AI 中文总结
本研究通过LEGEND相关实验，测量得到76As俘获电子至76Ge第一激发态的分支比，为首个量化全部不确定度预算的该类测量，助力无中微子双β衰变研究。
AI 中文摘要
LEGEND大型实验正在搜寻76Ge的无中微子双β衰变，测量该过程的半衰期可借助核矩阵元获取中微子质量。实验上，可通过76As的β⁻衰变和电子俘获衰变的分支比，研究其基态对核矩阵元的贡献。从能量角度看，76As俘获电子至76Ge第一激发态是可行的，且此前已有一次测量，但尚未观测到76As俘获电子至76Ge基态的情况。本研究以75As(n,γ)反应产生的76As为研究对象，采用薄As₂O₃样品开展实验：硅漂移探测器测量电子俘获后内层空位引发锗原子发射的特征X射线，高纯锗探测器测量电子俘获至激发态后发射的562.9keVγ射线，通过分析两个探测器的符合信号，得到76As俘获电子至76Ge第一激发态的分支比为ν_{EC*}=(0.0572±0.0029（统计）±0.0074（系统）)%，这是首个量化了全部不确定度预算的测量结果。
英文摘要
The neutrinoless double beta decay of $^{76}$Ge is searched for in the large-scale experiment LEGEND. The measurement of the half-life of this process would give access to the neutrino mass using the nuclear matrix element. Experimentally the contribution of the $^{76}$As ground state to the nuclear matrix element can be investigated via the branching ratios of its $β^-$ and electron capture decay. While energetically, the electron capture of $^{76}$As into the first excited state of $^{76}$Ge is possible and was measured once before this work, the electron capture into the $^{76}$Ge ground state was not observed yet. The present study investigates the branching of $^{76}$As that is produced via $^{75}$As(n,$γ$) on a thin As$_2$O$_3$ sample. A silicon drift detector measures characteristic X-rays emitted by the germanium atoms caused by an inner vacancy after the electron capture. A high-purity germanium detector is used to measure the 562.9$\,$keV $γ$-rays emitted after electron capture into the excited state. Investigation of coincident signals in both detectors leads to the branching ratio of the $^{76}$As electron capture into the first excited state of $^{76}$Ge of $ν_{\mathrm{EC}^\ast} = (0.0572 \pm 0.0029 (\mathrm{stat.}) \pm 0.0074(\mathrm{syst.}))\%$. This is the first measurement with the full uncertainty budget quantified.
