Request for continued operation and study of the ZEPLIN II dark matter detector

包括膨胀、星系团、引力透镜和微波背景在内的大尺度天文观测表明，宇宙由不明暗物质主导，其总质量比正常(重子)物质的质量高出5-10倍。一种受欢迎的暗物质候选者是一种质量粒子，它与正常物质只有微弱的相互作用，但仍会产生稀有的核反冲，在合适的目标如液体氙气中可以探测到。加州大学洛杉矶分校的这个小组要求为32公斤的两相ZEPLIN II液体氙暗物质探测器的继续运行和性能改进提供资金，该探测器目前正在英国博尔比矿运行。该计划基于一种新技术，利用液体氙气中的闪烁和电离过程，从暗物质碰撞中识别低能核反冲。在2005年完成实验室测试后，探测器被安装在地下，中子源和伽马源的初始运行显示了符合预期的初级S1和次级S2闪烁脉冲，并且中子和伽马群具有不同的参数S2/S1的平均值。需要开展的新工作包括调查和防止氡流入探测器，去除内表面的氡衰变产物，改进数据采集，改进事件选择，以及通过更有效的触发降低能量阈值。粒子暗物质的探测将为天文学和粒子物理学打开一扇新的窗口，更先进的探测器将能够确定粒子属性的细节以及我们银河系中暗物质的光谱和流动。因此，它将改变和扩大世界在粒子物理学和天文学领域的活动。此外，这些技术本身还可以进一步扩大，并应用于其他基本实验，如双贝塔衰变和太阳中微子。与其他颗粒检测技术一样，新的位置敏感性和颗粒识别方法可能会产生新的医学诊断技术。

Large scale astronomical observations, including expansion, galaxy clustering, gravitational lensing and microwave background, indicate that the universe is dominated by unidentified dark matter whose total mass exceeds that of normal (baryonic) matter by a factor 5-10. A favored dark matter candidate is a massive particle interacting only weakly with normal matter but nevertheless producing rare nuclear recoils detectable in suitable targets such as liquid xenon.This UCLA group requests funding for the continued running and performance improvements for the 32 kg two-phase ZEPLIN II liquid Xenon dark matter detector which is now running in the UK Boulby Mine. The program is based on a new technique for identifying low energy nuclear recoils from dark matter collisions, using scintillation and ionization processes in liquid xenon. After completion of laboratory tests in 2005, the detector was installed underground and initial runs with neutron and gamma sources show primary S1 and secondary S2 scintillation pulses in accordance with expectation, and with neutron and gamma populations having different mean values of the parameter S2/S1. New work needed includes the investigation and prevention of radon influx into the detector, removal of radon decay products from interior surfaces, improvements to data acquisition, improved event selection, and reduction of energy threshold by a more efficient trigger. The detection of particle dark matter would open a new window in astronomy and particle physics, with more advanced detectors able to determine both details of the particle properties and the spectrum and flow of the dark matter in our Galaxy. It will thus transform and extend world activities in the particle physics and astronomical communities. Moreover, the techniques themselves can be further scaled up and applied to other fundamental experiments such as double beta decay, and solar neutrinos. As with other particle detection techniques, new methods of position sensitivity and particle discrimination may give rise to new medical diagnostic techniques.