Search for Deviations from Newtonian Gravity at Micron Scale (a continuation proposal)

该奖项支持一项实验项目，该项目旨在探测超出基本粒子相互作用标准模型的物理理论所预测的距离为25微米的牛顿引力偏差。低温氦气轴承用于在安装在微机械悬臂上的小测试质量下旋转包含交替密度驱动质量模式的圆盘。两者之间的任何与质量相关的力都会对测试质量产生时变力，从而产生悬臂梁的时变位移。用激光干涉仪读出该位移，同时用光学编码器记录驱动质量的位置。将测量到的力与有限元分析预测的力进行比较，得出了新的类引力的界限，这可能标志着新的物理学。该实验使用了几种新颖的技术来克服与必要的精确测量相关的一些挑战，这些测量可能在类似的实验或其他领域被证明是有用的。这些包括辐射压力冷却微机械悬臂，封装微机电系统（MEMS）传感器与集成低温泵的组合，使用宏观气体轴承作为通用低温电机，简单而精确地制造中等规模金属结构的方法，以及一些尺寸稳定的平面化技术。虽然标准模型成功地统一了电磁、强相互作用和弱相互作用，但它忽略了引力。这给基础物理学带来了一个巨大的谜团：为什么即使是最微弱的亚原子力，即弱力，也比引力强得多？试图回答这个问题的现代理论预测，牛顿定律将在更长的尺度上修正，达到1毫米。本实验中使用的技术是微型制造设备的前沿技术。

This award supports an experimental program to probe deviations from Newtonian gravity at distances on the order of 25 micrometers as predicted by theories of physics beyond the Standard Model of fundamental particle interactions. A cryogenic helium gas bearing is used to rotate a disc containing a drive mass pattern of alternating density under a small test mass mounted on a micromachined cantilever. Any mass-dependent force between the two will produce a time-varying force on the test mass, and consequently a time-varying displacement of the cantilever. This displacement is read out with a laser interferometer, and the position of the drive mass is simultaneously recorded using an optical encoder. Comparison of the measured force to predictions from finite element analysis yields bounds on new gravity-like forces which could signal new physics. The experiment uses several novel techniques to overcome some of the challenges associated with the necessary precision measurements that could prove to be useful in similar experiments or other areas. These include radiation pressure to cool a micromachined cantilever, the combination of encapsulated Micro-Electrical-Mechanical-System (MEMS) sensors with an integrated cryopump, the use of a macroscopic gas bearing as a general-purpose low-temperature motor, the methods of simple and precise fabrication of intermediate-scale metallic structures, and some of the techniques of dimensionally stable planarization. While the Standard Model successfully unifies the electromagnetic, the strong and the weak interactions, it ignores gravity. This poses a great mystery in fundamental physics: why is even this most feeble subatomic force, i.e. the weak force, so much stronger than gravity? Modern theories that attempt to answer this question predict modifications to Newton's law at much longer length scales, up to 1 millimeter. The technology used in this experiment is at the cutting edge of micro-fabricated devices.