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

该奖项支持一项实验计划，该计划旨在探测基本粒子相互作用标准模型之外的物理理论所预测的距离约为25微米的牛顿引力偏差。低温氦气轴承被用来在安装在微机械悬臂梁上的小测试质量下旋转包含交替密度的驱动质量图案的圆盘。两者之间的任何与质量有关的力都会对测试质量产生时变的力，从而产生悬臂的时变位移。该位移用激光干涉仪读出，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的预测进行比较，得出了新的类似重力的力的界限，这可能标志着新的物理现象。这项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的实验或其他领域被证明是有用的。其中包括冷却微机械悬臂梁的辐射压力，封装的微电子机械系统(MEMS)传感器与集成低温泵的组合，宏观气体轴承作为通用低温电机的使用，中等规模金属结构的简单而精确的制造方法，以及一些尺寸稳定的平坦化技术。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。这在基础物理学中提出了一个巨大的谜团：为什么即使是这种最弱的亚原子力，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，牛顿定律的修正将在更长的尺度上进行，最大可达1毫米。这项实验中使用的技术处于微制造设备的前沿。

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.