Study of Argon for WIMP Dark Matter Detectors and Earth Sciences

暗物质存在的证据现在令人信服，但它的组成仍然是一个根本的谜。特别有趣的是，暗物质可能是由弱相互作用大质量粒子（wimp）形式的基本粒子组成的。wimp可以通过它们与原子核的碰撞来检测，但是预期的低速率和低能量的反冲原子核给探测器带来了令人生畏的尺寸和背景要求。液态氩是一种优秀的闪烁和电离探测器，具有独特的特征，使其对WIMP暗物质的探测特别有吸引力。作者建议为液态氩作为wimp探测器的发展做出贡献。在过去的一年里，普林斯顿小组在意大利格兰萨索地下实验室参与了3.2公斤WARP液态氩探测器的开发和测试。测试的结果是非常积极的，并且证明了使用大型LAr探测器进行敏感的WIMP搜索的可行性。他们建议增加对更大的液态氩探测器的开发和操作的参与，下一步是140公斤的探测器。除了本提案所要求的关键电子设备外，140公斤的WARP探测器已得到资助并正在建造中。预计在2007年夏季进行调试。研究计划包括以下三个目标：1)脉冲形状判别：利用新型0.5-1 GHz瞬态数字化仪（1- 2ns数字化）进一步发展脉冲形状判别。2)光收集：pi建议研究改进光收集系统的方法，包括在探测器底部的液态氩气中添加pmt阵列的可能性。3)地下氩：由于宇宙射线与大气中的氩相互作用，在商业氩中发现了放射性的39Ar，在氩探测器中产生了显著的β背景。从天然气井中有可能获得39Ar含量较低的氩。来自地幔的气体，如新墨西哥州东北部的二氧化碳气井，应该有非常低的39Ar含量。美国地质氩源的开发将对低背景计数有许多更广泛的影响应用，除了WIMP搜索之外，还将成为即将成立的深地下科学与工程实验室（DUSEL）的主要资产。地质氩气的研究也构成了DUSEL所涉及的物理学和地质学两个学科之间科学合作的一个很好的例子。

Evidence for the existence of dark matter is now compelling, but its composition remains a fundamental mystery. Particularly intriguing is the possibility that dark matter consists of elementary particles in the form of Weakly Interacting Massive Particles (WIMPs). WIMPs may be detected by their collisions with nuclei, but the expected low rate and low energy of the recoil nuclei present daunting size and background requirements for the detector. Liquid argon is an excellent scintillation and ionization detector and has unique features that make it particularly attractive for detection of WIMP dark matter. The authors propose to contribute to the development of liquid argon as a detector for WIMPs. During the past year the Princeton group participated in development and tests of the 3.2-kg WARP liquid argon detector at the Gran Sasso underground laboratory in Italy. The results of the tests are very positive and demonstrate the feasibility of a sensitive WIMP search with a large-scale LAr detector. They propose to increase their involvement in the development and operation of larger liquid argon detectors, with the next step being a 140-kg detector. Except for critical electronics that is requested in this proposal, the 140-kg WARP detector is funded and under construction. Commissioning is expected to occur in Summer 2007. The research plan consists of the following three goals: 1) Pulse Shape Discrimination: further development of pulse shape discrimination with new 0.5-1 GHz transient digitizers (1-2 ns digitization). 2) Light Collection: the PIs propose to investigate ways to improve the light collection system, including the possibility of adding an array of PMTs in liquid argon at the bottom of the detector. 3) Underground Argon: the radioactive 39Ar found in commercial argon, which is due to cosmic ray interactions with the argon in the atmosphere, produces a significant beta background in argon detectors. It is likely that argon with a low content of 39Ar could be obtained from natural gas wells. Gas that originates from the Earth's mantle, such as at the CO2 gas wells in Northeast New Mexico, should have a very low level of 39Ar. The development of US sources for geological argon would have many broader impacts applications to low background counting, in addition to WIMP searches, and would be a major asset for the upcoming Deep Underground Science and Engineering Laboratory (DUSEL). The study of geological argon also constitutes a good example of scientific cooperation between two of the disciplines involved in the DUSEL, physics and geology.