ZEPLIN- III中的放射性背景
Radioactivity Backgrounds in ZEPLIN-III
摘要：
我们研究电子和核反冲背景的放射性ZEPLIN-III暗物质实验在博尔比。液态氙WIMP靶中的低能电子反冲率为0.75 $\pm$ 0.05事件/kg/天/keV，这比第一次科学运行期间观察到的速率提高了20倍。能量和空间分布与组件级蒙特卡罗模拟预测的一致，传播实验中使用的材料测量的放射性污染的影响。预计中子弹性散射将产生3.05 $\pm$ 0.5核反冲，能量为5-50 keV/年，这意味着在1年数据集中预期0.4个事件，与否决探测器的实际信号接受反符合。不太明显的背景来源进行了讨论，特别是在未来的实验。这些包括来自康普顿电子和光电倍增管内部的$β$活动的切伦科夫光对闪烁脉冲的污染，这会增加闪烁响应的大小并降低闪烁响应的表观时间常数。另一个挑战是由多重散射$γ$ -在不产生电离的区域中具有一个或多个顶点的射线提出的。如果第一次运行中获得的分辨能力可以复制，ZEPLIN-III应该达到$\sim 1 \times 10^{-8}$ pb $\cdot$ year对标量WIMP-核子弹性截面的灵敏度，正如最初设想的那样。
英文摘要：
We examine electron and nuclear recoil backgrounds from radioactivity in the ZEPLIN-III dark matter experiment at Boulby. The rate of low-energy electron recoils in the liquid xenon WIMP target is 0.75$\pm$0.05 events/kg/day/keV, which represents a 20-fold improvement over the rate observed during the first science run. Energy and spatial distributions agree with those predicted by component-level Monte Carlo simulations propagating the effects of the radiological contamination measured for materials employed in the experiment. Neutron elastic scattering is predicted to yield 3.05$\pm$0.5 nuclear recoils with energy 5-50 keV per year, which translates to an expectation of 0.4 events in a 1-year dataset in anti-coincidence with the veto detector for realistic signal acceptance. Less obvious background sources are discussed, especially in the context of future experiments. These include contamination of scintillation pulses with Cherenkov light from Compton electrons and from $β$ activity internal to photomultipliers, which can increase the size and lower the apparent time constant of the scintillation response. Another challenge is posed by multiple-scatter $γ$-rays with one or more vertices in regions that yield no ionisation. If the discrimination power achieved in the first run can be replicated, ZEPLIN-III should reach a sensitivity of $\sim 1 \times 10^{-8}$ pb$\cdot$year to the scalar WIMP-nucleon elastic cross-section, as originally conceived.
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