有源背景抑制的虚深度：再论GERDA相II的宇宙μ子诱导背景
Virtual depth by active background suppression: Revisiting the cosmic muon induced background of GERDA Phase II
摘要：
通过宇宙μ子相互作用原位产生长寿命同位素可能会为深层地下罕见事件搜索产生不可忽视的背景。在LNGS的GERDA实验中，先前的蒙特卡罗研究确定了$^{77}$ Ge及其亚稳态$^{77m}$ Ge的延迟衰变是寻找$^{76}$ Ge的无中微子双β衰变的主要宇宙成因背景。这可能会限制下一代实验的灵敏度，目的是在无背景条件下增加$^{76}$ Ge质量，从而定义最小深度要求。用一组蒙特卡罗模拟对GERDA实验中的$^{77(m)}$ Ge背景进行了重新评估。获得的$^{77(m)}$ Ge生产率为（0.21 $\pm$ 0.01）核/（kg $\cdot$ yr）。在应用最先进的主动背景抑制技术和简单的延迟符合切割后，这对应于（2.7 $\pm$ 0.3）$\cdot10^{-6}$ cts/（keV $\cdot$ kg $\cdot$ yr）的背景贡献。通过这种策略实现的抑制相当于一个有效的μ子通量减少超过一个数量级。这种虚拟深度的增加为下一代罕见事件搜索开辟了道路。
英文摘要：
In-situ production of long-lived isotopes by cosmic muon interactions may generate a non-negligible background for deep underground rare event searches. Previous Monte Carlo studies for the GERDA experiment at LNGS identified the delayed decays of $^{77}$Ge and its metastable state $^{77m}$Ge as dominant cosmogenic background in the search for neutrinoless double beta decay of $^{76}$Ge. This might limit the sensitivity of next generation experiments aiming for increased $^{76}$Ge mass at background-free conditions and thereby define a minimum depth requirement. A re-evaluation of the $^{77(m)}$Ge background for the GERDA experiment has been carried out by a set of Monte Carlo simulations. The obtained $^{77(m)}$Ge production rate is (0.21$\pm$0.01) nuclei/(kg$\cdot$yr). After application of state-of-the-art active background suppression techniques and simple delayed coincidence cuts this corresponds to a background contribution of (2.7$\pm$0.3)$\cdot10^{-6}$ cts/(keV$\cdot$kg$\cdot$yr). The suppression achieved by this strategy equals an effective muon flux reduction of more than one order of magnitude. This virtual depth increase opens the way for next generation rare event searches.
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