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

该奖项支持一项实验计划，以探测偏离牛顿引力的距离在25微米的数量级上，如基本粒子相互作用标准模型之外的物理理论所预测的那样。一种低温氦气轴承用于旋转一个盘，该盘包含在安装在微机械悬臂上的小测试质量下的交替密度的驱动质量图案。两者之间的任何质量相关力将在测试质量上产生随时间变化的力，从而产生悬臂随时间变化的位移。该位移用激光干涉仪读出，并且同时使用光学编码器记录驱动质量块的位置。将测得的力与有限元分析的预测进行比较，可以得出新的类重力力的界限，这可能是新物理学的信号。该实验使用了几种新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实验或其他领域中有用。这些包括辐射压力冷却微机械悬臂梁，封装的微机电系统（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的低温电机，简单而精确的制造方法的中间规模的金属结构，和一些技术的尺寸稳定的平面化。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，也就是弱力，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在更长的长度尺度上的修正，可达1毫米。本实验中使用的技术处于微制造设备的最前沿。

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.