PICO-500: Improving Acoustic Particle Identification in Superheated-Liquid WIMP Detectors

多次天文观测已经证实，宇宙中大约85%的物质不是由已知粒子构成的。破译这种所谓的暗物质的本质对宇宙学、天体物理学和高能粒子物理学至关重要。一个主要的假设是，它是由大爆炸后瞬间产生的弱相互作用大质量粒子（wimp）组成的。如果wimp是暗物质，那么它们在我们星系中的存在可以通过位于地下深处的探测器的原子核散射来检测，以帮助排除宇宙射线造成的背景。PICO是由PICASSO和COUPP合作项目合并而成，采用室温超热液体来寻找暗物质候选粒子。以前e& # 64256;在SNOLAB的PICO实验中，对自旋依赖的wimp -质子耦合的灵敏度达到了世界领先水平。近年来在α粒子和粒子诱导背景的声学识别方面取得了一些进展。这些进展将使下一代PICO气泡室在WIMP质量范围内（小于10 GeV/c2）对自旋无关耦合的灵敏度也更高，从而为解决暗物质究竟是什么的基本问题做出重大贡献。该奖项将在教育和指导领域产生更广泛的影响。PICO合作有着悠久的历史，致力于为本科生提供实验室研究机会，并为研究生和博士后提供指导和专业发展。在所有暗物质探测器中，过热液体提供了对主要电子反冲背景的最佳辨别（在~ keVnr阈值下为10^-10，即比液体氙探测器好7个数量级）。PICO室旨在通过自旋依赖的相互作用对剩余的超对称暗物质参数空间进行广泛的探测，这是一种与其他实验高度互补的方法。这使发现WIMP的机会最大化。在支持期间设想的活动包括参与PICO-500的设计，PICO-500是一个最近由加拿大创新基金会批准建造的大型（500升）腔室，以及将PICO的声学检测方法扩展到迄今尚未探索的有前途的更高频率范围。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。

Multiple astronomical observations have established that about 85% of the matter in the universe is not made of known particles. Deciphering the nature of this so-called Dark Matter is of fundamental importance to cosmology, astrophysics, and high-energy particle physics. A leading hypothesis is that it is comprised of Weakly Interacting Massive Particles, or WIMPs, that were produced moments after the Big Bang. If WIMPs are the dark matter, then their presence in our galaxy may be detectable via scattering from atomic nuclei in detectors located deep underground to help reject backgrounds due to cosmic rays. PICO, a merger of the PICASSO and COUPP collaborations, employs room-temperature super-heated liquids to search for dark matter particle candidates. Previous efforts by PICO at SNOLAB have resulted in a world-leading sensitivity to spin-dependent WIMP-proton couplings. Recent progress has been made in acoustic discrimination against alpha particles and particulate-induced backgrounds. These developments will enable the next-generation of PICO bubble chambers to also lead in sensitivity to spin-independent couplings in the WIMP mass range below 10 GeV/c2, thus contributing substantially to the search to address the fundamental question of what Dark Matter actually is.This award will generate substantial broader impacts in the areas of education and mentoring. The PICO collaboration has a long history of commitment to providing undergraduates with laboratory research opportunities, and to the mentoring and professional advancement of graduate students and postdocs.Superheated liquids provide the best discrimination of any dark matter detector against dominant electron recoil backgrounds (10^-10 at ~ keVnr threshold, i.e., seven orders of magnitude better than liquid-xenon detectors). PICO chambers aim to perform an extensive probing of the remaining supersymmetric dark matter parameter space via spin-dependent interactions, an approach that is highly complementary to other experiments. This maximizes the chances of WIMP discovery. The activities envisioned during the period of support include participation in the design of PICO-500, a large (500 liter) chamber recently approved for construction by the Canadia Foundation for Innovation, and an expansion of PICO's acoustic detection methods to a promising higher frequency range, thus far unexplored.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.