University of Chicago Contribution to PICO-500 Engineering and Construction

确定暗物质的问题已经伴随我们80多年了。在此期间，天文学证据证明这种神秘形式的物质的存在已经涌入。它不能吸收或发射光，它的存在是通过它对发光物体的引力来证明的，如恒星，星系和更大的结构。如果由新的基本粒子组成，那么位于地下实验室中的专用探测器-受到宇宙辐射的保护-有机会解决这个长期存在的谜团，现在是粒子物理学，宇宙学和天文学的核心。皮科-500是这些探测器之一，由有史以来最大的气泡室之一组成，位于加拿大SNOLAB实验室地下一英里多的地方。它的设计对大多数已知的辐射源不敏感，而对粒子暗物质预期的特征相互作用高度敏感。 该奖项将允许美国博士后在这个有前途的暗物质探测器的建设，调试和提取第一批数据中发挥核心作用。过热液体，如皮科气泡室中使用的那些，提供了对任何暗物质探测器对电子反冲的最佳区分，主要环境背景限制了这些搜索的灵敏度。皮科探测器还具有对无处不在的α发射体引起的信号的有效声学抑制。这导致了皮科计划中暗物质灵敏度持续增加的记录，因为它的气泡室尺寸已经增加。最近的唯象学工作强调了含氟皮科目标的重要性：这些目标对于全面探索暗物质粒子相互作用的所有可能模式是必要的。本提案中所描述的工作的完成将使皮科的灵敏度扩展到1 E-42 cm ^2的自旋相关截面（比目前的极限提高100）。这将提供一个详尽的探索超对称暗物质通过这一渠道，特别是少数GeV/c^2粒子，质量范围的现象学兴趣。这一奖项反映了NSF的法定使命，并已被认为是值得支持的评估使用基金会的智力价值和更广泛的影响审查标准。

The problem of the identification of Dark Matter has been with us for more than eight decades. In the interim, astronomical evidence for the existence of this mysterious form of matter has poured in. Unable to absorb or emit light, its presence is made evident by its gravitational pull on luminous objects such as stars, galaxies, and larger structures. If composed of new elementary particles, dedicated detectors housed in underground laboratories -protected there from cosmic radiation- stand a chance of solving this long-standing riddle, now central to particle physics, cosmology and astronomy. PICO-500 is one of these detectors, consisting of one of the largest bubble chambers ever built and housed more than a mile underground in the Canadian SNOLAB laboratory. It is by design insensitive to most known sources of radiation, while highly responsive to the characteristic interactions expected from particle dark matter. This award will allow a US postdoc to play a central role in the construction, commissioning, and extraction of first data from this promising dark matter detector.Superheated liquids like those used in PICO bubble chambers provide the best discrimination of any dark matter detector against electron recoils, the dominant environmental background limiting the sensitivity of these searches. PICO detectors additionally feature an efficient acoustic rejection against signals induced by ubiquitous alpha emitters. This has resulted in a track-record of continuous increase in dark matter sensitivity from the PICO program, as its bubble chambers have grown in size. Recent phenomenological work has emphasized the importance of fluorine-containing PICO targets: these are necessary for a comprehensive exploration of all possible modes of dark matter particle interaction. The completion of the work described in this proposal will extend the sensitivity of PICO down to spin-dependent cross sections of 1E-42 cm^2 (an improvement of 100 beyond present limits). This will provide an exhaustive exploration of supersymmetric dark matter via this channel, and in particular for few GeV/c^2 particles, a mass range of much phenomenological interest.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.