Dark Matter Search Experiment with 20 kg xenon detector

我们重新考虑了探测器的形状，以提高光子收集效率。通过精确的蒙特卡罗模拟，我们得到了一个结论，一个15公斤的探测器的小一点的形状有最好的性能。根据这一决定，腔室的内部部分被修改为15公斤。用高纯锗探测器测量了探测器周围物质和探测器本身的放射性活度。将这些结果用于Monte Carlo模拟，以了解各元素背景的影响。结果发现，对γ射线本底来源影响最大的材料是光电倍增管。那么我们需要更多的努力来减少光电倍增管的放射性活动。用~ 3 He探测器和液体闪烁体对中子本底进行了精确测量。结果比暗物质的预期事件率高出一个数量级。建立了一个蒸馏系统，以避免氙中含有的85氪的β衰变背景。我们成功地将液体氙中的氪污染降低了1/1000。提出了利用双相氙探测器同时进行136-Xe双β衰变实验、p-p和7-Be低能太阳中微子实验以及暗物质实验的设想。

We reconsidered a shape of the detector in order to improve photon collection efficiency. We had a conclusion of a little bit smaller shape of a 15 kg detector had the best performance from the results of precise Monte Carlo simulation. The inner part of the chamber was modified to 15 kg from this decision. Radio activities of materials surrounding the detector and the detector itself were measured by a high purity germanium detector. These results were used to Monte Carlo simulation to understand the influence of background from each element. As a result, it was found out that the most influential material for the origin of gamma ray background was photo multiplier tubes. Then we need more effort to reduce radio activities from the photo multiplier tube. The precise measurements for neutron background were also made by a 3-He detector and a liquid scintillator. The results were one order higher than the expected event rate of dark matter. A distillation system was built to avoid the beta decay background from 85-krypton which are contained in xenon. We succeeded to reduce the krypton contamination in liquid xenon by a factor of 1/1000. 136-Xe double beta decay experiment and p-p and 7-Be low energy solar neutrino experiment as well as dark matter experiment at the same time using a double phase xenon detector were proposed.