Liquid-noble Bubble Chambers for Dark Matter and CEvNS Detection

暗物质占宇宙物质的近85%，暗物质的身份和物质/反物质不对称的起源是现代物理学中两个基本的未知数。新的仪器正在开发中，旨在通过搜索gev尺度的暗物质和通过反应堆中微子的相干弹性散射（CEvNS）精确测量中微子性质来解决这两个挑战。可扩展的背景识别技术，如闪烁气泡室（SBC），有可能彻底改变这些搜索的灵敏度。该奖项支持西北大学和东北伊利诺伊大学的工作人员操作和分析来自位于美国巴达维亚附近的费米国家加速器实验室的10公斤液体氩气SBC的数据。该团队将表征SBC的响应，以确定该技术的低阈值范围，以区分电子和核反冲低于约1 keV。该奖项为本科生研究人员提供了独特的动手仪器体验机会，并为当地低收入和第一代学生提供了直接努力，以扩大对物理界的接触和参与。核反冲在液体惰性气体气泡室中同时产生闪烁光，并在过热的液体目标中形成单个气泡。通过结合仪器的电子反冲不灵敏度和气泡室的位置重建以及闪烁体的逐事件能量分辨率，SBC技术具有消除所有已知暗物质和CEvNS信号背景的潜力。此外，与现有的分子流体气泡室相比，过热的贵金属液体在更高的过热度下仍能保持电子反冲不敏感，这有可能将SBC的准无背景操作扩展到低至100 eV的阈值。SBC区分低能电子反冲和核反冲的能力可能会将背景事件水平抑制到在暗物质搜索中达到太阳中微子相干散射流所需的水平，并在反应堆CEvNS研究中实现优于1的信噪比。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The identity of dark matter, which makes up nearly 85% of the matter in the Universe, and the origin of the matter/anti-matter asymmetry are two of the current fundamental unknowns in modern physics. Novel instrumentation is under development aimed at resolving both challenges via searches for GeV-scale dark matter and precision measurements of neutrino properties via coherent elastic scattering (CEvNS) of reactor neutrinos. Scalable background-discriminating techniques, like Scintillating Bubble Chambers (SBC), hold the potential to revolutionize the sensitivity in these searches. This award supports personnel at Northwestern University and Northeastern Illinois University in operating, and analyzing the data from, a 10kg liquid-argon SBC located at the Fermi National Accelerator Laboratory located near Batavia IL USA. The team will characterize response of the SBC to determine the low-threshold reach of this technology to distinguish electron and nuclear recoils below approximately 1 keV. The award provides unique opportunities for hands-on instrumentation experiences for undergraduate researchers, with a directed effort to broaden access to, and participation within, the physics community for local low-income and first-generation students. Nuclear recoils in liquid-noble gas bubble chambers simultaneously create a flash of scintillation light and nucleate a single bubble in a superheated liquid target. By combining the electron-recoil insensitivity of the instrument and the position reconstruction of a bubble chamber with the event-by-event energy resolution of a scintillator, the SBC technique holds the potential to eliminate all known backgrounds to dark matter and CEvNS signals. In addition, superheated noble liquids maintain electron-recoil insensitivity at far higher degrees of superheat than can be achieved in existing molecular-fluid bubble chamber, potentially extending the quasi-background-free operation of the SBC to thresholds as low as 100 eV. The SBC ability to discriminate the electron- and nuclear-recoils at low-energy may suppress background event levels to that needed to reach the solar neutrino coherent scattering flow in a dark matter search, and to achieve signal-to-noise of better than 1 in reactor CEvNS studies.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.