Dark matter search with a scintillating bubble chamber

宇宙中缺失物质的性质是当今物理学领域最重要和最神秘的未知方面之一（例如，参见美国P5委员会为2014-2023年制定政策的报告）。许多研究小组为探测失踪物质付出了相当大的努力，但到目前为止，在寻找宇宙中这种难以捉摸的成分方面还没有取得成功。拟议的研究通过在女王大学建造一个新的10kg闪烁气泡室（SBC）探测器来探索直接暗物质搜索，最终将位于安大略省萨德伯里郊外的SNOLAB。SBC合作建立在PICO合作[1]的世界领先研究的基础上，是氙气泡室b[2]工作的延伸，扩大了对低质量暗物质的灵敏度，这是社区b[3]特别感兴趣的领域。与大多数暗物质项目一样，由于无法可靠地将背景事件与作为暗物质相互作用标志的核反冲分离开来，PICO的结果受到了限制。所提出的探测器在电子反冲辨别方面有显著的提高，为进一步研究低质量候选粒子提供了极好的机会。SBC的操作类似于任何气泡室-反冲核在规定的半径内沉积临界量的热量（通过控制温度和压力可以控制这两个参数），并激发相变（沸腾）。目前的过热液体探测器虽然在典型的操作阈值下具有出色的电子反冲抑制能力，但在探索较低能量时受到这种背景的限制。伊利诺斯州西北大学氙气泡室的运行证据表明，SBC的情况并非如此。从该原型中获得的数据表明，电子反冲的拒绝因子至少与其他原型一样好，并有迹象表明它得到了显着改善。此外，探测器的能量阈值大大降低，但不影响稳定运行。有了这些证据在手，这个实验的下一步需要增加统计数据，以便适当地量化可实现的阈值，从而研究暗物质的能力，以及诸如惰性中微子、中微子磁矩和非标准相互作用等主题。将闪烁测量添加到用于暗物质探测的更传统的气泡室中，不仅可以改善结果并领先世界，还可以补充该项目。参与该项目的HQP也将接触到新技术及其在尖端项目中的应用。因此，该项目是培养未来科学家的理想场所，包括获得这项资助的五位科学家。

The nature of the missing matter in the Universe is one of the most important and mysterious unknown aspects in the physics field today (see for example the report by the P5 committee in the US, setting policy for the 2014-2023 period). Considerable effort toward the detection of missing matter has been expended by many research groups without success thus far in the search for this elusive component of the Universe. The proposed research explores a direct dark matter search through the construction of a novel 10kg Scintillating Bubble Chamber (SBC) detector at Queen's University, to be ultimately located at SNOLAB outside of Sudbury, Ontario. The SBC collaboration builds on the world-leading research of the PICO collaboration [1] and is an extension of the work with xenon bubble chambers [2], expanding the sensitivity to lower mass dark matter, a region of particular interest in the community [3].  As with the majority of dark matter projects, limitations are placed on the PICO results due to the inability to reliably separate background events from the nuclear recoils which are the signature of the dark matter interaction. The proposed detector improves dramatically on particularly the electron recoil discrimination, providing an excellent opportunity to further investigate low mass candidates. Operation of the SBC is similar to that of any bubble chamber - a recoiling nucleus deposits a critical amount of heat within a defined radius (with both of those parameters controllable through control of the temperature and pressure) and a phase transition (boiling) is incited.  Current superheated liquid detectors, while having excellent rejection of electron recoils at typical operating thresholds, become limited by this background when exploring lower energies. Evidence from operation of a xenon bubble chamber at Northwestern University in Illinois indicates that this is not the case for the SBC. Data taken from this prototype indicates that the rejection factor for electron recoils is at least as good as that achieved in others, with indications that it is improved significantly. In addition, the energy threshold of the detector has been lowered considerably without any impact on stable operation. With this evidence in hand, the next steps for this experiment call for increased statistics in order to properly quantify the achievable threshold and therefore the ability to study dark matter, as well as topics such as sterile neutrinos, the neutrino magnetic moment, and non-standard interactions. The addition of the scintillation measurement to the more traditional bubble chambers being operated for dark matter detection supplements the project not only by improving the results and leading the world.  The requested HQP working on this project will also be exposed to novel technologies and their use in a cutting-edge project.  This project is then an ideal training ground for future scientists including the five sponsored by this grant request.