RUI: Continuation of Support for Short-range Tests of Gravity at Humboldt State University

洪堡州立大学（HSU）是联邦政府认可的西班牙裔服务机构，位于北加州的一个主要农村地区，重力物理实验室（GPL）是物理和天文学系唯一专门的动手物理研究实验室。该奖项确保HSU本科生（其中许多是第一代大学生和STEM领域代表性不足的群体的成员）获得追求研究生学习或行业职业所需的宝贵研究技能。本科生还将通过与华盛顿大学重力研究小组的合作，被派往那里进行研究。这种合作使学生在世界一流的研究环境中工作。该实验室的校友获得了著名的研究生奖学金和工业职位。该奖项极大地促进了HSU在STEM领域的研究扩展。在主要项目中，为这个项目开发的软件和硬件将转移到高年级课堂的教育机会。该奖项还允许本科生通过在国家和地区会议上发表演讲以及发表研究成果来参与有价值的传播工作。最后，从天体物理学和宇宙学到粒子物理学和精密测量科学等各个领域的研究都对重力测试非常感兴趣。该奖项支持高精度实验，将在前所未有的水平上测试广义相对论的弱等效原理（WEP）和引力平方反比定律（ISL）。WEP将在毫米尺度上进行测试，ISL将在亚毫米距离上进行探测，其无与伦比的灵敏度可低至约25微米。两个试验都采用了一种新颖的平行板扭摆和吸引子质量设计。近年来，在短（亚毫米）距离尺度上对引力相互作用的研究受到了广泛关注，这在很大程度上是由于弦理论或M理论中出现的需要三维以上空间维度的统一场景，其中一些可能是宏观的。引力的短程测试和WEP也研究了可能提出的机制，试图解释宇宙的加速膨胀，通常归因于暗能量。最后，这样的测试提供了寻找由外来粒子或其他现象引起的假设的新相互作用的可能性。关于这些效应的许多设想都预测在短距离上会发生WEP或ISL的破坏。自1999年以来，实验限制得到了极大的改善，因此ISL已被证明在距离低至约55微米的范围内有效。然而，WEP的专用测试尚未在毫米尺度以下进行。本提案中描述的工作将探测WEP在亚毫米尺度上的测试质量分离。这项测量将通过一个平行板扭摆设计来完成，这将提供一个本质上无效的实验，并使用多个组成偶极子组合。同样，将通过将钟摆/吸引子测试质量间隔减小到100微米来实现对引力ISL的无与伦比的测试。

Humboldt State University (HSU) is a federally-recognized Hispanic Serving Institution in a predominantly rural area of Northern California, and the Gravitational Physics Laboratory (GPL) is the only dedicated hands-on physics research laboratory in the Department of Physics and Astronomy. This award ensures that HSU undergraduates, many of whom are first-generation college students and members of underrepresented groups in STEM fields, gain valuable research skills necessary for the pursuit of graduate studies or careers in industry. Undergraduates will also be sent to perform research at the University of Washington through a collaboration formed with a gravity research group there. This collaboration gives the students experience working in a world-class research environment. Alumni of the laboratory have secured prestigious graduate fellowships and industrial positions. This award greatly contributes to the expansion of research at HSU in the STEM fields. Within the major program, software and hardware developed for this project will be transferable to educational opportunities in the upper division classroom. This award also allows undergraduates to participate in valuable dissemination efforts through presentations at national and regional conferences, as well as publication of research results. Finally, tests of gravity are of great interest to research in diverse fields ranging from astrophysics and cosmology to particle physics and precision measurement science. This award supports high-precision experiments that will test the Weak Equivalence Principle (WEP) of General Relativity and the gravitational Inverse-Square Law (ISL) at unprecedented levels. The WEP will be tested at the millimeter scale and the ISL will be probed over sub-millimeter distances with unmatched sensitivity down to approximately 25 microns. Both tests use a novel parallel-plate torsion pendulum and attractor mass design. In recent years the study of the gravitational interaction at short (sub-millimeter) distance scales has gained much attention due in a large part to unification scenarios arising in string or M theory that require more than three spatial dimensions, some of which could be macroscopic. Short-range tests of gravity and the WEP also investigate possible proposed mechanisms that attempt to explain the accelerated expansion of the universe, generally attributed to Dark Energy. Finally, such tests present the possibility to search for hypothetical new interactions due to exotic particles or other phenomena. Many scenarios concerning these effects predict a violation of the WEP or ISL at short distances. Since 1999, experimental limits have improved dramatically so that the ISL has proven valid over distances down to approximately 55 microns. A dedicated test of the WEP, however, has not been performed below the millimeter scale. The work described in this proposal will probe the WEP for test mass separations at the sub-millimeter scale. This measurement will be accomplished with a parallel-plate torsion pendulum design that will provide an essentially null experiment and use multiple composition dipole combinations. Similarly, an unparalleled test of the gravitational ISL will be pursued by decreasing the pendulum/attractor test mass separation to 100 microns.