High-Frequency Search for New Sub-Millimeter Range Forces

该奖项支持对1毫米以下自旋相关力的实验研究。目前的实验极限允许自然界中存在比重力强几百万倍的未发现的力，其作用距离可以用肉眼分辨。 在过去几十年中发展起来的理论模型试图解释为什么涉及强核力的相互作用总是保持一定的时空对称性，这些模型对亚毫米范围内的自旋相关力做出了具体的预测。 因此，拟议中的实验代表了在这一范围内发现的绝佳机会。 该实验使用1千赫平面振荡器作为测试质量，它们之间有一个薄屏蔽来抑制背景，这种技术已经证明了使用相对较大的质量（平方厘米）探测微米级距离的能力，并在室温下在仪器热噪声的极限下工作。 具有高自旋密度但低固有磁性的自旋极化材料，包括表现出与对齐的电子自旋相关的磁性的轨道补偿的亚铁磁体，将作为测试质量进行研究。 在适度的对齐自旋密度和良好的磁背景控制下，实验的预计灵敏度比目前在1毫米以下的范围内的最佳极限高出几个数量级。自旋是基本粒子的基本属性，也是量子物理学的一个重要方面。依赖于自旋的宏观力的发现将对从亚原子到宇宙尺度的物理学产生巨大的影响。 标准模型（迄今为止最成功的粒子物理学理论，但人们普遍认为是不完整的）的各种扩展预测了短程自旋相关力。 这些力是由粒子介导的，这些粒子可能有助于“暗物质”的假设，以解释星系的表观质量分布。 神秘的“暗能量”假设解释了观测到的宇宙膨胀，似乎也指出了几十微米量级的长度尺度，作为一个特殊的范围，在这个范围内可能出现以前未被发现的现象。 在执行过程中，这个基础项目还将为所有参与者（包括对该提案做出贡献的几名本科生）提供机械设计，真空技术，低噪声电子学，半导体和磁性材料加工以及其他实用技术的经验。 该实验也将成为印第安纳州大学时空对称中心（IUCSS）的一个重点，该中心由PI及其同事创立，旨在加强和宣传IU在时空结构研究方面不断增长的专业知识。 拟议实验的成功将支持IUCSS的目标，即建立一个长期计划，在亚毫米长度尺度上对新物理进行协调的实验和理论研究。

This award supports an experimental search for spin-dependent forces below 1 millimeter. Present experimental limits allow for undiscovered forces in nature several million times stronger than gravity acting over distances resolvable by the unaided eye. Theoretical models developed over the past few decades that attempt to explain why interactions involving the strong nuclear force always conserve certain spacetime symmetries make specific predictions of spin-dependent forces in the sub-millimeter range. The proposed experiment thus represents an excellent opportunity for discoveries in this range. The experiment uses 1-kilohertz planar oscillators as test masses with a thin shield between them to suppress backgrounds, a technique that has demonstrated the capability to probe micron-scale distances using relatively large (square-centimeter) masses, and to operate at the limit of instrumental thermal noise at room temperature. Spin-polarized materials with high spin density but low intrinsic magnetism, including ferrimagnets that exhibit orbital compensation of the magnetism associated with the aligned electron spins, will be investigated as test masses. With modest aligned-spin densities but good control of magnetic backgrounds, the projected sensitivity of the experiment is several orders of magnitude greater than the current best limits at ranges below 1 millimeter.Spin is a fundamental property of elementary particles and a crucial aspect of quantum physics. The discovery of a macroscopic force that depends on spin would have enormous implications for physics from subatomic to cosmological scales. A variety of extensions to the Standard Model (the most successful theory particle physics to date, but widely believed to be incomplete) predict short-range spin-dependent forces. These forces are mediated by particles that could contribute to the "dark matter" hypothesized to pervade all of space in order to explain the apparent mass distributions of galaxies. The mysterious "dark energy" postulated to explain the observed expansion of the universe also seems to point to a length scale on the order of tens of microns as a special range at which previously undetected phenomena might appear. During its execution, this fundamental project will also provide all participants (including several undergraduates who have contributed to this proposal) with experience in mechanical design, vacuum technology, low-noise electronics, semiconductor and magnetic materials processing, and other practical techniques useful in a wide range of science and engineering fields. The experiment will also be a key focus of the Indiana University Center for Spacetime Symmetries (IUCSS), which was founded by the PI and his colleagues to strengthen and publicize IU's growing expertise in the investigation of the structure of spacetime. Success of the proposed experiment will support the IUCSS goal to establish a long-term program of coordinated experimental and theoretical investigation of new physics at sub-millimeter length scales.