Collaborative Research: Multi-Mode Apparatus to Resolve the Discrepancy Concerning Big G

合作研究：解决大G差异的多模式装置

• 批准号: 2207796
• 负责人: Ricardo Decca
• 金额: $ 36万
• 依托单位: Indiana University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-07-01 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2207796&HistoricalAwards=false
• 关键词: Collaborative; Research; Multi; Mode; Apparatus

Of all the fundamental constants of nature, G, the universal gravitational constant, is known with the least precision. The current situation surrounding the uncertainty in the knowledge of G is puzzling the fundamental physics and precision measurement communities. The world's best experiments yield values which are incompatible with one another and differ by about 40 times the uncertainty of the most precise experiment. Furthermore, knowing the true value of G is important in various fields, as it is necessary in efforts to unify general relativity with quantum mechanics in a quantum theory of gravity. The project enabled by this collaboration will be to carry out carefully controlled metrological experiments where the precision of the measurements will be in the part-per-million. Since part of the past discrepancies between determinations of G can be traced back to the methodology used, the group will combine different approaches to determine G within the same apparatus, hoping to obtain highly precise values of G from each approach, but with the expectation that the values obtained using different methodologies will mimic the current situation in the community, namely, that different methodologies, no matter how precise, yield different results. With the experiments carried out in the same apparatus the effort would then help understand the current discrepancies among existing experimental results. In addition to broad scientific interest, undergraduate and graduate students will be integral to the success of the project. They will be trained in experimental physics and precision measurement techniques. The project will provide training and education for first-generation college students and undergraduates from diverse backgrounds by recruiting from a rural, federally-recognized Hispanic Serving Institution that has limited research opportunities on campus. Students from three different universities will be in contact, enhancing their exposure to different academic cultures and providing networking opportunities. The project will establish a torsion pendulum facility dedicated to measuring the Newtonian gravitational constant G with unprecedented sensitivity using three different experimental techniques within the same apparatus. An agreed upon value for G remains elusive as recent measurements by different experimental groups have scattered widely, or have had low precision. The spread in measured values and the relatively low precision of the measurements is recognized by the precision measurement community as something that needs to be addressed. This project will finish building a system based upon the ideas introduced in previous torsion pendulum experiments, but will expand the scope and breadth of the measurements by the multi-mode nature of the apparatus. In the primary mode G will be determined by measuring the angular acceleration needed to keep a torsion pendulum's fiber from twisting while it rotates on a turntable in the presence of carefully designed attractor masses (that also rotate on a separate turntable). This angular acceleration feedback mode has yielded the most precise measurement of G to date, yet it has only been performed once. Compared to previous efforts, the proposed system will achieve smaller metrology errors by using advanced measurement and characterization techniques. Incidentally, using attractor masses that are transparent in the vissible/near infrared will permit a much more precise determination of the mass distribution. Using the same apparatus, G will be determined by measuring the change in the resonant frequency of the torsion pendulum with the attractor masses present and removed by measuring the thermally induced oscillation of the pendulum. In the third approach, G will be determined by large amplitude determination of the change in the resonant frequency of the pendulum when the attractor masses are at two different positions. Each technique is expected to provide a measurement with a relative error of approximately 2 ppm. The three methods will also shed light in the possible overlooking of systematic effects.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.

在自然界的所有基本常数中，人们对万有引力常数G的了解是最不精确的。围绕G知识的不确定性的现状使基础物理学和精密测量界感到困惑。世界上最好的实验得出的结果彼此不相容，其不确定性是最精确实验的40倍左右。此外，知道G的真实值在各个领域都很重要，因为它是在量子引力理论中统一广义相对论和量子力学的必要条件。这一合作项目将进行精心控制的计量实验，其测量精度将达到百万分之一。由于过去测定G之间的部分差异可以追溯到所使用的方法，因此该小组将在同一仪器中结合不同的方法来测定G，希望从每种方法中获得高精度的G值，但期望使用不同方法获得的值将模拟社区的现状，即不同的方法，无论多么精确，都会产生不同的结果。在同一设备上进行的实验将有助于理解现有实验结果之间的当前差异。除了广泛的科学兴趣外，本科生和研究生将是项目成功的组成部分。他们将接受实验物理和精密测量技术方面的培训。该项目将为来自不同背景的第一代大学生和本科生提供培训和教育，招募来自联邦政府认可的农村西班牙裔服务机构的学生，该机构在校园内的研究机会有限。来自三所不同大学的学生将进行接触，增强他们对不同学术文化的接触，并提供交流机会。该项目将建立一个扭摆设备，专门用于测量牛顿引力常数G，在同一设备内使用三种不同的实验技术，具有前所未有的灵敏度。由于不同的实验小组最近的测量结果很分散，或者精度很低，所以对G的一致值仍然难以捉摸。测量值的分散和相对较低的测量精度被精密测量界认为是需要解决的问题。本项目将在先前扭摆实验的基础上建立一个系统，但将通过仪器的多模式特性扩大测量的范围和广度。在主模式下，G将通过测量角加速度来确定，当扭摆在转盘上旋转时，在精心设计的吸引子质量（也在单独的转盘上旋转）的存在下，保持扭摆纤维不扭曲所需的角加速度。这种角加速度反馈模式产生了迄今为止最精确的G测量，但它只执行了一次。与以前的工作相比，所提出的系统将通过使用先进的测量和表征技术实现更小的计量误差。顺便说一句，使用在可见/近红外中透明的吸引子质量将允许更精确地确定质量分布。使用同样的仪器，G将通过测量有吸引子质量的扭摆共振频率的变化来确定，通过测量钟摆的热诱导振荡来消除吸引子质量。在第三种方法中，当吸引子质量处于两个不同位置时，G将通过对钟摆谐振频率变化的大幅度测定来确定。预计每种技术提供的测量相对误差约为2ppm。这三种方法也将为可能忽略系统效应提供启示。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。