Dark Matter Search Experiment with Double Phase Xenon Detector at Kamioka Underground Laboratory

我们搭建了0.3升基准体积的探测器，并对其基本性能进行了测试。我们成功地将聚四氟乙烯反射镜用于液体氙气闪烁光，并利用直接闪烁和比例闪烁成功地区分了核反冲和电子反冲。从2001年开始，我们在神冈煤矿开始了一项使用原型探测器的地下实验。本底研究是在矿山使用高纯Ge探测器进行的，对探测器所用材料的放射性进行了研究。低本底PMTs为本课题组研制。样机探测器的结果比WIMP-核子截面上的电流极限差1个数量级。然而，放射源的来源已经确定，本底水平也得到了定量的了解。下一阶段15公斤探测器的预期结果将比目前的限制好三个数量级。

We built the detector with 0.3-liter fiducial volume and measured its basic performance. We succeeded to utilize a PTFE reflector for liquid Xenon scintillation light and have been able to distinguish nuclear recoil from electron recoil using the direct scintillation and the proportional scintillation. From 2001, we started an underground experiment using a prototype detector in Kamioka mine. The background study, the radioactivity of all the materials used for this detector, was carried out using high purity Ge detector in the mine. Low background PMTs were developed by our group. The result of the prototype detector was 1 order of magnitude worse than the current limit in the WIMP-nucleon cross section. However, the origin of the radioactive source has been identified and the background level is understood quantitatively. The expected results with a 15 kg detector in the next phase will be three orders of magnitude better than the current limit.