_1$态是扁的，并强调了核极化率在轻核库仑激发研究中的重要作用。
英文摘要：
A Coulomb-excitation reorientation-effect measurement using the TIGRESS $γ-$ray spectrometer at the TRIUMF/ISAC II facility has permitted the first determination of the $\langle 2^+_1\mid\mid \hat{E2} \mid\mid 2^+_1\rangle$ diagonal matrix element in $^{12}$C from particle$-γ$ coincidence data. Required state-of-the-art no-core shell model calculations of the nuclear polarizability for the ground and first-excited (2$^+_1$) states in $^{12}$C using chiral NN N$^4$LO500 and NN+3NF350 interactions have been performed. Consistent predictions show a larger polarizability than previously anticipated. The polarizability of the 2$^+_1$ state is introduced into the current and previous Coulomb-excitation reorientation-effect analysis of $^{12}$C. Spectroscopic quadrupole moments of $Q_{_S}(2_1^+)= +0.053(44)$ eb and $Q_{_S}(2_1^+)= +0.08(3)$ eb are determined, respectively, yielding a weighted average of $Q_{_S}(2_1^+)= +0.071(25)$ eb, in agreement with recent ab initio calculations. The present measurement confirms that the 2$^+_1$ state of $^{12}$C is oblate and emphasizes the important role played by the nuclear polarizability in Coulomb-excitation studies of light nuclei.
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