The form factor of the electromagnetic excitation of $^{12}\mathrm{C}$ to its ${2}_{1}^{+}$ state was measured at extremely low momentum transfers in an electron-scattering experiment at the Superconducting Darmstadt Electron Linear Accelerator (S-DALINAC). A combined analysis with the world form-factor data results in a reduced transition strength $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})=7.63(19)\phantom{\rule{4pt}{0ex}}{e}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{fm}}^{4}$ with an accuracy improved to 2.5%. In-medium no-core shell-model results with interactions derived from chiral effective field theory are able to reproduce the result. A quadrupole moment $Q({2}_{1}^{+})=5.97(30)\phantom{\rule{4pt}{0ex}}e\phantom{\rule{0.16em}{0ex}}{\mathrm{fm}}^{2}$ can be extracted from the strict correlation with the $B(E2)$ strength emerging in the calculations.

中文翻译：

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精确测量 E2 跃迁强度到 C12 的 21+ 状态

$^{12}\mathrm{C}$ 到其 ${2}_{1}^{+}$ 状态的电磁激发的形状因子是在电子散射实验中以极低的动量转移测量的超导达姆施塔特电子直线加速器 (S-DALINAC)。与世界形状因子数据的综合分析导致转换强度降低 $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+}) =7.63(19)\phantom{\rule{4pt}{0ex}}{e}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{fm}}^{4}$准确率提高到 2.5%。具有源自手性有效场理论的相互作用的介质中无核壳模型结果能够重现该结果。四极矩 $Q({2}_{1}^{+})=5.97(30)\phantom{\rule{4pt}{0ex}}e\phantom{\rule{0.