Dark Matter Direct Search with Liquid-Gas Double Phase Xenon Detector

为了提高探测器的性能，我们进行了以下修改。*安装保护线，保持探测器电场恒定，不产生阳极线振动。*在光电倍增管和MgF2窗口之间引入Krytox，提高光收集效率。*增设净化装置，提高氙气纯度。我们尝试了与XENON10组相同的实验方法，因为他们使用了与我们类似的两相氙气检测器，并且得到了目前最好的结果。该探测器采用比例闪烁信号代替直接闪烁信号作为触发器，并限制了一个敏感区域（自屏蔽），作为三维位置探测器工作。例如，3cm厚的液态氙屏蔽层（活性氙~5kg）可实现80%以上的本底降低。用中子（241Am-Be）照射探测器，研究了核后坐力信号。分析了直接闪烁和比例闪烁的光子数与能量的关系，分别用于电子反冲（γ射线或δ衰变）和氙核反冲。经过两天的搜寻，氙核反冲事件只有一次。预计经过两个多月的研究，现有装置的研究灵敏度将达到XENON10实验的相同或更好的区域。

Following modifications were done to improve the detector performance.* Protection wires were installed to keep the constant electric field of the detector without a vibration of the anode wires.* Krytox was introduced between photomultipliers and MgF2 windows to improve light collection efficiency.* Additional purification device was introduced to improve with the purity of xenon.We tried the same experimental method as XENON10 group because they used a two phase xenon detector similar to our detector and got the best result at present. The detector is operated as a three-dimensional position detector by using a signal of the proportional scintillation as trigger in substitution for a signal of the direct scintillation and restricted a sensitive region (self-shielding). For example, more than 80% reduction of background was achievable with the3cm thickness of liquid xenon shielding (active xenon~5kg). The signal from nuclear recoil was studied by irradiation of neutrons (241Am-Be) to the detector. The correlation between the ratio of the number of photons from direct scintillation and proportional scintillation and the energy was analyzed for electron recoil by gamma rays or δ decays and xenon nuclear recoil, respectively. As a result from about two days search, the event to be xenon nuclear recoil was only one.More than two months search is expected that the research sensitivity reaches to the same or better region which was obtained by XENON10 experiment by the present device.