NEXT双β衰变实验中的放射性本底
Radiogenic backgrounds in the NEXT double beta decay experiment
摘要：
天然放射性是寻找无中微子双β衰变的主要背景之一。在NEXT物理程序中，使用NEXT-White探测器测量放射性诱导的背景。分析了坎弗朗克Subterráneo核电站37.9天低本底运行的数据，其中$^{136}$中氙耗尽，得出1000 keV以上的总本底率为（0.84 $\pm$ 0.02）mHz。使用和不使用氡消减系统的数据样本的比较表明，空气氡的贡献可以忽略不计。一个放射性背景模型是建立在广泛的放射性纯度筛选活动进行的下一个合作。对该模型的光谱拟合产生了$^{60}$ Co、$^{40}$ K、$^{214}$ Bi和$^{208}$ Tl对总背景速率的特定贡献，以及它们在检测器体积中的位置。结果用于评估双β衰变分析中的放射性背景的影响，拓扑切割后的应用程序，减少总速率为（0.25 $\pm$ 0.01）兆赫。根据最佳拟合的本底模型，经过一年的观测，NEXT-White对双中微子双β衰变的灵敏度中值为3.5 $σ$。在Q $_{ββ}\pm$ 100 keV能量窗口中的背景测量验证了最佳拟合背景模型，也适用于NEXT-100的无中微子双β衰变搜索。仅发现一个事件，而模型预期值为（0.75 $\pm$ 0.12）个事件。
英文摘要：
Natural radioactivity represents one of the main backgrounds in the search for neutrinoless double beta decay. Within the NEXT physics program, the radioactivity-induced backgrounds are measured with the NEXT-White detector. Data from 37.9 days of low-background operations at the Laboratorio Subterráneo de Canfranc with xenon depleted in $^{136}$Xe are analyzed to derive a total background rate of (0.84$\pm$0.02) mHz above 1000 keV. The comparison of data samples with and without the use of the radon abatement system demonstrates that the contribution of airborne-Rn is negligible. A radiogenic background model is built upon the extensive radiopurity screening campaign conducted by the NEXT Collaboration. A spectral fit to this model yields the specific contributions of $^{60}$Co, $^{40}$K, $^{214}$Bi and $^{208}$Tl to the total background rate, as well as their location in the detector volumes. The results are used to evaluate the impact of the radiogenic backgrounds in the double beta decay analyses, after the application of topological cuts that reduce the total rate to (0.25$\pm$0.01) mHz. Based on the best-fit background model, the NEXT-White median sensitivity to the two-neutrino double beta decay is found to be 3.5$σ$ after 1 year of data taking. The background measurement in a Q$_{ββ}\pm$100 keV energy window validates the best-fit background model also for the neutrinoless double beta decay search with NEXT-100. Only one event is found, while the model expectation is (0.75$\pm$0.12) events.
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