ZEPLIN-III反巧合否决探测器
The ZEPLIN-III Anti-Coincidence Veto Detector
摘要：
介绍了ZEPLIN-III直接暗物质探测仪的反符合否决探测器的设计、优化和结构。一吨塑料闪烁体被排列成52个条，由光电倍增管分别读出，并与一个装有钆的被动聚丙烯屏蔽层相连。对放射性内容给予了特别关注。总的目标是实现低阈值和高效率的否决探测器，而不会在ZEPLIN-III中产生额外的背景，所有这些都在合理的成本下。对这些部件进行了广泛的实验测量，包括放射性水平和性能特征。这些已被用于通知一个完整的端到端的蒙特卡罗模拟，然后已被用于计算新仪器的预期性能，无论是单独操作，并作为ZEPLIN-III的反符合探测器。否决装置将能够在ZEPLIN-III感兴趣的能量范围内拒绝来自中子背景的65%以上的符合核反冲事件。这将使ZEPLIN-III在WIMP接受区的背景从每年约0.4次减少到约0.14次，这是非零观测事件的一个重要因素。此外，除了提供有价值的诊断能力之外，否决权还能够标记超过15%的伽马射线排斥，而所有这些都不会产生显著的额外背景。结合更换内部ZEPLIN-III光电倍增管阵列，新的否决权预计将大大提高ZEPLIN-III仪器对暗物质的灵敏度，允许探测低于1 E-8 pb的自旋无关WIMP核子截面。
英文摘要：
The design, optimisation and construction of an anti-coincidence veto detector to complement the ZEPLIN-III direct dark matter search instrument is described. One tonne of plastic scintillator is arranged into 52 bars individually read out by photomultipliers and coupled to a gadolinium-loaded passive polypropylene shield. Particular attention has been paid to radiological content. The overall aim has been to achieve a veto detector of low threshold and high efficiency without the creation of additional background in ZEPLIN-III, all at a reasonable cost. Extensive experimental measurements of the components have been made, including radioactivity levels and performance characteristics. These have been used to inform a complete end-to-end Monte Carlo simulation that has then been used to calculate the expected performance of the new instrument, both operating alone and as an anti-coincidence detector for ZEPLIN-III. The veto device will be capable of rejecting over 65% of coincident nuclear recoil events from neutron background in the energy range of interest in ZEPLIN-III. This will reduce the background in ZEPLIN-III from ~0.4 to ~0.14 events per year in the WIMP acceptance region, a significant factor in the event of a non-zero observation. Furthermore, in addition to providing valuable diagnostic capabilities, the veto is capable of tagging over 15% for gamma-ray rejection, all whilst contributing no significant additional background. In conjunction with the replacement of the internal ZEPLIN-III photomultiplier array, the new veto is expected to improve significantly the sensitivity of the ZEPLIN-III instrument to dark matter, allowing spin independent WIMP-nucleon cross sections below 1E-8 pb to be probed.
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